Institute of Fundamental Technological Research

This study investigates thermal strains in fibre reinforced polymeric samples manufactured using a modified Fused Deposition Modelling (FDM) method. The investigated material was a composition of polylactic acid (PLA) resin and continuous carbon fibres. Each test sample was equipped with two Bragg grating (FBG) sensors, one embedded inside and the other bonded to the surface. Both sensors monitored temperature-induced deformations
during the conditioning of the specimens in a thermal chamber. Multiscale, analytical and finite element method based models were implemented to quantify the temperature deformations. Research has revealed that in investigated samples, bending occurs due to thermal loading. This can result in an inaccurate estimation of the coefficient of thermal expansion when relying on surface deformation measurements. A proposed solution involves the use of one FBG sensor embedded inside the specimen or two FBG sensors placed symmetrically, capable of measuring axial thermal deformation and averaging the effects associated
with bending.

Continuous Carbon Fibre Reinforced Polymer Composites, Fibre Bragg gratings, Thermal expansion , Additive manufacturing, Multiscale modelling

The paper presents a novel approach for prototyping and modelling of the Adaptive Tuned Particle Impact Damper (ATPID). After introducing the operation and potential disadvantages of the classical Particles Impact Dampers (PIDs) the authors propose the concept of single-grain controllable damper, which can adapt to actual dynamic excitation by a real-time change of the container height. The investigations focus on the methodology of simplified mathematical modelling of the ATPID damper based on grain physical properties, nonlinear soft contact theory, and control function of the absorber height being a novel component used to optimize dynamic response of the system. The proposed ATPID model is positively verified against the experimental results obtained from the developed test stand including a vibrating beam equipped with the proposed innovative attenuator. The conducted analyses clearly reveal the operating principles of the ATPID damper, the types of grain movement, the influence of shock absorber parameters on the vibrating system response and the energy balance of the system. The solution of the formulated optimization problem aimed at minimization of vibration amplitudes allows to find the optimal damper height for various physical parameters of the grain and the external excitation and to achieve a high efficiency of the proposed damper reaching 90%. In addition, a real-time control strategy providing adaptation of the ATPID damper to changing amplitude of kinematic excitation and effective mitigation of steady-state vibrations is proposed and verified experimentally.

Adaptive Tuned Particle Impact Damper, Damping of vibrations, Semi-active damping, Controllable damper, Control function, Sensitivity analysis, System optimization, Real-time control strategy

The paper presents the concept of equivalent parameter predictive control (EPPC) elaborated for semi-active fluid-based (hydraulic and pneumatic) shock absorbers equipped with controllable valves and subjected to impact excitation. The undertaken problem concerns the absorption and dissipation of the impact energy with the requirement to minimize the generated reaction force and corresponding impacting object deceleration. The development of a control strategy for a challenging problem with unknown impacting object mass and unknown changes of external and disturbance forces is proposed and discussed in detail. The innovative solution utilizes the paradigm of model predictive control supplemented by the novel concept of equivalent system parameters identification. The EPPC is based on the online measurement of system response, the computation of the equivalent mass of the impacting object, and the repetitive solution of the optimal control problem with various prediction intervals and constraints imposed on valve opening. The presented method is proven to operate robustly for unknown excitations, including double-impact conditions, and it has similar efficiency to control methods developed previously for known impact parameters.

adaptive impact absorption,semi-active control,self-adaptive shock absorber,adaptive model predictive control,model identification adaptive control,model predictive control

The paper introduces Extended Identification-Based Predictive Control (EIPC), which is a novel control method developed for the problem of adaptive impact mitigation. The model-based approach utilizing the paradigm of Model Predictive Control is combined with sequential identification of selected system parameters and process disturbances. The elaborated method is implemented in the shock-absorber control system and tested under impact loading conditions. The presented numerical study proves the successful and efficient adaptation of the absorber to unknown excitation conditions as well as to unknown force and leakage disturbances appearing during the process. The EIPC is used for both semi-active and active control of the impact mitigation process, which are compared in detail. In addition, the influence of selected control parameters and disturbance identification on the efficiency of the impact absorption process is assessed. As a result, it can be concluded that an efficient and robust control method was developed and successfully applied to the problem of adaptive impact mitigation.

adaptive control,optimal control,predictive control,impact mitigation,shock absorber

In this paper, the authors propose, investigate, and discuss a concept of novel type of deployable helium-filled aerostat as a low-cost mean of transport. Internal construction of the aerostat is based on ultra-light tensegrity structure equipped with prestressed tensioned elements of controllable lengths. Such tensegrity structure allows for adaptive morphing of the aerostat understood as simultaneous controllable modifications of aerostat volume and shape during the flight. The controlled volume changes enable influencing buoyancy force and obtaining desired vertical motion during the ascending and descending process. In turn, external shape changes allow for lowering the aerodynamic drag and energy usage needed to uphold stable horizontal position or maintain the desired flight path. Moreover, such internal structure allows for convenient storage, transportation and deployment of the aerostat construction on the ground or in required point at the atmosphere. The article presents an analysis of the exemplary operational mission of the aerostat. The authors introduce the mechanical model capturing interaction of the internal tensegrity structure and aerostat envelope based on the finite-element method, as well as dynamic model allowing for simulation of the aerostat’s vertical and horizontal motion influenced by buoyancy and drag forces. Both these models are used to positively verify the feasibility of the proposed concept of deployable tensegrity-based aerostat with adaptive morphing and its efficiency in realization of the assumed flight mission.

tensegrity structure, internal construction, shape modification, helium-filled aerostat, vertical mobility, horizontal mobility

In this paper, we present a method that allows for the quick and efficient simulation of the comminution process in high-speed rotor mills. The method requires only the feed’s macroscopic material data and the geometry of the machine. Consisting of two stages, the method couples Computational Fluid Dynamics (CFD) with the Discrete Element Method (DEM) to obtain the collisional velocities and angles of a representative group of particles passing through the machine. Due to this coupling, any mill which relies on fluid forces acting on the ore particles can be simulated. After obtaining these values, the second stage commences wherein a single ore particle consisting of DEM elements collides against a rigid surface. The data obtained from this stage is then used to determine the minimum required working parameters of the chosen machine to achieve proper ore comminution. The proposed methodology was applied to analyse the novel concept of using beater mills for the comminution of copper ore.

CFD, DEM, comminution modelling, particle breakage, beater mill, sandstone, copper ore

The paper is aimed at detailed discussion of the Identification-based Predictive Control (IPC) developed for semi-active fluid-based shock-absorbers which protect structures and machines against impact excitations. The problem addressed is the optimal impact absorption providing adaptive mitigation of dynamic response of the mechanical system. The goal of applied control is dissipation of the entire impact energy and minimization of the impacting object deceleration during the process. Three proposed implementations of the IPC are based on sequentially repeated procedures, which include identification of excitation parameters and calculation of the valve opening providing minimization of tracking error of the optimal path. The presented numerical examples concerning mitigation of the dynamic excitation acting on the double-chamber pneumatic shock-absorber reveal high efficiency and prove robustness of the proposed control methods. The developed algorithms are compared against each other in terms of path-tracking efficiency and character of required control actions. The most important challenges in practical implementation of the proposed methods are indicated.

adaptive control, adaptive impact absorption, identification-based predictive control, model predictive control, self-adaptive shock-absorber, semi-active control

In this article, the authors propose and investigate a new concept of HAPS aerostat design in a modular form, which allows for sequential increasing or decreasing of the total volume, up to the desired size. In its initial form, the aerostat has relatively small dimensions but its central cylindrical part is multi-segmented and can be easily extended. The application of controllable construction couplings enables precise control of the aerostat expansion process and significantly improves its vertical mobility. The paper describes details of telescopic aerostat construction, presents a mathematical model of its vertical motion and investigates numerically two volume control strategies aimed at maximization of operation efficiency and minimization of operation cost. The results obtained reveal the main problems that have to be addressed and the factors that play a key role in design of such telescopic aerostats and control of their vertical mobility.

helium airship, control of vertical mobility, reduced energy consumption, optimum ascending and descending path

This paper presents equilibrium mechanics and a finite element model for analysing a scissor structure that contains pivots with zero bending stiffness representing structural instability. The pivot at the centre of each structural unit, which is a feature of scissor structures, can be used to transfer the displacement between the units. It cannot, however, transfer the rotation between these units, and the angular stiffness must be considered independently for each unit. To construct a general model of the scissor structure, a scissor unit was developed using the left and right boundary connections of adjacent units to simulate a periodically symmetric structure. The proposed method allows us to obtain an accurate distribution of the internal forces and deflections without the use of special elements to account for central pivots.

scissor structure, deployable structure, smart bridge, scissors finite element, equilibrium mechanics

This paper analyzes the relations between the theory of Michell structures, which is one of the most important theories in structural optimization, and some remarkable engineering structures, including selected high-rise buildings, large-scale roof coverings and long-span bridges. The first part of this study briefly presents the development of Michell's theory, its basic concepts, assumptions, and examples and fundamental features of Michell structures. Then, several untypical engineering structures that make use of said concepts are presented, including skyscrapers proposed by the Polish structural designer W. Zalewski and the international architectural office of Skidmore, Owings and Merill (SOM). Next, large-scale roof coverings of "Spodek" arena in Poland as well as selected bridges are thoroughly analyzed in the context of similarity to Michell structures. The conducted study reveals that considered structural forms of the analyzed structures follow some of the concepts known from Michell's theory and thus possess many features of the optimal structural designs.

topology optimization, Michell structures, high-rise buildings, large-scale roofs, long-span bridges

The paper covers detailed discussion on novel control system developed for adaptive fluidbased shock-absorbers serving for mitigation of unknown impact excitations. In order to provide complete independence of the control system from the loading conditions, the Hybrid Prediction Control (HPC) was elaborated. The proposed method is an extension of previously introduced kinematic feedback control which ensures optimal path finding, tracking and path update in case of high disturbance or sudden change of loading conditions. Implementation of the presented control system allows to obtain self-adaptive fluid-based absorbers providing robust impact mitigation. In contrast to previously developed methods of Adaptive Impact Absorption, the proposed control strategy does not require prior knowledge of impact excitation or its preliminary identification. The independence of applied control system from parameters of impact loading results in the capability of automatic path correction in the case of disturbance occurrence and readaptation to a number of subsequent impacts. The successful operation of the selfadaptive system is investigated with the use of numerical examples involving doublechamber pneumatic shock-absorber equipped with controllable valve. Efficiency of the HPC is proved by comparison with passive absorber as well as device equipped with adaptive and optimal control modules.

hybrid prediction control, kinematic feedback control, adaptive impact absorption, unknown impact mitigation, self-adaptive system

The paper presents development, evaluation and comparison of various control systems for adaptive fluid-based absorbers serving for absorption of the impact loading. The investigations concern two competitive approaches: i) standard control systems with single determination of the optimal system path based on identified impact conditions, and ii) newly-developed control systems with on-line determination and update of the system path during the process. It is revealed that low robustness of the standard control systems to imprecise impact identification and unknown disturbances results from the assumed path-determination approach and utilized simple path-tracking methods. The proposed solution to this problem is application of the innovative control systems, which utilize Automatic Path Finding and Automatic Path Update algorithms based on full kinematic feedback as well as Hybrid Path Tracking method dedicated for fluid-based absorbers. The introduced approach to absorber control is used to develop three different self-adaptive systems of increasing complexity and robustness. The favourable capabilities of proposed systems including no need for impact identification, high robustness against force disturbances and reduction of leakages influence are proved. Detailed discussion is presented using the illustrative example of single-chamber adaptive pneumatic shock-absorber mitigating impact loading.

adaptive impact absorption, automatic path finding, automatic path update, full kinematic feedback, hybrid path tracking, self-adaptive system, pneumatic shock-absorber

Scissors mechanisms are commonly used in safety engineering during the construction of temporary structures, owing to their inherent advantages of foldability, transformability, and reusability. We effectively utilized these scissors mechanism features to develop a lightweight, deployable emergency Mobile Bridge (MB) based on optimization, and control of the folding structure. Here, we discuss the problems of optimal reinforcement layout for the MB by formulating and solving three optimization problems, namely: (a) the load capacity maximization problem, (b) the weight minimization problem, and (c) coupling the load capacity maximization problem and the weight minimization problem. The potential benefits resulting from the application of reinforcement were evaluated using a combination of finite element analysis and an optimization algorithm based on the differential evolution method. The results demonstrate the significant positive influence of the additional reinforcing members. In particular, the limit load was increased by over 10 times, while the weight was decreased to approximately half. The proposed methodology enabled the development of a substantially improved version of the MB characterized by a higher load capacity and lower weight in comparison to the initial bridge design.

This paper investigates an application of a ball-screw inerter for mitigation of impact loadings. The problem of impact absorption is to provide a minimum reaction force that optimally decelerates and eventually stops an impacting object within the available absorber stroke. It significantly differs from vibration mitigation problems which are typical application of inerters. The paper demonstrates that the optimum absorption can be achieved by fully passive means. For known values of the object mass and inerter parameters, the obtained solution is independent of the impact velocity. The optimum passive absorption is achieved by employing a variable thread lead. As a result, two force components emerge, the typical inertance-related force and a damping-like term, and sum up to provide the optimum constant deceleration force. This result is relatively unique: conventional absorbers do not provide a constant force even with complex active control systems. Finally, an optimization problem is formulated to reduce the influence of process uncertainties (range of possible mass values, unknown friction). The results are verified and analyzed in a numerical example.

Recent progress in the field of sensors, actuators, and smart materials allows the construction of more and more efficient controllable pneumatic dampers for shock absorption. Typically, such devices apply online semi-active control techniques, which utilize electromagnetic, piezoelectric, or magnetostrictive valves. As a result, they are characterized by a high efficiency of impact absorption, but simultaneously by a complicated construction and a specialized electronic system. The alternative solutions are semi-passive absorbers that ensure a similar performance by using a much simpler, low-cost construction and a less complicated adaptation mechanism. This paper introduces an adaptable semi-passive single-chamber pneumatic shock absorber, SOFT-DROP, which provides the optimal impact absorption and energy dissipation after a single reconfiguration performed at the beginning of the process. The high effectiveness of the proposed concept is proved in numerical and experimental investigations of the device. Moreover, the proposed semi-passive damper is also compared against already known pneumatic absorbers that utilize semi-active control methods. Ultimately, the device might be used in an airdrop system for delivery of light packages.

adaptable, semi-passive, impact absorption, optimal design, pneumatic shock absorber

This paper studies the effect of prestress force magnitude on natural frequencies and dynamic behaviour of eccentrically prestressed glass fibre reinforced polymer composite beams, including the theoretical background, numerical results and experimental verification. The term prestress indicates the initial tensile stress applied to the fibres embedded in selected external layers of the composite material. First, the paper presents the theoretical background of the finite element method modelling of prestressed composites. Then, the results of numerical simulations conducted for a five-layered glass-epoxy composite beam are presented. The natural frequencies corresponding to three initial bending modes are analyzed for different prestressing force levels and for different fibre volume content. Finally, the results are verificated by experimental modal analysis conducted on three different glass-epoxy composite specimens of various mechanical parameters. Both the numerical results obtained from finite element method and the experimental results obtained from experimental modal analysis reveal that the first bending frequency increases and the two subsequent bending frequencies decrease due to the prestressing force. The comparison of numerical and experimental data confirms the effect and allows to quantify the influence that the prestress force has on the natural frequencies of composites, which is an interesting and practically relevant phenomenon.

Prestressed structures, laminated composites, prestressed reinforced composites, glass fibre reinforced polymer composite materials, vibrations, finite element method

This paper attempts to fill the gap in the literature by introducing and discussing an enhanced physical model of the MR damper. The essence of the presented model is to combine the effect of compressibility of the MR fluid enclosed in each chamber with the effect of blocking the flow between the chambers in the case of a low pressure difference. As it will be shown, the concurrence of both considered phenomena significantly affects mechanical behaviour of the damper, influences its dissipative characteristics, and in particular, it is the reason behind the distinctive 'z-shaped' force–velocity hysteresis loops observed in experiments. The paper presents explanation of the observed phenomena, detailed derivation of the thermodynamic equations governing response of the damper, their implementation for various constitutive models of the magnetorheological fluid and, finally, formulation of the corresponding reduced and parametric models. Experimental validation shows that proper identification of physical parameters of the proposed mathematical model yields the correct shapes of force–velocity hysteresis loops.

Magnetorheological fluid dampers, Smart fluids, Hysteresis modelling

Mobile Bridge™ is a deployable bridge that uses a scissors mechanism to achieve its useful structural form. The bridge has a compact size in its undeployed state and can be transported easily to where it is needed. Its rapid deployment makes this type of bridge very useful in areas struck by natural disasters by enabling vehicles to cross terrain that has been made impassable. In previous research, experiments and analyses were conducted on a small-scale bridge designed for pedestrians. In order to consider a bridge of increased size, it is necessary to assess whether design and analysis techniques of the small scale bridge are applicable to the full-scale one. In this paper, we consider a full-scale deployable bridge with a lower deck and two scissor units, that allows for a light vehicle to pass across. We have carried out a light vehicle loading test in order to investigate its basic structural characteristics. Furthermore, the paper presents the theoretical design method and numerical models based on the experimental work followed by validation and comparison with the obtained experimental values.

Full-scale Mobile Bridge, Scissor type of emergency bridge, Scissors mechanism, Vehicle loading test

The paper describes various approaches for the mathematical modelling of Adaptive Inflatable Structures (AIS) along with the corresponding numerical methods. The introductory part presents a general idea of adaptive impact absorption (AIA) and the concept of inflatable structures equipped with controllable valves serving for internal pressure control. Application of AIS for adaptive absorption of the impact loading is briefly explained. The paper focuses on diverse methods of modelling of inflatable structures, which are based on interaction between solid walls and fluid enclosed inside. Modelling of the solid walls is based on rigid body dynamics or initial-boundary value problem of solid mechanics. In turn, modelling of the fluid utilizes either classical equilibrium thermodynamics or Navier–Stokes equations. Consequently, four possible combinations of the above approaches are distinguished, precisely analyzed and applied for the modelling of different types of inflatable structures. Each model takes into account controllable valves, which requires introducing additional coupling between parameters defining the valves and selected results of the analysis. Corresponding numerical methods include classical methods of solving ordinary differential equations, finite volume method (FVM) applied for problems with mobile boundaries, finite element method (FEM) applied for problems involving additional ODEs and, finally, FEM coupled with FVM. Proposed numerical methods and software tools are utilized for the simulation of adaptive pneumatic cylinders, adaptive pneumatic fenders and membrane valves.

Inflatable structures, Impact absorption, Fluid–structure interaction

This paper presents a preliminary research aimed at developing a comprehensive approach to modeling, manufacturing and optimal design of prestressed FRP composite structures. A simple and effective analytical model of prestressed composite is derived and further verified by two numerical models and the results of the experimental tests conducted on manufactured prestressed composite samples. The model reveals beneficial influence of prestress on strain and stress distribution in particular plies and resulting improvement of the global response of the composite. A design case-study of prestressed composite is presented and challenges related to design and application of more complicated composite prestressed structures are discussed.

Prestressed structures, Laminated composites, Prestressed FRP reinforced composites

The paper describes application of innovative, inflatable thin-walled structures for absorption of the impact loading and thoroughly investigates their crash characteristics. The proposed concept assumes inflation of thin-walled structures with compressed gas of appropriately adjusted pressure in order to improve their basic mechanical properties, enhance energy dissipation capabilities, and increase corresponding durability to impact loading. In the first part of the paper the influence of compressed gas on mechanical characteristics of aluminium beverage can is analysed experimentally and by the corresponding numerical simulations. The following section proposes and numerically verifies three diverse engineering applications of inflatable thin-walled structures for impact absorption. Finally, the last part introduces the concept of adaptive inflatable barrier and briefly presents three simple strategies of pressure control. Both the performed basic experiment and the conducted numerical simulations show the advantageous influence of compressed gas and prove the feasibility of using inflatable thin-walled structures for impact absorption.

thin-walled structures, inflatable structures, crashworthiness

Adaptive Impact Absorption focuses on adaptation of energy absorbing structures to actual dynamic loading by using system of sensors detecting and identifying impact in advance and embedded semi-active dissipaters with controllable mechanical properties. Application of such devices allows to modify dynamic characteristics of the structure during the period of impact and to precisely control the process of energy dissipation. The paper presents an overview of research conducted at the Department of Intelligent Technologies of the Institute of Fundamental Technological Research dedicated to design and applications of various systems of Adaptive Impact Absorption. Wide range of presented examples covers adaptive hydraulic and pneumatic landing gears, skeletal systems equipped with controllable elements and detachable joints as well as adaptive inflatable structures.

adaptive impact absorption, safety engineering, smart structures, optimal control

The so-called Adaptive Impact Absorption (AIA) is a research area of safety engineering devoted to problems of shock absorption in various unpredictable scenarios of collisions. It makes use of smart technologies (systems equipped with sensors, controllable dissipaters and specialised tools for signal processing). Examples of engineering applications for AIA systems are protective road barriers, automotive bumpers or adaptive landing gears. One of the most challenging problems for AIA systems is on-line identification of impact loads, which is crucial for introducing the optimum real-time strategy of adaptive impact absorption. This paper presents the concept of an impactometer and develops the methodology able to perform real-time impact load identification. Considered dynamic excitation is generated by a mass M1 impacting with initial velocity V0. An analytical formulation of the problem, supported with numerical simulations and experimental verifications is presented. Two identification algorithms based on measured response of the impacted structure are proposed and discussed. Finally, a concept of the AIA device utilizing the idea of impactometer is briefly presented.

Impact load identification, Adaptive Impact Absorption, adaptive structures, real-time systems, impact tests

The paper delivers the benchmark results for the Michell cantilevers constructed within a half strip, for selected values of the σT /σC ratio, σT, σC being the admissible stresses in tension and compression, respectively.

Michell structures, Minimum weight design, Topology optimization, Trusses

Collisions with small service ships are serious danger for offshore wind turbines. Installing torus-shaped adaptive inflatable structure that surrounds a wind turbine tower at water level is one method of effective protection. Proposed pneumatic structure contains several separate air chambers equipped with devices for fast inflation and pressure release. The system can be adapted to various impact scenarios by adjusting the level of initial pressure in each chamber and by controlling the release of compressed air during collision. The paper presents finite element simulation of ship collision with wind turbine tower protected by pneumatic structure, conducted using ABAQUS software. Introduced methods of pressure adjustment are aimed at mitigating tower and ship response. The performed feasibility study proves that inflatable structure can effectively protect the wind turbine tower and the ship against serious damage.

Adaptive inflatable structures, pneumatic structures, adaptive impact absorption, flow control, offshore structures, ship collisions

The article presents a review of recent research carried out in the Department of Intelligent Technologies of Institute of Fundamental Technological Research, dedicated to application of systems for adaptive impact absorption to adaptive aircraft landing gears, novel concept of protective MFM structures, flow-control based airbags, maritime applications of inflatable structures, and development of adaptive wind turbine blade – hub connections.

Adaptive Impact Absorption, Adaptive Structure, Optimal Control

Podwozia lotnicze są traktowane przez konstruktorów samolotów jako elementy konieczne, ale z wielu względów mające negatywny wpływ na projekt. Z punktu widzenia aerodynamiki podwozia w trakcie lotu, stawiają dodatkowy opór aerodynamiczny (mniejszy w przypadku podwozi chowanych), a z punktu widzenia możliwości przewożenia ładunków, pochłaniają część masy startowej samolotu, która mogłaby być wykorzystana na transport towarów lub pasażerów. Biorąc pod uwagę takie uwarunkowania, idealne podwozie lotnicze powinno ważyć jak najmniej i zajmować minimalną ilość miejsca.
Obecnie najpopularniejszym rodzajem podwozia stosowanego w lotnictwie jest typ olejowo-gazowy, który charakteryzuje się najkorzystniejszym stosunkiem sprawności do wagi. Sprawność obecnie stosowanych podwozi lotniczych dochodzi do 80%. Aczkolwiek jest to wartość, która jest uzyskiwana dla jednego predefiniowanego przypadku lądowania z określoną energią uderzenia samolotu o pas startowy. Praktyka pokazuje, że w rzeczywistości zmienność warunków lądowania jest dużo większa niż zakres, na jaki można zaprojektować klasyczne podwozie pasywne. Najczęściej energia uderzenia przy lądowaniu jest znacząco mniejsza od tej, jaką konstruktorzy zakładają do obliczeń w procesie projektowania.
Dwa przedstawione problemy w projektowaniu podwozi lotniczych mogą zostać rozwiązane dzięki koncepcji nowego podwozia gazowego przedstawionego w tym artykule. Po pierwsze, dzięki zastosowaniu technologii inteligentnych i wykorzystaniu materiału funkcjonalnego stało się możliwe zaprojektowanie amortyzatorów czysto gazowych w podwoziach do aparatów latających, dzięki czemu możliwe jest wyeliminowanie oleju hydraulicznego o znacznie większej gęstości od gazu i efektywne obniżenie ciężaru podwozia samolotu. Po drugie dzięki wprowadzeniu inteligentnego sterowania przepływem gazu w amortyzatorze, stała się możliwa adaptacja rzeczywistych charakterystyk pracy amortyzatora do aktualnej wartości energii uderzenia samolotu o pas startowy.
Artykuł przedstawia wstępną fazę badań koncepcyjnych nad gazowym absorberem uderzeń przeznaczonym od zastosowania w podwoziu aparatu latającego, sterowanym przy pomocy zaworu piezoelektrycznego. W trakcie badań wykonano serię prób na modelu numerycznym, która została zweryfikowana przy pomocy badań eksperymentalnych, do których zaprojektowano i zrealizowano sterowanie w pętli zamkniętej dla szybkiego zaworu piezo elektrycznego zintegrowanego z absorberem gazowym.

podwozia lotnicze, podwozie adaptacyjne, adaptacyjna dyssypacja energii

This paper demonstrates progress in Adaptive Impact Absorption (AIA) research field obtained recently in our research group and is based on previously published conference communicates. The monograph (Ref.[1]), under preparation, will present soon more detailed discussion of the considered problems. In contrast to the standard passive systems the proposed AIA approach focuses on active adaptation of energy absorbing structures (equipped with sensor system detecting and identifying impact in real time and controllable semi-active dissipaters, so called structural fuses) with high ability of adaptation to extreme overloading. A semi-active or fully-active solutions can be applied, which depend on constant or time-dependent modifications realized via controllable dissipative devices. Feasible, adaptive dissipative devices under considerations can be based on MR fluids or (hydraulic or pneumatic) piezo-valves. The presentation will be devoted to the following applications of AIA concept: Adaptive Landing Gears (ALG) for mitigation of exploitative aircraft loads and adaptive flow control based airbags for emergency landing of the helicopter.

Adaptive Impact Absorption, Controlled Shock-absorbers, Adaptive Landing Gear, Inflatable Structures

This paper complements the analysis of geometric properties of the Hencky nets within the Michell cantilevers constructed in the trapezoidal domains by providing the analytical formulae for the force fields. The force field analysis introduces a new division of the cantilever domain and enables an alternative method for computing the optimal weights.

Michell cantilevers, layout optimization, minimum weight design

The paper concerns the Michell-like cantilevers transmitting a point load to a straight segment of a support. The feasible domain is of trapezoidal infinite shape, as in the previous parts of the paper. The ratio of allowable stresses in tension and compression is arbitrary, not necessarily equal to 1. The present, last part of the paper includes detailed geometric and static analyses of the optimal cantilevers for various admissible data, thus providing new benchmarks of topology optimization. All results are found by using analytical methods developed in the previous parts of the paper. Particular attention is put on the force field distribution within the fibrous domains. These force fields turn out to be defined in certain subdomains forming a static division. The volumes of the optimal cantilevers are computed in two manners: by direct integration of the density of fibres and summing it up with the volume of the reinforcing bars of finite cross sections, and by using the kinematic formula of Michell according to which the volume is proportional to the virtual work. The examples analysed prove that both approaches lead to identical results of the volumes, thus showing that the possible duality gaps vanish. The analytical solutions are verified by considering appropriately chosen sequences of trusses of finite number of joints converging to the exact Michell cantilevers.

Michell cantilevers, layout optimization, minimum weight design

The present paper is the first part of the four-part work on Michell cantilevers transmitting a given point load to a given segment of a straight-line support, the feasible domain being a part of the half-plane contained between two fixed half-lines. The axial stress sigma in the optimal cantilevers is assumed to be bounded by −sigma_C=< sigma<=sigma_T, where sigma_C and sigma_T represent the allowable compressive and tensile stresses, respectively. The work provides generalization of the results of the article of Lewinski et al. (Int J Mech Sci 36:375–398, 1994a) to the case of sigma_T unequal sigma_C. The present, first part of the work concerns the analytical formation of the Hencky nets or the lines of fibres filling up the interior of the optimal cantilevers corresponding to an arbitrary position of the point of application of the given concentrated force.

Michell cantilevers, layout optimization, minimum weight design

The present second part of the paper deals with the virtual displacement fields associated with the optimality conditions epsilon_1=1, epsilon_2 = -k, k=sigma_T/sigma_c, where sigma_T and sigma_C represent the allowable values of the tensile and compressive stress, respectively. The displacement fields vanish along a straight segment of a line support and are constructed within an infinite domain bounded by two half-lines. The displacement fields are provided by the integral formulae involving the Lamé fields found in part I of this paper. All the results are expressed in terms of Lommel-like functions. These results make it possible to determine the volumes of the optimal cantilevers designs within the feasible domain considered. Computation of the volumes along with analyses of concrete cantilevers will be the subject of part IV of the present paper.

Michell cantilevers, layout optimization, minimum weight design

The paper refers to the problem of Michell (1904) of finding the lightest fully stressed structures, composed of possibly infinite number of members, trasmitting a given load to a support forming a circle. The point load can be located within or outside the circle. The known analysis by Hemp (1973) is enhanced here by disclosing the explicit formulae for the weights of the ribs and the interior (fibrous domain). The optimal weight can be found by two manners: by applying the primal integral formula involving the density of the reinforcement or by computing the work of the load on the adjoint displacement. One of the aims of the paper is to show that both these formulae are equivalent. This identity is essential since in the case of point loads the equivalence of the primal and dual formulations has not been proved till now. The analytically found layouts are confirmed by analysis of trusses (of finite number of joints) approximating the exact Michell-like solutions.

Michell cantilevers, layout optimization, minimum weight design

The contribution describes three innovative external airbag systems developed by the
authors for the protection of flying objects during emergency landings. The first one is the
AdBag system dedicated for small drones, which is designed to protect the carried equipment
and prevent damages to objects or injuries to people at the crash location. The second system
is external airbag designed for ultralight aircraft Skyleader 600, which provides significant
reduction of touchdown velocity and deceleration levels during emergency landings, thereby
improving protection of the pilot and the passengers. Finally, the last presented solution is the
Spring-Drop system with specialized airbag deployment technique, which is dedicated for
specialised airdrop operations where the touchdown conditions can be extremely harsh and
unexpected, while protection of transported cargo is of crucial importance. Both conceptual
studies, numerical simulations and experimental tests of the three proposed systems are
presented and discussed.

External airbags, adaptive system, emergency landing, human safety

This contribution introduces the concept of sky sailing, which combines the
advantages of airships and standard fixed-wing aircraft, albeit in a vertical plane alignment.
The proposed vehicle is equipped with rigid aerodynamic sails and auxiliary engines, enabling
navigation and control with minimal power consumption along the desired trajectory. The
proper orientation of the airship relative to the wind direction is achieved through the
adjustment of the sails' angle of attack and the use of auxiliary lateral engines. Consequently,
the system enables efficient maneuvering, particularly in windy conditions, while requiring low
energy input. In the current stage of our research, we focus on 2D sky sailing in a horizontal
plane. This study formulates mathematical model which employs a combined approach of
analytical methods and numerical simulations based on finite volume method. Then, the
corresponding control problem aimed at following the desired fly path with the lowest possible
energetic cost. The motivation behind this work stems from the potential applications of aerial
monitoring, such as crop or forest surveillance.

Airship, flight control, optimization, aerospace

Within this contribution a challenging problem of adaptive impact absorption is considered and studied in detail. The paper is focused on practical implementation of the self-adaptive system and experimental assessment of its performance. For this purpose a novel kinematics feedback control method is applied and used to adjust in real-time the opening of piezo-electric valve, which is an important part of the smart pneumatic shock-absorber devel-oped in the Institute of Fundamental Technological Research Polish Academy of Sciences (IPPT PAN). As a result, an outstanding shock-absorbing system, capable to adaptively mitigate the impact, is obtained and decelerations acting on the amortized object are significantly reduced for varying parameters of the dynamical excitation. Within the paper the control system im-provement based on proportional control of the piezo-electric valve opening is considered. This improvement may provide much better response of the system in terms of reaction force, which is transferred to the amortized object. Indeed, such control in real-time is very hard to be realized in practice. Nevertheless, the authors make an effort to develop the electronic system allowing for proportional adjustment of the valve opening and replacing the on-off control, which gives worse performance and higher control cost.

self-adaptive impact absorber, adaptive control system, real-time control, pneu-matic absorber, drop tests, piezo-electric valve, braking system

In this contribution, the authors propose a concept of novel type of an ultra-light helium-filled aerostat. The internal construction of the proposed aerostat is based on a self-deployable tensegrity structure equipped with prestressed tensioned elements of controllable lengths. Such construction enables convenient transportation of the aerostat and its fast deployment at the required operational point at the atmosphere. The controllable tensegrity structure can be used for simultaneous changes of the aerostat volume and external shape during the flight. This enables modification of buoyancy and drag forces and obtaining a desired vertical and horizontal motion as well as a desired flight path. The authors propose a method of numerical modelling of self-deployable helium-filled aerostats based on the finite element method as well as CFD and FSI models presenting behaviour of aerostat during typical operational conditions. The presented results show the interaction of the internal tensegrity structure and aerostat envelope and positively verify the feasibility of the proposed concept of tensegrity-based aerostats.

tensegrity structure, internal construction, helium-filled aerostat, numerical modelling

In this contribution the authors propose and investigate the concept of adaptive morphing for recently introduced tensegrity-based helium-filled aerostats. The proposed aerostat is based on an ultra-light tensegrity structure equipped with prestressed ensioned elements of controllable lengths. Such internal structure allows for adaptive morphing of the aerostat defined as simultaneous controllable modifications of aerostat volume and external shape during the flight. The controlled volume changes enable influencing buoyancy forces acting on the envelope and obtaining desired vertical motion of the aerostat during the ascending and descending process (“vertical mobility”). In turn, the controlled changes of external shape of the aerostat can be used either for lowering the aerodynamic drag forces and reducing energy usage needed to maintain stable horizontal position or to follow the desired path of aerostat horizontal motion (“horizontal stability”). The authors effectively apply the previously introduced mechanical FEM model of the tensegrity-based aerostat and dynamic model of the aerostat’s vertical and horizontal motion to conduct simulations of the process of adaptive morphing and maintain a proper position in the atmosphere. The obtained results positively verify the idea of adaptive morphing and its efficiency in controlling vertical and horizontal motion of the aerostat.

tensegrity structure, helium-filled aerostat, adaptive morphing, vertical mobility, horizontal stability

The discussed study is focused on implementation of a novel kinematics-based control technique. Presented results are based on theoretical and numerical analyses as well as on experimental investigations, which are focused on elaboration of the efficient self-adaptive energy absorption system. The developed control method has been originally dedicated to the impact mitigation problem, but it can be adjusted to other types of dynamic excitations. Superior performance of the method results from the fact that proposed system adapts automatically to unidentified dynamic excitations and compensates possible unexpected disturbances during the impact absorption process. The analyzed self-adaptive impact absorption system is based on the pneumatic shock-absorber with piezoelectric valve and real-time control system. This contribution is focused on chosen factors which can lead to undesired imperfections in practical implementation of the control method.

For over two decades, inerter-based devices are a subject of research papers, patents and engineering reports. Since 2002, when the inerter was introduced as the missing element of mechanical networks, various applications of the inerter have been proposed. They include solutions for earthquake engineering, suspensions of vehicles, aircraft landing gears and even systems improving walking performance of humanoid robots. In contrast to majority of the inerter-based systems, which are mainly developed for vibration mitigation problems, this paper concerns the inerter as the shock-absorber protecting objects excited by the impact. In particular, adaptive performance of the ball-screw inerter with variable moment of the flywheel inertia is investigated. In order to ensure efficient adaptation of the inerter to various excitation conditions, the single reconfiguration technique, which was successfully applied for pneumatic absorber, is now adjusted and implemented in the proposed inertial system. The contribution consists of the concept introduction, discussion of the mathematical model of the system, theoretical as well as numerical analyses. Results of the presented study show that optimal impact absorption can be obtained in semi-passive manner. The properly adjusted geometry of the surface guides for the inertial elements ensure appropriate variability of the flywheel moment of inertia. Variable moment of the flywheel inertia provides optimal deceleration of the amortized object. The calculated moment of inertia depends on the mass of amortized object and friction but it is independent of the impact velocity.

ball-screw inerter, impact absorption, passive absorber, variable inertance, variable moment of inertia, inertial damping

In this article we propose a new concept of adaptive telescopic high-altitude aerostat designed in a modular form which allows for sequential changes of volume during the flight. The proposed telescopic aerostat can be easily enlarged or contracted due to application of multi-segmented construction, controllable segments’ couplings and precise adjustment of internal pressure obtained using additional gas tank, valve and compressor. Conducted changes of aerostat volume allow to precisely control generated lift force and to obtain desired paths of ascending and descending. The paper briefly presents development of control strategies aimed at: i) reaching the subsequent altitudes in the shortest period of time, ii) reaching these altitudes at the smallest cost defined as total work done by the compressor. The obtained results show high potential of the proposed innovative concept of the aerostat.

helium airship, control of vertical mobility, reduced energy consumption, optimal ascending and descending paths

The paper presents development of innovative, self-adaptive, fluid-based absorbers and investigation of their application for mitigation of impacts and forced vibrations. The considered absorbers are composed of two chambers filled with fluid and separated by a piston equipped with a controllable valve. The valve enables control of the fluid flow between the chambers and adjustment of the actual value of force generated by the absorber. The aim of the research is to develop the strategy of valve control providing self-adaptive operation of the absorber ensuring dissipation of submitted energy by using minimal value of generated force. The paper includes description of self-adaptive impact absorber, presentation of the control system and numerical simulation of its effectiveness in the case of impact excitation and harmonic loading. It is concluded that self-adaptive system provides optimal mitigation of impact excitation, but its response in the case of harmonic loading is not always optimal and requires further improvement.

The paper analyzes the influence of prestressing force on the natural frequencies on Glass Fibre Reinforced Polymer (GFRP) composite beams. Prestress is introduced by applying initial tensile forces to the fibres embedded in selected layer of the composite material during the manufacturing process. Release of prestressing forces results in deformation and self-equilibrated state of stress of the entire composite which changes both its static properties and dynamic characteristics. The paper is focused on analysis of shifts in natural frequencies corresponding to initial bending modes of the composite beams of various fibre volume fraction and prestressed layer location. The problem is analyzed with the use of finite element simulations and experimental modal analysis. The conducted numerical and experimental work reveals that shifts in the natural frequencies caused by non-axial prestressing can be significant and they are important phenomenon which has to be taken into account during design of the composite material.

Small drones with total mass of a few kilograms are becoming more and more popular in many applications increasing the probability of occurrence of emergency situations caused by an equipment failure or a human error. In case of a fall from a high altitude very often it is possible to use parachute rescue systems, which however require relatively long time for deployment and development of braking forces. The touchdown velocity may be large enough to exceed limit accelerations for UAV equipment. The paper presents the concept of deployable airbag systems, in particular with adaptive flow control, which provides a possible solution to the above-mentioned problems. The paper discusses the overall control and adaptation strategy. Simplified methods for mathematical modeling are proposed and formulated for an example on a cylindrical airbag. The conceptual part is concluded with the presentation of the methodology of experimental verification and results of initial tests of the integrated airbag system.

The paper is aimed at discussion of various control techniques developed for adaptive impact-absorbers protecting structures and machines. Different approaches to the problem of optimal damper design are presented and systems comparison is provided with the example of pneu-matic shock-absorber. The influences of selected control strategy on the absorber characteris-tics, its efficiency and adaptation capabilities are shown. The contribution includes both numerical and experimental examples. The authors highlight the fact that the final design of the device should be elaborated simultaneously with the development of dedicated control system. In some cases properly assumed architecture of the control system enables significant simplifi-cation of the absorber. The paper covers analyses of semi-passive devices with single reconfig-uration to identified excitation conditions and semi-active absorbers capable of adaptation to unknown impact loading. Adaptation mechanisms of such devices and their robustness are com-pared in reference to volatility of system parameters and variety of loading conditions. Limita-tions of smart devices (e.g. piezo-electric valve in pneumatic absorbers) used in practice for absorbers' control are described in relevant mathematical models. Technological challenges in the design and manufacturing of absorbers are identified and methods of their overcoming are proposed.

Adaptive Impact Absorption, adaptive control, adaptable system, damper

We have experienced many times a phenomenon in which a bridge is washed away due to a typhoon, heavy rain in the rainy season, localized torrential rain, tsunami, and other flood disasters, or in which a bridge is damaged by an earthquake or a tremor. There is accordingly increasing demand for new technology and science to restore bridges that have been washed away or damaged. The paper presents a new type of emergency bridge, called Mobile Bridge™(MB), which can be quickly constructed in case of damages after a natural disaster. The concept of the bridge is based on the application of scissor-type mechanism, which provides its rapid deployment. Up to now several experimental MBs of different size were constructed and tested. The presented research reviews fundamental numerical and experimental results for the MB version 4.0 (MB4.0). Experimental testing included strain and acceleration measurements in free and forced loading conditions. From these results, it was possible to estimate basic dynamic characteristics of the bridge. Besides, in order to provide a basis for development of new construction methods for structural reinforcement and suppression of vibrations, various numerical analyses were conducted. The conducted research allows for a better and safer design of the movable and foldable full-scale bridge, the MB.

deployable bridge, scissors-type bridge, emergency bridge, light-weight structure, temporary bridge

The paper describes mathematical modelling of adaptive skeletal structures, which are equipped with semi-active dissipaters based on smart fluids or fast-operating valves and utilize the paradigm of real-time adaptation to external loading. The proposed approach is based on three subsequent stages: i) exact thermodynamic modelling of a single semi-active dissipater with the use of mass, momentum and energy conservation laws, ii) global description of the entire skeletal structure considered as an assembly of semi-active dissipaters in certain geometrical configuration, iii) real-time control of the fluid flow inside semi-active dissipaters providing instantaneous adaptability to actual dynamic loading. This methodology enables accurate representation of mechanical characteristics of the skeletal structure and reliable analysis of its adaptation capabilities.

adaptive structures, skeletal structures, impact absorption, vibration damping

The paper presents a new type of emergency bridge, which can be quickly constructed in case of damages after a natural disaster. The concept of the bridge is based on the application of scissor-type mechanism, which provides its rapid deployment. In case of deployable structures apart from static analysis of different configurations of expansion, it is very important to investigate the dynamic behavior of the system. High compliance and flexibility of the scissors-type bridge may influence user's comfort and safety in case of heavy dynamic loads such as human induced impacts, wind gusts or earthquakes. Up to now, the authors constructed several types of the experimental MBs. The presented research reviews fundamental numerical and experimental results for the Mobile Bridge 4.0. Experimental testing included strain and acceleration measurements in free and forced loading conditions. From these results, it was possible to estimate basic mechanics characteristics, that is statics and dynamic property, of the bridge. The conducted research allows for a better and safer design of the structure of the Mobile Bridge.

Deployable Bridge, Scissors-type bridge, Emergency Bridge, Dynamic property, Natural frequency, Acceleration measurement

The paper presents a two-stage simplified method for the simulation of comminution process which takes place in a beater mill. The first stage of the proposed method is a simulation of the flow of gas and ore particles through a mill based on a two-phase continuous-discrete model. It allows to capture the interaction between the fluid flow and embedded particles, to determine trajectories of their motion and average velocities and frequencies of their collisions against the flywheel and the mill's walls. The second stage of the proposed method is a discrete element method simulation of the process of comminution of a single ore particle. It allows to determine the size distribution of created smaller particles in terms of normal velocity and angle of impact and to estimate the global efficiency of the comminution process. The proposed simulation methodology is applied for the verification of the innovative concept of the pplication of high–speed beater mill for the comminution of the copper ore.

Pneumatic dampers are still an attractive subject of research in both modelling and experimental testing. Progress in the field of sensors and actuators allows to construct more and more efficient absorbers and dampers based on active or semi-active control algorithms. However, passive and semi-passive solutions are also developed because of their lower costs and simplicity. This paper presents adaptable pneumatic shock-absorber that allows to obtain optimal impact absorption and energy dissipation by a single reconfiguration performed at the beginning of the process. The absorber is composed of two cylinders including at least one narrow rectangular slot and adequate number of outflow vents precisely shaped for certain impact scenarios. During operation of the device the air is released through overlapping slots and selected vents, which provides constant value of the generated force. As a result, the shock-absorber works as a passive device but provides minimal value of the reaction force in similar manner as semi-active system equipped with fully controllable mechanical valve. The paper presents the results of numerical simulations of adaptable shock-absorber operation and attempts of demonstrator construction aimed at conducting experimental verification of the concept.

Adaptable, Semi-passive, Impact Absorption, Pneumatic Shock-absorber

In recent years, vibration damping strategies based on semi-active management of strain energy have attracted a large interest and were proven highly effective. However, most of published research considers simple one degree of freedom systems or study the same basic example (the first vibration mode of a cantilever beam) with the same control strategy. This contribution focuses on truss-frame nodes with controllable moment-bearing ability. It proposes and tests an approach that allows the control strategy to be extended to more complex structures and vibration patterns.

adaptive impact absorption, smart structures, semi-active control, safety engineering

This contribution reviews the challenges in adaptive self-protection of structures. A proper semi-active control strategy can significantly increase structural ability to absorb impact-type loads and damp the resulting vibrations. Discussed systems constitute a new class of smart structures capable of a real-time identification of loads and vibration patterns, followed by a low-cost optimum absorption of the energy by structural adaptation. Given the always surging quest for safety, such systems have a great potential for practical applications (in landing gears, road barriers, space structures, etc.). Compared to passive systems, their better performance can be attributed to the paradigm of self-adaptivity, which is ubiquitous in nature, but still sparsely applied in structural engineering. Being in the early stages of development, their ultimate success depends on a concerted effort in facing a number of challenges. This contribution discusses some of the important problems, including these of a conceptual, technological, methodological and software engineering nature.

adaptive impact absorption, smart structures, semi-active control, safety engineering

Modelowanie i symulacje numeryczne są obecnie nieodłączną częścią projektowania i optymalizacji różnorodnych procesów technologicznych. Zastosowanie metod numerycznych w projektowaniu procesów mechanicznego urabiania i przeróbki rud metali jest w dalszym ciągu stosunkowo niewielkie. Procesy odspajania kawałków skały od calizny i ich rozdrobnienia z zastosowaniem różnego rodzaju maszyn, wiążą się silnie nieciągłymi zjawiskami zniszczenia materiału i są bardzo trudne do modelowania za pomocą standardowych metod numerycznych, takich jak metoda elementów skończonych, opartych na ciągłym sformułowaniu zagadnienia mechaniki ciała stałego. Duże możliwości w zastosowaniu do tych procesów ma intensywnie rozwijana w ostatnich latach metoda elementów dyskretnych, w której materiał jest reprezentowany przez liczny zbiór ziaren, oddziałujących między sobą poprzez siły kontaktu. Model ten w sposób naturalny uwzględnia materiał rozdrobniony. Uwzględnienie wiązań kohezyjnych między ziarnami oraz możliwości ich zrywania umożliwia modelowanie inicjacji i propagacji pęknięć w materiale. W niniejszej pracy zostaną przedstawione możliwości wykorzystania metody elementów dyskretnych do symulacji urabiania skał za pomocą noży stożkowych i dysków oraz do symulacji zachowania się materiału w młynie. Sprzężenie metody elementów dyskretnych z modelem przepływu płynu umożliwi modelowanie zawiesiny pyłowej rozdrabnianego materiału.

modelowanie dyskretne, mechaniczne urabianie, rudy metali

The so-called Adaptive Impact Absorption (AIA) is a research area of safety engineering devoted to problems of shock absorption in various unpredictable scenarios of collisions. It makes use of smart technologies including systems equipped with sensors, controllable dissipaters and specialized tools for signal processing. One of the most challenging problems for AIA systems is on-line identification of impact lo ads, which is crucial for introducing optimum real-time strategy of adaptive impact absorption. This paper presents development of methodology which enables real-time impact load identification. In considered problem a dynamic excitation is generated by a mass M 1 impacting with initial velocity V 0. An analytical formulation of the problem, corresponding numerical simulations and experimental tests are presented. Two identification algorithms based on measured response of the impacted structure are proposed and thoroughly discussed. Finally, a concept of the AIA device utilizing the idea of detecting device (the so called “impactometer”) is briefly described.

Impact Load Identification, Adaptive Impact Absorption, Real-time Systems

The paper describes enhanced physical model of MR damper which takes into account the effects of blocking the flow between the chambers in case of low pressure difference and the compressibility of the fluid enclosed in each chamber. Combination of both effects is considered as the reason of gene ration of the characteristic shapes of force-velocity hysteresis loops. The subsequent sections of the paper contain derivation of the thermodynamic equations governing response of the damper and their implementation for two constitutive models of the magnetorheological fluid. Successful qualitative comparison against the experiment proves the correctness of applied assumptions and the relevance of the proposed model.

magnetorgeological fluids, MRF dampers, physical-based modeling

The paper introduces the concept of prestressing selected layers of laminated composite in order to increase its stiffness and improve its overall mechanical response. Both analytical and numerical models of prestressed composites are proposed and utilized to optimize applied prestressing forces. Further, dedicated laboratory stand and developed methodology of experimental evaluation are described. The final part of the paper briefly discusses prospective applications of prestressed composites.

prestressed structures, laminated composites, prestressed reinforced composites

The paper presents a concept of new adaptive valve s, which can be applied in the Adaptive Inflatable Structures for impact absorption - high-performance membrane and bistable snap-through valve. The main idea behind those concepts is to employ fluid flow in order to assist actuation of the system.

adaptive impact absorption, inflatable structures, high performance valves

This contribution presents the concept of smart, deployable skeletal structures along with existing and prospective applications. The first part introduce s the concept of multi-folding, which is the basis for the design of all smart deployable skeletal structures. In the second part three diverse innovative applications are described: deployable mobile bridge, adaptive impact absorber and controllable valve.

smart skeletal structures, adaptive impact absorption, safety engineering

The paper describes various approaches for mathematical modelling of adaptive inflatable structures (AIS) along with corresponding numerical methods. The introductory part presents a general idea of adaptive impact absorption (AIA) and the concept of inflatable structures equipped with controllable valves serving for internal pressure control. Application of AIS for adaptive absorption of the impact loading is briefly explained. The paper focuses on methods of modelling of inflatable structures, which are based on interaction between solid wall s and fluid enclosed inside. Modelling of the solid walls is based on rigid body dynamics or initial boundary value problem of solid mechanics. In turn, modelling of the fluid utilizes either classical equilibrium thermodynamics or Navier -Stokes equations. Consequently, f our possible combinations of the above approaches are distinguished, precisely analyzed and applied for modelling of different types of inflatable structures. Each model takes into account controllable valve s, which require introducing additional coupling between parameters defining the valve s and selected results of the analysis. Corresponding numerical methods include Runge - Kutta methods, finite volume method ( FVM ) applied for problem s with mo bile boundaries, classical finite element method ( FEM ) and finally FEM coupled with FVM. Proposed numerical methods and software tool s are utilized for simulation of adaptive pneumatic cylinders, adaptive pneumatic fenders and membrane valves.

inflatable structures, impact absorption, fluid-structure interaction

Adaptive Impact Absorption focuses on adaptation of energy absorbing structures to actual dynamic loading by using system of sensors detecting and identifying impact in advance and semi -active dissipaters with controllable mechanical properties which enable change of system dynamic characteristics in real time. The article present s a review of research conducted at the Department of Intelligent Technologies of the Institute of Fundamental Technological Research dedicated to applications of systems for Adaptive Impact Absorption. Wide range of presented examples covers pneumatic landing gears, bumpers for offshore towers, wind turbine blade-hub connections and d protective barriers for automotive applications.

adaptive impact absorption, safety engineering, smart structures, optimal control

Collisions with small service ships are serious dangers for offshore wind turbines. Installing of the adaptive torus-shaped pneumatic fender that surrounds wind turbine tower at water level constitutes on e method of effective protection against such events. Innovative pneumatic fender proposed in this paper contains several internal air-chambers equipped wit h fast inflators and high-performance valves allowing for control of gas migration and release. The system ca n be adapted to various impact scenarios by adjusting the level of initial pressure in each chamber and by controlling transfer of compressed gas during impact. The paper presents numerical simulations of ship collision against wind turbine tower protected by adaptive fender conducted by means of FEM-based software. Several control strategies aimed at mitigating tower and ship response are introduced. Performed feasibility study proves that inflatable structure can effectively protect the wind turbine tower and the ship against serious damages.

Adaptive Inflatable Structures (AIS), pneumatic fenders, Adaptive Impact Absorption (AIA), offshore collisions, off-shore docking operations

Adaptive Impact Absorption focuses on active adaptation of energy absorbing structures to actual dynamic loading by using system of sensors detecting and identifying impact in advance and controllable semi-active dissipaters with high ability of adaptation. The article presents a review of research carried out in the Department of Intelligent Technologies of Institute of Fundamental Technological Research dedicated to applications of systems for adaptive impact absorption. Wide range of presented examples covers pneumatic landing gears, adaptive crashworthy structures, wind turbine blade-hub connections and flow control based airbags for maritime and aeronautical applications.

smart structures, adaptive structures, Adaptive Impact Absorption, crashworthiness, safety engineering

This paper proposes a benchmark for conceptual devices dedicated to adaptive impact absorption (AIA) and protection against shock excitations. The problem of the exploitation impacts is present in a wide class of applications, and particularly where direction of the object’s movement is well-defined, for example: precise docking systems, rail car buffers or landing gear shock absorbers. In those applications the objective is to equalize the values of velocities of the bodies in order to minimize the deceleration peak. The proposed benchmark establishes a comparing procedure for materials or devices in the field of AIA in a simplified regime in order to improve the comparability of the solutions. A drop test device is proposed to be used for testing the proposed devices in the predefined experimental regime. Besides, an example of the adaptive absorber is presented.

Adaptive structures, Shock absorption, Impact energy absorption, Piezoelectric valve

The class of ultra-light aircraft becomes more and more popular among the enthusiasts of aviation due to low formal requirements of getting the pilot license and low costs of the equipment. Therefore, the training of the pilots starts to be a large-scale task. One of the most difficult operation for the inexperienced pilots is touch-down and it often happens to strike the ground with a high sink speed. In consequence the training machines are endangered of fast structural damage. A potential solution would be to mount a system of adaptive landing gear for light aircraft with a capability of recognition of the actual landing impact and tuning the landing struts in order to conduct the smoothest landing operation possible. In the case of the ultra-light aircraft class the weight of the components is the crucial task and therefore the low-weight pneumatic system is proposed for these application.
The paper presents a concept of an adaptive landing system and adequate control strategy for a small aerial vehicle. The objective of the work was to develop a fully functional model of the landing system and experimental verification of it. The system is based on the new pneumatic impact absorbers actuated via piezo-stacks. The concept assumes designing of the system with the capability of adaptation to actual energy of impact scenario identified by a dedicated sensing system for impact energy recognition.
The designed control system was dedicated to process the data from the system of impact energy recognition in order to perform the optimal landing scenario. The objective of the control strategy was minimization of the structure’s deceleration peaks during the touchdown.
The presented results consist of numerical analysis of the adopted strategy of control and experimental verification of the concept on the dedicated experimental device. The results proved that the proposed method allowed minimization of the maximal deceleration level acting on the demonstrator.

Additive Manufacturing is one of the most rapidly developing production technologies in the last decade. In case of polymeric materials the Fused Deposition Modelling (FDM) provides low cost and high versatility, however is limited by low accuracy and mechanical properties of applied polymeric materials. One of the ways of overcoming the latter deficiency is the modification of the FDM process allowing for the reinforcement of the printed composites with continuous fibres. The objective of the research is to present the performance of additively manufactured Carbon Fibre Reinforced Polymer (CFRP) sample with embedded Fiber Bragg Grating sensors (FBG) under the influence of mechanical loading and temperature changes. FBG sensors were introduced to the middle of the specimen during manufacturing process. Experimental results show high nonlinearity due to a relatively low glass transition temperature of the PLA material. Additionally, the numerical modelling using the Finite Element Method provides more complex insight into the influence of embedded fibre optic on the AM composite material.

The contribution presents recent progress in development of the control systems for
semi-active fluid-based dampers equipped with fast-operating valves. The attention is focused
on the case when the damper is subjected to impact of mass moving with initial velocity and
additional excitation force acting during the process. The objective of the corresponding control
problem is to find the change of valve opening which provides absorption of the entire impact
energy with minimal value of generated reaction force. The contribution presents two different
approaches to solution of the challenging control problem with unknown excitations and disturbance
forces, which are based on the concept of Model Predictive Control.

fluid-based dampers, semi-active dampers, Hybrid Prediction Control, Identification-based Predictive Control

The current progress in the field of sensors and actuators has triggered increasing application of semi-active shock-absorbers for mitigation of dynamic excitations in car suspensions, aircrafts landing gears and buildings seismic protection systems [1]. The problems related to design of semi-active shock-absorbers include not only their proper construction providing reliable operation, but also elaboration of control strategies ensuring optimal mitigation of dynamic excitations of various kinds [2,3]. Development of optimal control strategies is especially difficult because of limitations of applied actuators, e.g. their finite stroke and speed, which are often critical for system operation and strongly influence efficiency of the shock-absorbing device. The contribution concerns the fundamental problem of mitigation of the rigid object’s impact using fluid-based shock-absorber equipped with a controllable valve with predefined performance limitations. The problem of impact mitigation is formulated as optimal control problem aimed at dissipation of the entire impact energy and minimization of the global deviation of generated force and corresponding impacting object's deceleration from the theoretical optimal values [4]. The considered limitations of valve operation cause that solution of the control problem is no longer intuitive and sophisticated mathematical tools have to be applied. First, the application of Pontryagin's maximum principle to impact mitigation problem is analyzed and the difficulties in obtaining final solution are discussed. Secondly, the possibilities of solving the problem using gradient-based methods of variational calculus are considered and the influence of initially assumed control scenario is investigated. Eventually, the solution of impact mitigation problem is obtained using direct methods with various discretization and schemes of numerical integration. The
obtained solutions are thoroughly analyzed and compared against each other, which allows to draw general conclusions about application of optimal control methods for semi-active shock-absorbers subjected to impact loads and to evaluate the influence of valves limitations on the efficiency of impact absorption process.

Despite the fact that airbag systems are well-known and used in safety engineering for many years the growth of research and development activities and increasing number of new applications of airbags are observed. Advances in the field includes among others: development of advanced car airbags, analyses of airbag cushioning for landing on Mars, elaboration of emergency landing system for drones. Another field of airbags application and simultaneously the main motivation for the study presented in the paper is the evacuation of people conducted by the fire brigade. When people are forced to leave the building by jump from the window or roof the rescue cushion is placed on the ground in order to mitigate the impact and safe life of evacuated people. The aim of the study is to develop the relevant adaptation strategy for the system and provide efficient operation of the airbag in case of different impact velocities and different masses of the landing person. Several approaches to the system adaptation are analyzed and they include semi-active as well as semi-passive solutions. Also possibility of implementing the concept of self-adaptive impact absorption is assessed. Technical and operational requirements for the rescue cushion are considered and based on them the final adaptation principles are selected. Evaluation of the system performance is conducted with the use of numerical models of dummies provided in the LS Dyna software environment. In Fig. 1. the overloads acting on pelvis of three different dummies dropped from assumed height are shown. The obtained mitigation of the impact loading is significant for all considered cases.

The inerter is a subject of intensive research in the field of structural dynamics and control since 2002, when it was introduced by Malcolm Smith. Inerter-based devices are implemented in various practical applications, which include protective systems in earthquake engineering, suspensions of trains, road vehicles and aircraft landing gears. The majority of inerter applications proposed in the literature concerns vibration mitigation problems, e.g., implementation of the inerter in tuned mass dampers. In contrast, this contribution discusses an application of the inerter for solving the problem of impact absorption. The inerter was previously considered as a shock-absorber in [Ref.] but optimal impact mitigation was not provided. Recently, the authors have studied a simple inerter device based on the ball-screw mechanism with a variable thread lead, which ensures minimization of the generated reaction force and the optimal impact absorption. This contribution sums up the results obtained in the full-length journal paper, currently under review.

ball-screw inerter, impact absorption, passive absorber, variable inertance, variable moment of inertia, inertial damping

Novel semi-active shock-absorbers dedicated to impact absorption utilize high-performance valves to control actual flow of the fluid between absorber chambers, modify generated reaction force and obtain optimal process of energy dissipation. Although various control strategies providing optimal impact mitigation were elaborated, they were based on strict assumptions such as apriori knowledge of impact loading and lack of system disturbances. In contrast, more challenging objective is to develop control systems maintaining efficient and robust operation in the case of incomplete information about system excitation and disturbances in the process. The possible solution is application of self-adaptive systems based on sequential measurements of system state, such as elaborated by authors Hybrid Prediction Control involving bang-bang and continuous valve actions. In this contribution improvement of self-adaptive system is achieved by introduction of the online identification of system parameters and its application to compute optimal control.

impact mitigation, fluid-based shock-absorber, Model Identification Adaptive Control, semi-active control

The world has seen many kinds of natural disasters, which have critically influenced the residents' lives by causing damage to infrastructure. To realize rapid rescue efforts in an emergency situation, we propose a deployable emergency bridge, called Mobile Bridge TM [1], based on the theory of foldable structures[2]and the concept of Multi-Folding Microstructures (MFM)[3]. The current research presents the fundamental,numerical and experimental results obtained for the pedestrian and vehicle Mobile Bridges. In this paper, it is considered the localized linearization problem with the fixed an angle although this bridge contains a geometrical nonlinearity of scissors structure. Additionally, a seismic response analysis is conducted for the case where the Mobile Bridge is used in the disaster area as an emergency bridge. This allows for a better and safer structural design of the Mobile Bridge, which is patented in [4],[5].

The paper presents a new type of emergency bridge, which can be quickly constructed in case of damages after a natural disaster. The concept of the bridge is based on the application of scissor-type mechanism, which provides its rapid deployment. In case of deployable structures apart from static analysis of different configurations of expansion, it is very important to investigate the dynamic behavior of the system. High compliance and flexibility of the scissors-type bridge may influence user's comfort and safety in case of heavy dynamic loads such as human induced impacts, wind gusts or earthquakes. Up to now, the authors constructed several types of the experimental MBs. The presented research reviews fundamental numerical and experimental results for the Mobile Bridge 4.0. Experimental testing included strain and acceleration measurements in free and forced loading conditions. From these results, it was possible to estimate basic mechanics characteristics, that is statics and dynamic property, of the bridge. The conducted research allows for a better and safer design of the structure of the Mobile Bridge.

Deployable Bridge, Scissors-type bridge, Emergency Bridge, Dynamic property, Natural frequency, Acceleration measurement

The concept of increasing strength capacity of structural elements by introducing preliminary stresses, counteracting the exploitation stresses, is known for years. Large number of applications of pre-stressed materials in civil engineering proves that proper compression of material can effectively increase the strength of structural elements. Because of the rapid development of composite materials, and growing demand for light materials with particularly high stiffness and strength properties, the pre-stressed FRP composites application in industry seems to be a question of time. This assumption is confirmed by increasing number of publications concerning the problem of mechanical characteristics for such materials. This paper presents the results of preliminary research on the pre-stressing of the FRP composite structures, while the term pre-stress indicates initial tensile stress applied to the fibres embedded in selected layers of the composite material. Manufacturing process and shape forming possibilities as well as short-term static and dynamic behaviour of the pre-stressed composites are discussed. Presented results are achieved by the use of the experimental methods (three-point bending tests and Experimental Modal Analysis) and experimentally verified Finite Element Method model of pre-stressed structure.

The paper introduces the concept of eccentrical prestressing of fiber reinforced polymer materials in order to improve their mechanical properties and global mechanical behaviour. Prestressing is here understood as application of the initial tensile stress to the fibres embedded in selected external layers of the composite material. The objective of prestressing is to increase stiffness of the composite and to obtain desired response to applied external loading. The main objective of this research work is to develop a comprehensive approach to analysis of prestressed composites, which includes analytical and numerical modelling of the static behaviour, optimal composite design, as well as, simulation of dynamic response. Initially, we derive simple and effective analytical model of prestressed composite based on models of individual prestressed plies and their homogenization. The analytical model is used to reveal beneficial influence of prestress on strain and stress distribution in particular plies and resulting increase of the composite stiffness. Further, three options for the FEM-based numerical modelling of prestressed composites are proposed and thoroughly compared with each other. Developed analytical and numerical models are used to propose methods of prestressed composite design in which optimization of prestressing forces is used to minimize required composite thickness or fiber volume fraction. Eventually, FEM simulations are applied to assess the influence of prestress force magnitude on natural frequencies and modal shapes of eccentrically prestressed composite beams of various fibre volume fraction. The final part of the paper summarizes the potential advantages of the prestressed composites and unveils their superiority in comparison to the standard ones. Potential applications of prestressed composite materials in civil engineering and aerospace industry are briefly discussed. In addition, challenges related to design and manufacturing of structures made of prestressed composite materials are presented.

Pneumatic dampers are still an attractive subject of research in both modelling and experimental testing. Progress in the field of sensors and actuators allows to construct more and more efficient absorbers and dampers based on active or semi-active control algorithms. However, passive and semi-passive solutions are also developed because of their lower costs and simplicity. This paper presents adaptable pneumatic shock-absorber that allows to obtain optimal impact absorption and energy dissipation by a single reconfiguration performed at the beginning of the process. The absorber is composed of two cylinders including at least one narrow rectangular slot and adequate number of outflow vents precisely shaped for certain impact scenarios. During operation of the device the air is released through overlapping slots and selected vents, which provides constant value of the generated force. As a result, the shock-absorber works as a passive device but provides minimal value of the reaction force in similar manner as semi-active system equipped with fully controllable mechanical valve. The paper presents the results of numerical simulations of adaptable shock-absorber operation and attempts of demonstrator construction aimed at conducting experimental verification of the concept.

Adaptable, Semi-passive, Impact Absorption, Pneumatic Shock-absorber.

scissor type of bridge, emergency bridge, strut reinforcement, sectional optimization

adaptive inflathigh performance valves, adaptive inflatable structures

Smart And Adaptive Structures, Adaptive Impact Absorption, Safety Engineering

high performance valve, bistable elements, snap-through, adaptive impact absorption

Many natural disasters such as earthquakes, floods, torrential rains occur around the world, and we to undertake quick rescue actions. However, there are many recovery problems because of the occurrence of secondary disasters at each rescue worksite.So, from the previous study of optimal structures and control regulation of MFM[1]-[2], we propose a new type of foldable bridge with scissors structure called Mobile Bridge[3]. Applying scissors mechanism to bridge form, Mobile Bridge provides not only mobility but also good structural performance, because the whole bridge can be expand or fold quickly. In this paper, we discuss the vehicles passing test on the real scale Mobile Bridge in order to evaluate the design method and application limits.

Mobile Bridge, deployable structures, temporary bridges, scissors-type structures

Dissipation of the energy in mechanical systems is a vitally important engineering and scientific problem. Current stringent safety requirements enforce substantial change of methods of structural design and application of new solutions and technologies which ensure structural integrity.
Currently applied passive safety systems are typically not equipped with control devices. Their dynamic characteristics remains unaltered and thus it is well adjusted to a narrow range of actual loadings. In case of impact loading, it is highly advantageous to apply systems of Adaptive Impact Absorption (AIA), which are capable of fast change of the dynamic characteristics. Recent fast development of the material technologies and, in particular, development in the field of functional (smart) materials and electronic measurement and control systems had created new possibilities of practical applications of the AIA systems.
During the adaptation process the choice of optimal control strategy is followed by adjustment of the dynamic characteristics of adaptive elements of the absorber. These elements can entirely made of functional materials (as e.g. shape memory alloys) or, alternatively, they can be equipped with controllable devices, so-called structural fuses, which provide controlled response of the element. Depending on type of applied control, the changes of structural parameters occur only once (usually before impact) or they are controlled in real time during the impact process.
The systems of Adaptive Impact Absorption can be effectively used to increase the level of safety during the action of the impact loading. In particular, very promising results are obtained with the use of adaptive inflatable structures. However, the possibilities of their practical applications are limited due to the lack methods allowing for the efficient and fast control of the gas flow during impact.
The presented work focuses on the pneumatic adaptive impact absorbing system equipped with a novel, high performance valve, which utilizes bistable snap-through effect. Snap-through effects are mainly the subject of theoretical analysis and they do not find many practical engineering applications.

smart structures, high performance valves, adaptive pneumatic systems, adaptive impact absorption