Institute of Fundamental Technological Research

Classical approaches to attenuation of vibrations usually aim at dissipation or absorption of the vibration energy in especially designed devices mounted to the structure. A less common approach but recognised as very effective is to induce mechanisms of transferring the vibration energy associated with low-frequency modes into higher-order vibration modes, where it is quickly dissipated by material damping (in structural volume). In the present work, a novel semi-active modal control methodology is proposed for precise control of mechanical energy transfer between vibration modes by means of lockable joints. Moreover, this control strategy is well-suited also for energy harvesting purposes. Energy of the currently induced vibration modes can be transferred into a preselected structural vibration mode that is tuned with an energy harvester. The proposed control strategy is verified numerically, whereas its experimental validation is shown in the accompanying article within the present proceedings.

In this work an experimental study is presented aiming at demonstration of a controlled modal energy transfer concept in frame structures equipped with semi-active members. The proposed semi-active members – lockable joints – allow for local modification of the frame’s stiffness. The objective of the introduced control approach is to provide mechanical energy transfer between particular eigenmodes. A demonstrator has been fabricated for the purpose of the investigation consisting of a double beam frame structure in a cantilever configuration, which is equipped with the semi-active members. The investigated control algorithm employs two types of input signals: local velocity of the structure and local strain of the frame. As a result, a verification of the system effectiveness has been revealed in a variety of frequency ranges. The excitation bandwidth has been appropriately suited to the particular tested cases. The experimentally obtained results confirmed a possibility of the energy transfers between particular structural eigenmodes.

Recent research has shown that visual and inertial measurements can serve as a powerful, robust and accurate odometry source when processed by state-of-the-art algorithms. One of the main benefits of such approach is short latency, even for on-board computers working on Miniature Autonomous Vehicles (MAV). However, depending on environmental conditions or sensor motion patterns, this type of odometry may be prone to drift or even divergence. In the presented work, it is shown that employing occupancy maps can limit such undesirable behaviour while still providing pose estimate at high frequencies. This is of particular importance for highly dynamical MAV control with limited on-board numerical capabilities.

3D maps, Visual-inertial odometry, Aerial systems, MAV control, Occupancy maps

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

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 paper describes concepts of two different technologies developed for control of gas flow in High Performance Actuator (HPA) and control of gas discharge from airbag system through High Performance Valve (HPV). The HPA technology utilizes piezoelectric valve to govern flow in the pneumatic cylinder, used as an impact absorber or smart damper, while the HPV uses membrane surfaces driven by flow and controlled by explosive rings to mode discharge of an airbag system. Both techniques, different in their nature realizes comparatively similar function in flow different scales but similar time scale, where each cycle of operation is near single milliseconds. The paper also covers experimental results and a simple numerical study on the High Performance Valve (HPV) concept developed for a control of an adaptive inflatable impact energy absorber (gas-bag). Patent pending concept of the HPV is utilizing a flow energy drive method, using the flow energy to move and seal working parts of the valve.

Adaptive devices, Piezo-valve, Airbag, Valve, Explosion, Control

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

adaptive inflathigh performance valves, adaptive inflatable structures

Control of crash or impact process may be based on change of mechanical characteristics due to modification of inner structural connections. Presented work covers numerical and experimental analysis of sandwich fabric composite cantilever beam subjected to a low velocity impact. A set of metallic electrical conductors was placed between composite layers causing their controlled delamination when subjected to an electrical explosion. In result, separation of initially connected components in the vicinity of the exploded conductor is obtained, leading to the change of global mechanical characteristics, allowing for modification of beam behavior. Exploding bridge wire (EBW) phenomenon is known from the end of the 18th century [1] and being in use today, mainly for ignition of high explosive materials [2] as well as in physics of high energy [3]. This effect is caused by a rapid heating of a conductor subjected to a pulse of high voltage electric current, what changes its state of matter from solid to vapor, expanding in surrounding continuum and forming a strong pressure wave. Afterwards, in result of current discharge through the formed plasma channel, additional heat is applied to the system increasing the effect. Depending on explosion parameters and properties of continuum elastic, elasto-plastic or shock waves can be observed. In case of action on the composite, exploding wire embedded between layers acts on adjacent surfaces causing their progressive separation in the vicinity of the explosion. Delamination decoupling adhesive is being extended by the pressure acting in the direction normal to the surface of the composite. Figure 1 depicts an example of experimental delamination process from a medium voltage EBW system. A cantilever beam made of layered sandwich composite was modelled with shell finite elements. Problem was solved in a commercial FEM LS-DYNA package using explicit time integration with nonlinear material and geometric formulation. The delamination was simulated by a controlled separation of a connection between layers in the area surrounding the predefined location of the EBW wire. The initiation time of layers’ separation was one of controllable parameters allowing for a wide search for solution dependencies. Numerical solution was compared with experimental results, showing good convergence and proving control feasibility. Also an analytical, rigid perfectly plastic model for explanation of first order effects was used for demonstration of governing principles [4].

Exploding bridge wire

Smart And Adaptive Structures, Adaptive Impact Absorption, Safety Engineering