Institute of Fundamental Technological Research

In the paper we demonstrate how Particle Swarm Optimization (PSO) can be employed to solve the Adaptive Impact Absorption (AIA) problem. We consider a truss structure which is subjected to impact loads. Stiff bars can be replaced by elastoplastic fuses which control theirs dynamical response. The point of optimization is to maximize or minimize a given objective function by redesigning the structure. This is realized by redistributing the initial mass, finding proper fuse localizations and adjusting, in real-time, the elastoplastic limits. Comparing to the previous results, we show that PSO is capable of achieving results at least as good as gradient-based optimization, having at the same time much larger flexibility regarding the definition of the objective function. This gives significantly broader field of potential applications. In particular, we present how PSO can be used to solve the simultaneous optimization problem: mass redistribution and fuse positioning for a set of expected, various impacts.

adaptive impact absorption, particle swarm optimization, truss structures

The paper (written in two parts) is devoted to the presentation of numerical tools, based on the so-called virtual distortion method (VDM) for fast structural reanalysis and to the application of this tools for optimal design of adaptive structures exposed to impact loads. The first paper deals with fast modifications of the material distribution (coupled stiffness and mass redistribution) in dynamically loaded structures, which allows their optimal remodeling, e.g., to minimize average deflections. The VDM-based approach allows analytical sensitivity determination, which is very helpful in efficient implementation of the optimization procedure, utilized to solve the defined remodeling problem. The presented methodology is illustrated with a numerical example of truss–beam structure exposed to random impact loads.

Fast structural reanalysis, Virtual distortion method, Adaptive impact absorption, Optimal design, Impact loads

This paper is a continuation of the article entitled “Remodeling for Impact Reception.” It presents a generalization of the previously discussed concept on optimal remodeling of elasto-plastic structures exposed to impact load, where remodeling process is simulated via virtual distortion method (VDM). The resultant stiffest structure determined in the first part of this paper determines the initial configuration to design the optimal adaptive structure. It is assumed that considered structure can be equipped with so-called structural fuses with plastic-like behavior and controllable yield stress levels. Such an adaptive structure can still be optimized by the proper selection of locations for structural fuses and by the proper tuning of yield stress levels to the identified impact load. Maximization of the impact energy dissipation as the objective function allows significant reduction of residual vibrations after a few milliseconds. VDM-based algorithms for fast, complex reanalysis of dynamically loaded elasto-plastic structures and their sensitivity analysis are the key tools for the above-mentioned optimization procedures.

Fast structural reanalysis, Virtual distortion method, Adaptive impact absorption, Optimal design, Impact loads

For 20 years of development, the virtual distortion method (VDM) has proved to be a versatile reanalysis tool in various applications, including structures and truss-like systems. This article presents a summary of principal achievements, demonstrating the capabilities of the VDM both in statics and dynamics, in linear and nonlinear analysis. The major advantage of VDM is its exactness and no need for matrix inversion in the reanalysis algorithm. The influence matrix—numerical core of the VDM—contains the whole mechanical knowledge about a structure, by looking at all global responses due to local disturbances. The strength of the method is demonstrated for truss structures.

Exact structural reanalysis, Sherman–Morrison–Woodbury formulas, Nonlinear statics and dynamics, System analysis

The paper presents a novel methodology for robust post-accident reconstruction of spatial and temporal characteristics of the load. The methodology is based on analysis of local structural response, and identifies an observationally equivalent load, which in a given sense optimally approximates the real load. Compared to previous researches this approach allows to use a limited number of sensors to reconstruct general dynamic loads of unknown location including multiple impacts and moving loads. Additionally, the problem of optimum sensor location is studied.

impact identification, inverse dynamics, smart systems, structural health monitoring

A new methodology for load identification is proposed. The global dynamic structural response is modeled using only pre-computed, time dependent, dynamic influence matrix, describing structural response to locally generated unit impulses. Then, the impact load identification procedure is based on distance minimization between the modeled and measured local dynamic responses in sensor locations. The theoretical background as well as numerical examples is presented.

structural health monitoring, impact detection, inverse dynamics

The concept of the design of adaptive materials composed of elements with controllable yield stresses is presented and the corresponding, gradient-based numerical design tools are described. Numerical simulation of the adaptation effect to various impact scenarios is demonstrated. The crucial point to get an additional value of energy dissipation (due to synergy of repetitive use of dissipaters in honeycomb-like cellular microstructure) is
to pre-design an optimal distribution of yield stress level in all controllable elements, triggering the desired sequence of local collapses. High effectiveness of active impact energy absorption by the yield stress adjustment demonstrates the potential application of the concept e.g. in shock-absorbing systems.

This paper presents an improved numerical tool for identification of damage in skeletal structures. The problem of identification has been formulated in the time domain within the framework of the Virtual Distortion Method (VDM). VDM generally belongs to fast structural reanalysis methods and can be applied to Structural Health Monitoring problems, among others. The major computational asset of VDM is the influence matrix, containing all the local-global inter-relations for a structure due to given perturbations e.g. initial strain or external force. A non-linear least squares problem with strains, entering the objective function, is the subject of consideration. Strains are used in order to have relatively smooth variations (compared to accelerations) of the analyzed signal in time. The change of stiffness is the design variable. Analytical gradients are implemented in the optimization code based on the Levenberg-Marquardt algorithm with some penalty function terms. The efficiency of the software tool is demonstrated for a numerical example of a 2D truss structure. A breakthrough in terms of computational time reduction has been observed compared to the previously used steepest-descent optimization. The presented software assumes the feasibility of reliable measurements of strains in time for real skeletal structures (e.g. truss bridges). Future research will include experimental verification of the idea with piezoelectric sensors acting as tensometers.