Georgios E. Stavroulakis

Quasidifferentiability and Nonsmooth Modelling in Mechanics, Engineering and Economics

Inevitably, reading is one of the requirements to be undergone. To improve the performance and quality, someone needs to have something new every day. It will suggest you to have more inspirations, then. However, the needs of inspirations will make you searching for some sources. Even from the other people experience, internet, and many books. Books and internet are the recommended media to help you improving your quality and performance.

Design and robust optimal control of smart beams with application on vibrations suppression

This paper presents the design of a vibration control mechanism for a beam with bonded piezoelectric sensors and actuators and an application of the arising smart structure for vibrations suppression. The mechanical modeling of the structure and the subsequent finite element approximation are based on Hamiltons principle and classical engineering theory for bending of beams in connection with simplified modeling of piezoelectric sensors and actuators. Two control schemes LQR and H2 are considered. The latter robust controller takes into account uncertainties of the dynamical system and moreover incompleteness of the measured information, it therefore leads to applicable design of smart structures. The numerical simulation shows that sufficient vibration suppression can be achieved by means of the proposed general methods.

On the rigid body displacements and rotations in unilateral contact problems and applications

Abstract This paper deals with the treatment of rigid body displacements and rotations in unilateral contact problems. In the presence of rigid body modes the equivalent formulations of the problem, i.e. the variational inequality, the quadratic programming and the linear complementarity formulation involve positive semidefinite matrices. The basic differences from the classical bilateral problems is that in unilateral problems the rigid body modes must be compatible with the inequality constraints. This is a fairly difficult problem to solve and in its generality was open until now. In this paper a systematic analysis including convergence results is presented with respect to some methods already in use, namely the method of coupling with additional elastic bodies or ‘soft’ springs and the method of consideration of certain nodes as fixed. Moreover a new linear complementarity formulation of the problem which explicitly includes the rigid body ‘displacements’ is proposed and is numerically treated by a complementary pivoting technique. Necessary and sufficient conditions for the solution of the problem are derived and the theory is illustrated by examples from structural analysis and from robotics.

Inverse and crack identification problems in engineering mechanics

Preface. Part I: Introduction. Problem Description. 1. Direct and Inverse Problems. Part II: Theoretical and Computational Tools. 2. Computational Mechanics. 3. Computational and Structural Optimization. 4. Selected Soft Computing Tools. Part III: Applications to Inverse Problems. 5. Static Problems. 6. Steady-State Dynamics. 7. Transient Dynamics. References.

Vibration control of beams with piezoelectric sensors and actuators using particle swarm optimization

Research highlights? We design a vibration control mechanism for a beam with bonded piezoelectric sensors and actuators. ? We apply three different variants of the Particle Swarm Optimization for the vibration control of the beam. ? We use a linear feedback control law and a quadratic cost function. ? We compare the results of the proposed method with the results of a Genetic Algorithm and of a Differential Evolution algorithm. ? We conclude that sufficient vibration suppression can be achieved by means of Particle Swarm Optimization. This paper presents the design of a vibration control mechanism for a beam with bonded piezoelectric sensors and actuators. The mechanical modeling of the structure and the subsequent finite element approximation are based on the classical equations of motion, as they are derived from Hamiltons principle, in connection with simplified modeling of the piezoelectric sensors and actuators. One nature-inspired intelligence method, the Particle Swarm Optimization, is used for the vibration control of the beam. Three different variants of the Particle Swarm Optimization were tested, namely, the simple Particle Swarm Optimization, the inertia Particle Swarm Optimization and the Constriction Particle Swarm Optimization. A linear feedback control law and a quadratic cost function are used, so that the results are comparable with the classical linear quadratic regulator approach. The same problem has been solved with two other stochastic based optimization algorithms, namely a Genetic Algorithm and a Differential Evolution and the results are used for comparison. The numerical simulation shows that sufficient vibration suppression can be achieved by means of this method.

Parameter identification of materials and structures

Preface.- Bolognini, L., An overview of enhanced modal identification.- Bui, H. D., Constantinescu, A., Maigre, H., The reciprocity gap functional for identifying defects and cracks.- Maier, G., Bocciarelli, M., Fedele, R., Some innovative industrial prospects centered on inverse analyses.- Mroz, Z., Dems, K., Identification of damage in beam and plate structures using parameter dependent modal changes and thermographic methods.- Stavroulakis, G. E., Engelhardt, M., Antes, H., Crack and flaw identification in statics and dynamics, using filter algorithms and soft computing.- Toropov, V., Yoshida, F., Application of advanced optimization techniques to parameter and damage identification problems.- Waszczyszyn, Z., Ziemianski, L., Neutral networks in the identification analysis of structural mechanics problems.

The delamination effect in laminated von Kármán plates under unilateral boundary conditions. A variational ― hemivariational inequality approach

This paper deals with the delamination effect for laminated plates undergoing large displacements (v. Kármán plates). The interaction between the laminae due to the binding material as well as the delamination effect are described by means of a nonmonotone, possibly multivalued law, while on the boundary of each lamina general unilateral boundary conditions obeying monotone laws are assumed to hold. The interface and the boundary laws are written in terms of nonconvex and convex superpotentials, respectively. The problem is written in the form of a variational-hemivariational inequality. Certain results on the existence and the approximation of the solution of this problem are obtained by means of compactness, monotonicity and average value arguments.

Optimal prestress of cracked unilateral structures: finite element analysis of an optimal control problem for variational inequalities

Abstract The structural analysis problem concerning static stabilization of cracked structures through prestress reinforcement is studied in this paper. A linearly elastic structure with given crack interfaces along which frictionless no-tension no-penetration mechanism hold (the so called unilateral contact mechanism) is assumed. The prestressing control, which in most civil engineering applications is realized by externally placed prestressed cables, is modelled by means of prestressing (control) forces. The static analysis (state) problem turns out to be a variational inequality. The goal of the stabilization is taken to be the healing of the cracks in the structure with the minimum reinforcement among an available and technologically feasible set and this is expressed by means of a suitably written combined cost function. The arising optimal control problem is a nonsmooth and nonconvex one, thus appropriate techniques recently developed in the area of nonsmooth analysis are used for its solution. Numerical examples illustrate the theory and parametric numerical experimentation with various algorithms permit us discuss certain aspects of the computer application. Appropriate condensation techniques for the reduction of the problem dimensionality and the integration of the studied algorithms in a general purpose finite element software are given.

Robust H/sub 2/ vibration control of beams with piezoelectric sensors and actuators

This paper studies vibration control of a beam with bonded piezoelectric sensors and actuators. Basic equations for piezoelectric sensors and actuators are presented. The equation of motion for the beam structure is derived by using the Hamiltons principle. A robust H/sub 2/ controller is designed. The numerical simulation shows that the vibration can be significantly suppressed by the proposed controller.

A linear complementarity approach to the frictionless gripper problem

This article deals with static unilateral phenomena arising in grasping mechanisms and caused by the possible loss of contact between elastic grippers and rigid objects. The problem is formulated as a linear complementarity problem (LCP) that is derived from the equilibrium equations of forces and the compatibility equations for the displacements, as well as from the complementarity inequality restriction describing the contact. A variant of the infeasibility-reducing, complementary pivot al gorithm of Lemke is used for the numerical solution of the arising LCP. Form and force closure conditions are fulfilled in an auto matic way from the solution of the aforementioned LCP. The used algorithm guarantees rapid convergence to the solution of the problem. The theory is illustrated by numerical examples.