Abstract: The Maxwell equations are derived from thermodynamic principles. While flux density divergence-free is obtained everywhere from the stationary condition on the Gibbs' free energy, the Maxwell-Faraday equation and the Ohm's law with motion are obtained, in conductors, by assuming an adiabatic and reversible evolution of the field. Hence, the Maxwell-Faraday equation may be extended in the dielectric region for any time-varying excitation. Besides, magnetic- and dielectric-behavior laws result from the convexity of the magnetic and electrostatic Gibbs' potentials. Furthermore, the conservation of the power yields the so-called Lorentz force from virtual work principle. Extension to high frequency is also proposed beyond the plasma pulsation of metal. To sum up, the approach is shown to be: 1) consistent with the finite element method; 2) coherent with a coarse graining optimization, from "scratch" to the design scale; and 3) suitable to consolidate energy processes involved in electromagnetic and electromechanical conversion.

Abstract: The three dimensional elasto-viscoplastic composite element method is formulated in this paper for rock masses reinforced by a fully-grouted bolt. If a bolt segment penetrates a finite element representing the rock mass, then a composite element is formed including five sub-elements corresponding to the rock material, the grout material, the bolt material, the rock-grout interface and the bolt-grout interface. The displacements in each sub-element are interpolated from the corresponding nodal displacements of the composite element. By the virtual work principle the governing equation for the solution of the nodal displacements can be formulated. The elasto-viscoplastic characteristics of the materials are considered in the formulation. The new model can be incorporated into the conventional finite element analysis grid, in which several composite elements have fully grouted bolts embedded. In this way the mesh generation of large scale bolted rock structures becomes convenient and feasible. The model has been implemented in a FEM program, and a comparative study between the numerical analysis and a pull out field test has been carried out, from which the validity and the robustness of the new model are justified.

Abstract: A new zig-zag coupled theory is developed for hybrid cross-ply plates with some piezoelectric layers using third-order zig-zag approximation for the inplane displacements and sublayer wise piecewise linear approximation for the electric potential. The theory considers all electric field components and can model open and closed-circuit boundary conditions. The deflection field accounts for the transverse normal strain due to the piezoelectric d 33 coefficient. The displacement field is expressed in terms of five displacement variables (which are the same as in FSDT) and electric potential variables by satisfying exactly the conditions of zero shear stresses at the top and bottom, and their continuity at layer interfaces. The governing equations are derived from the principle of virtual work. Comparison of the Navier solutions for the simply-supported plates with the analytical three-dimensional piezoelasticity solutions establishes that the present efficient zig-zag theory is quite accurate for moderately thick plates.

Abstract: The constraint distribution in nonholonomic mechanics has a double role. On the one hand, it is a kinematic constraint, that is, it is a restriction on the motion itself. On the other hand, it is also a restriction on the allowed variations when using D’Alembert’s principle to derive the equations of motion. We will show that many systems of physical interest where D’Alembert’s principle does not apply can be conveniently modeled within the general idea of the principle of virtual work by the introduction of both kinematic constraints and variational constraints as being independent entities. This includes, for example, elastic rolling bodies and pneumatic tires. Also, D’Alembert’s principle and Chetaev’s principle fall into this scheme. We emphasize the geometric point of view, avoiding the use of local coordinates, which is the appropriate setting for dealing with questions of global nature, like reduction.

Abstract: In the present work the virtual fields method (VFM) has been used to extract the whole set of material parameters governing a nonlinear behaviour law for composite materials. The nonlinearity considered here is due to the damage inherent to the in-plane shear response. The identification method is performed by applying the principle of virtual work knowing the whole strain field onto the surface of a tested specimen. The test chosen here is a shear bending test using a rectangular coupon loaded in a Iosipescu fixture. To illustrate the capabilities of the method, the identification is performed on data provided by finite element simulations. First, the nonlinear finite element model is described. Then, numerical aspects of the VFM are discussed, in particular the stability of the technique with respect to noise in the data. Finally, first elements of test optimisation are given by studying the effect of the length of the active area and the effect of the material anisotropy. This work contributes to the development of the VFM as a tool adapted to the processing of full-field measurement to identify parameters from general constitutive equations.

Abstract: Procedures for modelling multibody systems are well known and many formulations and tools are available for these types of systems. For several years, emphasis has been placed on the modelling of electromechanical systems, particularly multibody systems, such as robots, which are driven by electrical actuators. In this paper, three different unified modelling strategies, based on the virtual work principle, linear graph and bond graph theories, are presented and compared. Three examples, including non-academic applications, illustrate this comparison.

Abstract: This paper presents a complete derivation and implementation of the Arbitrary Lagrangian Eulerian (ALE) formulation for the simulation of large deformation quasi-static and dynamic problems. While most of the previous work done on ALE for dynamic applications was mainly based on operator split and explicit calculations, this work derives the quasi-static and dynamic ALE equations using a fully coupled implicit approach. Full expression for the ALE virtual work equations and finite element matrices are given. Time integration relations for the dynamic equations are also derived. Several quasi-static and dynamic large deformation applications are solved and presented.

Abstract: The constraint distribution in non-holonomic mechanics has a double role. On one hand, it is a kinematic constraint, that is, it is a restriction on the motion itself. On the other hand, it is also a restriction on the allowed variations when using D'Alembert's Principle to derive the equations of motion. We will show that many systems of physical interest where D'Alembert's Principle does not apply can be conveniently modeled within the general idea of the Principle of Virtual Work by the introduction of both kinematic constraints and variational constraints as being independent entities. This includes, for example, elastic rolling bodies and pneumatic tires. Also, D'Alembert's Principle and Chetaev's Principle fall into this scheme. We emphasize the geometric point of view, avoiding the use of local coordinates, which is the appropriate setting for dealing with questions of global nature, like reduction.

Abstract: The definition of energy/coenergy in permanent magnets (PMs) is still in dispute when virtual work is used to compute magnetic forces using finite-element methods. There is also no current practical method for computing forces when PMs touch objects. These problems are addressed in this paper in terms of a new definition of energy/coenergy in PMs and by using shell elements. The results are verified by analytical computations.

Abstract: The failure assessment of smart composite structures requires efficient analytical and numerical techniques in order to tackle electrical and mechanical field concentrations. The present work is directed to the analysis of interface corner and crack configurations which occur in smart composite materials. It delivers a new technique to solve the corresponding piezoelectric boundary value problems. The purpose of the given paper is to describe exactly the asymptotic behaviour at piezoelectric interface corner configurations using the eigenfunction expansions on the one hand, and in the linking of these expansions to regular finite elements on the other. Specific singular eigenfunctions for homogeneous and interface crack configurations are discussed. For the considered cases, the classical crack modes (Mode I and Mode II) and a new Electric Mode are identified. The coupling of the full eigenfunction expansions to the finite elements surrounding the tip region is based on the principle of virtual work applied to the orthogonalised eigenfunctions. Finally, one gets an asymptotic stiffness matrix which does not depend on the distance to the tip. The coefficients of the eigenfunctions can be obtained efficiently from the generalised displacements of the global solution by means of the orthogonalised eigenfunctions. The technique allows to numerically bypass possible singular oscillatory terms in the weak sense, although they actually exist in the strong solution. The given approach is proven and verified in numerical test examples. Standard finite element methods encounter difficulties to give correct solutions at piezoelectric interface crack tips.

Abstract: In this paper, the modelling strategy of a Cosserat rod element (CRE) is addressed systematically for 3-dimensional dynamical analysis of slender structures. We employ the exact nonlinear kinematic relationships in the sense of Cosserat theory, and adopt the Bernoulli hypothesis. For the sake of simplicity, the Kirchoff constitutive relations are adopted to provide an adequate description of elastic properties in terms of a few elastic moduli. A deformed configuration of the rod is described by the displacement vector of the deformed centroid curves and an orthonormal moving frame, rigidly attached to the cross-section of the rod. The position of the moving frame relative to the inertial frame is specified by the rotation matrix, parametrized by a rotational vector. The approximate solutions of the nonlinear partial differential equations of motion in quasi-static sense are chosen as the shape functions with up to third order nonlinear terms of generic nodal displacements. Based on the Lagrangian constructed by the Cosserat kinetic energy and strain energy expressions, the principle of virtual work is employed to derive the ordinary differential equations of motion with third order nonlinear generic nodal displacements. A simple example is presented to illustrate the use of the formulation developed here to obtain the lower order nonlinear ordinary differential equations of motion of a given structure. The corresponding nonlinear dynamical responses of the structures have been presented through numerical simulations by Matlab software.

Abstract: This paper deals with the direct identification of parameters governing anisotropic elastic constitutive equations. These parameters are identified from heterogeneous strain fields with the virtual fields method. This method is based on a relevant use of the principle of virtual work. Different numerical aspects of the implementation of the method are discussed in the paper, mainly in terms of stability of the identified parameters when noisy data are processed. It is shown that the sensitivity of the method to noisy data is compatible with a practical use during experiments.

Abstract: The phenomenon of strain localisation is often observed in shear deformation of particulate materials, e.g., fault gouge. This phenomenon is usually attributed to special types of plastic behaviour of the material (e.g., strain softening or mismatch between dilatancy and pressure sensitivity or both). Observations of strain localisation in situ or in experiments are usually based on displacement measurements and subsequent computation of the displacement gradient. While in conventional continua the symmetric part of the displacement gradient is equal to the strain, it is no longer the case in the more realistic descriptions within the framework of generalised continua. In such models the rotations of the gouge particles are considered as independent degrees of freedom the values of which usually differ from the rotation of an infinitesimal volume element of the continuum, the latter being described for infinitesimal deformations by the non-symmetric part of the displacement gradient. As a model for gouge material we propose a continuum description for an assembly of spherical particles of equal radius in which the particle rotation is treated as an independent degree of freedom. Based on this model we consider simple shear deformations of the fault gouge. We show that there exist values of the model parameters for which the displacement gradient exhibits a pronounced localisation at the mid-layers of the fault, even in the absence of inelasticity. Inelastic effects are neglected in order to highlight the role of the independent rotations and the associated additional parameters. The localisation-like behaviour occurs if (a) the particle rotations on the boundary of the shear layer are constrained (this type of boundary condition does not exist in a standard continuum) and (b) the contact moment-or bending stiffness is much smaller than the product of the effective shear modulus of the granulate and the square of the width of the gouge layer. It should be noted however that the virtual work functional is positive definite over the range of physically meaningful parameters (here: contact stiffnesses, solid volume fraction and coordination number) so that strictly speaking we are not dealing with a material instability.

Abstract: In this Technical Note, the adaptive block element method of rock masses is formulated, in which the elastoplastic characteristics of both rock blocks and discontinuities are taken into account. The concept of an overlay element is illustrated first; then the displacement fields of rock blocks are expressed as functions of so-called general degree of freedoms using the shape functions of the hierarchical finite element method; the governing equations of the rock block system are deduced on the basis of the virtual work principle; and the p-version adaptive algorithm based on the energy norm error estimation of each block element is proposed. The method is applied to the deformation and stability study of a gravity dam, and the parallel laboratory physical test is used to check the validity and ability of the method.

Abstract: This chapter addresses empirical methods for obtaining data on virtual teams, organizations and professional communities. We begin by reviewing different ways of defining virtual work. We then examine two epistemological paradoxes involved in empirical research on virtual work: (1) virtual work is simultaneously mobile and motionless, and (2) virtual work is simultaneously distributed and situated. We address these paradoxes by identifying four data generation approaches that can be used separately or in combination: participant observation, computer logs, interview, and questionnaire. The chapter describes each of these methods and illustrates each with one or more exemplary studies. By studying virtual teams, organizations, and communities from various angles with different types of data, researchers can better inform the process of theorizing. 701 E. Chocolate Avenue, Suite 200, Hershey PA 17033-1240, USA Tel: 717/533-8845; Fax 717/533-8661; URL-http://www.idea-group.com IDEA GROUP PUBLISHING This chapter appears in the book, The Handbook of Information Systems Research, edited by Michael E. Whitman and Amy B. Wosczynski. Copyright © 2004, Idea Group Inc. Copying or distributing in print or electronic forms without written permission of Idea Group Inc. is prohibited. INTRODUCTION This chapter addresses empirical methods for obtaining data on virtual teams, organizations, and professional communities. Because virtual work settings are enabled by advanced information and communication technologies, IS researchers are often in an advantageous position to conduct rigorous studies on the design, development, implementation, use, and consequences of virtual work arrangements. Such studies are needed because work is increasingly mediated by technologies that potentially liberate workers from specific places and times. However, studies of virtual work face fundamental ontological and epistemological challenges that must be addressed before research findings can be considered valid and applicable. This chapter identifies these challenges and offers methodological guidance to researchers investigating virtual work in teams, organizations, and communities. The chapter begins by emphasizing the importance of defining virtual work. Given the variety of definitions of virtuality in research, it is essential that researchers choose a definition that suits their purposes and allows comparison with other studies. Researchers’ definitions comprise their ontological assumptions about virtual work. We review a range of definitions of virtual work, noting that all uses of the term virtual are not equal. We then turn to two epistemological paradoxes involved in obtaining data for empirical research on virtual work. The first paradox is that virtual work is simultaneously mobile and motionless. That is, virtual workers are able to move freely from place to place, but their work activities require stationary attention to technology interfaces. The second paradox is that virtual work is simultaneously distributed and situated. That is, workers can connect with people in different places whom they may never meet in person, yet each individual is situated in a particular physical and social context. We address these paradoxes by identifying four data generation approaches that can be used separately or in combination: participant observation, computer logs, interview, and questionnaire (including Web-based surveys). The chapter describes each of these methods and illustrates each with one or more exemplary studies. WHAT IS VIRTUAL WORK? Taken literally, work described as virtual means work that exists “in effect or essence, although not in actual fact or name” (Webster’s New World Dictionary). The literal meaning of virtual derives from its use in computer science to describe virtual machine environments and its use in science fiction, where concepts like virtual reality were born. In most contemporary research, the literal definition has been abandoned, allowing the term virtual to acquire many meanings. We briefly review the conventional assumptions about virtual work when applied to teams, organizations, and communities. Following this, we identify alternative conceptions of virtual work that researchers might usefully exploit. In teams, virtuality has most often been used to describe work that is distributed across time and space (Saunders, 2000; Townsend, DeMarie, & Henrickson, 1998). Because distributed work is enabled by information and communication technologies, virtual teams have also been defined as teams that rely upon electronic communication 14 more pages are available in the full version of this document, which may be purchased using the "Add to Cart" button on the publisher's webpage: www.igi-global.com/chapter/studying-virtual-work-teamsorganizations/30348

Abstract: A new breed of finite element is developed to analyze the nonlinear behavior of plain-weave fabrics in the in-plane problems of arbitrary boundary condition. A nondimensional parameter called crimp parameter is introduced as an unknown to represent the crimp condition of warp and weft, and handled as a component of the displacement vector. The plain-weave fabric is homogenized by means of a newly defined strain-displacement relationship including the crimp parameter for the sake of consistent dealing with the three types of thread deformations, that is, skewing, straightening and extension. This homogenized model called pseudo-continuum model induces the geometrical nonlinearity with respect to the finite rotation of the threads, and its finite element is formulated by the principle of virtual work in the total Lagrangian description. The mechanism of nonlinear behavior of the plain-weave fabrics is elucidated through several examples by the proposed finite element.

Abstract: We describe a virtual sculpture environment suited to the needs of artists. In this approach, the user is immersed in a virtual environment by the use of haptic devices and immersive display. The project is focused around four main research topics: the sculpture model, the tools and their actions on the model, the display of the sculpture, and the interface between the artist and its virtual work. First results are presented and future works are discussed.

Abstract: The active magnetic bearings (AMB) and linear electrical actuators (LEA) are the important elements for high precision systems such as semiconductor equipment and machine tools. This paper concerns the initial design of a single I U-shaped electromagnetic module as a part of six degrees of freedom (6-DoF) contactless sliding system reached by integration of electromagnetic and mechanical structures of magnetic bearing and electrical actuator. The initial performance (magnetostatic behaviour) of the non-optimized electromagnetic module is investigated. Its vertical suspension forces (1), depending on the bias flux originated from the permanent magnets and planar position of the rotor, are obtained by means of the numerical solutions for electromagnetic field and application of the Coulomb virtual work (CVW) principle. The results obtained by means of finite element models (Ansys 3-D and Maxwell 3-D software packages) are validated by measurements. It allows the understanding of the electromagnetic behavior, flux leakage distributions in the air gaps, values of the generated forces in the contactless sliding system and further evaluation of the structure.

Abstract: Many structures of practical importance are too complex to be analyzed by classical, analytical techniques and, hence, numerical analysis is generally used. The finite element method is the most widely used numerical technique for structural and system analyses.

Abstract: Multidomain modeling has become more and more important, especially since integrated design strategies have imposed themselves for reaching higher standards in system efficiency and precision. This research deals with electromechanical systems with large multibody structure and tight interaction between electrical and mechanical parts. In the first part of this work, the author present an in depth confrontation of existing unified modeling theories: Bond Graphs, Linear Graphs and Virtual Work Principle. A simple example is used to illustrate the use of these theories and their application on multibody systems is discussed. A new modeling strategy is proposed in the second part of this text. On the basis of a symbolic implementation of dedicated formalisms, the author proposes to generate the symbolic submodels for the mechanical and the electrical parts separately and to couple the obtained equations into one global symbolic model, provided to the numerical integrator. This modeling strategy is then applied to several applications. Firstly, simple electrical circuits and electromechanical systems are considered in order to validate the tools which were developed during this work. The validation was achieved by comparison with existing modeling tools and also with experimental measurements. Secondly, more complex industrial applications are presented : 1. a parking gate system, consisting in a flexible barrier mounted on a six-bar mechanism driven by a three phase induction motor, 2. an articulated railway bogie actuated by two induction motors.