Abstract: In this paper, the nonlinear governing equations of motion for viscoelastic moving belt are established by using the generalized Hamilton’s principle for the first time. Two kinds of viscoelastic constitutive laws are adopted to describe the relation between the stress and strain for viscoelastic materials. Moreover, the correct forms of elastic strain energy, kinetic energy, and the virtual work performed by both external and viscous dissipative forces are given for the viscoelastic moving belt. Using the generalized Hamilton’s principle, the nonlinear governing equations of three-dimensional motion are established for the viscoelastic moving belt. Neglecting the axial deformation, the governing equations of in-plane motion and transverse nonlinear oscillations are also derived for the viscoelastic moving belt. Comparing the nonlinear governing equations of motion obtained here with those obtained by using the Newton’s second law, it is observed that the former completely agree with the latter.

Abstract: This paper presents finite element formulations for transient dynamic analysis in structural systems with damping treatments in which viscoelastic materials are characterized by means of fractional derivative models. In contrast to other formulations, such as that of Padovan employing the principle of virtual work, the proposed formulations begin from the local equation of linear momentum and make use of the weighted residual method, providing a matrix equation of motion involving fractional operators. The numerical approximations of these are developed through the Grunwald–Letnikov definition, which allows to formulate explicit and implicit numerical schemes. The principal advantage of the proposed formulations is that the history of the displacements and external forces must be stored, but not that of the stress, which reduces computational time and storage needs. Numerical applications are presented for a cantilever beam, where a viscoelastic treatment has been applied using damping material modelled by a five-parameter fractional derivative model. The results of the proposed formulation are compared among them and with those of Padovan for different damping values and for different load cases. The influence of the truncation of Grunwald coefficients and of the integration time-step is also investigated. Copyright © 2006 John Wiley & Sons, Ltd.

Abstract: Lightweight, portable air-pressurized beams and arches serve as primary load-carrying members for a number of civilian and military structures These members are made from synthetic fibers that are woven or braided into a circular cross section The pressurized air provides structural capacity by pretensioning the fabric and through its behavior as a confined gas In this paper, a beam finite element is developed for the analysis of pressurized fabric beams based on virtual work principles Work done by internal pressure due to deformation-induced volume changes is included in the formulation A nonlinear moment-curvature relationship accounts for fabric wrinkling, and shear deformations are incorporated A mixed-interpolation Timoshenko beam element is used to discretize the virtual work expression A numerical method for determining the moment-curvature relationship of an inflated beam made from a fabric obeying a nonlinear stress–strain relationship is developed Results of experiments on pressurized f

Abstract: The present paper is concerned with the design of distributed sensors and actuators. Strain type sensors and actuators are considered with their intensity continuously distributed throughout a continuous structure. The sensors measure a weighted average of the strain tensor. As a starting point for their design we introduce the concept of collocated sensors and actuators as well as the so-called natural output. Then we utilize the principle of virtual work for an auxiliary quasi-static problem to assign a mechanical interpretation to the natural output of the sensors to be designed. Therefore, we take the virtual displacements in the principle of virtual work as that part of the displacement in the original problem, which characterizes the deviation from a desired one. We introduce different kinds of distributed sensors, each of them with a mechanical interpretation other than a weighted average of the strain tensor. Additionally, we assign a mechanical interpretation to the collocated actuators as well; for that purpose we use an extended body force analogy. The sensors and actuators are applied to solve the displacement tracking problem for continuous structures; i.e., the problem of enforcing a desired displacement field. We discuss feed forward and feed back control. In the case of feed back control we show that a PD controller can stabilize the continuous system. Finally, a numerical example is presented. A desired deflection of a clamped-clamped beam is tracked by means of feed forward control, feed back control and a combination of the two.

Abstract: 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.Thepresent,lastpartofthepaperincludesdetailedgeomet- ric 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 meth- odsdevelopedinthepreviouspartsofthepaper.Particularat- tention 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 integrationofthedensityoffibresandsummingitupwiththe volume of the reinforcing bars offinite 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.

Abstract: The previous low-order approximate nonlinear formulations succeeded in capturing the stiffening terms, but failed in simulation of mechanical systems with large deformation due to the neglect of the high-order deformation terms. In this paper, a new hybrid-coordinate formulation is proposed, which is suitable for flexible multibody systems with large deformation. On the basis of exact strain–displacement relation, equations of motion for flexible multibody system are derived by using virtual work principle. A matrix separation method is put forward to improve the efficiency of the calculation. Agreement of the present results with those obtained by absolute nodal coordinate formulation (ANCF) verifies the correctness of the proposed formulation. Furthermore, the present results are compared with those obtained by use of the linear model and the low-order approximate nonlinear model to show the suitability of the proposed models.

Abstract: Virtual teams and management processes in them have been researched mainly theoretically. Most of these papers concentrate on presenting the definition and/or on outlining the advantages/disadvantages of virtual teams. Use of virtual teamwork is still relatively new field for academic research and even when researched empirically usually case study, interviewing or some other small sample approach is used. Current paper tries to test on a bigger sample of data, based on a questionnaire type of research, is the use of virtual teams really growing as usually stated in theoretical papers on this subject. As use of ICT is one of the main characteristics of virtual teams the study concentrates on issues related to ICT-mediated communication for co-operation purposes. The empirical results presented in the article are based on a sample of 226 Estonian service sector organizations.

Abstract: The flexible multi-body dynamic theory is applied into the dynamic characters analysis of 4-arms concrete pump truck arms. The arms are thought as flexible ones for simulation based on which the flexible multi-body dynamic equation for ann system is built by Lagrange equation and virtual work the- ory. The equation is deduced and numerically solved to analyze the movement situation of each arm. With a dynamic simula- tion software, a rigid model and a flexible model are both built for the arms. These two models are simulated with the same driving moment, and the deformation curves of each model and the angular velocity curve of the 4th arm are analyzed and compared. The result shows that it is necessary to consider the flexible deformation when studying the arm system of the light and long arm concrete pump truck. At the same time, the mathematic model can support the study for automatic casting.

Abstract: This article concentrates on describing the complexity and work load factors of mobile work done in virtual environments. A qualitative multi case study was carried out. Six mobile employee groups were examined. The data was collected by interviews and questionnaires. A model of complexity factors was used in analyzing the data. The complexity factors interrelated with different types of workload components, i.e. physical, mental and social and, furthermore, they induced distinct workload factors. To reduce the manifestation of the workload factors and to enhance well-being, fundamental requirements for the virtual environment can be presented. At the levels of connection, device and application the issue lies in the transfer capability of communication. Compared to this at the levels of cognitive and cultural factors of the virtual space the question is in the ability of semantic transfer of the message.

Abstract: The global deformation model of virtual object by force is a key issue for haptic interaction between human and virtual reality. A discrete globe mass -spring model is proposed for flexible object deformation, and its surface is divided radially along the force center. The mass-spring system is composed of the nodes connected with radial distributed springs. Using the theory of virtual work, the relations between virtual force and nodal displacements are analyzed to get global deformations. Object globe deformation is simulated by measuring the nodal deformations based on a force equation at each node. According to the model, the deformation of the flexible object is simulated, and synchronously the real-time virtual contact force is provided with delta haptic device.

Abstract: This paper demonstrates deriving upper-bound solutions of geometrically nonlinear problems for beams and plates from rigid perfectly plastic material by the principles of virtual work in general form and stationary of total energy. Presented noncomplicated examples justify that the first is more appropriate when a kinematically admissible displacement field is defined by several generalized displacements. The second can serve as effective means for comparison in accuracy solutions corresponding to different displacement fields playing the same role as the upper-bound theorem in the limit analysis. Procedures of the latter for obtaining upper-bound solutions mainly remain valid. Solutions for a beam and rectangular plate subjected to uniformly distributed load illustrate importance of taking into account transformation forms of displacements in loading process.

Abstract: This paper presents a one-dimensional finite element for creep buckling analysis of structures comprised of straight and prismatic beam members. Spatial displacements and rotations are allowed to be large while strains are assumed to be small. Material is assumed to be homogenous and isotropic. The corresponding equilibrium equations are formulated in the framework of co-rotational description, using the virtual work principle. In contrast to conventional co-rotational formulation, which is linear on element level and unable to model Wagner effect, in this paper an additional nonlinear part of stiffness matrix is evaluated and added to standard elastic stiffness. Implementation of developed numerical algorithm is demonstrated through few test problems.

Abstract: We propose an extension of the principle of virtual work of mechanics to random dynamics of mechanical systems. The total virtual work of the interacting forces and inertial forces on every particle of the system is calculated by considering the motion of each particle. Then according to the principle of Lagrange-d'Alembert for dynamical equilibrium, the vanishing ensemble average of the virtual work gives rise to the thermodynamic equilibrium state with maximization of thermodynamic entropy. This approach establishes a close relationship between the maximum entropy approach for statistical mechanics and a fundamental principle of mechanics, and constitutes an attempt to give the maximum entropy approach, considered by many as only an inference principle based on the subjectivity of probability and entropy, the status of fundamental physics law.

Abstract: A unified approach to solving driving forces in spatial parallel manipulators with less than six DOFs is proposed. First, the geometric constrained equations of the parallel manipulators are derived, and some independent pose parameters and a common transformation matrix with three translations and three Euler rotations are determined. Second, the common formulas for solving inverse kinematics, the Jacobian matrix, and velocity are derived. Third, a common virtual serial mechanism with three virtual prismatic joints and three virtual revolute joints corresponding to three Euler rotations is constructed. Fourth, a common analytic formula for solving driving forces in spatial parallel manipulators with less than six DOFs is derived by using the principle of virtual work and the virtual serial mechanism. Finally, a 3-SPR parallel manipulator with three DOFs and a 4SPS+SPR parallel manipulator with five DOFs are presented to illustrate the use of the unified approach to solve their inverse kinematics and the driving forces. The solving results are verified by the simulation mechanisms.

Abstract: After the justification of the maximum entropy principle for equilibrium mechanical system from the principle of virtual work, i.e., the virtual work of microscopic forces on the elements of a mechanical system vanishes in thermodynamic equilibrium, we present in this paper an application of the same principle to dynamical systems out of equilibrium. The aim of this work is to justify a least action principle and the concurrent maximum path entropy principle for nonequilibrium thermodynamic systems.

Abstract: In the current digital knowledge economy, virtual communication is often used as a medium for knowledge exchange. Research has demonstrated that knowledge exchange is a complex social process which, at least in part, relies upon the social capital between exchange partners. The question of research interest is to examine whether virtual communication can generate and support social capital, thus enabling knowledge exchange across space and time boundaries. I use the literatures in the knowledge-based view of the firm, virtual work, and social capital theory to develop some hypotheses that explore the relationship between virtual communication and social capital generation in virtual teams.

Abstract: When applying safety integration principles, work equipment designers are required to imagine future operating situations and assess a priori associated risk levels. Virtual reality techniques contribute partly to achieving this objective. Based on a feasibility study, this paper discusses the contribution of a dynamic risk-indexing tool applied in conjunction with these techniques. Following a brief reminder of the problem, this paper describes firstly the concepts underlying a generic model permitting a work situation risk index to be estimated. We then introduce the method retained for validating these virtual reality simulations. This focuses on the possibility of reproducing a reference activity through simulation. In spite of differences between the same task performed under real and virtual conditions, examples of industrial machinery is used to illustrate how risk indexing enables the designer to better assess the relevance of his choices and thus to act retrospectively on his design.