Virtual reality, as a technology that allows a user to interact with a computer-simulated environment, requires in many areas of application real-time or nearly real-time simulation of deformable objects' behaviour. Furthermore, it is often necessary to handle large deformations, which cannot be adequately described with linear models. Formulations that allow consideration of geometrical nonlinearities to a large extent, but without a significant numerical overhead, are required. At first, the well-known simplified approach based on a mass-spring system in combination with explicit time integration scheme is considered. Advantages and disadvantages of the approach are pointed out and the approach is exemplified on a two and three-dimensional structure. In the following, an improved approach based on a three-dimensional finite element formulation is presented. In order to achieve the level of numerical efficiency required for virtual reality simulators, a linear tetrahedral element and a co-rotational approach are used. The basics of the approach, which accounts for large deformations in a simplified manner and with a satisfying accuracy, are explained. If it is aimed at plausible behaviour solely, i.e. at realistic appearance whereby the level of accuracy is not particularly specified, a possible strategy on how to model objects with complex geometry by using approximate finite element meshes is described and exemplified on several models. Force feedback is very important in some applications and special attention is dedicated to the issue since the warped stiffness method does not provide satisfactory accuracy at this point.

Programs for simulating dynamics of multibody systems (MBS) were originally developed for rigid bodies. However, many physical systems require consideration of flexible bodies in MBS for an adequate simulation of their behavior. In order to retain numerical efficiency this is done in modal space, which intrinsically only allows for the consideration of elastic deformations within the local coordinate system of the flexible body. The paper proposes two possible extensions of the solution based on modal reduction with the aim of accounting for moderately large nonlinear effects. The first extension is applicable to bodies which do not undergo large configuration changes during the deformation, so that the nonlinear effects are mainly a consequence of stress stiffening. The second extension is developed for deformations, in which some parts of the flexible body perform moderately large rotations with respect to the rest of the body. Examples for both approaches are provided, demonstrating their advantages.

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