Automatic differentiation based formulation of coupled problems

Our work will show that complex transient coupled problems can be formulated and solved effectively with AceGen and AceFEM using an automatic differentiation based formulation (ADB-formulation). From scalar pseudo-potential function consistent tangent matrix for strongly coupled problems can be derived, leading to quadratically convergent Newton-Raphson type procedure. Another problem considered is the implementation of finite element. Typically, all equations are written inside a single finite element and a single pseudo-potential is defined. Such implementation is efficient but rigid, therefore, a different implementation was considered. Within the second approach we wrote a separate finite element for each field, but in a way that quadratic convergent Newton-Raphson procedure is preserved. The paper presents examples where unified and field-by-field implementations are compared according to computational efficiency. The results show that with increasing ratio between the complexity of constitutive equations and discretization, generated code size and evaluation time of implementations become comparable

modelling of deformable polymer to be used for joints between infill masonry walls and r c frames

Abstract In the paper an idea to use a deformable polymer material for the joint between R.C. frames and masonry infills is presented. As an early step of testing the idea, experimental tests of the polymer in monotonic uniaxial tension at different load rates are performed and analyzed. The load rates range from very fast (8.3 mm/s) to very slow (0.00083 mm/s). The material exhibits a very strong strain rate effect and viscous behavior. In the second part of the paper a numerical model is developed and implemented into a finite element to simulate the results of the tests. The model is based on a new family of strain measures, called the Darjani-Naghdabadi strain measures and a classical viscosity formulation. Almost perfect model predictions up to collapse at 50-150% elongation are obtained by using calibration based on minimization of error

Combined sticking: a new approach for finite-amplitude Coulomb frictional contact

Engineering-level accuracy of discretization methods for frictional contact originates from precise representation of discontinuous frictional and normal interaction laws and precise discrete contact techniques. In terms of discontinuous behavior in the quasi-static case, two themes are of concern: the normal interaction (i.e. impact) and the jumps in tangential directions arising from high frictional values. In terms of normal behavior, we use a smoothed complementarity relation. For the tangential behavior, we propose a simple and effective algorithm, which is based a stick predictor followed by corrections to the tangential velocity. This allows problems with impact and stick-slip behavior to be solved with an implicit code based on Newton–Raphson iterations. Three worked examples are shown with comparisons with published results. An extension to node-to-face form in 3D is also presented

NURBS-based Smooth Surface Contact for the Numerical Simulation of Balloon Angioplasty

This paper presents a strategy for the finite element implementation of ¤¦ ¥ continuous contact surfaces for deformable bodies undergoing finite deformations, whereby § represents an arbitrary level of continuity. The proposed novel approach avoids the non-physical oscillations of contact forces which are induced by the traditional enforcement of kinematic contact constraints via faceted surfaces discretizing the interacting boundaries. In particular, for certain problems, the level of continuity may influence the rate of convergence significantly within a nonlinear solution scheme. A representative numerical example on the simulation of balloon angioplasty demonstrates the increased rate of convergence and the prevention of pressure jumps of the proposed method