SummaryAdaptive hierarchical refinement in isogeometric analysis is developed to model cohesive crack propagation along a prescribed interface. In the analysis, the crack is introduced by knot insertion in the NURBS basis, which yields  −1 continuous basis functions. To capture the stress state smoothly ahead of the crack tip, the hierarchical refinement of the spline basis functions is used starting from a coarse initial mesh.A multilevel mesh is constructed, with a fine mesh used for quantifying the stresses ahead of the crack tip, knot insertion to insert the crack, and coarsening in the wake of the crack tip, since a lower resolution suffices there. This technique can be interpreted as a moving mesh around the crack tip. To ensure compatibility with existing finite element programs, an element-wise point of view is adopted using Bézier extraction. A detailed description is given how the approach can be implemented in a finite element data structure. The accuracy of the approach to cohesive fracture modelling is demonstrated by several numerical examples, including a double cantilever beam, an L-shaped specimen, and a fibre embedded in an epoxy matrix.

C e n t r u m v o o r W i s k u n d e e n I n f o r m a t i c a Modelling, Analysis and Simulation Modelling, Analysis and SimulationFLECS, a flexible coupling shell, application to fluid-structure interaction M. Nool, E.J. Lingen, A. de Boer, H. Bijl FLECS, a flexible coupling shell, application to fluidstructure interaction ABSTRACT Numerical simulations involving multiple, physically different domains can be solved effectively by coupling simulation programs, or solvers. The coordination of the different solvers is commonly handled by a coupling shell. A coupling shell synchronizes the execution of the solvers and handles the transfer of data from one physical domain to another. In this paper, we introduce Flecs, a flexible coupling shell, designed for implementing and applying an interface for multidisciplinary simulations with superior accuracy. The aim is not to achieve the best possible efficiency or to support a large feature set, but to provide a flexible platform for developing new data transfer algorithms and coupling schemes. A coupling shell synchronizes the execution of the solvers and handles the transfer of data from one physical domain to another. In this paper, we introduce FLECS, a flexible coupling shell, designed for implementing and applying an interface for multidisciplinary simulations with superior accuracy. The aim is not to achieve the best possible efficiency or to support a large feature set, but to provide a flexible platform for developing new data transfer algorithms and coupling schemes. REPORT MAS-E0624 DECEMBER 2006 IntroductionFluid-Structure Interaction (FSI) considers coupled fluid-solid problems, characterized by the interaction of fluid forces and structural deformations, which occur in many applications in industry and science. Nowadays, the simulation of FSI becomes more and more important, since future structures become lighter and more flexible and can be applied, e.g., to reduce the load on turbine blades, or, to reduce the noise on cars. Such applications require a real interdisciplinary approach, that can deal with complex physical models and very different scales. The Faculty of Aerospace Engineering of the Delft University of Technology has started a project to develop a generic, open-source coupling shell, named FLECS [3], that can be used to join two or more arbitrary solvers. FLECS should provide an innovative combination of high order coupling in space and time. Moreover, to improve the accuracy and the efficiency of the computation, multilevel acceleration techniques for the coupling process [2], and fast prototyping and parallelization techniques will be supported.The majority of coupling shells are embedded subprograms that have been developed for coupling two specific solvers. One exception is the coupling library MPCCI (Mesh based Parallel Code Coupling) [5], which can be used as a separate program. Although MPCCI is relatively easy to use and provides §

Abstract. In this paper we discuss the second version of FLECS, a generic, open-source coupling shell that can be used to join two or more arbitrary solvers. In general multidisciplinary computations are very computing-intensive. A remedy against long computing times is large-scale parallelism. The challenge of the present parallelization work is to obtain acceptable computing times and to get rid of severe memory requirements that exist on sequential machines, for the generic flow problems at hand. The aim is to provide a flexible platform for developing new data transfer algorithms and coupling schemes.