Ansys 显示动力学.ppt

Element Formulations Tetrahedral Solid Elements Pull-out test simulated using both hexahedral elements (top) and ANP tetrahedral elements (bottom). Similar plastic strains and material fracture are predicted for both element formulations used. Shell Elements Quadrilateral shell element Belytschko-Tsay, with Chang-Wong correction Co-rotational formulation, bi-linear, 4 noded Single quadrature point with hourglass stabilization Isotropic and layered orthotropic formulations Number of through thickness integration points can be specified Triangular shell element C0 Triangular Plate Element (Belytscho, Stolarski and Carpenter 1984) Should be used in quad-dominant meshes Thickness is a parameter (not modelled geometrically) Actual thickness can be rendered Time step is controlled by the element length, not by thickness 1 2 3 E 1 2 3 4 E Element Formulations Element Formulations Hourglass Control (Damping) for Hexahedral Solid and Quad Shell Elements For the hexahedral and quad element formulations, the expressions for strain rates and forces involve only differences in velocities and / or coordinates of diagonally opposite corners of the element If an element distorts such that these differences remain unchanged there is no strain increase in the element and therefore no resistance to this distortion On the left, the two diagonals remain the same length even though the element distorts. If such distortions occur in a region of several elements, a pattern such as that shown on the right occurs and the reason for the name “hourglass instability” is easily understood In order to avoid such hourglass instabilities, a set of corrective forces are added to the solution Two formulations are available for hexahedral solid elements AD standard (default) Most efficient option in terms of memory and speed Flanagan-Belytschko Invariant under rotation Improved results for large rigid body rotations 2D 3D Element Formulatio