ANSYS/LS-Dyna Multi-Material M t i l ALE Modeling Prepared by Steven Hale, M.S.M.E. M Senior Engineering Manager
Multi-Material ALE Basics What is the Multi-Material ALE method (MMALE) MMALE stands for Multi-Material Arbitrary Lagrangian Eulerian Combines Lagrangian and Eulerian methods Lagrangian step mesh moves with the material in the first part of the step Eulerian step the mesh is smoothed out to minimize element distortion and material flows between elements. This is also known as the advection step. ADVANTAGE over a pure Eulerian method Elements are allowed to move and distort which minimizes advection. This minimizes energy dissipation and speeds up run time. 2
Multi-Material ALE Basics MMALE requires a domain mesh with some elements that contain solid or fluid materials. The outer elements of the domain mesh typically contain a vacuum or fluid material. Solid materials are then assigned to elements within the domain mesh. *INITIAL_VOLUME_FRACTION can be used to assign volume fractions of different materials in each element of the domain 3
Support for MMALE in ANSYS The ANSYS pre-processor does not support inputs for the MMALE method The following model features can be assigned in ANSYS: Geometry Mesh Material properties Hourglass controls Boundary constraints Initial velocities Time and output controls All inputs specific to lagrangian parts The following model features must be added directly to the LS-Dyna input file: Contact definitions MMALE control settings: advection control, mesh smoothing, movement, and expansion control MMALE group definitions used to define discrete MMALE parts 4
Element formulation *SECTION_SOLID SECID, ELFORM ELFORM = 5 (single-material ALE) ELFORM = 6 (pure Eulerian) ELFORM = 11 (multi-material ALE) * 5
*CONTROL_ALE: MMALE control settings DCT,NADV,METH,AFAC,BFAC,CFAC,DFAC,EFAC DCT (ignored) NADV: Number of time steps between mesh smoothing and advection cycles Can speed up run time but reduce stability METH: Advection method Meth = 1 (1 st order advecton fast, valid for fluids only) Meth = 2 (2 nd order advection slower, minimizes i i energy loss) AFAC,BFAC,CFAC,DFAC: Mesh smoothing parameters AFAC = -1 (no smoothing), 1 (simple average smoothing) -1 does not allow element distortion, only expansion and contraction 1 simple average method commonly used BFAC = 1 (volume-weighted smoothing) CFAC = 1 (isoparametric smoothing) DFAC = 1 (equipotential smoothing) - commonly used EFAC = 1 (equilibrium smoothing) 6
7
*ALE_MULTI-MATERIAL_GROUP Defines MMALE groups Part/Set ID list 8
*ALE_REFERENCE_SYSTEM_GROUP Defines the motion of the ALE mesh 9
10
11
12
*CONSTRAINED_LAGRANGE_IN_SOLID SOLID Defines contact between MMALE groups and Lagrangian elements Slave part must be lagrangian, Master part is MMALE CTYPE = 2 (constrained acel and vel (default). Cannot be used with rigid bodies. Does not conserve energy) CTYPE = 4 (penalty coupling without erosion) CTYPE = 5 (penalty coupling wih erosion in Lagrangian part) DIREC = 1 (glued together in tension and compression) DIREC = 2 (compression only) 13
14
15
16
17
Example: Lagrange Sphere MMALE Block MMALE Input Defines contact between MMALE groups and Lagrangian elements $ $ 2nd order advection, No smoothing *CONTROL_ALE,1,2,-1., *ALE_MULTI-MATERIAL_GROUP 2, 1 3, 1 $ $ ALE mesh motion/expansion control $ 7 = no rotations *ALE_REFERENCE_SYSTEM_GROUP 4,0,4,0,5,3,7, 000 0,0,0,, $ $ Define coupling between Part 1 (ALE) and Part 3 (Lagrangian) $ Use 2 x 2 quadrature *CONSTRAINED_LAGRANGE_IN_SOLID 1,4,1,0,-2,4,2,1,, $ *SET_PART_LIST 4, 2,3, 18