ANSYS User s Group Non-Linear Adaptive Meshing (NLAD)

Transcription

1 19.2 Release ANSYS User s Group Non-Linear Adaptive Meshing (NLAD) Sriraghav Sridharan Application Engineer, ANSYS Inc Sriraghav.Sridharan@ansys.com ANSYS, Inc. October 10, 2018

2 Topics Background on Rezoning Introduction to Mesh Nonlinear Adaptivity Defining Nonlinear Adaptivity Criteria Demonstration Limitations Learning resources Questions ANSYS, Inc. October 10, 2018

3 Background on Rezoning Many applications can benefit from the ability to strategically modify a mesh during solution, based on certain criteria to: Simulate challenging large deflection/distortion which otherwise cannot be solved. Improve the accuracy of simulation results. Distortion of mesh is severe and nonrecoverable Mesh refinement is inadequate ANSYS, Inc. October 10, 2018

4 Introduction to Mesh Nonlinear Adaptivity Unlike manual rezoning, mesh nonlinear adaptivity is completely automatic, requiring no user input during solution. Automatic During Solution ANSYS, Inc. October 10, 2018

5 Introduction to Mesh Nonlinear Adaptivity Supported in MAPDL: NLADAPTIVE NLMESH Supported in WB-Mechanical GUI ANSYS, Inc. October 10, 2018

6 New Features At and Beyond 19.0 Nonlinear adaptivity (NLAD) Support 10 node tetrahedral elements: Solid 187 and Solid 227 New option to refine elements of Plane182, Plane222, Solid187 and Solid227 through general remeshing Allow combined criterion options CONTACT/ENERGY/BOX/MESH in the same input Support 3D fluid penetration 2D to 3D analysis MAP2DTO3D Support distributed ANSYS 2D PLANE 182/282 (Structural/Coupled-field) 3D SOLID 187/227 (Structural/Coupled-field) ANSYS, Inc. October 10, 2018

7 NLAD: to fix mesh distortion Support high order 10 node tetrahedral elements Solid187/Solid227 Remesh the regions of distorted elements caused by large deformation Solve the large deformation problems otherwise can not be solved Only remesh the regions of distorted elements Identified by NLADPTIVE,,,MESH,SKEW,VAL1,VAL2 Where VAL1 is skewness and VAL2 is Jacobian ratio Rubber Sealing simulation Regenerate contact, target and surface elements automatically if necessary ANSYS, Inc. October 10, 2018

8 NLAD: to fix mesh distortion All boundaries, loads and solutions mapped to the new mesh completely Allow partial and whole domain remeshing and follow the initial mesh size gradients Support self-contact and fluid penetration Can have 3D fluid penetration Built-in acceptance criteria to accept the new mesh or continue to solve with current mesh if no improvement Work with most of material models, including history dependent materials Support distributed ANSYS solve Maximum number of remeshings: 99; doesn t allow dropping of mid-side nodes ANSYS, Inc. October 10, 2018

9 NLAD: Cross-bar impression Elasto-plastic materials with 13 remeshing cycles ANSYS, Inc. October 10, 2018

10 NLAD: Glass Blowing Visco-plastic material using PEIRCE rate law: 12 remeshings ANSYS, Inc. October 10, 2018

11 NLAD: Threading Simulation ANSYS, Inc. October 10, 2018

12 NLAD: Metal Extrusion Very large elongation with 93 remeshings ANSYS, Inc. October 10, 2018

13 Example Liner Hanger Casing Packer Expander Distortion of mesh is severe and nonrecoverable Mesh refinement is inadequate Credit: Texas Iron Works ANSYS, Inc. October 10, 2018

14 Introduction to Mesh Nonlinear Adaptivity Nonlinear adaptivity is based on criteria checking at the end of each specified substep after it converges. After generating the new mesh, the program moves to the next substep. Three inputs from user are necessary to define Mesh Nonlinear Adaptivity: Defining Element components Defining Nonlinear Adaptivity Criteria Defining Criteria Checking Frequency ANSYS, Inc. October 10, 2018

15 Defining Nonlinear Adaptivity Criteria To use Nonlinear Adaptivity most effectively, it is very important to understand the Criterion that will trigger mesh modification. Energy Based. Position Based. Mesh Quality Based. Contact Based (available via MAPDL only). NLADAPTIVE, Component, Action, Criterion, Option, VAL1, VAL2,VAL3 Criterion: - Contact - Energy - Box - Mesh ANSYS, Inc. October 10, 2018

16 Defining Nonlinear Adaptivity Criteria Energy Based Criterion Criterion for remeshing Element Strain Energy (Factor) X (Mean Strain energy) Refines the mesh in regions of high concentration of stress exists and elements are too large. Applies to current technology 2D elements and 3- D linear tetrahedral elements (SOLID285). Position Based Criterion Criterion for remeshing All nodes of an element are within a user defined region, the element is split and remeshed. For example, a small cavity filled by the deformation of a compressed seal. Applies to current technology 2D elements and 3- D elements ANSYS, Inc. October 10, 2018

17 Defining Nonlinear Adaptivity Criteria Mesh Based Criterion Criterion for remeshing Element Skewness (User defined threshold) The element is remeshed V el is the volume of the element under calculation. V reg is the volume of the standard tetrahedral element Contact Based Criterion (MAPDL) Criterion for remeshing Number of contact elements with target element User defined value Contact region is remeshed to follow the geometry of targets more accurately. Contact Surface Wear can also be modeled in MAPDL ANSYS, Inc. October 10, 2018

18 Defining Nonlinear Adaptivity Criteria When Criterion is defined as Mesh, additional mesh control options become available in the Details Window of Analysis Settings Branch. Refer to NLMESH command for details ANSYS, Inc. October 10, 2018

19 Result ANSYS, Inc. October 10, 2018

20 Nonlinear Adaptivity Limitations The following materials properties are not supported: Cast Iron Concrete Cohesive Zone Damage Microplane Shape Memory Alloy Swelling ANSYS, Inc. October 10, 2018

21 Nonlinear Adaptivity Limitations Mesh nonlinear adaptivity via splitting or refinement, in general cannot repair an already distorted mesh. In some cases, it can exacerbate mesh distortion by creating smaller elements. Original Mesh After 1 st Mesh Refinement To reduce the effect, the code uses built-in morphing and topology repair after splitting; even so, mesh quality improvement is slight. Avoid splitting or refinement in highly distorted regions, therefore, as doing so may lead to convergence problems ANSYS, Inc. October 10, 2018

22 Nonlinear Adaptivity Limitations Unstable Structures For some geometries and loads, a deformation may cause a "snap-through," or local buckling. Rubber seal problems O A K T = 0 B C D Such behavior can also manifest itself as a mesh distortion, but one that nonlinear adaptive region cannot repair. The effect can be detected by closely checking the deformed region or the loadversus- time (displacement) curve ANSYS, Inc. October 10, 2018

23 Learning resources ANSYS Basic Structural Nonlinearities course Instructor led or Self-paced learning Register via the ANSYS Learning Hub ANSYS Workbench Documentation Detailed reading ANSYS, Inc. October 10, 2018

24 ANSYS, Inc. October 10, 2018 Questions?

25 18.2 Release APPENDIX ANSYS, Inc. October 10, 2018

26 Background on Rezoning R13: Rezoning for 3d geometries (SOLID185, SOLID186) R16: Nonlinear adaptivity introduced mesh splitting (SOLID181) R17: NLAD full remeshing (SOLID181) R18: NLAD full remeshing (SOLID285) ANSYS, Inc. October 10, 2018

27 Defining Nonlinear Adaptivity Criteria Contact-Based Criterion (MAPDL only) : Number of Contacting Elements If the number of contact elements in contact with the target element is less than the defined value, the underlying element is split. Contact elements on the faces of the solid elements are regenerated as well. If contact elements are moving away from target, no splitting occurs. This criterion is used to allow a contact region to follow the geometry of targets more accurately. Component that bears the criterion consists of target elements only ANSYS, Inc. October 10, 2018

28 Defining Nonlinear Adaptivity Criteria Contact-Based Criterion : (cont d) Contact Surface Wear (MAPDL only) : During a substep, when the amount of wear at a contact element exceeds a user defined critical value, the mesh is morphed at the interface to improve the quality of the mesh. Only applies to contact elements having surface wear, specified via the TB,WEAR command. User defines critical ratio of magnitude of wear at the contact element to the average depth of the solid element underlying the contact element. Wear distorting elements at interface Adaptive Mesh Morphing improves mesh ANSYS, Inc. October 10, 2018

29 2D to 3D Analysis MAP2DTO3D Support distributed ANSYS now for performance Map 2D axisymmetric analysis results to 3D Migrate all BCs and Loads to 3D Regenerate contact and surface elements Rebalance the 2D solutions on 3D domain MAP2DTO3D ANSYS, Inc. October 10, 2018

30 Procedure When the defined criteria are met, mesh modification occurs either by a combination of splitting followed by morphing or by general remeshing: During splitting, the current elements are divided into elements having a half-edge length. Some transition layers are created automatically to connect the refined regions to the unrefined regions. For 3-D tetrahedral element, some topology changes and morphing occur during splitting to improve the quality of the new mesh. For 2-D meshes, morphing is only done after the element-splitting operation. Splitting applies to Energy-based, Position-based and Contact-based criterion ANSYS, Inc. October 10, 2018

31 08.06 Procedure Create User Defined Results (using the PNUMELEM Expression) to view the new elements that have relatively larger element identities than the original element identities ANSYS, Inc. October 10, 2018

32 Procedure For each mesh modification, mesh quality metrics stats are recorded in the Solver output comparing previous mesh with new mesh. Source Column represents previous mesh. Target Column represents modified mesh. In general, lower Skewness and Aspect Ratio values for the Target mesh, indicate improved quality. If these stats indicate a deterioration of the mesh, try adjusting NLMESH options ANSYS, Inc. October 10, 2018

33 Nonlinear Adaptivity Limitations Cannot be used in combination with the following features/conditions on the same part: Cyclic Symmetry Contact Formulations: Normal Lagrange (3D), MPC, and Beam Contact Behaviors: Auto Asymmetric Point Mass, Beam Connection, Joints, Spring, and Bearing Remote Force, Remote Displacement, Moment, Thermal Condition, and Remote Point Spatially varying boundary conditions Cannot be used in combination with the following boundary conditions: Coupling Constraint Equation ANSYS, Inc. October 10, 2018

34 Nonlinear Adaptivity Limitations Nonlinear Adaptivity cannot resolve numerical instabilities. The constraints can include kinematic constraints such as applied displacements, couplings, and constraint equations, and volumetric constraints introduced by fully incompressible material in mixed u-p elements. In many cases, numerical instability is apparent even in the early stages of an analysis ANSYS, Inc. October 10, 2018

35 Nonlinear Adaptivity Limitations Combinations of criteria might be required for applications involving complex geometry under complex loading (i.e. local deformations in buckling or rubber seal problems). The contact-based criterion should be used only when solid elements touch target elements and more elements/nodes are necessary to simulate details of contact boundaries and filling. The position-based criterion should be used for refining elements moving in to particular regions (for example, small cavities). Without a fine enough mesh and a sufficient number of degrees of freedom, the simulation might not accurately predict the behavior of material moving into such regions ANSYS, Inc. October 10, 2018

36 Nonlinear Adaptivity Limitations When used during a restart, the Nonlinear Adaptive Region object does not support Named Selections if your model contains a mesh change prior to the restart point. If analysis failed to converge and you are adding a new Nonlinear Adaptive Region object, it is necessary that the contact object property, Behavior, was set to either Symmetric or Asymmetric for the initial solution that was processed ANSYS, Inc. October 10, 2018