1 / 72

General Preprocessing

Chapter Three. General Preprocessing. Chapter Overview. In this chapter, performing analyses without the use of the Wizards will be covered: Geometry Contact Meshing Named Selections Coordinate Systems

larryk
Download Presentation

General Preprocessing

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Chapter Three General Preprocessing

  2. Chapter Overview • In this chapter, performing analyses without the use of the Wizards will be covered: • Geometry • Contact • Meshing • Named Selections • Coordinate Systems • The capabilities described in this section are generally applicable to the ANSYS DesignSpace Entra licenses and above and are noted in the lower-left hand tables. March 29, 2005 Inventory #002215 3-2

  3. Introduction • In the previous chapter, the Simulation GUI was introduced by the use of the Simulation Wizards • In this chapter, navigating through the GUI without the Wizards will be covered. March 29, 2005 Inventory #002215 3-3 Model shown is from a sample Mechanical Desktop assembly.

  4. Use of the Outline Tree is the means by which users navigate through the Simulation GUI. … Introduction • The Outline Tree is the main way of setting up the analysis • The Context Toolbar, Details View, and Graphics Window update, depending on which Outline Tree branch is selected • Use of the Outline Tree will be emphasized in this chapter March 29, 2005 Inventory #002215 3-4

  5. A. Geometry Branch • After importing a model either (a) directly from a supported CAD system or (b) from the Context Toolbar in a blank database, the Geometry branch lists available parts. • In Simulation, there are three types of bodies which can be analyzed. • Solid bodies are general 3D or 2D volumes/areas/parts. • Surface bodies are only areas. • Line bodies are only curves. March 29, 2005 Inventory #002215 3-5

  6. … Types of Bodies • Solid bodies are geometrically and spatially 3D or 2D: • 3D solids are meshed with higher-order tetrahedral or hexahedral solid elements with quadratic shape functions • 2D solids are meshed with higher order triangle or quadrilateral solid elements with quadratic shape functions • Currently 2D geometry can be obtained from: • DesignModeler, ProEngineer, Solid Edge, SolidWorks and Unigraphics • Each node has three translational degrees of freedom (DOF) for structural or one temperature DOF for thermal • Good for general representation of CAD models March 29, 2005 Inventory #002215 3-6

  7. … Types of Bodies • Considerations for 2D Geometry: • Geometry must consist of surface models lying on the XY plane • The “2D” switch must be set on the Project page prior to import • Geometry type cannot be changed from 2D to 3D (or vice versa) after import • Plane stress, plane strain and axisymmetric behaviors are supported • Certain load types are unavailable with 2D geometry • Be sure to consult the Simulation documentation for all details regarding 2D analysis March 29, 2005 Inventory #002215 3-7

  8. … Types of Bodies • Surface bodies are geometrically 2D but spatially 3D: • Surface bodies are meant to represent structures which are thin in one dimension (through-thickness), so that thickness is not explicitly modeled but supplied as an input value. For example, mid-surfaces extracted in the CAD software could be used, but the “sheet metal” or “shelled” parts are still 3D and are not considered surface bodies. Consequently, if a “sheet metal” or “shelled” part is to be analyzed as a surface body, the midsurface needs to be extracted first in the CAD system. • Surface bodies are meshed with linear shell elements • Each node has three translational and three rotational DOF for structural applications but one temperature DOF for thermal • Efficient for representation of thin sheet-like parts March 29, 2005 Inventory #002215 3-8

  9. … Types of Bodies • Line bodies are geometrically 1D but spatially 3D: • Line bodies are meant to represent structures which are thin in two dimensions compared to the length, so the cross-section is not explicitly modeled. • Currently, only DesignModeler supports creation of line bodies since it can define cross-sections and orientations of lines. • Line bodies are modeled with linear beam elements • Each node has three translational and three rotational DOF for structural analysis and one temperature DOF for thermal • Good for representation of beam-like structures March 29, 2005 Inventory #002215 3-9

  10. … Multibody Parts • For many applications, bodies and parts are the same. In DesignModeler, however, multibody parts are possible. • In some CAD systems, multiple bodies in a single part is supported for import. However, these do not import as a single multibody part. The difference is that each body will be independently meshed. • Support of mixed surface and solid bodies in the same part is not supported for most CAD systems. An assembly may contain surfaces and solids, but a single part cannot. • In DesignModeler, multiple bodies can be joined together to form a multibody part. This means that if the parts share common boundaries, the nodes are shared at that interface. • No contact is needed in these situations if the nodes are shared. • For surface bodies, “Surface Extension” and “Joint” operations are also available in DesignModeler to ensure congruent mesh at intersecting surfaces. March 29, 2005 Inventory #002215 3-10

  11. Multibody parts made of surface and line bodies share nodes at common boundaries. This allows modeling of shells with stiffeners. Multibody parts made of solid bodies share nodes at common boundaries. Material properties can be different for each body. … Multibody Parts • Multibody parts allows the user to define more complex bodies with common nodes, as shown below: March 29, 2005 Inventory #002215 3-11

  12. … Material Properties • To assign material properties to a body, select that body from the tree and select a “Material” from the pull-down menu • Materials can be selected from external XML files • New material data can be added or imported in the “Engineering Data” application. The new material will then be available from the pull-down menu. • For surface bodies, as noted earlier, a thickness needs to be supplied as well • Thicknesses will import directlyfrom DesignModeler, if defined. March 29, 2005 Inventory #002215 3-12

  13. … Geometry Worksheet • A summary of bodies and assigned materials is available • Select “Geometry” branch and then the “Worksheet” tab March 29, 2005 Inventory #002215 3-13

  14. B. Contact • When multiple parts are present, a means of defining the relationship between parts is needed. • Contact regions define how solid and/or shell parts interact with each other. • Spot welds provide a means of defining shell assemblies. • Without contact or spot welds, parts will not interact with each other • In structural analyses, contact and spot welds prevent parts from penetrating through each other and provide a means of load transfer between parts. • In thermal analyses, contact and spot welds allow for heat transfer across parts. • Contact will be introduced first, then spot welds. March 29, 2005 Inventory #002215 3-14

  15. … Solid Body Contact • When an assembly is imported, contact surfaces are automatically detected and created • The mating relationships are not used from the CAD software. Proximity of surfaces is used instead to define contact. • Tolerance for contact detection is available under the “Contact” branch as a slider bar in “Tolerance Slider” March 29, 2005 Inventory #002215 3-15 Model shown is from a sample SolidWorks assembly.

  16. Note the non-matching mesh at the interface between parts. Mix of hexahedral elements contacting tetrahedral elements is possible. … Solid Body Contact • Proven ANSYS Contact Technology allows the user to model without shared nodes between parts • Contact elements, which act as a ‘skin’ on the surface of the contacting regions, provides the relationship between parts. • This means that one small part will not drive mesh density of the entire assembly. The user can make parts of interest have a finer mesh than other parts March 29, 2005 Inventory #002215 3-16

  17. The contacting bodies are partially transparent. Bodies not in the contact region are more fully transparent. The contacting surfaces which are oriented with surface normals pointing towards the view are opaque for easier viewing. … Solid Body Contact • When a contact region is highlighted in the “Contact” branch, parts are made translucent for easier viewing • Selecting a contact pair makes the other bodies not involved in that contact region translucent • Amount of translucency is controlled via “Tools > Options… > Simulation: Contact: Transparency”. Transparency can be turned off in the Details view of the “Contact” branch March 29, 2005 Inventory #002215 3-17

  18. … Solid Body Contact • If a geometric entity is highlighted, use right-mouse button in the Graphics window to quickly select associated contact • The right-mouse pop-up menu allows the user to select the corresponding body in the “Geometry” branch or highlight all associated contact regions under the “Contact” branch March 29, 2005 Inventory #002215 3-18

  19. Selection of contact and target surfaces is performed in the “Details” view. The contact bodies associated with selected surfaces will be listed below. Ensure that unique bodies are for each “Contact” and “Target” body. The “Contact” surfaces will be shown in red while “Target” surfaces will be displayed in blue. … Solid Body Contact • Defining a contact pair involves selecting “contact” and “target” surfaces. • In ANSYS DesignSpace, the distinction between “contact” and “target” is unimportant. Select surfaces for one body as “contact” and choose the surfaces for the other as “target”. • Using “Contact” from the Context Toolbar allows manual definition of contact regions March 29, 2005 Inventory #002215 3-19

  20. … Selection Planes • Selection planes allow for users to easily select surfaces which are hidden from view by other surfaces. • User selects a plane; if more planes lie directly underneath the cursor, selection planes appear. Selection planes are color-coded with the same color as its parent part and are ordered by depth from the cursor. March 29, 2005 Inventory #002215 3-20

  21. When moving the cursor over selection planes, those surfaces will get highlighted. Use of wireframe mode may make visualization easier. One can select a particular surface or even use Ctrl-select to select multiple surfaces. In this example, two surfaces highlighted on the screen are selected to define a contact pair manually. Without selection planes, the selection of the specific surfaces would be tedious. … Selection Planes • Through the use of selection planes, users can define contact regions more easily • Example below shows two surfaces selected from two parts. A contact region can be defined manually with these surfaces March 29, 2005 Inventory #002215 3-21

  22. … Renaming Contact Regions • Select the “Contact” branch and right-click and select “Rename Based on Geometry” to rename all contact pairs, based on their constituent parts, for easier readability. March 29, 2005 Inventory #002215 3-22

  23. In this example, because of the tolerance used by automatic contact detection, some fillets shown here are included in the contact definition. The user may wish to remove the fillets from the contact region definition, especially in the case of bonded contact, in order to prevent spurious behavior. … Verifying Contact Regions • Although Simulation automatically detects contact, one should review each contact pair to ensure that contact is properly defined. March 29, 2005 Inventory #002215 3-23

  24. … Advanced Solid Body Contact • For ANSYS Professional licenses and above, advanced contact options are available. • Auto detection of contact surfaces supports entering value rather than just using a slider • Specification of asymmetric contact possible • Postprocessing contact results possible • For each contact region, changing contact formulations, etc. possible, including entering & visualizing pinball radius (discussed next). March 29, 2005 Inventory #002215 3-24

  25. The pinball region enables the user to verify that contact is detected for a large gap. … Advanced Solid Body Contact • Example of the use of the pinball region: • The pinball radius may be entered to ensure that bonded contact is established for a large clearance or gap • In the example below, the visualization of the pinball region enables the user to verify that the pinball region covers the gap between the hole and shaft. March 29, 2005 Inventory #002215 3-25

  26. . . . 2D Solid Body Contact • Surface contact for solids composed of 2D plane geometry is defined on edges rather than faces March 29, 2005 Inventory #002215 3-26

  27. … Surface Body Contact • For ANSYS Professional licenses and above, mixed assemblies of shells and solids are also supported • Allows for more complex modeling of assemblies, taking advantage of the benefits of shells, when applicable • More contact options are exposed to the user • Contact postprocessing is also available March 29, 2005 Inventory #002215 3-27

  28. … Surface Body Contact • Shell contact includes edge-to-face or edge-to-edge contact • Shell contact is not turned on by default.However, default behavior can be changedunder “Tools menu > Options … > Simulation:Contact: Auto Detection” • Activate automatic shell contact detectionunder the “Contact” branch • Tolerance controls include ability to inputabsolute search distance to detect contact,very important for shell assemblies with gaps. • User can turn on detection of face-to-edge or edge-to-edge contact • Priority can be set to prevent multiple contactregions from being formed in a given regionby setting priority. March 29, 2005 Inventory #002215 3-28

  29. If needed, use the “Label” button on the Graphical Toolbar to move the “Contact Region” label & pinball sphere to a location which may be more convenient. … Surface Body Contact • Another example of the use of the pinball region is below: • Surfaces represent midplanes of thin structure. At the “T” intersection of two shells, a gap is present • If the pinball region is large enough, bonded contact can be established between the shells despite the gap. Too large of a value makes the solution inefficient, however. • If “Pinball Region: Radius” is input under the Details view, the pinball region is shown graphically as a sphere. For bonded regions, the radius should be large enough to fill any ‘gap.’ • Pinball region, by default, is based on the size of the underlying mesh (solid body) or thickness (surface body). March 29, 2005 Inventory #002215 3-29

  30. … Spot Weld • Spot welds provide a means of connecting shell assemblies at discrete points • For ANSYS DesignSpace licenses, shell contact is not supported, so spotwelds are the only way to define a shell assembly. • Spotweld definition is done in the CAD software. Currently, only DesignModeler and Unigraphics define spotwelds in a manner that Simulation supports. • Spotwelds can also be created in Simulation manually, but only at discrete vertices. March 29, 2005 Inventory #002215 3-30

  31. … Contact Options • The different contact options will be covered in detail in later chapters: • In structural analysis, contact elements allow for various interactions between parts • In thermal analysis, contact elements allow for heat transfer and thermal contact resistance between parts March 29, 2005 Inventory #002215 3-31

  32. Right-click on the spreadsheet to hide/show specific columns. … Contact Worksheet • The “Worksheet” tab of the “Contact” branch provides a summary of various contact and spot weld definitions: March 29, 2005 Inventory #002215 3-32

  33. C. Meshing • The nodes and elements of the mesh participate in the finite element solution • The solid model geometry is meshed, and the resulting mesh is solved in the matrix equation. • A “default” mesh is automatically generated during initiation of the solution • The user can “preview” the mesh to check whether it is adequate or not for his/her needs. March 29, 2005 Inventory #002215 3-33 Model shown is from a sample Inventor assembly.

  34. … Meshing • The user needs to balance the computational cost with the numerical accuracy of the mesh • A finer mesh produces more precise answers but also increases CPU time and memory requirements • Ideally, having a solution not dependent on the mesh density is what users want (i.e., answers do not change appreciably as mesh is refined) • Convergence controls (discussed later) aid in this • A finer mesh does not compensate for incorrect assumptions and inputs, however! March 29, 2005 Inventory #002215 3-34

  35. Relevance = -100 Nodes: 9968 Elements: 5808 Relevance = 0 Nodes: 19040 Elements: 10909 Relevance = +100 Nodes: 40764 Elements: 24687 … Global Meshing Controls • Basic meshing controls are available under the “Mesh” branch • With “Global Controls” as “Basic” (default), user has control with a single slider bar • “Relevance” setting between –100 and +100 • Default Relevance is set to 0 but can be changed in “Tools > Control Panel > Meshing: Relevance” March 29, 2005 Inventory #002215 3-35

  36. … Global Meshing Controls • User can change to “Advanced” global controls • Five options are available to user: • “Element Size” defines average element edge size • One way to determine this is to use the “edge” selection filter and select a representative edge (like thickness of a rib) to use • “Curv/Proximity” tells Simulation to put more elements near curvature or proximity of edges to each other • Set slider bar from –100 to +100. If “Element Size” left to “Default”, “Curv/Proximity” behaves the same as “Relevance” • The “Proximity” of lines to each other is accounted for sweepable bodies or if “Part Proximity” branches are added (discussed later) • “Shape Checking” defines element shape quality tests used • For linear analysis, “Standard” is suitable. For nonlinear analysis or field analyses, stricter tests may be needed (“Aggressive”) March 29, 2005 Inventory #002215 3-36

  37. … Global Meshing Controls • Five options are available to user (cont’d): • “Solid Element Order” allows users to toggle between lower- or higher-order solid elements. • Higher-order solid elements are default • Lower-order tetrahedral elements should not be used for structural analyses, as these result in constant strain tets (stiff behavior). Lower-order solid elements should not be requested with Hex-Dominant meshing (discussed later) for structural and thermal analyses since lower-order pyramids are not supported. • This option not supported for Shape Optimization analyses • “Initial Size Seed” controls what the mesh seeding is based on Part-Based Mesh Seeding Nodes: 52,484 Elements: 19,816 (Mesh seeding is based on parts, so less uniform between parts) Assembly-Based Mesh Seeding Nodes: 13,001 Elements: 5,666 (Mesh seeding is more uniform between parts) March 29, 2005 Inventory #002215 3-37

  38. Part Relevance=+100 Part Relevance=-100 … Local Mesh Controls • Part Relevance allows controlling mesh by parts • “Part Relevance” is similar to the “Basic” globalmesh control except it is for selected parts • Control is given with a slider (-100 to +100) March 29, 2005 Inventory #002215 3-38

  39. … Local Mesh Controls • Sizing allows for local element size specification • An average element size, sphere of influence, ornumber of divisions per edge can be specified • “Element Size” produces elements with specified average edge length • “Number of Divisions” puts specified number of elements on edge(s) • “Sphere of Influence” allows specification of a ‘sphere,’ where elements lying in sphere have a given average element size • Sizing enables users to specify local mesh densities which are finer or coarser than global average element size • Available options above depend on which entities are scoped: March 29, 2005 Inventory #002215 3-39

  40. In the adjacent example, a “Sphere of Influence” (shown in red) has been defined. Elements lying in that sphere for that scoped entity will have a given average element size. A surface (purple) has the sizing, so elements on the surface in the sphere of influence will have the average element size. For the example on right, the left side has initial “Element Size” whereas the right size is left with default mesh settings. Note that the left side with sizing controls has a relatively uniform mesh density of the specified edge length. … Local Mesh Controls March 29, 2005 Inventory #002215 3-40

  41. In this example, the contact region between the two parts has a Contact Sizing specified (by Element Size). Note that the mesh is now consistent at the contact region. … Local Mesh Controls • Contact Sizing provides a way of generatingsimilar-sized elements on contact faces • Because contact regions define the interactionbetween parts, it may be preferred to have similarmesh densities between contact region surfaces • An “Element Size” or “Relevance” can be specified for a given contact region March 29, 2005 Inventory #002215 3-41

  42. … Local Mesh Controls • Element refinement divides existing mesh • Although transparent to the user, an ‘initial’ meshis created with global and local size controls first,then element refinement is performed on the specified vertices, edges, or surfaces. • Refinement level of “1” is recommended. This breaks up the edges of the elements in the ‘initial’ mesh in half. • Refinement is an easy way to get a finer mesh in areas of interest after generating a coarse mesh. For example shown, the left side has refinement level of 1 whereas the right side is left untouched with default mesh settings. Note that the refined mesh is not uniform since the original mesh is not uniform. The refined mesh breaks element edges in half. March 29, 2005 Inventory #002215 3-42

  43. … Local Mesh Controls • There is considerable difference between using sizing and refinement • Sizing puts constraints on the mesh on the average element edge length prior to meshing. Generally speaking, this produces a uniform mesh on specified geometric entities, and the mesh transition is smoother. • Refinement breaks elements after an ‘initial’ mesh. If the original mesh is non-uniform, the refined mesh will be non-uniform, also. Refinement also leads to less smooth transitions, although a smoothing algorithm is used. • Sizing and refinement controls can be specified on the same surface. Sizing will occur first during the ‘initial’ mesh, then it will be refined in the second pass during meshing (all transparent to the user). March 29, 2005 Inventory #002215 3-43

  44. … Mapped Face Meshing • Mapped Face Meshing allows for the generationof structured meshes on surfaces: • In example below, mapped face meshing on theinternal cylindrical face provides a more uniformmesh pattern. This may be useful to provide better resolution • If surface cannot be mapped mesh for any reason, meshing will continue and this will be shown in Outline Tree with icon: March 29, 2005 Inventory #002215 3-44

  45. … Mapped Face Meshing • Mapped quad or tri mesh also available for surface bodies • A surface can be mapped meshed with quadrilateral or triangular elements. (It is not recommended to use triangular shell elements whenever possible due to accuracy reasons.) March 29, 2005 Inventory #002215 3-45

  46. For model shown on right, the solid body in middle is swept-meshed with hexahedral (and pentahedral) elements, whereas other volumes are meshed with tetrahedral elements. … Solid Element Shape • By default, Simulation determines how to mesh solid bodies: • Sweep-meshable volumes will have hex (and possible wedge) elements. Other volumes willbe meshed with tet elements. • Sweep-meshing is done in cases where a volume has the same topology in one direction. • Right-click on “Mesh” branch gives user ability to see what volumes may be ‘swept’ with “Preview Sweep”. Sweepable solid bodies will be selected. March 29, 2005 Inventory #002215 3-46

  47. … Solid Element Shape • The “Element Shape” branch provide the user with control over how selected solid bodies are meshed: • “Auto Sweep if Possible” lets Simulation mesh sweepable volumes with hexahedra (and possibly also pentahedra) • “All Tetrahedrons” lets Simulation mesh all volumes with tetrahedras • “Hex Dominant” only appears with ANSYS Structural licenses and above March 29, 2005 Inventory #002215 3-47

  48. Cut Boundaries Matched Faces Full Model Cyclic Symmetry Model . . . Match Face Meshing • Matches mesh pattern on symmetry faces to facilitate cyclic symmetry analyses typical of rotating machinery • Because cyclic symmetry employs constraint equations linking each cut boundary the nodal locations on each face must be identical except for the offset (see below) March 29, 2005 Inventory #002215 3-48

  49. . . . Match Face Meshing • Procedure: • Insert “Match Face Meshing” control under Mesh branch • Identify faces of symmetry boundary • Identify the coordinate system (Z axis is rotation axis) Rotation CS March 29, 2005 Inventory #002215 3-49

  50. … Hex-Dominant Meshing • Advanced Structural Meshing introduction: • The hex-dominant meshing algorithm creates a quad-dominant surface mesh first, then extrudes those bricks/wedges inward. Pyramid and tetrahedral elements are then filled in. This generally results in hexahedral elements on the outside and tetrahedral elements on the inside, which is preferred • As noted in the previous slide, the “Hex Dominant” option for the “Element Shape” branch is only available with the ANSYS Structural license and above • “Control Messages” will appear to warn user if volume may not be suitable for hex-dominant meshing March 29, 2005 Inventory #002215 3-50

More Related