ansys_12.0_workbench_training_-_WB-Mech_120_Ch03_Analysis

nullChapter 3 General PreprocessingChapter 3 General PreprocessingChapter OverviewChapter OverviewIn this chapter, using features without the use of the Wizards will be covered Topics: Geometry Contact Workshop 3-1, “Contact Control” Meshing Named Selections Coordinate Systems Workshop 3-2, “Meshing Control” 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 IntroductionIntroductionIn the previous chapter, the Mechanical GUI was introduced through the use of the Mechanical Wizards In this chapter, navigating through the GUI without the Wizards will be covered… Introduction… IntroductionThe Outline Tree is the main way of setting up an 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 chapterUse of the Outline Tree is the means by which users navigate through the Simulation GUI.A. Geometry BranchA. Geometry BranchThe Geometry branch lists the part(s) that make up the model. 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 Each is explained next . . . … Types of Bodies… Types of BodiesSolid 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 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 Each node has three translational degrees of freedom (DOF) for structural or one temperature DOF for thermal 3D Solids2D SolidsAxisymmetric cross section… Types of Bodies… Types of BodiesSurface bodies are geometrically 2D but spatially 3D: Surface bodies represent structures which are thin in one dimension (through-thickness). Thickness is not modeled but supplied as an input value. Surface bodies are meshed with linear shell elements having six DOF (UX, UY, UZ, ROTX, ROTY, ROTZ). Line bodies are geometrically 1D but spatially 3D: Line bodies represent structures which are thin in two dimensions. The cross-section is not modeled. Line bodies are modeled with linear beam elements having six DOF (UX, UY, UZ, ROTX, ROTY, ROTZ).Line BodySurface Body… Multibody Parts… Multibody PartsIn general, bodies and parts are the same. In DesignModeler however, multiple bodies may be grouped into multibody parts. Multibody parts share common boundaries so nodes are shared at that interface. No contact is needed in these situations. Example: Common nodes are shared by adjacent bodies… Material Properties… Material PropertiesTo assign material properties to a body highlight it and select from the available properties in the “Assignment” field : The only materials appearing in the list will be materials added using the “Engineering Data” application (see previous chapter). For surface bodies a thickness needs to be supplied as well.… Geometry Worksheet… Geometry WorksheetA summary of bodies and assigned materials is available Select “Geometry” branch and then the “Worksheet” tab B. ContactB. ContactWhen multiple parts are present, a means of defining the relationship between parts is needed. Contact regions define how parts interact with each other. 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. Multibody parts do not require contact or spot welds.Surface contact elements can be visualized as a “skin” covering the regions where contact will occur.Load… Solid Body Contact… Solid Body ContactWhen an assembly is imported contact surfaces are automatically detected and created: The proximity of surfaces is used to detect contact. Tolerance for contact detection is available in the “Connections” branch details. Contact is also used for 2D geometry. Contact “surfaces” are represented by edges. Certain license levels allow surface to edge, edge to edge and mixed solid/surface contact. Note, automatic contact should always be checked and verified before proceeding with an analysis.… Solid Body Contact… Solid Body ContactContact elements provide the relationship between parts. Each part maintains a separate mesh. This means that one small part will not drive mesh density of the entire assembly and/or the user can make parts of interest have a finer mesh than other parts Note the non-matching mesh at the interface between parts. Mix of hexahedral elements contacting tetrahedral elements is possible.… Solid Body Contact… Solid Body ContactWhen a contact region is highlighted in the connections branch, parts are made translucent for easier viewing. Selecting a contact region makes non participating bodies translucent. Contact surfaces are color coded for easy identification. … Solid Body Contact… Solid Body Contact“Go To” utilities allow a more detailed investigation of contact definitions: Corresponding bodies in tree Bodies without contact Contact regions for selected bodies Contacts common to selected bodies Contacts can be quickly renamed to match part namesRMB… Solid Body Contact… Solid Body ContactTo manually define a contact pair insert a manual contact region and select and apply “contact” and “target” surfaces.… Advanced Solid Body Contact… Advanced Solid Body ContactFor ANSYS Professional licenses and above, advanced contact options are available: Auto detection dimension and slider Asymmetric contact Contact results tool More contact formulations available Pinball control… Advanced Solid Body Contact… Advanced Solid Body ContactThe Pinball region represents a contact detection zone: Contact calculation/detection occurs when contact gap is within the pinball radius. The pinball radius dimension may be entered to ensure that bonded contact is established for a large clearance or gap. Pinball radius is displayed as a sphere in the graphics window. Status: near field, far field, closed/sliding, closed/sticking.… Surface Body Contact… Surface Body ContactShell contact includes edge-to-face or edge-to-edge contact: Shell contact is not turned on by default. User can turn on detection of face-to-edge or edge-to-edge contact. Priority can be set to prevent multiple contact regions from being formed in a given region by setting priority. … Spot Weld… Spot WeldSpot welds provide a means of connecting assemblies at discrete points: Spot weld is defined in the CAD software. Currently, only DesignModeler and Unigraphics define spot welds supported by Mechanical.Spot weld pairs… Contact Worksheet… Contact WorksheetThe “Worksheet” tab of the “Connections” branch provides a summary of various contact and spot weld definitions: nullWorkshop 3.1 – Contact Control Goal: Investigate several types of contact behavior.C. Workshop 3.1 – Contact ControlD. MeshingD. MeshingThe nodes and elements representing the geometry model make up the mesh: A “default” mesh is automatically generated during initiation of the solution. The user can “generate” the mesh prior to solving to verify mesh control settings. A finer mesh produces more precise answers but also increases CPU time and memory requirements. … Global Meshing Controls… Global Meshing ControlsPhysics Based Meshing allows the user to specify the mesh based on the physics to be solved. Choosing the physics type will set controls such as: Solid element mid-side nodes Element shape checking Transitioning Physics preferences can be: Mechanical Electromagnetics CFD Explicit Setting the physics preference pre-configures the Advanced meshing defaults discussed on subsequent pages. Note: only Mechanical meshing preferences are discussed in this course.… Global Meshing Controls… Global Meshing ControlsBasic meshing controls are available under the “Defaults” group in the “Mesh” branch The user has control with a single slider bar “Relevance” setting between –100 and +100 - Relevance = coarse mesh+ Relevance = fine mesh… Global Meshing Controls… Global Meshing ControlsAdvanced global controls: Relevance Center: sets the mid point of the “Relevance” slider control. Element Size: defines element size used for the entire model. Shape Checking: Standard Mechanical – linear stress, modal and thermal analyses. Aggressive Mechanical – large deformations and material nonlinearities. Solid Element Midside Nodes: Program Controlled (default), Dropped or Kept.KeptDropped… Global Meshing Controls… Global Meshing ControlsStraight Sided Elements : Displayed when solids are present in the model or enclosures from DesignModeler are present. Must be used for Electromagnetic simulations. Initial Size seed: Controls the initial seeding of the mesh size for each part. (Explained in more detail on next slide) Smoothing : Attempts to improve element quality by moving nodes. Number of smoothing iterations can be controlled (Low, Medium, High). Transition : Controls the rate at which adjacent elements will grow (Smooth, Fast)… Global Meshing Controls… Global Meshing ControlsInitial Size Seed: Active Assembly (default) : Initial mesh sizing will be determined by the active set (unsuppressed) of parts. Full Assembly: Initial mesh will not be affected by the suppressed/unsuppressed state of parts. Part: Initial seeding based on each part’s size independently. Mesh will not change due to part suppression. Generally gives finer mesh. Mesh may not be uniform through out the assembly.Part-Based Mesh Seeding Nodes: 44,013 (Mesh seeding is based on parts, so less uniform between parts)Assembly-Based Mesh Seeding Nodes: 15,670 (Mesh seeding is more uniform between parts)… Local Meshing Controls… Local Meshing ControlsLocal Mesh Controls can be applied to either a Geometry Selection or a Named Selection. These are available only when the mesh branch is highlighted. Available controls include : Method Control Sizing Control Contact Sizing Control Refinement Control Mapped Face Meshing (EMAG and cyclic, not covered) Inflation Control Pinch Control Gap Tool (EMAG only, not covered) … Local Meshing Controls : Method (continued)… Local Meshing Controls : Method (continued)Method Control : Provides the user with options as to how solid bodies are meshed: (Valid only for bodies). Automatic (default): Body will be swept if possible. Otherwise, the “Patch Conforming” mesher under “Tetrahedrons” is used. Continued . . . nullTetrahedrons: An all Tetrahedron mesh is generated. Patch Conforming: Expansion Factor controls the internal growth rate of the tetrahedrons. Patch Independent Meshing: Faces and their boundaries may or may not be respected during meshing operations. The exception is when a boundary condition is applied to a surface, its boundaries are respected. See next page for Patch Independent options.… Local Meshing Controls : Method (continued)nullPatch Independent Options: Maximum Element Size: size of the initial element subdivision Approx Number of Elements: desired number of elements in model (can be overridden by other mesh controls). Define defeaturing Tolerance – Filters out edges based on size and angle. If set to “Yes”, a Defeaturing Tolerance field appears where a numerical value is to be entered. Note: defeaturing can cause a mesh to “ignore”, and therefore mesh over, small features. The Simulation documentation contains a full description and examples. Continued . . . … Local Meshing Controls : Method (continued)nullCurvature and Proximity Refinement = Yes: Define by: maximum element size or approximate number of elements. Defeaturing Tolerance (yes): adds tolerance controls to defeature edges. Curvature and Proximity: automatically refines mesh based on curvature and proximity of features. Num Cells across Gap – Specifies the number of cells desired in narrow gaps. Refinement is limited by the Min Size Limit. Span Angle – Mesh will subdivide in curved regions till the individual elements span the specified angle. Limited by Min Size Limit. … Local Meshing Controls : Method (continued)nullHex Dominant : Creates a free hex dominant mesh. Useful for meshing bodies that cannot be swept. Recommended for meshing bodies with large interior volumes. (only available with ANSYS Structural licenses and above) The hex-dominant meshing algorithm creates a quad-dominant surface mesh first, then pyramid and tetrahedral elements are filled in as needed. “Control Messages” will appear to warn user if volume may not be suitable for hex-dominant meshing Solid Model with Hex dominant mesh : Tetrahedrons – 443 (9%) Hexahedron – 2801(62%) Wedge – 124 (2%) Pyramid – 1107 (24%)… Local Meshing Controls : Method (continued)nullSweep : Sweep-mesh (hex and possible wedge) elements, otherwise tetrahedra. RMB on mesh branch to “Show Sweepable Bodies”. Type : Number of Divisions or Element Size in the sweep direction. Sweep Bias Type : Bias spacing in sweep direction. Src/Trg Selection : Automatic, manual source or manual source and target. Automatic Thin Model – One hex or wedge through the thickness. Can choose between Solid Shell (SOLSH190) element and a Solid element (Solid185) Manual Thin Model – Allows user to pick a source face. … Local Meshing Controls : Method (continued)… Local Meshing Controls… Local Meshing ControlsSizing: “Element Size” specifies average element edge length or number of divisions (choices depend on geometry selection). “Soft” control may be overridden by other mesh controls. “Hard” may not. Mesh biasing is available. Available options above depend on which entities are scoped: Sphere of Influence sizing, see next page.Face Sizing Applied to a part.… Local Mesh Controls… Local Mesh ControlsSphere of Influence: Center is located using local coordinate system. All scoped entities within the sphere are affected by size settings. “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.Scoped to 2 surfacesScoped to single vertex… Local Mesh Controls… Local Mesh ControlsContact Sizing: generates similar-sized elements on contact faces for face/face or face/edge contact region. “Element Size” or “Relevance” can be specified. Choose “Contact Sizing” from the “Mesh Control” menu and specify the contact region. Or drag and drop a Contact Region object onto the “Mesh” object. In this example, the contact region between the two parts has a Contact Sizing Type Relevance is specified. Note that the mesh is now consistent at the contact region.… Local Mesh Controls… Local Mesh ControlsElement refinement divides existing mesh An ‘initial’ mesh is created with global and local size controls first, then element refinement is performed at the specified location(s). Refinement range is 1 to 3 (minimum to maximum). Refinement splits the edges of the elements in the ‘initial’ mesh in half. Refinement level controls the number of iterations this is performed. For example shown, the left side has refinement level of 2 whereas the right side is left untouched with default mesh settings.… Local Mesh Controls… Local Mesh ControlsMapped Face Meshing: generates structured meshes on surfaces: In example below, mapped face meshing on the outer face provides a more uniform mesh pattern. If surface cannot be mapped mesh for any reason, meshing will continue and this will be shown in Outline Tree with icon: Mapped quad or tri mesh also available for surface bodies… Local Mesh Controls… Local Mesh ControlsInflation Control: useful for adding layers of elements along specific boundarys. Note: Inflation is more often used in CFD and EMAG applications but may be useful for capturing stress concentrations etc. in structural applications.… Local Mesh Controls… Local Mesh ControlsPinch: allows the removal of small features by “pinching” out small edges and vertices (only). Master: geometry that retains the original geometry profile. Slave: geometry that changes to move toward the master. Can be automatic (Mesh level) or local (add Pinch branch).… Meshing Failures… Meshing FailuresIf the mesher is not able to generate well-shaped elements, an error message will be returned: The problematic geometry will be highlighted on the screen, and a named selection group “Problematic Geometry” will be created, so the user may review the model.… Meshing Failures… Meshing FailuresMeshing failures can be caused by a number of things: Inconsistent sizing controls specified on surfaces, which would result in the creation of poorly-shaped elements Difficult CAD geometry, such as small slivers or twisted surfaces Stricter shape checking (“Aggressive” setting in Mesh branch) Some ways to avoid meshing failures: Specify more reasonable sizing controls on geometry Specify smaller sizing controls to allow the mesher to create better-shaped elements In the CAD system, use hidden line removal plots to see sliver or unwanted geometry and remove them Use virtual cells to combine sliver or very small surfaces This option will be discussed next … Virtual Topology… Virtual TopologyVirtual Topology: combines surfaces and edges for meshing control: “Virtual Topology” branch is added to the “Model” branch. A “Virtual Cell” is a group of adjacent surfaces that “acts” as a single surface. Interior lines of original surfaces will no longer be honored by meshing process. For other operations such as applying Loads and Supports, a virtual cell can be referenced as a single entity. Virtual cells can be generated automatically via RMB: The “Behavior” controls the aggressiveness of the “Merge Face Edges?” setting for auto generation. Example . . . … Virtual Topology Example… Virtual Topology Example Consider the example below:Virtual Cell… Virtual Topology Example… Virtual Topology ExampleKeep in mind that the topology can change! Example: a chamfer is added to the top surface in this virtual cell. The interior lines are not recognized anymore.Element’s edge is shown as a solid line and the original chamfer and top surface is shown as a dotted blue line. The chamfer representation is no longer present.Mesh using virtual topologyOriginal meshE. Named SelectionsE. Named SelectionsThe Named Selection Toolbar provides functionality for grouping together geometric entities: Named Selections allow users to group together vertices, edges, surfaces, or bodies. Named Selections can be used for defining mesh controls, applying loads and supports, etc. Provides an easy method to reselect groups that will be referenced often Defining contact regions Scoping results Etc. Note, visibility and suppression are only applicable to body named selections. … Defining Named Selections… Defining Named SelectionsTo create Named Selections: Select the vertices, edges, surfaces, or bodies of interest, then click on the “Create Selection Group” icon Enter a name in the dialog box The new group will appear in the Named Selection Toolbar as well as in the Outline Tree Note: Only one type of entity can be in a particular Named Selection. For example, vertices and edges cannot exist in the same Named Selection. Named Selection groups can be imported from some CAD systems (see Chapter 10) … Using Named Selections… Using Named SelectionsIn many detail window fields Named Selections can be referenced directly: Example (pressure load): In the Details view, change “Method” from “Geometry Selection” to “Named Selection” Select the “Named Selection” from the pull-down menu Simulation will filter non-applicable types of Named Selections.