Procedure For Analysis And Simulation Using Ansys

This section describes the overall workflow involved when performing dynamic transient structural analysis in the Mechanical application by using ANSYS Workbench 12.0. Each step will include with figure that show how the analysis and the result been prepared.

5.2 Create Analysis System

There are several types of analyses you can perform in the ANSYS Mechanical application. However, in this chapter only Transient Structural Analysis procedure will be cover to determine the dynamic response of a structure under the action of any general time-dependent loads. The following steps explain how to build a system in ANSYS Workbench. The appropriate group in the Toolbox has been selected with the Analysis Systems group.

The appropriate template has been selected which is Transient Structural (ANSYS). The template in the Toolbox has been double-click, or drag it onto the Project Schematic. All possible drop locations has been preview by using a drag-and-drop operation.

Alternatively, right-click in the Project Schematic whitespace and select the type of analysis you want to add.

During creating a new system, the name of the system is automatically highlighted and ready for editing. If you wish to change the name, simply type the new name. You can change the name later by double-clicking the name to highlight it and typing the new name, or by selecting the Rename option from the context menu (available via right-mouse click on the header cell).

Figure 5.2: New Analysis System has been created for Transient Structural (ANSYS) which is shown the location of the Toolbox and Project Schematic. Also shown the step to import geometry.

If necessary, define appropriate engineering data for your analysis. Right click the Engineering Data cell, and select Edit, or double-click the Engineering Data cell. The Engineering Data workspace appears, where you can add or edit material data as necessary.

Attach geometry to your system or build a new geometry in DesignModeler. Right click the Geometry cell and select Import Geometry to attach an existing model or select New Geometry to launch DesignModeler.

Figure 5.3: Windows for attaching geometry from SolidWorks 2009 file to the system.

Define all loads and boundary conditions. Right click the Setup cell and select Edit. The appropriate application for the selected analysis type will open the Mechanical application. Set up your analysis using that application’s tools and features.

You can solve your analysis by issuing an Update, either from the data-integrated application you’re using to set up your analysis, or from the ANSYS Workbench GUI.

5.3 Engineering Data

Engineering Data is a resource for material properties used in an analysis system. The Engineering Data workspace is designed to allow you to create, save, and retrieve material models, as well as to create libraries of data that can be saved and used in subsequent projects and by other users. Engineering Data can be shown as a component system or as a cell in any Mechanical analysis system. When viewed as a cell in a Mechanical analysis system, the workspace shows the material models and properties pertinent to that system’s physics.

To access Engineering Data:

Insert an Engineering Data component system or a Mechanical system into the Project Schematic.

Select Edit from the Engineering Data cell’s context menu, or double-click the cell.

The Engineering Data workspace appears. From here, navigate through the data for the analysis system, access external data sources, create new data, and store data for future use.

Figure 5.4: The Engineering Data workspace is designed to allowed to create, save, and retrieve material models.

5.4 Geometry

Use the Geometry cell to import, create, edit or update the geometry model used for analysis. For this analysis, the geometry has been import from SolidWorks 2009 assembly file format “.SLDASM” to the DesignModeler and there no need to be redraw again and proceed to the next step. Before Attaching CAD geometry to the Mechanical application, specifying several options that determine the characteristics of the geometry you choose to import.

Figure 5.5: Selecting desired length unit option before start DesignModeler workspace.

Procedure attaching CAD geometry to the Mechanical application in condition CAD system is running:

Select the Geometry cell in an analysis system schematic.

Right-click on the Geometry cell listed there.

Double-click on the Model cell in the same analysis system schematic. The Mechanical application opens and displays the geometry.

If required, set geometry options in the Mechanical application by highlighting the Geometry object and choosing settings under Preferences in the Details view.

Figure 5.6: DesignModeler workspace with successfully imported from SolidWorks 2009 assembly file format which can be adjust as desired.

5.5 Stiffness Behaviour

In addition making changes to the material properties of a part, designate a part’s Stiffness Behaviour as flexible or rigid. Setting a part’s behaviour as rigid essentially reduces the representation of the part to a single point mass thus significantly reducing the solution time.

For this analysis, the cylindrical workpiece will be a rigid body and thus both top and bottom clamp will be define as flexible body. This is because the analysis itself is to determine the response of the clamping to the time-vary load. A rigid part will need only data about the density of the material to calculate mass characteristics. Note that if density is temperature dependent, density will be evaluated at the reference temperature. For contact conditions, Young’s modulus has been specified.

Figure 5.7: Shown the Details view for “rod 16-2-1” changing the Stiffness behaviour of the cylindrical workpiece to the Rigid.

5.6 Define Connections

Connections include contact regions, joints, springs, or beams. Contact conditions are formed where bodies meet. When an assembly is imported from a CAD system, contact between various parts is automatically detected. In this analysis there are only two type of connection that will be used which is contact regions and joints.

5.6.1 Contact Regions

The differences in the contact settings determine how the contacting bodies can move relative to one another. This is the most common setting and has the most impact for this analysis. Most of these types only apply to contact regions made up of faces only.

Bonded: This is the default configuration and applies to all contact regions (surfaces, solids, lines, faces, edges). If contact regions are bonded, then no sliding or separation between faces or edges is allowed.

No Separation: This contact setting is similar to the bonded case. It only applies to regions of faces (for 3-D solids) or edges (for 2-D plates).

Frictionless: This setting models standard unilateral contact; that is, normal pressure equals zero if separation occurs. It only applies to regions of faces (for 3-D solids) or edges (for 2-D plates). A zero coefficient of friction is assumed, thus allowing free sliding.

Rough: Similar to the frictionless setting, this setting models perfectly rough frictional contact where there is no sliding. It only applies to regions of faces (for 3-D solids) or edges (for 2-D plates).

Frictional: In this setting, two contacting faces can carry shear stresses up to a certain magnitude across their interface before they start sliding relative to each other. It only applies to regions of faces. The model defines an equivalent shear stress at which sliding on the face begins as a fraction of the contact pressure. Once the shear stress is exceeded, the two faces will slide relative to each other. The coefficient of friction can be any non-negative value.

Choosing the appropriate contact type depends on the type of problem that are trying to solve. Modelling the ability of bodies to separate or open slightly is important and/or obtaining the stresses very near a contact interface is important, nonlinear contact types (Frictionless, Rough, Frictional) has been considered to be used. However, using these contact types results in longer solution times and can have possible convergence problems due to the contact nonlinearity. When determining the exact area of contact is critical, finer mesh has been considered to be used (using the Sizing control) on the contact faces or edges that will be explain on the next sub chapter.

Friction Coefficient: Allows you to enter a friction coefficient. Displayed only for frictional contact applications.

Scope Mode: Read-only property that displays how the contact region was generated.

Automatic – Program automatically generated contact region.

Manual – Contact region was constructed or modified by the user.

Behavior: Sets contact pair to one of the following:

Asymmetric: Contact will be asymmetric for the solve. All face/edge and edge/edge contacts will be asymmetric.

Asymmetric contact has one face as Contact and one face as Target (as defined under Scope Settings), creating a single contact pair. This is sometimes called “one-pass contact,” and is usually the most efficient way to model face-to-face contact for solid bodies.

The Behavior must be Asymmetric if the scoping includes a body specified with rigid Stiffness Behavior.

Symmetric: (Default) – Contact will be symmetric for the solve.

Auto Asymmetric: Automatically creates an asymmetric contact pair, if possible. This can significantly improve performance in some instances. When you choose this setting, during the solution phase the solver will automatically choose the more appropriate contact face designation. Of course, you can designate the roles of each face in the contact pair manually.

Figure 5.8: Shown are the summary of the connection in Worksheet view including contact information, joint DOF checker, and joint information.

5.6.2 Setting Contact Conditions Manually

Manual contact regions represent contact over the entire extent of the contact scope, for example, faces of the contact region.

Procedure to set contact regions manually:

Click the Connections object in the Tree Outline.

Click the right mouse button and choose Insert> Manual Contact Region. You can also select the Contact button on the toolbar.

A Contact Region item appears in the Outline. Click that item, and under the Details View, specify the Contact and Target regions (faces or edges) and the contact type. See the Contact and Target topics in the Scope Settings section for additional Contact Region scoping restrictions.

5.7 Joints

A joint typically serves as a junction where bodies are joined together. Joint types are characterized by their rotational and translational degrees of freedom as being fixed or free. For all joints that have both translational degrees of freedom and rotational degrees of freedom, the kinematics of the joint is as follows:

Translation: The moving coordinate system translates in the reference coordinate system. If your joint is a slot for example, the translation along X is expressed in the reference coordinate system.

Once the translation has been applied, the center of the rotation is the location of the moving coordinate system.

5.7.1 Types of Joints

You can create the following types of joints in the Mechanical application:

Fixed Joint

Revolute Joint

Cylindrical Joint

Translational Joint

Slot Joint

Universal Joint

Spherical Joint

Planar Joint

General Joint

Bushing Joint

5.7.2 Applying Joints

Procedure to add a joint manually:

After importing the model, highlight the Model object in the tree and choose the Connections button from the toolbar.

Highlight the new Connections object and choose either Body-Ground> {type of joint} or Body-Body> {type of joint} from the toolbar, as applicable.

Highlight the new Joint object and scope the joint to a face.

Reposition the coordinate system origin location or orientation as needed.

The Body Views button in the toolbar displays Reference and Mobile bodies in separate windows with appropriate transparencies applied. You have full body manipulation capabilities in each of these windows.

Configure the joint. The Configure button in the toolbar positions the Mobile body according to the joint definition. You can then manipulate the joint interactively (for example, rotate the joint) directly on the model.

Consider renaming the joint objects based on the type of joint and the names of the joined geometry.

Display the Joint DOF Checker and modify joint definitions if necessary.

Create a redundancy analysis to interactively check the influence of individual joint degrees of freedom on the redundant constraints.

Procedure to move a joint coordinate system to a particular face:

Highlight the Coordinate System field in the Details view of the Joint object. The origin of the coordinate system will include a yellow sphere indicating that the movement “mode” is active.

Select the face that is to be the destination of the coordinate system. The coordinate system in movement mode relocates to the centroid of the selected face, leaving an image of the coordinate system at its original location.

Click the Apply button. The image of the coordinate system changes from movement mode to a permanent presence at the new location.

Procedure to change the orientation of a joint coordinate system:

Highlight the Coordinate System field in the Details view of the Joint object. The origin of the coordinate system will include a yellow sphere indicating that the movement “mode” is active.

Click on any of the axis arrows you wish to change. Additional “handles” are displayed for each axis.

Click on the handle or axis representing the new direction to which you want to reorient the initially selected axis.

The axis performs a flip transformation.

Click the Apply button. The image of the coordinate system changes from movement mode to a permanent presence at the new orientation.

You can change or delete the status of the flip transformation by highlighting the Reference Coordinate System object or a Mobile Coordinate System object and making the change or deletion under the Transformations category in the Details view of the child joint coordinate system.

When selecting either a Reference Coordinate System object or a Mobile Coordinate System object, various settings are displayed in the Details view.

5.8 Meshing

In this stage, the model need to be mesh in order to analyze the model. The goal of meshing in ANSYS Workbench is to provide robust, easy to use meshing tools that will simplify the mesh generation process. These tools have the benefit of being highly automated along with having a moderate to high degree of user control.

5.8.1 Physics Based Meshing

When the Meshing application is launched from the ANSYS Workbench Project Schematic, the physics preference will be set based on the type of system being edited. For a Mechanical Model system as in this analysis, the Mechanical physics preference is used. For a Mesh system, the physics preference defined in Tools> Options> Meshing> Default Physics Preference is used.

Upon startup of the Meshing application from a Mesh system, the Meshing Options panel shown below in figure 5.5. This panel allows to quickly and easily set meshing preferences based on the physics are prepared to be solved. Remove the panel after startup, the panel can be display again by clicking the Options button from the Mesh toolbar.

Figure 5.9: Meshing option in Mechanical application.

The first option the panel allows to set is Physics Preference. This corresponds to the Physics Preference value in the Details View of the Mesh folder. Setting the meshing defaults to a specified “physics” preference sets options in the Mesh folder such as Relevance Center, midside node behavior, shape checking, and other meshing behaviors.

ANSYS Workbench meshing capabilities, arranged according to the physics type involved in the analysis. For this analysis, Mechanical physics is used, the preferred meshers for mechanical analysis are the patch conforming meshers (Patch Conforming Tetrahedrons and Sweeping) for solid bodies and any of the surface body meshers.

5.8.2 Using 3D Rigid Body Contact Meshing

This section describes the basic steps for using 3D rigid body contact meshing.

Procedure to define a 3D rigid body for contact meshing:

Open the model in the Mechanical application.

In the Tree, expand the Geometry object so that the body objects are visible.

Click on the body that you want to define as a rigid body.

In the Details> Definition view for the body, change the value of the Stiffness Behavior control to Rigid.

If you wish to control the mesh method, insert a mesh method by right-clicking on the Mesh object in the Tree and selecting Insert> Method.

In the Details View, scope the mesh method to the rigid body.

If desired, change the value of the Element Midside Nodes control.

Generate the mesh by right-clicking on the Mesh object in the Tree and selecting Generate Mesh.

Figure 5.10: meshing result for current design analysis.

5.9 Establish Analysis Settings

In transient structural analysis includes a group of analysis settings that allow to define various solution options customized to the specific analysis type, such as large deflection for a stress analysis. Default values are included for all settings.

Procedure to verify/change analysis settings in the Mechanical application:

Highlight the Analysis Settings object in the tree. This object was inserted automatically when you established a new analysis in the Create Analysis System overall step.

Verify or change settings in the Details view of the Analysis Settings object. These settings include default values that are specific to the analysis type. Accept these defaults. In this analysis involves the use of steps, by refering to the procedures presented below.

Procedure to create multiple steps:

Highlight the Analysis Settings object in the tree. Modify the Number of Steps field in the Details view. Each additional Step has a default Step End Time that is one second more than the previous step.

These step end times can be modified as needed in the Details view. Adding more steps simply by adding additional step End Time values in the Tabular Data window.

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Figure 5.11: The following demonstration illustrates adding steps by modifying the Number of Steps field in the Details view

Procedure to Specifying Analysis Settings for Multiple Steps:

Create multiple steps following the procedure “To create multiple steps” above.

Most Step Controls, Nonlinear Controls, and Output Controls fields in the Details view of Analysis Settings are “step aware”, that is, these settings can be different for each step.

Activate a particular step by selecting a time value in the Graph window or the Step bar displayed below the chart in the Graph window. The Step Controls grouping in the Details view indicates the active Step ID and corresponding Step End Time.

Figure 5.12: The following demonstration illustrates turning on the legend in the Graph window, entering analysis settings for a step, and entering different analysis settings for another step.

To specify the same analysis setting(s) to several steps, select all the steps of interest as follows and change the analysis settings details.

To change analysis settings for a subset of all of the steps from the Tabular Data window:

Highlight the Analysis Settings object.

Highlight steps in the Tabular Data window using either of the following standard windowing techniques:

Ctrl key to highlight individual steps.

Shift key to highlight a continuous group of steps.

Click the right mouse button in the window and choose Select All Highlighted Steps from the context menu.

Specify the analysis settings as needed. These settings will apply to all selected steps.

To specify analysis settings for all the steps:

Click the right mouse button in either window and choose Select All Steps.

Specify the analysis settings as needed. These settings will apply to all selected steps.

Figure 5.13: The following demonstration illustrates multiple step selection using the bar in the Graph window, entering analysis settings for all selected steps, selecting only highlighted steps in the Tabular Data window, and selecting all steps.

Figure 5.14: The Worksheet tab for the Analysis Settings object provides a single display of pertinent settings in the Details view for all steps.

5.10 Joint Load

When using joints in a Transient Structural (ANSYS) analysis, use a Joint Load object to apply a kinematic driving condition to a single degree of freedom on a Joint object. Joint Load objects are applicable to all joint types except fixed, general, universal, and spherical joints. For translation degrees of freedom, the Joint Load can apply a displacement, velocity, acceleration, or force. For rotation degrees of freedom, the Joint Load can apply a rotation, angular velocity, angular acceleration, or moment. The directions of the degrees of freedom are based on the reference coordinate system of the joint and not on the mobile coordinate system.

A positive joint load will tend to cause the mobile body to move in the positive degree of freedom direction with respect to the reference body, assuming the mobile body is free to move. If the mobile body is not free to move then the reference body will tend to move in the negative degree of freedom direction for the Joint Load. For the joint with the applied Joint Load, dragging the mouse will indicate the nature of the reference/mobile definition in terms of positive and negative motion.

Procedure to apply a Joint Load:

Highlight the Transient environment object and insert a Joint Load from the right mouse button context menu or from the Loads drop down menu in the Environment toolbar.

From the Joint drop down list in the Details view of the Joint Load, select the particular Joint object that you would like to apply to the Joint Load. You should apply a Joint Load to the mobile bodies of the joint. It is therefore important to carefully select the reference and mobile bodies while defining the joint.

Select the unconstrained degree of freedom for applying the Joint Load, based on the type of joint. You make this selection from the DOF drop down list. For joint types that allow multiple unconstrained degrees of freedom, a separate Joint Load is necessary to drive each one. Joint Load objects that include velocity, acceleration, rotational velocity or rotational acceleration are not applicable to static structural analyses.

Select the type of Joint Load from the Type drop down list. The list is filtered with choices of Displacement, Velocity, Acceleration, and Force if you selected a translational DOF in step 3. The choices are Rotation, Rotational Velocity, Rotational Acceleration, and Moment if you selected a rotational DOF.

Specify the magnitude of the Joint Load type selected in step 4 as a constant, in tabular format, or as a function of time using the same procedure as is done for most loads in the Mechanical application.

On Windows platforms, an alternative and more convenient way to accomplish steps 1 and 2 above is to drag and drop the Joint object of interest from under the Connections object folder to the Transient object folder. When you highlight the new Joint Load object, the Joint field is already completed and you can continue at step 3 with DOF selection.

Figure 5.15: All load applied to the structural for current design analysis including Earth Gravity, Horizontal Joint Load and Vertical Joint Load.

5.11 Solve

This step initiates the solution process. The solution has been carried out on the local machine. Since transient solutions can take significant time to complete, a status bar is provided that indicates the overall progress of solution. More detailed information on solution status can be obtained from the Solution Information object which is automatically inserted under the Solution folder for all analyses.

Figure 5.16: More detailed information on solution status can be obtained from the Solution Information in Worksheet view.

The overall solution progress is indicated by a status bar. In addition the Solution Information object has been used which is inserted automatically under the Solution folder. This object allows to:

View the actual output from the solver,

Graphically monitor items such as convergence criteria for nonlinear problems and

Diagnose possible reasons for convergence difficulties by plotting Newton-Raphson residuals.

5.12 Review Results

For this transient structural analysis, the interested will be in total deformation and maximum shear results. The Results in the Mechanical Application will show as figure and tabular data.

Procedure to add result objects in the Mechanical application:

Highlight a Solution object in the tree.

Select the appropriate result from the Solution context toolbar or use the right-mouse click option.

Figure 5.17: Shown the right-click mouse option to add result in Mechanical application for Total Deformation.

Procedure to review results in the Mechanical application:

Click on a result object in the tree.

After the solution has been calculated, review and interpret the results in the following ways:

Contour results – Displays a contour plot of a result such as stress over geometry.

Vector Plots – Displays certain results in the form of vectors (arrows).

Probes – Displays a result at a single time point, or as a variation over time, using a graph and a table.

Charts – Displays different results over time, or displays one result against another result, for example, force vs. displacement.

Animation – Animates the variation of results over geometry including the deformation of the structure.

Stress Tool – to evaluate a design using various failure theories.

Fatigue Tool – to perform advanced life prediction calculations.

Contact Tool – to review contact region behavior in complex assemblies.

Beam Tool – to evaluate stresses in line body representations.

Figure 5.18: A contour result of Maximum Shear Stress for current design. All the contour colour indicate different value of shear stress over a geometry.