Dynamic Analysis of a Three-body Model Using OptiStruct - OS-1200

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In this tutorial problem, dynamic analysis on a simple three rigid bodies model will be performed using OptiStruct. The force of gravity acts along the global Y axis, and the system has one degree of freedom.

This exercise includes the creation of PRBODY (rigid body definition), JOINT and boundary conditions in HyperMesh. An existing finite element model will be used in this tutorial problem.

The following exercises are included:

· Setting up the problem in HyperMesh

- PRBODY

- JOINTS

- Boundary conditions (Gravity and MBSIM)

· Submitting the job

· Viewing the results in HyperView

$image\rigid_bodies_model.gif$

Rigid bodies model

Setting up the Problem in HyperMesh

To retrieve the structural model and define the OptiStruct template:

Launch HyperMesh.
Select the OptiStruct in the User Profile dialog and click OK.
Select the Files panel toolbar button $image\files_panel.gif$ .
Select the hm file subpanel using the radio buttons on the left-hand side of the panel.
Click retrieve… .

An Open file… browser window pops up.

Select the 3bodies_dynamics.hm file, located in the HyperWorks installation directory under <install_directory>/tutorials/os/.
Click open.
Click return to go to the main menu.

To define the parts as PRBODY (Rigid Body definition):

Select the bodies panel on the Analysis page.
Select the create subpanel using the radio buttons on the left-hand side of the panel.
Click name= and enter blue.
Click type= and select PRBODY.
Click the comps button below type= and select body1.
Click create.
Repeat the above operation to define PRBODY for the component named body2 with the name lime, and for body3 with the name orange.
Click return.

To create the component for the joints:

Select the Collectors toolbar button $image\collectors.gif$ .
Select the create subpanel using the radio buttons on the left-hand side of the panel.
Click the collector type switch and select components from the pop-up menu.
Click name= and enter joints.
Click the switch beside card image= and select no card image from the pop-up menu.
Click color and select any color.
Click create.

This creates the new component called joints.

Click return to the main menu.

In this tutorial problem, two revolute joints, one ball joint, and one universal joint are created to constrain the degrees of freedom (shown in the following figure), such that the remaining degree of freedom will be just 1.

DOF = 3*6 – (5+5+4+3) = 1

Type of Joint	Removes translational dof	Removes rotational dof	Removes total number of dof
Revolute	3	2	5
Universal	3	1	4
Ball (spherical)	3	0	3

$image\6000_joints_in_model.gif$

Joints in the model

To create the joints:

Select the joints panel from the 1D page of the main menu.

First, the revolute joint at the lower right corner of body3 will be created.

Click the joint type selection switch and select revolute.

$image\j_body3.gif$

Joint at body3

Select node ID 12319 as the first terminal.
Select node ID 13158 as the second terminal.

Note:

Nodes 12319 and 13158 are coincident. Coincident node picking in options panel -> graphics subpanel in HyperMesh will help pick these coincident nodes in the HyperMesh screen.

Select node ID 12910 as a node for first orientation.

The vector 12319 to 12910 defines the axis of rotation of the revolute joint.

Click create.

Next, the revolute joint at the lower left corner of body1 will be created.

$image\j_body1.gif$

Joint at body1

Select node ID 11115 as the first terminal.
Select node ID 13159 as the second terminal.
Select node ID 11706 as a node for first orientation.
Click create.

The vectors 11115 to 11706 define the axis of rotation of the revolute joint.

A universal joint between body3 and body2 will be created next.

$image\univ_joint.gif$

Universal joint between body2 and body 3

Click the joint type selection switch and select universal.
Select node ID 12330 as first terminal which belongs to body3.
Select node ID 7589 as second terminal which belongs to body2.
Select node ID 12921 as a node for first orientation.
Select node ID 11944 as a node for second orientation.

The vector 12330 to 12921 defines the first cross pin axis, and the vector 7589 to 11944 defines second cross pin axis.

Click create.

A ball (spherical) joint between body1 and body2 will be created next.

$image\ball_joint.gif$

Ball joint between body1 and body 2

Click the joint type selection switch and select ball.
Select node ID 11104 as first terminal which belongs to body1.
Select node ID 7578 as second terminal which belongs to body2.
Click create.

To apply the boundary condition to the model:

The gravity force that applies to the model and MBSIM bulk data card, which is to specify the parameter for multi body simulation, will be created in this step.

Create the gravity force:

Click the Collectors on toolbar button $image\collectors.gif$ .
Select the create subpanel using the radio buttons on the left-hand side of the panel.
Click the collector type switch and select load collectors from the pop-up menu.
Click name= and enter gravity.
Click color and select any color.
Click the creation method switch and select card image from the pop-up menu.
Click card image= and select GRAV.
Click create/edit.

Input the values as illustrated below.

$image\input_vals.gif$

Click return to go to the main menu.

A new load collector, gravity, is created.

Create an MBSIM card:

Click the collector type switch and select load collectors from the pop-up menu.
Click name= and enter SIM.
Click color and select any color.

It is recommended that this color be different from the one for gravity load collector.

Click the creation method switch and select card image from the pop-up menu.
Click card image= and select MBSIM.
Click create/edit.
Input the values as illustrated below.

$image\input_vals2.gif$

Create an OptiStruct subcase:

From the Analysis page, select the subcase panel.
Select the type multi-body dynamics.
Click name= and enter dynamic.
Check the box preceding MLOAD.

An entry field appears to the right of MLOAD.

Click on the entry field and select gravity from the list of load collectors.
Check the box preceding MBSIM.

An entry field appears to the right of MBSIM.

Click on the entry field and select SIM from the list of load collectors.
Click create.
Click return to go to the main menu.

Submitting the job:

To launch OptiStruct:

From the Analysis page, select the OptiStruct panel.
Click save as… following the input file: field.

A Save file… browser window pops up.

Select the directory where you would like to write the OptiStruct model file and enter the name for the model, 3bodies_dynamics_complete.fem, in the File name: field.

The .fem filename extension is the suggested extension for OptiStruct input decks.

Click Save.

Note that the name and location of the 3bodies_dynamics_complete.fem file displays in the input file: field.

Set the memory options: toggle to memory default.
Click the run options: switch and select analysis.
Set the export options: toggle to all.
Click OptiStruct.

This launches an OptiStruct run in a separate shell (DOS or UNIX) which appears.

The default files written to the directory are:

3bodies_dynamics_complete.html	HTML report of the analysis, giving a summary of the problem formulation and the results from the final iteration.
3bodies_dynamics_complete.out	OptiStruct output file containing specific information on the file set up, estimates for the amount of RAM and disk space required for the run, and compute time information. Review this file for warnings and errors.
3bodies_dynamics_complete.log	Log file containing the information on the joints and markers, simulation etc., which are specific to MBD analysis.
3bodies_dynamics_complete.xml	Model file in .xml format – solver intermediate input deck.
3bodies_dynamics_complete.h3d	Binary results file.
3bodies_dynamics_complete.mrf	Binary results file for plotting.
3bodies_dynamics_complete.stat	Summary of analysis process, providing CPU information for each step during analysis process.

Viewing the Results in HyperView

This section describes how to view the results in HyperView which will be launched from within the OptiStruct panel of HyperMesh.

HyperView is a complete post-processing and visualization environment for finite element analysis (FEA), multi-body system simulation, video and engineering data.

To view a contour plot of the displacement:

While in the OptiStruct panel of the Analysis page, click the green HyperView button.

Note that the path and file name for 3bodies_dynamics_complete.h3d appears in the fields to the right of Load model and Load results. This is fine because the .h3D format contains both model and results data.

The model and results are loaded in the current HyperView window.

Click the Contour panel toolbar button $image\contour.gif$ .
Under Results type:, select Displacement.
Click Apply.
Verify the Animate Mode Menu is set to Transient, $image\light.gif$ .
Click the traffic light icon $image\traffic.gif$ to start the animation.

$image\animation.gif$

Click the director's chair icon, $image\directors.gif$ , to go to the Animation Controls panel.
With the animation running, use the slider bar next to Speed: on the left side of the panel to adjust the speed of the animation.
Click the traffic light icon $image\traffic.gif$ to stop the animation.

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