OS-1940: MBD Rigid Contact

In this tutorial, you learn how to:

•	Model Contacts using HyperMesh 2017

Contact constraints are very common in the mechanisms/general machinery domain. MotionSolve uses the penalty-based Poisson contact force model for calculating the magnitude and direction of the contact and friction forces. For more information on this, refer to the MotionSolve help.

The Curved Pentagon Positive Return Cam system is used to define the contacts. In this system the curved pentagon rolls inside the circle and translates the slider.

rd4040_rigid_body_model

Rigid body model

Exercise

Step 1: Retrieve the structural model and define the OptiStruct template

1.	Launch HyperMesh Desktop.

2.	Select OptiStruct in the User Profiles dialog and click OK.

3.	Click File > Open > Model. An Open file browser window opens.

4.	Select the for_contact_tutorial.hm file you saved to your working directory from the optistruct.zip file. Refer to Accessing the Model Files.

5.	Click Open. The model has five components and a few free nodes that will be used to create bodies and joints for the MBD model.

Step 2: Creating PRBodies

PRBODY is the Rigid Body Definition for Multi-body Simulation. PRBODY defines a rigid body out of a list of finite element properties, elements and grid points.

There will be five bodies apart from the ground body in our model via: the stand, the slider, the driver, the pentagon and the circle. Pre-defined free nodes will be used to define the bodies and joints.

1.	From the Analysis page, enter the bodies panel.

2.	Select the create subpanel using the radio buttons on the left-hand side of the panel.

3.	Click body= and enter stand.

4.	Click type= and select PRBODY.

5.	Click props and select Stand1.

6.	Click props and select by id option and enter 2, 19391, and 19402.

7.	Click create.

8.	Use the table to repeat the above operation to define PRBODY for the remaining components.

body=	type=	props	free nodes
Slider	PRBODY	Slider2	4, 19399
Driver	PRBODY	Driver3	19392, 19395
Pentagon	PRBODY	Pentagon4	4246, 19396
Circle	PRBODY	Circle5	414, 19400
Ground	GROUND	-	19401

Note:

To define the ground body the selection of props is not required.

9.	Click return.

Creating Joints (Steps 3 and 4)

Here, all the necessary joints required for this model will be defined. Five joints for the model are required, as shown in the table below.

Type of Joint	Body 1	Body 2
Fixed	Stand	Ground
Revolute	Stand	Driver
Translational	Stand	Slider
Revolute	Driver	Pentagon
Fixed	Slider	Circle

Step 3: Create the component for the joints

1.	In the Model browser, right-click and select Create > Component.

2.	For Name, enter joints.

3.	Click Color and select any color.

In this tutorial step, two revolute joints, two fixed joints, and one translational joint are created to constrain the degrees of freedom (shown in the following figure), such that the remaining degree of freedom will be just 2.

DOF = 5*6 – (5+5+6+6+5+1) = 2

Type of Joint	Removes translational dof	Removes rotational dof	Removes total number of dof
Revolute	3	2	5
Fixed	3	3	6
Translational	2	3	5
Motion (rev)	3	2	1

rd4040_joint_locations

Joint locations in the model

Step 4: Create the joints

1.	Click Mesh > Create > 1D Elements > Joints to open the Joints panel.

First, the fixed joint between the stand and ground will be created.

2.	Click the joint type: selector switch and select fixed.

3.	Select node ID 19401 as the first terminal.

4.	Select node ID 19402 as the second terminal.

Note:

The first and second terminals are corresponding to the bodies that are connected by the joint. Nodes 19401 and 19402 are coincident. Coincident node picking is in options panel > graphics subpanel in HyperMesh will help select these coincident nodes in the HyperMesh screen.

5.	Click create.

Next the fixed joint between the slider and the circle is created.

6.	Select node ID 19399 as the first terminal.

7.	Select node ID 19400 as the second terminal.

8.	Click create.

To create the revolute joints in the model (b/w stand-driver and driver-pentagon bodies), refer to the image below and follow the steps.

os_1940_01

Defining a revolute joint

9.	Click the joint type: selector switch and select revolute.

10.	Select the node ID 19391 as the first terminal.

11.	Select the node ID 19392 as the second terminal.

12.	Select the vector option and for the first orientation, select y-axis.

13.	Click create.

14.	Click the joint type: selector switch and select revolute.

15.	Select the node ID 19395 as the first terminal.

16.	Select the node ID 19396 as the second terminal.

17.	Select the vector option and for the first orientation, select y-axis.

18.	Click create. To create the translational joint in the model (b/w slider-stand), refer to the image below and follow the steps.

os_1940_02

Defining a translational joint

19.	Click the joint type: selector switch and select translational.

20.	Select the node ID 2 as the first terminal.

21.	Select the node ID 4 as the second terminal.

22.	Select the vector option and for the first orientation, select x-axis.

23.	Click create.

24.	Click return to exit the panel.

Step 5: Defining a Contact in the model

Use pre-defined element sets to add a Contact to the model.

Note:

These element sets are defined from the Analysis page, entity sets by choosing a set of elements. The set of elements on the face of the pentagon body is named master and the sets elements on the face of the circle body is named slave.

1.	From the Analysis page, enter the interfaces panel.

2.	Click the create radio button.

3.	Click name= and enter Contact.

4.	Click type= and select MBCNTR.

5.	Click create.

rd4040_interfaces

6.	Click the add radio button.

7.	Select sets option for both master: and slave:.

8.	Click on the sets for the master: and select the entity set named mas and click update.

9.	Click on the sets for the slave: select the entity set named Sla, and click update.

rd4040_interfaces2

Interfaces panel – contact

10.	Click the card image radio button and click edit.

rd4040_interfaces3

11.	Select POISSON for CNFTYPE and enter the values, as shown in the image below:

rd4040_mbcntr_v11

12.	Click return twice to close the Interface panel.

Defining External Inputs and Simulation Parameters (Steps 6 - 8)

The motion which drives the mechanism, 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.

Step 6: Define the motion constraint

1.	Click BCs > Create > Constraints to open the Constraints panel.

2.	Click nodes and select the option by id and enter node id 19392.

3.	Uncheck all fields; except for dof5 and enter a value of 1 (refer to the image below).

rd4040_constraints

Constraints panel - motion

4.	Click load types = and select MOTNG(V).

5.	Click create to create the constraint.

6.	Click return to go to the Analysis page.

Note:

You can find a new load collector (auto1) added to the model after completing this step. The motion is assigned to this load collector and will be used as reference in the OptiStruct subcase.

Step 7: Create the gravity force

1.	In the Model browser, right-click and select Create > Load Collector.

2.	For Name, enter gravity.

3.	Click Color and select any color.

4.	For Card Image, select GRAV.

5.	Input the values, as illustrated below.

os_1940_03

A new load collector, gravity is created.

Step 8: Create an MBSIM card

1.	In the Model browser, right-click and select Create > Load Collector.

2.	For Name, enter SIM.

3.	Click Color and select any color.

4.	For Card Image, select MBSIM.

5.	Input the values, as illustrated below.

os_1940_04

Step 9: Create an OptiStruct subcase

1.	Click Setup > Create > LoadSteps to open the LoadSteps panel.

2.	Set the Analysis type to Multi-body dynamics.

3.	For Name, enter Dynamic.

4.	For MLOAD, click Unspecified > Loadcol.

5.	In the Select Loadcol dialog, select Gravity from the list of load collectors and click OK.

6.	For MBSIM, click Unspecified > Loadcol.

7.	In the Select Loadcol dialog, select SIM from the list of load collectors and click OK.

8.	For MOTION, click Unspecified > Loadcol.

9.	In the Select Loadcol dialog, select auto1 from the list of load collectors and click OK.

Step 10: Submit the job

1.	From the Analysis page, enter the OptiStruct panel.

2.	Click save as following the input file: field. A Save As browser window opens.

3.	Select the directory where you would like to write the OptiStruct model file and enter the name for the model, for_contact_tutorial.fem, in the File name: field. The .fem filename extension is the suggested extension for OptiStruct input decks.

4.	Click Save.

The name and location of the for_contact_tutorial.fem file displays in the input file: field.

5.	Set the memory options: toggle to memory default.

6.	Set the run options: toggle to analysis.

7.	Set the export options: toggle to all.

8.	Click OptiStruct. This launches an OptiStruct run in a separate command prompt (DOS or UNIX).

The default files written to the directory are:

for_contact_tutorial.html	HTML report of the analysis, giving a summary of the problem formulation and the results from the final iteration.
for_contact_tutorial.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.
for_contact_tutorial.log	Log file containing the information on the joints and markers, simulation etc., which are specific to MBD analysis.
for_contact_tutorial.xml	Model file in .xml format – solver intermediate input deck.
for_contact_tutorial.h3d	Binary results file.
for_contact_tutorial.mrf	Binary results file for plotting.
for_contact_tutorial.stat	Summary of analysis process, providing CPU information for each step during analysis process.

Note:

There are a few more files written to the directory with the name for_contact_tutorial_mbd.

Step 11: View the Results in HyperView

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

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

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

Note:

That the path and file name for for_contact_tutorials.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.

2.	Click the Contour panel toolbar icon .

3.	For Results type:, select Displacement(v).

4.	Click Apply.

5.	Verify that the Animate Mode is set to Transient .

6.	Click the Start/Pause Animation icon to start the animation.

7.	The Animation Controls are in the panel next to the playback controls.

animation_mini_toolbar

The HyperView playback controls

8.	With the animation running, use the bottom slider bar to adjust the speed of the animation.

9.	Click the Start/Pause Animation icon again to stop the animation.