1. Workshop 7 using contacts and modal force

3. Workshop 7 – Using Contacts and Modal Force
Problem statement
For the following manufacturing material transfer device, determine if a maximum vacuum force of 1/2 atmosphere is adequate to move the flexible sheet.
Mechanism information
The model represents a material transfer mechanism, as shown in Figure 5:
Figure 5. Material Transfer Mechanism
VACUUM
TABLE
Discuss (or if time permits, demonstrate):
Creation of plane geometry
Sphere-to-plane contact (with friction)
Sphere geometry is a useful contact primitive
Using the MARKER command in an ACF
Demonstrate the use of:
Modal force on an unconstrained sheet, without gravity
Sphere-to-plane contact
FLEX_SHEET
Sphere (dummy part)

4. Workshop 7 – Using Contacts and Modal Force (Cont.)
Setting up the model
Import the model, set its viewing attributes, and then simulate it.
To set up the model:
Start Adams/View
From the Welcome dialog box, select Existing Model.
Select the Working Directory as exercise_dir/mod_07_contact.
In the File Name field select mod_07_start.cmd.
Click OK
Set the view mode to isometric.
Set the render mode to shaded.
Run a scripted simulation using SIM_SCRIPT_1.
To better understand the mechanism, animate from different viewpoints.

5. Workshop 7 – Using Contacts and Modal Force (Cont.)
Importing the flexible body
Import the flexible body and set its color to blue.
To import the flexible body:
Create a flexible body
From the Ribbon Menu “Flexible Bodies” select
Flexible Body Name: FLEX_SHEET
Modal Neutral File Name: sheet_load.mnf
Use default damping
Select OK.
Select FLEX_SHEET.
From the Main Menu, select the Color tool stack, select the tool for the color blue .
Clear the selection of FLEX_SHEET.
For Step 4: setting colors is covered in Replacing Rigid Bodies (part I).

6. Workshop 7 – Using Contacts and Modal Force (Cont.)
Connecting the flexible body
The spheres act as dummy parts and are attached to ground with fixed joints. Attach the spheres to the flexible body by modifying the joints. Later you will use the spheres to create sphere-to-plane contact forces.
After you connect the flexible body, perform a static equilibrium simulation.
To connect the flexible body:
To see the fixed joints, turn on the icons.
Adams/View displays the icons as shown next:

7. Workshop 7 – Using Contacts and Modal Force (Cont.)
Modify the five fixed joints (named using the convention FX_JOINT_#) so the First Body is always the FLEX_SHEET.
To perform a static equilibrium simulation:
Under the Simulation tab, click Run an Interactive Simulation in the Simulate group and then select the Static Equilibrium tool

8. Workshop 7 – Using Contacts and Modal Force (Cont.)
Creating the vacuum force
Create a parabolic vacuum distribution using a modal force. This modal force forms a negative pressure causing lift on FLEX_SHEET.
To create the vacuum force:
Under the Forces tab, click Create a Modal Force in the Special Forces Group .
Create the modal force as follows:
Force Name: .model_1.MFORCE_1
Flexible Body: .model_1.FLEX_SHEET
Reaction Part: .model_1.VACUUM
Define Using: Function
Load Case: parabolic one atu overpressure
Scale Function: -STEP5(TIME, T1-0.1, 0.0, T1+DW1-0.1, 0.5)
+STEP5(TIME, 1.55, 0.0, 1.60, 0.5)

9. Workshop 7 – Using Contacts and Modal Force (Cont.)
Select OK.
Adams/View displays the icon for the modal force:
Modal Force Icon
For Step 2, T1 and DW1 are design variables.
Describe that the parabolic distribution is really a 2D parabola extruded in 3D space—this may not be obvious to the students.

10. Workshop 7 – Using Contacts and Modal Force (Cont.)
Changing render mode of VACUUM
To be able to see the contact planes, and to see the deformation of FLEX_SHEET, make the VACUUM extrusion visible as wireframe geometry.
To make VACUUM wireframe:
Right-click VACUUM, and then select Appearance.
Set Render to Wireframe.
Select OK.
Now you’ll have an unobstructed view of the flexible sheet when the model is rendered shaded.

11. Workshop 7 – Using Contacts and Modal Force (Cont.)
Creating the contact forces
Create sphere-to-plane contact forces between the ellipsoids attached at the corners of the FLEX_SHEET and the VACUUM surface planes. These forces prevent the FLEX_SHEET from passing through the VACUUM block as it is lifted. To transport the FLEX_SHEET, you need to enable coulomb friction forces.
The arrows in Figure 6 show the pairing of the contact forces between the right and the left sides.

12. Workshop 7 – Using Contacts and Modal Force (Cont.)
Figure 6. Contact Forces
PLANE_1
PLANE_0
ELLIPSOID_1
ELLIPSOID_4
Notice that the surfaces, denoted by the markers, are inclined at 45º angles, as a self-centering feature of the vacuum design.
ELLIPSOID_2
ELLIPSOID_3

13. Workshop 7 – Using Contacts and Modal Force (Cont.)
To create the contact forces:
Under the Forces tab, click Create a Contact in the Special Forces group
Create the sphere-to-plane contact forces as follows:
Tip: Select the appropriate plane markers, as shown in Figure 6.
Contact Name: model_1.Contact_1
Contact Type: Sphere to Plane
Sphere: model_1.PART_5.ELLIPSOID_1
Plane: model_1.VACUUM.PLANE_1
Force Display: on
Normal Force: Impact
Stiffness: (1.0E+04(newton/mm))
Force Exponent:
Damping: (100.0(newton-sec/mm))
Penetration Depth: (0.1mm)
Friction Force: Coulomb
Coulomb Friction: On
Static Coefficient:
Dynamic Coefficient:
Stiction Transition Vel.: (100(mm/sec))
Friction Transition Vel.: (200(mm/sec))

14. Workshop 7 – Using Contacts and Modal Force (Cont.)
Select OK.
You have created contact for one corner of the flexible sheet. Now you must create similar contacts for the remaining three corners. It is easiest to create the others by copying the one you've just created and modifying the sphere and plane. You will use a method of copy- rename-modify so that the same contact impact and friction parameters are used without your having to re-type them every time.
Select .model_1.CONTACT_1, and from the Edit menu, select Copy.
Pull down Edit > Rename.
Change the name of the copy to .model_1.CONTACT_2.

15. Workshop 7 – Using Contacts and Modal Force (Cont.)
Modify .model_1.CONTACT_2 and change its sphere from ELLIPSOID_1 to ELLIPSOID_2.
Repeat Steps 4 through 7 to create the other two contacts, as shown next:
Why do you think there is no contact at the center (ELLIPSOID_5)? ________________________________________________________________________________________________________________________________________________________________________________________________________________________________
For Step 7, start a discussion on warnings.

16. Workshop 7 – Using Contacts and Modal Force (Cont.)
Simulating the flexible body when rigid
The sphere radii were artificially enlarged so you could easily select them when creating the forces. Before you run another scripted simulation, reduce the sphere radii to make the model more realistic.
To reduce the sphere radii:
In the model browser tree, expand the Design Variable
Right-click on sphere_rad1 and select modify
In the Standard Value text box, enter (5mm).
Select OK.
Because the spheres are parameterized, Adams/View reduces the radii of all the spheres.

17. Workshop 7 – Using Contacts and Modal Force (Cont.)

18. Workshop 7 – Using Contacts and Modal Force (Cont.)
To simulate:
Right click on the FLEX_SHEET and select modify
Make the FLEX_SHEET rigid by setting Inertia modeling to Rigid body.
Before simulating, save the model in its current configuration:
Pull down File > Save Database As.
Save the database as rigid_model.
Under the Simulation tab, click Run an Interactive Simulation in the Simulate group, point to Scripted Controls, and then browse for .model_1.RIGID_SCRIPT.
The script uses the following Adams/Solver commands:
SIMULATE/STATIC
SIMULATE/TRANSIENT, END=1.61, DTOUT=1.0E-02
MARKER/555,QP = -1675, -1290, 2200
SIMULATE/TRANSIENT, END=2.6, DTOUT=1.0E-02
The MARKER command instantaneously repositions a plane marker for contact with the table that the sheet is being dropped on.
In your Adams/Solver setting, change your Solver Executable to use Adams/Solver (FORTRAN or C++) .
Run the simulation.
As radius of the sphere reduce to 5mm, static equilibrium may fail for 25 iteration, increase maxit to 50

19. Workshop 7 – Using Contacts and Modal Force (Cont.)
Adams/Solver may issue a warning indicating that it has had difficulty solving portions of the simulation. For example:
WARNING: The symbolic refactorization failed. The matrix is structurally singular at time =
WARNING: The corrector has not converged after 3 attempts. No. of iterations = 10.
Investigate what modeling decisions could possibly be causing trouble for Adams/Solver. You may have seen similar warning in your own models. Based on your experiences can you suggest alternate modeling choices that would minimize this problem? ________________________________________________________________________________________________________________________________________________________________________
Save the simulation results as rigid.

20. Workshop 7 – Using Contacts and Modal Force (Cont.)
Perform a looped animation and select the best answer.
When the sheet falls on the TABLE, it:
_____ Bounces high
_____ Bounces a little
_____ Doesn’t bounce at all
Running a flexible body simulation
Before you run another simulation, make the FLEX_SHEET flexible, turn deformation on, and disable unnecessary modes.
To prepare the flexible body:
Right click on the FLEX_SHEET and select Modify
Set Inertia modeling to Partial coupling and set Plot Type to Contour.
Disable the following modes: 8, 15, 19, 24, 27-28, 33-35,
To run the simulation:
Pull down File > Import
In the File Type field select Adams/Solver Script (*.acf)
Right click the File to Read field and select browse.

21. Workshop 7 – Using Contacts and Modal Force (Cont.)
Select the file script_commands and click on the open button
In the Simulation Script Name enter .model_1.SIM_SCRIPT_2.
Click OK
The simulation script looks as -
SIMULATE/STATIC
SIMULATE/TRANSIENT, END=1.61, DTOUT=1.0E-02
MARKER/555,QP = -1675, -1290, 2200
INTE/GSTIFF,ERR=1E-3,ADAPT=1.0e-05, HINIT=1.0E-06,HMAX=1e-3
SIMULATE/TRANSIENT, END=2.6, DTOUT=1.0E-02
The MARKER command instantaneously repositions a plane marker for contact with the table that the sheet is being dropped on.
Run another simulation using SIM_SCRIPT_2.
You can ignore the convergence warnings that Adams/Solver issues.
Was the parabolic vacuum force strong enough to transfer the FLEX_SHEET to the TABLE? _______ Yes _______ No.
Many modes have been disabled to speed up simulation and to work around the insufficient amount of damping. This might be a good candidate for a DMPSUB.

22. Workshop 7 – Using Contacts and Modal Force (Cont.)
After the simulation has completed, rename the analysis. By doing this, you can save disk space because you are not retaining a duplicate copy of the analysis (for example, when you save, not only do you have the saved copy, but you also have Last_Run).
From the Edit menu, select Select List, and then select Clear All.
From the Edit menu, select Rename.
Select .model_1.Last_Run with a single click.
Select OK.
Rename the analysis Last_Run to flexible.
Save the database as flexible_model.

23. Workshop 7 – Using Contacts and Modal Force (Cont.)
Comparing simulation results
In Adams/PostProcessor, perform two animations using different contour options. Notice how the sheet deforms as it is being lifted and how much it bounces when it is dropped.
To view the MFORCE:
Launch Adams/PostProcessor from the Ribbon menu Postprocessor
In the upper left corner, change the pull-down menu to Animation.
In the dashboard, under the Animation tab, select Include Contacts.
In the viewport, load the animation flexible.
Select the Contour Plots tab.
Set Contour Plot Type to MFORCE FMAG.
Make sure that Display Legend is selected.
Animate the model.
A parabolic vacuum distribution defines the MFORCE. Turning the contour plot on, allows you to view the MFORCE and ensure that it was defined correctly.
Steps 2 and 3 were added as a workaround for CRs and If students skip these steps, the contours for the MFORCE animation will be very wrong. If a student skips these steps, have him/her right-click in Adams/PostProcessor, select Clear View, and then redo the steps in this section to correct the contour colors.

24. Workshop 7 – Using Contacts and Modal Force (Cont.)
To compare results:
Reset the model.
Set Contour Plot Type to Deformation.
Zoom in on the flexible sheet such that it is centered on the screen.
Select the Camera tab.
Right-click the Follow Object text box, select Marker, and then browse for the marker FLEX_SHEET.INT_NODE_1.
Select the Play tool.
Now compare the behavior of the sheets, rigid versus flexible. See Step 7 and select the best answer (you may have to animate the flexible sheet again):
When the flexible sheet falls on the TABLE, it rebounds:
_____ Less than the rigid sheet
_____ Same as the rigid sheet
_____ Higher than the rigid sheet
If you chose the last option, can you explain why it rebounds that way? ________________________________________________________________________________________________________________

25. Workshop 7 – Using Contacts and Modal Force (Cont.)
Optional tasks
Plot the modal force results components.
Try different pressure distributions or use a smaller magnitude (0.1 atm). Does the sheet come loose? ________________________________________________
Try to limit the spring-back effect by adding contact at the center sphere, between the sheet and the vacuum.
As the flexible sheet deforms, it stores strain energy, like a spring. The energy transforms to kinetic energy when the vacuum force is removed, causing the sheet to spring back rapidly.