1. WORKSHOP 1 CUSTOM TIRE SUBROUTINE

3. Workshop Objectives Software Version Files Required
Tune a suspension damper element to minimize transmitted forces due to a road disturbance. Use a custom tire subroutine to model the tire element.
Software Version
Adams 2013
Files Required
test_rig_start.cmd
Problem Description
This is a simple ‘testrig’ model, meant for exercising a tire model. In this example, the tire element will scale a ‘curb’ obstruction on the road. The damper element in the suspension will then be tuned to minimize transmitted force for this event.

4. Suggested Exercise Steps
Investigate the model
Specify a custom library in Adams/View
Verify the USER specification in Adams/View
Set the USER specification in Adams/View
Simulate and measure
Refine the model

5. Step 1. Investigate the Model
Open the model file test_rig_start.cmd in Adams/View
Notice that there is a solver simulation script in the model
View the simulation script named run_it by selecting it from the Model Browser, in the Simulations folder
Right-click the script and select Info
Running this simulation script should result in errors of the form:
ERROR: Encountered error "No Library given and no default library for Difsub" while processing user subroutine for test_rig.tire_force_dif1
This error is expected and indicate that an appropriate Adams/Solver subroutine library is missing and the simulation cannot proceed. This will be sorted out in the following step.

6. Step 2. Specify a Custom Library in Adams/View
Look at the files in the working directory of Adams/View (should be the same directory as the test_rig_start.cmd file)
Considering the extension names of the files present, write the name of the file that is likely a library file containing Adams/Solver custom code on the Windows platform: ________________
Adams/View lets a user dynamically alter which Adams/Solver library is currently being used. From the Settings menu, select Solver and Executable:
In particular the Solver Library field is used for specifying the currently loaded library file. Right-click in this field and browse to select the file in the working directory named myTire.dll (or myTire_x64.dll if you are running Adams on a 64-bit Windows machine).

7. Step 3. Verifying the USER Specification in Adams/View
The previous custom library specification indicates to the Adams/Solver that all user-written subroutines will be implemented within the specified file. In addition, each element using a custom library must specify the USER() parameter in its function expression.
Verify the function setting in Adams/View by inspecting one of the DIFF element in this model. Do this by selecting it from the Model Browser. The diff equations can be found in the Elements – System Elements folder.
Right-click tire_force_dif1 and select Modify to inspect.
What is the setting for this element in the Definition field?_________________________
Verify that the User written subroutine specification for this DIFF element gets written to a .adm file as a USER() statement by doing the following:
Export an adm-file for this model: File → Export
In the Adams/Solver Dataset export dialog box, select Write to Window to display the model statements on the screen.
Find the DIFF/2 statement in the dataset file.
What is the function expression for this DIFF element? _________________________

8. Step 4. Set the USER Specification in Adams/View
Before this model will simulate properly the GFORCE element must be modified to use the user-written subroutine. Alter the GFORCE by modifying the element named tire_forces (select it from the Model Browser).
The current model has Define Using set to be Function. Change this field to be Subroutine and then specify the following values for the User Parameters field:
900,1,100
Note: these ‘input parameters’ direct the subroutine to additional data that is contained in the model. Input parameters, in general, will be discussed in the following lecture.

9. Step 5. Simulate and Measure
Run the simulation script run_it. Note: the tire should roll forward, contacting, then mounting, the curb obstruction.
Go to the PostProcessor (F8 key) and plot the Measure named strut_upper_acceleration.
What is the maximum acceleration of the upper strut through the simulation? ___________

10. Step 6. Refine Model
A Design Variable in the model specifies the damping constant between the lower wheel and upper strut assembly. Run a simple sensitivity analysis on the shock damping factor to gauge the effect on the maximum force transmitted to the upper strut.
To do this select Design Evaluation Tools from the Design Exploration tab:
In the dialog box select the following:
Select Design Study
Study a Measure, specifically the Maximum value of strut_upper_acceleration
Choose the Design Variable shock_c
Specify 10 as the number of Default levels
The design study should create a new strip chart that plots maximum acceleration vs. damping factor. Right-click in the white area of this plot and select the Transfer to Full Plot option to view this curve in the Adams/Postprocessor.
Use the plot you just created (shown in figure 1 on the next page) to find the approximate damping coefficient that yields the minimum acceleration for the upper strut part. _______________________

11. Step 6. Refine Model (Cont.)
Figure 1: Upper strut acceleration vs. Damping Coefficient