WS3-1 ADM703, Workshop 3, August 2005 Copyright  2005 MSC.Software Corporation WORKSHOP 3 SUSPENSION SYSTEM

WS3-2 ADM703, Workshop 3, August 2005 Copyright  2005 MSC.Software Corporation

WS3-3 ADM703, Workshop 3, August 2005 Copyright  2005 MSC.Software Corporation WORKSHOP 3 – SUSPENSION SYSTEM n Problem Statement u Make use of differential equation elements and functions to represent a bushing failure and the degradation of shock performance in the following suspension model. Use ADAMS/Linear to examine the model’s system modes. n Model Description u This model includes a quarter suspension of SLA (short-long arm) type. The lower arm to body connection is modeled as a bushing. The shock force is modeled as a single- component force linear relationship between force and velocity.

WS3-4 ADM703, Workshop 3, August 2005 Copyright  2005 MSC.Software Corporation WORKSHOP 3 – SUSPENSION SYSTEM (CONT.) n Examining and simulating the baseline model u First, you look at the baseline model. Then, you simulate it. n To examine and simulate your model: 1. Import the file, install_dir/suspension/sla.cmd, where install_dir is the directory where the training files are installed. 2. Examine the current modeling methodology of the lower arm-to-body connection and the shock force. Tip: Use Graphical Topology in the Database Navigator (Tools  Database Navigator). 3. Simulate a static equilibrium, and then a dynamic simulation of 2.0 seconds and 200 steps. 4. Save your simulation results as baseline.

WS3-5 ADM703, Workshop 3, August 2005 Copyright  2005 MSC.Software Corporation WORKSHOP 3 – SUSPENSION SYSTEM (CONT.) n To examine and simulate your model (Cont.): 5. Plot the shock force, the force in the lower arm bushing, and the displacement of the road patch all versus time (see titles in plot for tips on which data to choose).

WS3-6 ADM703, Workshop 3, August 2005 Copyright  2005 MSC.Software Corporation WORKSHOP 3 – SUSPENSION SYSTEM (CONT.) n Modify the Shock u Here, you modify the shock so that it degrades after a certain amount of work is performed. n To modify the shock: u Create an explicit differential equation named thermal_retention to represent the work done by the shock force. Generally, the function should look as follows: u ydot = “shock force”*|”shock velocity”| u Specifically, you will need to obtain the shock force and the shock velocity for this equation using MSC.ADAMS functions. Tip: Use the SFORCE function in the ADAMS/View Function Builder to obtain the shock force magnitude. To compute the shock velocity, examine the SFORCE shock_force in the model to get the I and J markers. Also, use the VR function to get relative velocity for the shock. For example: SFORCE(shock_force,0,1,0)*ABS(VR(MAR1320, MAR2317,0))

WS3-7 ADM703, Workshop 3, August 2005 Copyright  2005 MSC.Software Corporation n To modify the shock (Cont.): WORKSHOP 3 – SUSPENSION SYSTEM (CONT.)

WS3-8 ADM703, Workshop 3, August 2005 Copyright  2005 MSC.Software Corporation n To modify the shock (Cont.): 2. Modify shock_force so that its existing coefficient of damping is gradually reduced by 0.5, after the shock has performed 25,000 in-lb of work. Tip: Use a STEP function whose independent variable is the integral of the function you created in Step 1. For example, STEP(DIF(thermal_retention),0,1,25000,0.5). 3. Rerun the initial simulation (static, then dynamic for 2.0 seconds and 200 steps). 4. Save the simulation results as degrade, and then compare the shock performance. WORKSHOP 3 – SUSPENSION SYSTEM (CONT.)

WS3-9 ADM703, Workshop 3, August 2005 Copyright  2005 MSC.Software Corporation WORKSHOP 3 – SUSPENSION SYSTEM (CONT.) n To modify the shock (Cont.): 5. At what time is the shock’s damping coefficient reduced to half its original value?_____________________________________________________

WS3-10 ADM703, Workshop 3, August 2005 Copyright  2005 MSC.Software Corporation WORKSHOP 3 – SUSPENSION SYSTEM (CONT.) n Modifying the lower arm connection u Next, define the lower arm connection, and then modify it. n To define the lower arm connection : 1. Right-click the left_lower_bushing bushing and deactivate it. 2. Replace it with an equivalent GFORCE called left_lower following the steps below: 1. From the Forces toolstack on the Main Toolbox, select the GFORCE tool. 2. From the pull-down menus under Construction, select 2 Bod-1 Loc and Pick Feature. 3. From the pull-down menu under Characteristics, select Custom. 4. Select lower_arm and body as the parts. Note: The order of selection determines the action and reaction parts. This affects the force function.

WS3-11 ADM703, Workshop 3, August 2005 Copyright  2005 MSC.Software Corporation WORKSHOP 3 – SUSPENSION SYSTEM (CONT.) n To define the lower arm connection (Cont.): 2. (Cont.) 5. Choose body.left_lower_body as the location. ADAMS/View automatically creates a reference marker. However, since it does not have the correct orientation, you will choose a new reference marker. 6. Modify the GFORCE’s reference marker to be left_lower_body and select Apply. You should see the GFORCE icon move. 7. Rename the GFORCE to left_lower. 3. Modify the following force functions in the GFORCE: l FX = *DX(I,J,R)-10*VX(I,J,R) l FY = *DY(I,J,R)-10*VY(I,J,R) l FZ = -6200*DZ(I,J,R)-5*VZ(I,J,R) l TX=TY=TZ=0 Tip: Right-click the deactivated left_lower_bushing and select Info to get the I, J, and R markers. In this example, set the R marker to be the same as the J marker.

WS3-12 ADM703, Workshop 3, August 2005 Copyright  2005 MSC.Software Corporation WORKSHOP 3 – SUSPENSION SYSTEM (CONT.) n To define the lower arm connection (Cont.): 3. (Cont.)

WS3-13 ADM703, Workshop 3, August 2005 Copyright  2005 MSC.Software Corporation WORKSHOP 3 – SUSPENSION SYSTEM (CONT.) n To define the lower arm connection (Cont.): 4. Create an explicit differential equation called DIFF_1_for_break that will track the force in the newly created GFORCE representation of the bushing, and will step itself from zero to one when the force magnitude of the GFORCE goes from 2240 lb to 2250 lb. Select Keep value constant during static analysis to solve the static analysis. The Along/About Axes should be set to the R marker found in Step 3. Tip: STEP(GFORCE(left_lower,0,1,left_lower_body)-2250,-10.0,0,0.0,1)

WS3-14 ADM703, Workshop 3, August 2005 Copyright  2005 MSC.Software Corporation WORKSHOP 3 – SUSPENSION SYSTEM (CONT.) n To modify the lower arm connection so that it breaks: 1. Create an explicit differential equation called.DIFF_2_for_break that multiplies the integral of DIFF_1_for_break by The goal is to create a ramp function that turns off the GFORCE. 2. Select Keep value constant during static analysis to solve the static analysis.

WS3-15 ADM703, Workshop 3, August 2005 Copyright  2005 MSC.Software Corporation WORKSHOP 3 – SUSPENSION SYSTEM (CONT.) n To modify the lower arm connection so that it breaks (Cont.): 3. Modify the GFORCE created in Step 1 to turn off when DIFF_2_for_break becomes nonzero. In other words, use the ramp function to turn off the GFORCE, which represents the bushing breaking. For example, FX = (-28000*DX(I,J,R)-10*VX(I,J,R))* step(dif(DIFF_2_for_break),0,1,0.001,0) 4. Similarly, apply a STEP function for the FY and FZ components.

WS3-16 ADM703, Workshop 3, August 2005 Copyright  2005 MSC.Software Corporation WORKSHOP 3 – SUSPENSION SYSTEM (CONT.) n Following is an example of the STEP function only: step(dif(DIFF_2_for_break),0,1,0.001,0)

WS3-17 ADM703, Workshop 3, August 2005 Copyright  2005 MSC.Software Corporation WORKSHOP 3 – SUSPENSION SYSTEM (CONT.) n Simulating the enhanced model 1. Run a static equilibrium simulation. 2. Run a dynamic simulation for 0.35 seconds in 350 steps. You should see the connection break between the lower arm and the body. 3. At what time in the simulation does the lower arm-to-body connection break? ___________________________________________________________ 4. In modeling this break, why was it necessary to scale DIFF_1_for_break by 1000, and then use that as the trigger for switching off the GFORCE? ___________________________________________________________ 5. What is the fundamental difference between this method of simulation-time model-topology manipulation and the method used in Workshop 6: Jet Engine Turbine? __________________________________________________________________ __________________________________________________________________

WS3-18 ADM703, Workshop 3, August 2005 Copyright  2005 MSC.Software Corporation WORKSHOP 3 – SUSPENSION SYSTEM (CONT.) n Analyzing with ADAMS/Linear 1. Perform a static simulation. 2. Perform a linear-modes analysis. 3. Review the mode shapes and natural frequencies using animation. 4. View the ADAMS/Linear results in tabular format and save the table to a file. 5. What are the undamped natural frequencies of modes 9 and 10? (Note: These might be slightly different, depending on modeling variations.) _________________________________________________________________ 6. What are the damping ratios of modes 9 and 10? __________________________________________________________________ 7. Do the motions of the system as expressed by the linear analysis seem to make sense given the model topology? __________________________________________________________________