MV-2040: Load Estimation for a Fore Canard Actuator Mechanism Under Aero-dynamic Loads
In this tutorial, you will learn how to represent pressure/distributed loads as Modal Forces on a CMS flexible body and scale Modal Forces to real world loads in MotionView/MotionSolve.
Forces acting on a flexible body may be an aerodynamic load, liquid pressure, a thermal load, an electromagnetic force or any force generating mechanism that is spread out over the flexible body, such as non-uniform damping or visco-elasticity. It may be even a contact force between two bodies. These distributed loads can be conveniently transformed from Nodal to Modal domain and represent as Modal Forces.
If we define as the mode shapes of the flexible body, and as the Nodal load acting on the flexible body, the equivalent Modal load on the flexible body is defined as:
Create a Fore Canard Flexible Body
In this step, you will create the Fore Canard flexible body.
- Open ForeCanard.hm in HyperMesh with OptiStruct selected as the user profile.
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Review the model.
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The HM file contains a meshed model of Fore Canard with material
properties and control cards defined.
Note: Model units are Newton-Meter-KG-Sec, therefore all properties defined are consistent with this unit system.
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The HM file contains a meshed model of Fore Canard with material
properties and control cards defined.
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Create aerodynamic loads from CSV files.
Average pressure distribution over the surface of canard is exported as text file from AcuFieldView. This file contains the location and value of the pressure. The AerodynamicLoad_0deg.csv, AerodynamicLoad_Negative10deg.csv, and AerodynamicLoad_Positive10deg.csv files contain the pressure distribution information for 0deg, -10 deg, and 10 deg of canard orientation respectively.Add load collectors for three cases:
- Left-click on the Load Collector icon from the toolbar.
- In the panel, verify that the create radio button is selected.
- Specify the new load collector name as AerodynamicLoad_0deg.
- In the drop-down menu, select no card image.
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Click Create.
- Follow steps 3.a through 3.e to create two more load collectors named AerodynamicLoad_Negative10deg and AerodynamicLoad_Positive10deg.
- Click Return.
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Browse to the Pressure load panel.
- Click the Analysis radio button.
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On the Analysis page, click on the Pressure
button.
This will open the pressure panel.
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Set the pressure load type to linear
interpolation.
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Verify that the create radio button is
selected.
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Next to the faces button, click the drop-down
arrow. Change the surface selection type from faces to
elems.
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In the magnitude drop-down menu, click linear
interpolation.
Now you can select elements on which pressure loads are applied and a CSV file for pressure load info. -
Verify that the create radio button is
selected.
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Create pressure loads on a canard surface.
Pressure loads for each position are created under their respective load collectors so you can scale them in MotionSolve with respect to the canard position.
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Left-click on Set Current Load Collector.
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From the load collector list, choose
AerodynamicLoad0_deg.
This will set AerodynamicLoad_0deg as the current load collector.
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Click the elems button. Select by
collector from the list.
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From the component collector list, click Fore
Canard. Click the select button
to return to the pressures panel.
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Click the ellipse button to browse for a
file.
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In the Open dialog, browse your
<working directory> and select
AerodynamicLoad_0deg.csv. Then click
Open.
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Click create to create pressure loads for the
0deg position.
Note: The pressure load on each element is obtained by a linear interpolation of pressure values with respect to its location.
- Follow step 6 again to create pressure loads for the AerodynamicLoad_Negative10deg and AerodynamicLoad_Positive10deg load collectors.
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Left-click on Set Current Load Collector.
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Specify load sets for CMS method.
Three load cases modeled in previous step represent nodal forces. These nodal forces are transformed as modal forces using CMS method. In this step you modify the existing CMSMETH card image to include three load sets.
- In the Entities browser, right-click on the CMS load collector.
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In the context menu, click Card
Edit.
This will open the load collector card image.
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Specify load sets for CMSMETH.
- In the Card Image dialog, activate the LOADSET checkbox.
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Specify the CMS_LOADSET_LSID_NUM value as
3.
The card image shows an option to specify three load sets.
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Double-click LSID(1).
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From the load collectors list, click
AerodynamicLoad_0deg. Click the
return button to go back to the CMS card
image.
- Use steps 8.c and 8.d to specify AerodynamicLoad_Negative10deg for LSID(2) and AerodynamicLoad_Positive10deg for LSID(3).
- Click Return.
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Generate flexbody.
Your model is now ready for solving to generate a flexbody. The two control cards required to solve for flexbody creation are already specified in the model.
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On the Analysis page, click on control cards
button.
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Click on the DTI_UNITS button from the first
page to review flexible body units. Then click
Return.
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In the next card, click on GLOBAL_CASE_CONTROL
to see the CMS load collector specified for CMSMETH solution. Click
return twice.
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From the Analysis page, click on
Optistruct.
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In the panel, set the following options:
- Set export options to all.
- Set run options to analysis.
- Browse to your <working directory> and specify input file name as flex_ForeCanard.fem.
- Click on the Optistruct button.
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Review flexbody modes.
On successful completion of solver run, open the flexbody flex_ForeCanard.h3d created from OptiStruct run in HyperView to review the various mode shapes. Your flexbody contains 34 modes constituting normal modes, constraint modes, and Static modes.
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On the Analysis page, click on control cards
button.
Create a MotionView Model
In this step, you will create a MotionView model of the Fore Canard.
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Open the ForeCanard_Model.mdl in MotionView. Review the model.
The model contains the following elements:
- Four bodies namely Fore Canard, Torque Arm, Piston, and Cylinder.
- A motion on the Piston with an expression 0.025*SIN(2*PI*TIME) to extend and retract the piston by 25mm at 1 Hz. This piston motion varies the fore canard angular position between -9.619 deg to +9.984 deg.
- An expression type Output request to measure the “ForeCanard angular position” and “Piston force along its axis”. The Fore canard angular position is measured from the RevJnt_TorqueArm_Gnd joint rotation angle using the expression `RTOD({j_4.AZ})`. The Piston force is measured from the Piston Motion using the expression `MOTION({mot_0.idstring},{0},{4},{j_2.i.idstring})`.
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Solve the model with the rigid Canard to review piston forces without
aerodynamic loads.
- Click the (Run) panel icon.
- Specify the MotionSolve file name as ForeCanard_withoutAeroloads.xml.
- Specify the Simulation type as Quasi-static, the End time as 1 second, and the Print interval as 0.01.
- Click the Run.
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After the simulation is complete, click the
Animate button to view the animation in
HyperView.
- On the Run panel in MotionView, click the Plot button to load the ForeCanard_withoutAeroloads.abf file in HyperGraph 2D.
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Use the data in Table 1and Table 2 to plot the Piston Force versus Fore Canard Angular
Position in HyperGraph.
Table 1. X-axis Data X Type Expression X Request REQ/70000000 Fore Canard Angular Position (deg)F2, Piston Force (N)F3 X Component F2 Table 2. Y-axis data Y Type Expression Y Request REQ/70000000 Fore Canard Angular Position (deg)F2, Piston Force (N)F3 Y Component F3
- Return to MotionView.
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Switch the rigid fore canard to a flexible body.
- From the Project Browser, select the Fore Canard body.
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In the Body panel, activate the Flex Body(CMS)
check box.
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Browse your <working directory> and specify
flex_ForeCanard.h3d for the Graphic and H3D
files.
- Click the Nodes button and resolve the flexbody interface nodes.
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Model Aero-dynamic loads through Modal Force Entity.
The aero-dynamic loads are estimated at three distinct positions of canard namely - 10 deg, 0deg, 10deg. Assume each pressure load to linearly vary in interval ±10deg on a 0 to 1 scale. This variation of the aero-dynamic loads is achieved by scaling Modal Forces with respect to canard angle using an expression.
- Right-click on the (SolverVariable) icon.
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In the dialog, specify the Label as Angle
Measure and the Variable name as
sv_ang.
- Click OK.
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In the SolverVariable panel, under the Properties
tab, specify the Type as Expression and enter
`RTOD({j_4.AZ})` in the Expression
field.
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On the Force Entity toolbar, right-click on the (ModalForce) icon.
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In the Add Modal Force dialog, specify the Label
as AerodynamicLoad_0deg and the Variable name as
mfrc_0deg.
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Click OK.
This will display the ModalForce panel.
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Configure the ModalForce panel.
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In the Connectivity tab, specify Fore Canard for
the Flexbody.
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From the Properties tab, specify the Scale type as
Expression, the LoadCaseID as
3, and the Expression as
`STEP(VARVAL({sv_ang.idstring}),-10,0,0,1)*STEP(VARVAL({sv_ang.idstring}),0,1,10,0)`.
The product of the two STEP functions evaluates to gradually increasing the value of the scale from 0 to 1 and then back to 0, while the canard angular position varies from -10deg to 10 deg as shown in the expression in Figure 49:
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Follow steps .5.e through 6.b to
create the remaining Modal Forces as specified in Table 3:
Table 3. S.No Label Variable name Flexbody Scale Type Load Case ID Expression 1 AerodynamicLoad_Negative10deg mfrc_neg10deg Fore Canard Expression 4 `STEP(VARVAL({sv_ang.idstring})-20,0,-10,1)*STEP(VARVAL({sv_ang.idstring}), -10,1,0,0)` 2 AerodynamicLoad_Positive10deg mfrc_pos10deg Fore Canard Expression 5 `STEP(VARVAL({sv_ang.idstring}),0,0,10,1)*STEP(VARVAL({sv_ang.idstring}),10,1,20,0)`
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In the Connectivity tab, specify Fore Canard for
the Flexbody.
Solve and Post-Process the Model
In this step you will run the Fore Canard model with the flex body and post-process the results of the run.
- Click the (Run) panel icon.
- Specify the MotionSolve file name as ForeCanard_withAeroloads.xml.
- Specify the Simulation type as Quasi-static, the End time as 1 second, and the Print interval as 0.01.
- Click Run.
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After the simulation is complete, click the Animate
button to view the animation in HyperView.
You can use the (Start/Pause Animation) button to play the animation.
- Click on the (Contour) panel button.
- In Contour panel under Result type, select Stress (t) and click Apply.
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This will show you the stress contours.
- In the MotionView run panel, click Plot to load the ForeCanard_withAeroloads.abf file in HyperGraph 2D.
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Plot the Piston Force versus the Fore Canard Angular Position by selecting the
information specified in Table 4 and Table 5.
Table 4. X-axis Data X Type Expression X Request REQ/70000000 Fore Canard Angular Position (deg)F2, Piston Force (N)F3 X Component F2 Table 5. Y-axis data Y Type Expression Y Request REQ/70000000 Fore Canard Angular Position (deg)F2, Piston Force (N)F3 Y Component F3 Note: You can overlay the plots to observe the difference in piston forces with and without aero-dynamic forces.