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:

In this exercise, you will create a flexible body of a Fore Canard of an aircraft with aerodynamic loads using OptiStruct. Aero-dynamic loads for three operating positions of the fore canard, namely -10 deg, 0 deg, and 10deg, considering an air speed of 200m/sec at 1 atm pressure are available from a CFD simulation using AcuSolve. A later section of the exercise involves embedding this flexible body in the actuator mechanism model in MotionSolve to estimate actuator loads required for the operation of fore canard.

Figure 1. Fore Canard of an Aircraft

Create a Fore Canard Flexible Body

In this step, you will create the Fore Canard flexible body.

Before you begin, copy all of the files located in the mbd_modeling\flexbodies\modalforce folder to the <working directory>.

  1. Open in HyperMesh with OptiStruct selected as the user profile.
  2. Review the model.

    Figure 2.
    1. The HM file contains a meshed model of Fore Canard with material properties and control cards defined.

      Figure 3. HyperMesh Model Browser
      Note: Model units are Newton-Meter-KG-Sec, therefore all properties defined are consistent with this unit system.
  3. 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:
    1. Left-click on the Load Collector icon from the toolbar.
    2. In the panel, verify that the create radio button is selected.
    3. Specify the new load collector name as AerodynamicLoad_0deg.
    4. In the drop-down menu, select no card image.
    5. Click Create.

      Figure 4.
    6. Follow steps 3.a through 3.e to create two more load collectors named AerodynamicLoad_Negative10deg and AerodynamicLoad_Positive10deg.
    7. Click Return.
  4. Browse to the Pressure load panel.
    1. Click the Analysis radio button.
    2. On the Analysis page, click on the Pressure button.

      Figure 5.
      This will open the pressure panel.
  5. Set the pressure load type to linear interpolation.
    1. Verify that the create radio button is selected.

      Figure 6.
    2. Next to the faces button, click the drop-down arrow. Change the surface selection type from faces to elems.

      Figure 7.

      Figure 8.
    3. In the magnitude drop-down menu, click linear interpolation.

      Figure 9.

      Figure 10.
    Now you can select elements on which pressure loads are applied and a CSV file for pressure load info.
    Figure 11.
  6. 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.
    1. Left-click on Set Current Load Collector.

      Figure 12.
    2. From the load collector list, choose AerodynamicLoad0_deg.

      Figure 13.
      This will set AerodynamicLoad_0deg as the current load collector.
    3. Click the elems button. Select by collector from the list.

      Figure 14.

      Figure 15.
    4. From the component collector list, click Fore Canard. Click the select button to return to the pressures panel.

      Figure 16.
    5. Click the ellipse button to browse for a file.

      Figure 17.
    6. In the Open dialog, browse your <working directory> and select AerodynamicLoad_0deg.csv. Then click Open.

      Figure 18.
    7. Click create to create pressure loads for the 0deg position.

      Figure 19.

      Figure 20.
      Note: The pressure load on each element is obtained by a linear interpolation of pressure values with respect to its location.
    8. Follow step 6 again to create pressure loads for the AerodynamicLoad_Negative10deg and AerodynamicLoad_Positive10deg load collectors.
  7. 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.
    1. In the Entities browser, right-click on the CMS load collector.
    2. In the context menu, click Card Edit.

      Figure 21.
      This will open the load collector card image.

      Figure 22.
  8. Specify load sets for CMSMETH.
    1. In the Card Image dialog, activate the LOADSET checkbox.
    2. Specify the CMS_LOADSET_LSID_NUM value as 3.

      Figure 23.
      The card image shows an option to specify three load sets.
    3. Double-click LSID(1).

      Figure 24.
    4. From the load collectors list, click AerodynamicLoad_0deg. Click the return button to go back to the CMS card image.

      Figure 25.

      Figure 26.
    5. Use steps 8.c and 8.d to specify AerodynamicLoad_Negative10deg for LSID(2) and AerodynamicLoad_Positive10deg for LSID(3).
    6. Click Return.
  9. 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.
    1. On the Analysis page, click on control cards button.

      Figure 27.
    2. Click on the DTI_UNITS button from the first page to review flexible body units. Then click Return.

      Figure 28.
    3. In the next card, click on GLOBAL_CASE_CONTROL to see the CMS load collector specified for CMSMETH solution. Click return twice.

      Figure 29.
    4. From the Analysis page, click on Optistruct.

      Figure 30.
    5. 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.

      Figure 31.
      This will solve the model.
    6. 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.

      Figure 32.

      Figure 33.

      Figure 34.

Create a MotionView Model

In this step, you will create a MotionView model of the Fore Canard.

A MotionView model of the fore canard mechanism has been provided. In this model, the Fore Canard body is modeled as a rigid body. In this next step we will replace the rigid Fore Canard body with a flexible body created in the previous step and use ModalForce entities to scale the pressure loads with respect to canard position.

  1. 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.

      Figure 35.
    • 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})`.

      Figure 36.
  2. Solve the model with the rigid Canard to review piston forces without aerodynamic loads.
    1. Click the (Run) panel icon.
    2. Specify the MotionSolve file name as ForeCanard_withoutAeroloads.xml.
    3. Specify the Simulation type as Quasi-static, the End time as 1 second, and the Print interval as 0.01.
    4. Click the Run.
    5. After the simulation is complete, click the Animate button to view the animation in HyperView.

      Figure 37.
    6. On the Run panel in MotionView, click the Plot button to load the ForeCanard_withoutAeroloads.abf file in HyperGraph 2D.
    7. 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

      Figure 38.
  3. Return to MotionView.
  4. Switch the rigid fore canard to a flexible body.
    1. From the Project Browser, select the Fore Canard body.
    2. In the Body panel, activate the Flex Body(CMS) check box.

      Figure 39.
    3. Browse your <working directory> and specify flex_ForeCanard.h3d for the Graphic and H3D files.

      Figure 40.
    4. Click the Nodes button and resolve the flexbody interface nodes.
  5. 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.
    1. Right-click on the (SolverVariable) icon.
    2. In the dialog, specify the Label as Angle Measure and the Variable name as sv_ang.

      Figure 41.
    3. Click OK.
    4. In the SolverVariable panel, under the Properties tab, specify the Type as Expression and enter `RTOD({j_4.AZ})` in the Expression field.

      Figure 42.
      After completing steps 5.a through 5.d, you have created an explicit variable that measures the fore Canard angle.
    5. On the Force Entity toolbar, right-click on the (ModalForce) icon.

      Figure 43.
    6. In the Add Modal Force dialog, specify the Label as AerodynamicLoad_0deg and the Variable name as mfrc_0deg.

      Figure 44.
    7. Click OK.
      This will display the ModalForce panel.
  6. Configure the ModalForce panel.
    1. In the Connectivity tab, specify Fore Canard for the Flexbody.

      Figure 45.
    2. 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)`.

      Figure 46.

      Figure 47.

      Figure 48.
      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:

      Figure 49.

      Figure 50.
    3. 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)`

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.

  1. Click the (Run) panel icon.
  2. Specify the MotionSolve file name as ForeCanard_withAeroloads.xml.
  3. Specify the Simulation type as Quasi-static, the End time as 1 second, and the Print interval as 0.01.
  4. Click Run.
  5. 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.
  6. Click on the (Contour) panel button.
  7. In Contour panel under Result type, select Stress (t) and click Apply.
  8. This will show you the stress contours.

    Figure 51.
  9. In the MotionView run panel, click Plot to load the ForeCanard_withAeroloads.abf file in HyperGraph 2D.
  10. 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

    Figure 52.
    Note: You can overlay the plots to observe the difference in piston forces with and without aero-dynamic forces.

    Figure 53.