HOW TO INTERPOLATE PRESSURE DATA OBTAINED BY OTHER TOOLS INTO STRUCTURE FE MODEL VIA PATRAN

1- Complete the solid model and finite element mesh of the wing by creating all sub-structure groups; Upper skin, Lower skin , Front and rear spar webs, Front and rear spar flanges, Ribs.

Create an additional group which includes upper skin and lower skin of the wing and the tip rib of the wing. This group will receive the aerodynamic load since they are the exposed faces.

You should have a mesh such as the one seen below.Do not forget the mesh the rib at the wing tip.

2- Create a new group to import the aerodynamic load calculated by other tools. For instance call that group “Aero” and make it current.

3- Import the aerodynamic load into your model file from : file – import

File to import: pressure_data.bdfDuring the import operation do the following selections:

Object: Model Source: MSC Nastran InputMSC Nastran Input Options: Select nodes, elements and load sets only from the right menu

Click on pressure_data.bdf and press Apply.

You should get very dense CFD mesh such the one shown below.

IMPORTANT NOTE: Your aero mesh and the structural mesh must have the same origin and the global coordinate frame of both models must be identical. Therefore, it may be a good idea to first import the aero mesh and check the origin. In addition, check the unit of the wing that you import for the aero mesh. Check whether the wing dimensions are in mm, cm or m and prepare your structural model accordingly !.

4- While the CFD mesh viewport is clicked on with the mouse create another viewport from the top menu and give it a name like Aero Viewport and view both viewports at the same time by the help of the “tile” command.

5- Plot pressure contours of the CFD mesh by making the selections shown below from the Loads and Boundary Condition top menu. For the fringe attributes select continuous style and no element edges.

6- At this step you need to create a Spatial FEM continuous field using the pressure information obtained from CFD solution. You can also follow these steps also from the video.

Name the new field as NewPressure and under the options menu do not click 2D to 3D interpolation.

Note that the viewport displaying the CFD mesh should be the active viewport while you generate the spatial field. You can activate a viewport by clicking on it.

Note:

Continuous FEM Fields are used to map data (interpolate) from one analysis to another (thermal or aero to structural) or from one mesh to another (global to local analysis). You can have more information on Spatial FEM fields (discrete or continous) from the Patran_Course_Notes document that is under the ftp site ftp.ae.metu.edu.tr under the AE 464 directory.

7- Now you need to apply the pressure on the CFD mesh to structure mesh. To do this first you need to create a pressure and use the field you generated in the previous step to do the interpolation job.

First click on the viewport displaying the structure mesh and from the loads and boundary conditions menu do the following selections: create-pressure-Element Uniform as shown below.

Give a new set name for the pressure interpolated to the structure mesh such as PressureOnStructure and select 2D for the target element type.

Under the input data menu click on top pressure and select the Spatial FEM field you generated in step 6.

Note: We will apply the pressure to the top surface of the shell elements.

Press OK and select the application region and select all the elements on the upper and lower wing surface and tip rib of the wing. IMPORTANT NOTE: The element normals of the upper skin, lower skin and the tip rib must point outward. (Out of the wing not towards the wing !!)

Press apply and you will see that pressure has been transferred to the structure mesh.

8- As the last step draw the pressure contours on the structure mesh and compare both contours side by side. Below figure shows the pressure plot on the lower wing surface.

9- During the solution phase try the cases we discussed in the “HOW TO INTERPOLATE PRESSURE DATA_Ders örneğinin adımları.doc” document.

First method: Do not erase the aero grids and elements ! Post the default group which has all the sub-structures. Apply the boundary condition on the spar roots while default group is posted and make a run.

Second method: If the first method does not work, this time erase the aero grids and elements. Post the default group which has all the sub-structures. And apply the boundary condition on the spar roots while default group is posted and make a run.

If there is problem during the solution, follow steps 12-14 in the “HOW TO INTERPOLATE PRESSURE DATA_Ders örneğinin adımları.doc” document. Steps 12-14 in the “HOW TO INTERPOLATE PRESSURE DATA_Ders örneğinin adımları.doc” document is for the simple plate problem but procedure is the same.