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Nonlinear wind pressure load on a cylindrical surface

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VonFea

VonFea

Mechanical
Nov 23, 2012
27
Hi,
I’m trying to model nonlinear wind pressure load on a cylindrical surface (see attachment). I think I should use cylindrical coordinate and function dependent pressure load. Does anyone have an idea how to create a function for this? Pressure should change in proportion to angle.

Regards
VonFea
 
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I know I should use cylindrical CSYS and THETA direction to vary the load, but I don't know how to do it in practice.

Here is the function I have created (I think you can find my mistake here more quickly). X is angle in radians and Y is factor to multiply basic pressure. I think the problem is how to tell that X=THETA. When I expand my load I get only linear distribution and I know it's wrong.

Regards
VonFea
 
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In fact you can do it by using the Data Surface powerful tool.
Here is an example I made quickly to apply pressure on element depending on the Theta angle.

getfile.aspx


step by step:

1/ go to data surface editor and choose Tabular Data Surface

getfile.aspx


2/ Under Variation type choose XYZ Table, under Data Options select Scalar and hit Options to select your cylindrical CSYS.

getfile.aspx


getfile.aspx


3/ Under Define Variation Data Select Define Data and hit Theta (you can also vary the load in Z at the same time) choose a number of divisions (six for your case).
R, T, Z must appears in the dialog box if you properly selected the cylindrical CSYS:

getfile.aspx



4/ Now fill your table with the THETA value and P value to be applied and save the data surface as shown in the next figure:

getfile.aspx


5/ Go to Load / Pressure on Element / put 1 in load value in order to take into account the data surface that you will select from the menu.
Under Method choose Data Surface and select the one you created.

6/ Tip: to visualise the load pressure with a magnification scale, go to View Options (F6) Labels, Entities and Color / Load Vectors / select scale by magnitude and hit OK.

Hope this helps,





Seif Eddine Naffoussi, Stress Engineer
33650 Martillac – France
 
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You can also visualize the pressure application as a contour plot by creating an output from the applied load.

To do so, Create a new output set from Model / Output / Create/Manage Set

Activate this output set from the model info tree and activate the load set containing the pressure application.

Go to Model / Output / From Load / Select Elemental Pressure hit OK.

Press F5 and select the output vector created for the pressure output set.

And you are done!

Regards,


Seif Eddine Naffoussi, Stress Engineer
33650 Martillac – France
 
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Hi,
Thanks for the excellent tips. I got the nonlinear pressure, but I have little problem with the distribution. When I expand the load it shows only on half circle. Is there something wrong with my data surface?

Pressure load

Pressure load expanded

Regards
VonFea
 
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It depends on how you 2D elements normal are orientated. Be sure that all your elements have the same normal vector. Go to F6 / Labels, Entities and colors / Element Directions / Backface shading or Normal Vectors /Ok.
So You can pick one of the CQUAD face and see in which direction the pressure will be applied. Then you will be able to edit the face, front face/ back face... to invert the pressure path. Right click on the load definition / Edit Load, click no to access to the face selection dialog box..

You can also keep the pressure definition and reverse the elements normal , Modify/Update Element/Reverse Normal..

Regards,




Seif Eddine Naffoussi, Stress Engineer
33650 Martillac – France
 
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I check element normal vectors and those are correct.
I get error message "Unable to create 620 Load(s) on Element(s). Locations in Data Surface evaluate to zero or are outside the extents of the Data Surface." I tried to change all zero values to something else but it didn't help.

 
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Try to put -135, -85,-60,-30,0 instead of 225,275...
List a node at approximately Theta = 225 in the cylindrical CSYS and you will see that a negative value is shown (-85)...


Seif Eddine Naffoussi, Stress Engineer
33650 Martillac – France
 
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