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-   -   how to extract x,y and z direction components of force (http://www.cfd-online.com/Forums/star-ccm/110735-how-extract-x-y-z-direction-components-force.html)

 dke December 19, 2012 08:45

how to extract x,y and z direction components of force

Hi all,

Im currently working on a student research project and i'm computing wave loads on an offshore structure.
The simulation is working fine, but i'm stuck at extracting force components.

My intention is to extract the force components. Force in X, Y, and Z direction at specific coordinates.
For example at the point [1,2,3] i want to extract a force in form of [200N,300N,500N].

I already tried Force report, but this gives me only the accumulated force for the whole structure.

My second try was to use a XYZInternalTable, but i only receive the pressure at specific coordinates given by star ccm+ without knowing the reference surface to calculate the force from pressure.

Currently i'm stuck at trying user defined field functions.

Maybe any suggestions?:confused:

 dke December 19, 2012 12:02

update

Well, i found a part solution:

Now i'm able to extract components for Forces caused by wall shear stress.

For example:
Force components [i j k]: [0.0 0.0 0.025]
corresponding Position: [x y z] [-29.73 -18.75 -64.5]

Im using a XYZInternalTable with the following user defined function as scalar field function:

Code:

`\$\$Area * \$\$WallShearStress.mag()`
Now the next problem occured. I cant use the same code syntax for pressure related forces, because pressure function is of scalar type.
My first idea was that i could use the scalar pressure value just as the magnitude of a potential pressure vector. Star reacts with an an error : "Pressure is not a type of array".
Now i'm confused how to continue to get the values i'm looking for :confused:

 dke December 19, 2012 12:43

Yay simple syntax mistake.

\$Pressure instead of \$\$Pressure works ;)

So field function for Pressure induced Force:

Code:

`\$\$Area * \$Pressure`

 rwryne December 19, 2012 15:30

Don't bother making field functions, a force report is the right way to do this.

In the force report, there is a "direction" component. You can set up 3 reports, one for X, one for Y, one for Z.

edit: I misunderstood your problem, my apologies! Ignore the above

 JBeilke December 19, 2012 15:51

The report doesn't help you for displaying the distribution of the force on a surface within a scalar plot. It just gives you a final number.

For a scalar plot of the y-component you have to create a scalar field function like this:

Code:

`\$Pressure * \$\$Area_Normal[1]`
where \$Area_Normal is a vector FV:

Code:

`\$\$Area/\$\$Area.mag()`

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