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hydrostatic reverse surface normals

Valued Contributor
Valued Contributor

I am trying to do a hyrostatic analysis using NX CAE.   Some of the surfaces I meshed had the normals reversed.   I reversed the normals on the elements, but the hydrostatic pressure was linked to the surface.   How to I flip the surfaces I want or link to the element normals?


Seems simple enough, but I cannot find it in the documenation or hunting through menus.   Maybe I will find in in some of the contact documentation.




Re: hydrostatic reverse surface normals

Gears Esteemed Contributor Gears Esteemed Contributor
Gears Esteemed Contributor

In the modeling application, there is a "reverse normal" command that will reverse the normal direction of a sheet body.

Re: hydrostatic reverse surface normals

Valued Contributor
Valued Contributor
Edit-->Surface-->Reverse normal

Thanks. That mostly worked. One surface on the polygon body did not reverse. Any idea how to force it to elements which seems easier to control or separate a surface from a polygon body to get the last one to reverse?

Re: hydrostatic reverse surface normals

Valued Contributor
Valued Contributor

After talking with GTAC, it seems there is no way to reverse the normal of a surface within a body.   The only other option is to adjust element normals using a seed and then expanding the hydrostatic pressure from the surfaces to the elements...a bit messy, but the only option I have found. 

Re: hydrostatic reverse surface normals



if you still have surfaces which need negative hydrostatic pressure after reversing all surfaces which would tolerate it, there is another way to solve the problem.


Define your own pressure function, because hydrostatic pressure checks the physical correctness of gravity, density and start pressure but your own function does not.


You need the same parameters to describe your hydrostatic pressure. And the results should be the same, because hydrostatic pressure also defines "Pload4" bulk data entries with constant values for all nodes of affected elements.


The best is using a special coordinate system CS-kart_fluid with z_fluid=0 at "fluid surface level" and direction into fluid.


The formula than should be:

if (z_fluid >0) then  (

    pressure = orientation *{pressure_at_fluid_surface_level + (rho_fluid *gravity_constant *z_fluid)}

    ) else (

    pressure = orientation *{pressure_at_fluid_surface_level}



And now you can define negative values with orientation =-1 and positive values with orientation +1


You could use the same function for both surface types with and without demand of negative values. Put the orientation value into the scaling outside the function in spatial pressure definition. And then select surfaces into different pload-entities with or without negative scaling. That should work.


An easy way to modify your funtion is defining your parameters as expressions and use them instead of constant values in function creator.


Best wishes,


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