Learning Forum

[kravky]

Hello,

I am trying to define boundary conditions on midsurface according to following picture 

 

radius of inner circle is 0,2127m, outer circle: 0,8508m  and the thickness of membrane (modelled as a midsurface) is 0,001metres.
Youngs modulus of material is E=11,9*10^10 Pa, density is 790kg/m^3. 

The goal is to create uniform normal tension 11,9N/mm in whole membrane (create pretension for further modal analysis).

Red arrows in the picture represents uniformly distrubuted tension (11,9N/mm), normal to inner circle. Outer circle is clamped.

It is not difficult to define clamped (outer) edge, however i dont know how to define this tension, which is normal to inner edge.

I created cylindrical coordinate system, however i have problem to define direction of tension (radial direction). 

In this picture You can see what i got: 

The problem is, tension is applied in x-axis. Not in radial direction. There has to be an easy way how to define radial direction.

[peteroznewman]

In a Cylindrical coordinate system, the X axis is the Radial Direction.

[kravky]

In a Cylindrical coordinate system, the X axis is the Radial Direction.

 

Well, it can not be in my case, since the results of tension i got were not riadially symmetric. Actually, the reslutant tension corresponded to the fixed X axis, not radial axis.

[peteroznewman]

Why don't you use the method I described in your other discussion and use a fixed inner edge, a CTE material property and a thermal change to create a uniform tension in the membrane? That worked perfectly.

[kravky]

Why don't you use the method I described in your other discussion and use a fixed inner edge, a CTE material property and a thermal change to create a uniform tension in the membrane? That worked perfectly.

because now the inner radius is free - not clamped and that method does not work now.

[peteroznewman]

Please show the results you got that you interpret to not being radially symmetric.  I just built a similar model and I got a radially symmetric result.

 

 

[kravky]

Oh, acttually i got the same result now. It is correct. However is it possible to create somehow UNIFORM tension? in whole structure?

i searched for INISTATE in help, but it did not help me

inner edge is free and outer edge is clamped, therefore we cant use thermal load.

[peteroznewman]

A uniform membrane tension is possible with fixed edges as I demonstrated in another discussion. It is physically impossible with a free edge because equilibrium requirements forbids that from happening at a free edge.