bulk modulus of oil

[dorios]

Hi,
I am modelling (FE) a floating roof (crude oil tank). The roof floats on a fluid of 225,000 psi.
I would like to avoid representing the fluid using hex/brick elements and therefore thought that I could translate this buylk modulus into an axial stiffness and put underneath the roof a series of springs to represent the fluid. I don't see how the stiffness of such a spring can be calculated.

Alternatively, I could discretise the fluid using hex elements and give elastic properties (bulk modulus instead of Young, and a Poisson's of 0.48-0.49 to make this material incompressible ).. fully poisson's of 0.5 would make an elastic stiffness matrix singul;ar, numerical problems etc... I am not interested in the fluid but rather in the resistance (stiffness ) that it produces on the roof. any ideas?
thanks

 

[THSavo]

Hi,

Just of the top of my head, I would say the pressure created by a displacement deltaX in a fixed volume is:

p = B*deltaX*A / V = F / A = k*deltaX / A.

Solve for spring constant k. Hope this helps you at all.