>>The structure the pipes sit on looks like it is made from steel beams of various cross-sections. In SpaceClaim, use the Midsurface button on the Prepare tab to replace the solid model of the structure with a surface model.

In this case, the pipes will be solid and the base surfaces?

>>You must end up with the same mass in the idealized geometry as you have in the original geometry. You can do that by adjusting the density of the material to make up the missing mass.

Thanks for the advice. I achieved mass with Point Mass in the Geometry section of the boundary conditions problem.

>>What is in the pipe, is it a gas or a liquid?  If it is a liquid, you need to include the mass of the liquid.

There is water and pressure. Will I need to set pressure? Can I take into account the mass of water also using Point mass? Can I select the entire pipe (without valves) and assign a single point mass to it with water?

Thank you!