Reply To: Help to do quasistatic analysis in static structural module

[peteroznewman]

The HSFLD242 elements include a pressure node at the center to report the pressure in fluid and can be defined as fully incompressible using KEYOPT(6) which defines the hydrostatic fluid element compressibility:

Use KEYOPT(6) = 0 (default) to model the hydrostatic fluid element as compressible. You need to define a fluid material property (use the TB command with Lab = FLUID) to relate changes in fluid pressure to fluid volume.

Use KEYOPT(6) = 1 or 2 to model the hydrostatic fluid element as incompressible. The fluid volume is kept constant, even as the solid enclosing the fluid undergoes large deformations. The fluid volume, however, can change when fluid mass is added to or taken out of the containing vessel; this is achieved by applying a fluid mass flow rate or by prescribing a non-zero hydrostatic pressure degree-of-freedom constraint at the pressure node. The fluid volume can also change when a temperature load is applied at the pressure node for a fluid with a non-zero coefficient of thermal expansion. When KEYOPT(6) = 1, the change in volume is accommodated by a change in fluid mass (mass flows into or out of the cavity). When KEYOPT(6) = 2, the change in volume is accommodated by a change in fluid density such that fluid mass is held constant.

 

Read Chapter 15 for how to model hydrostatic fluid models.

Note that HSFLD242 elements must have the shape of a pyramid, with the pressure node at the apex in the center of the cavity. That means the solid elements that define the enclosed volume must be either pyramid or hex elements. Your current mesh uses tetrahedral elements, which is incompatible with HSFLD242 elements. A significant effort would be required to achieve hex element meshing throughout your model. The benefits of using HSFLD242 elements is that it has a direct pressure output that is constant over the entire fluid volume and there is a fluid volume output.

If you mesh the solid Inside body with tetrahedral elements, assign a water property defined with orthotropic elastic material properties so you can set the Shear Modulus to practically zero. This discussion that has my definition of water that has a practically zero shear modulus. The benefit is the meshing is easy. You can create a stress ouput for hydrostatic stress, but it may vary throughout the volume.