This option defines loads due to hydrostatic pressure acting on the planar FEs of a structure. Open the Pressure dialog by clicking 
in the Load Definition dialog.
This option lets you define loads caused by the pressure from a column of liquid which is perpendicular to an element's surface. The pressure can be constant or linearly varied. The "+" sign by the pressure value indicates that the pressure acts with the rotation of the vector normal to the surface FE. The "-" sign indicates that it acts in the opposite direction.
The direction of the hydrostatic pressure is perpendicular to the element surface at each point. The load can be uniform (pressure p and the liquid level h must be specified) or variable. For a variable load, the following values must be specified: uniform pressure value p, specific gravity of the liquid (grav) and the base liquid level h. Also, you can select the gravity force orientation:
- With respect to the X, Y, or Z axes of the global coordinate system (the sense of the gravity force is consistent with the axis sense)
- With respect to the X, Y, or Z axes of the global coordinate system (the sense of the gravity force is opposite to the axis sense).
The pressure value at any point is defined with the following formula:
Where:
- p - Constant component of the hydrostatic load
- grav - Specific gravity of liquid
- z - The coordinate of an arbitrary point in the selected direction (in this case, the variable z was selected from the global coordinate system)
- h - Coordinate of the liquid level (that is, for which the value of the variable pressure component is zero) up to which the constant or variable hydrostatic load is acting.
Hydrostatic loads normally apply to panels up to the height of a liquid level. To facilitate the load definition, mainly for curved panels (such as, a cylinder created by means of the Extrude option), you can select a certain set of finite elements (geometrical limitations). Note that during the generation of a finite element mesh, loads on panels are applied to the generated elements. If geometrical limitations are defined for the load, the load is applied to the entire finite element even if it is only partially within the load limits.
At the bottom of the dialog, the Geometrical limits button is accompanied by a selection option:
- If the option is cleared, the Geometrical limits button is not available and no limitations have influence on the loads.
- When the option is selected, the Geometrical limits button becomes available, which lets you define geometrical limitations related to the selected load type.