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 Subsection 3.12.2: Surface Loads Up Subsection 3.12.2: Surface Loads Subsubsection 3.12.2.2: Traction Load 

3.12.2.1 Pressure Load

Pressure loads are applied to the surface of the geometry and are defined by the surface_load element with the type attribute set to pressure. These pressure forces are also known as follower forces; they change direction as the body is deformed and, in this case, are always oriented along the local surface normal. The sign convention is so that a positive pressure will act opposite to the normal, so it will compress the material. The surface that the load is applied to is specified with the surface attribute.The surface must be defined in the Mesh section.
parameter Description default
pressure The applied pressure values (1) 0 [P]
symmetric_stiffness symmetric stiffness flag (2) 1
linear linear flag (3) 0
shell_bottom shell bottom flag (4) 0
Comments:
  1. The pressure element defines the pressure value [P]. The optional parameter lc defines a loadcurve for the pressure evolution. If lc is not defined a constant pressure is applied.
  2. The optional symmetric_stiffness parameter (0 or 1) determines whether to use the exact form of the stiffness matrix for this surface load (0=non-symmetric), or the symmetric form (1=default). The non-symmetric form is numerically more robust, but it may also require using a globally non-symmetric stiffness matrix (see Section 3.3.4↑).
  3. If the optional linear parameter is set to 1, a constant, deformation independent pressure load is applied. This is not recommend for large deformations.
  4. When the shell_bottom flag is set to 1, the surface is assumed to be a shell surface and the pressure is applied to the bottom part of the shell surface.
Example:
<surface_load type="pressure" surface="surface1">
  <pressure lc="1">1.0</pressure>
  <symmetric_stiffness>0</symmetric_stiffness>
</surface_load>
 Subsection 3.12.2: Surface Loads Up Subsection 3.12.2: Surface Loads Subsubsection 3.12.2.2: Traction Load