**static_torsor

Description

The static_torsor BC imposes a static torsor (resultant and momentum) on a nset. This means that the sum of the action of every nodal forces of the nset is equivalent to the specified static torsor. It is an ill-posed problem since we add \(3N\) unknowns (nodal forces in the three directions) and only \(6\) equations (3 equations for the resultant and 3 for the momentum). This BC is therefore associated to a rigid body motion of the nodes of the nset through a **mpc_rb relationship (see page ). Note that the user doesn’t have to define the **mpc_rb relationship, it is done automatically.

When a **mpc_rb is applied, only master 6 dofs over every dofs of the nset remain in the linear system. A small system of equations is then solved where the \(6\) remaining external forces associated to the 6 master dofs are computed.

Syntax

**static_torsor \(~\,\) *nset nset \(~\,\) *resultant vector \(~\,\) *momentum vector \(~\,\) (*point vector) || (*point_node id/node_name) \(~\,\) *table value table_name [*updated_configuration]

nset

is the name of the nset where the torsor is applied.

*resultant and *momentum

define the resultant and the momentum at the point defined by the *point command. The application point can also be defined using either the ID of a prexisting mesh node or the name of nset containing only this node. value and table_name define the multiplicative factor of the torsor.

*updated_configuration

a flag to apply the static torsor on the updated configuration (finite strains). By default, the static torsor is applied on the initial configuration.

Example

***bc
 **static_torsor
  *nset       top
  *resultant  (5.    1.   0.)
  *momentum   (0.01  0.0  0.)
  *point      (1.    0.5  0.5)
  *table      1.  time