SOLVERS: Load (Quasi-static)

Description

Selects the load and freedom cases to include in the Quasi-static solver, and assigns Factor vs Time tables and Factor vs Position tables for each load and/or freedom case. All included cases are combined and act simultaneously.

If a case is excluded (i.e., not checked), it makes no contribution to the solution.

If a case is included (i.e, checked), its contribution depends on the tables assigned to it. If no tables are assigned to an included case, its unscaled loads are always added to the solution.

The factor at a particular time step for an included case is determined from the product of factors due to the vs time and vs position tables.

Factor vs Time Table and Add Time Steps

This applies to both load cases and freedom cases.

The factor at a particular time step for an included case is determined from the vs time table. If a table is not specified (i.e., <None> is selected), a factor of 1.0 is used. If a table is specified, the factor is calculated by interpolating the table data at each time step of the analysis. If the time instance at any time step is outside the range of the table, the factor is set to zero.

When applied to freedom cases, the factor scales the enforced displacement values at nodes. If restraints at nodes are all zero values (i.e., only fixed restraints are included), the factor has no effect.

If a Factor vs Time table is selected and Add Time Steps is set, additional time steps may be inserted automatically by the solver. These additional time steps correspond to data points (time values) in the Factor vs Time table that occur within the solution time range specified for the analysis (SOLVERS: Time Steps). Furthermore, if Save table-inserted steps is set (SOLVERS: Time Steps), those additional time steps are saved to the result file.

Factor vs Position Table, Factor vs Position UCS, Factor vs Position Axis and Position Offset vs Time Table

This applies only to load cases, not to freedom cases.

These tables with corresponding UCS and axis settings can be used to scale the load applied to a node based on the position of the node at any time step. During the analysis, the current position of a node is transformed to the selected Factor vs Position UCS. The corresponding ordinate specified by the Factor vs Position Axis is then used as the x axis on the selected Factor vs Position Table to calculate a factor by interpolation. This factor scales the external load applied to the node. An example of the use of this feature is the modelling of a floating ship - here the pressure at any point on the hull depends on the position of the hull with respect to the water line (i.e., its depth).

If the selected ordinate of a node exceeds the range of the Factor vs Position table, the table is extended by maintaining the first or last y value. Therefore, the position factor will be equal to the first or last value in the table, depending on which end of the table has been exceeded.

To provide more flexibility, the effective position of the specified ordinate of the node can also be offset as a function of time. This is achieved by assigning another table to the load case, the Position Offset vs Time Table. If assigned, this table will apply a position offset to the specified ordinate of the node as a function of time. This offset position, rather than the true position of the node, is then used to look up the Factor vs Position Table. An example of the use of this feature is the modelling of the filling of a tank with fluid. A Factor vs Position table can be defined to represent a hydrostatic pressure distribution, and the tank can then be effectively moved up and down, relative to the pressure distribution, by the use of the Position Offset vs Time Table. Note that this movement is a virtual movement. It does not generate any inertia or momentum in the structure.