Use the Time Discrete Solver (
) to find the solution to time-dependent problems (dynamic or unsteady problems) that have already been discretized in time using, for example, the
prev operator or the
bdf operator. This solver is automatically used when a
Time Discrete study is added to the model.
Use the Defined by study step list to specify if the settings are synchronized with the corresponding study step.
Use the Times field to enter a vector of times that define the simulation’s time span.
The time step is specified in the Time step field. Valid entries are a scalar, a vector of times, or an expression containing global expression variables.
Discretizing time derivatives using the prev operator or the
bdf operator requires the solution at previous discrete times. How many previous time steps should be stored is specified in the
Number of time discrete levels field. If you, for example, use the first-order
bdf operator (
bdf(u,1)), the solution at one previous time step is required. Using the second-order
bdf operator (
bdf(u,2)) requires the solution at two previous time steps. The default value is 2.
Use the Relative tolerance field to enter a positive number. This number controls how accurately the nonlinear system of equations is solved in each time step. In general, the desired relative error in the solution should be entered here.
Use the Global method list to select how the specified absolute tolerance is to be interpreted for the variables that use the global method (by default, all variables use the global method). Select:
Select a Tolerance method to specify how to enter and compute the absolute tolerance. Select:
If you select Scaled or
Unscaled, additional fields appear. Use the
Tolerance field to modify the absolute tolerance for the selected variable.
Use the Times to store list to control at what times the solver stores a solution. Select:
When Specified times is selected, the solution to output is computed through interpolation. Therefore, the solution at previous time steps is not computed, which means that expressions with the
prev and
bdf operators cannot be used in analysis. Such expressions can only be used in analysis when you have selected
Steps taken by solver.
Click the Add button (
) to add a constant and then define its name in the
Constant name column and its value (a numerical value or parameter expression) in the
Constant value column. By default, any defined parameters are first added as the constant names, but you can change the names to define other constants. Click
Delete (
) to remove the selected constant from the list.