For a transient magnetic analysis, you can specify dynamic options, initial conditions, general options, nonlinear options, and output controls.
Dynamic options for transient magnetic analyses are as follows.
Time integration effects
These load step options determine whether the analysis includes transient effects such as eddy current damping effects and inductance.
Important: Mechanical APDL assumes time integration effects to be on in a transient analysis (unless they were turned off to establish initial conditions). If time integration effects are turned off, Mechanical APDL calculates a static solution.
To specify time integration effects, use one of the methods shown below:
Command(s): TIMINTGUI:Transient integration parameters
These parameters control the nature of your time integration scheme and specify the criteria for automatic time stepping. See the Mechanical APDL Theory Reference for details.
To specify transient integration parameters, use either of the following:
Command(s): TINTPGUI:
When you activate time integration effects, you can specify initial conditions at select nodes of your model. The initial conditions, which you choose for the valid degrees of freedom for your model, can be AZ, VOLT, or MAG.
If you do not specify an initial condition for your model's DOFs, the default is an initial condition of value 0.0.
To set the degree of freedom and initial DOF value, use either of the following:
To list initial conditions, use either of the following:
General options include the following:
Time option
This option specifies time at the end of the load step. For details on how to specify it, see Using the Alternative Solution Option for 2D Static Magnetic Analysis.
Number of substeps or time step size
The integration time step is the time increment used in the time integration scheme. You can specify it directly via the DELTIM command or its equivalent menu path, or indirectly via NSUBST or its menu path equivalent.
Time step size determines the accuracy of your solution. The smaller the time step size, the higher the accuracy. The size of the first integration time step following any large step change in loading conditions is especially critical. You can reduce inaccuracies such as overshoot by reducing the integration time step size.
Caution: Avoid using extremely small time steps, especially when establishing initial conditions. Very small numbers can cause calculation errors. For instance, on a problem time scale of unity, time steps smaller than 1E-10 can cause numerical errors.
If you step-apply loads, the program applies the entire load value at the first substep and holds it constant for the remainder of the load step. If you ramp loads (default), the program increments the load values at each substep.
To specify time step size directly, use the following command or menu path:
Command(s): DELTIMGUI:Automatic Time Stepping
Also called time step optimization in a transient analysis, automatic time stepping allows Mechanical APDL to determine the size of load increments between substeps. It also increases or decreases the time step size during solution, depending on how the model responds.
For most problems, you should turn on automatic time stepping and set upper and lower limits for the integration time step. The limits help to control how much the time step varies. However, time step optimization is not available for the CURR degree of freedom (voltage-fed conductors) or the EMF degree of freedom (circuit-fed models).
To specify automatic time stepping, use the following command or menu path:
Command(s): AUTOTSGUI:
Specify nonlinear load step options only if nonlinearities are present. Nonlinear options include the following:
Number of equilibrium iterations
This option obtains a converged solution at each substep. The default is up to 25 equilibrium iterations, but you may need to increase the number depending on the degree of nonlinearity. For linear transient analysis, specify one iteration.
For details on specifying the number of substeps, see Using the Alternative Solution Option for 2D Static Magnetic Analysis.
Convergence tolerances
Mechanical APDL considers a nonlinear solution to be converged whenever specified convergence criteria are met. Convergence checking may be based on magnetic potential (A), magnetic current segment (CSG), or both. You specify a typical value for the desired item (
VALUEfield) and a tolerance about the typical value (TOLERfield). The program then calculates the convergence criterion viaVALUE*TOLER. For example, if you specify 5000 as the typical value for magnetic current segment and 0.001 as the tolerance, the convergence criterion for magnetic flux would be 5.0.Ansys, Inc. recommends that
VALUEbe left to the default (program-calculated) and thatTOLERbe set to 1.0E-3.For potentials, the program compares the change in nodal potentials between successive equilibrium iterations (ΔA = Ai - Ai-1) to the convergence criterion.
For magnetic current segment, the program compares the out-of-balance load vector to the convergence criterion. If the solution does not converge within the specified number of equilibrium iterations, the program either stops or moves on to the next load step, depending on whether you activated the option to terminate an unconverged solution (see below).
Mechanical APDL enables you to graphically track convergence norms via its Graphical Solution Tracking (GST) feature, available for both interactive and batch runs of the program. For a detailed description of this feature, see the /GST command description in the Command Reference.
For details on specifying convergence tolerances, see Using the Alternative Solution Option for 2D Static Magnetic Analysis.
Terminate an unconverged solution
If the solution does not converge within the specified number of equilibrium iterations, the program either stops the solution or moves on to the next load step, depending on what you specify as the stopping criteria.
For details on terminating unconverged solutions, see Using the Alternative Solution Option for 2D Static Magnetic Analysis.
This class of load step options enables you to control output. For details on specifying any of the output controls, see Using the Alternative Solution Option for 2D Static Magnetic Analysis. Output controls options are as follows:
Control printed output
This option enables you to include any results data in the printed output file (Jobname.out).
Control database and results file output
This option controls what data goes to the results file (Jobname.rmg).
By default, the program writes only the last substep of each load step to the results file. If you want all substeps (that is, the solution at all frequencies) on the results file, specify a frequency or ALL or 1.
Extrapolate results
This option allows you to review element integration point results by copying them to the nodes instead of extrapolating them. (Extrapolation is the default.)