Follow these steps to perform a transient edge-based magnetic analysis:
Specify the electromagnetics edge formulation by choosing from the GUI. Doing so lets you filter out other Mechanical APDL commands not involved in an edge-based magnetic analysis.
Define a jobname and title for your analysis. To do so, use the commands or GUI paths shown below:
Enter the preprocessor to begin defining your model:
Command(s): /PREP7GUI:Choose element type SOLID236 or SOLID237 via either of the following:
Command(s): ETGUI:Select the formulation option suitable for the specified element type and physics region.
Command(s): KEYOPTGUI:Define material properties. 2D Static Magnetic Analysis describes the material properties you can use and tells you how to specify them. For an eddy current region, you must specify the electric resistivity, RSVX.
Build the model. For instructions on building and meshing models, see the Modeling and Meshing Guide.
Assign attributes to the volumes (that is, associate the element types, the conducting and nonconducting regions, the material properties, etc. with the appropriate volumes).
Command(s): VATTGUI:Mesh the model, specifying brick or tetrahedral element shape.
Command(s): VMESHGUI:Enter the SOLUTION processor, using either of the following:
Command(s): /SOLUGUI:Apply flux-parallel and flux-normal solid model boundary conditions to the boundaries.
Command(s): DAGUI:For edge-based analyses, the label AZ (when set to zero) applies the flux-parallel boundary condition. No prescription is required to set flux-normal, because it is the natural boundary condition. In the rare case where the AZ = 0 condition is not general enough for flux-parallel conditions, you can prescribe constraints using individual D commands (or the equivalent GUI path).
Apply source loading. See Characteristics and Settings for Physical Regions of a Model for more information on source loading.
Note: You can use constraint equations to define cyclic symmetry.
Choose the transient analysis type.
Command(s): ANTYPE,TRANSIENT,NEWGUI:To restart a previous analysis (for example, to specify additional loads), issue the command ANTYPE,TRANSIENT,REST. You can restart an analysis only if you previously completed a 3D edge-based magnetic analysis, and the files Jobname.emat, Jobname.esav, and Jobname.db from the previous run are available.
Define analysis options.
Next, you define which solution method and which solver you want to use.
To select a solution method, use either of the following:
Command(s): TRNOPTGUI:Transient magnetic analyses require the full solution method.
Edge formulation analyses can use the sparse solver (default), the Jacobi Conjugate Gradient (JCG) solver, or the Incomplete Cholesky Conjugate Gradient (ICCG) solver. Select an equation solver using either of the following:
Command(s): EQSLVGUI:Choose load step options. Load step options are described in the following sections.
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 thermal 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 that 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 (the default), the program increments the load values at each substep.
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.
These options specify how often the tangent matrix is updated during a nonlinear solution. Available options are:
Program-chosen (default)
Full
Modified
Initial-stiffness.
For a nonlinear analysis, the full Newton-Raphson option is recommended. The adaptive descent option may help convergence in transient problems. To specify Newton-Raphson options, use either of the following:
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.
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 (VALUE field) and a tolerance about
the typical value (TOLER field). The program then
calculates the convergence criterion via VALUE X
TOLER. For example, it 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 VALUE be left to the default
(program-calculated) and that TOLER be 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, Mechanical APDL compares the out-of-balance load vector to the convergence criterion. If the solution dies 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).
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.
This option enables you to include any results data in the printed output file (Jobname.out).
This option controls what data goes to the results file (Jobname.RMG).
Note: 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.
Use the SAVE_DB button on the Toolbar to save a backup copy of the database. This enables you to retrieve your model should your computer fail while analysis is in progress. To retrieve a model, re-enter Mechanical APDL and use one of the following:
In this step, you initiate the solution for all loads steps using one of the following:
If only a single load step is used, you may use one of the following:
When you use the edge-element formulation, by default the program gauges the problem domain over all selected elements and nodes. Gauging removes unneeded degrees of freedom by setting them to zero; this in turn reduces solution time. You can control gauging using either of the following:
Gauging is required for static electromagnetic analyses with elements using an edge formulation. Therefore, in most cases you should not turn automatic gauging off. The GAUGE,OFF command is designed for expert Mechanical APDL users who wish to apply their own gauging. The program removes the extra constraints set by gauging after solution; therefore, gauging is transparent to users.
To leave the SOLUTION processor, use one of the following:
Command(s): FINISHGUI:Do postprocessing and review the analysis results, as described below.