Release 11.0 Documentation for ANSYS
www.kxcad.net Home > CAE Index > ANSYS Index > Release 11.0 Documentation for ANSYS
As in any other type of ANSYS analysis, for harmonic magnetic analyses you create a physics environment, build a model, assign attributes to model regions, mesh the model, apply boundary conditions and loads, obtain a solution, and then review the results. Most of the procedures for conducting a 2-D harmonic magnetic analysis are identical or similar to the procedures for doing 2-D static analyses. This chapter discusses the tasks that are specific to harmonic analysis.
A 2-D harmonic magnetic analysis uses the same procedures to set GUI preferences, the analysis title, element types and KEYOPTS, element coordinate systems, real constants, and a system of units. "2-D Static Magnetic Analysis" describes these procedures.
When specifying material properties, in general use the same methods discussed in "2-D Static Magnetic Analysis". That is, where possible use existing material property definitions from the ANSYS material library or that other ANSYS users at your site have developed.
The next few topics provide some guidelines for setting up physics regions for your model, including an illustrated discussion of terminal conditions you can model within a simulated physical region.
The ANSYS program gives you several options to handle terminal conditions on conductors. These options offer enormous flexibility in modeling, for example, stranded and massive conductors, short circuit and open circuit conditions, and circuit-fed devices. To model each of these entities, you perform these tasks:
Add extra degrees of freedom (DOFs) to the conducting region.
Assign required real constants, material properties, and special treatments to the DOFs. Element types and options, material properties, real constants and element coordinate systems are defined as "attributes" of the solid model; you assign them using the AATT and VATT commands or equivalent GUI paths.
Conductors modeled with the AZ DOF simulate short-circuit conditions, due to the absence of electric scalar potential which implies zero voltage drop along the length of the conductor.
The AZ-VOLT option allows you to model massive conductors with various terminal conditions by including an electric potential in the overall electric field calculation:
E = δA/δt -
V
This gives you additional flexibility to consider open circuit conditions, current-fed massive conductors, and multiple conductors with end connections, by allowing control over the electric field (VOLT).
The potential, ν, has units of volt-seconds and uses the ANSYS DOF VOLT. In a planar or axisymmetric analysis, ν is constant over the conductor cross-section (that is, the voltage drop is in the out-of-plane direction only). To enforce this requirement, you must couple nodes in each conducting region using one of the following:
| Command(s): | CP |
| GUI: | Main Menu> Preprocessor> Coupling/Ceqn> Couple DOFs |
The coupling essentially reduces the unknowns to a single potential drop unknown in the conducting region.
You use the AZ-CURR option to model a voltage-fed stranded coil. The CURR DOF represents the current per turn in the coil. You can apply a voltage drop to the coil using one of the methods shown below (this applies to all coil elements):
| Command(s): | BFE,VLTG |
| GUI: | Main Menu> Solution> Define Loads> Apply> Magnetic> Excitation> Voltage drop> On Elements |
Alternatively, you can apply voltage-drop loadings to areas of the solid model by using the BFA command. You can then transfer the specified voltage-drop loadings from the solid model to the finite element model by using either the BFTRAN command or the SBCTRAN command.
No eddy currents are calculated in a stranded coil source, because it is assumed that the strands are insulated. The coil is described by "real" constants that the ANSYS program uses to calculate the coil resistance and inductance.
Voltage-fed stranded coils are available only for the PLANE53 and SOLID97 elements. For them, you must specify real constants which characterize the stranded conductor. All nodes in a stranded coil region must be coupled in the CURR degree of freedom, which will result in a single equation solving for the current flowing in the coil.
The ANSYS program offers several options you can use to handle terminal conditions on conductors in 2-D magnetic analyses. Figure 3.2: "Physical Region With Optional Terminal Conditions for Conductors" below pictures a physical region for a 2-D magnetic analysis and the conditions (options) that can exist within it.
| Short circuit conductor | DOFs: AZ Material Properties: MUr, (MURX), rho (RSVX) Eddy currents flow in a closed loop; there is no voltage drop due to a short-circuit condition. |
| Open circuit conductor | DOFs: AZ, VOLT Material Properties: mur (MURX), rho (RSVX) Special characteristics: Couple VOLT DOF |
No net current flows in an open circuit conductor. The axisymmetric case simulates a conductor with a finite cut (slit).
| Current-fed massive conductor | DOFs: AZ,
VOLT Material Properties: MUr (MURX), rho (RSVX) Special characteristics: Couple VOLT DOF in region; apply total current (F,,AMPS command) to single node Assumes a short-circuit condition with a net current flow from a current source generator. Net current is unaffected by surroundings. |
| Voltage-fed stranded coil | DOFs: AZ, CURR Material Properties: MUr (MURX), rho (RSVX) Real constants: CARE, TURN, LENG, DIRZ, FILL Special characteristics: Apply voltage drop (VLTG) using the BFE command (or alternatively using the BFA command and transferring the load to the finite element model by using the BFTRAN or the SBCTRAN command); couple CURR DOFs in region You can use element PLANE53 to model this source. Applied voltage is unaffected by surroundings. |
| Multiple massive conductors terminated by a common ground plane | DOFs: AZ, VOLT Material Properties: MUr (MURX), rho (RSVX) Special characteristics: Couple VOLT DOF of all conductor regions into a single coupled node set. |
Used to simulate devices such as squirrel cage rotors where end effects can be ignored.
| Current-fed stranded coil | DOF: AZ Material properties: MUr (MURX) Special characteristics: No eddy currents; can apply source current density (JS ) using BFE,,JS command (or alternatively using the BFL or BFA command and transferring the load to the finite element model by using the BFTRAN or SBCTRAN command) |
Assumes a stranded insulated coil producing a constant AC current, unaffected by surrounding conditions. Current density can be calculated from the number of coil turns, the current per turn, and the cross-section area of the coil.
| Circuit-fed stranded coil | DOFs: AZ, CURR,
EMF Material Properties: MUr (MURX), rho (RSVX) Real constants: CARE, TURN, LENG, DIRZ, FILL Special characteristics: Couple CURR DOF and couple EMF DOF in region. |
Model stranded coils fed by an external circuit (CIRCU124 element). See the Coupled-Field Analysis Guide for details on electromagnetic-circuit coupling.
| Circuit-fed massive conductor | DOFs: AZ,
CURR, EMF Material Properties: MUr (MURX), rho (RSVX) Real Constants: CARE, LENG Special characteristics: Couple CURR DOF, and couple EMF DOF in region. |
Model massive conductor fed by an external circuit (CIRCU124 element). See the Coupled-Field Analysis Guide for details on electromagnetic-circuit coupling.
| Laminated iron | DOF: AZ Material Properties: MUr (MURX) or B-H curve Simulating permeable regions where eddy currents can be neglected. Requires only the AZ DOF. |
| Air | DOF: AZ Material Properties: MUr (MURX = I) |
| Moving conductor (velocity effects) | You can model velocity effects from conductors moving at constant velocity with the PLANE53 element. For details on moving conductors, see the sections on velocity effects in this chapter and "2-D Static Magnetic Analysis". |
You may solve electromagnetic fields for special cases of moving bodies under the influence of an AC excitation. Velocity effects are valid for static, harmonic, and transient analyses. "2-D Static Magnetic Analysis" discusses applications and limitations for motion analysis. For harmonic analysis, velocity effects are limited to linear analysis (no B-H curves permitted).
The procedure for solving a 2-D harmonic analysis with a moving conductor is identical to that for a static analysis in terms of element KEYOPT options and real constants. Applied velocities are constant and do not vary sinusoidally (as do the coil or field excitation) in a harmonic analysis.
The magnetic Reynolds number is calculated and available in the postprocessor for viewing. This magnetic Reynolds number characterizes the velocity effect and numerical stability of the problem. The equation used to produce this number is shown below:
Mre = μ νd/ρ
In the above equation, μ is permeability, ρ is resistivity, ν is velocity, and d is characteristic length (in the directional motion) within a finite element of the conducting body. The magnetic Reynolds number is meaningful only in a static or transient analysis.
The motion formulation is valid and accurate for relatively small values of the Reynolds number, typically on the order of 1.0. Accuracy for higher Reynolds number values will vary from problem to problem. The magnetic Reynolds number is calculated and available in the postprocessor for viewing. In addition to a field solution, the motion solution includes currents in the conductor due to motion. This is available in the postprocessor.
Vdt
(time-integrated potential)
