Finite Element Analysis

Similar to the mesh generation, FEA is computed in a separate thread to enable you to continue to work on other designs. Before starting FEA, it is important that you set the proper settings for non-linear analysis.

The basic parameters to view the fields can be set in the FEA properties Visual page. The colors of the contours, the number of contours plotted, and color, line widths of vector arrows can be set here. The FEA legend box properties are also set from here.

The FEA properties, Iteration page lets you control certain aspects of the iterations. Most important of these are the "Steel total saturation" group. The number of histograms in the thread logger can be set here along with other properties. The Relax parameter is a coefficient used in the Newton-Raphson non-linear iteration process and the user can set it if required. In some cases where convergence is not apparent, the user can set this to a small value such as 0.1 to see if convergence is improved. This parameter needs to be manually set only in cases where extreme saturation is taking place in the non-linear steel.

Spline extrapolation - Extrapolate the steel BH curve (from database) when the flux density is higher than the maximum value available in the steel database table. You can either turn this ON or OFF.

Use saturation- Alternatively you can specify the value of flux density when the steel is totally saturated, i.e. when the relative permeability is equal to 1. If you use this, you have to specify values for both the stator steel and the rotor steel. If you use this, Spline extrapolation is automatically turned off.

After starting FEA, the progress made is shown in a Thread logger to give an idea of convergence. Once it has been completed, you have access to visualize the fields with some additional features that make visualization better. As in other parts of Samarium, use the mouse to get a better feel of the fields. Remember to turn OFF OpenGL lighting when viewing the fields, otherwise the colors will not be right (compared to the legend) and the results will be misleading.

There is the option to turn off or on the full motor calculations after FEA when only a partial motor model is used. Please use this in case the winding is not symmetric or repeatable. Full motor calculations can be turned off to investigate the results obtained directly from FEA where the post processing does not use the motor symmetry and only considers the partial motor model. This option is ignored for full motor model simulations.

NOTE- FEA IS NOT AN ABSOLUTELY ACCURATE METHOD. The accuracy of the results are highly dependant on the choices made for the iteration process and the steel data fed into the FEA engine. These choices being reliable all the time may come only after some experience playing with the input data and the properties. To overcome the problems with non-linear materials Samarium offers three choices-

1) Prevent extrapolation (turn OFF Spline extrapolation)

2) Allow spline extrapolation (turn ON Spline extrapolation)

3) If you know enough about the steel, turn ON "Use Saturation" and feed in the correct data for the lamination and hub saturation flux densities.

It is recommended to use Spline extrapolation while using the steels available from the default Samarium steel database.

The Fields page in the FEA options property pages help set the length of the arrays for all graphs. The user can choose to limit the graphs to one electrical cycle or let the graphs span the entire electrical angle of the motor model. Data is extracted from the FEA results based on what is chosen. Automatic post-processing after an FEA run can be set from here. It is recommended that this option be turned on. Display lists can be used to store the fields so there is smooth visualization during zooming, rotating, etc. Exact interpolation can also be turned on. See the toolbar section for more details.

If the size of the mesh is extremely large and the PC has limited RAM, the display list option in OpenGL may not work. If this happens the fields will not be visible on the screen even though the mouse interpolation will function. Please disable the "Enable display lists" option if this occurs, and the fields will be displayed normally without the use of display lists.

If a partial motor has been modeled, mirroring can be used to see the full motor cross section for better visualization. If only a very small part of the motor has been modeled, the user has control over how many sections to mirror. The mirroring mode works efficiently with partial 2 pole motor model. With a single pole or with odd number of poles, there may be some limitations in the appearance of the mirrored sections. The vector arrows will not be correct for single pole partial models displayed with mirroring. While the direction of the contours are correct, the colors of the positive and negative contours may not be appropriate with single pole partial models with mirroring enabled.

The steel BH curves for the stator lamination and the rotor hub are not used in the same format for several reasons. It is converted to 1/mu vs. B2 (B*B). These curves can be inspected from the popup menu-

Samarium supports viewing the fields computed by FEA in several ways. Both the base color map can be changed as well as the number of sub-colors used in each map. This helps in visualizing the fields in a intuitive and user-friendly manner.

The Color map combo box can be used to switch base colors, the number of sub-colors is set to 24 now. The depth of recursive triangular divisions is set to 3 in this screen shot.

This image shows the magnitude of flux density in the motor cross section. Mirroring has been enabled to view the full motor model even though the analysis was carried out on just a quarter of the motor cross section. A third order mesh was used. Several color maps that are available in Samarium are shown.

The red hot color map is used here with the number of sub-colors changed from minimum to maximum. The x-component of the flux density, Bx, is shown. Only the calculated part of the motor is show here, mirroring has been turned off.