Chapter 10: PowerGraphics

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10.1 The Two Methods of Graphics Displays

There are two methods available for graphics displays:

The Full Model display method. You invoke this method using /GRAPHICS,FULL command (Utility Menu>PlotCtrls>Style> Hidden-Line Options).
The Power Graphics display method. You invoke this method using the /GRAPHICS,POWER command (Utility Menu>PlotCtrls>Style> Hidden-Line Options).

The PowerGraphics method is the default when the ANSYS GUI is on. This method is valid for all element types except for circuit elements. The Full Model method can be used for all element types. The display method you choose depends upon the size of your model and the type of elements used in the model. If your model contains circuit elements, for example, you select the Full Model method, because PowerGraphics is not valid for circuit element types. If you select the PowerGraphics method for a model containing circuit elements, ANSYS automatically uses the Full Model method instead. On the other hand, if you are creating a large model containing element types that are supported by PowerGraphics, the PowerGraphics method offers significantly faster performance than the Full Model method.

Note-The use of PowerGraphics as the default method in the GUI applies only to new analyses. If you continue to use files created in earlier releases of ANSYS, the method that was used to create those analyses is retained.

10.2 Characteristics of PowerGraphics

Displays for large models are plotted at a much greater speed than with the Full Model method.
PowerGraphics plots quadratic (curved) surfaces for midside node elements.
This method can display discontinuous results due to material type and real constant discontinuities.
Shell element results are displayed at both top and bottom layers, simultaneously.
You can use the Query picking option to query subgrid results for some elements in the Graphical User Interface.
PowerGraphics is not available for circuit elements.
When requested results data are not supported by PowerGraphics, the results are output using the Full Model method.
Results averaging occurs using only the data at the model surface.
PowerGraphics supports only the results coordinate system for plotting results data. (The elements-based coordinate system is not supported.)

10.3 When to Use PowerGraphics

Using the PowerGraphics display method has distinct advantages, since graphics displays are plotted at a much faster rate of speed than with the Full Model method. In addition, PowerGraphics produces more realistic results at material type and real constant discontinuities in the model. Although PowerGraphics is not available for circuit elements, you can use it in most cases to greatly increase plotting speed for large models. See the description of the /GRAPHICS command (in the ANSYS Commands Reference) for more information.

Note-If you choose the PowerGraphics method and circuit elements are active, ANSYS does not plot the circuit elements, nor does it include these elements in the results printout or in element averaging calculations. Similarly, if a model contains coupling between supported and non-supported elements (that is, circuit elements), only the elements PowerGraphics supports are plotted and included in printout.

10.4 Activating and Deactivating PowerGraphics

There are two ways to activate and deactivate the PowerGraphics display method: Through the Graphical User Interface (GUI), and through the /GRAPHICS command.

PowerGraphics is the default method when the ANSYS GUI is active. You can switch to the Full Model method, however, by taking one of the following actions:

Utility Menu>PlotCtrls>Style>Hidden-Line Options

You can deactivate PowerGraphics by issuing the command /GRAPHICS,FULL, or you can activate PowerGraphics by issuing the command /GRAPHICS,POWER.

Note-Issuing the /PMETH,ON command activates PowerGraphics unless you issued a prior /GRAPHICS,FULL command. Similarly, /PMETH,OFF deactivates PowerGraphics unless /GRAPHICS,POWER has been previously issued.

10.5 How to Use PowerGraphics

When the PowerGraphics method for graphics displays is active, it is used for element, area, volume, line, and result displays and result data listings. PowerGraphics does not support the graphics display or listing for circuit elements; for such cases, ANSYS automatically activates the Full Model graphics method and uses it for that display or listing. See the /GRAPHICS command description for more information.

10.6 What to Expect from a PowerGraphics Plot

Since PowerGraphics plots or listings are given for the exterior surface of the model, you can expect to see differences in these results, compared to those given when using the Full Model method. The averaging calculations for PowerGraphics include results for only the model surface. The averaging calculations, plots, and listings for the Full Model method include results for the entire model (interior and exterior surfaces). Therefore, the PowerGraphics and Full Model methods display results values differently for nodal results (but not for element results).

PowerGraphics makes the EPLOT, APLOT, VPLOT, LPLOT, PLDISP, PLNSOL, and PRNSOL commands behave differently than with the Full Model method. For details, see the commands' descriptions in the ANSYS Commands Reference.

10.6.1 Viewing Your Element Model

PowerGraphics uses a subgrid approach for plotting the model, in which you control the amount of displayed element curvature. You can plot varying degrees of curvature in your model by specifying the number of facets to be used for element display. Facets are piecewise linear approximations of the actual curve represented by the element face or edge. You specify the number of facets per element edge using one of the following:

Command(s):

/EFACET

GUI:

Main Menu>General Postproc>Options for Outp
Utility Menu>List>Results>Options
Utility Menu>PlotCtrls>Style>Size and Shape

The more facets you specify, the smoother the representation of the element surface for PowerGraphics plots.

The subgrid approach affects both the display of geometric curvature and the display and printout of results quantities (displacements, stresses, etc.). However, when you use PowerGraphics in POST1 for derived quantities on solid elements, the maximum value on the plot and the maximum value in the printout may not agree. Averaging does not occur for plotting across any geometric discontinuities (for example, 90 degree angle faces), but does occur for the printout.

10.6.2 Printing and Plotting Node and Element Results

You can list displacements, stresses, and strains at all node locations (both corner and midside nodes), using the PRNSOL command (Utility Menu>List>Results> Nodal Solution). For shell elements, you can list results and plot them at the top/bottom and middle layer locations. Likewise, these nodal values can be contoured for display purposes using the PLNSOL command (Utility Menu> Plot>Results>Contour Plot>Nodal Solution). The number of facets per element edge that you specify determines contour resolutions.

Note that results values for shell elements are displayed simultaneously for the top and bottom layers.

When viewing nodal results using PowerGraphics (PRNSOL, PLNSOL, or the GUI Query function), you can average results in various ways. To choose how results are averaged, use the AVRES command (Main Menu>General Postproc>Options for Outp or Utility Menu>List>Results>Options). (AVRES has no effect on the Degree of Freedom solution values (UX, UY, TEMP, etc.). You can average results at all boundaries (default), or at all boundaries except where real constant and/or material discontinuities exist. Results are not averaged at geometric discontinuities..

Note-In Full Graphics mode, it is possible to deselect an individual node, select all elements (including the element that contains that node), and then perform postprocessing calculations on those elements and have that unselected node not be considered in those calculations. However, if PowerGraphics is active postprocessing always displays based on selected elements.

Plotting and printing of element results are similar to that for the Full Model graphics method; you use the PLESOL or PRESOL command, or one of the following GUI paths:

GUI:

Main Menu>General Postproc>Plot Results>Element Solu
Utility Menu>Plot>Results>Contour Plot>Elem Solution
Main Menu>General Postproc>List Results>Element Solution
Utility Menu>List>Results>Element Solution

The program unaverages nodal results and sorts them by element number. Averaging results does not affect element results plots. Results are for all nodal locations on the model surface. If you issued the /EFACET,1 command, the results for the midside nodes are not listed.

PowerGraphics does not support safety factor calculations.

Caution: In unusual cases, your model may contain element types having different results data sets. If so, be sure to unselect those element types which do not have the data set you are reviewing. This prevents zero values from being averaged with valid results. For example, if your model contains FLUID30 (Acoustic Fluid) and SOLID45 (Structural Solid) elements, unselect all SOLID45 elements before viewing a pressure gradient.

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