Center of Loads

To obtain the correct center of loads report for a simulation containing symmetry or periodic boundary conditions, you must activate the Account for Idealization property.

The fluid loads acting on the part at the predicted location represent as closely as possible a pure force acting through such a point. In 2D it is always possible to find a point around which the resultant moment is zero. In 3D this is not always possible, because the resultant moment vector may have a component in the same direction as the resultant force. A pinwheel is a good example of this. In such a case, the resultant moment vector about a center of load may not be zero but is always parallel to the force.

The location of the center of load of a part is not necessarily unique – any point on the line of action of the resultant force is an equally good center of load. To appreciate this principle, suppose $P$ is a center of load, with resultant force $F$ and resultant moment $M_P$ . Let $Q=P+aF$ be any other point along the line of action of the resultant force. Then the resultant moment of the loads on the part about $Q$ is:

If $M_P$ is the smallest possible resultant moment, then so is $M_Q$ . The Locate On property of this report offers two options to refine the location of the center of loads to a single point.

Console Output

The format of the console output of the center of loads report depends on what options are selected in the properties, as well as whether errors occur while the report is being computed:

• If the Pressure or Shear force options are selected, only centers of loads for loads of the selected type are shown, along with force and residual moment values for loads of the selected type if requested. One row is printed in the tabular report output for each input part, and one row for the total across all parts.
• The reference pressure is not printed to the console if the Shear force option is selected, because it does not affect the report results in this case.
• If the Pressure + Shear force option is selected, centers of loads (and loads if requested) are shown for pressure and shear individually, along with net loads (combined pressure and shear). Three rows are printed in the tabular output for each input part and for the total across all parts, and an additional column is printed specifying what type of load is shown in each row.
• If the Show Loads in Console option is activated, the force and residual moment are displayed for each part and for the total loads across all parts.
• If errors occur during the computation of the report, they are shown in an additional column at the far right of the console output.

Inability to Intersect Geometry

The center of loads report displays the error message no geometry intersection when the line of action of the resultant force does not intersect either:

• part geometry (when the Part Geometry location option is selected)
• the specified reference plane (when the Reference Plane location option is selected).

In this case the reported center of loads is the point on the line of action of the resultant force that is closest to the origin of the laboratory coordinate system. If the resultant force is exactly zero, the reported center of loads is the origin of the laboratory coordinate system.

Monitors and Field Functions

You can monitor the center of loads report like all other reports. As with many other reports, you can also monitor per-part values from the center of loads report. The monitored value is the dot product of the position vector of the center of loads (relative to the report’s coordinate system origin) with the unit vector specified in the Direction property of the report.

Part values from the center of loads report can also be accessed using the getReportValue field function operator. As with the monitored value, the value accessed this way is the dot product of the position vector of the center of loads (relative to the report’s coordinate system origin) with the Direction property of the report.

Visualizing the Center of Loads

To see the location of the center of loads, you can create an annotation from the report that you can add to a scene. The action for creating this annotation is on the right-click menu of the report node itself (Create Visual Annotation from Report). If your simulation has symmetry or periodic boundaries, activate the Account for Idealization property—the location shown is then correct for the whole domain. For details about working with this annotation, see Visual Annotation from Report. The following example shows an external aerodynamics simulation where only half the geometry was modeled. With idealization accounted for, the center of load is correctly located along the center line.

Center of Loads Report Properties

Reference Plane Properties

When the Locate On property of the center of loads report is set to Reference Plane, you can use the properties of the sub-node by that same name to specify the reference plane: