This final subsection for this appendix provides a short description of a resource that is available in MSC.Nastran for evaluating the quality of the splines. It entails activating special prints within the MSC.Nastran that provide summary information for each of the splines. Although this feature is not available directly from the FlightLoads GUI, it may be of utility for especially problematic cases and therefore is documented here.

The special prints are invoked by setting a system cell at the top of the MSC.Nastran input file that says either:

NASTRAN SPLINE_METRICS

This can be done from the FlightLoads GUI by using the Direct Text Input feature, and inserting the text into the File Management portion of the input.

With this input, summary information on the spline is created and printed in the .f06 output from the run. An example of this output is given in Figure B‑5.

The output first lists the spline id and its type followed by the number of aero points and structural points that are being used in the spline. This is followed by two sets of tables that provide information on the maximum value and the minimum value for the translational and rotational coefficients in the spline matrix. It is difficult to assign physical meaning to the rotational coefficients, but the translational coefficients can be thought as a percentage of force that is being transformed for the aero/structural grid point listed. If the two sets of grids were identical in number and location, the max translation coefficient would be 1.0 and the min would be 0.0. If the meshes are not coincident, an estimate of the average coefficient value is given by the ratio of the number of aero points to the number of structural points. The maximum and minimum values would be somewhat above and below this number and judgment is required to determine if the values indicate problems with the spline. If the maximum value differs from the average value by over an order of magnitude, it may be beneficial to refine the spline in the area of the offending aero/structure pair. (Note that "refinement" may require removing one or more "nearly coincident" structural points -- a common cause of large couples.) A similar comment applies if the minimum value has an change of sign from the average and is greater in magnitude by over a factor of ten.

The matrix print shown above also prints the maximum and minimum sums of the spline matrix. Theoretically, each translation sum should be 1.0 and each rotational sum should be numerically 0.0 to indicate equilibrium. Recent experience has indicated that this is always the case for nonsingular splines.