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Keyword type: step
With *FILTER the sensitivities can be modified to obtain a more smooth result. It can only be used in a *SENSITIVITY step and at least one *DESIGN RESPONSE must have been defined before.
There are four optional parameters: TYPE, BOUNDARY WEIGHTING, EDGE PRESERVATION and DIRECTION WEIGHTING.
The TYPE of the filter can be either EXPLICIT or IMPLICIT. The explicit filter is a monotonically decreasing linear hat function within a sphere at the node at stake taking the value 1 at the center of the sphere and 0 at its boundary. Filtering can also be performed implicitly by solving an elliptic partial differential equation whose inverse operator is a local smoother based on the so-called Sobolev/Helmholtz operator. Default is the implicit filter.
With BOUNDARY WEIGHTING=YES the sensitivities near the boundary between the design space and the nodes not belonging to the design space are gradually decreased to zero. The distance across which this happens can be specified by the user. Default is no boundary weighting. If the BOUNDARY WEIGHTING parameter is active but no boundary weighting distance is given (or zero) the filter radius is taken is boundary weighting distance.
The EDGE PRESERVATION=YES parameter indicates that sharp corners at the boundary of the design space should be kept. This means that for the calculation of the normal on the design space, only the faces internal to the design space are used. Default is no edge preservation.
Finally, DIRECTION WEIGHTING=YES indicates that the values within the filter radius should be weighted with the scalar product of the local normal with the normal at the center of the filter.
First line:
Second line:
Example: *FILTER,TYPE=IMPLICIT 3.
defines an implicit filter with a filter radius of 3 length units. Boundary weighting, edge preservation and direction weighting are not active.
Example files: beam_sens_freq_coord1.