## *FILTER

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 filter itself is a monotonically decreasing function within a sphere at the node at stake taking the value 1 at the center of the sphere and 0 at its boundary. The TYPE of filter can be LINEAR, QUADRATIC, CUBIC or GAUSS. If no TYPE is specified, no filtering will be active.

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:

• *FILTER and any appropriate parameters.

Second line (only necessary if TYPE and/or BOUNDARY WEIGHTING was selected):

Example: