Is short for evolutionary ratio and defines the ratio between the volumes and of the optimized structure in two consecutive steps: . The sign of “ER” depends on whether elements shall be added or removed. In case that – which is the default –is set automatically: . In case that “ER” is too small, the target mass of the optimized structure can not be reached within “MaxIter” steps.
The ratio between maximum number of elements to be added per step and all shell elements.
Number of iterations between those steps which are used for calculating the convergence criteria.
Relative change of the mass between two iterations cycles apart below which convergence is assumed.
In order to avoid the formation of checkerboard patterns a filter scheme is used for calculating the fitness of individual elements (see , section 3.3.2). defines the radius of influence in meters for determining the element sensitivity. It is thus important to choose this value according to the mean element size. If (the default) then is set equal to the characteristic element length which is calculated as .
Determines how the strain energy at nodes within the distance of the element center is weighted for calculating an elements sensitivity. The weight is determined as . Here with being the distance between a sample node and the center of the element. is the sum of the center distances of all nodes closer than to the element center.
The BESO for shell procedure makes use of a so called “soft kill”-approach. Instead of removing elements from the model they are made very soft by reducing their thickness. With the input-plug “KillThick” a value other than the default 0.00001 m can be selected.