In topology optimization the number of load cases should typically be rather high. The reason for this is that all possible load situations, even if they might seem to be of minor importance, should be carefully identified and included into the set of separately applied load cases. Namely, failure in doing this very carefully, may quickly result in the final design that is neither reliable nor robust and may fail very quickly at some minor load variation.
Thus, the number of applied load cases should be relatively high to be on the safe side. In a typical optimization job, however, it often turns out that more or less load cases do not contribute anything useful to the optimization process. In other words, the set of these vain load cases could be dropped or deactivated without changing the final optimized design. It should be noted that deactivation of vain load cases might result in huge savings in CPU time.
The set of vain load cases is not known in advance and can be identified accurately only after the optimization problem is solved. However, during an optimization job in progress, ProTOp can monitor the situation and make estimates whether a particular load case tends to be vain. This estimate can be made on the basis of the so called impact factor which is a scalar quantity defined for each particular load case as follows.
Impact factor = (Volume part attributed to particular load case) / (Volume part)
The range of the impact factor is obviously [0,1], where a value of ImpFac = 0 indicates that the corresponding load case is useless. Note however, that this information is true only for the current optimization cycle, while this situation may change in later cycles.
ProTOp allows the user to monitor the impact factors during a running optimization process. According to impact factor values the user can deactivate any load case manually at any time by suppressing it. Once a particular load case is deactivated, it will be ignored in all optimization cycles until the user activates it back again. Typically, the load cases with the impact factor value ImpFac = 0 can be deactivated, but should be activated back again occasionally to check whether their corresponding impact factor is still zero.
IMPORTANT. After the optimization process completes, all deactivated load cases should be activated again and the optimization should be continued until convergence is reached with all load cases being active.
Besides of manual management, ProTOp offers also to manage the load cases automatically. If this option is checked, ProTOp will monitor the impact factors of individual load cases. Each load case whose impact factor reaches the specified lower limit, will be deactivated for a specified number of optimization cycles. After this number of cycles has elapsed, the corresponding load case is activated again to check for its impact factor.
NOTE. After the optimization process completes while the automatic management option is selected, ProTOp will switch off automatic management and run additional optimization cycles until convergence is reached again.