Setting constraint to erp

hello all

 

I am defining optimisation to reduce erp by topology optimisation. My objective is to find optimum material distribution to have low erp

 

my defination goes as

 

dconstraint:

 

Erp: upper bound > (Target values) ####

Volumefrac= upperbound  0.3 design volume

 

objective= minimize design volume

 

Loadstep = Modal frequency Response.

 

###For this setup I get error selected subcase not compatible with type of response while setting constraint on ERP

 

how do i set the erp as target value.

 

Regards

Pratik