Constraining an Eigenfrequency

You can define constraints for eigenfrequencies in the topology optimization tasks such as stiffness optimization or minimizing the mass.

This task shows you how to:

Before you begin:

This example uses the conditions that the first eigenfrequency is above 100 Hz and the second eigenfrequency is above 250 Hz.

For each condition, a separate eigenfrequency design response is to be defined as follows: 


DRESP
 ID_NAME    = eigenfrequency_1
 DEF_TYPE   = SYSTEM
 TYPE       = DYN_FREQ
 LC_SET     = MODAL, ALL, 1
END_

DRESP
 ID_NAME    = eigenfrequency_2
 DEF_TYPE   = SYSTEM
 TYPE       = DYN_FREQ
 LC_SET     = MODAL, ALL, 2
END_

CONSTRAINT
 ID_NAME    = con_eigen_1
 DRESP      = eigenfrequency_1
 MAGNITUDE  = ABS
 GE_VALUE   = 100.0
END_

CONSTRAINT
 ID_NAME    = con_eigen_2
 DRESP      = eigenfrequency_2
 MAGNITUDE  = ABS
 GE_VALUE   = 150.0
END_

OPTIMIZE
 ...
 CONSTRAINT = con_eigen_1
 CONSTRAINT = con_eigen_2
 ...
END_

Define a Design Response for a Specific Eigenfrequency in Tosca Structure.gui

  1. To create a new Design Response, choose Command > Design Response.
  2. Set DefType = System, Category = Base and Type = DYN_FREQ.
  3. To choose the load cases, press Add LC and set Analysis Type to MODAL, enter the load case ID and the numbers of eigenmodes (for example, 1) in the Eigenmode/Subcase field.