Constraining an Eigenfrequency

Constraints for eigenfrequencies are allowed 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.

  • Define a separate eigenfrequency design response for each condition:

    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 an Eigenfrequency Constraint in Tosca ANSA® environment

  1. To add a new eigenfrequency constraint, choose CONSTRAINT and select New > EIGENFREQUENCY.

  2. In CONSTRAINT_ITEM dialog, choose MAGNITUDE = ABS, VALUE = GE_VALUE and VALUE = 100.

  3. Choose the appropriate load case in LC_SET field either directly or by pressing "?" key in the text field and using the window that appears.

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 (e.g., 1) in Eigenmode/Subcase field.

Define a Design Response for a Specific Eigenfrequency in Tosca Extension for ANSYS® Workbench

  1. Add a Design Response to your project.

  2. To set up the Design Response for an eigenfrequency task, select Def Type = System, Category = Eigenfrequency and Response Type = DYN_FREQ.

  3. Set the Load Case selection to Manual and select the desired eigenfrequency in the Steps/Mode field in a new created tab.