Maximizing the Eigenfrequency of a Certain Eigenmode

You can increase a specific eigenfrequency in the eigenfrequency spectrum belonging to a certain eigenmode. In this case, a specific eigenfrequency is defined using TYPE = DYN_FREQ.

This task shows you how to:

Before you begin:

When optimizing a specific eigenfrequency, the order of the eigenfrequencies might change during the optimization iterations. Consequently, the eigenfrequencies might have to be tracked during the optimization iterations. This is done by mode tracking. For more information, see Mode Tracking.

Related Topics
Overview of Eigenfrequency
  • By default the modes are not tracked during the optimization. Mode tracking is activated in OPT_PARAM command:

    DRESP
 ID_NAME = single_lowest_eigenfrequency_1
 DEF_TYPE = SYSTEM
 TYPE = DYN_FREQ
 LC_SET = MODAL, ALL, 1
END_

OBJ_FUNC
 ID_NAME = maximize_single_eigenfrequency
 DRESP = single_lowest__1
 TARGET = MAX
END_

OPT_PARAM
 ID_NAME = opt_params
 OPTIMIZE = maximize_single_eigenfrequency
 MODETRACKING = ON
 MODENUMBERS = 8
END_

    For this example, at least 8 eigenfrequencies should be requested in the finite element input model defined by the user.

Define an Objective Function for a Minimization of a Specific Eigenfrequency in Tosca ANSA® environment

  1. To add a new objective term for the optimization, apply OBJ_FUNC > New.

    The OBJFUNC_TERM dialog appears:

  2. Choose TYPE = DYN_FREQ_KREISSEL.

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

    Note: The 3rd parameter is the eigenfrequency number, so that 1 corresponds to the smallest eigenfrequency.

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

  1. To create a new Design Response, select Command > DRESP.

    The DRESP dialog appears.

  2. Set DefType = System, Category = Base and Type = DYN_FREQ.

  3. Choose the load case by pressing Add LC button and setting Analysis Type to MODAL, entering the load case ID and the numbers of eigenmodes (e.g., 1) in Eigenmode/Subcase field.