State-Space Characterization

State-space characterization generates linear time-variant reduced order models (LTI ROMs). State-space characterization can significantly reduce the model size and transient simulation time for LTI systems. This approach represents the thermal problem as a system that processes a set of input signals (or simply inputs) yielding a set of output signals (or simply outputs). For a typical thermal problem, the inputs are heat sources at certain locations, and the outputs are temperature rise at specified locations.

When to Use State-Space Characterization

The state-space approach is generally valid for linear systems consisting of forced convection flow and insignificant radiative heat transfer.

Overview of State-Space Characterization

Run a Steady-State Analysis
  1. Create a steady-state Icepak design.
  2. After importing or building model geometry, assign thermal boundary conditions that contain parameters to which you'll assign variables the subsequent transient optimetrics analysis.
    Note:

    For the steady-state analysis, ensure the Value is 0 for the parameters to which you intend to assign variables in the transient design.

  3. Create Temperature monitor points to record the temperature of the boundary condition geometry.
  4. Analyze the steady-state design.
Run a Transient Optimetrics Analysis
  1. After the steady-state simulation is finished, copy the steady-state design and paste it in the project.
  2. Change the Solution Type to Transient.
  3. Create variables for the boundary condition parameters of interest for the optimetrics analysis.
  4. Add a solution setup.
    • On the General tab, select LTI ROM Defaults from the solutions setup defaults drop-down list.
    • On the Solver Settings tab under Import Options, select Start/Continue from a previously solved setup and click Setup Link.
  5. In the Setup Link dialog box next to Source Design, deselect Use this design and select the steady-state design you previously analyzed and click OK. If the steady-state design solves for flow and temperature, select Frozen flow simulation.
  6. Click OK in the Icepak Solve Setup dialog box.
  7. From Optimetrics, create a parametric setup using all of the variables you've created. Each row in the parametric table should have one variable with the same nonzero value and all other variables with a value of 0. The example below features a nonzero value of 5W.
    8. Note:

    Use the LTI ROM Parametric Setup toolkit to quickly create a parametric setup for the transient design. See LTI ROM Parametric Setup for more information.

  8. Analyze the transient parametric setup.
Export LTI ROM
  1. From the Icepak menu, select Export ROM > LTI ROM.
  2. In the Export LTI ROM dialog box, ensure that the variables are set as inputs and the monitor points as outputs.
    Note:

    If a variable was not used in the setup, select Unused for its Type.

  3. Select an Export Directory.
  4. Click Export to generate the files required for TwinBuilder ROM setup.