September 22, 2023 at 3:30 pm
Edward Carman
Ansys Employee

Hi,

There are generally three ROM methods that can be applied to dynamic problems, depending on the problem type:

  1. Linear Time Invariation (LTI) ROM - applicable to systems whose behaviour satisfies the linear and time-invariant assumptions. Typically this is applied to conduction-only thermal problems e.g. forced-cooled systems where the flow field is a assumed to be constant and only temperature varies. This would cover applications like battery packs are power electronics.
    These are built by sequentially applying step inputs
  2. Linear Parameter Varying (LPV) ROM - applicable to systems whose behaviour is nonlinear, but could satisfy the linear and time-invariant assumptions if one of the input parameters was fixed. Typically this applied to similar applications as LTI, but where the cooling flow rate varies e.g. battery packs or power electronics with a varying flowrate going into the cooling plate.
  3. Nonlinear Dynamic ROM - general nonlinear dynamic systems. Applied to nonlinear dynamic applications whose behaviour is well outside the range of the LTI and LPV assumptions. These could be systems with significant radiation or natural convection or other forms of nonlinearity.
All three methods can build ROMs based on point probe (scalar / 0D) or full field (vector / 3D) data. To generate scalar training data, you can simple export report plots to .csv files. There is also an add-on package on the Customer Portal called 'ROM Builder Preprocessing for Fluent'. This automates some of the scalar data export and is also the preferred method for 3D data export (both for static and dynamic ROMs).
 
The ROMs themselves are built using Ansys Twin Builder (installed as part of the AEDT installation package).
 
Some documentation for the Dynamic ROM can be found here:
 
The LTI and LPV wizards are accessed under Toolkits:
 
There are also examples included with the installation under "\Win64\Examples\Twin Builder\Applications" e.g. "C:\Program Files\AnsysEM\v232\Win64\Examples\Twin Builder\Applications"