Keywords: *ICFD_POROUS_MODEL vs. *ICFD_DEFINE_POROUS_MODEL

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Guillaume RENEDO

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Sep 20, 2026, 1:43:03 PMSep 20
to LS-DYNA2

Dear all,

Does anyone know the difference between the two keywords *ICFD_POROUS_MODEL and *ICFD_DEFINE_POROUS_MODEL?

*ICFD_POROUS_MODEL is linked to *ICFD_MAT + *ICFD_PART + *ICFD_MESH_INTERFACE keywords.

But can *ICFD_POROUS_MODEL be used on its own?

Thank you,

Gred


James Kennedy

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Sep 21, 2026, 6:09:35 PM (13 days ago) Sep 21
to Guillaume RENEDO, LS-DYNA2

Dear Guiltaume,

 

Some notes that can be found on the internet

 

In LS-DYNA, both keywords are used to model porous media in the Incompressible CFD (ICFD) solver, but they serve completely different purposes in the keyword hierarchy.

The core difference is that *ICFD_DEFINE_POROUS_MODEL defines the material properties of the porous media, while *ICFD_POROUS_MODEL applies those properties to a specific volume.

 

 

Direct Comparison

Feature

*ICFD_DEFINE_POROUS_MODEL

*ICFD_POROUS_MODEL

Primary Purpose

Defines the physics and flow resistance characteristics (permeability, inertial drag, Ergun constants).

Binds the properties to the actual geometry/mesh parts.

Keyword Type

Property/Material Definition

Part/Application Assignment

ID Reference

Generates a PMODID (Porous Model ID).

References a PMODID and applies it to a PID (Part ID).

Analogy

Creating a recipe or buying a specific type of insulation.

Installing that insulation into a specific wall of a house.

 

Detailed Breakdown

1. *ICFD_DEFINE_POROUS_MODEL

This keyword is where you specify how difficult it is for fluid to flow through the porous medium. It does not know where the porous media is in your model; it only describes its physical behavior.

Key Inputs: You choose a porous model type (like the Ergun equation, Darcy-Forchheimer, or anisotropic power law) and input parameters like permeability (k), pressure loss coefficients, or porosity (ε).

Output: It generates a Porous Model ID (PMODID).

 

2. *ICFD_POROUS_MODEL

This keyword acts as the bridge between your geometry and your material properties. It tells the solver exactly which parts of your mesh should behave like the porous media you just defined.

Key Inputs: You input the Part ID (PID) of the fluid mesh volume that represents the porous zone, and you link it to the PMODID defined in the previous keyword.

Additional Features: It also allows you to define moving porous media or time-dependent porosity changes if your simulation requires it.

 

 

How They Work Together (Example Workflow)

 

To set up a porous media simulation (like a catalytic converter or a windshield filter), you must use both keywords in tandem:

text

..

Step 1: Define the flow resistance properties ..

*ICFD_DEFINE_POROUS_MODEL

$#  pmodid      type

         1         1   (Type 1: Ergun Correlation)

$#   perme     irres

    1.0e-4       0.0

 

Step 2: Apply those properties to your fluid part ..

*ICFD_POROUS_MODEL

$#     pid    pmodid

       501         1   (Applies Porous Model 1 to Fluid Part 501)

 

 

Sincerely,

James M. Kennedy

KBS2 Inc.

September 21, 2026

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