Comsol Multiphysics

COMSOL Multiphysics Integration

Comprehensive guide for setting up and automating coupled fluid-structure interaction (FSI) simulations using COMSOL Multiphysics, with a focus on pump vibration analysis and related multiphysics applications.

Overview

COMSOL Multiphysics is a leading commercial simulation platform for modeling and solving complex multiphysics problems. It provides:

• Unified Environment: Single platform for multiple physics domains
• Flexible Coupling: Built-in tools for coupling different physics
• Equation-Based Modeling: Direct access to underlying PDEs
• Java API: Programmatic control and automation
• MATLAB LiveLink: Integration with MATLAB for pre/post-processing
• Application Builder: Create custom simulation apps

COMSOL excels at coupled physics problems including:

• Fluid-structure interaction (FSI)
• Thermal-structural coupling
• Electromagnetics with thermal effects
• Acoustics-structure interaction
• Electrochemistry with transport phenomena

COMSOL Architecture

Model Structure

• Component: Independent geometry and physics
• Study: Solution sequence with one or more steps
• Physics Interfaces: Pre-configured PDE systems for specific phenomena
• Multiphysics Couplings: Automatic or manual coupling between physics
• Solver Configurations: Automatic or customized solver sequences

Solver Technology

• COMSOL Solver: Direct and iterative solvers
• Fully Coupled Approach: Simultaneous solution of all equations
• Segregated Solver: Physics-based segregation for large models
• Time-Stepping: Implicit methods for transient analysis
• Mesh Adaptation: Automatic refinement based on solution

Licensing Requirements

Commercial Licensing

COMSOL Multiphysics requires commercial licenses for all production use:

• Base Package:
• COMSOL Multiphysics license (required for all users)
• Includes basic PDE interfaces and computational tools
• License managed via FlexNet License Server

• Module Licenses:
• Individual modules purchased separately
• Floating licenses (checked out during use)
• Batch mode requires license checkout
• HPC add-ons for parallel computing

• License Server Setup:

```bash # Set license server environment variable (Linux/Mac) export LMCOMSOLLICENSEFILE=1718@license-server.company.com

# Or in Windows set LMCOMSOLLICENSEFILE=1718@license-server.company.com ```

• License Types:
• Floating Network License: Shared among users
• Node-Locked License: Tied to specific machine
• HPC License: Additional cores for parallel computing
• Batch License: For batch/automated simulations

Academic Licensing

• Classroom Kit: Limited to educational use
• Research licenses: Available for academic institutions
• Restrictions on commercial applications
• May have feature or model size limitations

Important Licensing Notes

• License Check: Always verify license availability before batch runs
• License Release: Properly close COMSOL to release licenses
• Batch Operations: Require special batch/HPC licenses
• Module Dependencies: Some modules require others (e.g., FSI needs CFD + Structural)
• API Access: Requires base license plus relevant modules

Key Modules for Pump Applications

CFD Module

Comprehensive computational fluid dynamics for single-phase and multiphase flows:

Capabilities:

• Turbulence Models:
• RANS: k-epsilon, k-omega, SST
• LES and DES for high-fidelity simulations
• Wall functions and low-Re formulations

• Flow Types:
• Incompressible and compressible
• Laminar and turbulent
• Steady-state and transient
• Rotating machinery (frozen rotor, sliding mesh)

• Multiphase Flow:
• Euler-Euler multiphase
• Phase field methods
• Level set tracking
• Bubbly flow models

Pump-Specific Features:

• Rotating reference frames for impellers
• Mixing plane interfaces
• Cavitation modeling
• Pressure pulsation analysis

Structural Mechanics Module

Comprehensive structural analysis including linear and nonlinear behavior:

Capabilities:

• Analysis Types:
• Static structural analysis
• Eigenfrequency analysis (modal analysis)
• Frequency response analysis
• Transient dynamics
• Prestressed analysis

• Material Models:
• Linear elastic
• Hyperelastic (rubber, polymers)
• Plasticity (metals under high stress)
• Composite materials
• Contact and friction

• Dynamic Analysis:
• Modal analysis for natural frequencies
• Harmonic response
• Time-dependent loading
• Damping models (Rayleigh, modal)

Pump-Specific Features:

• Rotating machinery stress analysis
• Bolt preload and assembly stress
• Fatigue analysis
• Contact between impeller and casing

Fluid-Structure Interaction (FSI)

Couples CFD and Structural Mechanics for two-way interaction:

Coupling Approaches:

1. One-Way FSI:

• Fluid loads applied to structure
• Structure does not affect fluid
• Faster computation
• Suitable for rigid-like structures

1. Two-Way FSI:

• Fully coupled fluid and structure
• Deforming mesh methods
• Accounts for large deformations
• Required for flexible structures

1. Weak Coupling:

• Sequential solution (staggered approach)
• Fluid → Structure → Fluid iteration
• Better for loosely coupled problems

1. Strong Coupling:

• Fully implicit simultaneous solution
• Better convergence for tightly coupled problems
• Higher computational cost

FSI Features:

• Automatic mesh deformation (ALE method)
• Remeshing for large deformations
• Fluid loads computed automatically
• Pressure and viscous forces transferred
• Support for multiple solid bodies

Pump FSI Applications:

• Impeller blade vibration under fluid forces
• Casing vibration and acoustic radiation
• Seal deflection under pressure
• Shaft deflection and critical speeds
• Cavitation-induced vibration

Additional Relevant Modules

Acoustics Module:

• Pressure pulsation analysis
• Noise radiation from pump casing
• Structure-borne noise
• Coupled acoustic-structure-fluid problems

Heat Transfer Module:

• Thermal loads in pumps
• Coupled thermal-structural analysis
• Conjugate heat transfer (fluid-solid)
• Thermal expansion effects

Optimization Module:

• Design optimization
• Topology optimization
• Shape optimization
• Parameter sweeps

Java API for Automation

COMSOL provides a comprehensive Java API for programmatic model building and automation:

API Structure

Core Components:

• Model object: Top-level container
• Component: Geometry and physics
• Physics interfaces: Add and configure physics
• Study: Define solution procedures
• Results: Post-processing and visualization

Basic Java API Workflow

import com.comsol.model.*;
import com.comsol.model.util.*;

public class PumpFSI {
    public static Model run() {
        // Create model
        Model model = ModelUtil.create("PumpFSI");

        // Create component
        model.component().create("comp1", true);

        // Create geometry
        model.component("comp1").geom().create("geom1", 3);

        // Import CAD geometry
        model.component("comp1").geom("geom1").create("imp1", "Import");
        model.component("comp1").geom("geom1").feature("imp1")
            .set("filename", "/path/to/pump_geometry.step");
        model.component("comp1").geom("geom1").run();

        // Add fluid physics (CFD)
        model.component("comp1").physics().create("spf", "LaminarFlow", "geom1");
        model.component("comp1").physics("spf").selection()
            .named("geom1_fluid_domain");

        // Add structural physics
        model.component("comp1").physics().create("solid", "SolidMechanics", "geom1");
        model.component("comp1").physics("solid").selection()
            .named("geom1_solid_domain");

        // Add FSI coupling
        model.component("comp1").multiphysics().create("fsi1", "FluidStructureInteraction", 3);
        model.component("comp1").multiphysics("fsi1")
            .selection().named("geom1_fsi_boundary");

        // Create mesh
        model.component("comp1").mesh().create("mesh1");
        model.component("comp1").mesh("mesh1").automatic(true);
        model.component("comp1").mesh("mesh1").run();

        // Create study
        model.study().create("std1");
        model.study("std1").create("time", "Transient");
        model.study("std1").feature("time").set("tlist", "range(0,0.01,1)");

        // Solve
        model.sol().create("sol1");
        model.sol("sol1").study("std1");
        model.sol("sol1").feature().create("st1", "StudyStep");
        model.sol("sol1").feature().create("v1", "Variables");
        model.sol("sol1").feature().create("t1", "Time");
        model.sol("sol1").attach("std1");
        model.sol("sol1").runAll();

        // Save model
        model.save("/path/to/pump_fsi_model.mph");

        return model;
    }

    public static void main(String[] args) {
        run();
    }
}

Running Java API Scripts

# Compile Java file
comsol compile PumpFSI.java

# Run with COMSOL
comsol batch -inputfile PumpFSI.class -outputfile results.mph

# Or run directly
java -cp /path/to/comsol/plugins/*:. PumpFSI

API Advantages

• Reproducibility: Scripts ensure consistent model building
• Parametric Studies: Easy to vary parameters
• Batch Processing: Run multiple cases automatically
• Integration: Connect with other tools and databases
• Version Control: Track model changes in source control

MATLAB LiveLink

COMSOL integrates seamlessly with MATLAB for enhanced scripting and data processing:

LiveLink Features

Model Control from MATLAB:

• Build and modify COMSOL models
• Run simulations from MATLAB scripts
• Extract results into MATLAB workspace
• Use MATLAB's data analysis tools

Installation:

• Requires separate LiveLink for MATLAB license
• Configure MATLAB path to COMSOL installation
• Start COMSOL server or use direct connection

Basic MATLAB LiveLink Usage

% Initialize COMSOL with MATLAB
import com.comsol.model.*
import com.comsol.model.util.*

% Start COMSOL server (if not already running)
mphstart

% Create or load model
model = mphload('pump_model.mph');

% Modify parameters
model.param.set('inlet_velocity', '5[m/s]');
model.param.set('outlet_pressure', '101325[Pa]');

% Run study
model.study('std1').run();

% Extract results
pressure = mpheval(model, 'p', 'dataset', 'dset1');
velocity = mpheval(model, 'u', 'dataset', 'dset1');

% Process in MATLAB
mean_pressure = mean(pressure.d1);
max_velocity = max(sqrt(velocity.d1.^2 + velocity.d2.^2 + velocity.d3.^2));

% Plot using MATLAB
figure;
plot(pressure.p, pressure.d1);
xlabel('Position');
ylabel('Pressure [Pa]');
title('Pressure Distribution');

% Save results
save('pump_results.mat', 'pressure', 'velocity');

% Close COMSOL
ModelUtil.remove('model');

Parametric Study with MATLAB

% Parametric study of inlet velocity effects
velocities = 1:1:10;  % m/s
results = struct();

for i = 1:length(velocities)
    fprintf('Running case %d: velocity = %.1f m/s\n', i, velocities(i));

    % Set parameter
    model.param.set('inlet_velocity', sprintf('%f[m/s]', velocities(i)));

    % Solve
    model.study('std1').run();

    % Extract force on impeller
    force = mphint2(model, 'spf.Fp_x', 'surface', 'selection', 5);
    results(i).velocity = velocities(i);
    results(i).force = force;

    % Extract vibration amplitude
    displacement = mphmax(model, 'sqrt(u^2+v^2+w^2)', 'volume', 'selection', 3);
    results(i).max_displacement = displacement;
end

% Plot results
figure;
subplot(2,1,1);
plot([results.velocity], [results.force], '-o');
xlabel('Inlet Velocity [m/s]');
ylabel('Force on Impeller [N]');
grid on;

subplot(2,1,2);
plot([results.velocity], [results.max_displacement]*1e6, '-o');
xlabel('Inlet Velocity [m/s]');
ylabel('Max Displacement [μm]');
grid on;

% Save results
save('parametric_results.mat', 'results');

Common Workflows

Workflow 1: Pump Casing Vibration Under Fluid Loads

Application: Analyze vibration of pump casing due to pressure pulsations from fluid flow.

Approach: One-way FSI (fluid loads mapped to structure)

Steps:

1. Geometry Setup:

• Import pump casing geometry
• Create fluid domain inside casing
• Define FSI boundary (fluid-structure interface)

1. CFD Setup:

• Define inlet and outlet boundaries
• Set up turbulence model (k-epsilon or k-omega SST)
• Configure transient solver
• Apply rotating reference frame if analyzing flow with rotating impeller

1. Structural Setup:

• Define material properties (steel, cast iron)
• Apply boundary conditions (fixed support at mounting points)
• Set up transient structural analysis
• Include damping if known

1. FSI Coupling:

• Map fluid pressure and shear stress to structure
• One-way coupling (structure assumed rigid relative to fluid)
• Time synchronization between fluid and structural solvers

1. Solution:

• Solve transient CFD first
• Extract time-varying pressure loads
• Apply loads to structural model
• Solve structural dynamics

1. Post-Processing:

• Extract displacement at critical points
• FFT analysis for frequency content
• Compare with natural frequencies
• Stress concentration analysis

Workflow 2: Impeller FSI Analysis

Application: Coupled analysis of impeller blade deformation under fluid forces.

Approach: Two-way FSI with moving mesh

Steps:

1. Geometry and Mesh:

• Import impeller geometry
• Create fluid domain around impeller
• Define FSI interface at blade surfaces
• Mesh solid impeller and fluid domain
• Fine mesh at FSI boundary

1. Fluid Physics:

• Turbulent flow (k-omega SST recommended)
• Rotating reference frame for impeller
• Inlet velocity or mass flow boundary
• Outlet pressure boundary
• Moving mesh (ALE) enabled

1. Structural Physics:

• Linear elastic material initially
• Fixed at shaft connection
• Prestress from centrifugal loading
• Include rotation effects

1. Two-Way FSI Coupling:

• Fluid applies loads to structure
• Structure deformation moves mesh
• Iterative coupling within each time step
• Convergence criteria for FSI iteration

1. Prestressed FSI:

• First: Stationary structural analysis with centrifugal load
• Second: Use prestressed state as initial condition for FSI
• Improves convergence and accuracy

1. Solution Strategy:

• Start with coarse time steps for initial transient
• Refine time stepping for periodic solution
• Monitor residuals and FSI iterations
• Expect longer solve times for strong coupling

1. Post-Processing:

• Blade tip displacement vs. time
• Stress distribution on blades
• Effect of deformation on flow field
• Comparison of rigid vs. flexible results

Workflow 3: Coupled Thermal-Flow Analysis

Application: Thermal effects in pumps handling hot fluids.

Approach: Conjugate heat transfer with thermal expansion

Steps:

1. Multi-Domain Setup:

• Fluid domain (hot liquid)
• Solid domains (casing, impeller)
• Define fluid-solid boundaries

1. Coupled Physics:

• CFD for fluid flow
• Heat Transfer in Fluids (energy equation)
• Heat Transfer in Solids (conduction)
• Thermal Stress in solids
• Automatic temperature coupling at boundaries

1. Boundary Conditions:

• Inlet: Temperature and velocity
• Outlet: Pressure outflow
• External surfaces: Convection or radiation
• Solid boundaries: Fixed temperature or insulation

1. Material Properties:

• Temperature-dependent viscosity
• Thermal expansion coefficients
• Thermal conductivity

1. **Solution Seque

…

Source & license

This open-source skill is cataloged on AgentStack and links to its original source — we do not rehost the code.

• Author: Soljourner
• Source: Soljourner/claude-engineering-skills
• License: MIT

Install and usage instructions live in the source repository linked above.