Fluid Structure Interaction Simulations with COMSOL
Daniel Ahlman, Ph.D.
Nagi Elabbasi, Ph.D.
COMSOL
Veryst Engineering
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Traditional approach approach to modeling modeling Electromagnetic Fields
Acoustics
Heat Transfer
Chemical Reactions
Fluid Flow
Structural Mechanics
The COMSOL Multiphysics approach Electromagnetic Fields
User Defined Equations Acoustics
Heat Transfer
Chemical Reactions
Fluid Flow
Structural Mechanics
The COMSOL Multiphysics approach User Defined Equations
Electromagnetic Fields
Acoustics
Heat Transfer
Chemical Reactions
Structural Mechanics
Fluid Flow
FSI
Introduction to Fluid-Structure Interaction (FSI) simulations
POLL QUESTION 1
Which simulation tool do you currently use to model FSI? •
COMSOL Multiphysics
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Other commercial software
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Non-commercial software (in-house code, freeware, open source, …)
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None
Different levels of FSI •
Small elastic deformation –
•
Large rigid displacement –
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Fluid flow Solid stress
Rigid structure displacement Fluid flow
Large elastic deformation –
Structural deformation Fluid flow
Fluid/solid coupling;
Small elastic deformations 1
1. Solve for fluid flow. 2.
Calculate total stresses.
3.
Apply fluid stresses on solid boundaries.
4.
Solve for the displacements in solids.
2
3
4
All steps automated in COMSOL! Fluid-Solid interface on shared mesh boundary!
Fluid/solid coupling;
Large rigid rotations 1
1.
Solve for displacements of the rigid structure to compute a fluid flow mesh.
2.
Apply the velocity of the solid boundaries on the fluid walls.
3.
Solve for fluid flow
4.
Repeat for next time step.
2
3
All steps automated in COMSOL!
Large elastic deformations 1
1. Solve for fluid flow. 2.
Calculate total stresses.
3.
Apply fluid stresses on solid boundaries.
4.
Solve for the displacements in solids.
5.
Use the solid displacements to;
2
•
Update the fluid flow mesh
•
Apply the solid boundary velocity to the fluid
3
6.
Repeat until solution converges.
7.
If Transient; Compute next time step
4 5
All steps automated in COMSOL!
POLL QUESTION 2 Which type of solid deformation, or displacement, best defines your FSI application? •
Small elastic deformations (Fluid Solid )
•
Large rigid displacements (Solid Fluid)
•
Large elastic deformations (Fluid Solid)
How to handle large elastic deformations?
Account for large deformation in solids
Solve for computational mesh for fluid flow
Large Deformation; Moving mesh
Reference mesh
Structural mechanics
Moving mesh
Fluid flow
Demo Exercise
Obstacle in a flow channel
Modeling overview
Fluid domain Inlet: u_fluid = f(t,y)
Outlet: p = 0
Solid domain
• •
Lower boundary of solid is fixed. Top and bottom boundaries of fluid domains are walls, i.e. zero fluid velocity.
Modeling in COMSOL
•
INSERT DEMO
®
FSI Analysis of a Peristaltic Pump Veryst Engineering® , LLC Engineering Through the Fundamentals®
Nagi Elabbasi, Ph.D.
[email protected] www.veryst.com
Peristaltic Pumps •
•
•
®
Valuable for pumping abrasive fluids, corrosive fluids and delicate fluids Rugged pump design requiring minimal maintenance Used in pharmaceutical, petrochemical, biomedical and food processing industries
Veryst Engineering
Pump Modeling •
Nonlinear, coupled fluid-structure interaction
•
Structural nonlinearities include:
•
•
®
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Tube material behavior
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Contact
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Large deformations
Important to know tube stresses and strains for lifetime prediction Optimal design depends on fluid properties and flow rate
Veryst Engineering
Rotary Peristaltic Pump Model
®
Veryst Engineering
Two metallic rollers and an elastomeric tube pumping a viscous Newtonian fluid at a speed of 60 Hz Model setup parametrically using native COMSOL geometry
Tube Modeling
Fixed boundary
Hyperelastic tube
Fixed along outermost edge for simplicity Fixed boundary ®
Veryst Engineering
Tube material one of main limiting factors affecting pump performance Typically made of elastomers like silicone or thermoplastic elastomers such as Norprene® or Tygon® Used Mooney-Rivlin hyperelastic material model
Fluid Modeling
Open fluid boundaries
Fluid-structure interface: ®
Veryst Engineering
Incompressible Newtonian fluid Laminar Navier-Stokes equations Peristaltic pumps commonly used for nonNewtonian fluids Moving fluid-mesh follows solid deformation FSI interface automatically handled by COMSOL
Contact Modeling
Source surfaces
Contact Pair 1 ®
Veryst Engineering
Contact Pair 2
Rollers are contact “source”, tube is contact “destination” due to higher relative stiffness of rollers No friction, rollers not allowed to rotate Contact Lagrange multipliers solved for as “Lumped Step” in segregated solver
Step 1: Move Rollers in Place •
Damped transient analysis to get rollers in correct starting configuration
Roller displacement
Initial model configuration ®
Veryst Engineering
Initial pump configuration
Step 2: Rotate Rollers •
Transient analysis with prescribed roller rotation –
®
Wait until transient dies out
Veryst Engineering
Solution Approaches for FSI Problem •
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®
Solve both solid and fluid fields simultaneously –
Two-way coupled solution
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More accurate (for some pump configurations)
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More computational resources (memory and time)
Solve solid field followed by fluid field –
Coupling only from solid to fluid
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Less accurate
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Less computational resources
Veryst Engineering
Mises Stresses and Fluid Velocity
Solid contours: Mises stress (MPa) Fluid arrows: Velocity field ®
Veryst Engineering
Flow Rate (and Fluctuations)
Significant flow fluctuations including flow reversal at point of roller separation from tube (vertical roller position) In practice fluctuations reduced by roller design
For more details on peristaltic pump modeling visit www.veryst.com/peristalticpump.html ®
Veryst Engineering
Benefits of using COMSOL for FSI •
Automatic calculation of total fluid forces.
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Automatic identification of solid-fluid interface.
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Automatic application of correct boundary conditions at the solid-fluid interface. Ability to move computational mesh based on deformation of solid. Accurate calculation of fluid flow stresses on moving mesh.
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