Fluid Structure Interaction in COMSOL
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Transcript of Fluid Structure Interaction in COMSOL
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Fluid Structure Interaction Simulations with COMSOL
Daniel Ahlman, Ph.D.
COMSOL
2012 COMSOL. COMSOL and COMSOL Multiphysics are registered trademarks of COMSOL AB. Capture the Concept, COMSOL Desktop, and LiveLink are trademarks of COMSOL AB. Other product or brand names are trademarks or registered trademarks of their respective holders.
Nagi Elabbasi, Ph.D.
Veryst Engineering
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Traditional approach to modeling
Chemical Reactions
Acoustics
Electromagnetic Fields
Heat Transfer
Structural Mechanics
Fluid Flow
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The COMSOL Multiphysics approach
Chemical Reactions
Acoustics
Electromagnetic Fields
Heat Transfer
Structural Mechanics
User Defined Equations
Fluid Flow
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The COMSOL Multiphysics approach
Chemical Reactions
Acoustics
Electromagnetic Fields
Heat Transfer
Structural Mechanics
User Defined Equations
Fluid Flow
FSI
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Introduction to Fluid-Structure Interaction (FSI) simulations
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POLL QUESTION 1
Which simulation tool do you currently use to model FSI?
COMSOL Multiphysics
Other commercial software
Non-commercial software (in-house code, freeware, open
source, )
None
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Different levels of FSI
Small elastic deformation
Fluid flow Solid stress
Large rigid displacement
Rigid structure displacement Fluid flow
Large elastic deformation
Structural deformation Fluid flow
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1. Solve for fluid flow.
2. Calculate total stresses.
3. Apply fluid stresses on solid boundaries.
4. Solve for the displacements in solids.
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Fluid/solid coupling; Small elastic deformations
All steps automated in COMSOL! Fluid-Solid interface on shared mesh
boundary!
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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.
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Fluid/solid coupling;
Large rigid rotations
All steps automated in COMSOL!
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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;
Update the fluid flow mesh
Apply the solid boundary velocity to the fluid
6. Repeat until solution converges.
7. If Transient; Compute next time step
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Large elastic deformations
All steps automated in COMSOL!
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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)
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How to handle large elastic deformations?
Account for large deformation in solids
Solve for computational mesh for fluid flow
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Large Deformation; Moving mesh
Reference mesh
Structural mechanics
Moving mesh
Fluid flow
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Obstacle in a flow channel
Demo Exercise
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Modeling overview
Inlet: u_fluid = f(t,y) Outlet: p = 0
Fluid domain
Solid domain
Lower boundary of solid is fixed. Top and bottom boundaries of fluid domains are walls, i.e. zero fluid
velocity.
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Modeling in COMSOL
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INSERT DEMO
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FSI Analysis of a Peristaltic Pump
Veryst Engineering , LLC Engineering Through the Fundamentals
[email protected] www.veryst.com
Nagi Elabbasi, Ph.D.
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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
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Pump Modeling
Nonlinear, coupled fluid-structure interaction
Structural nonlinearities include:
Tube material behavior
Contact
Large deformations
Important to know tube stresses and strains for lifetime prediction
Optimal design depends on fluid properties and flow rate
Veryst Engineering
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Rotary Peristaltic Pump Model
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
Veryst Engineering
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Tube Modeling
Hyperelastic tube
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
Fixed along outermost edge for simplicity
Fixed boundary
Fixed boundary
Veryst Engineering
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Fluid Modeling
Open fluid boundaries
Incompressible Newtonian fluid
Laminar Navier-Stokes equations
Peristaltic pumps commonly used for non-Newtonian fluids
Moving fluid-mesh follows solid deformation
FSI interface automatically handled by COMSOL
Fluid-structure interface:
Veryst Engineering
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Contact Modeling
Contact Pair 1 Contact Pair 2
Source surfaces
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
Veryst Engineering
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Step 1: Move Rollers in Place
Damped transient analysis to get rollers in correct starting configuration
Initial model configuration Initial pump configuration
Roller displacement
Veryst Engineering
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Step 2: Rotate Rollers
Transient analysis with prescribed roller rotation Wait until transient dies out
Veryst Engineering
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Solution Approaches for FSI Problem
Solve both solid and fluid fields simultaneously
Two-way coupled solution
More accurate (for some pump configurations)
More computational resources (memory and time)
Solve solid field followed by fluid field
Coupling only from solid to fluid
Less accurate
Less computational resources
Veryst Engineering
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Mises Stresses and Fluid Velocity
Solid contours: Mises stress (MPa) Fluid arrows: Velocity field
Veryst Engineering
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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
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Benefits of using COMSOL for FSI
Automatic calculation of total fluid forces.
Automatic identification of solid-fluid interface.
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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