Fluid-Structure Interaction
Andrew Young
Applications Engineer
COMSOL UK
Kyle Mucha
Marketing Manager
COMSOL UK
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Agenda
• Why Simulate?
– Simulating with COMSOL Multiphysics®
• Introduction to Fluid-Structure Interaction
– Poll Question
• Fluid-Structure Interaction Interface
– Poll Question
– Moving Mesh
• Live Demo
• Q&A
• How To
– Try COMSOL Multiphysics
– Contact Us
Fluid-Structure Interaction simulation of wind acting on solar panelWhy Simulate?
• Conception and understanding
– Enables innovation
• Design and optimization
– Achieve the highest possible
performance
• Testing and verification
– Virtual testing is much faster than
testing physical prototypes
Fluid-Structure Interaction (FSI) in the cast and mold of an aluminum extrusion
Simulating with COMSOL Multiphysics
®
• Electrical, mechanical, fluid, and
chemical simulations
• Multiphysics – Include and couple all
relevant physical effects
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They can be run in a COMSOL® Client for
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Introduction to Fluid-Structure Interaction (FSI)
• Examples of FSI analyses
Cardiovascular modelling Peristaltic pump: A roller pumps fluid
along a flexible tube. Image credit: Veryst Engineering.
Stirred mixing vessel. The air flow around a solar
panel and the resultant structural stresses are
• Examples of FSI analyses
The sound pressure level radiated by a loudspeaker.
Introduction to Fluid-Structure Interaction (FSI)
The pressure field in a lubricating layer and deformation of a tilted
pad thrust bearing.
The stresses in the soil and the fluid velocity in the poroelastic domain
Types of FSI Problems in COMSOL
• Fluid flow coupled with structural
deformation in solids
• Acoustic-structure interaction
• Porous Media and Poroelasticity
• Particulate flow
Types of FSI Problems in COMSOL
• Fluid flow coupled with structural
deformation in solids
• Acoustic-structure interaction
• Porous Media and Poroelasticity
• Particulate flow
Types of FSI Problems in COMSOL
• Fluid flow coupled with structural
deformation in solids
• Acoustic-structure interaction
• Porous Media and Poroelasticity
• Particulate flow
Types of FSI Problems in COMSOL
• Fluid flow coupled with structural
deformation in solids
• Acoustic-structure interaction
• Porous Media and Poroelasticity
• Particulate flow
Poll Question 1
• What types of FSI application are you interested in?
– Fluid flow coupled with structural deformation in solids
– Acoustic-structure interaction
– Porous media and poroelasticity
– Particulate flow
One-Way Coupling: Small Solid Displacements
• Automated solution steps:
– Solve for fluid flow
– Calculate total fluid stresses
– Apply fluid stresses on solid boundaries
– Solve for the displacements in solids
Stresses in neonatal aortic arch as a result of pressure load calculated byOne-Way Coupling: Rigid Structures
• Automated solution steps:
– Calculate displacements and rotations of the rigid
structure
– Prescribe mesh motion according to rigid structure
– Apply the velocity of the solid boundaries on the
fluid walls
– Solve for fluid flow
vessel as a result of prescribed rigid Fluid velocity in a stirred mixing deformations.• Set up FSI equations for:
– Fluid flow
– Structural mechanics
– Moving mesh
• COMSOL automatically detects FSI boundary and sets conditions at FSI interface
• Apply conditions at FSI interface:
– Apply fluid boundary forces on solid boundary
– Impose fluid boundary velocities based on velocity of solid boundary
– Set boundary mesh displacement equal to displacement of solid boundary
Two-Way Boundary Coupling
Features Available for FSI Analysis
• All solid and fluid capabilities in COMSOL Multiphysics are available for FSI analysis
• FSI problems can also be coupled with any other physics field
Solid Capabilities
• Large deformations
• Contact
• Shells
• Plastic materials
• Hyperelastic materials
• Geotechnical materials
Fluid Capabilities
• Laminar flow
• Turbulent flow
• Stokes flow
• Non-Newtonian fluids
• Multiphase flow
• Thin fluid films
Peristaltic pump includingPoll Question 2
• Which FSI coupling are you most interested in?
– One way: Fluid flow → Structural deformation
– One way: Structural deformation → Fluid flow
– Two way: Structural deformation ↔ Fluid flow
Moving Mesh: The Challenge
Mesh displacement of vibrating beam
• COMSOL automatically sets up additional Partial
Differential Equations (PDEs) for the mesh
movement
• Mesh follows structural deformation at FSI
boundaries
• Two main convergence issues:
– Excessive mesh distortion
Handling the Moving Mesh
• Arbitrary Example:
– Solid object (purple) moves in fluid (pink) by displacement x(t)
– As solid deforms, the original mesh is distorted (in time) resulting in
excessive mesh distortion and convergence difficulties
Original mesh at t = 0 s. Solid object displacement described by x(t)
Mesh quickly becomes distorted for t > 0 s.
Helping the Mesh with Geometry Features
• Additional geometric features can be added to help solve the Moving Mesh
PDEs:
– Helps mesh deformation maintain quality
– Easiest when displacement is known
• e.g. on wall boundaries where normal mesh displacement is zero but mesh nodes
can still ‘slide’
Helping the Mesh with Geometry Features
• Additional geometric features can be added to help solve the Moving Mesh
PDEs… Even when displacement is not known!
– Prescribe mesh translation based on how a point moves through FSI
coupling
– Use Point Integration Component Coupling to allow helper line to slide
along boundary
Automatic Remeshing
• COMSOL provides several criteria for initiation of remeshing
• Default criterion is mesh distortion
• Once threshold is me a new mesh is built on deformed geometry
Original mesh at t = 0 s. Mesh is deformed after some time tN, where
element quality is reduced
Mesh is rebuilt on geometry at t = tN
How this Micropump Works
• When flow is against the flaps, they bend
backward, narrowing the channel and
increasing flow resistance
• When flow is in the direction of flap tilt, the
flaps bend forward, widening the channel
and decreasing flow resistance
• By placing titled flaps on either side of the
inlet, the bending happens on opposite
sides out of phase, thereby pumping net
fluid to the right
Why Use COMSOL Multiphysics for FSI
• Easy, automated setup of fluid, structure, and moving mesh parts of
FSI problems including interface conditions
• Extensive capabilities in structural mechanics, fluid flow, and moving
mesh
• Ease of interfacing with any other physics field
• Flexibility in solver selection including fully coupled direct solver for
strongly coupled FSI problems
Multiphysics Simulation Story:
SEA FLOOR ENERGY HARVESTING
NAGI ELABBASI, BRENTAN ALEXANDER, AND STUART BROWN
VERYST ENGINEERING, NEEDHAM, MA, USA
Extract from COMSOL News 2011 © 2016 COMSOL. All rights reserved.
Q&A Session
Micropump with two way coupled fluid flow and structural deformation