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Ramji KamakotiTechnical Specialist

May 13, 2013

Multiphysics in Abaqus with Emphasis on Fluid Modeling

2

Overview

• Introduction• SIMULIA Multiphysics • Abaqus/CFD• Fluid-Structure Interaction• Coupled Eulerian-Lagrangian (CEL) approach • Smoothed Particle Hydrodynamics (SPH) approach • Comparison of CFD, CEL and SPH

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Introduction

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What is Multiphysics?Definition: Multiphysics is the inclusion of multiple physical representations to capture real-world phenomena • Collection of individual physical phenomena

• Full 3-D physical “field” models (structural, thermal, EMag, chemistry, …)

• Efficient abstractions of physical phenomena (1-D/logical models, substructures)

• Interaction between various physical phenomena• Sequential simulation chains (EM→thermal→structural,

submodeling, multiscale …)• Co-simulation (FSI, logical-physical, multiscale,

embedded, …)

5

Why Multiphysics?

• Crucial to include multiphysics in the design of many engineering systems• Fluid-Structure interaction - Important to include fluid-

structure interaction (FSI) in the design of aircraft wings and turbine blades

• Multiple physics representation has to be taken into account for the analysis of Aneurysms and heart valves

• Thermal-mechanical coupling - Sections of bridges and highways expand on hot days, and many plastics become extremely brittle at low temperatures

• Electrical-thermal interactions - high-density microchip circuits often create large heat loads that need to be managed with heat-transfer techniques

• Etc …• Failure to include multiphysics can lead to

catastrophic phenomenon • Tacomas Narrows Bridge – Wind-induced collapse

due to aeroelastic flutter in 1940

6

Fluid-Structure Interaction

• Fluid-Structure Interaction (FSI) represents multiphysics problems where • fluid flow affects compliant structures which in turn affect the fluid flow.

Ink droplet formation and discharge from a piezoelectric inkjet printer nozzle

Fluid

PressureVelocity

Temperature

Structure

Displacement

ElectricalTemperature

TemperatureTemperature

Fields

Fields

Electrical

7

Specialized FSI

• Contact increases solution complexity and requires specialized analysis techniques.

ElectricalElectrical

Temperature

Temperature

Temperature

Temperature

Fluid

PressureVelocity

Structure

Displacement Fields

Fields

Contact

Vacuum removal of paper trim

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SIMULIA Multiphysics

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Overview of SIMULIA Multiphysics

• Multiphysics solutions offered by SIMULIA broadly falls into three different areas

• Native multiphysics capabilities available in Abaqus• Broad range of physics

Abaqus Multiphysics

10


• Extended multiphysics capability• CEL in Abaqus/Explicit• SPH in Abaqus/Explicit• Abaqus/CFD

Extended Multiphysics

CEL SPH

CFD


Abaqus Multiphysics


11


• Open scalable platform for partners and customers• Co-simulation engine• Native FSI capability• Coupling with third-party CFD codes

Multiphysics Coupling

SIMULIA Co-simulation Engine

Abaqus/Structural

Abaqus/CFD

Abaqus/EM

Other codes

• Extended multiphysics capability• CEL in Abaqus/Explicit• SPH in Abaqus/Explicit• Abaqus/CFD

Extended Multiphysics


Abaqus Multiphysics


Abaqus 6.12 MpCCI 4 Fluent 12

CSEAbaqus 6.12 Abaqus/CFD 6.12

Abaqus 6.12 Star-CCM+ 7.02CSE

12

Abaqus Mulitphysics

• Abaqus enables coupling of multiple fields

Courtesy: Honeywell FM&T

Courtesy of Dr. Michelle Hoo Fatt (University of Akron)

Tire noise

Bottle dropUltrasonic motor

Ball grid array

Earthen Dam

Thermal-Mechanical Structural-Acoustic

PiezoelectricFluid-Mechanical

Structural-pore fluid diffusion

Thermal-Electrical

Fuse

13

Coupled Eulerian-Lagrangian (CEL)

Courtesy: JP Kenny

Eulerian material definitions can interact with Lagrangian elements through contact in Abaqus/ExplicitMulti-material finite element formulation (Volume-of-Fluids method) tracks material boundary in EuleriandomainInterface interactions created using general contact definitionsAutomatic refinement of Eulerian elements improves accuracy and performance

14

Particle Methods: SPH

Mesh-free Lagrangian particlesAutomatic conversion from conventional elements to SPH particlesApplications include ballistic impact with fragmentation, class of fluid problems

Courtesy of US Dept of Health

15

• 88% efficiency for fixed-work per processor at 64 cores

• Mesh sizes limited only by pre and post capabilities

Abaqus/CFD – General purpose flow solver

Coupling with Abaqus/Standard and Abaqus/Explicit

2nd-order accurate in space and time

Turbulence modelingSpalart-Allmarask-epsilonILES

Incompressible pressure-based

flow solverTransient ,

Laminar and Turbulent flows, Heat transfer and

Natural convection

Superior and robust hybrid

FV/FEM discretization

Robust and fast iterative solvers, AMG, GMRES,

etc.

Fully parallel and scalable

Arbitrary Lagrangian-

Eulerian (ALE)

Native FSI capability

Abaqus/CAE pre and post support

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• SIMULIA’s next generation open communications platform that seamlessly couples computational physics processes in a multiphysics simulation

• Physics-based conservative mapping technology

• Superior coupling technology

Co-simulation Engine (CSE)

• Enables Abaqus to couple directly to 3rd party codes

• Currently in maintenance mode

SIMULIA Direct Coupling

• Enabled through MpCCI from Fraunhofer SCAI

• Allows coupling Abaqus with all codes supported by MpCCI

Independent code coupling interface

Abaqus

AcuSolve Star-CD FlowvisionOther CFD

codes

MpCCI

Abaqus Star-CD Fluent Other CFD codes

SIMULIA Co-simulation Engine

Abaqus/Standard

Abaqus/Explicit

Abaqus/CFD

Other CFD

Codes

Star-CCM+Star-CCM+

17

SIMULIA FSI Solutions

• Several methods available to address diverse industry needs

SIMULIA FSI Solutions

Con

tact

com

plex

ity a

t int

erfa

ce

Linear structures

SWAGELOK pressure regulator

Specialized techniques

Coupled Eulerian-

Lagrangian (CEL)

Smoothed Particle

Hydrodynamics (SPH)


Partitioned approach

Structural solver

Fluid solver

Solenoid Valve

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Abaqus/CFD

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Abaqus/CFD

• Abaqus/CFD is the computational fluid dynamics (CFD) analysis capability offered in the Abaqus product suite to perform flow analysis

• Scalable CFD solution in an integrated FEA-CFD multiphysics framework

• Based on hybrid finite-volume and finite-element method

• Incompressible, pressure-based flow solver:

• Laminar & turbulent flows

Pressure contours

Aortic Aneurysm

Pressure contours on submarine skin

Submarine

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Abaqus/CFD

• Incompressible, pressure-based flow solver:• Transient (time-accurate) method

• 2nd-order accurate projection method

• Steady-state using pseudo-time marching and backward-Euler method

• 2nd-order accurate least squares gradient estimation

• Implicit and explicit advection schemes

• Unsteady RANS approach (URANS) for turbulent flows

• Energy equation for thermal analysis

• Buoyancy driven flows (natural convection)

• Uses the Boussinesq approximation

• Isotropic porous media flow modeling • Includes isothermal and non-isothermal

flow modeling

Flow Around Obstacles(Vortex Shedding)

Electronics Cooling(Buoyancy driven flow due to

heated chips)

Velocity contours

Velocity vectors

Inlet

Outlet

Substrate

Pressure

porous media flow

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Abaqus/CFD

• Turbulence models• Spalart-Allmaras• RNG k-with wall functions• ILES (Implicit Large-Eddy Simulation)

• Inherently transient

• Boundary conditions• Inlet, outlet and wall boundary conditions• User-subroutines for velocity and pressure

boundary conditions

• Iterative solvers for momentum, pressure and transport equations

• Krylov solvers for transport equations• Momentum, turbulence, energy, etc.

• Algebraic Multigrid (AMG) preconditioned Krylov solvers for pressure-Poisson equations

• Fully scalable and parallel

88 % efficiency (fixed work per processor at 64 cores)

Helicity isosurfaces

Prototype Car Body(Ahmed’s body)

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Abaqus/CFD

• Fluid material properties• Newtonian fluids and non-Newtonian fluids

• A variety of shear-rate dependent viscosity models are available

• Temperature dependence of material properties

• CFD-specific diagnostics and output quantities• Arbitrary Lagrangian-Eulerian (ALE) capability for moving deforming mesh

problems• Prescribed boundary motion, Fluid-structure interaction

• “hyper-foam” model, total Lagrangian formulation

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Abaqus/CFD

• Abaqus/CAE support• Concept of “model type” in Abaqus/CAE

• Model type “CFD” enables CFD model creation

• Support for CFD-specific attributes

• Step definition

• Initial conditions

• Boundary conditions and loads

• Job submission, monitoring etc.

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Abaqus/CFD

• Abaqus/Viewer support for Abaqus/CFD• CFD output database

• Isosurfaces

• Multiple cut-planes

• Vector plots

• Instantaneous particle traces

Temperature contours

Temperature isosurfaces

Velocity vectors on intermediate plane

Pressure contours

Velocity vectors


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Fluid-Structure Interaction

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What is Fluid-Structure Interaction or FSI?

• FSI represents a class of multiphysics problems where fluid flow affects compliant structures, which in turn affects the fluid flow

• Coupling between the fluid and structure occurs at the wetted interface

• Conjugate fields exist at the wetted interface, e.g., traction & displacement

• Kinematic constraints provide continuity in the primary fields, e.g., velocity and displacement

• Normal stresses are also continuous at the wetted interface

Heat Flux

Fluid

TractionPressure

Fields

Structure

Displacement Fields

Temperature

Velocity

f s

f s

f s

f f s s

f f s s

T T

u u

v u

σ n σ n

q n q n

27

Survey of FSI Technology

• Linear Structures Approach• Linear solid/structural deformation• Eigenmodes sufficient to represent the

dynamic behavior • Projection of dynamic system onto the

eigenspace• Segregated Approach

• Structural and fluid equations solved independently

• Interface loads and boundary conditions exchanged after a converged increment

• Stabilizing terms required• Monolithic Approach

• Fully-coupled system of Equations• Can be difficult to solve• Can avoid stability issues

• Specialized Techniques• Coupled Eulerian-Lagrangian

Ma Cv Kd F

my +cy +ky = f modes( ) 0 1,...,i i i n K M S

Structural Solver Fluid Solver

( )f f f f f f f f f f

Tf f f f

T

f x y z

p t

K p

v v v

MV A V V KV C F

CV

V

s s s s s s s

s x y z

K t

u u u

MU CU U F

U

Τ

Abaqus native FSI capability is based on a stabilized segregated approach

28

Native FSI Using Abaqus

Coupling Abaqus/Standard + Abaqus/CFD

Abaqus/Explicit + Abaqus/CFD

Fluid structure interaction (FSI)

Conjugate heat-transfer (CHT)

Fluid-structure interactionButterfly valve

Conjugate heat transferHeat exchanger

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• Abaqus/CFD can be ccoupled with both Abaqus/Standard and Abaqus/Explicit through the co-simulation engine

• The co-simulation engine operates in the background (no user intervention required)

• Physics-based conservative mapping on the FSI interface

• Significantly expands the set of FSI applications that SIMULIA can address

• Fluid-structure interaction

• Also supports conjugate heat-transfer applications

Abaqus/Standard

Co-Simulation

Abaqus/Explicit

Abaqus/CFD

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• Rigorous decomposition of the fully-coupled system

• Retain segregated solution approach

• Interfacial inertial effects

• Stabilization provides temporal convergence in a one-step algorithm

• Time increment may be selected to resolve the physical time-scales

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• Supported though Abaqus/CAE

• Support for creating “FSI” interactions in

• Structural analysis (in Abaqus/Standard or Abaqus/Explicit)

• CFD analysis (in Abaqus/CFD)

• FSI jobs launched through co-execution framework

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Coupled Eulerian-Lagrangian (CEL) Approach

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• Three relationships between the mesh and underlying material are provided in Abaqus/Explicit:

• Lagrangian• Arbitrary Lagrangian-Eulerian (ALE)

adaptive meshing• Eulerian

• Lagrangian description: Nodes are fixed within the material

• It is easy to track free surfaces and to apply boundary conditions.

• The mesh will become distorted with high strain gradients.

1

Lagrangian formulation

Impact of a copper rod

34


• Arbitrary Lagrangian-Eulerian (ALE) adaptive meshing: mesh motion is constrained to the material motion only at free boundaries • It is easy to track free surfaces.• Mesh distortion is minimized by adjusting mesh

within the material free boundaries.

Lagrangian formulationALE formulation

ALE formulation

2

35


• Eulerian description: nodes stay fixed while material flows through the mesh.

• It is more difficult to track free surfaces.

• No mesh distortion because the mesh is fixed.

Eulerian formulation

ALE formulation

Lagrangian formulation

Eulerian formulation

Eulerian mesh

rod material

Mesh refinement needed in impact zone to more accurately capture strain gradient

3

36


• Coupled Eulerian-Lagrangian (CEL) approach:• An Eulerian mesh and a Lagrangian mesh are assembled in the same

model.

• Interactions between Lagrangian bodies and materials in the Eulerian mesh are enforced with a general contact definition.

Front-load washing machine

Tub (Lagrangian)

Round object (Lagrangian)

Water (Eulerian)

37

CEL Analysis Technique

• Technical Approach• The Eulerian-Lagrangian capability uses a multi-material finite element

formulation

• Volume-of-Fluids (VOF) method tracks material boundary in the Eulerian domain

• Interface interactions created using general contact definitions

• Conforming meshes not required

• Specialized technique to handle certain types of Fluid-Structure Interaction (FSI) problems:

• Extreme contact including self-contact

• Large scale structural deformations and displacements

• High-speed dynamic events

• Damage, failure, or erosion of the interface

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Smoothed Particle Hydrodynamics (SPH) Approach

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• Smoothed Particle Hydrodynamics is a very general approach to the simulation of bulk matter in motion.

• SPH addresses modeling needs in cases where traditional methods (FEM, FDM) fail or are inefficient:

• Extremely violent fluid flows where mesh or grid-based CFD cannot cope (free surface)

• Extremely high deformations/obliteration where CEL is inefficient and Lagrangian FEM is difficult

Liquid spraying through a hoseWater fall under gravity

40


• The earliest applications of SPH were mainly focused on fluid dynamics.

• Then its use was extended to the simulation of:

• The fracture of brittle solids

• Metal forming

• High (or hyper) velocity impact (HVI)

• Explosion phenomena caused by the detonation of high explosives

Priming a PumpProjectile impact

continuum solid projectile

SPH patch

41


• The novelty of SPH lies in a specific method for smooth interpolation and differentiation within an irregular grid of moving macroscopic particles.

• Because nodal connectivity is not fixed, severe element distortion is avoided; hence, the formulation allows for very high strain gradients.

• The conservation of mass, linear momentum, and energy are satisfied exactly.

Kernel function W(r)Particle

Neighbors

42


• SPH in Abaqus• SPH analysis is an Abaqus/Explicit capability implemented for three-

dimensional models.

• Any of the material models available in Abaqus/Explicit, including user-defined materials, can be used.

• Initial and boundary conditions can be specified as for any Lagrangian model.

• Concentrated nodal loads can be applied in the usual way.

Spray can nozzle

44

Material Considerations

• Material types• SPH can use any material available in Abaqus/Explicit,

• CEL can use any isotropic material available in Abaqus/Explicit

• CFD can simulate only incompressible fluids

CEL SPH CFD

TypeSolids

isotropic

anisotropic

Fluids

Compressibility

Compressible

Nearly incompressible

Incompressible

45


• Multiple materials• CEL can simulate multiple materials interacting

Projectile impacting solid plate (SPH)

continuum solid projectile

SPH patch

sand

water

air

Multiple materials interacting (CEL)

CEL SPH CFD

Single material

Multiple materials interacting

Interactions via contact or FSI co-simulation

46


• Special CFD capabilities

• CFD can include turbulence modeling

• CFD can model flows through porous media

Inlet

Outlet

Substrate (porous media)

Pressure contours

porous media flow (CFD)

CEL SPH CFD

Turbulence modeling

Flows through porous media

47

• Material motion• CFD and CEL both allow for material flow through the mesh


CELtire Hydroplaning

fluid outflow

fluid inflow

CFD Vortex Shedding behind a cylinder

fluid inflow

fluid outflow

CEL SPH CFD

Material inflow and outflow

48


SPH Two-Lobe Cavity Pump: Water pushed while pump is rotating

• Material motion• CFD and CEL both allow for material flow through the mesh

• SPH uses a strictly Lagrangian formulation

• Inflow and outflow conditions can only be modeled via more expensive inflow and outflow volumetric regions

CEL SPH CFD

Material inflow and outflow

49

• Inflators• Inflators can be used to introduce gas in CEL simulations

• Limited inflators can be modeled in SPH via long columns with fluid pushed down via a plate

Initial geometry

Early deployment

Deployment complete


CEL Side curtain airbag deployment Inflator injects gas into the air bag throughout the simulation

Courtesy of TAKATA SPH inflation

Long column of fluid pushed in

CEL SPH CFD

Inflators

50

Contact Considerations

• Contact interface: conforming meshes• CEL allows you to create a simple mesh which does not conform to the

surrounding structure

• CFD FSI requires a conforming mesh

• SPH particles cannot overlap with other surrounding Lagrangian bodies

CEL structure moves through

Eulerian mesh

CFD FSI CFD mesh conforms to structure

SPHparticles inside structure

CEL SPH CFD

Mesh need not conform to surrounding structure

51


• Contact interface: topology changes• CEL and SPH can be used to perform FSI analyses with penetration

and/or pinching

• CFD FSI fluid boundaries can move or deform, but not change topologically

CEL projectile impact and penetration

SPH Grease filled CV joint

CEL SPH CFD

Contact interface topology can change

52


• Contact with immersed shell structures• With SPH and CFD FSI flow is discontinuous on either side of an

immersed shell structure because the boundaries are Lagrangian

• CEL smears the discontinuity over the element that the shell intersects

Discontinuous streamlines and pressure contours in flow over a

flexible flap in a converging channel (CFD/STD co-simulation)

Notes: • The same comparison is true for the

temperature field in heat transfer simulations (CFD FSI and CEL only)

• Abaqus/CAE includes a “seam” feature to support CFD in this regard.

1. Partition cell

2. Assign seam

CEL SPH CFD

Solution discontinuities on either side of an immersed shell

53

Geometry and Mesh

SPH liquid can pass through a narrow channel

initial

final

• Capturing flow near small geometric details

• SPH does not require high mesh refinement around obstacles with small geometric details, nor within narrow passages

• CEL and CFD require a minimum of several elements across a passage to represent flow

• However, CEL can automatically refine and coarsen the mesh locally during the simulation to better capture small details and local behavior

Indentation (CEL) with automatic mesh refinement

CEL SPH CFD

Does not require high mesh refinement around obstacles with small geometric details

54

Geometry and Mesh

• Element conversion• SPH allows for conversion of continuum finite elements into SPH

particles• You define a finite element mesh using brick, wedge and

tetrahedron elements that can convert to SPH particles • Conversion can happen either at beginning of the analysis or

during the analysis based on some criterion• With CFD and CEL the nature of the mesh does not change during

the analysis

Continuum elements progressively converted to SPH particles as the specified maximum principal strain is reached in each element representing the bird

Bird

Engine blade

CEL SPH CFD

Element conversion

55

Geometry and Mesh

CEL fluid surface rendered

CFD cannot represent a fluid

material free surface

SPH fluid particles rendered

• Free surface visualization

• Choose CEL over CFD, and SPH when you need clear visualization of the fluid material free surface

CEL SPH CFD

Clearest definition of material free surface NA

56

• Heat transfer• CFD and CEL can simulate heat transfer in addition to

stress/displacement analyses

• Conduction and convection; radiation not currently supported

Analysis Type Considerations

Electronic circuit board exampleHeat transfer within a solid region interacts with surrounding fluid (CFD)


Temperature isosurfaces

Velocity vectors on intermediate plane

CEL SPH CFD

Heat transfer

57

Computational Considerations

• Accuracy• CEL and CFD deliver approximately the same level of accuracy for the

same level of mesh refinement

• When applied to deformation regimes amenable to the Lagrangian finite element and CEL methods, SPH may produce less accurate results

• SPH technique is effective in applications involving extreme deformations and fragmentation

Relative accuracy(generally speaking) CFD ≈ CEL≥ SPH

58

Computational Considerations

• Performance and computational cost

• CFD can use large time increments to run long-duration transient simulations

• CEL and SPH are limited to explicit time integration and relatively small time increments

• For a given computer resource (memory and CPU) CFD can have a much finer mesh than CEL

• The high computational cost of CEL simulations for problems with a small material-to-void ratio may require the use of SPH

• For example, tracking fragments from primary impact through a large volume until secondary impact occurs

CEL SPH CFD

Large time increments

Much finer mesh for a given computer resource NA

Better performance with small material-to-void ratio

NA

abaqus/multiphysics

Documents

multiphysics problems

fluid flow

simulation fsi

substructures interaction

abaqusexplicit sph

heattransfer techniques

dlogical models

analysis of aneurysms