ABAQUS/Multiphysics

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3DS. CO M /SI MU LI A © Da ss au lt Sy st èm es | re f.: 3D S_ Do cu me nt _2 01 2

Ramji Kamakoti

Technical Specialist

May 13, 2013

Multiphysics in Abaqus with

Emphasis on Fluid Modeling

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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, …)

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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

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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 Pressure Velocity Temperature Structure Displacement Electrical Temperature Temperature Temperature Fields Fields Electrical

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Specialized FSI

• Contact increases solution complexity and requires specialized analysis techniques. Electrical Electrical Temperature Temperature Temperature Temperature Fluid Pressure Velocity Structure Displacement Fields Fields Contact

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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

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SIMULIA Multiphysics

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

Abaqus Multiphysics

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SIMULIA Multiphysics

• 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

CSE

Abaqus 6.12 Abaqus/CFD 6.12 Abaqus 6.12 CSE Star-CCM+ 7.02

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Abaqus Mulitphysics

• Abaqus enables coupling of multiple fields

Courtesy: Honeywell FM&T

Tire noise

Bottle drop Ultrasonic motor

Ball grid array

Earthen Dam

Thermal-Mechanical Structural-Acoustic

Piezoelectric

Fluid-Mechanical Structural-pore _{fluid diffusion}

Thermal-Electrical

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Coupled Eulerian-Lagrangian (CEL)

Courtesy: JP Kenny

Eulerian material definitions can interact with Lagrangian elements through contact in

Abaqus/Explicit

Multi-material finite element formulation (Volume-of-Fluids method) tracks material boundary in Eulerian domain

Interface interactions created using general contact definitions

Automatic refinement of Eulerian elements improves accuracy and performance

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Particle Methods: SPH

Mesh-free Lagrangian particles

Automatic conversion from conventional elements to SPH particles

Applications include ballistic impact with fragmentation, class of fluid problems

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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 modeling Spalart-Allmaras k-epsilon ILES Incompressible pressure-based flow solver Transient , 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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Multiphysics Coupling

• 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 Flowvision

Other 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+

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SIMULIA FSI Solutions

• Several methods available to address diverse industry needs

SIMULIA FSI Solutions

Contact complexity at interface Linear structures SWAGELOK pressure regulator Specialized techniques Coupled Eulerian-Lagrangian

(CEL) Smoothed Particle Hydrodynamics (SPH) Multiphysics Coupling 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

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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

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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 Temperature contours

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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 Traction Pressure 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 

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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

(

K





_i

M S

)

_i



0 i



1,...,

n

Structural Solver Fluid Solver

    ( ) f f f f f f f f f f T f f f f T f x y z p t K p v v v        M V A V V K V C F C V V 

 

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s s s s s s s s x y z K t u u u     MU CU U F U   Τ

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Native FSI Using Abaqus

Coupling Abaqus/Standard +

Abaqus/CFD

Abaqus/Explicit + Abaqus/CFD

Fluid structure interaction (FSI)

Conjugate heat-transfer (CHT)

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Native FSI Using Abaqus

• 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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Native FSI Using Abaqus

• 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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Native FSI Using Abaqus

• 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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Coupled Eulerian-Lagrangian (CEL) Approach

• 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

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Coupled Eulerian-Lagrangian (CEL) Approach

• 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.

ALE formulation

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Coupled Eulerian-Lagrangian (CEL) Approach

• 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

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Coupled Eulerian-Lagrangian (CEL) Approach

• 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

Tub (Lagrangian)

Round object (Lagrangian)

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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

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Smoothed Particle Hydrodynamics

(SPH) Approach

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Smoothed Particle Hydrodynamics (SPH) Approach

• 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 hose Water fall under gravity

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Smoothed Particle Hydrodynamics (SPH) Approach

• 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 Pump

continuum solid projectile

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Smoothed Particle Hydrodynamics (SPH) Approach

• 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

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Smoothed Particle Hydrodynamics (SPH) Approach

• 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

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Comparison of

CFD, CEL, and SPH

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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 Type Solids isotropic



anisotropic



Fluids



Compressibility Compressible



Nearly incompressible



Incompressible



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Material Considerations

• 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 

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Material Considerations

• 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 

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• Material motion

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

Material Considerations

CEL tire Hydroplaning fluid outflow fluid inflow CFD

Vortex Shedding behind a cylinder

fluid inflow

fluid outflow

CEL SPH CFD

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Material Considerations

SPH

• 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

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• 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

Material Considerations

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

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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 CFD FSI

SPH

particles inside structure

CEL SPH CFD

Mesh need not conform

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Contact Considerations

• 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 _{Grease filled CV joint}SPH

CEL SPH CFD

Contact interface

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Contact Considerations

• 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.

2. Assign seam

CEL SPH CFD

Solution discontinuities on either

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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

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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

Bird

Engine blade

CEL SPH CFD

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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

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• 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 example

Heat transfer within a solid region interacts with surrounding fluid (CFD)

Temperature contours

Temperature isosurfaces Velocity vectors on intermediate plane

CEL SPH CFD

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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

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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

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