ABAQUS/Multiphysics

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Multiphysics in Abaqus with Emphasis on Fluid Modeling Ramji Kamakoti Technical Specialist May 13, 2013

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

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 fluidstructure 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 5

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

Structure

Fluid

Displacement

Velocity

Temperature

Temperature

Electrical

Ink droplet formation and discharge from a piezoelectric inkjet printer nozzle 6

Fields

Fields

Pressure

Specialized FSI • Contact increases solution complexity and requires specialized analysis techniques. Contact Structure

Fluid

Displacement

Velocity

Temperature

Temperature

Electrical

Vacuum removal of paper trim

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Fields

Fields

Pressure

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SIMULIA Multiphysics

Overview of SIMULIA Multiphysics •

Multiphysics solutions offered by SIMULIA broadly falls into three different areas Abaqus Multiphysics • Native multiphysics capabilities available in Abaqus • Broad range of physics

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SIMULIA Multiphysics •

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

Abaqus Multiphysics

SPH

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

Extended Multiphysics • • • •

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

CFD

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SIMULIA Multiphysics •

Multiphysics solutions offered by SIMULIA broadly falls into three different areas SIMULIA Co-simulation Engine Abaqus Multiphysics Abaqus/ Structural

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

Abaqus/ CFD

Abaqus/ EM

Other codes

Extended Multiphysics • • • •

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

Abaqus 6.12

Abaqus 6.12

CSE

Abaqus/CFD 6.12

CSE

Star-CCM+ 7.02

Multiphysics Coupling • • • •

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

Abaqus 6.12

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MpCCI 4

Fluent 12

Abaqus Mulitphysics • Abaqus enables coupling of multiple fields Thermal-Electrical

Fuse

Ultrasonic motor

Piezoelectric

Thermal-Mechanical

Ball grid array

Bottle drop

Courtesy: Honeywell FM&T

Tire noise

Earthen Dam

Structural-pore fluid diffusion

Fluid-Mechanical 12

Structural-Acoustic

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

Coupled Eulerian-Lagrangian (CEL) Eulerian material definitions can interact with Lagrangian elements through contact in Abaqus/Explicit Multi-material finite element formulation (Volume-ofFluids method) tracks material boundary in Eulerian domain Interface interactions created using general contact definitions Automatic refinement of Eulerian elements improves accuracy and performance

Courtesy: JP Kenny 13

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

Courtesy of US Dept of Health 14

Abaqus/CFD – General purpose flow solver Incompressible pressure-based flow solver

Turbulence modeling Spalart-Allmaras k-epsilon ILES

Transient , Laminar and Turbulent flows, Heat transfer and Natural convection

Abaqus/CAE pre and post support

Superior and robust hybrid FV/FEM discretization

Native FSI capability

Robust and fast iterative solvers, AMG, GMRES, etc.

Arbitrary LagrangianEulerian (ALE) Fully parallel and scalable

2nd-order accurate in space and time

•

88% efficiency for fixedwork per processor at 64 cores

•

Mesh sizes limited only by pre and post capabilities

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Coupling with Abaqus/Standard and Abaqus/Explicit

Multiphysics Coupling

Co-simulation Engine (CSE)

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

SIMULIA Co-simulation Engine Abaqus/ Standard

Abaqus/ Explicit

Abaqus/ CFD

• Physics-based conservative mapping technology

Other CFD Codes

Star-CCM+

• Superior coupling technology

SIMULIA Direct Coupling

AcuSolve

• Currently in maintenance mode

Independent code coupling interface

Abaqus

• Enables Abaqus to couple directly to 3rd party codes

Star-CD

Flowvision

Other CFD codes

MpCCI

• Enabled through MpCCI from Fraunhofer SCAI • Allows coupling Abaqus with all codes supported by MpCCI

Abaqus

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Star-CD

Fluent

Other CFD codes

SIMULIA FSI Solutions • Several methods available to address diverse industry needs

Contact complexity at interface

Multiphysics Coupling

Coupled EulerianLagrangian (CEL)

Solenoid Valve

Structural solver

Fluid solver

Smoothed Particle Hydrodynamics (SPH)

SWAGELOK pressure regulator

Linear structures

Partitioned approach

SIMULIA FSI Solutions 17

Specialized techniques

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Abaqus/CFD

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 on submarine skin

Pressure contours

Submarine Aortic Aneurysm

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

2nd-order

Velocity contours

accurate projection method

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

Flow Around Obstacles (Vortex Shedding)

• 2nd-order accurate least squares gradient estimation • Implicit and explicit advection schemes • Unsteady RANS approach (URANS) for turbulent flows

Velocity vectors

Electronics Cooling (Buoyancy driven flow due to heated chips)

• 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

Substrate Inlet Pressure Outlet

porous media flow 20

Abaqus/CFD • Turbulence models • Spalart-Allmaras • RNG k-with wall functions • ILES (Implicit Large-Eddy Simulation)

Helicity isosurfaces

Prototype Car Body (Ahmed’s body)

• 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 21

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

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 Temperature isosurfaces

• Vector plots • Instantaneous particle traces

Velocity vectors on intermediate plane Temperature contours

Pressure contours Temperature contours

Velocity vectors 24

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Fluid-Structure Interaction

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

Structure

Fluid u f  us v f  u s

Displacement

Pressure

T f  Ts

Velocity

Heat Flux

σ f  n f  σs  ns

Temperature

q f  n f  qs  ns

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Fields

Fields

Traction

Survey of FSI Technology • Linear Structures Approach

Ma  Cv  Kd  F

• Linear solid/structural deformation

(K  i M )Si  0

• Eigenmodes sufficient to represent the dynamic behavior

i  1,..., nmodes

 + cy + ky = f my

• 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

Structural Solver

• Stabilizing terms required

  MU s s CU s s KsUs Fs  t

• Monolithic Approach

Us  ux uy uz 

Τ

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

Fluid Solver  A (V )V K V C p F  t Mf V f f f f f f f f f Kf  pf CTf Vf Vf vx vy vz

• Can avoid stability issues • Specialized Techniques • Coupled Eulerian-Lagrangian

Abaqus native FSI capability is based on a stabilized segregated approach 27

T

Native FSI Using Abaqus Coupling

Abaqus/Standard + Abaqus/CFD

Abaqus/Explicit + Abaqus/CFD

Fluid structure interaction (FSI) Conjugate heat-transfer (CHT)

Fluid-structure interaction

Conjugate heat transfer

Butterfly valve

Heat exchanger 28

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 Abaqus/ CFD

Co-Simulation Abaqus/ Standard

Abaqus/ Explicit

• Significantly expands the set of FSI applications that SIMULIA can address • Fluid-structure interaction • Also supports conjugate heat-transfer applications 29

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 timescales

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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

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 1• Lagrangian description: Nodes are

fixed within the material

Lagrangian formulation

• It is easy to track free surfaces and to apply boundary conditions. • The mesh will become distorted with high strain gradients. 33

Impact of a copper rod

Coupled Eulerian-Lagrangian (CEL) Approach 2 • 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

ALE formulation 34

Lagrangian formulation

Coupled Eulerian-Lagrangian (CEL) Approach 3 • 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 mesh

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

Eulerian formulation

rod material

Eulerian formulation 35

Lagrangian formulation ALE formulation

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.

Tub (Lagrangian)

Round object (Lagrangian)

Front-load washing machine

Water (Eulerian) 36

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

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

Water fall under gravity

Liquid spraying through a hose 39

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

SPH patch continuum solid projectile

Priming a Pump

Projectile impact 40

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. Particle Kernel function W(r)

Neighbors

• 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.

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Smoothed Particle Hydrodynamics (SPH) Approach • SPH in Abaqus • SPH analysis is an Abaqus/Explicit capability implemented for threedimensional models. • Any of the material models available in Abaqus/Explicit, including userdefined 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 42

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Comparison of CFD, CEL, and SPH

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 Compressible Compressibility



Nearly incompressible Incompressible 44

  

    





Material Considerations • Multiple materials • CEL can simulate multiple materials interacting air

water

SPH patch continuum solid projectile

sand

Multiple materials interacting (CEL)

Projectile impacting solid plate (SPH) CEL

SPH

CFD

Single material







Multiple materials interacting



Interactions via contact or FSI co-simulation







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Material Considerations • Special CFD capabilities

CEL

SPH

CFD

Turbulence modeling



Flows through porous media



• CFD can include turbulence modeling • CFD can model flows through porous media Substrate (porous media)

Inlet

Pressure contours Outlet

porous media flow (CFD) 46

Material Considerations

CEL Material inflow and outflow

• Material motion

SPH



CFD 

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

fluid inflow

fluid outflow fluid outflow

CFD Vortex Shedding behind a cylinder

fluid inflow CEL tire Hydroplaning 47

Material Considerations

CEL Material inflow and outflow

• Material motion

SPH



• 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

SPH Two-Lobe Cavity Pump: Water pushed while pump is rotating 48

CFD 

Material Considerations

CEL Inflators

• Inflators

SPH

CFD



• 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

Courtesy of TAKATA

CEL Side curtain airbag deployment Inflator injects gas into the air bag throughout the simulation 49

SPH inflation Long column of fluid pushed in

CEL

Contact Considerations

Mesh need not conform to surrounding structure

SPH

CFD



• 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 SPH particles inside structure

CEL structure moves through Eulerian mesh

CFD FSI CFD mesh conforms to structure 50

Contact Considerations

Contact interface topology can change

CEL

SPH





• 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

51

CFD

Contact Considerations

CEL

SPH

CFD





Solution discontinuities on either side of an immersed shell

• 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 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

Discontinuous streamlines and pressure contours in flow over a flexible flap in a converging channel (CFD/STD co-simulation)

1. Partition cell 52

Geometry and Mesh • Capturing flow near small geometric details

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

SPH

CFD



• 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

final

initial

SPH liquid can pass through a narrow channel

Indentation (CEL) with automatic mesh refinement 53

Geometry and Mesh

CEL Element conversion

SPH

CFD



• 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 Continuum elements progressively converted to SPH particles as the specified maximum principal strain is reached in each element representing the bird 54

Geometry and Mesh

CEL Clearest definition of material free surface



SPH

CFD NA

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

SPH fluid particles rendered

CEL fluid surface rendered 55

CFD cannot represent a fluid material free surface

Analysis Type Considerations

CEL Heat transfer

SPH



CFD 

• Heat transfer • CFD and CEL can simulate heat transfer in addition to stress/displacement analyses • Conduction and convection; radiation not currently supported

Temperature isosurfaces Velocity vectors on intermediate plane Temperature contours

Electronic circuit board example Heat transfer within a solid region interacts with surrounding fluid (CFD) 56

Computational Considerations

Relative accuracy (generally speaking)

CFD ≈ CEL≥ SPH

• 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

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Computational Considerations • Performance and computational cost • CFD can use large time increments to run long-duration transient simulations

CEL

SPH

Large time increments



Much finer mesh for a given computer resource

NA

Better performance with small material-to-void ratio



• 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 58

CFD

 NA

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