fluid structure interaction manual

FLUENT 6.3

Fluid-Structure Interaction (FSI)

Module Manual

September 2006

Copyright c 2006 by Fluent Inc.All Rights Reserved. No part of this document may be reproduced or otherwise used in

any form without express written permission from Fluent Inc.

Airpak, FIDAP, FLUENT, FLUENT for CATIA V5, FloWizard, GAMBIT, Icemax, Icepak,Icepro, Icewave, Icechip, MixSim, and POLYFLOW are registered trademarks of FluentInc. All other products or name brands are trademarks of their respective holders.

CHEMKIN is a registered trademark of Reaction Design Inc.

Portions of this program include material copyrighted by PathScale Corporation2003-2004.

Fluent Inc.Centerra Resource Park

10 Cavendish CourtLebanon, NH 03766

Contents

1 Introduction 1-1

2 The Fluid-Structure Interaction (FSI) Software Suite 2-1

2.1 An Overview of FLUENT, FEA Software, and MpCCI . . . . . . . . . . . 2-1

2.2 Capabilities of the FSI Suite . . . . . . . . . . . . . . . . . . . . . . . . . 2-2

2.3 Limitations of the FSI Suite . . . . . . . . . . . . . . . . . . . . . . . . . 2-2

2.4 FSI Package Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . 2-2

2.4.1 Licensing Requirements . . . . . . . . . . . . . . . . . . . . . . . 2-2

2.4.2 Hardware Requirements . . . . . . . . . . . . . . . . . . . . . . . 2-3

2.5 Installing the FSI Software Suite . . . . . . . . . . . . . . . . . . . . . . 2-3

2.6 Workflow for Solving an FSI Problem . . . . . . . . . . . . . . . . . . . . 2-4

3 Workflow and Coupling Schemes For an FSI Problem 3-1

3.1 Important Considerations Prior to Solving an FSI Problem . . . . . . . . 3-1

3.2 Coupling and Rendezvousing Schemes . . . . . . . . . . . . . . . . . . . 3-2

3.2.1 Coupling Schemes . . . . . . . . . . . . . . . . . . . . . . . . . . 3-3

3.2.2 Rendezvousing Schemes . . . . . . . . . . . . . . . . . . . . . . . 3-9

4 Using the MpCCI User Interface 4-1

4.1 MpCCI Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-1

4.2 The MpCCI User Interface . . . . . . . . . . . . . . . . . . . . . . . . . 4-2

4.2.1 Starting and Exiting the MpCCI GUI . . . . . . . . . . . . . . . 4-2

4.2.2 Components of MpCCIs Main Window . . . . . . . . . . . . . . 4-4

4.2.3 Other MpCCI GUI Components . . . . . . . . . . . . . . . . . . 4-6

c Fluent Inc. November 7, 2006 i

CONTENTS

4.3 Problem Setup Using the MpCCI User Interface . . . . . . . . . . . . . . 4-8

4.3.1 The Models Panel . . . . . . . . . . . . . . . . . . . . . . . . . . 4-11

4.3.2 The Coupling Panel . . . . . . . . . . . . . . . . . . . . . . . . . 4-14

4.3.3 The Edit Panel . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-21

4.3.4 The Go Panel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-22

4.3.5 Terminating the Coupled Simulation . . . . . . . . . . . . . . . . 4-24

4.4 Running the simulation interactively from FLUENT . . . . . . . . . . . . 4-24

4.5 Solution Strategies For an FSI Problem . . . . . . . . . . . . . . . . . . 4-26

4.5.1 Local Convergence . . . . . . . . . . . . . . . . . . . . . . . . . . 4-26

4.5.2 Global Convergence . . . . . . . . . . . . . . . . . . . . . . . . . 4-26

4.6 Postprocessing an FSI Problem . . . . . . . . . . . . . . . . . . . . . . . 4-27

4.6.1 Postprocessing Using ABAQUS/CAE . . . . . . . . . . . . . . . . 4-27

4.6.2 Postprocessing Using FLUENT . . . . . . . . . . . . . . . . . . . 4-27

4.6.3 Postprocessing Using MpCCI . . . . . . . . . . . . . . . . . . . . 4-27

4.6.4 Combined Fluid and Structure Postprocessing . . . . . . . . . . 4-27

A Starting MpCCI Code Coupling Between ABAQUS and FLUENT A-1

B Restarting MpCCI Code Coupling Between ABAQUS and FLUENT B-1

B.1 Creating the Restart Session . . . . . . . . . . . . . . . . . . . . . . . . . B-2

ii c Fluent Inc. November 7, 2006

Using This Manual

About This Manual

The FLUENT Fluid-Structure Interaction (FSI) Module Manual tells you what you needto know to model fluid-structure interaction with FLUENT. In this manual, you willfind background information pertaining to the feature, a theoretical discussion, and adescription of using the feature for your simulations.

Technical Support

If you encounter difficulties during your FSI simulation, please first refer to the section(s)of the manual containing information on the commands you are trying to use or the typeof problem you are trying to solve. The product documentation is available on the FluentInc. User Services Center (www.fluentusers.com).

If you encounter an error, please write down the exact error message that appeared andnote as much information as you can about what you were doing. Then refer to the follow-ing resources available on the Fluent Inc. User Services Center (www.fluentusers.com):

Installation and System FAQs - link available from the main page on the UserServices Center. The FAQs can be searched by word or phrase, and are availablefor general installation questions as well as for products.

Known defects for FLUENT - link available from the product page. The defects canbe searched by word or phrase, and are listed by categories.

Online Technical Support - link available from the main page on the User ServicesCenter. From the Online Technical Support Portal page, there is a link to theSearch Solutions & Request Support page, where the solutions can be searched byword or phrase.

The User Services Center also provides online forums, where you can discuss topics ofmutual interest and share ideas and information with other Fluent users, and the abilityto sign up for e-mail notifications on our latest product releases.

c Fluent Inc. November 7, 2006 UTM-1

Using This Manual

Contacting Technical Support

If none of the resources available on the User Services Center help in resolving the prob-lem, or you have complex modeling projects, we invite you to call your support engineerfor assistance. However, there are a few things that we encourage you to do before calling:

Note what you are trying to accomplish with FLUENT.

Note what you were doing when the problem or error occurred.

Save a journal or transcript file of the FLUENT session in which the problem oc-curred. This is the best source that we can use to reproduce the problem andthereby help to identify the cause.

UTM-2 c Fluent Inc. November 7, 2006

Chapter 1. Introduction

This manual contains information about solving fluid-structure interaction (FSI) prob-lems using FLUENTs computational fluid dynamics (CFD) software to solve the fluiddomain, and finite element analysis (FEA) software capabilities for solving the structuraldomain.

The types of problems you may encounter that require solutions to fluid and structuraldomains include, but are not limited to, heat exchange in a radiator, thermal stressesin a pipe, motion of a divers flippers in water, aeroelasticity in the aerospace industry(such as fluid-structure interaction in multi-blade rotorcraft), and hydroelasticity withrespect to marine structures.

The coupling of the FEA code and FLUENT is achieved using the Mesh-based parallelCode Coupling Interface (MpCCI), which is an interprocess communication software thattransfers solution data from the structural domain to the fluid domain and vice versa.This three-way coupling of the FEA code, FLUENT, and MpCCI will be referred toas the FSI Software Suite. In the chapters to come you will be introduced to theFSI software suite in greater detail. Chapter 2: The Fluid-Structure Interaction (FSI)Software Suite provides background information and requirements necessary for runningan FSI simulation. Chapter 3: Workflow and Coupling Schemes For an FSI Problemsummarizes the various solution approaches. Chapter 4: Using the MpCCI User Interfaceprovides instructions for setting up and running an FSI simulation, as well as solutionstrategies, convergence criteria, and postprocessing descriptions.

This coupling of fluid and structure code can be utilized by companies or individualscurrently experienced with both FEA and CFD. A sound knowledge of the physics usedin computational fluid dynamics and structural mechanics is necessary when performingFSI simulations.

c Fluent Inc. November 7, 2006 1-1

Introduction

1-2 c Fluent Inc. November 7, 2006

Chapter 2. The Fluid-Structure Interaction (FSI) SoftwareSuite

The FSI software suite consists of two analysis components and one coupling component.This chapter contains the following sections:

Section 2.1: An Overview of FLUENT, FEA Software, and MpCCI

Section 2.2: Capabilities of the FSI Suite

Section 2.3: Limitations of the FSI Suite

Section 2.4: FSI Package Requirements

Section 2.5: Installing the FSI Software Suite

Section 2.6: Workflow for Solving an FSI Problem

2.1 An Overview of FLUENT, FEA Software, and MpCCI

FLUENT is a computational fluid dynamics software used for simulation, visualization,and analysis of fluid flow, heat and mass transfer, and chemical reactions. Informationabout FLUENT features are described in the FLUENT Users Guide and can be found atthe FLUENT User Services Center (www.fluentusers.com).

The FEA code is a finite element analysis software used to solve linear and non-linear,explicit and multi-body dynamics problems. Contact the FEA software company forinformation about the capabilities of their product.

The Mesh-based parallel Code Coupling Interface (MpCCI) is a software interface thatallows the transfer of data between the meshes of simulation codes that are in the couplingregion. It is through this interface that data can be exchanged between two or moredifferent simulation codes, that are otherwise generally incompatible. The MpCCI userinterface provides you with a means to easily define the coupling setup and to start thesimulation of the two codes. The MpCCI coupling server controls the communication ofthe codes and performs interpolations. It is through MpCCI that adaptive time steppingis controlled. Information about MpCCI, including installation and setup, can be foundin the MpCCI documentation at www.scai.fhg.de .

i Note that MpCCI couples the FEA code and FLUENT using the staggeredapproach, where structural and fluid equations are solved separately. Loadsand boundary conditions are exchanged after each converged increment.


The Fluid-Structure Interaction (FSI) Software Suite

2.2 Capabilities of the FSI Suite

The FSI software suite is capable of solving fluid-structure interaction cases that areeither steady-state or transient, and involve mechanical and/or thermal changes at thestructure/fluid interface. The FEA code and FLUENT solvers run simultaneously withforce and displacement data shared implicitly at each time step. Dynamic mesh forsteady state applications is advantageous in the realm of FSI.

2.3 Limitations of the FSI Suite

Some of the limitations of the FSI software suite may be due to geometric incompatibil-ities, material failure and other material properties. Limitations of the FSI suite includethe following:

Vibroacoustic applications cannot be solved using the staggered (also known asright-hand side) approach, where the structural and fluid equations are solvedindependently.

Structures whose designs include trusses, rods, cables, or beams cannot be solvedaccurately. Such designs cause inconsistencies between the structure and fluid ge-ometries during discretization.

A fluid-structure interface that is changing and deforming (such as casting or in-jection molding) cannot be solved using FSI processes.

Material failure such as rupture or fragmentation, resulting in a changing fluiddomain will not be solved.

Poroelastic media do not have distinct fluid-structure interfaces and therefore can-not be solved.

2.4 FSI Package Requirements

To correctly setup the FSI package, you will require the corresponding software andsoftware licenses. You will also need to meet specific hardware requirements prior toinstalling the FSI suite which includes the FEA software, FLUENT, and MpCCI.

2.4.1 Licensing Requirements

To run the FSI package, you will need a software license for the FEA software, FLUENT,and MpCCI. The three codes are managed by FLEXlm licensing (www.macrovision.com).


2.5 Installing the FSI Software Suite

2.4.2 Hardware Requirements

The FEA code, FLUENT, and MpCCI will run on all platforms that are supported by allthree.

FLUENT supported platforms can be found at the User Services Center (www.fluentusers.com).Click on Fluent 6 under Product Information and click on the supported platforms link.

MpCCI code and platform support can be found at www.scai.fraunhofer.de/mpcci.htmlin the release notes, obtained by clicking the Manuals link.

i Note that the FEA code and FLUENT can run on different platforms duringa co-simulation.

Message Passing Interface (MPI/MPICH)

For Windows platforms, you must install the free package MPICH, available at http://www-unix.mcs.anl.gov/mpi/mpich.

Secure shell

Remote shell (rsh) or secure shell (ssh) is required only when performing simulationsacross multiple platforms. For most UNIX/Linux platforms, rsh and ssh are available.For Windows platforms, use the free OpenSSH package, available athttp://sshwindows.sourceforge.net/download .

2.5 Installing the FSI Software Suite

The FEA code, FLUENT, and MpCCI can be installed in any order. However, Perl, Java,and MPICH (on Windows) should be installed prior to installing MpCCI.

i It is recommended that you install, configure, and verify each softwarecomponent before installing the next software component which may be aprerequisite for the other software components.



2.6 Workflow for Solving an FSI Problem

The flowchart in Figure 2.6.1 summarizes the recommended workflow for solving FSIproblems. Solving FSI problems involves the coupling of the FEA code and FLUENTusing MpCCIs adapter capabilities and graphical user interface (GUI).

Install the FSI Software Suite

Structural Model Fluid ModelRun FLUENTonly

Verify Proper Solution andConvergence in FLUENTVerify Proper Solution and

Use MpCCI GUI to Connect

Use MpCCI GUI to RunCoupled Solution

Determine the Coupling and Rendezvous Schemes

Run FEAonly

Convergence in the FEA Code

FLUENT and the FEA Code

Figure 2.6.1: Workflow for Solving an FSI Problem

1. Set up the FEA-only model.

Identify the fluid-structure interfaces. Place the interface boundary between domains at the same spatial location in

each model.

Define the interface by specifying a surface in FEA/CAE or by using the*SURFACE option to create an element-based surface representing the fluid-structure interface. Underlying elements can be continuum, shells, and mem-brane elements.


2.6 Workflow for Solving an FSI Problem

i Two-dimensional second-order continuum elements and modified tetrahe-dral/triangles are not supported due to limitations with the current map-ping schemes.

Verify the FEA-only model using assumed pressure/heat flux loads at theinterface.

Apply pressure/heat flux load magnitudes that are reasonable and similar tothe expected fluid loads.

2. Set up the FLUENT -only model.

Define wall zones to identify the fluid-structure interface. Verify the FLUENT-only model by prescribing temperatures at the interface

wall and/or moving the interface wall. The temperature field should be similarto the expected wall (solid) temperature.

3. Interconnect the FEA and FLUENT models for the co-simulation.

Delete the assumed loads. Rename FSI interfaces in FLUENT as a moving deforming mesh (MDM) user-

defined type.

Use the MpCCI GUI for the remaining problem setup.

Details involving the steps illustrated in the flow chart (Figure 2.6.1) can be found in thefollowing sections:

Installing the FSI suite, go to Section 2.5: Installing the FSI Software Suite.

Running the structural model and fluid model independently with considerationsmade to code coupling, see Section 3.1: Important Considerations Prior to Solvingan FSI Problem to prepare your codes for coupling.

Determining the coupling and rendezvousing schemes (Section 3.2: Coupling andRendezvousing Schemes).

Interconnecting the FEA and FLUENT models using the MpCCI GUI (Section 4.3: Prob-lem Setup Using the MpCCI User Interface).

Running the coupled simulation using the MpCCI GUI (Section 4.3.4: The GoPanel).


Chapter 3. Workflow and Coupling Schemes For an FSIProblem

Implicit solvers in FEA and FLUENT solvers can be used to solve most steady-stateor transient FSI problems. The FEA explicit solver is recommended for flexible typeproblems with non-linear interactions and post-failure simulations. The explicit solver inFLUENT should be used in situations where the flow speed is very high and the flow iscompressible, as well as for rapidly moving shocks. The following sections discuss modelconsiderations and determination of how data will be exchanged and the frequency atwhich it should be transferred.

Section 3.1: Important Considerations Prior to Solving an FSI Problem

Section 3.2: Coupling and Rendezvousing Schemes

3.1 Important Considerations Prior to Solving an FSI Problem

Prior to coupling your structural and fluid models, consider the following checklist:

1. Verify that your structural model is running properly:

Check the form of the units used. The fluid-structure interface must be identified. The assumed pressure/heat flux loads at the fluid-structure interface should

have magnitudes that are comparable to the expected fluid loads.

2. Check your fluid model for proper convergence and solution. Your FLUENT modelshould be set up such that:

Wall zones are defined as a fluid-structure interface. A temperature is applied at the interface wall that is comparable to the ex-

pected structural conditions.


Workflow and Coupling Schemes For an FSI Problem

3. The FEA model will update the geometry through MpCCI once the following havebeen completed:

Remove the assumed load from the structural model. Remove the boundary condition from the fluid model. Rename the fluid-structure interface as an MDM user-defined function.

4. The final step prior to running your FSI case is to couple the structural and fluidcode using the MpCCI graphical user interface (GUI), as discussed in Chapter 4: Us-ing the MpCCI User Interface.

The frequency and the method of transferring data is done through coupling of thetwo codes. There are several sequences in which to transfer data. These schemes areoften referred to as coupling and rendezvousing schemes (see Section 3.2: Coupling andRendezvousing Schemes).

3.2 Coupling and Rendezvousing Schemes

Determining which coupling and rendezvousing scheme, depends on your problem defi-nition. Different schemes may be used for steady-state or transient problems, whetheryou selected an implicit or explicit solver, or if you are running your solution in serialor parallel. Depending on the coupling method chosen, data will be transferred at aspecific location when the coupled FEA and FLUENT simulation is suspended. This lo-cation is known as the synchronization point. In a bidirectional coupled simulation, thesynchronization point is when the solution time is identical for both analyses.

For example, the synchronization point in ABAQUS/Standard (FEA) is where data isexchanged at the end of a converged increment, when the target or rendezvous time isreached. In ABAQUS/Standard, the target time can be reached in either a loose or anexact manner. In ABAQUS/Explicit, the data is exchanged at the end of an incrementwhen the target time is reached. The target time is reached in a loose manner only(described in more detail in Section 3.2.2: Rendezvousing Schemes).

In FLUENT, the synchronization point is either at the beginning of the time step or atthe end of a time step. This is specified using function hooks defined in the MpCCI GUI.When FLUENT is run interactively, the transfer function is called in an unsynchronizedmanner. When FLUENT is run in batch mode, the transfer function is called in a syn-chronous manner and can be called either at the end of a completed time step, or at thebeginning of each time step, before the mesh motion routine is called.



3.2.1 Coupling Schemes

Coupling occurs through a common interface, where the surfaces in the FEA model definethe solid interface region and the zones in FLUENT define the fluid interface region.MpCCI maps the solution at the interface and at the incongruent interface mesh in thestructure and fluid codes.

Two coupling schemes exist: serial and parallel coupling. Serial or parallel coupling canbe performed depending on whether the implicit time integration is used for the transientsolver. Certain considerations have to be made before selecting your coupling scheme.For example, computer resources may be inefficient when running in serial, therefore itmay make more sense to run in parallel.

Serial Coupling

Serial coupling uses a Gauss-Seidel algorithm: while one code runs, the other code waits.When using serial coupling, the following assumptions must be made:

Bidirectional coupling is between two implicit solvers.

FLUENT uses the transient solver.

In the initial exchange of information, FLUENT sends data and the FEA modelreceives data.

The synchronization point is defined after the solver pass, at which time transferof quantities occurs.

Figure 3.2.1 illustrates how data is exchanged during serial coupling, the following stepsmust occur in the presented order. In the illustrations, FLUENT is assumed to be thesimulation leader with the FEA model (in this case ABAQUS) lagging by one couplingstep.



Step 1: Initializing the Solution

MpCCI

MpCCI

MpCCI

MpCCI

MpCCI

t t t t0 2 41 3t

FLUENT

ABAQUS

(a)

(b) (c)

Figure 3.2.1: Initializing the Solution

(a) FLUENT sends mesh and coupling information to MpCCI.

(b) ABAQUS sends mesh and coupling information to MpCCI.

(c) ABAQUS advances to t1, the first synchronization point, and waits to receive data.No co-simulations of loads occurs at this point.

Step 2a: Initial Coupling

MpCCI

MpCCI

MpCCI

MpCCI

MpCCI

t t t t0 2 41 3t

FLUENT

ABAQUS

(c)

(a)

(b)

Figure 3.2.2: Initial Coupling

(a) ABAQUS waits at t1 to receive data from FLUENT.

(b) FLUENT computes and advances solution to t1 based on FLUENT-only boundarycondition and loads introduced at t0.

(c) FLUENT sends solution data to ABAQUS and waits at t1.



Step 2b: Final Coupling

MpCCI

MpCCI

MpCCI

MpCCI

MpCCI

t t t t0 2 41 3t

FLUENT

ABAQUS

(a)

(b) (d)

(c)

Figure 3.2.3: Final Coupling

(a) FLUENT waits at t1 to receive data from ABAQUS.

(b) ABAQUS receives co-simulation loads from FLUENT at t1.

(c) ABAQUS computes and advances solution to t2.

(d) ABAQUS sends solution data to FLUENT and waits at t2.

Step 3a: Initial Coupling

MpCCI

MpCCI

MpCCI

MpCCI

MpCCI

t t t t0 2 41 3t

FLUENT

ABAQUS(a)

(d)

(b)

(c)

Figure 3.2.4: Initial Coupling

(a) ABAQUS waits at t2 to receive data from FLUENT.

(b) FLUENT receives interface boundary condition data from ABAQUS at t2 based onco-simulation load information applied at t1 in ABAQUS.

(c) FLUENT computes and advances solution to t2 based on FLUENT-only boundarycondition and loads introduced at t0.

(d) FLUENT sends solution data to ABAQUS and waits at t2.



Step 3b: Final Coupling

MpCCI

MpCCI

MpCCI

MpCCI

MpCCI

t t t t0 2 41 3t

FLUENT

ABAQUS

(d)(b)

(a)

(c)

Figure 3.2.5: Final Coupling

(a) FLUENT waits at t2 to receive data from ABAQUS.

(b) ABAQUS receives co-simulation loads from FLUENT at t2.

(c) ABAQUS computes and advances solution to t3.

(d) ABAQUS sends solution data to FLUENT and waits at t3.

The process is repeated until the total step time or solution time is reached. Note thatat the end of the step when the total solution time is reached, no data exchange occurs,as indicated in Figure 3.2.6.

MpCCI

MpCCI

MpCCI

MpCCI

MpCCI

t t t t0 2 41 3t

FLUENT

ABAQUSt n

Figure 3.2.6: Overall Sequence of Steps During Serial Coupling



Parallel Coupling

The parallel coupling scheme uses the Jacobi algorithm, where both codes run concur-rently, exchanging data from the previous transfer of information to update the solutionat the next target time. Parallel coupling generally makes more efficient use of computerresources by not having any one code wait while the other code runs.

Parallel coupling is a globally explicit algorithm and the sequence of solution advancementand exchanges between the two codes occurs as follows:

Step 1: Initializing the Solution

MpCCI

MpCCI

MpCCI

MpCCI

MpCCI

t t t t0 2 41 3t

FLUENT

ABAQUS

(a)

(a)(b)

(b)

(c)

Figure 3.2.7: Initializing the Solution

(a) ABAQUS and FLUENT send mesh and coupling information to MpCCI.

(b) ABAQUS and FLUENT compute and advance their solutions to t1 based on thefluid-only and structural-only loads and boundary conditions applied at t0.

(c) ABAQUS and FLUENT exchange solution data with one another at t1 and wait toreceive information from each other.



Step 2: Advancing the Solution

MpCCI

MpCCI

MpCCI

MpCCI

MpCCI

t t t t0 2 41 3t

FLUENT

ABAQUS

(b)

(a)

(a)

Figure 3.2.8: Advancing the Solution

(a) FLUENT computes and advances solutions to t2 based on interface displacementsreceived at t1.

(a) ABAQUS computes and advances solutions to t2 based on co-simulation loads re-ceived at t1.

(b) ABAQUS and FLUENT exchange solution data at ts and wait to receive informationfrom each other.

The process is repeated for the total step time. Similar to serial coupling, no dataexchange occurs at the end of the step when the total solution time is reached.

Implicit Versus Explicit Time Integration

Both ABAQUS and FLUENT support implicit and explicit solvers. Therefore, the fourviable coupling schemes are:

Explicit-Explicit Coupling: Use parallel coupling. The response at the successivetime steps is determined based on the previous coupling (see Section 3.2.1: ParallelCoupling).

Implicit-Implicit Coupling: Use serial coupling, forcing one code to lag and theother code to lead by one coupling step. It is recommended that the structuralcode lead the simulation giving precedence to displacement consistency over loadconsistency (see Section 3.2.1: Serial Coupling).

Explicit-Implicit or Implicit-Explicit coupling: Use serial coupling. The explicitcode will be the simulation leader. The explicit code calculates the solution at tn+1based on the solution at tn and passes the forcing function to the implicit codewhich computes the solution at tn+1 (see Section 3.2.1: Serial Coupling).



3.2.2 Rendezvousing Schemes

The rendezvousing scheme determines the frequency of data exchange. Depending on thescheme used, the accuracy of your solution and computational costs for transient casesmay be affected.

The rendezvousing scheme allows for data exchange at predetermined simulation times.Instead of coupling times to control data exchange frequency, ABAQUS and FLUENT usethe following time-stepping scheme:

ti+1 = ti + tc (3.2-1)

where tc is a coupling step size that is a constant, with identical values in FLUENT andABAQUS. It determines the frequency of data exchange and is initially set to the initialtime increment of ABAQUS.

Data exchange can occur in an exact manner, or loosely when automatic time incremen-tation or subcycling is used for ABAQUS. When meeting the target time in an exactmanner, ABAQUS/Standard will temporarily cut back the increment to meet the targettime. This is the default for ABAQUS/Standard. In other words, ABAQUS/Standardensures that the exchange occurs when the time increment is equal to the target time.

ABAQUS/Explicit exchanges data loosely. ABAQUS will do the data transfer if thetarget time has been reached or exceeded, or if the solution time is within half of thetime increment size from the suggested target time.

i Note that for steady-state flow problems, time is not a meaningful function.Therefore the aforementioned coupling times and rendezvousing schemesare a reflection of the computational step at which solution quantities aretransferred.

To have the density-based Coupled Explicit Solver with Explicit Timestepping (CESET)iterate to regular time intervals during the rendezvous cycle, a text command can beinvoked that will result in the user controlling the timestep of the CESET. In general,the CESET is controlled locally by the minimum Courant number. To find out about thiscommand, contact your support engineer.


Chapter 4. Using the MpCCI User Interface

MpCCI is the software environment that will enable the exchange of data between themeshes of two or more simulation codes, each specialized for specific physical regimes. Atthe start of the coupled simulation, the FEA code, ABAQUS, and the CFD code, FLUENT,send their interface meshes to the MpCCI server. MpCCI performs a neighborhoodsearch to determine how the coupling regions fit together and computes the mappingsbetween ABAQUS and FLUENT interface meshes. During the coupled simulation, eachdomain is computed independently by ABAQUS and FLUENT, only the interface loadsand boundary conditions are exchanged.

This chapter provides basic instructions to set up the coupling of FLUENT with ABAQUSusing the MpCCI user interface. It assumes that you are already familiar with FLUENTand/or ABAQUS.

Section 4.1: MpCCI Overview

Section 4.2: The MpCCI User Interface

Section 4.3: Problem Setup Using the MpCCI User Interface

Section 4.5: Solution Strategies For an FSI Problem

Section 4.6: Postprocessing an FSI Problem

4.1 MpCCI Overview

The MpCCI architecture comprises the following components:

MpCCI Code AdapterThe adapter allows MpCCI to adapt to other commercial codes through the stan-dard MpCCI code application programming interfaces without any change to thesource codes of the simulations.

MpCCI User InterfaceThe graphical user interface (GUI) enables the user to easily set up the couplingand to start the simulation. This is discussed in detail in Section 4.2: The MpCCIUser Interface

MpCCI Coupling ServerThe server is the main processing unit of the MpCCI system. It handles the com-munication between codes and the transfer and interpolation of data.


Using the MpCCI User Interface

4.2 The MpCCI User Interface

4.2.1 Starting and Exiting the MpCCI GUI

Starting the MpCCI GUI

Before creating a coupled simulation project, make sure you start from a directory whereyou have read/write permission of files. When the MpCCI GUI is started, a set of filesis generated which define the coupled simulation model, e.g. the MpCCI input file andMpCCI log files.

To obtain information about available subcommands and startup options, type mpcci-help on the command line. The following will be displayed on you screen:

Usage:

mpcci SUBCMD [OPTIONS] [ARGS] [HELPKEY] ...

Synopsis:

mpcci is the root for all MpCCI related commands. You need

to specify at least one subcommand (SUBCMD) on the commandline.

SUBCMD, OPTIONS (not file name ARGS!) may be typed in lowercase

or UPPERCASE letters or may even be abbreviated as long as there

is no ambiguity.

Since the command and help system is dynamically configured at

runtime some SUBCMDS and OPTIONS may not always appear in the list

below or may suddenly become ambiguous as they are activated only

under certain circumstances (existing file/installation etc.)

If you use mpcci in scripts you should never use the

abbreviated form of SUBCMD or OPTION.

You get online help for most of the SUBCMDS and OPTIONS if the

HELPKEY ([-]help, [-/]? ...) appears on the commandline.

Please type either

"mpcci SUBCMD HELPKEY" or

"mpcci HELPKEY SUBCMD"

to get more detailed help on the subcommands.



Subcommands:

ABAQUS Tools related to ABAQUS.

ANSYS Tools related to ANSYS.

FLUENT Tools related to FLUENT.

IcePak Tools related to IcePak.

MSC.Marc Tools related to MSC.Marc.

arch [-n] Print the MpCCI architecture without a newline or

with a newline [-n] at the end and exit. This is in

fact a shortcut for "mpcci info arch".

batch Start an MpCCI batch job with project file .

clean Remove all files from the temporary MpCCI directory

"C:\Documents and Settings\msh\.mpcci\tmp".

doc View the MpCCI documentation.

env Print out the environment used by MpCCI in various

formats for further processing.

gui Launch the MpCCI GUI.

help This screen.

home [-n] Print the MpCCI home directory without a newline or

with a newline [-n] at the end and exit. This is in

fact a shortcut for "mpcci info home".

info Print general information about MpCCI.

kill Platform independent process kill based on command

line pattern matching.

license Manage the license server and print license related

information.

list List information about the MpCCI installation and

the supported codes.

lmutil Run the FlexLM "lmutil [OPTIONS]" command

delivered with MpCCI. Avoid running the lmutil

command installed by codes other than MpCCI.

observe Start the MpCCI file observer.

playback Create a C source from an MpCCI debuglevel-3 logfile.

pm Launch the MpCCI project manager.

ps Unix "ps -ef" compatible ps for all platforms.

ptoi Convert an MpCCI project file into an MpCCI input file.

server Start the MpCCI server and control processes.

ssh Check/fix your ssh installation.

test Run some install/communication tests.

top Launch the taskmanager.

vis Launch the MpCCI visualizer.

where Find all locations of the executable in the PATH.

xterm Start a process inside an xterm.



To start the MpCCI GUI, type mpcci -gui on the command line.

Exiting the MpCCI GUI

To exit the MpCCI GUI session at any time, select File Exit from the main menu bar.If changes were made to the current coupled simulation project, MpCCI will ask you ifyou want to save the changes before exiting the session. The MpCCI GUI will then closethe current coupled simulation project file and exit the session.

4.2.2 Components of MpCCIs Main Window

The components of the main window are described below to familiarize you with theMpCCI GUI. While you can customize the components of the main window, customizingthe MpCCI GUI is beyond the scope of this manual. Figure 4.2.1 shows the componentsthat appear in the main window.

In the main window, you will find the following:

Title barThe title bar indicates the version of MpCCI you are running and the currentopened module.

Menu barThe menu bar contains the File and Help menus.

Navigation barThe navigation bar allows you to proceed to the Next or return to the previousPrevious module step.

The Menu Bar

When starting a session, the menu items that appear on the main menu bar are:

FileThe items in the File menu allow you to create a new project, open an existingproject, save and exit a coupled simulation project. The file types you can expectto encounter are *.csp files, which stands for coupled simulation project files.

HelpThe items in the Help menu allow you to request help and to get information aboutthe MpCCI GUI. Help Contents display a new window with information aboutthe MpCCI GUI. The About option under the Help menu displays the productinformation and third party products integrated in the MpCCI GUI.



Figure 4.2.1: The Main Window when Starting MpCCI

Figure 4.2.2: The Contents of the File Menu



Navigation Tools

When setting up a coupled simulation, you will need to progress from one panel to thenext and back. To do so, you have to use the navigation buttons on the bottom of theMpCCI GUI. Three buttons may be displayed depending on which step you are on. Referto Section 4.3: Problem Setup Using the MpCCI User Interface to follow the module stepsto successfully start your simulation computation.

Previous allows you to go to the previous panel.

Next: displays the next panel.

Undo: resets the panel entries to the default values in the panel.

Figure 4.2.3: The Navigation Tools at the Bottom of the Main Window

i During the setup, if you are modifying inputs in a previous panel, be sureto check the settings of the next panel as it may have affected some of theparameters.

4.2.3 Other MpCCI GUI Components

Dialog windows

In the MpCCI GUI, all information coming from external applications is displayed in apop up window. The types of dialog windows you may encounter are information windows(Figure 4.2.4) and error windows (Figure 4.2.5). The information window shows the resultor output of the application. The error information window displays errors related to theapplication configuration or setup.

For details on all other window components such as buttons, check boxes, radio buttons,text entry and number entry fields, and dropdown lists, refer to the FLUENT UsersGuide.



Figure 4.2.4: The Information Window

Figure 4.2.5: The Error Window



4.3 Problem Setup Using the MpCCI User Interface

Start with ABAQUS-only and FLUENT-only models with the assumed interface loadsremoved. Make sure the models are geometrically congruent and are co-located. ABAQUSand FLUENT files need to be stored in separate directories to ensure that the client codesdo not overwrite existing files with identical file names that are used by client codes.

The MpCCI graphical user interface (GUI) guides the user through several steps towardsrunning a coupled simulation. The sequence of steps that you will generally follow are:

1. Select the structural code and the fluid code, specifying any corresponding inputfiles that contain model data.

2. Select element groups in each of the coupled codes which define a region where thecoupling interaction takes place. Any number of independent coupling regions canbe specified during the MpCCI setup.

3. Specify the quantities to be transferred for each of the coupled components. Phys-ical quantities such as temperature and pressure may be specified.

4. Set all other coupling parameters, such as mesh quality checks or output parame-ters.

5. Start the simulation. The MpCCI server will be launched first, then the coupledcodes will be activated, either in batch or in interactive mode.

The MpCCI GUI consists of four panels, each of which has to be set up successfully priorto moving on to the next panel. You can think of the MpCCI GUI as a wizard thatwalks you through the steps required to interconnect the structural and fluid models, inthis case, ABAQUS and FLUENT. Selections are made in each of the four panels in theorder in which the panels are presented, completing the setup process by starting thecoupled simulation.

The four panels that exist in the MpCCI GUI are:

1. Models panel

2. Coupling panel

3. Edit panel

4. Go panel



Figure 4.3.1: The Model Panel with the Structure Model Selected



Figure 4.3.2: The Model Panel with the Fluid Model Selected



4.3.1 The Models Panel

The Models panel (Figure 4.3.1) will allow you to select and scan the structural code andthe fluid code, one at a time.

On the left side of the Models panel, select the application code from the Available ap-plications list. On the right side of the panel, specify application-specific parameters forthe selected application code.

1. Select ABAQUS, and specify the ABAQUS executable, scanning method, and ABAQUSinput file.

(a) Enable the ABAQUS option by clicking the checkbox, or by clicking the appli-cation name.

(b) Under Parameters for selected code, select the version of ABAQUS from theSelect ABAQUS release drop-down list to run the version of ABAQUS that isinstalled on your computer.

(c) Select the scan method. Two scanning methods are available: Scan for allregions scans the entire ABAQUS input file for all possible interface regions, andScan *CO-SIMULATION only scans only the *CO-SIMULATION option. Use theScan *CO-SIMULATION only method only if you have a *CO-SIMULATIONoption defined in the ABAQUS input file.

(d) Specify the ABAQUS input file. Use the Browse button to connect to anotherplatform if ABAQUS is run on a remote platform.

(e) Click Start Scanner near the bottom of the Models panel to scan the ABAQUSinput file for potential interface regions. These regions will be available inthe Coupling panel (see Section 4.3.2: The Coupling Panel) to define the fluid-structure interface meshes.

2. Select FLUENT, and specify the version, release, and case file.

(a) Enable the Fluent 6.X option.

(b) Specify the FLUENT version (2d for 2-D single precision version, 3d for 3-Dsingle precision version, 2ddp for 2-D double precision version, etc.).

(c) Specify the FLUENT release. The FLUENT release refers to the release number.

(d) Specify the FLUENT case file. Use the Browse function to connect to anotherplatform if FLUENT is run on a remote platform.

(e) Click Start Scanner near the bottom of the Models panel to scan the FLUENTcase file for all potential interface wall zones. These wall zones will be availablein the Coupling panel (see Section 4.3.2: The Coupling Panel) to define thefluid-structure interface meshes.

3. The model specification is complete. Click Next at the bottom of the Models panelto proceed to the Coupling panel.



Selecting Your Remote Machine

You can browse to an ABAQUS or FLUENT panel using the Browse button. The Openpanel appears, as in Figure 4.3.3.

Figure 4.3.3: Selecting a File and Connecting To a Remote Machine

The default file view that appears under the File system view is your local file systemand is highlighted with the name of the remote machine. If your files live on a remotemachine, you can access the files by clicking the Connect button in the Open panel to openthe Configure a connection to a remote machine panel. To disconnect a file system fromthe file browser, select the corresponding file system in the list and click the Disconnectbutton.

In the Configure a connection to a remote machine panel, enter the name of the remotemachine in the Host text-entry field (see Figure 4.3.4). You can select from a list ofmachines that already exist under Host, which have been read in by the MpCCI GUI.



Figure 4.3.4: Remote Connection Configuration



To configure the port of the Protocol, the secure file transfer program (sftp) service,change the default Port value of the sftp service by modifying the port entry. Specify thePath where you want to connect directly. By default, you are connected to your homedirectory of your remote system. Specify the User name used to connect to the remotemachine. Enter your Password to connect to the remote machine if you do not want touse an rsa key. If neither password nor rsa key has been provided, the MpCCI GUI willask you to choose an authentication method. If the rsa key method is chosen, you will beinstructed to select this key, or else to enter a password. Click the OK button to establishthe connection.

4.3.2 The Coupling Panel

The Coupling panel is the second step for setting up your coupled simulation. In theCoupling panel, define the interface regions and identify the solution quantities to beexchanged.

There are basically two types of components, global variables and element components.

Global Variables: These components are data structures that are not related tothe CFD or FEA grids. They contain global quantities such as time or time stepsize. These components can be found under the Global (0D) tab.

Element Components: These components comprise collections of elements. Theycontain model parts and the related grid based quantities, such as nodal positions,heat values and forces. In the case of coupling, elements should be gathered thatare part of the coupling region. The components are automatically sorted by theirelement type: 1D elements will be found in the Line (1D) tab, a collection of 2Delements in the Face (2D) tab, and a collection of 3D elements in the Volume (3D)tab.

For each element type, the panel is divided into three parts:

Regions: lists any interface regions that have been created.

Components: lists components to be coupled. These are surface definitions inABAQUS and wall zones in FLUENT.

Quantities: lists available quantities to be transferred from one application to theother.



Figure 4.3.5: The Coupling Panel



Regions

Under Regions you can rename any of the created interfaces in the list by right-clicking onthe region name and selecting Rename. The text-entry field will become active, allowingyou to rename the current region. You also have the option to delete an interface.Highlight the region name with the left mouse button, then right-click using the mouse.Select Delete from the list that appears. The region will be removed with its selectedcomponents.

To add a new region, click the Add button. This will add a new interface with a defaultname. You will then be able to add components. The addition is successfully performedif the selected coupled components are correctly set. In other words, the quantities tobe transferred have to be selected and configured before adding a new region for anothercoupling region.

If for each application list the components are defined with the same name, the Generatebutton will perform a component name-matching and will automatically add a new regionfor the next matching component set. After this generation you will have to configurethe exchanged quantities for each interface region.

Components

To define an interface region, double-click an ABAQUS or FLUENT component, locatedunder Components. The components to be coupled appear under the Coupled columns inthe Coupling panel, indicating that the component is selected. You can select multiplecomponents to define the interface regions. To deselect a component and return it to thelist of available components, double-click the component.

Quantities

For each interface region, specify the solution quantities being exchanged. Select frompredefined coupling schemes, or specify the solution quantities directly. When you selecta predefined coupling scheme and click Set, the quantities for that scheme are turned onin the list of available quantities to exchange.

You have to select at least one quantity to transfer. The Quantities section is dividedinto three parts:

At the top of the Quantities section, you will find predefined settings for fluid-structure interaction simulations in the Select Coupling Scheme section.

1. From the Select Coupling Scheme drop-down list, select the setting you want.

2. Clicking the Set button will automatically apply and select the quantities toexchange for this region. If you already selected the quantities to be trans-ferred, then you can Replace, Extend, or Cancel your current quantity selection.



Figure 4.3.6: The Meshes Portion of the Coupling Panel



Figure 4.3.7: The Components Portion of the Coupling Panel



Figure 4.3.8: The Quantities Portion of the Coupling Panel



3. The Copy from Region option allows you to copy a set of quantities and param-eter settings from another coupling region to the recently coupled componentssetting.

4. In the Copy from Region drop-down list there are a set of available couplingregions. Select one of them.

5. Clicking the Set button will transfer the same setting to the selected coupledcomponents. If you have some previous quantity settings, copying may replaceyour existing quantity settings or extend it by the quantity configuration ofthe selected coupling region.

On the left side of the Quantities section, a list of the available quantities for thiscoupling region is provided. For the Global components, only one quantity may beselected for the data exchange. Otherwise there is no limit for the other componenttypes: Line, Face, or Volume. When a Quantity is selected by clicking on its checkbox, the name and description is displayed on the right side.

On the right side of the Quantity list you can select the required settings. The name of the Quantity selected will appear.

The interpolation type will have to be selected from the drop-down list. Forthe Global quantity, you have the following choices for interpolation type:

max: provides the maximum value. min: provides the minimum value. prod: provides a multiplication of these values. sum: provides a summation of theses values.

For the other component types (line, face, volume), you have the followinginterpolation types:

flux leads to conservative interpolation. The sum of the quantity valuesover all nodes is preserved if you set the interpolation type to flux. It isused for quantities such as heat flux or forces.

field is the same as non-conservative interpolation. It is used for quanti-ties like velocity and pressure. Mesh deformation is also handled as fieldinterpolation.

Define the Sender of this quantity to exchange.

After defining the sender, configure the send/receive method for each applica-tion under Configuration.

The coupling definition is complete. Click Next at the bottom of the Coupling panelto proceed to the Edit panel.



4.3.3 The Edit Panel

In the Edit panel, you can modify the MpCCI parameters that control the search criteria,contact algorithm, diagnostic print, etc. The panel provides descriptions for all of theparameters.

Figure 4.3.9: The Edit Panel

The MpCCI GUI provides defaults for almost all settings. However, the default valuescan be changed by clicking on the parameter tree, displayed on the left side of the panel.A parameter that is selected in the navigation tree on the left side, will display thecorresponding parameters in a table on the right side of the panel. This table providesinformation such as the parameter name, displayed with an orange background, theparameter value, displayed with an yellow background, and a parameter description.You can edit the default values by clicking inside the value cell.

In general, you will not have to adjust the default settings. For detailed informationabout the MpCCI parameters, see the MpCCI Technical Reference (www.scai.fhg.de).



Click Next at the bottom of the Edit panel to proceed to the Go panel.

4.3.4 The Go Panel

The Go panel is the final step for the setup of your coupled simulation. Use the Go panelto specify job control parameters and to start the MpCCI coupling server, ABAQUS, andFLUENT.

Figure 4.3.10: The Go Panel



In the MpCCI portion of the Go panel, you can change the communication port (forsocket communication), select the communication scheme (remote shell or secureshell), and configure other MpCCI parameters.

In the ABAQUS portion of the Go panel, you can specify typical ABAQUS com-mand line parameters, such as job name, old job name for a restart analysis,user subroutines, number of processors, etc. Consult Execution procedure forABAQUS/Standard and ABAQUS/Explicit, Section 3.2.2 of the ABAQUS AnalysisUsers Manual, for detailed information (www.abaqus.com). In addition, you canturn on Rendezvous scheme to display options for specifying the coupling step sizeand the coupling protocol. By default, ABAQUS/Standard uses an exact couplingprotocol and the coupling step size is set to the initial suggested time increment ofthe ABAQUS procedure. For ABAQUS/Explicit analyses, you must turn on Ren-dezvous scheme, select a loose or exact coupling protocol, and set a coupling timestep size. For more information, see Section 3.2.2: Rendezvousing Schemes.

In the FLUENT portion of the Go panel, you can specify typical FLUENT commandline parameters, such as the graphics mode, journal file, number of processors,parallel communication scheme, etc. In addition, you can select from several au-tomation schemes:

Auto install/make libudf: Installs the MpCCI code adapter. If a user-definedfunction is located in libudf/src in the FLUENT working directory, then theuser-defined function is compiled and linked with the MpCCI code adapter.

Auto read case data: Reads the case and data file when FLUENT is started.

Auto load libudf: Loads the dynamic link library when FLUENT is started.

Auto hook functions: Hooks the code adapter functions to the FLUENT functionhooks. imported into FLUENT.

Auto set MDM zones: Sets the interface wall zone for a moving deformingmesh. This setting should be checked when the interface wall is updated.

Auto set BCs: Sets the boundary conditions.

After you specify all of the job control parameters, click Start at the bottom of eachapplication portion of the Go panel to start the MpCCI coupling server, ABAQUS,and FLUENT.



4.3.5 Terminating the Coupled Simulation

The couple simulation can be terminated normally or abnormally:

Normal Termination

Each client process terminates its connection with the server. When all clients havedisconnected, the server shuts down.

Abnormal Termination

Use the Kill button to kill all processes associated with the simulation. This is an abrupttermination as the Kill button uses the operating system kill command to terminatethe jobs immediately. Use the Stop button to terminate an ABAQUS job gracefully. Ajobname.stop file, written in the ABAQUS analysis directory, will terminate the ABAQUSjob prior to the next exchange.

4.4 Running the simulation interactively from FLUENT

To run the simulation interactively, you can use the MpCCI Control panel, which is ac-cessed using the FLUENT GUI:

Solve MpCCI Control...

The settings in the MpCCI Control panel can be used in lieu of the FLUENT journal filethat is specified in the Go panel, under the Fluent portion. The settings in the MpCCIControl panel gives you more control of the run settings

1. Enable Use MpCCI to expand the panel and access the settings.

2. You have three choices for specifying the Automated Exchange of Quantities:

Before each iteration - use ADJUST Before each time step - use dynamic function After each time step - EXECUTE AT END

ADJUST, dynamic function, and EXECUTE AT END are user-defined functions(UDFs) which allow you to customize FLUENT and can significantly enhance itscapabilities. For more information about UDFs, go to the FLUENT 6 product pageat User Services Center (www.fluentusers.com) and click on the Documentationlink.


4.4 Running the simulation interactively from FLUENT

Figure 4.4.1: The MpCCI Control Panel



3. When using the On Demand Init and Exit portion of the panel, click Initialize to ini-tialize MpCCI communication with FLUENT and ABAQUS. At this stage, the cou-pling server receives the mesh topologies and performs the neighborhood searchesto determine the mapping parameters. Finalize terminates the FLUENT connec-tion with the coupling server by providing a clean shutdown of the communicationsockets. Abort kills the process.

4. When using the On Demand Transfer portion of the panel, click Send to send thesolution quantities from FLUENT to ABAQUS. This is equivalent to setting themethod of quantity transfer in the Go panel.

5. List global variables, under Utilities, displays in the FLUENT console the global set-tings used by the adapter.

4.5 Solution Strategies For an FSI Problem

4.5.1 Local Convergence

Local convergence refers to each code having converged to specific criteria, based onresidual forces, moments, temperatures, etc. to establish convergence of each iterationduring the solution. For example, ABAQUS/Standard uses Newtons method to solvenonlinear problems iteratively. ABAQUS/Explicit does not use any convergence criteria;instead, accuracy is enforced by limiting the time increment.

In FLUENT the local convergence criteria are defined in terms of the residuals for the con-tinuity, velocity, and energy equations. Residual monitors and surface quantity monitorsare tools available in FLUENT to analyze the solution.

4.5.2 Global Convergence

Global convergence refers to the convergence of the coupled system. For unsteady sim-ulations, a noniterative, globally explicit approach is used. The global convergence isassumed to be equivalent to local convergence of both codes (i.e., both codes need toconverge prior to exchanging solution data). For steady simulations, there are a set num-ber of coupling steps, which you can manually monitor specific results in FLUENT. Forexample, surface monitors can be used to evaluate certain solution quantities.


4.6 Postprocessing an FSI Problem

4.6 Postprocessing an FSI Problem

Postprocessing solution data can occur on many levels. You can postprocess the ABAQUSsolution, your FLUENT results, MpCCI coupled components, and most importantly forthis application, you can postprocess the combined fluid and structure solution.

4.6.1 Postprocessing Using ABAQUS/CAE

Structural response and interface response can be postprocessed using ABAQUS/CAE.Fluid concentrated forces (CF) can be plotted when using ABAQUS/Standard. To displaythe fluid forces in ABAQUS/CAE, you will need to import concentrated forces (CF) ratherthan normal pressure (PRESS) for the co-simulation. You will also need to specifyconcentrated forces as a nodal output quantity to the output database:

*OUTPUT, FIELD

*NODE OUTPUT

CF,

4.6.2 Postprocessing Using FLUENT

Fluid response and the interface response can be postprocessed in FLUENT. The interfacewall is updated and can be visualized in FLUENT along with the flow solution quantities.Refer to the FLUENT Users Guide for details on graphics and visualization.

4.6.3 Postprocessing Using MpCCI

CCIVIS is a basic visualization tool distributed with MpCCI which allows you to visualizethe coupled components. It is a beneficial debugging tool, should you encounter anyproblems during the neighborhood search. Consult the MpCCI 3.0 Visualiser UsersManual for more information.

4.6.4 Combined Fluid and Structure Postprocessing

Third-party postprocessors, such as EnSight Gold from CEI (www.ceintl.com) and Tec-plot (www.tecplot.com)can be used to combine the fluid and structural solutions.


Appendix A. Starting MpCCI Code Coupling BetweenABAQUS and FLUENT

This chapter provides a step by step procedure to set up and run an FSI simulationusing the MpCCI GUI. To demonstrate this procedure, consider the problem of a 3Dflap, which is subjected to air flowing through a channel at a velocity of 6 m/s, as shownin Figure A.0.1. The flap is fixed at the upper wall of the channel, while it is free todeform at the bottom. As the air flows through the channel, the flap deforms. Thecoupled transient simulation calculates the deformation and distortions of the flap asthe air flows through. In this example, the flow is turbulent and therefore the standardk-epsilon model is used.

Velocity Inlet6 m/s

Wall

PressureOutlet

Flap

Z

Y

X

9.81 m/s2

Figure A.0.1: Schematic of the Problem Description

c Fluent Inc. November 7, 2006 A-1

Starting MpCCI Code Coupling Between ABAQUS and FLUENT

Before starting the simulation:

1. Set up the directory structure as follows:

MPCCI FLUENTABAQUS

Working Directory

Figure A.0.2: Directory Structure

2. Make sure the ABAQUS folder contains an .inp file, which consists of all the neces-sary settings.

3. Make sure the FLUENT folder contains a .cas file. In this file, the the transientsolver, gravitational acceleration, turbulence model, boundary conditions, and timestep size will all be defined.

4. Go to the MPCCI directory that you created and start the MpCCI GUI by typingmpcci -gui on the command line. The MpCCI GUI will start at the Model panel.For information about each of the options in the panels, go to Section 4.3: ProblemSetup Using the MpCCI User Interface.

Model Setup

In the Model panel:

1. Enable ABAQUS under Available codes and select the following settings as shownin Figure A.0.3:

(a) Select latest from the Select ABAQUS release drop-down list, assuming youhave the latest ABAQUS release installed on your system. Otherwise, selectthe version that you currently have installed.

(b) Select Scan for all regions from the Select scan method drop-down list.

A-2 c Fluent Inc. November 7, 2006


(c) Click the Browse button under Select ABAQUS input deck (*) to read in theABAQUS .inp file.

(d) Select the appropriate system of units from the Select unit system drop-downlist.

(e) Click Start Scanner. A successful scanning of the FEA code will result in acheck mark with the word Done appearing next to ABAQUS.

Figure A.0.3: Scanning the ABAQUS Input File

2. Enable FLUENT under Available codes and select the following settings as shown inFigure A.0.4:

(a) Select 3d from the Please select the FLUENT version drop-down list, assumingyour case is a 3d case. Otherwise, select the version that your case represents.

(b) Select latest from the Please select the optional FLUENT release drop-downlist, assuming you have the latest FLUENT release installed on your system.Otherwise, select the version that you currently have installed.

(c) (optional) Enable the Run 64 bit version if your case is very large and requiresadditional memory.



(d) Click the Browse button under Please select the FLUENT casefile for scanning(*) to read in the FLUENT .cas file. Note that you can also read in compressedFLUENT case files.

(e) Click Start Scanner. A successful scanning of the CFD code will result in acheck mark with the word Done appearing next to ABAQUS.

Figure A.0.4: Scanning the FLUENT Case File

(f) Click Next to access the Coupling panel (Figure A.0.5).



Coupling Setup

In the Coupling panel:

1. Click the Face (2D) tab to couple the ABAQUS and FLUENT elements.

(a) The Component section of this panel is divided into ABAQUS 6.5/6.6 and Flu-ent 6.x. Under ABAQUS 6.5/6.6, double-click on ASSEMBLY BLOCK-1 WALL.This will move this element down to the Coupled section. Under Fluent 6.x,double-click on wall, which will now appear in the Coupled section under Fluent6.x.

(b) In the Quantities portion of this panel, there are predefined sets of quantities tobe exchanged. For example, if you select Gauge pressure based Fluid-StructureInteraction from the drop-down list and click the Set button, then NPositionand RealWallForce will automatically be enabled.

Figure A.0.5: Setting Up the Coupling Panel

(c) The coupling definition is complete. Click Next to access the Edit panel.



Edit Setup

In the majority of FSI cases, the Edit panel does not need to be modified. Click Next toproceed to the Go panel (Figure A.0.6).

Go Setup

The Go panel is divided into three sections: server, ABAQUS, and FLUENT.

1. Keep the default settings under server.

2. Under the ABAQUS portion:

(a) Select receive from the Initial quantities transfer drop-down list.

(b) Keep the default job name of abaqus run.

(c) Keep the default co-simulation step number of 1.

(d) Enable Rendezvous times.

(e) Enter 2.5e-4 for the Coupling time step. This value can be found in the .inpfile.

(f) Select exact as the Rendezvous time enforcement.

(g) Enable Double precision for ABAQUS/Explicit for cases requiring higher preci-sion during the solution process.

3. Under the FLUENT portion:

(a) select send from the Initial quantities transfer drop-down list.

(b) Retain all other default settings.

4. Click the Start button under server, then under ABAQUS, and finally under FLU-ENT.

You will now run the rest of the simulation interactively, using the FLUENT GUI.



Figure A.0.6: Setting Up the Go Panel



Running the Simulation Interactively

You may want to have more control over the run settings, therefore, rather than havingall the run instructions stored in a journal file, you can use the MpCCI Control panel. SeeSection 4.4: Running the simulation interactively from FLUENT for detailed informationabout this panel.

1. If the settings are acceptable as they are, simply close the panel.

Solve MpCCI Control...

Figure A.0.7: The MpCCI Control Panel

2. Initialize the solution.

Solve Initialize Initialize...Click the Init button and close the panel.

3. Display any countours or views that are of interest to you prior to starting the run(Figure A.0.8).



Figure A.0.8: Velocity Contours Displayed Prior to Running the Simulation

In this example, the simulation was run for 10 time steps and the velocity contoursobserved at the end of the tenth time step (Figure A.0.9).

To postprocess using ABAQUS, go to www.abaqus.com.



Figure A.0.9: Velocity Contours Displayed After Running 10 Time Steps


Appendix B. Restarting MpCCI Code Coupling BetweenABAQUS and FLUENT

The restart option allows an analysis to be completed up to a defined point in a specificrun and restarted and continued in a subsequent run. Prior to using the restart optionfor code coupling, it is recommended that your directory is structured as follows:

MPCCI FLUENTABAQUS MPCCI_restart

Working Directory

Figure B.0.1: Directory Structure

To demonstrate, we will use the same example as in Appendix A: Starting MpCCI CodeCoupling Between ABAQUS and FLUENT. Therefore, it is highly recommended thatyou go through the example in Appendix A: Starting MpCCI Code Coupling BetweenABAQUS and FLUENT before proceeding.

Make sure the ABAQUS folder contains an .inp file. In the ABAQUS input file (file-name.inp), a restart row must be modified in the output request of the coupling step.The frequency in this row is the frequency of the stored increments in the restart file.Therefore, change *Restart, write, frequency=0 to *Restart, write, frequency=1,as shown in the example below:

** OUTPUT REQUESTS

**

*Restart, write, frequency=1

**

** FIELD OUTPUT: F-Output-1

**

*Output, field, variable=PRESELECT, frequency=1

*Output, history, frequency=0

*End Step

c Fluent Inc. November 7, 2006 B-1

Restarting MpCCI Code Coupling Between ABAQUS and FLUENT

With a frequency set to 1, the simulation can be restarted at any iteration. For detailedinformation about this feature, refer to the ABAQUS Analysis Users Guide, Chapter 7.1:Restarting an Analysis.

Run the simulation as described in Chapter A: Starting MpCCI Code Coupling BetweenABAQUS and FLUENT.

B.1 Creating the Restart Session

Go to the ABAQUS directory and open the created input file (mpcci filename.inp) usingany editor and modify it. Delete all nodal, elemental, boundary condition and materialinformation. Include a new line for the restart read option with the number of incrementsthat you would like to use.

i This is a step definition and MpCCI counts it as a uncoupled step. Renamethe old step definition. This is the coupling step, therefore, do not deletethe co-simulation portion so that MpCCI understands which coupling sur-faces are used from the ABAQUS side.

Rather than using the original input file, you can, alternatively, create a new file in youreditor of choice. Copy the step information, modify the step name, and add the restartand read options before the step card.

The restart file will have a heading, a step definition, an output request, and a co-simulation section, as shown in the example below:

*Heading

** Job name: Job-1 Model name: flap

*Preprint, echo=NO, model=NO, history=NO, contact=NO

** ----------------------------------------------------------------

**

** STEP: Restart

**

*RESTART, READ, STEP=1, INC=9, END STEP

*Step, name=Restart, nlgeom=YES, inc=1000

Flattersimulation

*Dynamic,alpha=-0.05,direct

0.00025,1.,

**

** OUTPUT REQUESTS

**

*Restart, write, frequency=0

**

** FIELD OUTPUT: F-Output-1

**

B-2 c Fluent Inc. November 7, 2006

B.1 Creating the Restart Session

*Output, field, variable=PRESELECT, frequency=1

*Output, history, frequency=0

**

** MpCCI automatically inserted this *Co-Simulation keyword.

** Therefore any existing *Co-Simulation keyword was removed.

**

*Co-Simulation, external interface=MpCCI

*Co-Simulation Region, type=Surface, Export

ASSEMBLY_BLOCK-1_WALL, COORD

*Co-Simulation Region, type=Surface, Import

ASSEMBLY_BLOCK-1_WALL, CF

*End Step

Rename the mpcci filename.inp file to restart.inp.

Running an MpCCI CO-SIMULATION

In the Models panel:

1. Start MpCCI from the MpCCI restart directory.

2. Set up the case in a similar manner to that described in Chapter A: Starting MpCCICode Coupling Between ABAQUS and FLUENT.

3. Change the scanning method for ABAQUS from Scan for all regions to Scan *CO-SIMULATION option only.

Note: It is necessary to use the Scan *CO-SIMULATION option only, otherwise thescanning will fail.

4. Select the input file restart.inp.

5. Start the scanner.

6. Select FLUENT as the second code and select the casefile created at the tenth timestep.

7. Start the Scanner.

In the Coupling and Edit panels:

1. Keep the default settings (which are the settings you used in the original MpCCIsession).

In the Go panel, change the settings in the ABAQUS field:

c Fluent Inc. November 7, 2006 B-3

Restarting MpCCI Code Coupling Between ABAQUS and FLUENT

1. Enter a new job name, for example, restart which is the new name for the ODBfile under Enter a jobname.

2. Enter a co-simulation step number of 3 to avoid overwriting the ODB and restartfiles.

3. Make sure Rendezvous times is enabled and that the Coupling time step is the sameas before.

4. The last setting for the restart is an Optional old job name for restart. You mustinclude the original ODB file, abaqus run.odb.

Figure B.1.1: Setting for the MpCCI Restart

In summary, the first step was the original step, the second step will be the restart readoption and the last step will be the restart run itself.

To complete the simulation, follow the steps outlined in Section A: Running the Simula-tion Interactively.

For detailed information about ABAQUS restart capabilities and options, please referto Section 9.1: Restarting an Analysis, of the ABAQUS Analysis Users Manual,available at www.abaqus.com .

B-4 c Fluent Inc. November 7, 2006

FLUENT 6.3 Fluid-Structure Interaction Module ManualTable of ContentsPreface1 Introduction2 The Fluid-Structure Interaction (FSI) Software Suite2.1 An Overview of FLUENT, FEA Software, and MpCCI2.2 Capabilities of the FSI Suite2.3 Limitations of the FSI Suite2.4 FSI Package Requirements2.4.1 Licensing Requirements2.4.2 Hardware Requirements

2.5 Installing the FSI Software Suite2.6 Workflow for Solving an FSI Problem

3 Workflow and Coupling Schemes For an FSI Problem3.1 Important Considerations Prior to Solving an FSI Problem3.2 Coupling and Rendezvousing Schemes3.2.1 Coupling Schemes3.2.2 Rendezvousing Schemes

4 Using the MpCCI User Interface4.1 MpCCI Overview4.2 The MpCCI User Interface4.2.1 Starting and Exiting the MpCCI GUI4.2.2 Components of MpCCI's Main Window4.2.3 Other MpCCI GUI Components

4.3 Problem Setup Using the MpCCI User Interface4.3.1 The Models Panel4.3.2 The Coupling Panel4.3.3 The Edit Panel4.3.4 The Go Panel4.3.5 Terminating the Coupled Simulation

4.4 Running the simulation interactively from FLUENT4.5 Solution Strategies For an FSI Problem4.5.1 Local Convergence4.5.2 Global Convergence

4.6 Postprocessing an FSI Problem4.6.1 Postprocessing Using ABAQUS/CAE4.6.2 Postprocessing Using FLUENT4.6.3 Postprocessing Using MpCCI4.6.4 Combined Fluid and Structure Postprocessing

A Starting MpCCI Code Coupling Between ABAQUS and FLUENTB Restarting MpCCI Code Coupling Between ABAQUS and FLUENTB.1 Creating the Restart Session

fluid structure interaction manual

Documents

fluent b

c fluent

overview of fluent

fsi suite

fsi simulation

fsi problem4

mpcci overview

fsi software suite2