multiphysics chapter 8. training manual may 15, 2001 inventory #001478 8-2 multiphysics chapter...

Multiphysics

Chapter 8

May 15, 2001Inventory

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Training ManualMultiphysics

• Chapter Goals -

– Describe Coupled Analyses - multiphysics

See Also:

• ANSYS Coupled-Field Analysis Guide

– Sequential Coupled-Field Analysis

– Show Results of some applications

– Provide a detailed, step-by-step Tutorial of a fluid structure interaction problem:

• The Multiphysics Tutorial


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Training ManualTypes of Coupled Analyses

• Indirect Method

– Involves two analyses, done in sequence, each belonging to a different field. The fields are coupled by applying results from one analysis as loads for another analysis

• Direct

– Involves a single analysis using a coupled-field element which contains all necessary degrees of freedom (DOF’s)

• Examples of one way and two way coupling for the indirect method will be shown next


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Training Manual“One-Way” Coupling Examples

• Fluid-Structure Interaction

– CFD results determine pressure loadings

– Resulting structural deformations have negligible effect on the flowfield.

• Fluid-Thermal Interaction (constant property)

– CFD flowfield necessary to compute temperatures

– CFD properties (sometimes!) unaffected by temperature changes.


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Training Manual

LDREAD - load transfers

Fluid Analysis

Structural Analysis

FluidsResults File

StructuralResults File

Performing an Indirect Coupled-Field Analysis


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Training Manual

Coupled Valve Analysis * Courtesy of Cybernet Systems Company, Ltd., 1995

• Multiphysics Example...

• 2D flow through a valve

• Coupled Analysis

• FLOTRAN used to calculate pressure

• These pressure loads applied to structural analysis in ANSYS to obtain equivalent stresses


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Training ManualThe Basic Procedure

• Converge Flow Analysis

• Switch element type to structural (or thermal or magnetic).

Note: delete the FLOTRAN element type, NOT the elements.

– In this example, the non-fluid elements could be a part of the FLOTRAN solution (as solids). Then the element type number for these elements is assigned to a structural element.

• Unselect the fluid elements and nodes.

• Apply structural constraints.

• Select nodes at the solid-fluid interface and transfer loads from fluid analysis (LDREAD).

• Run structural analysis.


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Training ManualThe FLOTRAN mesh


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Training ManualThe FLOTRAN mesh (continued)


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Training ManualVelocity Field


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Training ManualPressure Field


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Training ManualThe Structural Mesh


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Training ManualLoading - Pressure Forces


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Training ManualDisplacements


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Training ManualEquivalent Stresses


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Training ManualFluid - Magnetic Interaction

• Magnetic phenomena can produce effects that should be accounted for in CFD analyses in several ways

– Body forces ( FLOTRAN momentum equation)

• These can be the result of DC or AC currents (time-averaged).

• LDREAD,FORCE,… (FLOTRAN converts to Force/vol)

• Harmonic analyses require the calculation of time averaged JxB cross product from element data.

– Electromagnetic fields can also generate heat (Joule Heating) (FLOTRAN energy equation)

• Occurs through eddy currents

• LDREAD,HGEN,…..


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Training ManualFluid - Magnetic Interaction (continued)

• Magnetic phenomena are influenced by fluid phenomena as well...

– Properties

• Electric resistivity of a fluid is an input to the electromagnetic Analysis. It is often temperature dependent.

• Real constant

– Fluid Velocity

• Part of the Magnetic Reynolds Number

• Element input (no automatic load transfer exists)

– Fluid Surface configuration (shape)


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Training Manual

Example of Magnetics-Fluid Analysis: Induction Furnace

• In this case, the CFD analysis receives the loads, rather than generating them as magnetic effects produce body force terms….

– The model is axisymmetric

– Crucible for molten steel at 2500 F

– AC current applied to the coils produces eddy currents within the furnace

– The eddy currents produce heating (Joule heating) which melts the steel

– The interaction of the eddy currents with the Lorentz forces stirs the molten steel


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Training ManualSolid Model


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Training ManualInduction Furnace - The Mesh

• Note denser mesh around the coils and in the crucible

• Denser mesh in areas of large gradients, also the areas of interest

• Coarse mesh with infinite boundary elements at the far-field

• Approximately 6600 elements


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Training ManualFinite Element Mesh


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Training ManualEmag Solution - Flux

• First, ANSYS/Emag product is used to solve the electromagnetic field

• Axisymmetric, time-harmonic analysis

• This plot shows the electromagnetic flux lines resulting from the magnetically-induced field


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Training ManualEMAG Flux Lines


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Training ManualEmag Solution - Lorentz Forces

• Lorentz forces also result of the electromagnetic field

• Strongest closest to the coils

• Closeup of the Lorentz forces in the crucible

• These forces are strong enough to stir the molten steel...

– Velocities on the order of 3 meters/sec can be produced.


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Training Manual

Lorentz forces in molten steel Closeup of Lorentz forces in crucible


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Training ManualFLOTRAN Solution - Velocity Field

• Lorentz forces induce flow in the molten steel

• Velocity vectors show the turbulent fluid motion in the crucible

• Note the two turbulent eddies


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Training Manual

The flow field up close….The Crucible with Flow


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Training Manual“Two-Way” Coupling

• Necessary when the effects of the second analysis (i.e., structural deformation effects) on the flow field are not negligible and re-analysis of the flow field is required.

• Solve the initial fluid and structural (or thermal or magnetic) problems following the procedure for one-way coupling.

• Re-mesh (or perhaps merely move the nodes) the new flow field geometry according to structural /thermal/magnetic analysis deformations.


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Training Manual“Two Way” Coupling (continued)

• In the two-way coupling analysis involving FLOTRAN, care must be taken to ensure convergence of the flow analysis.

– Complete convergence of intermediate FLOTRAN runs is not usually required if a steady state problem is being solved.

• The entire sequential process may be put in a macro loop.


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Training Manual

Fluid is air.Wall is concrete:4 m by 0.25 m

Modulus of Elasticity = 1.39x108 N/m2

Poisson’s Ratio = 0.30

Vfree stream = 200 km/hr P = 0

Ground, no slip wall

H = 4 m

t = 0.25 m

The Wall Exercise

• Solve the problem of air flow over a “bendable” wall. What is the maximum von Mises stress in the wall? And what is the wall configuation under this load


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Training ManualThe Wall

• Note that a simple version of this problem was solved in the introductory course as a one-way coupling.

• In this case we relax the Modulus of Elasticity to the point where the deformation of the wall is significant enough to warrant re-analysis of the flow field.

• The FSSOLVE macro will be used to iterate to a steady state solution.


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Training Manual Instructor Exercise (continued)

• Extend the boundaries “far enough away” from the wall in all directions.

• Make the mesh finer at the wall and ground.

• Eliminate singularities if possible - round the top of the wall.

• Apply free stream conditions to the upper boundary and inlet.

• Treat the ground as a no slip wall.

• Apply P=0 at the outlet.

• Set Artificial viscosity =0.1

• Set Turbulence Inertia = 1.0


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Training Manual Instructor Exercise (continued)

• Run the FLOTRAN analysis for 100 iterations.

• Switch element type 1 from FLUID141 to PLANE42.

• Input the concrete properties.

• Unselect the fluid nodes and elements.

• Fix the bottom of the wall (Set Ux=Uy=0).

• Select the fluid/solid interface nodes and apply the pressure loads.

• Solve the static, structural problem.


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Training ManualThe Multiphysics Tutorial

• This tutorial describes in detail the use of various FLOTRAN features in a Multiphysics analysis.

– Features...

– Advanced turbulence model

– SUPG upwinding of advection terms

– Modification of CFD mesh using structural approach (UPCOORD)

• An alternate approach to moving the nodes near the deformed piece involves using MORPHING, a process of remeshing using boundary deformations.

– Use of Physics Environments, load transfers to solid and shell elements


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Training Manual

A Fluid Structure Analysis With FLOTRAN (Multiphysics)


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Training ManualThe Problem Described….

• As shown on the previous page, there are two flows (and the nozzle is axisymmetric) that come together.

• The outer and inner flows are at much different velocities, and are modeled with Flotran 141 elements.

• The two flows are separated by a thin piece

– The effect degree of deformation of this piece on the flowfields, is of interest.

– It will be modeled with Solid 42 elements

• The outer portion of the nozzle ,on the right side before the outlet region, is also subject to deformation and will be modeled with Shell 61 elements.

• The nodes in the fluid regions near the deforming pieces will be moved by considering them part of a “structural fluid”.


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Training ManualProblem Objectives - Step

• This is a fluid structure analysis where a mixing flow will be calculated while the resulting fluid pressures cause deformation of the boundaries of the flowfield.

• Milestones in the Analysis Sequence (these will be further subdivided into 14 stages)

– Development of the Geometry

– Establishment and execution of the meshing strategy

– Creation of Physics Environments

– Interactive Analysis

• The student may do the entire exercise interactively or elect to have certain portions performed with input files provided.


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Training Manual

Velocity 200 in/sec

Velocity 2000 in/sec

Axis of Symmetry

Separator (moveable)

Deformable portionof mixing nozzle

Problem - A Mixing Nozzle

• Axisymmetric geometry.

• Air Flow (2000 in/sec) through the outer portion mixes with a slower flow (200 in/sec) coming through the inner portion.

• A solid region separates the flows, and the deformation of this Separator will be calculated. The deformation of the outside of the nozzle is modeled with axisymmetric shell elements.


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Training ManualSummary of Steps

Stage 1: Geometry and mapped meshing parameters (mix1)

Stage 2: Assign the attributes (mix2)

Stage 3. Meshing and Mesh refinement

Stage 4: Create CFD environment and write physics file (mix4)

Stage 5. Create Structural environment and write physics file (mix5).

Stage 6. Activate fluid physics and execute initial FLOTRAN run.

Stage 7. Activate alternate advection scheme, extend solution.

Stage 8. Examine pressure solution.

Stage 9. Activate structural environment.

Stage 10. Reading in pressure loads from FLOTRAN.

Stage 11. Solve for stresses and displacements.

Stage 12. Examine deformations.

Stage 13. Update CFD mesh coordinates.

Stage 14. Continuing the Sequential solution process


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Training Manual

• Read in the input file that creates the solid model.

Utility Menu: File > Read Input from...

Choose mix1 (This completes Stage 1 completely)

• OK ( Then close the warning box about deactivating element shape checking)

1

2

1

2

Perform This Step to Bypass Interactive Creation of Stage 1


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Training ManualThe Geometry


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Training ManualWorking Plane and Parameter Settings

• Utility Menu > Work Plane > Display

• Utility Menu > Work Plane > Settings

• Utility Menu > Parameters > Scalar Parameters


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Training ManualBasic Geometry

• Preprocessor > Create

• Open the Scalar Parameter file just created

– Utility > Scalar Parameters

• Click on the desired parameter, move to the field in the command, then hit the middle mouse button…

– (Or just type it in…)


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Training ManualThe Other Rectangles

• Click Apply to get the box back…Last one gets OK


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Training ManualResulting Basic Areas


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Training ManualConnect the Dots...

• Preprocessor > Numbering Ctrls > Merge Items

• Pull down menu for label, Choose ALL

• Then zoom on the open space between the rectangles….


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Training ManualOperate on the Model

• Preprocessor >Create>Lines>Tan to 2 Lines

• Get the Picker and Choose Lines:

– First Line

– Point of Tangency

– Second Line

– Point of Tangency

– Oks all along...


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Training ManualCreate the remaining areas

• Create Arbitrary Areas - Through KPs

• First Area:

• Second Area


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Training ManualThe Areas are Complete

• (The keypoint numbers are turned on)


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Training ManualEstablish Line Divisions - Lengthwise

• Mesh Tool - Size Control - Lines

– Outlet: 25, Ratio 3

– Use Flip Bias on line 16

– Transition Region (2 lines)

• Use 20

– Beam

• Use 14

– Inlet Region (4 lines)

• Use 20, Ratio -3


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Training ManualMesh Tool


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Training ManualTransverse Lines

• Utility Menu > Plot Ctrl > Size and Shape

– X distortion factor is 5

• Inlet /Outlet:

– Use 12, Ratio -2

• Outer Inlet:

– Use 10, Ratio -2

• Separator

– Use 3, Ratio -2


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Training ManualDetails...

• Add two areas…..

– Preprocessor>Operate>Add>Areas

– Areas 5 and 6

• This completes Stage 1 (I.e. what is accomplished by the file “mix1”).


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Training ManualStage 2

• Before the Meshing Step, Element types must be assign and attributes must be set

• Elements will change between the two different physics, so the initial assignment is arbitrary

• Review– ANSYS Coupled-Field Analysis Guide

• Sequential Coupled-Field Analysis

• The input file for Stage 2 is “mix2”

• Set– Element types

– Attributes

• The Interactive Steps for Stage 2 follow the diagrams which illustrate attribute assignment.

The areas will be assigned attribute numbers based on the physics that will be modeled.

The table on the following slide shows how the attributes are to be assigned

Fluid Only Area 4

Area 1

Area 2

Area 7

Line 8

Line 10

Area 3Fluid and then “structural fluid”

Shell elementson these lines

(NOT TO SCALE!)


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Training ManualDefinition of Physics Regions

RegionGeometric

Entities Material

RealConstant

Set

ElementType

NumberFluid Only Area 4 1 1 1

Structural

Fluid

Areas1,3,7

1 1 2

Separator Area 2 2 1 3

The Outer Shells Lines 8,10 3 2 4


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Training ManualArea Attributes

• Since properties have not been defined yet, the GUI is not used to set the attributes….

• Select the Areas associated with a Physics Region and then assign attribute via the command line.

• For Example, the Structural Fluid region:– Select Areas 1,3,7 as shown

AATT,mat,real,element type number

– AATT,1,1,2

• Use LATT for shells

• Define Initial element types:– et,1,42

– et,2,42

– et,3,42

– et,4,61


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Training ManualArea plot, colors assigned to element types

This is the completion of Stage 2: after element types and attributes are set


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Training ManualStage Three - Meshing

• There is no input file for this step !

• Mapped meshes are used where possible

• Free meshing with quads is used in the central region

• Mesh refinement where necessary

• Note that we mesh with arbitrary elements assigned to the attribute numbers. What actual ANSYS element is assigned to “num” in the command ET,2,”num”, for example, will vary with the particular physics being solved. It is assigned in the physics environment file (later).


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Training Manual

Activate the Mesh Tool Main Menu:

PreProcessor > Mesh Tool

1

3

Use a mapped quadrilateral meshfor the upper and lower portions

2

4

2

Pick these three

Pick this one

4

1

Choose Quad elements

Mapped mesh

Mesh

Pick these four areas

OK

4

3

5

5

(Close any warningboxes that arise during

the meshing steps!)

Mesh the Model


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Training Manual

6

8

7

9 7Central Area

6


Free Mesh

Mesh

Pick the Centerl area 9

8 10

10 OK

Mesh the Central Region

• Create a free mesh of quads for this


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Training Manual

13

12

Pick this one 15

11


Free Mesh

Refine at areas

Click Refine

Pick Area

OK

OK (minimal refinement)

14

13

14 16

17

11

12

15

16

17

Refine the Mesh in the Central Area


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Training Manual

18

20

Create shell elements on the outside of the nozzle

19

20Pick lines

Lines

Mesh

Pick these lines

OK

Close

21

19 21

18

22

22

Mesh the Shell elements on the outside


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Training Manual

Stage Four - Fluid Physics Environment

• File “mix4” creates fluid physics environment (File shown at the end of the stage). Input the file or perform the steps interactively.

• Physics Environment files contain:

– Element assignments used for the element type numbers.

– Boundary Conditions

– Solid Material Properties

– FLOTRAN settings

• Solution options

• Stability Parameters

• Fluid Properties


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Training ManualElement Types

• Make these changes on the command line (GUI only allows certain element switching)

• Assign Element 141 (axisymmetric about Y) to element type numbers 1,2

– et,1,141,,,1

– et,2,141,,,1

• Assign Null Element Type to Shells and the Solid regions

– et,3,0

– et,4,0


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Training ManualFLOTRAN Boundary Conditions

SymmetryConditionsVX = 0

Inlet VY = 200 ,VX=0Inlet VY = 2000, VX=0

Walls: VX,VY=0

More Walls

Pressure: PRES=0


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Training ManualApplication of Boundary Conditions

• Use Solid Model Boundary Conditions for Velocity and Pressure

– Solution>Loads> Apply>Velocity


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Training ManualFLOTRAN Solution Options


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Training ManualFLOTRAN Properties

• Use AIR-IN for everything on the pull-down menu


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Training ManualFlow Environment

• Flow Environment >Reference Conditions

• Always make sure that the reference conditions are consistent with the property type used.


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Training ManualTurbulence Model

• Choose the RNG Turbulence Model..

• Solution > FLOTRAN Set Up > Turbulence Model

– Use default parameters for RNG


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Training ManualCreate FLUID PHYSICS file

• Solution > Physics Environment

This completes what is accomplished by the file “mix4”


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Training ManualFile “mix4”

Result of Physics,Write


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Training Manual

Stage Five - Structural Physics Environment

• File “mix5” (file shown at end of Stage 5) performs Stage 5.

• Details of Stage 5 are now shown.

– First Clear Existing Physics Information


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Training ManualElement Types

• ET,1,0

– Give most of the fluid region the null element type

• ET,2,42

– This is the “structural fluid”

• ET,3,42

– The deformable piece separating the two inlets

• ET,4,61

– The shell element on the outer surface


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Training ManualProperties

• Preprocessor > Material Props > Isotropic

• Material 1 is the structural fluid with “artificial properties”

– EX: 1.E-2

– NUXY: 0.000

• Making the fluid region a part of the structural solution will enable us to move the nodes via UPCOORD as the structure of interest deforms in the flowfield.


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Training ManualMore Properties…...

• The bendable (deformable) separator

– Thermoplastic elastomer

– Material Number 2

• EX: 2.3x104

• NUXY: 0.3000

• The Elastic Boundary Shell element

– More plastic

– Material Number 3

• EX: 4.0x102

• NUXY: 0.3000


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Training ManualReal Constants

• Thickness of the Shell Elements

– .01


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Training ManualConstraints on the structural problem

CenterlineRadial Constraint,

UX = 0

Axial and Radial Constraints at the bottom, UX,UY=0

Axial ConstraintTop of Domain

UY = 0

EliminateTwisting

UZ=0


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Training ManualCreate Structural Physics File

• Select everything

• Title is “struc”

This completes what is accomplished by the file “mix5”


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Training Manual

The Structural Physics Environment Input


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Training ManualStage Six: Initial Execution

1. Read in Fluid Physics

Choose Read

Choose Fluid

OK 3

2

1

2. Solve: Main Menu: Solution > Run FLOTRAN

1

2

3

Close any warning boxes that may arise regarding boundary conditions.


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Training ManualConvergence Monitors

• The first ten global iterations provide an approximate solution suitable for switching to the SUPG advection algorithm


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Training Manual

Stage 7: Extend case to Activate New Features

• Solution > FLOTRAN Setup

– After the first 10 global iterations, access FLOTRAN Setup to Change solution options


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Training Manual

Solution > FLOTRAN Setup

Choose Advection

Choose SUPG for turbulence

Choose SUPG for momentum

OK

8

7

6

5

5

6

7

8

Activate SUPG Advection Scheme


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Training Manual

Solution > FLOTRAN Setup

Choose Execution Ctrl

Set 90 global iterations

OK

10

6

9

11

9

10

11

Execution Control90 more global iterations


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Training ManualExecute !

Solution > Run FLOTRAN

The Analysis will end after 100

Global Iterations


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Training ManualConvergence Behavior


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Training ManualStage 8: Examine the Pressure Solution

1

2

2

OK

Pressure

PressureDistribution

1

General Postprocessor > Last Set > Plot Results > Nodal Solu


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Training ManualStage 9: Read in Structural physics

Once the CFD analysis is complete, the resulting pressures will be applied to the Separator in the nozzle and the outside

3

2

1

Solution > Physics Environ

1 Read

Choose struc

OK

2

3

Close boxes that arise


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Training Manual

1

2

3

4

1

2

3

4

Select Elements

By Attributes

Choose Material 2

OK

Elements

Stage 10: Reading In pressure loads from FLOTRAN

• Apply fluid pressures to the Separator : Select elements of Material 2 and associated nodes:

Utility Menu: Select > Entities


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Training Manual

Pressure Load From FLOTRAN (continued)

9

10

11

Where to get pressures

Solid for Elements

Loads from (jobname).rfl file OK

12

9

10

11

12

10

11

Solution > Loads -Apply- > - Structural -Pressure


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Training Manual

Now apply pressure loads to the shell elements.

17

• Select the Shell elements: Utility Menu: Select > Entities

– Elements

– By Attributes

– Element type number

– Shell elements have previously been defined as 4.

– OK

13

14

15

16

13

14

15

16

17


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Training Manual

18

19

20

21

18

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19

20

Pressure Load Transfer to Shells (continued)

Where to get pressures

Shell Face 1 for Shell 61s

Loads from jobname (mix).rfl file

OK


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Training Manual

• Select Everything Utility Menu > Select > Everything

Solve - Current load step

• Read and close any boxes that arise when solution is started.

1

1

Stage 11: Solve the Structural Problem

• Read in the last set of results: Main Menu: General Post Processor > Last Set

• Select elements by Type Number Utility Menu > Select > Entities

ElementsBy AttributesElement type2 and 4OK

• Select Nodes associated with the elements Utility Menu > Select > Entities

Nodes

Attached to

Elements

OK

1

2

5

4

6

8

7

9

3

6

7

8

9

1

2

3

4

5

Stage 12: Post Process - Examine the deformation

• PlotCtrls > Style > Disp Scaling

Set displacment scaling to 1.0

OK

• Plot Results > Deformed Shape

Deformed + Undeformed

OK

1

2

3

4

4

3

2

1

Post Process (continued) - Plot Actual Deformed Shape


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Training Manual

Post Process (continued) - The Deformed shape resulting from pressure loads


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Training Manual

• Solution > -Load Step Options - Other

Updt Node Coord…

Set to 1.0: Use all of the displacement

Do not zero displacements

OK

4

2

3

1

1

2

3

4

First select everything: Utility Menu > Select > Everything

Stage13: Update the Nodal Coordinates with the deformed mesh


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Training Manual

Stage 14: Continuing the Sequential Solution Process • Execution of the “new” CFD problem domain would result in a

slightly different pressure distribution since the mesh has changed. The structural problem can then be solved again to see if the new pressure distribution results in significantly different displacements. Continued sequential solution can be done interactively or in a batch environment.

• The CFD analysis may be continued:– The Fluid Physics environment is activated as in Step 6– Solve as in Step 7

• If the structural analysis is repeated, the nodes should be returned to their original locations with the upcoord command.– Read in Structural physics environment as in Step 9– Update nodal coordinates as in Step 13, with FACTOR set to -1– Apply new pressure loads as in Step 10– Re-solve structures as in Step 11

multiphysics chapter 8. training manual may 15, 2001 inventory #001478 8-2 multiphysics chapter...

Documents

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