RBF Morph - An Add-on Module for Mesh Morphing in ANSYS Fluent · RBF Morph Advantages • Faster...

RBF Morph – An Add-on Module for

Mesh Morphing in ANSYS Fluent

© 2011 ANSYS, Inc. May 14, 20121

Gilles EggenspielerSenior Product Manager

Morphing & Smoothing

• A mesh morpher is a tool capable of performing mesh modifications in order to achieve arbitrary shape c hanges and related volume smoothing without changing the mesh topology.

• In general, a morphing operation can introduce a re duction of the mesh quality

• A good morpher has to minimize this effect, and maxi mize the possible shape modifications.

• If mesh quality is well preserved, then using the s ame mesh

© 2011 ANSYS, Inc. May 14, 20122

• If mesh quality is well preserved, then using the s ame mesh structure has massive productivity benefits

RBF Morph Advantages

• Faster and more consistent than remeshing

• Simplifies the parameterization of models

• Cuts out any file i/o associated with traditional remeshing methods

• Fast convergence on new designs from previous results

• Ideal for robust design analysis or optimization

• Truly opens up the realms of design optimisation on large-scale CFD

models where remeshing and file i/o are very expensive

© 2011 ANSYS, Inc. May 14, 20123

models where remeshing and file i/o are very expensive

• The user-friendly RBF Morph addonmodule is fully integrated within Fluent (GUI, TUI & solving stage) and Workbench

• Mesh-independent RBF fit used for surface mesh morphing and volume mesh smoothing

• Parallel calculation allows to morph large size models (many millions of cells) in a short time

RBF Morph Features

© 2011 ANSYS, Inc. May 14, 20124

short time

• Management of every kind of mesh element type (tetrahedral, hexahedral, polyhedral, etc.)

• Ability to convert morphed mesh surfaces back into CAD

• Multi fit makes the Fluent case truly parametric (only 1 mesh is stored)

• Precision: exact nodal movement and exact feature preservation.

• A system of radial functions is used to fit a solution for the mesh movement/morphing, from a list of source points and their prescribed displacements

• Radial Basis Function interpolation is used to derive the displacement at any location in the space

How Does RBF-Morph work?

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• The RBF problem definition is mesh independent.

How it Works: The Work-Flow

• RBF Morph execution requires three steps:• Step 1 [SERIAL Fluent] setup and definition of the

problem (source points and displacements).• Step 2 [SERIAL Fluent] fitting of the RBF system.• Step 3 [SERIAL or PARALLEL Fluent] morphing of

the surface and volume mesh (available also in the

© 2011 ANSYS, Inc. May 14, 20126

the surface and volume mesh (available also in the CFD solution stage).

RBF-Morph is Integrated with Fluent

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RBF-Morph 1.3 Features

• RBF Morph allows exact prescription of surface movements which opens up several interesting capabilities, including:

© 2011 ANSYS, Inc. May 14, 20128

including:

• FEM deformed shape (static )

• FSI based on modal FEM analysis

• Target surfaces (STL)

Morphing a simple wind tunnel

• A bluff body (a perfect cube with edges of 1m) is immersed in a virtual wind tunnel

• The effect of cube attitude

© 2011 ANSYS, Inc. May 14, 20129

• The effect of cube attitude angle is explored using mesh morphing

Rotating the Cube – RBF Morph Setup

• Rigid movement is applied ( rotation about the vertical axis ) to all nodes on the cube.

• Rigid movement is applied ( null ) to all nodes on the tunnel, the inlet and the outlet.

© 2011 ANSYS, Inc. May 14, 201210

the inlet and the outlet. • All the areas without a

prescribed motion are left deformable by default: the ground and all the volume mesh.

• Cube can be rotated past 180 degrees without corruption of the volume mesh!

Internal flow example

© 2011 ANSYS, Inc. May 14, 201211

Here, a pipe is projected onto a previously defined STL shape

Internal Flow Example (2)

© 2011 ANSYS, Inc. May 14, 201212

courtesy of MIRA

Here, two cylinders are used to deform a duct to complex shapes

Compressor Blade Example

© 2011 ANSYS, Inc. May 14, 201213

External flow example

© 2011 ANSYS, Inc. May 14, 201214

courtesy of Ignazio Maria

Viola

Ship sail rotation

External Flow Example (2)

© 2011 ANSYS, Inc. May 14, 201215

• Volvo XC60 vehicle model

– Four shape parameters

– RBF Morph to define shape parameters

– ANSYS DesignXplorer

• To drive shape parameters

External Aerodynamics

© 2011 ANSYS, Inc. May 14, 201218

To drive shape parameters

• To create DOE

• To perform Goal Driven Optimization

• Ideal Aerodynamics Optimization Process

– Capacity

– Automatic

– Fast

– Accurate

• Volume Mesh – TGrid

• Cell Count : 50.2 Million Cells

• Prism Layers : 10 (First Aspect Ratio 10, Growth 1.1)

• Prism Count : 24.4 Million Cells

• Skewness < 0.9

Step #1 : Baseline Model

Prism Layers

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Cut Plane Y=0

Cut Plane Z = 1.4 m

• Boundary Conditions

– Inlet : Velocity Inlet 100 kmph

– Outlet : Pressure Outlet, 0 Pa (Gage)

– Side walls : Wall, no-slip

– Top wall : Wall, no-slip

• Solver Settings

– Steady, PBCS, Green Gauss Node

Step #2 : CFD Setup

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– Steady, PBCS, Green Gauss Node Based Gradient

– Fluid : Incompressible air,

– Density = 1.225 kg/m3,

– Turbulence : Realizable K-epsilon, Non-equilibrium wall treatment

– Discretization :

• Pressure – Standard

• Momentum, TKE, TDR – 2nd Order

• Solution Controls

– Courant Number = 200

– ERFMomentum, Pressure = 0.75

– URFs Density = 1.0, Body Forces = 1.0TKE, TDR = 0.8TR = 1.0

Step #3 : RBF-MorphNote: a separate webinar

looks at Fluent MMO in

more detail, but this

example used RBF-Morph

© 2011 ANSYS, Inc. May 14, 201221

Boat Tail Angle (P2) Roof Drop Angle (P3)

Green House (P4) Front Spoiler Angle (P5)

Step #3 : RBF-Morph

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Axis about which selected surface set gets morphedEncapsulation RegionSurface set selection

Step #3 : RBF-Morph

• Fully integrated within FLUENT and Workbench

• Easy to use

• Parallel => rapidly morph large size models

• Mesh independent solution works with all element types (tetrahedral, hexahedral, polyhedral, etc.)

• Superposition of multiple RBF-solutions makes the FLUENT case truly parametric (only 1 mesh is stored )

© 2011 ANSYS, Inc. May 14, 201223

FLUENT case truly parametric (only 1 mesh is stored )

• RBF-solution can also be applied on the CAD

• Precision: exact nodal movement and exact feature preservation.

Step #4 : Setup DesignXplorer

© 2011 ANSYS, Inc. May 14, 201224

DOE: Central Composite Design, Face

Centered, Enhanced

Step #5 : Running Simulations

768 Cores 384 Cores 288 Cores 240 Cores 144 Cores

Task Time (Seconds) Time (Seconds)Time

(Seconds)

Time

(Seconds)

Time

(Seconds)

Baseline Case (i.e. Design Point 1)

Read volume mesh of baseline

case into the CFD solver and

apply solver settings

225 340 365 481 228

CFD Solution 6979 11153 14409 17256 27246

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CFD Solution 6979 11153 14409 17256 27246

Writing CFD data file 681 538 558 600 532

Each Subsequent Design Point

Morph vehicle shape 84 59 65 69 100

CFD Solution 1284 1754 2208 2630 4100

Writing CFD data file 734 559 572 621 532

Total Run Time (Wall Clock)

Needed for All 50 Design

Points (Hours)

30.80 35.63 42.98 50.28 72.19

Design Boat Tail Angle Long Roof Angle Green House Front Spoiler Drag Force (N)

• Flow Results Discussion

– Design point 1, 9, 19 & 25

– Velocity contours

– Iso-surface of total pressure = 0.0

Results :

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Design

Points

Boat Tail Angle

(P2)

Long Roof Angle

(P3)

Green House

(P4)

Front Spoiler

Angle (P5)

Drag Force (N)

(P1)

1 0.000 0.000 0.000 0.000 388.01

9 0.000 1.500 0.000 1.900 393.01

19 1.850 -2.300 -0.700 0.000 372.30

25 -1.850 1.500 -0.700 0.000 397.33

• A CFD model can be accurately moulded in a parametric manner within ANSYS Fluent using the RBF Morph Addon Module

• Such parametric CFD model can be easily coupled with automatic optimization tools to steer the solu tion to an optimal design that can then be exported into the preferred CAD platform (using STEP)

Conclusions

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• The proposed approach dramatically reduces the man time required for shape optimisation set-up, thus widening the CFD calculation capability

• Reference: M.E. Biancolini, Mesh morphing and smoothing by means of Radial Basis Functions (RBF): a practical example using Fluent and RBF Morph in Handbook of Research on Computational Science and Engineering: Theory and Practice (http://www.cse-book.com/).

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