fluid structure interaction (fsi) with rbf morph generic...

www.rbf-morph.com

RBF Morph, an ANSYS Inc. Partner

2011 EnginSoft International Conference

20 - 21 October Verona

Fluid Structure Interaction (FSI) with RBF Morph

Generic Formula 1 Front Wing

• Outline

• RBF Morph Tool Presentation

• Industrial FSI application

• Conclusions

Dr. Marco Evangelos Biancolini

University of Rome “Tor Vergata”

www.rbf-morph.com




RBF Morph Tool Presentation

• Morphing & Smoothing

• The Aim of RBF Morph

• RBF Morph Features

• Background

• How It Works

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Morphing & Smoothing

• A mesh morpher is a tool capable to perform mesh modifications, in order to achieve arbitrary shape changes and related volume smoothing, without changing the mesh topology.

• In general a morphing operation can introduce a reduction of the mesh quality

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

• If mesh quality is well preserved, then using the same mesh structure it’s a clear benefit.

www.rbf-morph.com




The Aim of RBF Morph • The aim of RBF Morph is to perform fast mesh morphing using a mesh-independent

approach based on state-of-the-art RBF (Radial Basis Functions) techniques.

• The use of RBF Morph allows the CFD user to perform shape modifications, compatible with the mesh topology, directly in the solving stage, just adding a single command line in the input file

• The final goal is to perform parametric studies of component shapes and positions typical of the fluid-dynamic design like:

• Design Developments

• Multi-configuration studies

• Sensitivity Studies

• DOE (Design Of Experiment)

• Optimization

(rbf-morph ‘(("sol-1" amp-1) ("sol-2" amp-2)...("sol-n" amp-n)))

www.rbf-morph.com




RBF Morph Features

• Add on 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

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

• Support of the CAD re-design of the morphed surfaces

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

• Precision: exact nodal movement and exact feature preservation.

www.rbf-morph.com




Background: RBF Theory • A system of radial functions is used to fit a solution for the

mesh movement/morphing, from a list of source points and their displacements. This approach is valid for both surface shape changes and volume mesh smoothing.

• The RBF problem definition does not depend on the mesh

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• Radial Basis Function interpolation is used to derive the displacement in any location in the space, so it is also available in every grid node.

• An interpolation function composed by a radial basis and a polynomial is defined.

zyxh 431 x

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How it Works: the work-flow

• RBF Morph basically requires three different steps:

• Step 1 [SERIAL] setup and definition of the problem

(source points and displacements).

• Step 2 [SERIAL] fitting of the RBF system.

• Step 3 [SERIAL or PARALLEL] morphing of the surface

and volume mesh (available also in the CFD solution

stage).

www.rbf-morph.com




How it Works: the problem setup

• The problem must describe correctly the desired changes

and must preserve exactly the fixed part of the mesh.

• The prescription of the source points and their

displacements fully defines the RBF Morph problem.

• The problem is mesh-independent, and could be defined

using grid nodes as well as arbitrary point locations.

• Each problem and its fit define a mesh modifier or a

shape parameter.

www.rbf-morph.com




How it Works: the interface

• One of the key aspects of RBF Morph, in respect to FLUENT

integration, is related to the ability of extracting information from

the FLUENT mesh and to the

user interface GUI

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Let RBF-Morph talk now!

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www.rbf-morph.com




Fo

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Caro

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En

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Ge

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Sh

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)

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MIR

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(MIR

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Industrial FSI application

• Challenge

• Test Case Description

• Solution

• Morphing and FSI Set Up

• Results

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Challenge: Fast FSI Tool.

• CFD calculations are usually performed

considering the undeformed wing

configuration (i.e. rigid parts)

• When important effects are observed (wing

deformation and rotation) the CFD model

should be updated to the deformed

configuration.

• Even a slight deformation can have a

dramatic effect on performances (Drag, Lift,

Tyre-Wing interaction,…).

• A feasible solution is given by Fluent + RBF

Morph: the CFD model parameterized using

modal shapes becomes flexible!

www.rbf-morph.com




Test Case Description: Generic F1 Front End

• Attention is focused on the front wing that is connected to the body by means of two pylons

• The wing is composed by two profiles (Main and an adjustable Flap)

• Transversal flow is confined by the End Plate and a Fence

• Compliance of parts is critical! Loads are very high and even small deflections can affect the wing performance (drag, lift, wing tyre interaction)

www.rbf-morph.com




Solution: Modes Embedding with RBF Morph

1. Modal shapes are calculated using FEA

2. Fluid mesh is parameterized using modal shapes by RBF Morph each mode is stored as a standard shape modifier

3. fmorph module is initialized at the beginning of CFD parallel run

4. Modal Forces are integrated onto the CFD mesh within Fluent

5. The amplification of each mode is obtained dividing the modal force for the squared circular frequency

6. CFD mesh is updated using known amplifications

7. The CFD model becomes elastic i.e. is capable to update its shape using actual pressure with a single command

8. Usually the shape is updated during CFD iterations (typical updating interval is 25)

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Problem Definition

• Fluent Mesh: tet + 3 prisms layers 3167964 cells

• Steady simulation iterated until stable forces are achieved

• FEM modeling with ANSYS Mechanical (static + modal)

• Equivalent steel thickness to have 7 mm deflection at 126 kph

• Full coupled 2 ways simulation used as a reference

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RBF Morph Set Up (using GUI)

• A domain Encap around the wing is used to limit the morphing action

• The FEM field is imposed to all the threads on the wing and pylons

• A zero movement is imposed to constraint the remaining threads (body, wheel, ground)

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FSI Model Set up (using TUI)

• RBF Morph set-up used for first mode is replicated in batch for all required modes

• The modal approach is enabled during solution using the command (rbf-fmorph-init); it should disabled at the end with (rbf-fmorph-end)

• Mesh updating using modal approach is enabled adding a single calculation activity (modal-q-update-static)

(define (modal-q-update-static)

;; calculate modal forces

(set! modal-forces (rbf-fmorph-forces '("front_wing_flap" ... "fin")))

;; update q = F / k

(set! modal-q (map / modal-forces modal-k))

;; update mesh

(rbf-fmorph (list (list "mode1-new" (list-ref modal-q 0)) ...)))

)

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Results: Morphing with 5 Modes

• Modes are

normalized

with respect to

mass

• Each mode is

previewed in

the interval

0-0.01

• Actual

amplifications

depends on

pressure

loads!

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• Each mode refine

the deformation

• With five modes

the error is less

than 0.2 mm

(3%)

• Loads are

affected by

elastic

deformation

(drag 10% lift

1.5%)

Mode Max d(mm) Max err(mm) Max err (%)

1 5,58 1,61 22,39

2 6,33 0,86 12,00

3 6,34 0,85 12,15

4 6,53 0,66 9,50

5 7,00 0,19 2,76

2 Ways FSI 7,19 0,00 0,00

Part Fx (N) Fy (N) Fz (N) dFx (%)

dFy (%)

dFz (%)

Fin 1,00 1,21 0,07 -0,52 2,93 1,21

Flap 30,56 -0,38 -67,30 3,84 -23,15 0,35

Main 12,61 6,48 -319,94 30,60 -2,22 1,73

Plate 5,45 11,48 -19,37 5,12 -1,18 1,07

Vane 4,95 19,23 -0,71 3,41 1,70 -1,50

Total 54,57 38,02 -407,25 10,04 0,45 1,46

Results: mode convergence, loads (126kph).

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Resu

lts

: e

ffec

t o

f sp

ee

d

(54

-16

2k

ph

).

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Remarks Performances

• Loads are affected by structural

deformation

• Modal approach makes the CFD

model parametric with respect to

structural dynamics modes, i.e.

flexible.

• All calculations performed on a small

Hybrid mesh (tet+prisms) 3.2

millions cells using a laptop

(Fluent13 on Linux platform, RBF

Morph 1.3)

• Similar performances are expected

for larger models running on larger

calculation facilities (RBF Morph is

fully parallel)

• Transient implementation available

• CPU* Time to fit each mode

(120.000RBF points) 190 s

• CPU Time to init 5 modes 117 s

• CPU Time for each mesh update

using 5 modes 3 s

• CPU Time for a CFD iteration 15 s

• User Time to set-up modes (FEM

+ RBF Morph) 1/2 day

• User Time to set-up CFD + modal

simulation 1/2 day

• In transient analysis the mesh

can be updated at each time step

(but with MDM extra cost!)

*one Intel® Centrino2 dual-core processor, 2.26GHz 8GB

www.rbf-morph.com




Fluid Structure Interaction (FSI) with RBF Morph

Generic Formula 1 Front Wing

Thank you for your

attention!

Dr. Marco Evangelos Biancolini

E-mail: [email protected]

Web: www.rbf-morph.com

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