ioda project - esr 9 - open...

IODA projectESR 9 - Open CASCADE

Salvatore Auriemma

[email protected]

9th December 2016

Salome day, EDF Lab, Saclay

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IODA Project

IODA1: Industrial Optimal Design using Adjoint CFD:

• European Commission project that follows other two ECprojects (FlowHead2 and AboutFlow3).

• 15 Early Stage Researchers (ESR) displaced around severalEuropean Institution to develop new methods for the designoptimisation.

• Institutions: Universities (Queen Mary University of London,University of Paderborn) and Companies (Open CASCADE,Rolls Royce D., Volkswagen..).

Main GoalAerodynamic shape optimisation.

1http://ioda.sems.qmul.ac.uk/2http://flowhead.sems.qmul.ac.uk/3http://aboutflow.sems.qmul.ac.uk/

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Aerodynamic Shape Optimisation

Given a CAD-model, change the Shape to maximize/minimize athermo-fluid dynamics component (ex. velocity in a pipe, deltapressure, lift of a wing..)

• Two different approaches are possible:

CAD-free methodsResult is an optimised mesh7 No link to CAD

CAD-based methodsX Result is a CAD model with optimised design parameters

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CAD-based Shape Optimisation

CAD-model with design parameters α

Mathematical formulation for gradient-based optimisation

minα

J(U(X (α)),X (α), α) (1)

R(U(X (α)),X (α)) = 0 (2)

dJ

dα=

dJ

dXS

dXS

dα(3)

CFD Sensitivity dJdXS

: Efficient adjoint method

CAD Sensitivity dXSdα : FD, Analytical, AD

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CAD-based Shape optimisation

ESR 9 tasks

• Evaluate the CAD sensitivities using an AlgorithmicDifferentiation tool (ADOL-C, provided by University ofPaderborn (UPB) - close collaboration with ESR9 @ UPB).

• Design(Parametrise) the Industrial applications (U-bend pipe,car mirror, compressor stator blade..).

• Optimise the industrial applications using Open CASCADE +CFD tool from QMUL (close collaboration with ESR12 @QMUL).

Presentation Outline

Calculation CADsensitivities

Test case design(Parametrisation)

CAD sensitivities,Optimisation results Shaper application

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Calculating the CAD sensitivities

An exact way of calculating the shape sensitivities w.r.t. designparameters is to apply the Automatic Differentiation (AD) to theCAD sources. AD tool integrated to OCCT is ADOL-C.

Automatic Differentiation by OverLoading in C++

ADOL-C uses operator overloading concept to compute first andhigher derivatives of vector functions that are written in C or C++.

Concept of AD by operator overloading

All variables that may be considered as differentiable quantitiesmust be of an active type, which is named adouble in ADOL-C.

Original codeDifferentiated

code

adouble

injection

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Test Case under Investigation: U-bend

To test the differentiated OCCT in an optimisation, the IODA testcase U-bend was parametrised.

The U-bend pipe is a typical cooling channel used in turbine bladeapplication:

The parametrisation allows to deform the U-part and is based on across-sectional design approach which takes N-slices as inputs inorder to construct a final surface.

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U-bend Parametrisation

The generic slice (shown on the left) consists of 4 Bezier curves; itis orthogonal to a planar line named ”pathline”.

Each control point of the section is characterized by a law ofevolution along the pathline. In particular every law is B-splinecurve whose control points coordinates are the design parametersof the simulation.

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CAD Sensitivities

Example of sensitivities calculated using AD

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Optimisation Results

Cost function:Total pressure lossesbetween inlet/outlet

Design improvement:

16%

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Shaper application

Limit of this approach: All the code for the optimisation iswritten in c++; this is difficult for the designer:

• not all the designers are programmers.

• time consuming approach.

SolutionParametrise (design) the test cases in Shaper4 and involve it in theoptimisation loop.

4Under development (for SALOME CEA/EDF platform) ,to be published in LGPL in 2017.

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Further work and Conclusions

Current stateX AD tool ADOL-C coupled to Open CASCADE CAD kernel.X developed an approach to design/parametrise the U-bend testcase.X Performed the U-bend optimisation.

Future steps

7 Apply ADOL-C tool to Shaper7 Design (parametrise) a test case in Shaper and perform itsoptimisation.7 Application of the optimisation tool to the test cases provided byindustrial partners of IODA project.

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Research is conducted within IODA5 projectIndustrial Optimisation using Adjoint CFD

5http://ioda.sems.qmul.ac.uk/ Grant Agreement No. 642959.13 / 13

ioda project - esr 9 - open...

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