Multi -Objective Optimization of an America's Cup Class Yacht Bulb

MultiMulti--objective Optimization objective Optimization of an Americaof an Americas Cup Class Yacht Bulbs Cup Class Yacht Bulb

Matteo Ledri, Mauro Poian, Giorgio Contento

Multi-objective Optimization of an America's Cup Class Yacht Bulb2

IntroductionIntroduction

The present work is focused on the optimization of the bulb shape of an IACC (International Americas Cup Class)

There are no restrictions for the bulb shape according to the class rules (v 5.0)The weight has been fixed to maintain the same displacement of the boat


Problem definitionProblem definition

The bulb of an IACC yacht represents the 80% of the boat total weight.

The main features of an optimal design are:

Minimum drag to decrease the total resistance of the boat

Low centre of gravity to increase the righting moment(maximum draft according to the AC rule v 5.0 : 4.1m)


Problem definitionProblem definition

The optimization process consists of three phases:

Parametric modeling of the geometry (CATIA v5)

Automatic meshing (ICEMCFD)

CFD analysis (CFX5)


Parameterization strategyParameterization strategy

An initial ellipsoid is modified with Bezier curves to obtain a fair shape: Three input variables define the ellipsoid semi-axes Three Bezier curves are defined by a set of control points The coordinates of the Bezier curves are summed to the ellipsoid coordinates to

obtain the final shape of the profiles A set of sections is created using the profiles in x, y, z directions A lofted surface of the bulb is created using the sections

20 input variables: A,B,C: ellipsoid semi-axes X_top1, Z_top1, X_top2, Z_top2: coordinates of the control points to modify

the top profile of the bulb X_bottom1, Z_bottom1, X_bottom2, Z_bottom2: coordinates of the control

points to modify the bottom profile of the bulb X_side1, Y_side1, X_side2, Y_side2, X_side3, Y_side3 : coordinates of the

control points to modify the side view of the bulb m, n: parameters of the top and bottom section curves tail: dimension of the bulb tail relative to the bulb breadth



X_top1,Y_top1

X_top2,Y_top2

Ellipsoid top profile modification using bezier curve



Effect of parameters m and n on the section shape

Effect of parameter C on the section shape


MeshMesh generationgeneration

The computational domain has been meshed using ICEMCFD Reference lines to build the blocking imported from CATIA v5 Mesh Size: 2M Hexa Cells


CFD AnalysisCFD Analysis

The flow analysis has been performed using CFX 5.7.1

Automatic preprocessing using recorded script Parallel execution Automatic postprocessing

Simulation data:

Inlet Normal Speed: 5 m/s Turbulence Model: SST Convergence Criteria: Residual RMS < 1.0E-05


Workflow setupWorkflow setupInput variables

Input, Output, Transfer files

Output variables

Objectives and Constraints

Logic flow


Parallel processingParallel processing

Two degrees of parallelization have been implemented:

Parallel CFD analysis Domain partitioning Parallel optimization Submission of concurrent designs

Job performed on a Linux Cluster with 12 CPUs

4 concurrent designs 3 partitions for each design


ResultsResults


ResultsResults

Minimum Drag

Lowest VCG

Best Trade-off


Conclusion and further developmentsConclusion and further developments

A procedure for the development of an optimized bulb shape has been investigated solving practical problems related to:

Parameterization of geometry Automatic meshing CFD analysis

Results could be further improved by means of:

Use of the CFX transitional model in the CFD analysis Validation of the CFD model with experimental tests Integration of the results into a custom VPP (Velocity Prediction Program) to

evaluate the difference of boat speed due to drag and stability variations Comparison between different optimization algorithms applied to this problem

Multi-objective Optimization of an Americas Cup Class Yacht BulbIntroductionProblem definitionProblem definitionParameterization strategyParameterization strategyParameterization strategyMesh generationCFD AnalysisWorkflow setupParallel processingResultsResultsConclusion and further developments

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Multi -Objective Optimization of an America's Cup Class Yacht Bulb