Hydrodynamic Shape Optimization of Axisymmetric Bodies Using Multi-fidelity Modeling - Simulation and Modeling Methodologies, Technologies and Application - page 200

Hydrodynamic Shape Optimization of Axisymmetric
Bodies Using Multi-fidelity Modeling

Leifur Leifsson, Slawomir Koziel, and Stanislav Ogurtsov

Engineering Optimization & Modeling Center, School of Science and Engineering,
Reykjavik University, Menntavegur 1, 101 Reykjavik, Iceland
{leifurth,koziel,stanislav}@ru.is

Abstract. Hydrodynamic shape optimization of axisymmetric bodies is pre-
sented. A surrogate-based optimization algorithm is described that exploits a
computationally cheap low-fidelity model to construct a surrogate of an accu-
rate but CPU-intensive high-fidelity model. The low-fidelity model is based on
the same governing equations as the high-fidelity one, but exploits coarser
discretization and relaxed convergence criteria. A multiplicative response cor-
rection is applied to the low-fidelity CFD model output to yield an accurate and
reliable surrogate model. The approach is implemented for both direct and in-
verse design. In the direct design approach the optimal hull shape is found
by minimizing the drag, whereas in the inverse approach a target pressure dis-
tribution is matched. Results show that optimized designs are obtained at sub-
stantially lower computational cost (over 94%) when compared to the direct
high-fidelity model optimization.

Keywords: Shape Optimization, Surrogate-based Optimization, Multi-fidelity
Modeling, Axisymmetric Body, CFD, Direct Design, Inverse Design.

1 Introduction

Autonomous underwater vehicles (AUVs) are becoming increasingly important in
various marine applications, such as oceanography, pipeline inspection, and mine
counter measures [1]. Endurance (speed and range) is one of the more important
attribute of AUVs [2]. Vehicle drag reduction and/or an increase in the propulsion
system efficiency will translate to a longer range for a given speed (or the same
distance in a reduced time). A careful hydrodynamic design of the AUVs, including
the hull shape, the protrutions, and the propulsion system, is therefore essential.
The fluid flow around an underwater vehicle with appendages is characterized by
flow features such as thick boundary layers, vortices and turbulent wakes generated
due to the hull and the appendages [3]. These flow features can have adverse effects
on, for example, the performance of the propulsion system and the control planes.
Moreover, the drag depends highly on the vehicle shape, as well as on the
aforementioned flow features. Consequently, it is important to account for these
effects during the design of the AUVs.
The prediction of the flow past the full three-dimensional configuration of the
AUVs requires the use of computational fluid dynamics (CFD). Numerous