Hydrodynamic optimization of ship hull forms

Hull hydrodynamic optimization of autonomous underwater vehicles operating at snorkeling depth

This paper presents a state-of-the-art systems approach to statistical modelling of fuel efficiency in ship propulsion, and also a novel and publicly available data set of high quality sensory data. Two statistical model approaches are investigated and compared: artificial neural networks and Gaussian processes (GP). The data presented is a publicly available full-scale data set, with a whole range of features sampled over a period of 2 months. We further discuss interpretations of the operational data in relation to the underlying physical system.

Statistical modelling for ship propulsion efficiency

Multi-objective shape optimization of autonomous underwater glider based on fast elitist non-dominated sorting genetic algorithm

Hydrodynamic optimization of the hull forms can be realized through the implementation and integration of computational tools that consist of a hydrodynamic module, a hull surface representation and modification module, and an optimization module. In the present paper, a new bulbous bow generation and modification technique has been developed and integrated into the hull surface representation and modification module. A radial basis function based surrogate model is developed to approximate the objective functions and reduce the computing cost. A multi-objective artificial bee colony optimization algorithm is implemented and integra- ted into the optimization module. To illustrate the integrated hydrodynamic optimization tools, a cargo ship is optimized for reduced drag. The optimal hull forms obtained are then validated computationally and experimentally. Validation results show that the prese- nt tools can be used efficiently and effectively in the simulation based design of the hull forms for reduced drag.

Hull form optimization of a cargo ship for reduced drag

Simple analytical relations for the bow wave generated by a ship in steady motion are given. Specifically, simple expressions that define the height of a ship bow wave, the distance between the ship stem and the crest of the bow wave, the rise of water at the stem, and the bow wave profile, explicitly and without calculations, in terms of the ship speed, draught, and waterline entrance angle, are given. Another result is a simple criterion that predicts, also directly and without calculations, when a ship in steady motion cannot generate a steady bow wave. This unsteady-flow criterion predicts that a ship with a sufficiently fine waterline, specifically with waterline entrance angle 2αE smaller than approximately 25°, may generate a steady bow wave at any speed. However, a ship with a fuller waterline (25°<2αE) can only generate a steady bow wave if the ship speed is higher than a critical speed, defined in terms of αE by a simple relation. No alternative criterion for predicting when a ship in steady motion does not generate a steady bow wave appears to exist. A simple expression for the height of an unsteady ship bow wave is also given. In spite of their remarkable simplicity, the relations for ship bow waves obtained in the study (using only rudimentary physical and mathematical considerations) are consistent with experimental measurements for a number of hull forms having non-bulbous wedge-shaped bows with small flare angle, and with the authors' measurements and observations for a rectangular flat plate towed at a yaw angle.

Simple analytical relations for ship bow waves

This study considers the three-dimensional potential flow due to a ship advancing with constant average speed in a train of regular waves. A modified integro-differential equation for determining the velocity potential on the mean position of the hull surface is obtained, and a solid theoretical basis for obtaining a numerical solution of the equation via a panel method is developed following the approach used by Kochin more than 50 years ago. In short, the approach is essentially based on a Fourier representation of the solution of a modified integro-differential equation. This approach circumvents the fundamental difficulties associated with the numerical evaluation of the Green function and its gradient, and their subsequent integration over the panels used to approximate the hull surface of a ship.

On the theory of potential flow about a ship advancing in waves

Four methods of analysis—a nonlinear method based on Euler's equations and three linear potential flow methods—are used to determine the optimal location of the outer hulls for a wave cancellation multihull ship that consists of a main center hull and two outer hulls. The three potential flow methods correspond to a hierarchy of simple approximations based on the Fourier-Kochin representation of ship waves and the slender-ship approximation.

Practical CFD Applications to Design of a Wave Cancellation Multihull Ship

This study provides complete and precise rules for evaluating the steady velocity of a piece-wise-constant distribution of Kelvin-Havelock sources on flat triangular hull panels and straight waterline segments with three digits of accuracy. The recipes yield a reliable and practical basis for a numerical method to compute steady flow about a ship using a distribution of Kelvin-Havelock sources.

Recipes for computing the steady free-surface flow due to a source distribution

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