Ronald W Yeung | University of California, Berkeley (original) (raw)

Papers by Ronald W Yeung

Journal of Hydronautics, Oct 1, 1977

The hydrodynamic interactions of two vessels moving at the same speed in nearfield is considered ... more The hydrodynamic interactions of two vessels moving at the same speed in nearfield is considered by applying the slender-body theory. It is shown that, for a water depth that is the same order as the beam of the vessel, the problem reduces to a sequence of inner problems in the cross-flow plane. This reduction to strip-theory allows one to obtain the solution without the necessity of solving an outer problem. Applications were made to two pairs of ship models. Theoretical predictions generally are high as compared with available experimental measurments, but offer a fairly satisfactory qualitative description of the interaction phenomenon when the length of the overlap of the vessels is large as compared with the separation.

International Journal of Offshore and Polar Engineering, Dec 1, 2003

The Free-Surface Random-Vortex Method (FSRVM, Yeung, 2002) is applied to investigate two types of... more The Free-Surface Random-Vortex Method (FSRVM, Yeung, 2002) is applied to investigate two types of forced motion problems with the effects of viscosity considered. A submerged body undergoing periodic swaying oscillation is considered and compared with the results of the vorticity-diffusion theory of Yeung and Wu (1991), which had the convective terms of the Navier-Stokes equations neglected. A practical shape consisting of a rectangular cylinder with horizontal and vertical keels or baffle-plates is used to study the roll inertia and damping characteristics. Comparison is made with some recent experimental results to illustrate the efficacy and accuracy of the theory.

Journal of Engineering Mathematics, Jan 18, 2011

A methodology is presented for matching a solution to a three-dimensional free-surface viscous fl... more A methodology is presented for matching a solution to a three-dimensional free-surface viscous flow in an interior region to an inviscid free-surface flow in an outer region. The outer solution is solved in a general manner in terms of integrals in time and space of a time-dependent free-surface Green function. A cylindrical matching geometry and orthogonal basis functions are exploited to reduce the number of integrals required to characterize the general solution and to eliminate computational difficulties in evaluating singular and highly oscillatory integrals associated with the free-surface Green-function kernel. The resulting outer flow is matched to a solution of the Navier-Stokes equations in the interior region and the matching interface is demonstrated to be transparent to both incoming and outgoing free-surface waves. Keywords Integral equations • Open-boundary condition • Pseudo-spectral solutions • Time-dependent free-surface Green function • Viscous-inviscid matching • Wave-body interaction Dedication: In fond memory of my friend Ernie who kindly invited me to visit Adelaide in 1981 and provided the environment for the completion of my "Annual Review" article. R. W. Yeung.

Journal of Fluid Mechanics, Dec 1, 1989

Unsteady free-surface flow a t the bow of a steadily moving, two-dimensional body is solved using... more Unsteady free-surface flow a t the bow of a steadily moving, two-dimensional body is solved using a modified Eulerian-Lagrangian technique. Lagrangian marker particles are distributed on both the free surface and the far-field boundary. The flow field corresponding to an inviscid, double-body solution is used for the initial condition. Solutions are obtained over a range of Froude numbers for bodies of three different shapes: a vertical step, a faired profile, and a bulbous bow. A transition Froude number exists a t which the bow wave begins to overturn and break. The value of the transition Froude number depends on the bow shape. A stagnation point is observed to be present below the free surface during the initial stage of the wave formation. For flows occurring above the transition Froude number, the stagnation point remains trapped below the free surface as the wave overturns. Below the transition Froude number, the stagnation point rises to the surface as the crest of the transient bow wave moves upstream and away from the body.

Journal of offshore mechanics and Arctic engineering, Oct 12, 2015

The performance of an asymmetrical rolling cam as an ocean-wave energy extractor was studied expe... more The performance of an asymmetrical rolling cam as an ocean-wave energy extractor was studied experimentally and theoretically in the 70s. Previous inviscid-fluid theory indicated that energy-absorbing efficiency could approach 100% in the absence of real-fluid effects. The way viscosity alters the performance is examined in this paper for two distinctive rolling-cam shapes: a smooth “Eyeball Cam (EC)” with a simple mathematical form and a “Keeled Cam (KC)” with a single sharp-edged keel. Frequency-domain solutions in an inviscid fluid were first sought for as baseline performance metrics. As expected, without viscosity, both shapes, despite their differences, perform exceedingly well in terms of extraction efficiency. The hydrodynamic properties of the two shapes were then examined in a real fluid, using the solution methodology called the free-surface random-vortex method (FSRVM). The added inertia and radiation damping were changed, especially for the KC. With the power-take-off (PTO) damping present, nonlinear time-domain solutions were developed to predict the rolling motion, the effects of PTO damping, and the effects of the cam shapes. For the EC, the coupled motion of sway, heave and roll in waves was investigated to understand how energy extraction was affected.

The study on close-quarter manoeuvring of vessels carries great importance for the safety and eff... more The study on close-quarter manoeuvring of vessels carries great importance for the safety and efficiency of maritime operations. In this paper, the hydrodynamic interactions between two vessels in moderate-speed overtaking manoeuvres are studied. Computational investigation by free-surface panel method is performed, and the results are assessed against experimental measurements from towing-tank model tests. The influences of overtaking speed and the speed difference between vessels on the hydrodynamic loads are studied. It is found that the free-surface deformation, on account of the blockage effects of the bodies, wave-making properties of the vessels, and the interference of unsteady wave patterns between the vessels, considerably affects the hydrodynamic interactions. In addition, it is also discovered that the influence from the unsteady heave and pitch motions of the hulls on the hydrodynamic loads can be non-negligible. Furthermore, it is found that the slower vessel to be overtaken generally experiences larger loads with more variation than the overtaking vessel. The loads on both vessels become more similar to those of a steady-state di-hull system when the speed difference between vessels is small.

The “Deep Water Horizon” Mobil Offshore Drilling Unit (MODU) is one of several classes of floatab... more The “Deep Water Horizon” Mobil Offshore Drilling Unit (MODU) is one of several classes of floatable drilling machines. As a consequence of the accident on April 20, 2010, the worst ecological disaster with regard to oil spills in the US history was generated in the Gulf of Mexico, causing extensive damage to marine and wildlife habitats, as well as the Gulf’s fishing and tourism industries. Since that moment, experts are trying to estimate the total amount of oil being lost into the sea. The objective of this presentation is to report a procedure developed in the first author’s thesis1 an independent and logical estimate of the oil flow rate into the Gulf of Mexico produced by the rupture in this rig. There are a number of possible approaches to estimate the flow rate of oil spilling into the Gulf of Mexico. The Plume Modeling Team has developed an approach by observing video image of the oil/gas mixture escaping from the kinks in the riser and the end of the riser pipe. The Mass Balance Team has developed a range of values using USGS (US Geological Survey) and NOAA (National Oceanic and Atmospheric Administration) data analysis collected from NASA’s (National Aeronautics and Space Administration) Airborne Visible InfraRed Imaging Spectrometer (AVIRIS). Finally, a reality-check estimate was based on the amount of oil collected by the Riser Insertion Tube Tool (RITT) plus the estimate of how much oil is escaping from the RITT, and from the kink in the riser. However, there are several limitations in each of these techniques.

We present a numerical formulation and computational results for the hydrodynamic loads on bottom... more We present a numerical formulation and computational results for the hydrodynamic loads on bottom-mounted thin-shell vertical cylinders of arbitrary cross-sectional shapes, including open bodies. Such cylinders may undergo prescribed or free motion or may be subjected to a wave load. The formulation is based on linear theory and a hypersingular integral-equation results from sectional contours of zero thickness. The method reduces the fully three-dimensional problem into a number of two-dimensional ones in the horizontal plane and is therefore much faster than the usual boundary integral method used for water wave problems. This traditional method of solution is also known to become ill-conditioned as the body thickness decreases. As an example of the current method, radiation and diffraction loads are presented for the cases of a circular and square closed and opened cylinders with the effect of the increased opening size discussed at different frequencies. The free-surface elevation associated with this method of solution is presented for some cases as well.Copyright © 2014 by ASME

Journal of Engineering Mathematics, Nov 1, 2014

The wave elevation and flow near a moving pressure distribution of characteristic intensity p 0 a... more The wave elevation and flow near a moving pressure distribution of characteristic intensity p 0 and length 2a are investigated using a fully nonlinear and unsteady mixed Eulerian-Lagrangian method. Special attention is paid to the zero-wave-resistance (ZWR) conditions and the associated waveless free-surface profiles. Large-time solutions for free-surface elevation are in good agreement with linear steady-state solutions for small applied pressure parameter p 0 /(ρga), with ρg being the weight density of the fluid. The ZWR phenomenon predicted by the linear wave theory at certain critical speeds is recovered from these nonlinear solutions. As p 0 /(ρga) increases, large-time nonlinear solutions indicate that trailing waves of near-zero amplitude can still be achieved at certain adjusted critical speeds. The time evolution of the trailing waves is presented and discussed.

Applied Ocean Research, Oct 1, 2018

We present results for the added mass and moment of inertia of infinitely thin plates of arbitrar... more We present results for the added mass and moment of inertia of infinitely thin plates of arbitrary shapes in an infinite potential field. The problem is modeled using a hypersingular boundary-integral equation and is treated directly using a Galerkin approach without regularization. The results are used to fill some gaps in the literature of the values of added mass for these plates, particularly those plates with openings or holes and we compare the exact numerical results with those obtained by simply subtracting the added mass or inertia from those of the full plate (an algebraic approximation). The algebraic approximation gives incorrect values compared with actual three-dimensional results.

This paper evaluates two aspects of enhancements made to the UC-Berkeley ocean-wave energy extrac... more This paper evaluates two aspects of enhancements made to the UC-Berkeley ocean-wave energy extraction device first presented in [1]. First, the differences in hydrodynamic performance between flat- and hemispherical bottom floaters were investigated theoretically using UC Berkeley 2-D viscous-flow solver: FSRVM [2]. The predicted enhancement was compared with experimental results, demonstrating that an increase in motion of over 50% was realizable. Second, important modifications to the design, fabrication, and material of the rotor and stator of the permanent magnet linear generator (PMLG) were made with the aim of increasing both power output and mechanical-to-electrical conversion efficiency, ηel. Increased power extraction and efficiency were achieved, doubling what had been previously reported. The non-linear relationship between the generator damping and the magnet-coil gap width was also investigated to verify that the conditions for optimum power extraction presented in [1] were achievable with the PMLG. Experimental results, obtained from testing the coupled floater and PMLG system in the UC-Berkeley wave tank, revealed that measured capture widths were more than double those from the previous design. These results further confirmed that matching of the generator and floater damping significantly increased the global efficiency of the extraction process.

ABSTRACT The powering issue of a high-speed marine vehicle with multi-hulls is addressed, since t... more ABSTRACT The powering issue of a high-speed marine vehicle with multi-hulls is addressed, since there is an often need to quickly evaluate the effects of several configuration parameters in the early stage of ship design. For component hulls with given geometry, the parameters considered include the relative locations of individual hulls and the relative volumetric ratios. Within the realm of linearized theory, an interference resistance expression for hull-to-hull interaction is first reviewed, and then a new formula for hull-and-pressure distribution interference is derived. Each of these analytical expressions is expressed in terms of the Fourier signatures or Kochin functions of the interacting components, with the separation, stagger, and speed as explicit parameters. Based on this framework, examples are given for assessing the performance of a di-hull as opposed to a tetra-hull system. Also examined is the wave resistance generated by a Surface-Effect Ship (SES) in comparison with that by a baseline catamaran, subject to the constraint of constant total displacement.

Journal of Fluids Engineering-transactions of The Asme, Sep 1, 1995

A pseudo-spectral formulation for solving unsteady, three-dimensional fluid motion with a free su... more A pseudo-spectral formulation for solving unsteady, three-dimensional fluid motion with a free surface in cylindrical coordinates is presented. An effective method for treating the Laplace equation, as a special application of a generalized Poisson solver, is developed. This approach is demonstrated by studying the evolution of transient surface waves near a vertical circular cylinder enclosed in open or closed domains. Results are observed to have a high degree of precision and spatial resolution even at large time. Potential applications of this method to other problems are discussed.

Journal of offshore mechanics and Arctic engineering, Jul 15, 2008

The powering issue of a high-speed marine vehicle with multihulls and air-cushion support is addr... more The powering issue of a high-speed marine vehicle with multihulls and air-cushion support is addressed, since there is an often need to quickly evaluate the effects of several configuration parameters in the early stage of the design. For component hulls with given geometry, the parameters considered include the relative locations of individual hulls and the relative volumetric ratios. Within the realm of linearized theory, an interferenceresistance expression for hull-to-hull interaction is first reviewed, and then a new formula for hull-and-pressure distribution interference is derived. Each of these analytical expressions is expressed in terms of the Fourier signatures or Kochin functions of the interacting component hulls, with the separation, stagger, and speed as explicit parameters. Based on this framework, an example is given for assessing the powering performance of a catamaran (dihull) as opposed to a tetrahull system. Also examined is the wave resistance of a surface-effect ship of varying cushion support in comparison with that of a base line catamaran, subject to the constraint of constant total displacement.

Applied Energy, Dec 1, 2016

h i g h l i g h t s Flow past a micro Bach-type turbine is solved using a viscous Discrete-Vortex... more h i g h l i g h t s Flow past a micro Bach-type turbine is solved using a viscous Discrete-Vortex Method. Performance of Bach-type turbines is not significantly degraded at small scales. In laminar flow, performance of Bach-type turbines can be boosted with wake capture. Velocity fluctuation and decreased performance observed for free rotation in water. Micro-scale Bach-type turbines can potentially power wireless sensor nodes.

$Research paper thumbnail of Nonlinear Wave Diffraction Over Submerged Obstacles$

Recently there has been considerable interest in simulation of nonlinear waves diffracting over s... more Recently there has been considerable interest in simulation of nonlinear waves diffracting over submerged obstacles. For bodies which are shallowly submerged, strong nonlinear behaviour is observed in the immediate vicinity of the body. Another characteristic is the generation of higher harmonics in the reflected and transmitted waves. A sizeable number of past investigations have been devoted to interactions of solitary waves with bottom topography, e.g. The present work focuses more on the effects of periodic incident waves, specifically our goals include the determination of the magnitude of the shorter waves, the calculation of the forces and simulation of wave breaking, should that occur.

Real-time hybrid testing of floating wind turbines is conducted at model scale. The semisubmersib... more Real-time hybrid testing of floating wind turbines is conducted at model scale. The semisubmersible, triangular platform, similar to the WindFloat platform, is built instead to support two, counter-rotating vertical-axis wind turbines (VAWTs). On account of incongruous scaling issues between the aerodynamic and the hydrodynamic loading, the wind turbines are not constructed at the same scale as the floater support. Instead, remote-controlled plane motors and propellers are used as actuators to mimic only the tangential forces on the wind-turbine blades, which are attached to the physical (floater-support) model. The application of tangential forces on the VAWTs is used to mimic the power production stage of the turbine. A control algorithm is implemented using the wind-turbine generators to optimize the platform heading and hence, the theoretical power absorbed by the wind turbines. This experimental approach only seeks to recreate the aerodynamic force, which contributes to the power production. In doing so, the generator control algorithm can thus be validated. The advantages and drawbacks of this hybrid simulation technique are discussed, including the need for low inertia actuators, which can quickly respond to control signals.

ABSTRACT The performance of an unsymmetrical rolling cam as an ocean-wave energy extractor was st... more ABSTRACT The performance of an unsymmetrical rolling cam as an ocean-wave energy extractor was studied experimentally by Salter (1974) and then analyzed from the hydrodynamics standpoint by a number of workers in the 70’s (e.g. Evans, 1976). The analysis was carried out on the basis of inviscid-fluid theory and the energy-absorbing efficiency was found to approach 100%. This well-known result did not account for the presence of viscosity, which alters not only fluid damping but also, to some extent, the added-inertia characteristics. How fluid viscosity may alter these conclusions and reduce the energy-extraction effectiveness is examined in this paper, for two rolling-cam shapes: a smooth “Eyeball Cam” with a simple mathematical form and a “Keeled Cam” with a single sharp-edged bilge keel. The solution methodology involved the Free-Surface Random-Vortex Method (FSRVM), reviewed by Yeung (2002). Frequency-domain solutions in inviscid fluid were first sought for these two shapes as baseline performance metrics. As expected, without viscosity, both shapes perform exceedingly well in terms of extraction efficiency. The hydrodynamic properties of these two shapes were then examined in a real, viscous fluid, under a high Reynolds-number assumption. The added moment of inertia and damping are noted to be changed, especially for the Keeled Cam. With the power-take-off (PTO) damping chosen based on the viscous-fluid results, time-domain solutions are developed to understand the behavior of the rolling motion, the effects of PTO damping, and the effects of the cam shapes. These assessments can be effectively made with FSRVM as the computational engine, even at motion of fairly large amplitude, for which an actual system may need to be designed.

Proceedings of The Royal Society A: Mathematical, Physical and Engineering Sciences, May 1, 2019

The study on close-quarter manoeuvring of vessels is of great importance for the safety and effic... more The study on close-quarter manoeuvring of vessels is of great importance for the safety and efficiency of maritime operations. In this paper, the hydrodynamic interactions between two vessels in moderate-speed overtaking manoeuvres are studied. Computational investigation by free-surface panel method is performed, and the results are assessed against experimental measurements from towing-tank model tests. The influences of overtaking speed and the speed difference between vessels on the hydrodynamic loads are studied. It is found that the free-surface deformation, on account of the blockage effects of the bodies, wave-making properties of the vessels, and the interference of unsteady wave patterns between the vessels, considerably affects the hydrodynamic interactions. In addition, it is also discovered that the influence from the unsteady heave and pitch motions of the hulls on the hydrodynamic loads can be non-negligible. Furthermore, it is found that the slower vessel to be overtaken generally experiences larger loads with more variation than the overtaking vessel. The loads on both vessels become more similar to those of a steady-state di-hull system when the speed difference between vessels is small.