bluuebunny/crossref_metadata_2025 huggingface dataset:
Propeller Loading Distributions
Authors: Tsakonas S.
Published: January 2021

The present study reports the improvements made in the numerical procedure for evaluating propeller loading distributions which had been developed at Davidson Laboratory by adaptation of the unsteady-lifting-surface theory. A new approach, based on the fact that the assumed Birnbaum chordwise modes are not linearly independent, has achieved stability for the chordwise distribution, which had otherwise shown no sign of convergence with increasing number of modes. Other refinements of the numerical program, including provision for arbitrary blade camber variation and overlapping of blade wakes, have improved the accuracy of both chordwise and spanwise loading distributions and brought the theoretical results closer to experiment.
The Consistent Second-Order Wave Theory and Its Application to a Submerged Spheroid
Authors: Chey Young H.
Published: January 2021

Because of the recognized inadequacy of first-order linearized surface-wave theory, the author has developed, for a three-dimensional body, a new second-order theory which provides a better description of free-surface phenomena. The new theory more accurately satisfies the kinematic boundary condition on the solid wall, and takes into account the nonlinearity of the condition at the free surface. The author applies the new theory to a submerged spheroid, to calculate wave resistance. Experiments were conducted to verify the theory, and their results are compared with the theoretical results. The comparison indicates that the use of the new theory leads to more accurate prediction of wave resistance.
Lagally’s Theorem and the Lifting Body Problem
Authors: Zucker Robert D.
Published: January 2021

A review is presented on the use of Lagally's Theorem to determine forces and moments on bodies moving through an ideal fluid, including the extension to unsteady flows by Cummins and the evaluation of the virtual moment by Landweber and Yih for the case of sources and doublets. The latter is generalized to cover any type of singularity. Applications thus far have been restricted to distributions of singularities which lie entirely within the body. This paper considers the lifting body problem in which a vortex or doublet sheet cuts through the body. It is shown that direct application of the final Lagally equations to such a problem yields erroneous results. An approach is presented in which the Lagally integrals are correctly evaluated for this type of singularity distribution.
Analysis of Singly Symmetric Oval Rings with Variable Cross Section
Authors: Flaherty J. E. , Vafakos W. P.
Published: January 2021

An analysis of singly symmetric oval rings with variable cross-sectional properties, subjected to arbitrary radial and shear loads, is presented. The flange stresses in nonuniform reinforcing rings of ring-stiffened oval cylinders are obtained by assuming that such cylinders behave as composite rings. The stresses are shown to be in good agreement with available theoretical and experimental results.
Application of the Unsteady-Lifting-Surface Theory to the Study of Propeller-Rudder Interaction
Authors: Tsakonas S. , Jacobs W. R. , Ali M. R.
Published: January 2021

The propeller-rudder interaction problem is studied by means of the unsteady-lifting- surface theory. Both surfaces of arbitrary geometry are immersed in a non-uniform flow- field (i.e., hull wake) of an ideal incompressible fluid. The boundary-value problem yields a pair of surface integral equations, the inversion of which is achieved by the so- called "generalized lift operator" technique, a new approach developed by the authors, in conjunction with the presently used "mode-collocation" method. The analysis demonstrates the mechanism of the interaction phenomenon by exhibiting the filtering effects of the propeller on the harmonic constituents of the wake which allow the rudder to be exposed only to the blade harmonic and multiples thereof. A numerical procedure adaptable to the CDC 6600 computer has been developed which furnishes information about (i) the steady and time-dependent pressure distribution on both lifting surfaces, and (ii) the resultant hydrodynamic forces and moments. A limited number of calculations exhibit the importance of some parameters such as axial clearance, number of blades, and harmonic components of the hull wake.
Disturbance Induced by a Pressure Distribution Moving Over a Free Surface
Authors: Huang T. T. , Wong K. K.
Published: January 2021

This paper uses the linearized water-wave theory to analyze the disturbances induced by a constant pressure distribution with a rectangular planform moving over calm water. The methods developed, however, can be applied to other pressure distributions. Numerical schemes and computation results for typical speeds and beam/length ratios are presented for the pressure trace on the sea floor when the water depth is finite and the local flow pattern when the depth is infinite. For shallow waters, closed-form solutions for both the pressure trace and free-surface profile are obtained. A surface-effect ship acts like a moving pressure distribution as far as the induced disturbances in the water are concerned. Thus, the results of the present study may be useful for the design of surface-effect ships.
On Optimum Propellers with a Duct of Finite Length II
Authors: Slijper C. A. , Sparenberg J. A.
Published: January 2021

Numerical results are given for the quality coefficient of optimum ducted propellers. The influence of the number of blades, the advance ratio, the clearance between blade tips and shroud, and the hub diameter on this coefficient is shown.
Analysis of the Integral Pumpjet
Authors: Wald Quentin R.
Published: January 2021

Equations have been derived to describe the functioning of a pumpjet propulsion system which is closely integrated into the hull design and ingests some portion of the boundary layer. The varying velocity of the inducted fluid is taken into account. The conventional treatment using separate hull and propeller performance coefficients which are unified by a defined hull efficiency is inappropriate to the treatment of an integral propulsion system. Rational analysis of this type of propulsor requires a unified treatment. Maximum advantage of an integral propulsor is only to be attained if full advantage is taken of the separation inhibiting effect of the propulsor on the boundary layer of the afterbody. A vehicle of given displacement without restrictions on hull form may achieve significant reductions of required power compared with a conventional hull and propeller.
Ship Motions in Shallow Water
Authors: Tuck E. O.
Published: January 2021

The problem discussed concerns small motions of a ship, in all six degrees of freedom, but at zero speed of advance, due to an incident wave system in shallow water of depth comparable with the ship's draft. The problem is completely formulated for an arbitrary ship, and is partially solved for the case when the ship is slender and the wavelength much greater than the water depth. Sample numerical computations of heave, pitch, and sway added mass and damping coefficients and the sway exciting force are presented.
The Influence of Structural Characteristics on Slamming Impact Pressures
Authors: Sellars Frank
Published: January 2021

This paper presents an examination of seakeeping model and two-dimensional drop test peak impact pressure data in the fight of a theoretical pressure that takes account of model material and elastic characteristics. A model-size scale effect noted in drop tests is examined in the light of a panel parameter e which has been defined for theoretical pressure. The test results indicate qualitative agreement with theory when model size is accounted for by this panel parameter. It is concluded that differences in the magnitude of drop tests and seakeeping model peak impact pressure are consistent with predicted effects of different model material and elastic characteristics. Test results are all below the theoretical pressure for a plate with air on both sides.
An Efficient, General Method for the Analysis of Grillages
Authors: Chang Pin Yu , Pilkey W. D.
Published: January 2021

The transfer matrix method provides a simple approach for the analysis of grillages under general conditions. In contrast to other efficient methods, no simplifying assumptions are made; the transfer matrix approach is exact within the framework of the classical theory of bending and torsion of bars. The technique accepts arbitrary loading, nonprismatic beams, arbitrary spacing, in-span conditions such as supports and releases, and arbitrary boundary conditions. The special features in ship structures such as deck openings, stanchion supports, and various brackets can be easily handled. The theory is readily grasped and implemented in full generality for computer solution.
Natural Frequencies of a Body of Revolution Vibrating Transversely in a Fluid
Authors: Landweber Louis
Published: January 2021

IN A PREVIOUS PAPER [1]3 a procedure for determining the natural frequencies of a body vibrating in a fluid was described and applied to a flexible circular cylinder. A more practical and more difficult application of the method, to the case of a body of revolution, is presented in the present work. As was shown in [1], the natural frequencies are given by the eigenvalues of the potential energy matrix of the elastic body with respect to an inertia matrix, the latter being derived from the mass distribution of the body and the kinetic energy of the fluid. Thus two matrices must be obtained, and since the determination of the former is a problem in elasticity, and the determination of the latter one in hydrodynamics, these will be treated in separate sections. Then, in the final section, a particular body of revolution with prescribed elastic and inertial characteristics will be assumed, and its natural frequencies of vibration in air and in water will be calculated. For vibration in water, results obtained by means of strip theory and by the present matrix technique will be compared.
The Wave Resistance of a Thin Ship with a Rotational Wake
Authors: Beck Robert F.
Published: January 2021

An inviscid model for a ship with a viscous wake is developed. The wake is considered as a region of vorticity trailing behind the ship. The problem is systematically linearized by the use of a perturbation parameter representing the beam-to-length ratio. To first order it is found that the complete velocity potential is composed of two parts. The first is identical to the well-known solution for a thin ship without a wake. The second is the result of the specified vorticity distribution in the wake acting in the absence of the ship. The wake potential is determined for a semi-infinite, U-shaped vortex sheet. The wave resistance for a thin ship with a vortex sheet wake is analytically determined. The results clearly indicate the influence of the wake and its interactions with the ship. Numerical computations are presented for a mathematical form. They show that the wake-wave resistance is about 1 0 percent of the ship-wave resistance. The interaction term may be positive or negative depending on the wake attachment point. A comparison with experimental data is made. It is found that the present type of rotational wake model can account for the differences between Michell's integral and experiments for the mathematical form.
The Vertical Mean Force and Moment of Submerged Bodies Under Waves
Authors: Lee C. M. , Newman J. N.
Published: January 2021

A neutrally buoyant slender body of arbitrary sectional form, submerged beneath a free surface, is free to respond to an incident plane progressive wave system. The fluid is assumed inviscid, incompressible, homogeneous and infinitely deep. The first-order oscillatory motion of the body and the second-order time-average vertical force and pitching moment acting on the body are obtained in terms of Kochin's function. By use of slender-body theory for a deeply submerged body, the final expressions for the mean force and the moment are shown to depend on the longitudinal distribution of sectional area and added mass and on the amplitude and the frequency of the ambient surface waves. The magnitude of the mean force for various simple geometric cylinders is compared with that of a circular cylinder of equal cross-sectional area. The mean force on a nonaxisymmetric body is often approximated by replacing the section with circular profiles of equivalent cross-sectional area. A better scheme of approximation is presented, based on a simple way of estimating the two-dimensional added mass. It is expected that the effect of the cross-sectional geometry on mean vertical force and moment will be more significant when the body is very close to the free surface.
Methods of Computing the Probability of Failure Under Extreme Values of Bending Moment
Authors: Mansour Alaa
Published: January 2021

Methods for predicting the probability of failure under extreme values of bending moment (primary loading only) are developed. In order to obtain an accurate estimate of the extreme values of the bending moment, order statistics are used. The wave bending moment amplitude treated as a random variable is considered to follow, in general, Weibull distribution so that the results could be used for short-term as well as long-term analysis. The probability density function of the extreme values of the wave bending moment is obtained and an estimate is made of the most probable value (that is, the mode) and other relevant statistics. The probability of exceeding a given value of wave bending moment in "n" records and during the operational lifetime of the ship is derived. Using this information, the probability of failure is obtained on the basis of an assumed normal probability density function of the resistive strength and deterministic still-water bending moment. Charts showing the relation of the parameters in a nondimensional form are presented. Examples of the use of the charts for long-term and short-term analysis for predicting extreme values of wave bending moment and the corresponding probability of failure are given.
Stresses in Pressurized Circular Shells With Discontinuities, With or Without Stiffeners
Authors: Durelli A. J. , Parks V. J.
Published: January 2021

This paper is a summary of a series of five research programs dealing with the experimental determination of stresses, strains, and displacements in circular cylinders subjected to pressure. The vessels have either constant thickness or transverse reinforcing ribs. Circular holes, with either plain or reinforced edges, are located in different positions of the vessels. The methods used for the analysis are: brittle coatings, three-dimensional photoelasticity ("freezing" technique), and electrical and mechanical strain gages. The most important results are summarized in a table. These results will be of interest to designers of underwater ships and of pressure vessels in general.
An Experimental Study of a Series of Flapped Rudders
Authors: Kerwin Justin E. , Mandel Philip , Lewis S. Dean
Published: January 2021

Water tunnel experiments were performed to determine the free-stream characteristics of a series of twelve rudders with systematic variations in the amount of flap area and flap balance. The results include plots of lift, drag, rudder moment and flap moment coefficients for a complete range of angles of attack and flap deflections. A comparison is made of the effectiveness of all-movable rudders, rudders with a fixed skeg and movable flap, and rudders with movable "skegs" and flaps. The latter were found to be by far the most effective. Rudders with fixed skegs are inferior to all-movable rudders unless the proportion of flap is very large. Flap balance does not appear desirable. Maximum flap moments, even with zero balance, are generally less than or comparable to the maximum moment of an ideally balanced all-movable rudder.
Large Deflection of Plates Under Hydrostatic Pressure with Special Reference to Liquid Containers
Authors: Aalami B.
Published: January 2021

A large-deflection stress analysis is made for square plates under hydrostatic pressure with several flexural and membrane boundary conditions, and with special reference to conditions related to flat-plate components in liquid containers and partitions. The analysis is based on von Karman's nonlinear plate equations for elastic isotropic plates using graded-mesh finite-difference approximations together with an iterative procedure. The influence on plate behavior of membrane and flexural boundary conditions is discussed. It is concluded that in thin-plated containers membrane stresses of the same order of magnitude as bending stresses develop. Solutions are offered nondimensionally in a tabular form for a number of more frequent membrane and bending boundary conditions suitable for design purposes. The application of the solutions is illustrated through numerical examples.
Stresses in Spherical Shells Due to Local Loadings
Authors: Kao Robert , Perrone Nicholas
Published: January 2021

The maximum stresses are obtained for a spherical shell that is lifted or towed by a cable or any mechanical power hoist. In view of the highly localized nature of the maximum stress induced in a spherical shell due to local loading, the nonlinear (large deflection) shallow-shell theory is adopted for the analysis. A nonlinear relaxation technique in conjunction with finite difference approximations is introduced for the numerical integration. Results obtained here are presented in the graphic form that may be readily used by engineers in practical design.
Orthogonal Coordinate Systems for Three-Dimensional Boundary Layers, with Particular Reference to Ship Forms
Authors: Miloh T. , Patel V. C.
Published: January 2021

The problem of choosing orthogonal, curvilinear, coordinate systems for use in boundary-layer calculations on arbitrary three-dimensional bodies is considered in some detail. A general method is described for the practical evaluation of the various geometrical properties of the coordinates occurring in the three-dimensional boundary-layer equations. A particular coordinate system that appears to be the most convenient one for ship hulls is then proposed and analyzed further.
Derivation and Scope of the Dunkerley Equation
Authors: Mott-Smith H. M.
Published: January 2021

Dunkerley's equation is derived from Raleigh's principle and is shown to hold well under certain conditions for the fundamental mode of vibration, but not at all for the higher modes. This is checked by exact solutions for the cantilever with end load and for a shaft bearing a central load and held in pin-type end bearings. For the loaded cantilever, equations are given for the motion produced by a shock applied either to the base of the cantilever or to the end load.
Calculation of the Streamlines About a Ship Assuming a Linearized Free-Surface Boundary Condition
Authors: Adee Bruce H.
Published: January 2021

The problem of computing the inviscid-fluid flow about a ship hull is investigated. A boundary- value problem, including a linearized free-surface boundary condition, is posed for the velocity potential. Singularities distributed over the hull surface are used to determine this potential. Surface streamlines are computed by numerically integrating a set of differential equations along the hull surface. A sample calculation for a Series 60, block coefficient 0.60 hull at a Froude number of 0.259 is included.
Experimental Determination of the Components of Resistance of a Small 0.80 CB Tanker Model
Authors: Matheson N. , Joubert P. N.
Published: January 2021

A reflex and a normal model of a typical bulbous-bow tanker were fitted with different types of stimulators and tested in a wind tunnel and a towing tank respectively. The effects of the stimulators were accounted for by considering the virtual origin of the turbulent boundary layer. A shallower viscous-resistance curve than expected was found, which was partly attributed to the effects of the trailing vortices formed over the surface of the model.· Both the friction and pressure distributions were measured for the reflex model. Equations proposed for the viscous, frictional, and pressure resistance coefficients over the model Reynolds number range did not correlate satisfactorily when extrapolated to full-scale Reynolds numbers.
The Torque and Turbulent Boundary Layer of Rotating Disks with Smooth and Rough Surfaces, and in Drag-Reducing Polymer Solutions
Authors: Granville Paul S.
Published: January 2021

The resisting torque of disks rotating in an unbounded fluid is analyzed on the basis of three-dimensional boundary-layer theory. Smooth and rough surfaces in ordinary fluids and in drag-reducing polymer solutions are considered. A general logarithmic relation is derived for the torque as a function of Reynolds number for arbitrary roughness and arbitrary drag reduction. Special formulas are obtained for smooth surfaces, fully rough surfaces, polymer solutions with a linear logarithmic drag-reduction characterization, and polymer solutions with maximum drag reduction. Relations are also obtained for boundary-layer parameters such as thickness and wall shearing stress. The computed results are in excellent agreement with experimental data available in the literature.
Automated Optimal Design of Frame Reinforced, Submersible, Circular, Cylindrical Shells
Authors: Pappas M. , Allentuch A.
Published: January 2021

The Direct Search Design Algorithm and the Golden Search are utilized to produce an automated optimal dimensional synthesis procedure for the structural design of submersible, frame reinforced, circular shells. Using this procedure it was found that the shell weight/weight displaced ratio is independent of the diameter of the shell and the optimal shell dimensions are proportional to the diameter. Between frame shell buckling is generally the most important instability failure mode in optimal designs. Where significant out-of-roundness (eccentricity) of the shell exists, frame yield normally also controls the design. High-strength steels were found to be effective primarily by reducing the adverse effect of eccentricity and by controlling plating yield for shells under relatively high pressure.
A Note on the Distribution of Maxima of Ship Rolling
Authors: Dalzell J. F.
Published: January 2021

The methods and results of a digital computer simulation of a nonlinear random process are described. The process was one of the simpler analytical models for ship roll. The main objective of the simulation was to obtain "empirical" data on the distribution of roll maxima, and to test these data against the corresponding theoretical distribution for a random Gaussian (linear) process. Effect was made to confine the variation of parameters within ranges appropriate to ship rolling. Within this range of parameters, the frequency band of response is sufficiently narrow that the theoretical distribution of maxima of the corresponding linear process tends toward the Rayleigh. The results obtained by objective statistical test procedures indicate that the distribution of maxima of the nonlinear process is not Rayleigh in a substantial portion of the parameter range of interest. However, it was possible to conclude from the results that the Rayleigh assumption is reasonable for an important class of engineering predictions; that of the prediction of average, "significant" and "1/10 highest" maxima from a knowledge of the spectrum of roll.
Linear Theory on Water Entry and Exit Problems of a Ventilating Thin Wedge
Authors: Yim Bohyun
Published: January 2021

A simplified mathematical model is formed for the flow field caused by the ventilating blade of a partially submerged propeller. The model is formed to investigate the difference between the phases of entry and exit; that is, a two-dimensional flat-sided wedge and a two-dimensional cambered wedge entering a free surface and exiting at another free surface, located at a distance equivalent to the length of circular path of blade section in the water. Pressure and drag are calculated for a flat plate and a parabolic cambered wedge, each at the instantaneous position, by a conformal mapping technique. A great difference in pressure distributions between the phases of entry and exit is obtained.
Observations of a Surge in a Forced Vortex Flow
Authors: Granger Robert A.
Published: January 2021

This paper has two purposes. One is to report the results of some measurements of a steady vortex; the other is to report measurements of a surge in the vortex controlling the withdrawal. The experimental contribution is an empirical formula for the speed of a surge. The surge speed is shown to be proportional to the ambient circulation and inversely proportional to the viscous core radius.
A Numerical Method for Steady-State Cavity Flows
Authors: Mogel T. R. , Street R. L.
Published: January 2021

Our objective was to develop a numerical method for steady-state cavity flows that provides a systematic correction of an initial, assumed free streamline position. The method uses a finite-difference representation with velocities as dependent variables and obtains a solution by successive-over-relaxation. While applicable to three-dimensional flows, the method was implemented only for a two-dimensional flow. For the free streamline, the constant-pressure condition is satisfied on a known, but approximate location. Then, the tangency condition is used to compute a better location of the streamline. This technique overcomes problems encountered by previous investigators.
Buckling of a Circular Cylindrical Web-Stiffened Sandwich Shell Under Axial Compression
Authors: Volpe Vincent , Chen Youl-Nan , Kempner Joseph
Published: January 2021

A stability analysis of an infinitely long web-stiffened, circular cylindrical sandwich shell under uniform axial compression is presented. The formulation begins with the establishment of a set of suitable large-deflection shell equations that forms the basis for the subsequent development of the buckling equations. The mathematical model corresponds to two face layers that are considered as thin shells and a thick core that is capable of resisting both transverse shear and circumferential extension. The associated eigenvalue problem is solved. Results show that the lowest buckling load is associated with the axisymmetric mode and is less than one half the buckling load of an equivalent single-layer shell.
Finite-Element Analysis and Optimization of a Web Frame of a Tanker with Isolated Ballast System
Authors: Finifter D.
Published: January 2021

Finite-element analysis was used in the design of an unconventional tanker web frame which satisfies certain requirements stipulated by an isolated ballast system. The weight of the web frame was then minimized using an optimality criterion based on a fully stressed design. A double iteration procedure was developed which allowed for the efficient use of the optimization program in conjunction with the finite-element analysis. The reduction in the weight of the web frame is dependent on the minimum allowed plate thickness as shown in the results of the paper.
Icebreaking Modeling
Authors: Atkins A. G.
Published: January 2021

It is shown that the mechanics of cracking do not follow geometric similarity in the normal meaning of that term. Thus, translation of laboratory data concerning strength and toughness of ice to large-scale applications should be done with care. Regarding ice tank model data, it is demonstrated that a new nondimensional group should be satisfied if ice fracture effects are to be scaled properly. The Cauchy number is not appropriate.
On the Optimum Finite-Amplitude Motion of a Thrust-Producing Profile
Authors: Sparenberg J. A. , Takens F.
Published: January 2021

The semilinear theory for the optimum motion of a thrust-producing profile is discussed. Geometrical conditions on the motion of the profile are examined in connection with the existence or nonexistence of an optimum motion.
Cavitation Inception—A Selective Review
Authors: Acosta A. J. , Parkin B. R.
Published: January 2021

This paper reviews recent developments in selected cavitation research areas which have been active mainly within the past two years. The new understanding resulting from this work is summarized. Research topics discussed are cavitation inception on smooth surfaces, on vortex cavitation and scaling, on the measurement of cavitation nuclei, and on the effects of polymer additives. Because of the selective nature of the review, a fairly comprehensive listing of recent contributions to the literature on these and related aspects of cavitation research is an essential part of the exposition.
The Flow About Arbitrary, Three-Dimensional Smooth Bodies
Authors: Webster William C.
Published: January 2021

This study presents a new method for evaluating the flow about an arbitrary three-dimensional body using submerged triangular source patches. The patches are more sophisticated than used previously by Smith and Hess [1],2 since they allow a linear variation of the source strength across the patch. Calculations show that the combination of these new patches and submergence of the resultant faceted singularity sheet produces very accurate flows with a small amount of computer time.
Cavitation Inception Observations on Axisymmetric Bodies at Supercritical Reynolds Numbers
Authors: Arakeri V. H. , Acosta A. J.
Published: January 2021

A laminar separation on a body provides a site for the inception of cavitation. The separated region disappears when the boundary layer upstream becomes turbulent; this may occur naturally or by stimulation. The consequences of this disappearance on the values of the cavitation inception index and the type and appearance of the cavitation at inception are investigated on three different axisymmetric bodies. On one of these bodies, a hemisphere-cylinder, a trip near the nose so energized the boundary layer that it was impossible for any form of cavitation to remain attached to the body even when a tension of about one half atm. existed at the minimum pressure point on the body.
Comments by Douglas Faulkner and Charles V. Betts on“On the Shakedown Limit of a Ship’s Hull Girder”
Authors: Faulkner Douglas , Betts Charles V.
Published: January 2021

The subject of shakedown has been largely neglected in ship structures research. Professor Jones's paper 3 is therefore particularly welcome, and has been read with great interest. The discussers do feel, however, that an innocent designer could be misled by some of the statements and conclusions drawn.
Calculation of Propeller-Induced Vibratory Hull Forces, Force Distributions, and Pressures; Free-Surface Effects
Authors: Vorus William S.
Published: January 2021

It is shown how a formula originally developed for calculating the total unsteady propeller-induced forces on a ship hull can be used for calculating the associated hull force distributions and pressures as well. Total vertical forces and the axial distribution of vertical force on a flat plate are calculated using the formula. Two different conditions on the water free-surface are investigated. These conditions correspond to approximations to the exact linearized free-surface condition in the extremes of high and low frequency. The calculations are also performed for circumferentially uniform and nonuniform propeller inflows.
Optimum Propellers with Cavity-Drag and Frictional-Drag Effects
Authors: Yim B.
Published: January 2021

In a variational problem for the optimum pitch distribution of a propeller, the Euler differential equation with Munk's displacement theory is utilized. Effects of frictional-drag and cavity-drag are considered through simple approximate relations of drag-lift ratio and the circulation. Simple relations between the optimum pitch distributions and the drag-lift ratio are obtained both for free-running and wake-adapted propellers.
Power Extraction from Water Waves
Authors: Mei Chiang C.
Published: January 2021

Salter has demonstrated experimentally that a horizontal cylinder in the free surface of water can be a device to extract energy from the incident waves. This paper proposes a design which is based on the idea of a tethered-float breakwater, and gives the theoretical design criteria for maximum power extraction from a general floating cylinder with one or two degrees of freedom. It is shown that the rate of energy extraction must be equal to the rate of radiation damping and that the floating body must be made to resonate then for a body with one degree of freedom, the maximum efficiency at a given frequency can be at leastone half if the body is symmetrical about a vertical axis, and greater for an asymmetrical body. For a body with two degrees of freedom, all the wave power can be extracted. Hydrodynamical aspects of the controlled motion are examined. Viscous effects are ignored.
A Note on the Thin-Hydrofoil Theory of Keldysh and Lavrentiev
Authors: Plotkin Allen
Published: January 2021

The method of Keldysh and Lavrentiev for solving the vorticity integral equation of thin-hydrofoil theory is studied to ascertain its accuracy and limits of applicability. It is seen to provide accurate analytic solutions for hydrofoil lift coefficient for submergence depths greater than one chord length.
Lift Effects Associated with Drag-Reducing Polymer Injection on Two-Dimensional Hydrofoils
Authors: Fruman Daniel H.
Published: January 2021

The effect of a boundary-layer injection of drag-reducing additive solutions on the lift and drag of a 10-cm chord, NACA 63A020 symmetrical two-dimensional hydrofoil was investigated for various freestream and injection velocities, foil incidences, and additive concentrations ranging from 50 to 400 ppm of POLYOX WSR 301. The experimental results demonstrate that the lift of the hydrofoil can either increase or decrease depending upon whether the polymer injection is made on the suction or pressure side of the foil surface, respectively. In both cases, however, the drag is reduced. The net result of the injection of the drag-reducing agent is an augmentation of the lift-drag ratio. The magnitude of this augmentation and its dependence on the freestream velocity, the injection velocity, the concentration of polymer, and the incidence of the foil are analyzed.
Comparison of Numerical and Perturbation Solutions of Two-Dimensional Nonlinear Water-Wave Problems
Authors: Salvesen Nils , von Kerczek C.
Published: January 2021

Numerical solutions of the nonlinear problem of the steady two-dimensional potential flow past a submerged line vortex are obtained using the finite-difference iterative technique previously presented by the authors. These solutions are compared in detail with third-order perturbation theory solutions. It is found that very good agreement is obtained for cases of positive circulation of the vortex with strength large enough to produce downstream waves whose steepness is within 15 percent of the maximum possible steepness of irrotational free waves. These computed waves are as steep as the steepest waves obtained in a certain experiment involving the flow past a two-dimensional hydrofoil. For negative circulation, there is substantial difference between the numerical results and third-order perturbation theory. The failure of the perturbation theory is discussed. Details of the far-downstream wave system obtained by the numerical method are compared with other numerical solutions and very high-order perturbation theory solutions of the free-wave problem. Very good agreement is obtained in most cases.
Diffusion of a Tangential Drag-Reducing Polymer Injection on a Flat Plate at High Reynolds Numbers
Authors: Fruman Daniel H. , Tulin Marshall P
Published: January 2021

The diffusion of a thin tangential jet of an aqueous solution of drag-reducing polymer injected into the water-turbulent boundary layer of a flat plate at a freestream Reynolds number, 3.6 × 107, and the accompanying drag reduction are investigated for a variety of initial concentrations and ratios of injection to freestream velocities. The concentration distribution along the wall is found to be mainly represented by two regions. In the first region the wall concentration is practically constant and equal to the injected one; in the second region the concentration varies approximately as the inverse of the distance from the injection slit. The length of the first region is significantly increased by the polymer solution injection as compared with the pure solvent injection. The drag-reduction effect associated with the polymer injection depends on the trailing-edge concentration achieved as a result of the diffusion process.
Water Entry and Exit of a Fully Ventilated Foil
Authors: Wang D. P.
Published: January 2021

The motion of a fully ventilated foil in water of both infinite and finite depth is considered. Part 1 deals with a two-dimensional, thin foil entering vertically into a deep ocean at high speeds. The foil is allowed to have small, time-dependent deformations, and the resulting flow around it is assumed to become fully ventilated. The problem is solved by linearized theory, the solution being divided into two different phases: initial entry and complete entry. The initial entry phase concerns the flow motion in which the foil is only partially submerged, and the complete entry phase concerns that in which the entire length of the foil becomes submerged. The pressure distribution on the foil is determined analytically up to a function of the time variable. The determination of the function depends on the solution of an integral equation. For illustration, the present theory is applied to a flat-plate foil in both uniform and nonuniform motions and to circular-arc foils in uniform motions. Part 2 considers the same foil in a layer of water of finite thickness. Here, the solution is divided into three different phases: the initial entry phase, the complete entry phase, and the exit phase. For the exit phase, the pressure distribution on the foil is explicitly determined. The result obtained in this work is intended for use in the design of the partially submerged supercavitating propeller.
Review of Structural Response Aspects of Slamming
Authors: Nagai Tamotsu , Chuang Sheng-Lun
Published: January 2021

This paper is intended to provide a state-of-the-art review of the structural response aspects of slamming. The emphasis is on two specific aspects: (i) hull girder response to slamming and (ii) local structural response to slamming (for example, the forward bottom structure, forecastle deck, bow flare structure, and secondary structure at the bow). Results of drop tests and sea trials are used to illustrate the design procedure for ship bottom plating in the slamming area. The work cited here is considered to have important applications for practical design features of future ships. Several parts still require clarification, and recommendations for additional research are offered.
Comments on Rao and Garrison: “Interaction of Waves with a Rigid Submerged Spheroid”
Authors: Chakrabarti Subrata K. , Naftzger Robert A.
Published: January 2021

The title paper presents a Green's function formulation of the wave interaction with a large submerged object and obtains numerical results for spheroidal storage vessels having various aspect ratios. To check the numerical computations, the force coefficients are compared with asymptotic expressions developed for a hemisphere when the depth/radius ratio is large and the radius/ wave length ratio is small.
The Steady Wave Potential of a Unit Source, at the Centerplane
Authors: Noblesse F.
Published: January 2021

The paper is concerned with the linearized wave disturbance trailing downstream from a unit source in steady rectilinear motion at or below the free surface of a quiescent sea, at the "centerplane," that is, at the vertical plane of symmetry containing the source and parallel to its direction of motion.
Vibratory Forces on a Simulated Hull Surface Produced by Transient Propeller Cavitation
Authors: Lewis Frank M. , Kerwin Justin E.
Published: January 2021

An experimental setup is described for the measurement of propeller-induced vibratory force on a simulated segment of hull surface located above a model propeller operating in a water tunnel. Measurements are made of the influence of transient cavitation induced by a wake screen on the vibratory force. These experiments confirm recent observations that, in many cases, hull vibratory excitation is completely dominated by transient propeller cavitation.
On the Existence of Small-Amplitude Optimum Hydrofoil Propulsion
Authors: Sparenberg J. A.
Published: January 2021

This paper is concerned with small-amplitude sculling propulsion by means of a flexible hydrofoil. It is shown that when the constraints on the motion of the profile are too loose, no optimum motion exists. On the other hand, constraints are discussed which ensure the existence of an optimum motion. There is, however, a gap in which existence or nonexistence of motions is still unknown.
On the Behavior and Design of Stiffened Plates in Ultimate Limit State
Authors: Soreide T. H. , Moan T. , Nordsve N.T.
Published: January 2021

The behavior and design of stiffened plates in the ultimate limit state are studied. A finite element formulation for panel behavior considering general loading conditions, material properties, geometry, boundary conditions, and initial deflections is presented. Some results obtained by a finite element program are displayed and discussed. The problems considered comprise perfect and initially deflected plate-strips subjected to lateral pressure, single-span and two-span beam-columns under axial loading, and failure of a stiffened plate designed for simultaneous local and global buckling. Finally, design criteria are briefly discussed and recommendations for future work are given.
A Note on Lift and Drag Effects Due to Polymer Injections from Several Locations on a Symmetric Hydrofoil
Authors: Sinnarwalla A. M. , Sundaram T. R.
Published: January 2021

Introduction - It is well known that the injection of dilute polymer solutions into the boundary layer on two-dimensional hydrofoils produces changes in both the drag and lift of the foils, with the changes being dependent on the polymer [1], 3 its concentration [2], the injection technique [8], the location of the injection slit [1], and the rate of injection [1, 4, 5]. Previous tests [4] have also shown that the observed drag reduction does not necessarily increase linearly with the rate of injection of the polymer. Indeed, beyond a certain injection rate, further increases lead to little or no drag reduction and, in some cases, actually lead to a drag increase. Thus, one question that is of considerable practical interest is the effect of multiple injections of a given amount of polymer from several chordwise locations as compared with that due to the injection from a single location. The present study investigates the effects on lift and drag of a 20.16-cm (8 in) chord NACA 684–010 two-dimensional hydrofoil due to multiple injections of 200-ppm Polyox WSR 301 solution from several chordwise locations. The results indicate that, for a given flux of polymer injection, multiple injections from properly selected locations as compared with the injection from a single location result in a larger drag reduction without adversely affecting the foil lift.
Large-Amplitude Transient Motion of Two-Dimensional Floating Bodies
Authors: Chapman R. B.
Published: January 2021

A numerical method is presented for solving the transient two-dimensional flow induced by the motion of a floating body. The free-surface equations are linearized, but an exact body boundary condition permits large-amplitude motion of the body. The flow is divided into two parts: the wave field and the impulsive flow required to satisfy the instantaneous body boundary condition. The wave field is represented by a finite sum of harmonics. A nonuniform spacing of the harmonic components gives an efficient representation over specified time and space intervals. The body is represented by a source distribution over the portion of its surface under the static waterline. Two modes of body motion are discussed—a captive mode and a free mode. In the former case, the body motion is specified, and in the latter, it is calculated from the initial conditions and the inertial properties of the body. Two examples are given—water entry of a wedge in the captive mode and motion of a perturbed floating body in the free mode.
Oblique Water Entry and Exit of a Fully Ventilated Foil
Authors: Wang D. P.
Published: January 2021

The oblique entry of a two-dimensional, fully ventilated foil into a horizontal layer of water of arbitrary thickness is considered. When the thickness of the layer is finite, exit of the foil from the layer is studied. The present work is an extension of a previous one,2 in which only vertical entry and exit of the foil were considered. The consideration of oblique entry makes the present solution useful in studying not only the advance ratio effect on a partially submerged supercavitating propeller but also many other problems, such as the high-speed water entry and exit of a wing or a control surface, the operation of a high-speed hydrofoil in a high sea state. The results obtained in this work indicate that the force and moment coefficients of a foil decrease as the advance ratio is reduced.
Maneuvering Hydrodynamics of Ellipsoidal Forms
Authors: Miloh Touvia
Published: January 2021

The hydrodynamical forces and moments acting on a triaxial ellipsoid moving in an incompressible and inviscid fluid are analyzed. The rigid ellipsoid is allowed to move in the most general manner with time-dependent velocity and six degrees of freedom. The force and moment expressions are obtained by applying the Lagally theorem to the image singularities system representing the body in the presence of exterior disturbances. First, expressions for the Lagally force and moment acting on a maneuvering ellipsoid in an unbounded medium are derived and then these expressions are generalized to include the effect of an exterior source moving in an arbitrary manner. It is also shown how the Lagally expressions for an exterior source can be used to obtain closed-form expressions for the hydrodynamical forces and moments acting on a maneuvering ellipsoid in the presence of an arbitrary exterior disturbance. The analysis, which is based on the application of ellipsoidal harmonics, is demonstrated in a simple case of propeller-hull interaction. Here the motion of the ellipsoid is restricted to the major axis, and the propeller at the stern is represented by an isolated sink in accordance with Dickmann's model. 'Practical expressions for the thrust-deduction coefficient, wake fraction, and propeller-induced vibration are then derived for ellipsoidal, spheroidal and spherical hulls..
Digital Simulation of Short-Crested Sea Surface Elevations
Authors: Shinozuka Masanobu , Wai Peter
Published: January 2021

The present study develops a technique of digital generation of sample functions of multidimensional Gaussian random processes with the aid of the Fast Fourier Transform algorithm modified to optimize the computer memory and execution time requirements. The technique can be used as an essential tool in a general Monte Carlo method of solution for a variety of engineering problems, particularly those involving the difficulties arising from nonlinearity and random nonhomogeneity. Use of the technique has been demonstrated in the generation of the short-crested sea surface elevation, which provides a vital input to the performance evaluation analysis of marine vehicles.
Added Moment of Inertia of a Rotating Ship Section
Authors: Landweber L.
Published: January 2021

An expression for the added moment of inertia of a rotating ship section, in terms of the coefficients of the Laurent series of the function which maps the given section into a circle, has been derived. The method is applied to the two-parameter family of Lewis forms and the results are presented as a family of curves which gives the coefficient of the added moment of inertia as a function of the thickness ratio and the section-area coefficient of a form. A second application, to a square section, indicates that a sufficiently accurate value of the added moment of inertia can be obtained with little arithmetical work even in a case where the Laurent series is an infinite one.