bluuebunny/crossref_metadata_2025 huggingface dataset:
Approximate Probabilistic Method of Calculating Ship Longitudinal Strength
Authors: Mansour Alaa
Published: January 2021

Recently, classification societies have taken an interest in the statistical approach to ship longitudinal strength and the probabilistic methods for defining new design criteria. This interest is partially a result of the development and the growing demand for large tankers; it is reflected in the increasing research done by the regulatory bodies in these areas. This paper presents a framework for an approximate probabilistic method to calculate ship longitudinal strength with possible implementation in classification societies rules in mind. The most important features of this method are that it is simple, realistic, consistent, and distribution-free. No assumptions are made with regard to the forms of the distribution functions of the random variables involved in the procedure. Nevertheless, the uncertainties associated with these variables are taken into consideration and are quantified by their coefficients of variation. Analyses of eighteen ships of different types are made in order to serve as a preliminary investigation of the appropriate level of safety as measured by a proposed safety index.
A Modified Froude Method for Determining Full-Scale Resistance of Surface Ships from Towed Models
Authors: Granville Paul S.
Published: January 2021

The Froude method for extrapolating the resistance of towed ship models to full-scale conditions has been modified with respect to the prediction of viscous resistance from an equivalent flat-plate resistance. A form factor for extrapolation is to be determined from a boundary-layer calculation of a uniquely defined equivalent body of revolution. Examples of form factors calculated for the Lucy Ashlon and a hull with a block coefficient of 0.8 are shown to be quite satisfactory.
A Linear Analysis of Planar Motion Mechanism Data
Authors: Bishop R. E. D. , Burcher R. K. , Price W. G.
Published: January 2021

A linear analysis of ship motions (for example, of directional stability and control) does not require that slow-motion derivatives be employed to represent fluid forces and moments. Indeed the notion of such a representation implies the use of a Taylor series in circumstances where it is not strictly tenable. For linearity, it is only necessary that the principle of superposition be employed. Experimental data show that, when used in this sense, the assumption of linearity is by no means unreasonable.
The Effect of a Surface Layer of Viscous Fluid on the Wave Resistance of a Thin Ship
Authors: Tuck E. O.
Published: January 2021

A Modification to the gravity-wave free-surface condition is suggested, to account for dissipative properties of thin surface layers of material such as broken-up ice, slush, or oil spills. A corresponding correction to michell's wave-resistance integral is established, and computations are carried out for a parabolic strut.
Lobar Buckling of Thin-Walled Cylindrical and Truncated Conical Shells Under External Pressure
Authors: Ross C. T. F.
Published: January 2021

Numerical solutions have been produced for the asymmetric instability of thin-walled circular cylindrical and truncated conical shells under external pressure. The solutions for the circular cylinder have shown that the assumed buckling configurations of Nash [l]2 and Kaminsky [2] were quite reasonable for fixed ends. Comparison was also made of the finite-element solution of conical shells with other analyses. From these calculations, it was shown that the numerical solutions were superior to the analytical ones, as the former could be readily applied to vessels of varying thickness or those subjected to unsymmetrical loading or with complex boundary conditions.
Pressure Hull Optimization Using General Instability Equation Admitting More Than One Longitudinal Buckling Half-Wave
Authors: Pappas Michael , Allentuch Arnold
Published: January 2021

Current design procedures often assume that the critical buckling shape in general instability contains only one longitudinal half-wave. This assumption may be incorrect for optimal hulls if what appears to be a questionable independent frame buckling constraint, often employed in pressure hull design, is relaxed. A method for predicting general instability admitting more than one longitudinal l half-wave is, therefore, adapted to an automated optimal design procedure for the synthesis of frame-stiffened, cylindrical, submersible hulls. Design studies demonstrate that substantial weight reductions are possible for hulls designed for conventional operating depths (around 1000 ft) if ultrahigh-strength steels are utilized.
Interaction of Waves with Large Vertical Cylinder
Authors: Chakrabarti Subrata K. , Tam William A.
Published: January 2021

Dynamic effects due to waves on a large vertical circular cylinder were measured experimentally in a wave tank in the form of pressures, forces, and moments. The experimental data were compared with the wave diffraction theory following the classical analysis of Havelock on a fixed obstacle in waves. The viscous effects were neglected in the analysis on the assumption that for a cylinder of this size the inertia force is most predominant. The maximum horizontal force was found to correlate well with the theory. The pressure decay below the still water level followed the hyperbolic cosine law. Linear variation of pressure up to the free surface was found to be conservative.
Propeller-Induced Velocity Field Due to Thickness and Loading Effects
Authors: Jacobs W. R. , Tsakonas S.
Published: January 2021

Blade thickness plays a dual role, contributing to the lifting characteristics of the blade because of its nonplanar form as well as to its nonlifting characteristics due to the generation of a symmetrical flow disturbance. However, since the so-called "nonplanar thickness" has been shown to have little effect on the blade pressure distribution and thus presumably to have a negligible effect on the velocity and pressure fields around an operating propeller, the present investigation is limited to the so-called "symmetrical flow disturbance thickness." The effect of this thickness on the oscillatory velocity field around the propeller is studied by means of the "thin body" approach, where the blade section is represented by a source-sink distribution of strength proportional to the slope of the blade thickness distribution. A numerical procedure is devised and adapted to the CDC-6600 high-speed digital computer for the evaluation of the thickness effect on the velocity field. The total propeller-induced velocity field is then obtained by adding the computed velocity components due to thickness, with proper phase, to the results due to propeller loading calculated by means of the lifting-surface theory. Sets of calculations performed for a 3-blade propeller operating in a 3-cycle screen-generated wake and for a 5-blade propeller operating in a realistic hull wake reveal that the effect of thickness in forming the components of the resultant velocity varies from moderate to large, depending on the magnitude of the thickness distribution, on the location of the field point, and on the intensity of the nonuniformity of the inflow field.
The Analysis of Line Structures by Transfer Matrices Derived from Finite Elements
Authors: Pilkey W. D. , Haviland J. K. , Chang P. Y.
Published: January 2021

It is shown that the finite-element method can be efficiently employed in the analysis of line structures, in particular, ship structures, if it is combined with the transfer matrix method. Advantage is taken of the finite element method's structural modeling capability in representing complicated substructures. The substructures are pieced together along the length of the structure using transfer matrices. It is demonstrated that this approach can be superimposed on available large scale finite-element systems to improve their efficiency and increase their capabilities.
The Thin-Hydrofoil Thickness Problem Including Leading-Edge Corrections
Authors: Plotkin Allen
Published: January 2021

The method of Keldysh and Lavrentiev is used to study the potential flow of a uniform stream past a submerged thin symmetric hydrofoil. An expression for the surface speed is obtained and the method of matched asymptotic expansions is used to develop corrections at the round leading edge. The pressure, lift, drag, and pitching moment are presented for the Joukowski hydrofoil with emphasis on the variation with thickness, Froude number, and chord-to-depth ratio.
An Addition to Myklestad’s Method Giving Convergence to a Natural Frequency
Authors: Dawson B. , Davies M.
Published: January 2021

This paper presents an extension of Myklestad's method that within a limited range either side of a natural frequency enables an improved frequency value to be determined from the results of a previous calculation. The method has quadratic convergence within the vicinity of a natural frequency and is well suited for solution on a digital computer. The method is illustrated by determining the first five natural frequencies of a cantilever beam, and the rates and range of convergence of the method are shown.
Shell Vibration and Buckling Analysis Using a New Eighth-Order Equation
Authors: Becker Herbert
Published: January 2021

Doubly curved plates and regions of general shells may be easily investigated for both vibratory behavior and instability using a form of Donnell's equation. The new eighth-order equation provides more precision than Donnell's and also offers simple closed form relations that provide insight to the physical behavior of the shell. Examples are presented to depict the increased accuracy and the range of applicability of the equation. One result is a particularly simple relation between instability loading and natural frequency. In another demonstration the cylinder form of the general shell equation is shown to yield Levy's result for ring mode buckling of a cylinder under external pressure, which Donnell's equation does not do.
Propeller-Rudder Interaction Due to Loading and Thickness Effects
Authors: Tsakonas S. , Jacobs W. R. , All M. R.
Published: January 2021

The previous analysis of the propeller-rudder interaction problem by means of the lifting-surface theory has been modified to include the effects of thickness of both surfaces. The effect of propeller blade thickness and rudder thickness on the "flow displacement" in the field is taken into account by the "thin body" approach. The blade thickness effect on the loading of the propeller blade due to its nonplanar form, being small, is neglected. The resulting onset velocities on both lifting surfaces due to the thickness effects on the flow field are incorporated, together with the onset velocities due to hull wake and camber and incident angle of the surfaces, into the existing iterative procedure. The numerical procedure, which has been adapted to the CDC 6600 high speed digital computer, furnishes the steady and time-dependent pressure distributions on both lifting surfaces and the resulting hydrodynamic forces and moments. From the limited number of calculations, it is seen that the thickness effect does not change the general conclusions reached in the previous study of the interaction problem. The interaction apparently is governed principally by the loading effects. The mean and blade-frequency thrust and torque and the mean rudder force and moment are very little affected by the inclusion of thickness even at the smallest possible axial clearance between propeller and rudder. The influence of thickness is greater on the propeller bearing forces and bending moments, on the steady-state values more than on the unsteady, and decreases with increase in axial clearance. The thickness effect is most pronounced in the case of unsteady rudder forces and moments at certain axial clearances, varying cyclically with clearance.
Introductory Note to Companion Papers on Wave Resistance
Authors: Noblesse F. , Dagan G.
Published: January 2021

The following two papers were submitted independently by the authors in April 1974 to the JOURNAL OF SHIP RESEARCH. Both studies were motivated by the desire to establish a sound theoretical foundation for Guilloton's method, which has been found by Gadd (1978) to be particularly successful in predicting the wave resistance of ship models. Noblesse, F., " A Perturbation Analysis of the Wavemaking of a Ship, with an Interpretation of Guilloton's Method"; see page 140. Dagan, G., " A Method of Computing Nonlinear Wave Resistance of Thin Ships by Coordinate Straining"; see page 149.
A Perturbation Analysis of the Wavemaking of a Ship, with an Interpretation of Guilloton’s Method
Authors: Noblesse F.
Published: January 2021

A thin-ship perturbation analysis, suggested by Guilloton's basic ideas, is presented. The analysis may be regarded as an application of Lighthill's method of strained coordinates to a regular perturbation problem. An inconsistent second-order approximation in which the Laplace equation is satisfied to first order, and the boundary conditions both at the free surface and on the ship hull are satisfied to second order, is derived. When sinkage and trim, incorporated into the present analysis, are ignored, this approximate solution is shown to be essentially equivalent to the method of Guilloton.
A Note on Three-Dimensional Supercavitating Hydrofoils
Authors: Acosta A. J. , Furuya O.
Published: January 2021

The three-dimensional or finite-span effect on supercavitating hydrofoils has received much attention in recent years. Among others may be mentioned the work of Tsen and Gullbaud [1], 3 who give the numerical results of their own fully linearized supercavitating lifting-surface theory together with some experimental data, both their own and from other sources. The numerical results are somewhat different from what one might expect based on existing theories, and some of the experimental findings appear to differ from previously published results. The purpose of this brief note is to compare some of the theoretical and experimental results from reference [1] with other recent works both for fully linearized treatments (valid only for vanishing angles of attack), and nonlinear theories and other experimental data that have been used in the past.
Surface Waves Due to a Maneuvering Air-Cushion Vehicle
Authors: Yeung Ronald W.
Published: January 2021

Through the application of linearized water-wave theory, a hydrodynamic model is developed for predicting the surface waves generated by an air-cushion vehicle undergoing arbitrary maneuvers. The velocity potential is shown to be a convolution integral in time involving the trajectory history of the craft. Numerical methods are developed to compute and tabulate the associated kernel function, which contains all the dynamic properties of the fluid. The theoretical model is first applied to compute the wave profiles and resistance of an accelerating vehicle. Resistance calculations agree well with existing results. Next, transverse wave-profiles for a craft in steady turns are given. Finally, hydrodynamic derivatives for an oscillatorily swaying craft at constant forward speed are presented and compared with experimental data.
Torsional Vibrations in Reciprocating Engines
Authors: Pasricha M. S. , Carnegie W. D.
Published: January 2021

In the case of reciprocating engines, there are certain critical speeds of running at which the torsional vibrations in the shaft become large in amplitude and introduce an element of danger into the system. Fairly simple methods have been devised for the practical calculations to predict the torsional vibration characteristics from the constants of the machinery. The torsional vibration phenomenon in the running gear of reciprocating machinery is usually dealt with by considering a series of constant inertias connected by sections of massless shafting. In recent years several cases of fractures in the crankshafts of large marine engines have been attributed to the phenomenon of secondary resonance, which is explained from the fact that the effective inertia of each slider-crank mechanism varies about a mean value in relation to the position of the crank. Simplified theories predicted these designs of diesel engines as safe in practice. In view of the importance of the subject of torsional vibrations in engineering practice, the effects of variation in inertia on the torsional vibration of the system are examined in detail in the present paper. A comparison of theoretical results with Goldsbrough's experimental results is included.
The Effect of Probe Location on a Model Wave Resistance Survey Along a Longitudinal Cut
Authors: Ward Lawrence W. , van Hooff Richard W.
Published: January 2021

Longitudinal-cut wave survey experiments using lateral wave slope data and wave height data were carried out on a Series 60, 0.60-block model in the Webb Model Tank. The results in each case show a dependence on the lateral distance of the wave cut away from the model at the higher Froude numbers (speeds) tested. Consistently lower results were obtained when using lateral wave slope data compared with those obtained when using wave height data. A discussion of possible causes of these findings is given.
Free-Surface Effects for Yawed Surface-Piercing Plates
Authors: Chapman R. B.
Published: January 2021

The problem of a yawed surface-piercing flat plate is solved by applying the slender-body approximation and solving the resulting equations by a finite-difference method. The solution is shown to depend on two parameters & the product of the length Froude number and the square root of the aspect ratio of the plate, and the ratio of the angle of attack to the aspect ratio. Numerical methods are developed with linear, second-order, and nonlinear free-surface conditions. Calculated side force and yawing moment coefficients show good agreement with experimental values near the limit of zero angle of attack. At finite angles of attack, the experimental data exhibit nonlinearities not contained in the present formulation.
Motion of a System of Rigid Bodies Through an Ideal Incompressible Fluid
Authors: Moneim A. F. Abdel
Published: January 2021

A general theory of the motion of a system of rigid bodies through an unbounded ideal fluid is given. The exact mathematical formulation of such a boundary-value problem in the framework of the potential theory leads to a system of integral equations. The solution of these equations gives some expressions for the intensity of the singularities distributed over the surfaces of the bodies. The hydrodynamic forces acting on the bodies are determined by applying Lagrange's equation.
Motion Characteristics of Floating Bodies
Authors: Lee Choung M.
Published: January 2021

The motion characteristics of floating bodies, in and below a free surface, that are subject to surface waves are examined. The effects of various degrees of approximation of hydrodynamic coefficients on the results of the motion computations are investigated on the basis of linear theory. The behavior of hydrodynamic coefficients such as added mass, damping, and wave-exciting force with respect to frequency of oscillation (or wave length) and depth of submergence is also investigated. Numerical results are obtained for three cylindrical bodies of circular, rectangular, and rhombic cross sections. The results reveal that fairly crude approximations can be applied to compute the oscillatory motion of submerged bodies.
Interaction of Waves with a Rigid Submerged Spheroid
Authors: Rao V. Seetharama , Garrison C. J.
Published: January 2021

This paper considers the interaction of a train of regular surface waves with a half spheroid which is completely submerged in water of finite depth and oriented such that its two equal axes lie on the horizontal impermeable bottom. The boundary-value problem resulting from the interaction is dealt with by introducing a Green's function. A numerical scheme is developed for solving the integral equation which arises from application of the kinematic boundary condition on the surface of the spheroid, and numerical results are obtained for all of the physical quantities of interest. For the special case of a hemisphere, these numerical results are compared with results obtained from a closed-form asymptotic solution of the problem. Also, Haskind's relations and an energy balance are used in the general case to check the accuracy of the numerical results.
Influence of Viscous Effects on Model/Full-Scale Cavitation Scaling
Authors: Huang T. T. , Peterson F. B.
Published: January 2021

Pertinent experimental results and theoretical prediction techniques are summarized and evaluated in terms of the influence of viscous effects on cavitation inception and the extent to which the boundary-layer properties complicate the correlation of model and full-scale cavitation inception. Consideration is given both to bodies having natural transition and bodies having laminar flow separation. The present approach assumes that cavitation inception is controlled by the pressure fluctuations in the region of natural transition or laminar separation superimposed upon the static pressure. In general, these pressure fluctuations occur very close to the minimum potential-flow pressure for full-scale bodies but occur farther aft of the minimum pressure for corresponding models evaluated at a lower Reynolds number. Predictions are in good agreement with results from numerous experiments on cavitating bodies which have either natural transition or laminar separation. Numerical examples demonstrate the order of magnitude of viscous effects on model/full-scale cavitation-inception scaling for a typical propeller blade section. Areas for additional cavitation research to strengthen the present approach are recommended.
Effect of Wedges on the Performance Characteristics of Two Planing Hulls
Authors: Millward A.
Published: January 2021

An investigation has been made into the effect of adding wedges or trim tabs to two models of the DTMB Series 62 planing hulls over a range of longitudinal center of gravity positions and displacements to determine the optimum wedge configuration and the range of effectiveness of a wedge. Measurements were also made to confirm that a wedge has an effect on the dynamic lift on the hull and hence that there is a change in resistance other than that resulting from control of the trim angle.
Drag and Turbulent Boundary Layer of Flat Plates at Low Reynolds Numbers
Authors: Granville Paul S.
Published: January 2021

A new formula is derived for flat plates which gives higher values of drag at low Reynolds numbers than does the Schoenherr formula. This is due to anomalous effects at low Reynolds numbers which are accounted for by adding viscosity to the outer law in the velocity similarity law analysis.
Nonlinear Wave Interaction with Vertical Cylinder of Large Diameter
Authors: Raman H. , Shankar N. Jothi , Venkatanarasaiah P.
Published: January 2021

A nonlinear diffraction theory for interaction of waves with a vertical cylinder of large diameter is presented. The nonlinear second-order solution is examined in comparison with a linear solution and other existing second-order solutions. The computed nonlinear wave forces are found to compare very well with the experimental results. The effect of nonlinearity on the crest height distribution around the cylinder is also studied. It is found that as the ratio of wave height to water depth decreases the nonlinear solution approaches the linear solution.
The Fundamental Solution in the Theory of Steady Motion of a Ship
Authors: Noblesse F.
Published: January 2021

The paper presents a simplified new expression for the fundamental solution (the Green function) in the theory of steady motion of a ship, that is, the linearized disturbance velocity potential of the steady, inviscid free-surface gravity flow due to a unit source in an oncoming uniform stream, sometimes also referred to as the "Havelock source potential."
Alternative Methods of Evaluating Green’s Function in Three-Dimensional Ship-Wave Problems
Authors: Hearn Grant E.
Published: January 2021

This paper introduces new alternative forms of Green's function, and its derivatives, suitable for the calculations associated with three-dimensional ship-wave problems. Rather than infinite-range integral forms, new finite integral representations of Green's function for harmonic motions are derived for the "single-body" and "double-body" descriptions of the interactive problem. The usefulness of these finite integral descriptions is illustrated by carrying out a computing efficiency comparison with other alternative, but mathematically equivalent, descriptions of the Green's function. The calculations carried out indicate that the proposed forms of the Green function are numerically more efficient than the standard forms without affecting accuracy.
Unsteady Hydrodynamic Interactions Between Ships
Authors: King G. W.
Published: January 2021

A model is developed for the hydrodynamic interactions between any number of thin cylindrical bodies in unsteady two-dimensional motion on straight parallel paths. The model is applicable to interactions between ships in very shallow water, and enables prediction of the sway force and yaw moment on any one ship due to the others. Particular maneuvers include ships passing each other in opposite directions, overtaking of one ship by another, and a ship moving past a stationary moored ship. A numerical method is developed, and results obtained for a range of two-ship interaction problems compare satisfactorily with experimental observations.
Hydrodynamic Impact of a Falling Body upon a Viscous Incompressible Fluid
Authors: Koehler Buford R. , Kettleborough C. F.
Published: January 2021

The hydrodynamic impact of a falling body upon a viscous incompressible fluid is investigated by the development and solution of a mathematical model which simulates the impact of a rigid flat-bottomed body upon the quiescent free surface of viscous incompressible water. A one-dimensional compressible air layer exists between the falling body and the water free surface. Velocity and pressure distributions within the air layer are calculated using the continuity equation and the one-dimensional momentum equation derived from the Navier-Stokes equations. The water free surface is allowed to deform as the air pressures acting on it increase. The two-dimensional rectangular coordinate form of the Navier-Stokes equations for an incompressible fluid is applied to the water. A normalization scheme is used which causes the water free surface to appear straight and simplifies the application of free-surface boundary conditions. Water velocities are calculated from the momentum and continuity equations. Pressures are calculated using the pressure equation derived from the Navier-Stokes equations. Air-water interface velocities are obtained from boundary-layer relations. The governing equations of the air layer and water region are expressed in finite difference form and are solved on a high-speed digital computer. The behavior of the air layer before impact is discussed. Air layer velocity and pressure distributions are obtained. The influence of the air layer on the water is studied. Pressure and velocity distributions in the water are obtained before and at the instant of impact. Pressure distributions and pressure histories compare favorably with available experimental data. Corresponding plots of the moving free surface show the actual shape of the compressible air region. A slight variation in the body deadrise angle is found to significantly change impact pressures and the shape of the pressure distributions.
Wakes of Developed Cavities
Authors: Michel Jean-Marie
Published: January 2021

A linearized wake model with a momentum defect is presented for the two-dimensional cavity flow around a base-vented foil which is placed in a free-surface channel. The numerical results show that, for a given cavity underpressureσ, the boundary conditions on the wake of the cavity have repercussions on the cavity length and the lift coefficient, whereas the drag coefficient is not modified. Similar features can be expected whenever the flow configuration is made strongly asymmetric by the external boundaries, especially by a free surface.
Effect of Initial Acceleration on Ship Wave Pattern and Wake Survey Methods
Authors: Calisal S.
Published: January 2021

Wave resistance calculations based on wave survey methods assume a constant ship velocity. The possible effects of initial acceleration are studied for different wave survey methods, and a procedure for determining the existence of an initial acceleration wave is proposed.
Theoretical Determination of Porpoising Instability of High-Speed Planing Boats
Authors: Martin Milton
Published: January 2021

A theoretical method is derived for predicting trim angle and speed coefficient at the inception of propoising of prismatic planing hulls. Although equations are derived for the surge, pitch, and heave degrees of freedom, it is seen that the effect of surge is small at ordinary operating trim angles. Comparisons of theoretical predictions with existing experimental data on coupled pitch and heave porpoising show reasonably good agreement for a wide range of speed coefficients, load coefficients, and deadrise angles. The theory may also be used for estimating the natural frequencies and damping characteristics of prismatic hulls in the stable, high-speed planing range.
A Further Study of Bodies of Revolution
Authors: Joubert P. N. , Sinclair T. J. , Hoffmann P. H.
Published: January 2021

The use of a body of revolution is considered as a model of reflex ship forms, for the estimation of skin friction. The model examined was that proposed by Matheson and Joubert [1], and is based on equality of lengthwise perimeter variation between the hull reflex geosim and the body of revolution. Bodies of revolution corresponding to two hull shapes were tested and compared with results for the reflex models tested previously. Agreement was poor. One potential flow prediction method for the pressure distribution was applied to one model and two boundary-layer prediction methods for the variation of local skin friction coefficients were applied to each of the bodies of revolution. Agreement with measured results was fair.
Comments on Milgram: “Calculation of Attached or Partially Separated Flow Around Airfoil Sections”
Authors: Goldschmied Fabio R.
Published: January 2021

The title paper presents a relatively unified potential flow theory for attached and partially separated (trailing-edge separation) two-dimensional, incompressible airfoil sections. The partially separated flows are characterized by nonreattaching flow separation from a point on the suction side of the airfoil downstream from the leading edge; it is required that the location of this separation point and the corresponding separation pressure be specified a priori. Figures 5 and 6 of the subject paper present the test data and the theoretical results for the NACA 63–018 airfoil at 15- and 18-deg angle of attack, respectively, as the only experimental verification for partially separated flows.
Hydrodynamic Power Radiated by a Heaving and Pitching Air-Cushion Vehicle
Authors: Doctors Lawrence J.
Published: January 2021

The harmonic heave and pitch motion of an air-cushion vehicle traveling at a constant speed over water is studied here, with a view to determining the power radiated by the surrounding wave system. The planform of the particular craft considered is compartmented into forward and aft subcushions, and the fluctuations of pressure in these are utilized to represent the effect of the vehicle on the water. The usual linearized incompressible potential flow theory is used. The calculations show that at typical Froude numbers and encounter frequencies, considerable power can be radiated in this manner, and it is generally of similar magnitude to the power required to overcome the usual steady-state wave resistance. Surprisingly, the singularity in the linear theory that occurs at the critical speed-frequency condition was found to be extremely localized and is therefore only significant in the case of a two-dimensional pressure band, or in the case of a three-dimensional pressure patch, at low Froude numbers.
A Finite-Element Method Applied to the Vibration of Submerged Plates
Authors: Marcus Melvyn S.
Published: January 2021

A finite-element approach is used to simulate the free vibration of submerged cantilever plates. The method explicitly models an acoustic fluid with pressure as the basic fluid unknown. Only standard capabilities of structural analysis computer codes such as NASTRAN are required for implementation. The computations performed take into account liquid free surface and partial submergence effects. The numerical results obtained compare favorably with experimentally measured frequencies of vibrating plates. Modeling requirements are discussed. Application areas include the vibration in water of rudders, propeller blades, and other ship appendages.
Similarity-Law Entrainment Method for Thick Axisymmetric Turbulent Boundary Layers in Pressure Gradients
Authors: Granville Paul S.
Published: January 2021

Analytical relations have been derived for calculation of developing thick, axisymmetric, turbulent boundary layers in a pressure gradient from two simultaneous differential equations: momentum and shape parameter. An entrainment method is used to obtain the shape parameter equation. Both equations incorporate the velocity similarity laws that provide a two-parameter velocity profile general enough to include any range of Reynolds numbers. Newly defined "quadratic" shape parameters which arise from the geometry of the thick axisymmetric boundary layer are analytically related to the two-dimensional shape parameter by means of these velocity similarity laws. The variation of momentum loss, boundary-layer thickness, local skin friction, and local velocity profile may be calculated for the axisymmetric turbulent boundary layers on underwater bodies, including the thick boundary layers on the tails. The various formulations are shown to correlate well with available experimental data.
Theoretical Prediction of Motions of High-Speed Planing Boats in Waves
Authors: Martin Milton
Published: January 2021

A theoretical method is derived for predicting the linearized response characteristics of constant deadrise high-speed planing boats in head and following waves. Comparisons of the theoretical predictions of the pitch and heave response amplitude operators and phase angles with existing experimental data show reasonably good agreement for a wide variety of conditions of interest. It appears that nonlinear effects are more severe at a speed to length ratio of 6 than of, say, 4 or less, principally because of the reduction of the damping ratio of the boat with increasing speed, and the consequent increase in motions in the vicinity of the resonant encounter frequency. However, it is concluded that the linear theory can provide a simple and fast means of determining the effect of various parameters such as trim angle, deadrise, loading, and speed on the damping, natural frequency, and linearized response in waves, and that this can furnish valuable insight into the actual boat dynamics, even though the accurate predictions of large motions and peak accelerations would require a nonlinear analysis.
Waves and Wave Resistance for Air-Cushion Vehicles with Time-Dependent Cushion Pressures
Authors: Haussling H. J. , Van Eseltine R. T.
Published: January 2021

Wave patterns and wave resistance are computed for air-cushion vehicles with time-dependent cushion pressures moving at uniform speed over deep and shallow water. The effect of beam-to-length ratio, Froude number, and water depth on the resistance is investigated. The resistance is found to exhibit a distinctive behavior at a critical frequency. This behavior corresponds to a singularity in the resistance at the critical frequency. The importance of this behavior is found to diminish with decreasing beam-to-length ratio and increasing Froude number.
Some New Aspects of Slamming Probability Theory
Authors: Psaraftis Harilaos N.
Published: January 2021

A systematic investigation of some probabilistic aspects of slamming is presented. This investigation includes the assessment of the unconditional probability of slamming at a random instant of time; the estimation of the conditional probability of slamming at a given instant after a particular slam; and the consequent rejection of the hypothesis that slamming is a Poisson process. In addition, a procedure to approximate the distribution of slamming interarrival times2 is presented. Finally, new slamming statistics, obtainable from the theory of this work, are presented and compared with the existing slamming criteria. The theory of this paper can be readily applied to other seakeeping events such as deck wetness, keel emergence, and propeller racing.
Nonlinear Aspects of Subcritical Shallow-Water Flow Past Two-Dimensional Obstructions
Authors: Salvesen Nils , von Kerczek C.
Published: January 2021

Some nonlinear aspects of the two-dimensional problem of a submerged body moving with constant speed in otherwise undisturbed water of uniform depth are considered. It is shown that a theory of Benjamin which predicts a uniform rise of the free surface ahead of the body and the lowering of the mean level of the waves behind it agrees well with experimental data. The local steady-flow problem is solved by a numerical method which satisfies the exact free-surface conditions. Third-order perturbation formulas for the downstream free waves are also presented. It is found that in sufficiently shallow water, the wavelength increases with increasing disturbance strength for fixed values of the free-stream-Froude number. This is opposite to the deepwater case where the wavelength decreases with increasing disturbance strength.
On the Fundamental Function in the Theory of Steady Motion of Ships
Authors: Noblesse F.
Published: January 2021

Simplified new expressions for the gradient of the fundamental solution (the Green function) in the theory of steady motion of ships are presented. These expressions supplement the expression for the fundamental function obtained previously by the author.
A Supercavitating Hydrofoil with Mechanical and Jet Flaps Beneath a Free Surface
Authors: Kida Teruhiko , Take Takanori , Miyai Yoshihiro
Published: January 2021

The flow around a supercavifating hydrofoil equipped with both mechanical and jet flaps, moving beneath a free surface, was analyzed by second-order theory, and the method of matched asymptotic expansions was used to solve the governing integro-differential equation. Hydrodynamic forces which are valid up to the second order of small angles of foil incidence and of jet deflection are determined by asymptotic expansions in terms of the jet-momentum coefficient. Moreover, it is found that Oba's correction factors are not reasonable.
Generalization of Rayleigh Probability Distribution and its Application
Authors: Ochi Michel K.
Published: January 2021

The Rayleigh probability distribution has been used extensively for statistical prediction of ocean waves, responses of ships, and marine structures in a seaway. However, the Rayleigh distribution cannot be used for statistical prediction of non-Gaussian random processes, a typical example of which is ship rolling motion with nonlinear characteristics. To evaluate the statistical properties of the maxima (peak values) of non-Gaussian random processes, this paper discusses generalization of the Rayleigh distribution and its application to practical problems. As examples of application, the problems associated with rolling motion of a vessel stabilized by rudders, responses of a surface effect ship in a seaway, and rolling motion of a ship with nonlinear damping are presented.
Added Moment of Inertia of Two-Dimensional Cylinders
Authors: Newman J. N.
Published: January 2021

This paper treats the classical problem of a two-dimensional body rotating in an ideal unbounded fluid. The added moment of inertia is derived, after mapping the body profile onto a straight line and using Hilbert techniques to solve the resulting boundary-value problem in the transformed plane. Specific geometries considered are a circle with symmetric fins, and a square. The method of solution differs from that which is commonly used, and the present results are simpler or more accurate by comparison with earlier works.
Scattering of Waves by Two-Dimensional Circular Obstacles in Finite Water Depths
Authors: Naftzger Robert A. , Chakrabarti Subrata K.
Published: January 2021

The wave forces on a fixed two-dimensional object submerged in water of finite depth are obtained under the assumptions of linear wave theory. The far-field characteristics of the wave interaction with the object are also examined. The boundary-value problem for the wave potential is formulated in terms of Green's theorem, and the resulting integral equation is solved numerically. Results for a submerged and half-submerged circular cylinder and a bottom-seated half cylinder are presented. In the limiting case of infinite depth the numerical results compare quite well with known solutions.
Nonlinear Stability Analysis of Pressure-Loaded imperfect Stiffened Cylinders
Authors: Simitses G. J. , Sheinman I. , Giri J.
Published: January 2021

This paper deals with the buckling of imperfect, thin, circular, cylindrical, stiffened shells under the application of external pressure. The methodology is based on the smeared technique, the Von Karmgn-Donnellnonlinear kinematic relations, and linearly elastic behavior, and it considers both axisymmetric and symmetric imperfections. Numerical results for various configurations are presented. These include some optimal stiffened configurations which exemplify submarine hull designs for operating depths of 1000 and3000 ft (305 and 915 m).
An Experimental Study of the Viscous Resistance of a 0,564-CB Form
Authors: Joubert P. N. , Hoffmann P. H.
Published: January 2021

Wind tunnel tests were performed to determine the viscous resistance and its components for a 0.564-CB model from the BSRA Trawler Series. It was found that the sum of the pressure and skin friction resistance coefficients agreed well with the viscous resistance coefficient determined from drag balance tests. The range of Reynolds number examined was from 1.15 × 106 to 5.17 × 106. The results for the viscous resistance and its components were fitted using least-squares methods to various equations. The results were also compared with the results of previous tests done at the University of Melbourne on models of Lucy Ash-. ton and a 0.80-CB tanker. It was found that the skin friction and viscous resistance coefficients had curves of quite different position and slope. Local skin friction distribution showed noteworthy differences, especially at the stern, with high values at the keel and low values approaching the waterline.
A Brief Note on Linearized, Unsteady, Supercavitating Flows
Authors: Acosta A. J. , Furuya O.
Published: January 2021

Three different models for the unsteady fluctuations of a slender cavity in the limit of small reduced frequency are compared with the results of quasi-steady calculations. Tulin's kinematically closed model in unsteady flow is seen to tend smoothly to a limiting quasi-steady motion having the same value for the compliance of the cavitating flow, unlike other models that have been used in the past.
Propeller Blade Pressure Distribution Due to Loading and Thickness Effects
Authors: Tsakonas S. , Jacobs W. R. , Ali M. R.
Published: January 2021

A theoretical approach is developed and a computational procedure adaptable to a high-speed digital computer is established for the evaluation of the blade pressure distribution of a marine propeller due to thickness and loading effects. The dual role of the blade thickness is considered. The contribution of the "non-planar thickness" to the propeller loading and pressure distribution and the effect of the "flow distortion thickness" are studied by means of the "thin body" approximation. The surface integral equation which relates the unknown loading to the known velocity distribution on the blades is solved by the mode approach in conjunction with the "lift operator" technique. The analysis treats both design and off-design conditions in steady-state and unsteady flows, and the proper chordwise modes are selected for each condition. The numerical solution yields the blade loading and resulting hydrodynamic forces and moments and blade bending moments, and, in addition, the blade pressure distributions on each blade face due to both loading and thickness effects, thus providing information necessary for the prediction of cavitation inception. Calculations have been performed for a set of three 3-bladed propellers of different EAR operating in a screen-generated wake, for comparison with experimental data.
A New Approach To High-Aspect-Ratio Supercavitating Hydrofoils
Authors: Kida Teruhiko , Miyai Yoshihiro
Published: January 2021

A three-dimensional cavity hydrofoil with a high aspect ratio is analyzed by a new lifting-line theory. Unlike Leehey's (1971) approach, which formulates the lifting-line theory from differential equations, the present theory has extracted the similar lifting-line theory from integral equations derived from the lifting-surface theory. The chief advantage of this method is that it is not necessary to match the inner and outer solutions. This lifting-line theory seems to be close to experimental results for the elliptic planform with aspect ratio 3 and 5, and for the rectangular planform with aspect ratio 6, in the case of δ/α ≥ 1, where σ is the cavitation number and α the incidence of the foil.
Optimal Shape and Nonhomogeneity of a Timoshenko Beam for Maximum Load
Authors: Adali Sarp , Sadek Ibrahim
Published: January 2021

The best possible distributions of Young's modulus or the cross-sectional area or both are determined explicitly for a cantilevered Timoshenko beam which, for a given volume and end deflection, carries the maximum possible load at its free end. Closed-form solutions are given for the optimal height, width and/or Young's modulus functions. Numerical results are presented in graphical form. It is found that the inclusion of shear deformation decreases the efficiency of the optimal design, and that optimization with respect to Young's modulus in addition to shape increases the efficiency considerably in comparison with optimization of the shape only.
Polynomial Families for Flat-Faced Underwater Bodies and Wall-Sided Ship Sections
Authors: Granville Paul S.
Published: January 2021

Polynomial families that contain a cube-root term are developed to satisfy requirements of infinite slope and zero curvature. Adjustable parameters are used to provide a wide range of curves without inflection points. Applications are to flat-faced underwater bodies and wall-sided ship sections.
Transcritical Heave and Pitch Motions in Shallow Water
Authors: Plotkin Allen
Published: January 2021

The problem of small heave and pitch motions of a slender ship in shallow water in the transcritical speed range is analyzed. Formulas valid to first order in slenderness are given for the added-mass and damping coefficients in terms of the Froude number and moderate values of the reduced frequency.