bluuebunny/crossref_metadata_2025 huggingface dataset:
Loading Conditions for Exposed-Waters Towing Vessels Regulated under Subchapter M
Authors: Morgan Erin , Bragaw William , Bruno Stephen , Schock James , Skimmons Jacob , Wheeler Judson , Taylor Todd
Published: January 2021

A set of five vessel loading conditions was developed for exposed-waters towing vessels in support of compliance with applicable stability regulations invoked under the U.S. Code of Federal Regulations (CFR) Title 46, Subchapter M. These loading conditions are envisioned as a starting framework for the naval architect or third-party organization when pursuing a U.S. Coast Guard stability letter with the fewest operational restrictions. These conditions do not represent required operational scenarios. For each loading condition, variable loads based on both tank location and tank contents were specified with the goal of encouraging conservative stability evaluations, while maintaining a level of realism to the resulting vessel attitude at each condition. Use of these developed loading conditions as a replacement for the nearly forty-year-old McGowan and Meyer conditions is anticipated. Using 3D models and General HydroStatics stability software, three vessels representative of modern exposed-waters towing vessels, but designed before the enactment of Subchapter M, were tested against 46 CFR Subchapter S stability criteria at each loading condition. Results of the analysis are presented for each vessel and for each applicable Subchapter S criterion. As expected, vessels not designed for Subchapter M/Subchapter S stability regulations can have trouble passing using the proposed loading conditions. The authors experimented with simple changes to the tank geometry of these pre-Subchapter M vessels, creating compliance with nearly all stability criteria for all loading conditions. Based on relevant literature and the results of this work, it is recommended that, for conservatism, the free-to-trim method be used for stability analysis regardless of the loading conditions applied. It is recommended that if an exposed-waters towing vessel passes the applicable Subchapter S stability criteria using the loading conditions developed in this work, then the vessel should be considered for a stability letter with minimal operational restrictions.
Application of Ship-Wave Theory to the Hydrofoil of Finite Span
Authors: Breslin John P.
Published: January 2021

It is demonstrated in this paper2 that the deepwater wave drag of a hydrofoil of finite span can be found directly from the theory developed largely for ship hydrodynamics by Havelock and others. The wave drag is then studied at high Froude numbers and from the observed behavior the induced drag of the hydrofoil can be deduced from existing aerodynamic formulas. Evaluation of the resulting formulas is effected for two arbitrary load distributions and a comparison with some model test results is made. A practical approximation which gives the influence of gravity over a range of high Froude numbers is found and from this one can deduce a Froude number beyond which the effects of gravity may be ignored. It is also shown that an expression for the waves at some distance aft of the hydrofoil can be deduced from the general formulas developed for ship hydrodynamics. A discussion of the wave pattern is given with particular emphasis on the centerline profile at high Froude numbers and a contrast is pointed out in regard to the results of the two-dimensional theory for the hydrofoil waves and wave resistance.
A Comment on Ship Research
Authors: Kane J. R.
Published: January 2021

Shipbuilding and shipping are old and traditional fields in which practice has, to a large degree, preceded theory. Progress has occurred for the most part by a gradual process of trial and elimination, reminiscent of Darwin's principle of natural selection in the biological species, rather than by a studied plan of theoretical development.
Water Tunnel Techniques for Force Measurements on Cavitating Hydrofoils
Authors: Parkin Blaine R. , Kermeen Robert W.
Published: January 2021

The paper reviews briefly experimental techniques and data-correction procedures developed in connection with studies in the High Speed Water Tunnel, California Institute of Technology, for hydrofoil force measurements. The matters discussed relate chiefly to problems of force measurement in cavitating flow and to procedures devised to solve them. Items considered in this connection are water-tunnel balances, the effects of tip-clearance flows, tare corrections, the importance of cavity-pressure measurements, cavitation scaling, tunnel-wall effects, and hydroelastic effects.
Wall Effects in Cavitating Hydrofoil Flow
Authors: Cohen Hirsh , Sutherland C. D. , Yih-O Tu
Published: January 2021

A linearized version of the transition-flow cavity model is used to obtain the effects of solid channel walls on cavitating hydrofoils. The formulation is in terms of two dimensional flow but includes any shape hydrofoil within the scope of the linear theory and any location of the foil between the walls. The case of the flat plate foil is considered in numerical detail. Three special cases of position, the foil midway between walls, near to only one wall, and the foil in an infinite stream (walls infinitely far apart), are taken up. The effect of the walls on lift and cavity length are discussed for each case.
A Comment on Hull Structural Research
Authors: Comstock John P.
Published: January 2021

A great deal of work is being done or is planned looking to a better knowledge of the loads and stresses actually experienced by ships at sea. Several projects aimed at a more "realistic" or "logical" design of hull structure are under way. The Five-Agency Hull Structure Committee and its working subcommittee, through its advisory Committee on Ship Structural Design, are taking a long look at the matter. The Classification Societies are deeply interested, particularly as regards the large ships. The Society's Hydrodynamics Committee and Hull Structures Committee have several panels engaged along this line. Our S-10 Panel is measuring hull-girder stresses on ships at sea, and is studying thermal stresses in hull structures.
Experiments on Circular-Arc and Flat-Plate Hydrofoils
Authors: Parkin Blaine R.
Published: January 2021

An investigation in the High-Speed Water Tunnel of the two-dimensional hydrodynamic characteristics of sharp-edged hydrofoils is described. The lift, drag, and pitching moment were measured in cavitating and noncavitating flows for flat-plate and circular-arc profiles. The theory of Wu for the forces on sharp-edged profiles in full-cavity flow and the experimental results showed good agreement over a wide range of attack angles.
The Pressure Field Near a Ship Propeller
Authors: Breslin John P.
Published: January 2021

A brief summary is given of efforts in the field of naval architecture on the problem of determining the vibratory forces and moments produced by a ship propeller, and an account of the principal contributions made by aeronautical researchers on the problem of computing the fluctuating pressure field near a propeller. This pressure is derived from a lifting-line representation and the expressions are then interpreted in terms of the fields of two doublet distributions. It is shown that this result can be verified by specializing the expressions for the sound-pressure field of a propeller. Some characteristics of the pressure field are discussed briefly. Detailed evaluations and comparison with experiment will be presented in a subsequent paper.
Effect of the Free Surface on the Flutter of Submerged Hydrofoils
Authors: Chu Wen-Hwa , Abramson H. Norman
Published: January 2021

Expressions for the unsteady lift and moment acting on an oscillating hydrofoil submerged under a free surface are derived by an extension of classical unsteady thin-airfoil theory. The method of images is employed to account for the free surface, but the additional contribution resulting from surface waves, considered small, is neglected. The results of flutter computations are presented for a hypothetical example, using a simple representative station analysis, for ratios of depth of submergence to semi-chord of 2 and infinity; it is found that the lower flutter speed corresponds to infinite depth of submergence.
The Axial Frictional Resistance of Long Cylinders in Turbulent Flow
Authors: Karhan K.
Published: January 2021

In ship-model extrapolation the frictional resistance of the ship surface is generally taken to be equal to that of the flat plate having the same length and area. Experiments carried out at several laboratories with models of different size show dearly that each model should have its own extrapolation curve. In spite of general agreement that this is so, the flat-plate extrapolation curve is still generally used. On the other hand it is not easy to derive mathematical relations for ship-form frictional resistance or to make extensive experiments for this purpose. It is obvious that a first step towards departing from the flat-plate resistance basis should be to study the effect of transverse curvature on frictional resistance.
A Theory for the Vibratory Effects Produced by a Propeller on a Large Plate
Authors: Breslin John P.
Published: January 2021

The flow generated on an infinite plane or wall by a single-bladed ship propeller rotating on a shaft parallel to the plane in a uniform superposed stream is first considered. After demonstrating that the pressure on the wall depends only on blade position and not upon the time-rate-of-change of blade position, the force and the moment on the plane about a transverse axis are computed and found to be given by very simple formulas. Under the assumed neglect of the interferences arising from the image of the propeller in the wall, it is shown that the net force and moment on the wall are zero for all lightly loaded propellers having two or more blades. The case of nonuniform inflow is considered and shown to give nonzero vibratory forces. The case of uniform inflow is still of interest because the zero force and moment result does not mean that an elastic wall would not vibrate, and to substantiate this, a formula for the deflections of a thin "infinite" plate is given. This formula has not been evaluated because of its complexity. It is recommended that numerical evaluation be undertaken through the use of a high-speed computer.
Preliminary Evaluation of a Semi-Submerged Ship for High-Speed Operation in Rough Seas
Authors: Lewis Edward V. , Odenbrett Clayton
Published: January 2021

This paper describes the evaluation by means of model tests of an unusual hull form intended for high-speed operation in rough seas. The form can be described as a surfaced submarine, made longer and more slender in order to attain high calm-water speed. A long natural pitching period is obtained by fine, hollow waterline endings and use of large peak ballast tanks for rough-water operation. It was considered best not to attempt to keep water off the deck, and therefore comparatively low freeboard and tumblehome were adopted. Tests in regular head seas of model length and twice model length confirmed the expectation that at high speeds the semi-submerged ship could exceed the speeds at which the peaks of synchronous pitching and heaving motions occur. Consequently, in irregular head seas corresponding to a storm of Beaufort force 6, motions decreased as speed increased. Heaving was more pronounced than pitching, but accelerations were not prohibitively high even at a speed of 40 knots. It is concluded that a semi-submerged ship of the type tested shows promise of attaining much higher rough-water speeds than conventional destroyers, provided sufficient power can be installed. It is recommended that further research be directed toward providing a super-structure design that will reduce wave-impact effects and a hull form which will require less power at high speed in rough water.
Three-Dimensional Stripwise Damping Coefficients for Heave and Pitch of a Submerged Slender Spheroid
Authors: Kaplan Paul , Hu Pung Nien
Published: January 2021

The distribution of the local damping force and moment along a submerged spheroid, oscillating in heave and pitch at zero forward speed, is found in this note. Two different methods of calculation (local energy radiation and the extended Lagally theorem) were used and they were shown to yield equivalent results. The influence of three-dimensional effects is shown to be important at all sections, including the mid-section, and this is not exhibited by ratios of total three-dimensional to two-dimensional damping. The importance of these findings for bending-moment calculations in waves is stressed.
A Study of the Hydroelastic Instabilities of Supercavitating Hydrofoils
Authors: Kaplan Paul , Henry C. J.
Published: January 2021

Presented herein are the results of a theoretical study of the static and dynamic hydroelastic instabilities of rigid supercavitating hydrofoils on elastic supports. A two-dimensional theory is used to define the unsteady hydrodynamic force and moment acting on the oscillating foil, which is assumed to be elastically restrained in translation normal to the free-stream direction and in rotation about a prescribed axis which is normal to the plane of flow. All other motions are neglected. The effects of variation in the elastic and inertial properties, as well as the effect of varying the position of the upper surface flow-separation point on the possibility of either form of instability, are determined. Also, the effect of cavitation number over a small range near zero is hypothesized. The theory predicts that dynamic instability (bending-torsion flutter) is possible at the density ratios typical of supercavitating operation. This is in contrast to the results for fully-wetted flow, where the occurrence of flutter is unlikely at the structural-to-fluid density ratios typical of hydrodynamic operation. The flutter possible in supercavitated operation is also more severe than that indicated for fully-wetted flow. Furthermore, it is shown that for the supercavitating hydrofoil, static instability (torsional divergence) and dynamic instability are of equal importance which again differs from the results in fully-wetted flow where static instability was shown to be the more important practical problem. Recommendations are made for experimental studies to verify these theoretical results.
Hydrodynamic Theories of Ship Slamming Review and Extension
Authors: Chu Wen-Hwa , Abramson H. Norman
Published: January 2021

A critical review and evaluation of existing hydrodynamic theories of body-water impact is presented. It is shown, partly by comparison with available experimental data, that fitting methods are adequate only for bodies of reasonably large deadrise angle during later stages of the impact process. The ellipse-fitting technique is extended to a much broader class of body forms and more accurate formulations of the general problem are proposed that avoid linearization of the free-surface boundary condition and can account for compressibility effects during the initial stage of impact, although numerical procedures must be employed.
Instability of Ventilated Cavities
Authors: Silberman E. , Song C. S.
Published: January 2021

Cavitation number σ is defined by σ = (p0pk)/q. It can be controlled by controlling the dynamic pressure q, the ambient pressure p0, or, in the case of quasi-steady cavities, the internal cavity pressure pk. The present investigation was undertaken to study methods of controlling pk by adding air to the wakes of fully submerged bodies. This process has been called ventilation. It was found that for small air-flow rates, pk increased and σ decreased nearly linearly with the rate of air supply. It was also found that onceσ had decreased to a certain critical value, further increase in the air supply rate would not produce a continuing linear decrease in σ. Rather, σ remained nearly constant and the cavities began to vibrate. Vibration occurred with one, two or more waves on the cavity surface. Only by going from a one-wave to a two-wave cavity could σbe reduced further, and the reduction was discontinuous. Both two-dimensional and finite aspect-ratio bodies were tested. The tests were conducted in the two-dimensional, vertical, free-jet water tunnel at the St. Anthony Falls Hydraulic Laboratory. All bodies tested, regardless of aspect ratio and whether lifting or nonlifting, behaved quite similarly within both the vibrating and nonvibrating regimes. That the vibration was not peculiar to the vertical free-jet tunnel was demonstrated by comparison with results from a hydrofoil towed in a tank. In the case of lifting bodies of finite span operating near a free surface, air was found to enter, rather than leave, the cavities through the trailing vortexes.
The Calculation of Marine Propellers Based on Lifting-Surface Theory
Authors: Pien Pao C.
Published: January 2021

Since the present theoretical propeller design method is based on the lifting-surface theory formulated by Ginzel and Ludwieg, an improvement to this lifting-surface theory is made first. Aside from the fact that the improved lifting-surface theory is more general with respect to blade outline and the loading distribution over the blade area, the most important improvement is in the method of obtaining the induced mean lines. In the new theory the induced mean line at any radius is derived from the down-wash distribution along the entire chord length rather than from the rate of change of the down wash at the middle chord as has been done by Ginzel and Ludwieg. The results obtained from the new method show that the induced mean line at any radius is not a function of the chordwise loading distribution at that radius alone but a function of the loading distribution over the entire blade area and the blade outline. Based on the improved theory a new theoretical propeller design method has been developed. The numerical work involved in this design method has been programmed into a high-speed computer for a special case of uniform chordwise loading distribution. Two design examples have been carried out in accordance with the new design procedure, one with skewed blade and the other with symmetrical blade. The experimental verification of the work presented here will be done in the near future.
Experimental Investigations of Three-Dimensional Effects on Cavitating Hydrofoils
Authors: Kermeen R. W.
Published: January 2021

An investigation in the high-speed water tunnel of the hydsrodynamic characteristics of a family of three-dimensional sharp-edged hydrofoils is described. Four rectangular plan-form, 6-deg wedge profiles with aspect ratios of 4.0, 2.0, 1.0 and 0.5 were tested over a range of cavitation numbers from noncavitating to fully cavitating flow. The effects of aspect ratio on the flow and cavity configurations and on the lift, drag and pitching moment are discussed. Where data were available the results have been compared with the two-dimensional case.
Minimum Weight Design of Ring Stiffened Cylinders Under External Pressure
Authors: Gerard George
Published: January 2021

Minimum weight analyses for unstiffened and ring-stiffened cylinders under external pressure are presented for designs based on stability and compressive yield-strength considerations. The results for both types of cylinders are compared in terms of a common set of parameters to establish the efficiency of the stiffening system. The results are then compared on a somewhat different basis to establish the relative efficiencies of various classes of materials. Finally, certain conclusions are drawn of particular pertinence to deep submersibles.
Design of Long Rectangular Elasto-Plastic Plates
Authors: Wah Thein
Published: January 2021

In a previous paper3 a theory was derived for the analysis of rectangular plates loaded with a uniform pressure and beyond the elastic range of the material. The theory took into account the strengthening effect of membrane tensions in the plane of the plate, the effects of edge displacements and of initial deflections and locked-in moments which might exist in the plate. In the present paper the salient features of the theory are put in the form of charts and tables for convenience in analysis and design.
On the Heaving Motion of Cylinders of Shallow Draft
Authors: MacCamy R. C.
Published: January 2021

A perturbation procedure is developed for the two-dimensional motion produced by a long ship in heave when the draft is assumed small. The procedure reduces the shallow draft problem to a series of problems for a "raft" of zero draft. A considerable simplification in the method of integral equations is found to occur. For the first approximation, that is, a raft of finite width, the integral equations are solved numerically to determine pressure, virtual mass and damping. The problem of heave of a circular disk of zero draft is treated by the same methods so that an evaluation of strip theory in this special case is possible.
The Coupled Damping Coefficients of a Symmetric Ship
Authors: Timman R. , Newman J. N.
Published: January 2021

A study is made of a floating or submerged body with longitudinal and transverse symmetry, which is moving with constant forward speed and performing small oscillations. The analysis is quite general in the sense that the shape of the body and the nature of the oscillations are unspecified, but it is assumed that the linearized free-surface condition holds. With this assumption the oscillatory velocity potential is found in terms of an unknown Green's function, the existence of which is also assumed. This potential is then used to show the symmetry properties of the cross-coupling damping coefficients.
Pulsation of Ventilated Cavities
Authors: Song C. S.
Published: January 2021

The problem of pulsating supercavities under artificial ventilation is analytically treated as a resonance problem of a two-dimensional gas-liquid system using a linearized method. A simple kinematical consideration and a dynamical model of the flow lead to solutions for frequency and amplitude of pulsations. The criteria of pulsation are given in terms of a formula relating σv. and σ Maximum air-carrying capacities of pulsating cavities are also estimated. Most of the formulas involve an undetermined constant which must be estimated by using experimental data. The analytical results are compared with the experimental data obtained at the St. Anthony Falls Hydraulic Laboratory, and, in general, good agreement is obtained. It is found that pulsation is possible only for a two-dimensional cavity or a cavity in which a substantial portion of the span can be regarded as two-dimensional. The existence of a free surface is also essential to pulsation. The strong effect of the free surface suggests that pulsation may become an important problem in the open sea only when submergence is relatively small.
The Exciting Forces on Fixed Bodies in Waves
Authors: Newman J. N.
Published: January 2021

General expressions, originally given by Haskind, are derived for the exciting forces on an arbitrary fixed body in waves. These give the exciting forces and moments in terms of the far-field velocity potentials for forced oscillations in calm water and do not depend on the diffraction potential, or the disturbance of the incident wave by the body. These expressions are then used to compute the exciting forces on a submerged ellipsoid, and on floating two-dimensional ellipses. For the ellipsoid, the problem is solved using the far-field potentials, and detailed results and calculations are given for the roll moment. The other forces agree, for the special case of a spheroid, with earlier results obtained by Havelock. In the case of two-dimensional motion the exciting forces are related to the wave amplitude ratio A for forced oscillations in calm water, and this relation is used to compute the heave exciting force for several elliptic cylinders. Expressions are also given relating the damping coefficients and the exciting forces. A = wave amplitude A = wave-height ratio for forced oscillations(a1 a2 a3) = semi-axis of ellipsoidBij = damping coefficientsC4 = nondimensional roll exciting-force coefficientDj = virtual-mass coefficients, defined by equations (18) and (19)g = gravitational accelerationh = depth of submergencei = √ — 1j = index referring to direction of force or motionn(z) = spherical Bessel function, K = wave number, K = ω2/gPj = functions defined following equation (17)R = polar coordinateV, = velocity components (x, y, z) = Cartesian coordinatesαi = Green's integrals, defined by equation (20)β = angle of incidence of wave systemθ = polar coordinateρ= fluid densityφj = velocity potentialsω = circular frequency of encounter
Dynamic Behavior of Ground-Effect Machines in Motion Over Waves
Authors: Lin J. D.
Published: January 2021

Dynamic motion in heaving and pitching of a ground-effect machine traveling over a train of sinusoidal waves is formulated on the basis of the small-disturbance theory. The equations of motion are derived as two third-order ordinary differential equations with coefficients which depend on the characteristics of the machine and the mass flow into or out of the cavity under the machine. The coefficienis are linearized at the equilibrium height; then, the solutions are obtained for the natural frequencies, the damping, and the steady periodic responses to motion over waves. It is found that a ground-effect machine with peripheral and central jet curtains is generally stable for heaving and pitching, but the damping is rather small. The effect of coupling due to the discontinuity of mass-flow coefficients is also shown to be very weak and thus may be neglected in this linearized analysis. A program, prepared for the IBM 1 620 digital computers at Hydronautics, Incorporated, allows study of the dynamic stability of a machine through variation of pertinent parameters, and also investigations of its dynamic response to various wave-encounter conditions. Theoretical predictions for practical machines, which have in model tests experienced dynamic motions over waves, are presented here and compared with experimental results. Satisfactory agreements are indicated in the natural frequency and response both for heaving and pitching.
A Comparison of Experimental and Theoretical Forces and Moments Acting on a Restrained Surface Ship in Regular Waves
Authors: Gersten Alvin
Published: January 2021

A mathematically defined, fully restrained, ship form has been towed in regular waves to measure the exciting forces and moments acting on it. The results of these tests are presented and compared with theoretical values computed both on the basis of assumptions made in the Froude-Krylov hypothesis and an extension of this hypothesis which accounts for ship-wave interference. For low values of draft to wavelength ratio, a number of the presently available prediction techniques are in agreement and are shown to be reasonably accurate. The need for a generally applicable correction for speed effect, however, is demonstrated.
Propeller-Incidence Correction Due to Blade Thickness
Authors: Kerwin J. E. , Leopold R.
Published: January 2021

It is shown that the presence of finite blade thickness results in a disturbance velocity normal to the blades which is in addition to that predicted by lifting-surface theory. The results show that as blade thickness is increased, an incidence correction must be applied in order to maintain the same load distribution. Numerical results indicate that the correction is small at the tip and increases towards the root of the blades. Its magnitude is sufficient to be of practical importance in design.
Damping and Inertia Coefficients for a Rolling or Swaying Vertical Strip
Authors: Kotik J.
Published: January 2021

Ursell's exact expression3 for the wave-amplitude coefficient for a swaying or rolling vertical strip is evaluated numerically over the entire frequency range. The added-mass and inertia coefficients are then obtained numerically, also over the entire frequency range, via the Kramers-Kronig relations.
Experimental Determination of Oscillatory Lift and Moment Distributions on Fully Submerged Flexible Hydrofoils
Authors: Ransleben Guido E. , Abramson H. Norman
Published: January 2021

Measured span wise distributions of steady state and oscillatory lift and moment on fully submerged cantilever hydrofoils are presented. The hydrofoils were of aspect ratio 5 rectangular platform, and were towed at speeds sufficiently low to avoid cavitation. The data are compared with theoretical predictions and wind-tunnel data previously obtained at higher values of reduced velocity.
Supercavitating Flows–Small Perturbation Theory
Authors: Tulin Marshall P.
Published: January 2021

This paper contains analytical results which are both old and new. It also contains an historical introduction briefly outlining events leading up to the formulation of linearized theory and indicating the scope of its subsequent development and engineering applications. A large number of references to the extensive literature are presented. The new analytical results include: The logical development of the linearized theory of steady supercavitating flows; the presentation of a general solution for the linearized problem; introduction of a new nonlinear model for finite cavity flows; the formulation of a simple second-order theory; and the application of this theory to the case of flat plates and symmetric wedges. The logical development of the linearized theory involves a small perturbation expansion of the nonlinear problem in which the dependent variable is the complex function In Ψ' and the independent variable is the complex potential Ψ; the problem is formulated for a nonlinear finite-cavity model which features cavity termination in spiral vortices followed by a "smooth" wake which is closed at infinity. The resulting boundary-value problems are of identical form for both the first and second-order theories. The first-order theory is identical to the usual linearized theory, which has previously been formulated by more intuitive means. The simple second-order theory leads in the special cases of inclined flat plates and symmetric wedges in supercavitating flow to results for lift and drag in simple (no quadratures necessary) terms of the first-order results. The old analytical results contained herein refer particularly to: The hydrofoil-airfoil equivalence and results related thereto, which has been so useful in practice for designing hydrofoils at zero cavitation number; and also to problems involving hydrofoils operating at high speeds beneath (hydrofoil boats) and over (supercavitating propeller sections) free surfaces.
Effect of the Initial Acceleration Upon the Wave Resistance of Ship Models
Authors: Wehausen John V.
Published: January 2021

In order to estimate the effect of the initial acceleration of a ship model upon its wave resistance after a steady velocity has been reached, an asymptotic expansion for large t is found for the wave resistance of a thin ship. Numerical computations are provided for a hull form of simplified type.
A Theory of Peripheral Jets in Proximity to the Ground With Application to Ground-Effect Machines
Authors: Wald Quentin
Published: January 2021

A theory of peripheral jets in proximity to the ground has been developed which yields results in a simple closed form and is in close agreement with the exact inviscid solution. By the introduction of one additional assumption beyond the usual assumption of inviscid incompressible flow, the pressure relations can be determined by a momentum integration. The additional assumption is the general form of the velocity distribution across the jet. The base pressure coefficient, lift coefficient, mass-flow coefficient and power coefficient are all obtained as simple functions of a velocity-ratio parameter which is in turn related to the thickness/height ratio and jet angle. Application to ground-effect machines is considered briefly.
A Systematic Asymptotic Expansion Procedure for Slender Ships
Authors: Tuck E. O.
Published: January 2021

Inner and outer expansions are used to formulate a systematic solution to the problem of the steady translation of a slender ship of arbitrary shape. Careful consideration is givien to finding the correct boundary conditions to be satisfied by successive terms in the expansions, and certain of the individual terms are determined partly or completely as functions of hull shape. Some results are given concerning the second approximations to the potential and wave resistance.
Buckling and Post Buckling Behavior of a Transversely Stiffened Ship Hull Model
Authors: Schultz H.G.
Published: January 2021

In the paper presented the behavior of a transversely formed box-girder model subjected to pure bending is discussed, where the deck plating of the model is loaded above the buckling load. The experimental results obtained are in reasonable agreement with theoretical investigations and show the influence of fabrication initiated plate deflections on the buckling and postbuckling behavior of the deck plating clearly. A method is suggested for determining the buckling load of plates having large initial deformations.
The Unsteady Loading on a Marine Propeller in a Nonuniform Flow
Authors: Greenberg Michael D.
Published: January 2021

The lifting-surface integral equation governing the unsteady loading on a marine propeller in a nonuniform free stream is derived using a classical vortex model. The induced downwash is split into a part corresponding to a locally tangent flat finite wing and wake, plus parts corresponding to the effects of the "helicoidal deviation" from this, of the true blade and wake, and the interference from the other blades and their wakes. Strip-type approximations are tolerated on these terms while a lifting-surface formulation is retained for the dominant finite flat-wing portion. A simple numerical example is carried out and these effects are indeed found to be quite small; so small, in fact, that it may suffice to retain only the flat finite-wing terms in practical applications.
Longitudinal Blade-Frequency Force Induced by a Propeller on a Prolate Spheroid
Authors: Tsakonas S. , Breslin J. P.
Published: January 2021

An expression has been developed for the longitudinal component of the vibratory force exerted on a prolate spheroid by the operation of a marine propeller in a space-varying field (wake). Two evaluation schemes have been considered: One by integration of the pressure signal over the surface of the ellipsoid and the other by means of Lagally's theorem with the ellipsoid represented by a known source-sink distribution. The former, considered exact, leads to a complicated analytic expression, whereas the latter, less accurate, yields simple and physically meaningful results. Numerical calculations indicate the important role played by propeller clearance and slenderness ratio in the magnitude of the vibratory force. Also considered is the vibratory force exerted on a fin tail under the same condition of propeller action in a wake. Conclusions are drawn as to the optimum propeller blade number for a given fin-tail configuration.
A Note on Gravity Effects in Supercavitating Flow
Authors: Street R. L.
Published: January 2021

Two approximations to the linearized theory for supercavitating flow about slender bodiesare applied to the case of flow past a slender wedge in a transverse gravity field. The additional lift and moment forces arising as a result of the gravity field are calculated by theories that are expected to hold when the gravity effects are of first-order smallnessconsistent with the linearization appi'oximations. The lift and moment coefficients obtained from the two approximations are in general quantitative agreement over the most important cavitation-number range. The results obtained confirm the validity of the average-value approximation introduced by Parkin.
Fully Cavitating Hydrofoils in Nonuniform Motion Under a Free Surface
Authors: Hsu C. C.
Published: January 2021

A simple linearized theory for the problem of a two-dimensional thin supercavitating hydrofoil in nonuniform motion is developed. General expressions are presented for frequency-response function, lift and moment coefficients. It is found that, in general, the lift and moment vary appreciably with the depth of submersion. At a depth-chord ratio of unity (typical value), the nonsteady characteristics are not well approximated by either the deeply submerged or surfaced hydrofoil results. Detailed numerical results for the cases of a rigid foil performing heaving oscillations or entering the sinusoidal gust, based on digital-machine calculation, are given.
The Virtual Inertia of Propellers Under Load
Authors: Norrie D. H.
Published: January 2021

Using a specially developed dynamometer, the hydrodynamic increase in inertia was determined for a variable-pitch propeller under load at various pitch settings and at various operating conditions. Tests also were carried out under "still-water" conditions. The results show the effect of amplitude of oscillation and propeller Reynolds number on the hydrodynamic inertia to be small. The influence of propeller load is also small over the normal range of operation. It would appear, therefore, that the hydrodynamic inertia can be determined to a reasonable degree of accuracy, by still-water tests with a nonrotating propeller.
Axisymmetric Buckling of Ring-Stiffened Cylindrical Shells Under Axial Compression
Authors: Wah Thein
Published: January 2021

The possibility of axisymmetric modes of buckling of ring-stiffened circular cylindrical shells under axial compression is investigated by the use of finite-difference calculus. The theory accounts for both the extensional as well as torsional rigidity of the rings.
An Experimental Determination of Pressure Forces on a Ship Model From an Analysis of the Wave Profile
Authors: Lewison Grant
Published: January 2021

A method for the analysis of the wave profile alongside a ship model is presented in a new form. The pressure distribution over an axisymmetric model is computed, and wave resistance and vertical forces are derived from it. The application of the method to other model forms and also to full-scale ships is discussed.
Hydrostatic Tests of Two Prolate Spheroidal Shells
Authors: Healey John J.
Published: January 2021

Two machined models were collapsed under external hydrostatic pressure to determine the elastic buckling strength of complete prolate spheroidal shells. The test results demonstrated that collapse pressures 40 percent greater than predicted by available theory can be achieved for a prolate spheroidal shell with a major to minor axis ratio of 3.0 and a thickness to diameter ratio of 0.015.
Gyrostatic Yawing of Ships in Random Seas
Authors: Goodman Theodore R.
Published: January 2021

Based on a theory originally presented by Suyehiro for a ship being acted upon by a single wave train, it is shown that all ships at zero speed, when acted upon by a fully developed random sea up to sea state 5 will tend to turn so that they lie parallel to the dominant wave direction. For higher sea states, the ultimate heading is found by reference to a graph within this paper. For the highest sea states the ship tends to turn beam to the dominant wave direction.
Determination of Ship Motion Parameters by a Step Response Technique
Authors: Kerwin J. E. , Narita H.
Published: January 2021

A method of determining the damping and virtual inertia of a ship hull is presented. These quantities are obtained by a numerical convolution technique utilizing an experimentally obtained step-response record. Results are given for damping and virtual inertia in pitch of the Series 60, CB = 0.60 hull at various speeds and frequencies.
Experiments on Flat-Bottom Slamming
Authors: Chuang Sheng-Lun
Published: January 2021

An experimental investigation of rigid flat-bottom body slamming was performed at the David Taylor Model Basin by dropping a 20-in. X 26.5-in. X 0.5-in. steel plate from various elevated positions above a calm water surface. Because of the effect of the trapped air between the falling body and the water, the maximum impact pressure measured was much lower than the pressure expected, if the generally accepted acoustic pressure formula ρcV0 is applied.
Drifting Force and Moment on Ships in Oblique Waves
Authors: Hu Pung Nien , Eng King
Published: January 2021

A general expression for the drifting moment about the vertical axis of an oscillating ship in regular oblique waves is derived from the potential theory, following a similar procedure developed by Maruo for drifting force. Explicit analytical solutions for the drifting side force and yaw moment on thin ships in long waves are obtained in terms of simple elementary functions. The effect of the wave frequency, the draft of the ship, the displacement, and the phase angle of the ship oscillation are discussed.
A Critical Re-Evaluation of Hydrodynamic Theories and Experiments in Subcavitating Hydrofoil Flutter
Authors: Chu Wen-Hwa
Published: January 2021

A review of relevant hydrodynamic information has been made, with emphasis on the possible cause of serious discrepancies between classical hydrodynamic theory and experiments for subcavitating hydrofoils. The usefulness of the best available wind tunnel and towing tank force measurements is also discussed. It is believed that these data are unreliable, and that the completion of the force calculation based on the classical lifting surface theory and subsequent flutter prediction for an actual flutter model is desirable. Some recommendations for possible future experimental research are also given.
Shallow Water and Channel Effects on Wave Resistance
Authors: Kirsch Maria
Published: January 2021

Based on Sretenski's formula, the wave resistance in shallow water and in a channel of rectangular cross section is computed for certain mathematical ship forms. The results are plotted as curves and compared with the wave resistance in an unbounded liquid. The use of these curves for the determination of the wave resistance from towing-tank experiments is illustrated through an example.
On the Effect of Short-Crestedness on Ship Motions
Authors: Tuck E. O.
Published: January 2021

A simple mathematical example, using the slender-body theory of ship motions, is given to illustrate the nature of errors due to short-crestedness in estimations of ship transfer functions from full-scale measurements in directionally random seas. As expected physically, any transfer function obtained in this manner is a smoothed estimate of the true transfer function which would be observed in a unidirectional sea. Computations of this "pseudotransfer function" are presented for heave and pitch of an idealized ship at zero speed, and the effects of forward speed are discussed briefly.
Mathematical Ship Lofting
Authors: Berger S. A. , Webster W. C. , Tapia R. A. , Atkins D. A.
Published: January 2021

The problem of fairing the hull surface of a ship is formulated as a linear programming problem using an analytic representation of the technique commonly employed in graphical lofts, i.e., the use of battens. With the help of a smoothing procedure devised for this problem it is shown how one may mathematically proceed from the naval architect's preliminary offsets to the faired, molded hull form with little, if any, human intervention; the final form satisfying the same continuity conditions as if it were faired graphically. The solution of the linear programming problem results in a surface equation from which all of the usual loft information needed for parts definition (shell-plate development, longitudinals, and so on) can be obtained. The method is intended to be accurate enough to be employed as a production tool in the shipyard. Examples of the application of the results to specific ship surfaces is presented.
The Disturbance Due to a Slender Ship Oscillating in Waves in a Fluid of Finite Depth
Authors: Monacella V. J.
Published: January 2021

The disturbance due to a ship, free to oscillate on the surface of an ideal fluid of finite depth, is studied. The ship is in the presence of oblique, incident, plane progressive waves. Green's theorem is used to represent the velocity potential, and an asymptotic approximation for the first-order slender-body potential valid for all points in the fluid to within a wave length of the ship is found. This is used to determine the hydrodynamic pressure on the bottom of the fluid. Numerical results are presented for the case of a spheroid.
Linearized Theory of a Partially Cavitating Plano-Convex Hydrofoil Including the Effects of Camber and Thickness
Authors: Wade R. B.
Published: January 2021

The linearized treatment of the flow over a partially cavitating single hydrofoil having a flat pressure surface and a circular-arc suction side is presented. The flow is treated as a two-dimensional, steady, inviscid flow. Further assumptions made are those of incompressibility and irrotationality. The results obtained are compared with experiment and generally good correlation is found for the ranges of validity of the linearization.
Supercavitating Flat Plate With an Oscillating Flap at Zero Cavitation Number
Authors: Song C. S.
Published: January 2021

The results of experimental and theoretical investigations on a supercavitating flat plate with an oscillating flap at zero cavitation number are presented. The experiment was carried out in a vertical free-jet water tunnel using 3-in. chord and 2-in. chord flat-plate hydrofoils, both having flap-chord ratios of 0.29. Various relative locations of the free surfaces were used and reduced frequency range of zero to four was covered. Amplitude and phase angle of lift, drag, and moment as well as the surface wave speed were measured. The problem was also solved analytically by means of a first-order perturbation theory and the results were compared with the experimental data.
Induced Curved-Flow Effect in the Lifting-Surface Theory of the Widely Bladed Propellers
Authors: Nishiyama Tetsuo , Sasajima Takao
Published: January 2021

The present paper is aimed to develop a more accurate lifting-surface theory of widely bladed propellers by applying the Scholz' technique. Curved-flow effect, which is of essential importance in the theory of widely bladed propellers, is analyzed and clarified in detail in the forms of correction coefficients to the lift-curve slope and zero lift angle of the blade element. Further, curved-flow correction to the lifting-line theory and the corresponding factor to the Ginzel's camber correction are shown by the present theory. The theoretical characteristics seem to be in good agreement with the experiment, so far as the assumption of linearization holds.
A Nonlinear Solution for a Fully Cavitating Hydrofoil Beneath a Free Surface
Authors: Larock B. E. , Street R. L.
Published: January 2021

Conformal mapping and the Riemann-Hilbert solution to a mixed-boundary-value problem in an auxiliary halfplane are used to solve a nonlinear problem for a flat-plate hydrofoil beneath a free surface. Results include the physical-plane plate-cavity-surface configuration, submergence, and the lift and drag coefficients as functions of angle of attack, cavitation number and spray-sheet thickness. All are given in terms of quadratures. A digital computer aided materially in the numerical manipulation of the resulting expressions. In addition, expressions are given in closed form for the limiting case of zero cavitation number.
Determination of the Wave Spectrum From Observed Motions of a Vehicle in a Seaway
Authors: Marks Wilbur
Published: January 2021

If, during full-scale trials, it is not possible to measure the state of the sea with a reliable wavemeter, then certain motion records may be combined to achieve the same end. The derivation of the wave spectrum from the time histories of pitch, heave (vertical acceleration), and bow immersion is presented. The problem of the conversion of acceleration to displacement is discussed. The method is applied to the particular case of the hydrofoil boat Sea Legs.
On the Efficiency of a Class of Nonstationary Ship Propellers
Authors: Sparenberg J. A.
Published: January 2021

Nonstationary ship propellers belonging to a certain class which includes, among others, the Voith-Schneider propeller, are considered. The free vorticity left behind by an optimum propeller is characterized. The theory is three dimensional, hence tip effects are included.