bluuebunny/crossref_metadata_2025 huggingface dataset:
Aeroelastic Stability of Lifting Surfaces in High-Density Fluids
Authors: Henry Charles J. , Dugundji John , Ashley Holt
Published: January 2021

The large increases anticipated in speeds of vehicles towed or propelled underwater suggests a re-examination of the problem of stability of flexible lifting surfaces mounted thereon. Experimental and theoretical evidence is assembled which suggests that oscillatory aeroelastic instability (flutter) is very unlikely at the structural-to-fluid mass ratios typical of hydrodynamic operation. It is shown that static instability (divergence) is the more important practical problem but that its occurrence can be predicted with greater confidence. Flutter data obtained in high-density fluids are reviewed, and various sources of inaccuracy in their theoretical prediction are analyzed. The need is expressed for more precise means of analytically representing both dynamic-elastic systems and three-dimensional unsteady hydrodynamic loads. For a simple hydrofoil with single degrees of freedom in bending and torsion, the theoretical influence of several significant parameters on high-density flutter is calculated and discussed. Recommendations are made for refinements to existing techniques of analysis to include the presence of channel boundaries, free surfaces, cavitation or separated flow.
A Study of the Transient Pitching Oscillations of a Ship
Authors: Golovato Paul
Published: January 2021

The motions of a deeply submerged body with vertical-plane symmetry, e.g., a submarine, are commonly treated in a manner completely analogous to that used for aircraft motions. The body is assumed to have its lateral and longitudinal modes uncoupled. The small motions are described by a set of force-and-moment equations which are linear, second-order differential equations with constant coefficients. These proportionality constants ("stability derivatives") relate the forces and moments to the instantaneous values of the position, velocity, and acceleration of the body. They are generally experimentally determined in the wind or water tunnel, and the controlled or uncontrolled motions of the craft are predicted based thereon.
Added Mass of a Three-Parameter Family of Two-Dimensional Forces Oscillating in a Free Surface
Authors: Landweber L. , Macagno Matilde
Published: January 2021

The added-mass characteristics of shiplike forms, oscillating vertically or horizontally in a free surface, are derived for a three-parameter family of forms. The parameters varied are the draft-beam ratio, the section-area coefficient, and the ratio to the draft of the radius of gyration about the transverse axis in the free surface. The added-mass coefficients are presented as a series of curves for about 70 members of this family. It is suggested that the added masses of arbitrary shiplike sections may be obtained, with only small error, from these curves by interpolation at the parametric values of the given section.
The Damping and Wave Resistance of a Pitching and Heaving Ship
Authors: Newman J. N.
Published: January 2021

This paper considers the damping and wave resistance of a thin ship which is moving in calm water with constant velocity and oscillating in pitch and heave. The velocity potential is obtained from Green's theorem after a process of systematic linearization in terms of perturbation parameters representing the beam-length ratio and the oscillation amplitude. An asymptotic expansion of the Green's function is derived from which the energy radiation is obtained. The coefficients of damping and increased wave resistance are then found by separation of the energy components. No separation of the two cross-coupling damping coefficients is obtained, however. Calculations are presented for a polynomial hull and compared with experimental data.
Note on Propeller-Excited Hull Vibrations
Authors: Tachmindji A. J. , McGoldrick R. T.
Published: January 2021

This note presents a summary of the information and techniques which are available to the designer for predicting the levels of service vibration of a ship in the design stage. This involves the two phases of estimating the exciting forces and the vibratory response of a hull to given forces. It is emphasized that at present the reliability of such predictions depends on the availability of data on the levels of service vibration or the exciting forces for ships actually in operation as a standard of comparison. It is pointed out that the concept of mechanical impedance at the stern of a ship is useful in predicting forced vibration.
Recent Contributions Under the Bureau of Ships Fundamental Hydromechanics Research Program
Authors: St. Denis M. , Craven J.P.
Published: January 2021

The third main nautical objective, Seakeeping, refers to that aspect of ship performance in which the seaway enters in a dominant manner and affects fundamentally the character of the problem. In the section on Control [3],1 a pattern was introduced according to which seakeeping was related to the uncontrolled as well as the controlled oscillations which take place with reference to a ship's inertial system. But, more broadly speaking, seakeeping includes all of the following subjects:Description of the seaway.Determination of the forces imposed by the seaway on the vessel—the excitation (hydrodynamic loadings, wave bending moment, slamming forces, and so on).Determination of the response of the ship in her six degrees of freedom (ship motions).Prediction of the perils to which a ship may be exposed (capsizing, foundering, safety at sea).Prediction of the loss in speed she will sustain in heavy weather.Evaluation of the amount of stabilization necessary to prevent unacceptable or undesirable displacements and accelerations.

The elastic response and strength of a vessel's structure, though not included under seakeeping, depend, nevertheless, in an essential manner thereon.
Differential Equations With Frequency-Dependent Coefficients
Authors: Tick Leo J.
Published: January 2021

In many derivations of ship-motion equations the result appears as a second-order linear differential equation with a sinusoidal driving force and frequency-dependent coefficients. The further assumption of linearity of the system with respect to any driving function is made. Thus the response to any function can be found by decomposing the forcing function into its frequency, components, using the given equation to find the response to each and summing the result.
A Discussion of the Flutter of Submerged Hydrofoils
Authors: Abramsorr H. Norman , Chu Wen-Hwa
Published: January 2021

This paper presents the results of a review and analysis of the problem of flutter of submerged surfaces. It is noted that certain rather serious discrepancies exist between theory and experiment leading to highly unconservative predictions of flutter speed. A number of possible reasons for such a wide discrepancy are investigated and discussed in detail, however none of them alone is adequate to bring theory and experiment into sufficiently good agreement for design purposes.
Evaluation of the Theory for the Flow Pattern of a Hydrofoil of Finite Span
Authors: Kaplan Paul , Breslin John P. , Jacobs Winnifred R.
Published: January 2021

Expressions for various properties of the flow field aft of a finite-span hydrofoil in smooth water are presented and discussed in this paper. Potential functions for the motion that have been derived previously on the basis of linearized free-surface theory serve as the basic terms from which the flow field is derived. Both two-dimensional and three-dimensional theories are used, and the expressions derived for the surface-wave elevation and downwash from the various theories are compared with experimental values. As a result of this study, it is shown that three-dimensional effects are of great importance and hence terms derived from the two-dimensional theory do not accurately represent the true flow properties. Recommended formulas, whose validity is demonstrated by the comparison with the limited data presented herein, are given for the evaluation of both the surface-wave amplitude and downwash.
Added Mass of a Rigid Prolate Spheroid Oscillating Horizontally in a Free Surface
Authors: Landweber L. , Macagno Matilde
Published: January 2021

The problem considered is the potential flow and added mass of a rigid prolate spheroid, half immersed in a free surface, and oscillating horizontally in the direction of its minor axis at high frequency. The resulting expression for the added mass is simplified mathematically, especially for the limiting cases of very elongated or nearly spherical ellipsoids, and a pleasingly simple, exact result is obtained for the sphere. The curve showing the variation of the added-mass coefficient with fineness ratio is compared with the corresponding values for vertical oscillations and that given by "strip theory."
Subcritical and Supercritical Operation of Ships in Waves and the Coincidence of Maximum Damping
Authors: Mandel Philip
Published: January 2021

Several papers by Lewis [1, 2, 3]3 have discussed the relationship between hull form and critical and supercritical operation in ahead seas. The present paper extends consideration to overtaking and following seas and defines subcritical, critical, and supercritical zones of operations in ahead, overtaking, and following seas. A region is pointed out where unorthodox ships may be designed to operate where resonant and near-resonant conditions with all important wave components may be almost entirely avoided throughout a substantial range of speeds in ahead and overtaking seas. In the limited case where resonance is encountered with important wave components in this region, it is shown that maximum wave damping might be simultaneously experienced. In the course of developing this subject, it was found that the theoretical condition for maximum wave damping is identical in overtaking seas with a particularly significant case of resonance.
A Note on the Stripwise Damping of a Submerged Spheroid
Authors: Newman J. N.
Published: January 2021

The stripwise clamping of a submerged prolate spheroid is derived utilizing spheroidal co-ordinates. For a slender spheroid the results agree with those of the preceding paper. Various limiting cases are investigated and the possibility of negative local damping is discussed.
Potential and Viscous Parts of the Thrust Deduction and Wake Fraction for an Ellipsoid of Revolution
Authors: Tsakonas Stavros , Jacobs Winnifred R.
Published: January 2021

Expressions are developed for wake fraction and thrust deduction due to the potential flow and to the boundary-layer effects for a fully-submerged prolate ellipsoid of revolution. The functional dependence of wake fraction and thrust deduction on axial-propeller clearance, body slenderness, after body geometry, and Reynolds number (scale effect) are exhibited for both potential and viscous-flow cases. Closed-form expressions are derived for the potential-flow case by representing the body by a line source-sink distribution and the propeller action by a sink disk. The boundary-layer effect is determined by Lighthill's method of equivalent sources distributed on the surface having strength proportional to the displacement thickness and its derivative. The wake is replaced by a cylinder of diameter equal to twice the displacement thickness at the stern. Although in practice the propeller is usually fully submerged in the wake of the hull, in this case the substitute cylinder has been shown by computation to be no wider than the hub diameter and thus the propeller is operating in a potential field. This consideration is fundamental to the construction of a possible mathematical model having the surface sources mentioned and an equivalent sink on the longitudinal axis whose position is determined on the basis of the velocity distribution in the wake. Computational work is carried out for a modification of the airship Akron. Four different methods, with various degrees of accuracy, are used for the evaluation of the boundary-layer growth in order to ascertain the degree of sensitivity of the thrust deduction and wake fraction to the boundary-layer development.
A Theory for the Plastic Design of Ship Plating Under Uniform Pressure
Authors: Wah Thein
Published: January 2021

A theoretical investigation is made of the behavior of a long rectangular plate loaded laterally beyond the elastic range of the material. The study takes into account the effects of the following phenomena:Initial deflections;initial locked-in moments; anddisplacements of the edges, in the plane of the plate.

The proposed method permits the design of plates based on allowable deflections under working loads and allowable permanent sets.
Water Waves Generated by Thin Ships
Authors: Plesset Milton S. , Wu T. Yao-tsu
Published: January 2021

The problem of interest is that of the water waves in a body of water of infinite depth generaied by a thin ship of given hull form, moving with constant velocity U along a straight course on the otherwise undisturbed water surface. A particular method is evaluated for computing the velocity field at an arbitrary distance (not too near the ship) fixed in the fluid. A new proposal is made here that the hull profile be represented by a double Fourier series with its half-periods spanning over the region occupied by the longitudinal mid-section of the ship. The convergence of this series representation is found to be satisfactorily rapid, especially when the tangent plane of the hull is everywhere continuous. In the latter case the longitudinal slope of the hull, which is the only partial derivative appearing in the analysis, is found in a specific case to be well represented by the partial derivative of the series. With this series representation of the hull, the analysis of the velocity-field calculation is greatly reduced so that the final result can be expressed in terms of a combination of several single and double Fourier integrals which are susceptible to numerical methods. However, for large values of or, where r is the distance from the ship, a = gL/U2, with g being the acceleration of gravity and L the ship length, these integrals can be evaluated with good approximation by asymptotic methods. The method of stationary phase and other asymptotic methods are employed in different regions in the water and the final expression for the velocity field is given explicitly. The numerical result for a specific ship will be given elsewhere.
Cavitation of Axially Symmetrical Bodies in Accelerating Motion
Authors: Oversmith Robert H.
Published: January 2021

This paper presents some results of recent model experiments with cavitating underwater flows in which the size, shape, drag and inception of cavitation were investigated. The effects of simulated underwater exhaust flows were also studied in this investigation, sponsored by the author's company as part of its general ASW program.
The Wave and Induced Drag of a Hydrofoil of Finite Span in Water of Limited Depth
Authors: Breslin J. P.
Published: January 2021

The wave resistance and the induced drag of a simple hydrofoil of finite span moving at a fixed submergence in water of finite depth are derived from a knowledge of the shallow water potential of a source. From this the waves produced by the semi-infinite doublet sheet which represents the undisturbed mathematical model of the hydrofoil are computed and the wave resistance is then inferred from the formula for the waves. Special cases which have been published previously are recaptured from the formulas. The induced drag is computed from a knowledge of the nature of the potential functions needed to satisfy the boundary conditions on the bottom and free surface. A comparison with one set of experimental data shows the theory to underestimate the experimentally determined lift-dependent drag curve at low Froude numbers F and to agree very well as high F. It is conjectured that the lack of good agreement at low F is due to the neglect of the influence of the free surface on the lift which has been omitted in this analysis.
Unsteady Lift and Moment on Fully Cavitating Hydrofoils at Zero Cavitation Number
Authors: Martin Milton
Published: January 2021

Expressions are presented for the lift and moment coefficients of a thin supercavitating foil performing generalized oscillations, in terms of the coefficients of a power series describing the chordwise amplitude distribution. The lift is in general made up of a circulation term, a pure damping term and an added mass term. The circulation term always acts at 5/10 of a chord length aft of the leading edge while the center of pure damping force and added mass depends on the mode of oscillation. The results are applied to the case of a foil moving through a stationary sinusoidal vertical gust and to that of a rigid foil performing heaving and rotational oscillations.
Investigation on the Influence of Stiffener Size on the Buckling Pressures of Circular Cylindrical Shells Under Hydrostatic Pressure
Authors: Nott James A.
Published: January 2021

A theoretical derivation is given for elastic and plastic buckling of stiffened, circular cylindrical shells under uniform external hydrostatic pressures. The theory accounts for variable shell stresses, as influenced by the circular stiffeners, and critical buckling pressures are obtained for simple support conditions at the shell-frame junctures. Collapse pressures for both elastic and plastic buckling are determined by iteration and numerical minimization. The theory is applicable to shells made either of strain-hardening or elastic-perfectly plastic materials. Using the developed analysis, it is shown that a variation in stiffener size can change the buckling pressures. Test data from high-strength steel and aluminum cylinders show agreement between the theoretical and experimental collapse pressures to within approximately six percent.
Supercavitating Flow About a Slender Wedge in a Transverse Gravity Field
Authors: Street R. L.
Published: January 2021

In this paper a linearized theory is developed for supercavitating flow past a slender strut or wedge in a transverse gravity field. The theory is expected to be valid when the effects of the gravity field are of first-order smallness consistent with the linearization approximations. The additional lift and moment forces acting on the strut as a result of the gravity field are calculated. The transverse gravity field is found to produce additional forces which should be considered in hydrodynamic design.
Production of Oblique Waves by a Bank of Wavemakers
Authors: Ogilvie T. Francis
Published: January 2021

The production of sinusoidal waves by an infinitely long bank of pneumatic wavemakers is studied. It is shown that, if the phase of the pressure applied to successive wavemakers differs by a constant amount, several wave trains may be produced. All of the waves produced have the same wave length but their directions of propagation vary. A numerical example is presented.
Integral Hull Form Parameters and a High-Speed Approximation to Michell’s Integral
Authors: Cuthbert Jerry W.
Published: January 2021

Michell's integral, the wave-making resistance formula of first-order thin ship theory, has been the subject of much study and discussion. Among the results of the study is the expansion at vanishing Froude number2 in terms of derivative properties of the hull form. The purpose of this paper is to show that the behavior of Michell's integral at high Froudenumber is related to certain integral properties or form parameters. The demonstration consists of the derivation of a high-speed approximation to Michell's integral in terms of these parameters.
Calculation of Nonlifting Potential Flow About Arbitrary Three-Dimensional Bodies
Authors: Hess John L. , Smith A. M. O.
Published: January 2021

A general method is described for calculating, with the aid of an electronic computer, the incompressible potential flow about arbitrary, nonlifting, three-dimensional bodies. The method utilizes a source density distribution on the surface of the body and solves for the distribution necessary to make the normal component of fluid velocity zero on the boundary. Plane quadrilateral surface elements are used to approximate the body surface, and the integral equation for the source density is replaced by a set of linear algebraic equations for the values of the source density on the quadrilateral elements. When this set of equations has been solved, the flow velocity both on and off the body surface is calculated. After the basic ideas and equations have been derived end discussed, the accuracy of the method is exhibited by means of comparisons with analytic solutions, and its usefulness is shown by comparing calculated pressure distributions with experimental data. Some of the design problems to which the method has been applied are also presented, to indicate the variety of flow situations that can be calculated by this approach.
On Line Distributions of Kelvin Sources
Authors: Tuck E. O.
Published: January 2021

The velocity potential for the flow due to point sources distributed arbitrarily along a straight line near to or at a linearized gravitational free surface is obtained in a new form by use of Fourier transforms. Such a method of representing the potential facilitates the determination of its behavior near to the line of singularities; this behavior is derived formally and its physical properties discussed. A brief illustration is given of a method of using this result in o theory for the motion of a slender ship.
On Testing Materials for Cavitation Damage Resistance
Authors: Thiruvengadam A. , Preiser H. S.
Published: January 2021

Recent experiments with a magnetostriction apparatus show that cavitation-damage rate is time dependent. This is confirmed by an analysis of the experimental data obtained in various earlier investigations. There are four zones of damage rate with respect to testing time; namely, (a) incubation, (b) accumulation, (c) attenuation, and (d) steady state. In the fourth, or steady-state zone, the damage rate varies as the square of the amplitude of oscillation within the range tested for water at 80 F. The damage rate increases with frequency and then decreases with increasing frequency. The depth of liquid in the beaker, the beaker diameter and the depth of immersion of the specimen do not seem to affect the damage rate substantially. The average depth of erosion is independent of the diameter of the specimen. Based on these experimental results, certain recommendations are made for testing materials for cavitation damage resistance.
Vibration Characteristics of Three Representative Hydrofoil Configurations
Authors: Ransleben Guido E. , Doshi Kishor D. , Irick Jack T.
Published: January 2021

Comparisons are made between theoretical and measured resonant frequencies for three representative hydrofoil configurations (inverted pi, vee and inverted tee), with variable end conditions and depth of submergence in water. Theoretical calculations were based on influence coefficients, accounting for the "apparent mass" effect of the water. Agreement on frequencies through the first six to eight modes of vibration for all configurations is generally excellent, being well within 10 percent in most instances and in no case greater than 1 8.1 percent. Agreement on mode shapes is also generally good.
Two-Dimensional Supercavitating Plate Oscillating Under a Free Surface
Authors: Song C. S.
Published: January 2021

The problem of a supercavitating flat plate at zero and nonzero cavitation numberoscillating under a free surface is analyzed by a linearized method using the accelerationpotential. The analysis is based on the concept of small velocity perturbations where in all second-order quantities are neglected. The flow is assumed two-dimensional, irrotational, incompressible, and gravitation-free. The potential-flow region is mapped on to an upper half-plane and the solution is expressed in an integral form using Cheng andRott's method. Special attention is given to the effect of approximate wake boundary conditions on the computed force and moment. It was estimated that the effect is of secondorder when the cavitation number is a first-order small quantity.
A Theorem on Buckling and Structural Stiffness
Authors: Vafakos William P.
Published: January 2021

Sufficient conditions are presented under which an increase (decrease) of the flexural, torsional, or extensional stiffness in any part of a structure cannot result in a decrease (increase) of the classical buckling load. A problem of axisymmetric buckling of a ringstiffened circular cylindrical shell under axial compression is considered for illustration.
Uniform Oval Reinforcing Rings—Power-Series Expansions
Authors: Vafakos William P. , Rostand Louis
Published: January 2021

Power-series expansions are employed in the analysis of oval reinforcing rings which are arbitrarily located on the inside or outside of oval cylindrical shells of prescribed cross section. The expansions are in terms of two small geometric parameters which are fixed by specifying the cross section of the ring and the major and minor-axis lengths of the oval. Analytical solutions are presented for the case of a uniform radial load. A graphical comparison is made with the results of a relatively lengthy energy solution. In addition, the effect of inside or outside rings is displayed in graphs, where the results are plotted versus the major-to-minor axis ratio.
Forces on a Submarine Hull Induced by the Propeller
Authors: Chertock George
Published: January 2021

The induced-flow field generated by a propeller operating in the wake of a submarine can exert forces on the submarine in some arbitrary mode of motion in two ways: Either by pressures applied to the propeller blades and resulting in the conventional propeller thrust or by pressures applied to the hull surface. The ratio of these forces is shown, by theoretical analysis, to depend most strongly on the flow velocity which the particular hull mode of motion would generate at the propeller, to be slightly dependent on the shape of the propeller, and to be negligibly dependent on the magnitude or distribution of the submarine wake. The derived relations are valid for both the inertial and quasi-steady components of the induced-pressure field. The predominant factor in the force ratio is evaluated by a numerical technique which is applicable to any surface of revolution moving in almost any pattern of motion. As one application, it is shown that the steady longitudinal force on the hull is 8 to 1 2 percent of the steady component of the propeller thrust, in good agreement with measurements of the thrust-deduction factor. As another application, it is shown that a particular vibratory component of the hull force, tending to vibrate the hull in the accordion-vibration mode, is 6 to 8 percent of the same component of the propeller thrust.
Supercavitating Propellers—Momentum Theory
Authors: Tulin Marshall P.
Published: January 2021

Based entirely on momentum and other simple considerations a reasonably complete picture of the one-dimensional pressure and velocity fields associated with heavily supercavitating propellers and drag disks has been constructed. It is shown that the flow is often retarded while approaching a heavily supercavitating propeller, so that the so-called ideal efficiency of such a propeller takes on values in excess of unity. The ideal efficiency actually increases with decreasing blade cavitational efficiency; however, the net efficiency at the same time decreases. This retardation causes a reduction of thrust deduction, or even a change in its sign. Charts are provided from which the inflow speed may be estimated readily. The effect of water-tunnel boundaries is discussed, particularly the phenomenon of choking.
Self-Propulsion Tests With Ship Models Using Separate Scale Factors for Hull and Propeller
Authors: Schoenherr Karl E.
Published: January 2021

Discrepancies have been noted on some recent ships between the RPM predicted from the model test and the RPM measured on the standardization trials of the ship. This is believed to be caused primarily by differences in the wakes of the model and the ship. To eliminate these discrepancies, a new method of conducting model self-propulsion tests is proposed. In this method, the model propeller is constructed to a different scale ratio than the model hull. For a given model scale ratio, the propeller scale ratio may be deduced by rational analysis on the assumption that the wake difference becomes zero when the ratio of propeller diameter to boundary-layer thickness is equal for the ship and the model. The method of conducting the self-propulsion test when separate scale ratios are used is explained and the equations for computing ship RPM, SHP, and so on from the corresponding values measured in the model test are given.
Mechanical Properties of Metals and Their Cavitation-Damage Resistance
Authors: Thiruvengadam A. , Waring Sophia
Published: January 2021

Detailed investigations with a magnetostriction apparatus were carried out to determine the cavitation-damage resistance of eleven metals in distilled water at 80 F. The cavitation-damage resistance is defined as the reciprocal of the rate of volume loss for a given metal. Among the mechanical properties investigated (ultimate tensile strength, yield strength, ultimate elongation, Brinell hardness, modulus of elasticity and strain energy) the most significant property which characterizes the energy-absorbing capacity of the metals, under the repeated, indenting loads due to the energy of cavitation bubble collapse in the steady-state zone, was found to be the fracture strain energy of the metals. The strain energy is defined as the area of the stress-strain diagram up to fracture. The correlation between the strain energy and the reciprocal of the rate of volume loss leads directly to the estimation of the intensity of cavitation damage; this intensity varies as the square of the displacement amplitude of the specimen. All these conclusions are limited to the steady-state zone of damage.
Cavitation Phenomena of Sterntube Bearings
Authors: Kessel P. G.
Published: January 2021

This paper contains a theoretical study of dynamically loaded journal bearings of finite length for the simultaneous journal loci and pressure distribution in the bearing. The analysis presented is applied to the case of sterntube bearings of ships with two specific aims in mind. The first of these is to firmly establish the existence of conditions permitting cavitation damage of the journal, and the second is to show how the peculiar patterns of cavitation damage observed on the journals of several ships may occur.
Estimation of Stability Derivatives and Indices of Various Ship Forms, and Comparison With Experimental Results2
Authors: Jacobs W. R.
Published: January 2021

The analytical method of reference [1]3 for estimating stability derivatives, and hence stability on course, which combines Albring's empirical modifications of simplified flow theory with low aspect-ratio wing theory, is extended to take into consideration the effects on course stability of higher aspect-ratio fins as well. The method, which has been applied in the earlier report to a family of eight hulls of 0.5 block coefficient, is tested further by application to eight Series 60 forms differing in block coefficient as well as in beam, draft, and displacement—with and without rudders; to an extreme vee modification of a Series 60 model; and to three other forms—a Mariner Class model, a destroyer, and a hopper dredge. Comparison with experimental results shows that the values of stability derivatives and indices determined by the analytical method are of the right orders of magnitude and indicate correct trends. Application to a variety of ship forms has demonstrated that the method can predict relative effects of changes in the geometry of a ship form, as well as the effects of changes in skeg and rudder area.
The Effect of Distortion of Subcavitating Foil Contours on Cavitation-Inception Velocity
Authors: Moeckel George P.
Published: January 2021

The purpose of this paper is to investigate the theoretical effect of distortions on sub-cavitating foil sections in regard to cavitation-inception velocities. The study is intended to give some prediction as to type and size of distortions that may be tolerated in foil construction. It is natural to expect errors in foil shape to occur as a result of inaccurate construction or damage. It is therefore the intention of this paper to provide estimates of admissible deviations from the intended foil geometry in order that cavitation may be prevented or at least anticipated.
The Drift Force and Moment on Ships in Waves
Authors: Newman J. N.
Published: January 2021

The second-order steady horizontal force and vertical moment are derived for a freely floating ship in regular waves. The fluid is assumed to be ideal and the motion is linearized. Momentum relations are used to derive general results for an arbitrary ship or other body, in terms of the Kochin function or far-field velocity potential of the body. Explicit results are derived for slender ships, based upon the assumptions of slender body theory. Computations are made for a Series 60 hull and are compared with experiments. The analysis of the vertical moment permits the prediction of stable heading angles in oblique waves, and it is shown that unless the waves are very short, the ship will be stable only in beam waves.
Experiments on Delta Wings in Superventilated Flow
Authors: Kiceniuk T.
Published: January 2021

An extensive water-tunnel investigation of super ventilated delta wings has been concluded. Force measurements and flow-visualization experiments were carried out for wings of several apex angles and various values of cavitation number, submergence, velocity, and angle of attack. Some unusual model geometries and orientations were also explored.
Stresses in Eccentric Nonuniform Rings Reinforcing Cylindrical Shells
Authors: Kempner Arnold , Kempner Joseph
Published: January 2021

Bending and membrane stresses are determined in nonuniform frames of an infinitely long reinforced circular cylindrical shell subjected to hydrostatic pressure. The Donnell shell equations and deep-ring theory are used to solve the interaction problem. The frames, periodically spaced along the shell, are composed of two uniform but different sections. Each section of each frame has a different centroidal radius. Analyses of bending and membrane stress distributions in the frames are presented. Approximate solutions of different degrees of simplicity and accuracy are also given.
Pressure Stability of Prolate Spheroids
Authors: Becker Herbert
Published: January 2021

A theoretical investigation of prolate spheroids was conducted using the Donnell-type equation for doubly curved shells. The results cover the range from a sphere to a cylinder, and show how the simplified form of Mushtari's relation is approached asymptotically from above within that range. Theory and experiment are shown to be in reasonable agreement for some of the test data available. However, the simplified theoretical approach underestimated the strengths of shells with large axis ratios.
Evaluation of Pressure Distribution on a Cavitating Hydrofoil With Flap
Authors: Harrison Z. L. , Wang Duen-pao
Published: January 2021

A general method is established to calculate the pressure distribution and the moment of force for a two-dimensional, supercavitating hydrofoil with a flap. The wake flow model is adopted to describe the configuration of the flow field. Some numerical results for a supercavitating flat plate with a flap are compared with the corresponding experimental data.
Exact Treatment of the Helicoidal Wake in the Propeller Lifting-Surface Theory
Authors: Tsakonas S. , Chen C. Y. , Jacobs W. R.
Published: January 2021

This study is fifth in a series concerned with the adaptation of lifting-surface theory to the marine propeller case. In the present investigation an accurate mathematical treatment of the helicoidal wake supersedes the deformation of the helicoidal integral path to a staircase path, introduced in the previous studies to simplify the solution. The kernel function is derived with correct directional derivatives normal to the helicoidal surface as well as with the simplified derivatives assumed in previous studies. The propeller blade is of sector form with arbitrary pitch, not necessarily low, and the loading distribution is taken to be that of a flat plate. The results of numerical calculations for the consistent mathematical model which treats the helicoidal wake exactly and uses the correct directional derivatives normal to the helicoid are found to compare favorably with the results obtained previously when a staircase approximation of the wake was used with the simplified, but physically consistent, directional derivatives in the axial direction. The closeness of the results for a propeller of not too low pitch indicates that the staircase approximation, which was introduced for low pitch angle, is a satisfactory model. This model can be used to avoid all complications arising from the rigorous treatment of the helicoidal wake, particularly when arbitrary blade form and sweep angle are incorporated in the problem.
The Impact of a Flat Plate on a Water Surface
Authors: Verhagen J. H. G.
Published: January 2021

The phenomena occurring during the impact of a fiat plate on a water surface are investigated both theoretically and experimentally. It is shown that, by taking the influence of the compressible air layer caught between the falling plate and the water surface properly into account, the experimental results can be fully explained. Numerical results showing the effects of falling mass, drop velocity, and plate dimensions on the maximum impact pressure are available.
Unsteady Propeller Lifting-Surface Theory With Finite Number of Chordwise Modes
Authors: Tsakonas S. , Jacobs W. R. , Rank P. H.
Published: January 2021

A continuing investigation at Davidson Laboratory is concerned with improvement of the mathematical model developed for the evaluation of the steady and time-dependent distributions on the blades of marine propellers operating in spatially nonuniform flow. In the present study, the surface integral equation resulting from the theory has been solved by means of the collocation method, in conjunction with the generalized lift operator, for a prescribed set of chordwise modes which reproduce the proper leading-edge singularity and fulfill the Kutta condition at the trailing edge. General programs have been developed to accommodate any geometry of propeller operating in a specified nonuniform inflow condition for a large but finite number of chordwise modes. The calculations indicate that the spanwise loading distribution and the steady and time-dependent thrust reach stable values after three to five chordwise modes, but the chordwise distribution does not converge to its final form, particularly in the neighborhood of the leading and trailing edges. A comparison of theoretical and experimental results for the vibratory thrust shows satisfactory agreement on the whole. It is believed that the principal cause of any existing discrepancies between measured and calculated results is lack of precise knowledge of the wake harmonics.
Unsteady Force Measurements on Fully Wetted Hydrofoils in Heaving Motion
Authors: Klose G. J. , Acosta A. J.
Published: January 2021

An experimental investigation is reported of the unsteady forces due to heaving motion of fully wetted hydrofoils of unity aspect ratio and also in two-dimensional flow. The tests covered a broad range of reduced frequency and determined the effects of variation in submergence depth, angle of attack, oscillation amplitude, and flow velocity. In general, the findings agree well with available theoretical calculations, but some unexpected variations were found for the case of a wedge-shaped foil and for changes in angle of attack.
On the Cushioning of Water Impact by Entrapped Air
Authors: Lewison Grant , Maclean W. M.
Published: January 2021

Impact between a rigid flat plate and the free surface of water has been investigated experimentally and theoretically. Under two-dimensional conditions, the experiments give values of peak pressure of the same order as those recorded on ships slamming at sea, but very much smaller than would be expected from existing theories. New theoretical work is presented which takes account of the air trapped between the model and the water surface, and of both compressible and incompressible water movement. This shows good general agreement with the experiments, though further work is needed to confirm some of the assumptions made.
Lowest Natural Frequencies of Structures With Rigid-Body Degrees of Freedom
Authors: Hylarides S.
Published: January 2021

To calculate the lowest natural frequencies, use can be made of the power method, for which the flexibility matrix or the inverted stiffness matrix has to be available. Structures with rigid-body degrees of freedom, however, have a stiffness matrix which is not invertible. In this paper three methods are described to derive from the singular stiffness matrix a regular one. These methods are based on the same principles, but differ in particulars. One method is recommended, since it involves less numerical operations, while its accuracy is the same.
Potential and Wave Height Expressions for Multipoles Moving Under the Free Surface
Authors: Kim Hun Chol
Published: January 2021

Expressions for velocity potential and wave height for multipoles of nonlifting type moving at a uniform speed under the free surface are given in the semi-infinite domain. This work is complementary to that of R. C. Thorne [1],2 which deals with unsteady cases only. The expressions in the present work, as in Thorne's, satisfy the free-surface condition that has been linearized.
Frictional-Resistance and Velocity Similarity Laws of Drag-Reducing Dilute Polymer Solutions
Authors: Granville Paul S.
Published: January 2021

The velocity similarity laws of shear flows are developed for drag-reducing dilute polymer solutions. Relations for boundary-layer parameters and frictional-resistance formulas of the logarithmic type are derived for pipe flow and for flat plates in parallel flow.
A Comparison of Three Methods for Computing the Added Mass of Ship Sections
Authors: Macagno Matilde
Published: January 2021

Three methods that have been developed for computing added-mass coefficients of two-dimensional forms, vibrating horizontally or vertically at a free surface, are compared by application to a set of four cargo ship sections. Computer programs are offered for two of these methods. The method employing conformal mapping is recommended as the best of the three.
The Second-Order Theory of Heaving Cylinders in a Free Surface
Authors: Lee Choung Mook
Published: January 2021

A second-order potential solution is sought for a two-dimensional symmetric cylinder placed horizontally in a free surface and forced to oscillate vertically. The forced motion is simple harmonic, and the amplitude is small compared to the beam of the cylinder. The resulting potential-theory problem is solved by placing singularities of all orders at the intersection of the water surface at rest with the vertical axis of symmetry, and by determining their strengths from the boundary condition on the body. The pressure distribution on the cylinder, the force acting upon it, and the waves generated by it are derived through the second order. Numerical computations are made for a circular cylinder and for a U-shaped cylinder, and the results are presented in graphs.
Undulating Plate Type Propeller: The Two-Dimensional Ideal Case
Authors: Szeless A. G.
Published: January 2021

The motion of a two-dimensional flexible undulating plate in an incompressible ideal fluid flow is investigated. Employing an iterative numerical technique the motion of the plate and the hydrodynamic pressure distribution are found together with the resulting thrust or drag. The power input is calculated from the work of the exciting force per cycle, and the propulsive efficiency is defined in terms of thrust, free-stream velocity, and power input. For a given plate configuration in the frequency ranges studied, the propulsive efficiency is dependent on the reduced frequency only and reaches 50 percent. Plans for the continuation of this investigation are indicated.
The Representation of Ship Hulls by Conformal Mapping Functions
Authors: von Kerczek C. , Tuckk E. O.
Published: January 2021

A method is described by which an arbitrary hull surface may be approximated by ananalytic function. The cross sections of the ship are represented by conformal mapping functions whose coefficients are polynomial functions of the longitudinal coordinate of the ship. Such a representation is intended to be used primarily for hydrodynamic calculations. However, the procedure used in generating the mapping function representation of the hull surface can, with some slight modifications, be used to freely form a hull surface. This could possibly be the basis of a mathematical hull design procedure.
Added Masses of Thin Rectangular Plates Calculated from Potential Theory
Authors: Meyerhoff W.Kay
Published: January 2021

In order to compute unsteady-pressure distributions and added mass of thin rectangular plates in incompressible, nonlifting potential flow, a description by means of a dipole distribution upon the plates was used. The distribution is written as a finite double series with unknown coefficients, which are determined from the boundary condition satisfied at a corresponding or higher number of discrete points. The quadratures are performed numerically. Calculations were carried out on a computer for 1 1 aspect ratios from 0.1 through 1.0. The results are presented in tables and graphs, and are compared with published experimental data and with empirical formulas. The results of the theoretical calculations are in close agreement with Pabst's measurements and with the formulas derived from these data by Pabst and by Blagoveshchensky. From these, the measurements published by Yu and his empirical formula differ up to 22 percent, which may be due to the low frequencies used by Yu.
Analysis of Piecewise Uniform Oval Rings with Transition Sections
Authors: Brodsky W. L. , Vafakos W. P.
Published: January 2021

An analysis of a doubly symmetric oval ring fabricated from uniform, dissimilar, circular segments connected by a smooth transition section is presented. The ring is subject to a uniform radial load applied on an oval reference line. For several ovals the stress distribution is determined for various lengths of transition section. For each oval there is found an optimum length of transition section as well as a length for which the stress at the foot of the transition section vanishes.
Viscosity, Wake, and Ship Waves
Authors: Brard Roger
Published: January 2021

In this paper a theory of the effect of viscosity on ship waves is presented. It is shown that the wake affects the singularities kinematically equivalent to the hull and generates waves which modify the resulting wave pattern. The theory may explain why the estimate of the viscous resistance obtained by means of a wake survey and the estimate of the wavemaking resistance obtained by means of a wave analysis do not add up, in general, to the total resistance measured by using a dynamometer. The discrepancy seems to be due essentially to the existence of a wavemaking viscous resistance.
Wind Tunnel Tests of Two Lucy Ashton Reflex Geosims
Authors: Joubert P. N. , Matheson N.
Published: January 2021

A 9-ft and a 4½-ft reflex model of the Lucy Ashton were tested in a wind tunnel. Both pins and wires were used as stimulators to promote a turbulent boundary layer. The effects of the stimulators could be taken into account by considering the virtual origin of the turbulent boundary layer. Slightly different viscous drag curves were found for each model, both with a slope much steeper than previously anticipated. The skin friction was determined using two independent methods. Large increases and deficits in local skin friction coefficients were found at the bow and stern of the models respectively as compared with those for a two-dimensional flat plate.