bluuebunny/crossref_metadata_2025 huggingface dataset:
Torsional Rigidity of Box Beams Having Multiple Cut-Outs
Authors: Penzien Joseph
Published: January 2021

The investigation reported herein is a part of a more general investigation which was initiated for the purpose of evaluating the effect of hatch opening sizes on the structural behavior of ship girders. This general investigation has included both a study of stress distribution and a study of rigidity of a model ship girder having hatch openings of various sizes. Loadings considered were hogging, sagging, athwartships bending and torsion. Only that portion of the program dealing with torsional rigidity will be presented in this paper.
Comparison of Two Analyses of Boundary-Layer Data on a Flat Plate
Authors: Landweber L. , Siao T. T.
Published: January 2021

In a recent paper (1) it was indicated that there appeared to be a need for generalizing the well-known logarithmic law of turbulent boundary layers and such a generalization was derived on the basis of a suggestion due to Townsend (2). It was found that the logarithmic formulas constitute only one member of a family of possible formulas, among which that one which best fits the boundary-layer data should be selected.
The Analytical Calculation of Ship Bending Moments in Regular Waves
Authors: Jacobs Winnifred R.
Published: January 2021

The longitudinal distribution of forces acting on a T2-SE-A1 tanker moving in regular head seas is found by an analysis based on the "strip method" used by Korvin-Kroukovsky in the development of his theory of ship motions, lending moments at the midship section are calculated and compared with bending moments measured during model tests. The theoretical values of bending moments are of the same order of magnitude as those found in the experiments. However, some discrepancies between them appear. These may be due to experimental error as well as to deficiencies in the method of calculation. Certain important facts are brought out by the theoretical calculations:The midship bending moment is virtually a second-order effect dependent on local variations in the longitudinal distribution of the loads.Dynamic bending moments at reasonable speeds are less than those obtained by the conventional static calculation with Smith correction.

This confirms experimental findings.
Certain Probabilities Associated With Bow Submergence and Ship Slamming in Irregular Seas
Authors: Tick Leo J.
Published: January 2021

A procedure is given for computing the average submergence time of the bow (or any selected point), and the average number of slams according to the definition given. Use is made of an alternative representation of Pierson's random process model of the sea surface and Korvin-Kroukovsky's equations of the response of a ship to a regular sea. An example of the application of the technique to a Series 60 model (0.60 block coefficient) is given.
The Stresses Around Square Holes with Rounded Corners
Authors: Brock Joseph S.
Published: January 2021

This paper presents an analytical solution for the stress distribution around a square hole with rounded corners in an infinite plate subjected to pure tension. The method of solution is a combination of a conformal mapping technique and the complexvariable method of Muskhelishvili. The form of the mapping function is obtained from the Schwarz-Christoffel transformation. The mapping function is general and gives a good approximation to square holes with rounded corners of arbitrary radius of curvature. The ratios of the corner radius to the width of the opening considered cover the range from 0.03 to 0.5. This is considered 1o be the interesting range for ship structures. The results are given in terms of stress concentrations around the boundary of the opening.
Potential Problem of the Optimum Propeller With Finite Number of Blades….
Authors: Tachmindji A. J.
Published: January 2021

The potential problem is solved for the circulation distribution of an optimum propeller with finite number of blades when operating in a cylindrical duct. The effects of the duct on both the circulation and the thrust increase have been calculated for specific cases, showing that they become important for propellers operating in a duct having a diameter which approaches the propeller diameter. The effect of the duct increases with decreasing number of blades and with increasing pitch. The percentage increase in thrust which has been computed is additive to the Woodand Harris correction resulting from the contraction of the slipstream.
Effect of Transverse Curvature on Turbulent-Boundary-Layer Characteristics
Authors: Yu Yun-Sheng
Published: January 2021

Tests made on the turbulent boundary layer on a circular cylinder in axial flow at zero pressure gradient are described. From the measurements, similarity laws of the velocity profile are formulated, and various boundary-layer characteristics are evaluated and compared with the flatplate results. It is found that the effect of transverse curvature is to increase the surface shearing stress and to decrease the boundary-layer thickness, and that the latter variation is more pronounced than the former.
Effect of Size of Hatches on Torsional Strength and Rigidity
Authors: Bailey James P.
Published: January 2021

The objective of the test described in this paper was to study the effect of hatch size on the torsional strength and rigidity of ships' hulls. Six plastic models, simulating the mid-ship portion of a cargo ship, with various sizes and arrangements of hatches, were tested by subjecting to torsion and determining the resulting angle of twist, the approximate intensity and distribution of stress, and the torque required to produce fracture. Torsional rigidity was found to decrease generally with total width of hatches and with length of hatches. The torque to failure showed a greater variation between models than did the torque required to produce a given strain. The highest stress concentrations were at the hatch corners, and in every case the models failed at a hatch corner.
Model Experiments With Fixed Bow Antipitching Fins
Authors: Stefun George P.
Published: January 2021

The purpose of this paper is to provide additional information relative to the problem of designing efficient antipitching devices. The results of seakeeping experiments are presented for a model fitted with several alternate designs of fixed bow fins. The bulk of the experiments is concerned with the effects that fins of different aspect ratios have on the pitching and heaving motions, the phase angles between pitch and heave, the vertical accelerations, and the speed reductions in waves. Results also are presented showing the effects on pitching of fin area and of fin-tip fences.
Supercavitating Flow Past Slender Delta Wings
Authors: Tulin Marshall P.
Published: January 2021

The supercavitating flow past slender delta wings is studied. Theory is developed for a conical flow involving cavities which spring from the leading edges of the delta and cover a part of the top of the wing; the center part of the wing top is assumed to be wetted by a kind of re-entrant jet flow. Results are obtained for the two separate asymptotic cases in which the cavitation number is either very small or very large. The widths of the cavities on the wing upper surface increase with decreasing σ and the lift decreases. It is shown that the upper surface never becomes completely enveloped in a cavity even for σ = 0. Finally, the lift of a fully cavitated wing (σ = 0) is estimated to be approximately 4/10 of its fully wetted lift.
Transfer of Local Axial Load Into Bulkhead Plating
Authors: Brock Joseph S.
Published: January 2021

The distribution of a vertical load on a bulkhead stiffener into the bulkhead plating was studied photoelastically. Both tapered and uniform stiffeners were investigated. The loads on the stiffener were resisted by two types of reaction; namely, by shear at the side shell and by compression at the bottom. It is concluded that, for practical purposes, the entire load is absorbed into the plating within one deck height for both uniform and tapered stiffeners and for both types of support.
The Theoretical Prediction of the Longitudinal Motions of Hydrofoil Craft
Authors: Ogilvie T. Francis
Published: January 2021

The nonlinear theory for predicting the longitudinal response of hydrofoil craft in waves due to Weinblum is modified and the results of analog computations based on this theory are presented for comparison with available data. The complete nonlinear equations were used in the computations, and it is shown that the nonlinearities affect the oscillatory amplitudes only slightly, but that they cause large steady components of heave. The steady heave is often comparable with the amplitude of oscillation; it is always downward, tending to cause the craft to crash. The effects of unsteadiness are investigated, and it is shown that the forces are reduced as much as 40 per cent because of unsteadiness, but that there is little net effect on the amplitudes of heave and pitch. From the experimental data, it is concluded that the theory gives good predictions of the amplitudes of heave and probably of pitch.
Vibrations of an Infinitely Long Cylindrical Shell in a Semi-Infinite Acoustic Medium
Authors: Butler Donald J.
Published: January 2021

Previous work on the vibrations of infinitely long cylindrical shells submerged in an infinite acoustic medium is extended to the case where the medium is bounded by a plane surface, either rigid or free. The solution leads to an infinite set of simultaneous, linear, algebraic equations, the coefficents of which are obtainable in closed form. If this set is replaced by a finite number of equations, a procedure is given for estimating the accompanying error. Typical numerical examples indicate that significant results can be obtained, in certain cases at least, using only a small number of equations. For steel shells in water, the results show that the presence of a fluid boundary has surprisingly little effect on either the response of the shell, in the case of forced vibrations, or the frequencies of free vibration, even when the shell is in close proximity to the boundary.
A Note on Hydroelasticity
Authors: Jewell David A.
Published: January 2021

This note is essentially a discussion of a paper, "Aeroelastic Stability of Lifting Surfaces in High-Density Fluids," by Henry, Dugundji, and Ashley [1].2 Additional viewpoints are presented which indicate that flutter phenomena are not unlikely in hydrodynamic operation; that the discrepancy between theory and experiment in a small range of values of the "mass ratio" is due to a transitional nature of flutter; and that either of two revisions to the theoretical oscillatory lift and moment expressions might provide better correlation with experiment.
Polynomial Surface Representation of Arbitrary Ship Forms
Authors: Kerwin J. E.
Published: January 2021

This paper is concerned with the approximation of an arbitrary hull shape by an analytic expression to be used primarily for hydrodynamic calculations. A method is described which permits high-degree polynomial surface equations to be used as approximations of a wide variety of hull shapes. Numerical examples obtained with an IBM 704 computer show that the procedure produces hull forms which are sufficiently accurate for most hydrodynamic calculations.
Longitudinal Bending and Torsional Moments Acting on a Ship Model at Oblique Headings to Waves
Authors: Numata Edward
Published: January 2021

Tests were conducted with a model of a T2-SE-AI tanker running at oblique headings to waves to measure torsional moments and vertical and lateral components of longitudinal bending moments at the midship section. Trends of moments with speed and wave direction in regular long-crested waves of various lengths are presented. Statistical characteristics of moment responses at one speed and heading in irregular long-crested waves are given. The relative importance of lateral bending is explored by using model results to predict longitudinal bending stresses in a T-2 tanker deck caused by the combined action of vertical and lateral moments, and it is shown that lateral bending can contribute significantly to these stresses.
Simplified Analysis of Boundary-Layer Oscillations
Authors: Betchov Robert
Published: January 2021

The stability of an incompressible boundary layer is analyzed in terms of three basic processes. These are (a) the oscillations of a boundary layer when friction is disregarded, (b) the effects of friction at the wall, and (c) the effects of friction at the critical layer. These processes are separately discussed and evaluated. Simple models are presented. A general equation leads to the eigenvalues. The neutral curves corresponding to five typical cases are determined—parabolic and Blasius boundary layers, boundary layers with suction and with adverse pressure gradient, two-dimensional Poiseuille flow. The unstable boundary layer is discussed briefly. The nonlinear effects of the oscillation on the velocity profile are evaluated. Finally, the case of a boundary layer along an elastic wall is considered, and it is found that the wall may have a significant effect on the layer. In particular, a wall with negative damping could completely stabilize the boundary layer.
The Analysis of Ship Structures Subjected to Slamming Loads
Authors: Borg S. F.
Published: January 2021

This paper describes the results of a fundamental study of various phases of the ship structural design problem, as affected by slamming-type loads. By a slamming load, we mean a suddenly applied impact-type load such as is introduced for example, by: (a) The pitching and heaving motions induced by waves, which in turn cause the ship's bow to emerge and then reenter the seaway at a relatively high velocity. Upon reentering the sea, suddenly applied impact-type loads may be applied to the ship hull. These cause a sudden change in acceleration, generally felt as a shudder (or series of shudders or vibrations) which introduces the slam loading. (b) Berthing or docking of ships. If, for any reason the berthing introduces heavy impact loads due to sudden contact between the ship hull and the fender-dock system then we have a response very similar to that described in (a). The study[1]2 was concerned with several different facets of the over-all slam problem. Among the topics considered (and reported upon herein) are 1) time effect in ship-slamming problems; 2) damping of slam oscillations; 3) model scaling requirements for slam phenomena; 4) an approximate method of analysis for ship hulls (in the elastic range) subjected to slam loads; 5) comparisons between the method 4) and other methods; 6) extension of 4) to the elastoplastic range.
Cavitating Flow Past a Large Aspect-Ratio Hydrofoil
Authors: Cumberbatch E.
Published: January 2021

Tip effects on the cavitating flow past a large aspect-ratio lifting hydrofoil are considered. The tip vortices arising from the flow leakage around the tip from the lower to the upper side of the hydrofoil are assumed to cavitate. The flow over the central section of the hydrofoil is taken as two-dimensional cavity flow and hence there is a wide planar cavity there. The separate cavity regions are taken not to coalesce. The flow is represented by a simple horseshoe-vortex model and descriptions of the flow over the central section, near the tip and well downstream, are derived and appropriately matched. The lift on the hydrofoil is then calculated, taking the downwash into account. The lift is seen to be reduced by the tip effects, and shows good comparison with experimental results.
Kinetic Energy of a Liquid Surrounding a Prolate Spheroid Vibrating at Its Free Surface
Authors: Macagno E. O. , Macagno Matilde
Published: January 2021

This paper is the third of a series reporting the results of an investigation of the motion around semisubmerged prolate ellipsoids of revolution. The first paper [1]4 dealt with the general motion around a vibrating spheroid and with its applications to vertical ship vibrations; correction factors for the evaluation of the added mass were there calculated. The second paper [2] contained an analysis of the motion generated by a prolate spheroid under translatory horizontal oscillations and the resulting expressions and values for the added-mass coefficients. In the present work the expressions for the kinetic energy and the correction factors are derived for horizontal vibrations of the spheroid with any number of nodes. The values corresponding to certain horizontal vibrations with two and three nodes are given.
The Ship Girder With Multiple Hatch Openings Under Torsion
Authors: Schade H. A.
Published: January 2021

Recently there have been many proposals for unconventional arrangements of hatch openings in cargo vessel decks involving either hatches of unusual width or two or more lines of hatches. The problems concerned with bending in the vertical plane of such ship girders do not seem to offer special difficulty, but the effects of such unusual hatch configurations when the ship girder is twisted (as a ship may be by oblique seas or unsymmetrical loading) are not so well known. Tests reported by Bailey2 were an interesting experimental effort to shed light on these questions. The computation schemes described in this paper were used to predict the results on the six models used by Bailey2 independently by analysis alone. In general, the analytical predictions of both strength and stiffness agree well with the experimental results
Linearized Theory for Supercavitating Hydrofoils With Spoiler-Flaps
Authors: Chen C. F.
Published: January 2021

The linearized problem of flow past a flat plate with a deflected upper flap is solved including the free-surface effects. The flow is assumed to detach at the trailing edges of the flap and of the plate, leaving an infinite cavity of constant pressure behind. The results are applicable to flaps of arbitrary length, hinged at an arbitrary distance from the leading edge and at arbitrary depth. Numerical results are presented to show the effect of depth on the lift and drag coefficients of a trailing-edge flap whose chord is 30 percent of the chord of the plate, the effect of the hinge position of such a flap on the hydrodynamic characteristics of a plate at infinite depth, and the pressure distribution on a flapped plate at infinite depth. The principal results obtained are as follows: As the depth decreases, the flap becomes less effective and less efficient; as the hinge position is moved rearward, the flap becomes more effective and more efficient.
Numerical Data on Hydrofoil Response to Nonsteady Motions at Zero Cavitation Number
Authors: Parkin Blaine R.
Published: January 2021

This paper presents a tabulation of hydrodynamic force response functions for steady sinusoidal and step-function motions and gusts for o fully cavitated two-dimensional fiatplate hydrofoil at zero cavitation number. The cavity separation points are fixed at the nose and at the tail of the profile. Some results from the present linearized theory are compared with corresponding results of L. C. Woods.
Pressure Field Around a Marine Propeller Operating in a Wake
Authors: Tsakonas S. , Breslin J. P. , Jen N.
Published: January 2021

The present study investigates the effect of nonuniform inflow conditions on the vibratory pressure generated by a marine propeller. In analyzing the pressure signals which are associated with propeller thrust and torque, general expressions are developed in terms of the harmonic constituents of the nonuniform inflow field. The analysis indicates that all possible combinations of propeller-loading blade harmonics with those of the field-point function contribute to the pressure signal. It is shown that the effect of the non-uniformity of the inflow conditions persists in the field and is felt at greater distances from the propeller plane than is the case for uniform flow. In fact, at a distance of one propeller radius the pressure associated with the nonuniform conditions is almost 60 percent of the total. Two mathematical models have been studied. In both, the thrust-producing forces are assumed to be generated from a circular sector projection in the propeller plane, whereas the torque-producing forces are assumed to be generated in the first from a rectangular projection, and in the second from a triangular projection, in the plane through the propeller axis and the line of mid-chord points. The study of both models indicates that the pressure associated with torque is local in effect, being limited to the neighborhood of the propeller. Asymptotic formulas describing the pressure field at large distances from the propeller plane have been developed and the rate of decay in the radial and axial directions has been studied in both uniform and nonuniform inflow conditions. It is found that the pressure signal associated with the nonuniform inflow condition decays as x−2 for fixed r and r−3 for fixed x, whereas in the uniform flow condition the pressure decays as x-2B+2) for fixed r and as r−2B for fixed x, where B is the number of propeller blades.
Analysis of Uniform Deep Oval Reinforcing Rings
Authors: Vafakos William P.
Published: January 2021

Equations which are applicable to uniform deep oval rings in which the local curvature of an arbitrary reference line is prescribed are derived and simplified for application to oval ring-shell combinations. Theoretical estimates of the stresses and displacements are obtained for a typical reinforcing ring of a ring-stiffened oval cylinder recently tested under hydrostatic pressure by the David Taylor Model Basin. These results are obtained by appropriately approximating the oval cross section and by assuming that the composite structure responds as an oval ring. The theoretical flange stresses are shown to be in good agreement with available test results.
The Asymptotic Approximation of Michell’s Integral for High Speed
Authors: Newman J. N.
Published: January 2021

An asymptotic approximation to Michell's integral is obtained for large values of the Froude number, providing an analytic estimate for the wave resistance of a thin ship at high speeds. The limiting value for a surface ship of arbitrary hull form is quite similar to that of an infinitely deep vertical strut, and in both cases the dominant term depends only on the waterplane area, while the displacement and details of the hull shape enter in the next term of the asymptotic expansion.
Force on a Prolate Spheroid in an Axisymmetric Potential Flow
Authors: Landweber L.
Published: January 2021

The present work is the first of a two-part contribution to the development of hydrodynamic procedures for determining forces on ship forms immersed in an external potential flow. In this first part, the case of a prolate spheroid in an axisymmetric flow is considered, and exact and linearized expressions for the image system of sources and doublets, valid under certain conditions, have been obtained. By means of the Lagally theorem, these yield the values of the forces acting on the spheroid for both steady and unsteady flow. The case of an external potential flow due to a source on the axis of symmetry is considered in detail. In the second part the results for a prolate spheroid in asymmetric flows will be presented.
Experimental Study of Propeller-Induced Vibratory Pressures on Simple Surfaces and Correlation With Theoretical Predictions
Authors: Breslin J. P. , Kowalski T.
Published: January 2021

Vibratory pressures exerted on cylindrical and flat-plate boundaries due to a model propeller were measured at three advance coefficients. A number of "free-space" measurements also were made. All measurements were made by driving a propeller past fixed pressure gages. This method yielded curves of pressure changes which are entirely free from background noise. The magnitudes of the free-space pressures were found to be larger than one half the corresponding magnitudes measured by gages mounted flush in a large plate at equal clearances from the propeller. By postulating that the finite area of the gage diaphragm produces a partial image of the propeller (and hence a larger pressure than that in free space) an experimental procedure was devised for correcting for this finite-area effect yielding results in good agreement with theory. A theoretical treatment of this effect of finite gage size is given in Appendix 2. The decay of maximum amplitudes of vibrating pressures is shown by means of three-dimensional plots. The pressures were found to become vanishingly small within approximately one propeller diameter fore and aft of the center of the propeller. The comparison with theoretically calculated pressures and forces gives very close agreement for free-space pressures and reasonable agreement for forces on a cylindrical surface. The agreement of both pressures and forces with theory is excellent for operation near the design advance ratio. A strong plea is made for further experiments with ship models in an effort to develop design criteria for practical application.
Lifting-Surface Theory of a Fully Submerged Hydrofoil
Authors: Nishiyama Tetsuo
Published: January 2021

Lifting-surface theory of a fully submerged hydrofoil advanced at constant forward speed under the fixed submersion depth is developed, and then the properties of the lift and resistance are discussed in detail in relation with the effect of the Froude number. The disturbing velocity potential is, first of all, derived from the linearized condition on the free water surface. Then, from the boundary condition over the lifting surface, constructed on the Küchemann's conception, a basic integral equation is obtained for the distribution of circulation over the span, from which the lift-curve slope and the sum of the induced and wave-making resistance can be computed readily. This integral equation is solved by DeYoung and Harper's method. Comparisons of theoretical lift and resistance with the experimental data by NASA confirm the appropriateness of the construction of the present theory; and also the effects of the Froude number on the characteristics is definitely clarified. Damping and Inertia Coefficients for a Rolling or Swaying Vertical Strip 1Discussion by W. R. Porter2IN Table 2, of this paper, the author presents values of the damping constant for a vertical strip in horizontal (sway) oscillation for tabular values of nondimensional frequency. In the Addendum, he relates that another table, Table 3, was independently checked and found to vary only by 1 in the fourth decimal place. An unwary person may assume the same to be probably true for Table 2; and, therefore, the misprinted value at frequency 2.000 is hereby reported. The interval in the table at this frequency is sufficiently large that the irregular value may be otherwise undetected. Table 2 Table 3 In addition to correcting the misprint, the table as calculated by the writer at the Computation Center, MIT, presents confirmation that the original Table 2, except at 2.000, varies at most by 1 in the fourth decimal place. This new table provides entry at more closely spaced and more conventional frequencies with digit zero in the third decimal place. The new table also presents the wave-height ratio for convenience. The relation between wave-height ratio and damping constant is mentioned in the Addendum to the paper. To complete the presentation, a graph is shown here for the wave-height ratio for the vertical strip and also for the circular cylinder in horizontal (sway) oscillation as calculated by the writer. Fig. 01Wave-height ratio as a function of nondimensional frequency for vertical strip and circular cylinder in horizontal (sway) oscillation
Theoretical Investigation of a Peristaltic Magneto-Fluid Dynamic Induction Compressor-1
Authors: Neuringer Joseph L. , Migotsky Eugene , Turner James H. , Haag Robert M.
Published: January 2021

A theoretical analysis of the operating characteristics of a peristaltic magneto-fluid dynamic induction compressor is made. Then, an evaluation of the feasibility of using the compressor as an element of a jet-propulsion system for undersea craft is performed. The results of the feasibility study indicate that the compressor has the potential to provide the necessary pressure rise required to propel large and small craft for reasonable current inputs in the primary driving circuitry. Part 2 will appear in the June issue.
Performance of a Propeller in a Wake and the Interaction of Propeller and Hull
Authors: Wald Quentin
Published: January 2021

Relations are developed which describe the propeller-hull interaction and the efficiency of the wake-operating propeller in the practical case where both potential and viscous effects are important. Momentum equations and the actuator disk representation of the propeller are used. Thrust deduction and efficiency are found to be functions of both the local and the ultimate wake velocity which are, in turn, expressible as functions of the static and total pressures in the propeller plane. The two velocity ratios have opposite effects on the thrust deduction, hence a potential-flow model simulating the velocity at the propeller plane and ignoring the ultimate wake-velocity deficiency arising from viscosity is inadequate.
Elastic Vibration Characteristics of Cantilever Plates in Water
Authors: Lindholm Ulric S. , Kana Daniel D. , Chu Wen-Hwa , Abramson H. Norman
Published: January 2021

An experimental study of the vibrations of cantilever plates in air and in water has been conducted, and the results are compared with theoretical predictions based on simple beam theory and thin-plate theory. Both theories are modified to include an apparent mass factor which is derived from chordwise hydrodynamic strip theory. Good theoretical and experimental correlation is achieved upon further including an empirical correction factor which allows for the influence of plate aspect ratio and thickness ratio on the results. Liquid free surface and partial submergence effects are determined experimentally.
Theoretical Investigation of a Peristaltic Magneto-Fluid Dynamic Induction Compressor-2
Authors: Neuringer Joseph L. , Migotsky Eugene , Turner James H. , Haag Robert M.
Published: January 2021

In Part 3, the nature of the electromechanically induced motions inside the compressor both of the fluid conductor and of the pumped fluid when the electromechanical coupling is weak, i.e., in the limit of small magnetic Reynolds number, is investigated. The analysis predicts the development of a constant pressure gradient in the pumped fluid when the condition is imposed that the time-average axial mass flow across the conducting fluid annulus is zero. In Part 4, a preliminary feasibility study is made to determine whether the induction compressor has the potential to provide the pressure rise required to propel large and small undersea craft by means of jet propulsion systems for reasonable power and current-sheet inputs. Also determined here are the geometric scaling laws for the appropriate operating and design parameters.
Some New Measurements on the Drag of Cavitating Disks
Authors: Klose G. J.
Published: January 2021

As part of an experiment on unsteady flow past a cavitating circular disk, it was necessary to make calibrating measurements of the drag on disks in steady flow. The measurements were made for greater cavitation numbers than have been previously recorded, and show that the drag coefficient is essentially linearly dependent upon cavitation number up to values of this parameter as high as 1.3.
Unified Lifting-Line Theory of Fully Wetted Hydrofoils
Authors: Nishiyama Tetsuo
Published: January 2021

Unified lifting-line theory is developed for the hydrofoil of fully-submerged and surface-piercing type. The indirect and direct problems are discussed in some detail in relation to the effect of the Froude number. The disturbing velocity potential is derived from the linearized boundary condition on the free water surface. Then from the boundary condition on the hydrofoil, a basic integral equation is obtained for the distribution of circulation over the span, from which the lift and resistance can be computed readily. Some numerical examples of practical interest are shown for the characteristics and optimum condition in a specified condition of operation for the fully-submerged and surface-piercing hydrofoils.
Unsteady Lifting Surface Theory for a Marine Propeller of Low Pitch Angle With Chordwise Loading Distribution
Authors: Tsakonas S. , Jacobs W. R.
Published: January 2021

This study is third in a series of investigations applying the unsteady lifting-surface theory to the marine propeller case. In the present investigation, the surface integral equation is solved for a mathematical model where the chordwise loading is taken as the first term of Birnbaum's lift distribution (flat-plate chordwise distribution), in conjunction with Glauert's lift operator, which, in essence, satisfies the chordwise boundary conditions by a weighted average. It is shown that this model is an improvement over the modified Weissinger model used previously in this series, because it contains as a nucleus the exact two-dimensional solution, and thus it provides a sounder basis for determining the three-dimensional effects. The blade-loading is determined for a propeller operating in flow disturbances induced by the presence of a hull and by the blade-camber and incidence-angle effects. The stationary loading obtained by the present model is less than that obtained by the modified Weissinger model, whereas the nonstationary loading is slightly larger. The results of numerical calculations are applied to the problem of propeller vibratory thrust and torque, and comparison is made with previous theoretical and experimental values. Conclusions of the earlier studies as to the dependence of loading on the important parameters—blade-area ratio, aspect ratio and pitch—are confirmed by the present results.
A Sea Spectrum for Model Tests and Long-Term Ship Prediction
Authors: Scott J. R.
Published: January 2021

This paper outlines one-dimensional spectrum terminology, and suggests a spectrum suitable as a standard for model and ship-prediction work. This spectrum is represented by= 0 elsewhere, in whichω0 = 3.15T-1 + 8.98T-2ω is angular frequency in radians per secS(ω) is energy density appropriate to an angular frequency baseΗ is significant wave height in feetωο is spectrum peak frequency T is average period of the waves. In applications where wind speed is specified in place of Τ the following supporting relations may be used, provided the specified wind speed is more than 15 knots:ωο-1 = 0.03Η + 1.35Η = 0.82W -5.8in which W is wind speed in knots
A Riemcann-Hilberf Problem for Nonlinear, Fully Cavitating Flow
Authors: Larock B. E. , Street R. L.
Published: January 2021

A nonlinear problem for a flat-plate hydrofoil is solved by using conformal mapping and the Riemann-Hilbert solution to a mixed-boundary-value problem in an auxiliary half-plane. Expressions are developed for plate length, lift and drag coefficients, and cavity configuration. All are given in terms of nonsingular quadratures for prescribed cavitation number and attack angle. The results are in quantitative agreement with experimental data and other nonlinear theories.
The Exciting Forces on a Moving Body in Waves
Authors: Newman J. N.
Published: January 2021

This paper generalizes the "Haskind relations" for the exciting forces in waves, to include the effects of constant forward speed. The analysis assumes the fluid to the ideal and incompressible, and the disturbance of the free surface to be small. The analytical relations are derived for the exciting forces in regular waves, in terms of the radiation potential associated with the forced harmonic oscillations of the same body in calm water. For this purpose it is sufficient to know the far-field asymptotic form of the radiation potential. The results are applied to the case of a submerged ellipsoid, to give the six exciting forces and moments as functions of the wave length, heading angle, and forward velocity.
On the Role of Corrosion in Cavitation Damage
Authors: Waring Sophia , Preiser H. S. , Thiruvengadam A.
Published: January 2021

The interacting influence of corrosion on cavitation damage was studied quantitatively using a magnetostrictive device. The relationship between the rate of weight Joss and the amplitude of oscillation for 1020 mild steel became modified as the NaCl concentration was increased. When 1100-F aluminum was used, this relationship was not affected. An attempt was made to estimate the contribution of electrochemical corrosion to total damage of four methods; namely, (a) static polarization measurements, (b) dynamic polarization measurements, (c) short-duration pulsing technique, and (d) long duration pulsing technique. The electrochemical corrosion rates thus estimated are very small compared to the total rate of damage. However, the rate of weight loss in 3 percent NaCl solution (in distilled water) for 1020 mild steel is about three times that in distilled water at a particular double amplitude and frequency (1.5 X 10 −3 in. and 15 kcs). It is concluded that this increase in the rate of damage is principally due to the deterioration in the mechanical properties of the material in a corrosive environment.
A Linearized Two-Dimensional Theory for High-Speed Hydrofoils Near the Free Surface
Authors: Bernicker Richard P.
Published: January 2021

A linearized two-dimensional theory is presented for high-speed hydrofoils near the free surface. The "direct" problem (hydrofoil shape specified) is attacked by replacing the actual foil with vortex and source sheets. The resulting integral equation for the strength of the singularity distribution is recast into an infinite set of linear algebraic equations relating the unknown constants in a Glauert-type vorticity expansion to the boundary condition on the foil. The solution is achieved using a matrix inversion technique and it is found that the matrix relating the known and unknown constants is a function of depth of submergence alone. Inversion of this matrix at each depth allows the vorticity constants to be calculated for any arbitrary foil section by matrix multiplication. The inverted matrices have been calculated for several depth-to-chord ratios and are presented herein. Several examples for specific camber and thickness distributions are given, and results indicate significant effects in the force characteristics at depths less than one chord. In particular, thickness effects cause a loss of lift at shallow submergences which may be an appreciable percentage of the total design lift. The second part treats the "indirect" problem of designing a hydrofoil sectional shape at a given depth to achieve a specified pressure loading. Similar to the "direct" problem treated in the first part, integral equations are derived for the camber and thickness functions by replacing the actual foil by vortex and source sheets. The solution is obtained by recasting these equations into an infinite set of linear algebraic equations relating the constants in a series expansion of the foil geometry to the known pressure boundary conditions. The matrix relating the known and unknown constants is, again, a function of the depth of submergence alone, and inversion techniques allow the sectional shape to be determined for arbitrary design pressure distributions. Several examples indicate the procedure and results are presented for the change in sectional shape for a given pressure loading as the depth of submergence of the foil is decreased.
On Nonlinear Ship Motions in Irregular Waves
Authors: Hasselmann K.
Published: January 2021

It is shown that the transfer functions characterizing the nonlinear response of ships in irregular seas can be obtained from high order moments of the ship motions by an extension of standard spectral-analysis techniques. Hence, full-scale measurements can be used to determine, for example, the coefficients of excess wave resistance and lateral drift. The method also has applications in model experiments.
Unsteady Loads on Supercavitating Hydrofoils of Finite Span
Authors: Widnall Sheila Evans
Published: January 2021

Linearized three-dimensional lifting-surface theory is derived for a supercavitating hydrofoil with finite span in steady or oscillatory motion through an infinite fluid. The resulting coupled-integral equations are solved on a high-speed digital computer using a numerical method of assumed modes similar to that used for fully wetted surfaces. Numerical results for lift and moment for both steady and oscillating foils are compared with other theories and experiments. Results of these calculations indicate that this numerical solution gives an efficient and accurate prediction of loads on a supercavitating foil.
Experiments on Gravity Effects in Supercavitating Flow
Authors: Kiceniuk T. , Acosta A. J.
Published: January 2021

Experiments on the effect of a transverse gravitational field on the supercavitating flow past a wedge tend to confirm predictions based on linearized free-streamline theory. A small though systematic dependence upon Froude number not accounted for by the existing theory is revealed, however.
Full-Scale Destroyer Motion Measurements
Authors: Gerritsma J. , Smith W. E.
Published: January 2021

The results of full-scale destroyer motion tests in head seas are presented. A comparison is made between motion response obtained from full-scale tests, model experiments, and computer calculations. Agreement is satisfactory.
General Instability of Shallow-Stiffened Orthotropic Cylinders Under Hydrostatic Pressure
Authors: Milligan R. , Lakshmikantham C. , Gerard G.
Published: January 2021

As a part of a general program to determine the applicability of linear orthotropic stability theory to the design of stiffened cylinders under various loading conditions, a theoretical and experimental investigation was performed on the general instability of orthotropic cylinders under hydrostatic pressure. Experimental results obtained herein have shown that the use of linear orthotropic theory results in accurate predictions of cylinder stability over a wide range of geometric parameters.
The Heave Damping Coefficients of Bulbous Cylinders, Partially Immersed in Deep Water
Authors: Frank W.
Published: January 2021

The heave added mass and damping coefficients of several partially immersed bulbous and nonbulbous cylinders are computed. For each of the bulbous forms there is a frequency at which the damping coefficient vanishes, whereas the nonbulbous cylinders exhibit nonzero damping over the frequency range considered.
Pressure Measurements on Flapped Hydrofoils in Cavity Flows and Wake Flows
Authors: Meijer M. C.
Published: January 2021

The purpose of the present experiments is to obtain detailed information about the flow field, such as the pressure distribution, at the surface of a flapped hydrofoil in full cavity or wake flows. The model and the experimental procedure are described. The experimental results obtained have been used to compare with the theoretical predictions, to investigate the tunnel wall effect and to estimate the viscous effect at a sharp corner. Anempirical method for correcting the tunnel wall effect is developed here, the validity of which is supported by tests with models of three different sizes. An appreciable Viscous effect has been found near the hinge of a deflected flap. Except for this effect, the theory and experiments are found to be in good agreement.
Experiments on Slamming of Wedge-Shaped Bodies
Authors: Chuang Sheng-Lun
Published: January 2021

A series of experimental investigations of rigid-body slamming was performed at the Naval Ship Research and Development Center by dropping one flat-bottom steel model and five wedge-shaped steel models with small deadrise angles (up to 15 deg) from various elevated positions above a calm water surface. The test results were used to provide a set of charts for estimating the maximum impact pressure due to rigid-body slamming of wedges.
Performance of a Jet-Flapped Hydrofoil Near a Free Surface
Authors: Hough G. R. , Moran J. P. , Erickson J. C.
Published: January 2021

The problem of a two-dimensional jet-flapped hydrofoil operating near a free surface at infinite and zero Froude numbers is treated using thin-airfoil theory. The pair of coupled integro-differential equations which governs the system is derived and is reduced to a set of linear algebraic equations by assuming appropriate series forms for the vortex distributions representing the hydrofoil and the jet. A collocation procedure is then used to solve these algebraic equations. The variation of the hydrofoil lift and pitching moment with submergence depth is calculated for several jet blowing configurations. The results indicate that free-surface effects on jet-flapped hydrofoil performance appear to be significant only for operating depths of less than about one chord length for all of the configurations studied.
Examination of Eggers’ Relationship Between Transverse Wave Profiles and Wave Resistance
Authors: Kobus H. E.
Published: January 2021

A two-dimensional vertical strut with a cross section obtained by conformal mapping of an ogive in an unbounded plane into a channel has been investigated. Eggers' relationship between transverse wave profiles and wave resistance has been applied to both analytical and experimental profiles. The basic assumption of a free wave system in the analysis seems to introduce only a small error in comparison to the effects of viscosity.
Experimental Boiler Tube Burnout as a Function of Downcorner Resistance
Authors: Woodward John B.
Published: January 2021

Experiments to determine the burnout heat flux in a simulated boiler tube are described. The principal independent variable is downcorner resistance to flow, measured by the parameter fL/D, and varied by adjusting a plug cock in the downcorner. The experimental results show an increase in burnout heat flux with increasing downcorner resistance, up to the point at which average flow reduction reverses this trend. The results are explained by the effect of downcorner resistance on the magnitude of flow oscillations, which begin to occur at heat fluxes less than the burnout heat flux, and which tend to promote the onset of burnout.
Study of Eggers’ Method for the Determination of Wavemaking Resistance
Authors: Landweber L. , Tzou K. T. S.
Published: January 2021

One of the assumptions of Eggers' method for measuring wavemaking resistance, that the effects of the near-field surface disturbance may be neglected, is investigated analytically for a family of vertical struts extending to various depths. It is found that the error in Eggers' transverse-cut method is less than 1 percent at strut drafts of shiplike dimensions, if surface profiles at downstream distances greater than one model length are used. For vertical struts, errors of about 5 percent would be expected for struts of drafts of about half to three times the model length at downstream distances between one and two model lengths. A graphical procedure for minimizing the errors due to the aforementioned assumption is proposed.
On the Stability of Grillage Beams
Authors: Chang Pin-Yu , Michelsen F. C.
Published: January 2021

A general method for obtaining the stability criteria of a grillage is presented. Axial loads in both sets of intersecting beams are considered. Properties and arrangements of beams are fairly arbitrary, as are permissible boundary conditions. However, the analysis is restricted to include only initially straight compression members.
Analyses of Waves and the Wave Resistance due to Transom-Stern Ships
Authors: Yim Bohyun
Published: January 2021

Waves and the wave resistance due to a ship with a transom stern are analyzed starting with an exact formulation of the general ship wave problem. Green's theorem is utilized together with the well-known Green's function which satisfies the linear free-surface boundary condition on the free surface. Here it is required to take at least the second-order terms in the formal development. It is found that the immersed transom stern acts to cancel stern waves. Using a limited form of Michell's wave-resistance formula, the wave resistance of the transom-stern ship is analyzed