bluuebunny/crossref_metadata_2025 huggingface dataset:
Motion of a Large Spar Buoy in Sea Waves
Authors: Rudnick Philip
Published: January 2021

Measurements and first-order calculations are given for the motion of the large spar buoy FLIP in response to ocean waves. Wave pressure and three components of acceleration were recorded over a one-month period. Within substantial tolerances, observed and calculated frequency-response ratios are in agreement. Observations of the damping of transient motions are also reported.
Determination of the Viscous Drag of a Ship Model
Authors: Tzou K. T. S. , Landweber L.
Published: January 2021

In recent years, experimental results obtained by means of the wake survey method have indicated that the viscous drag of a ship model varies with the Froude number; later studies have tended to confirm these findings. The present work was undertaken to establish the validity of this variation. In order to avoid the principal sources of inaccuracy of previous work, modifications to the equipment were made. Also, to obtain viscous drag, the authors applied a refinement of the Betz-Tulin formula.
Curvature Effects on Stress Concentrations at Reinforced Circular Holes
Authors: Van Dyke Peter
Published: January 2021

The primary purposes of this paper are: first, to present a summary of the results of recent investigations into the effects of the curvature on the stress conditions at circular boundaries in shallow cylindrical shells; and second, to apply these results, in the form of influence coefficients at the circular boundary in the shell, to a more complex problem of practical importance which might be encountered in the design of advanced marine or aerospace vehicles. When the boundary conditions at the shell edge specify either the stresses, deformations, or mixtures of both, solutions are obtained through direct use of the influence coefficients. When the stresses and deformations are linked elastically, as exemplified by problems concerning reinforced holes, solutions are more complex in nature. Results for stresses at the intersection of a shell with a flat circular reinforcement are presented here as a function of shell curvature for particular material and geometric properties of the shell and reinforcement. Also, the formulation of the problem where both reinforcement and shell are curved is included.
A Simple Method for Elastic Analysis of Grillages
Authors: Chang Pin-Yu
Published: January 2021

The theory of beams supported by elastic foundations has been shown to be particularly well-suited to the analysis of grillage beams [1, 2, 3[.2 This theory leads to a far more general formulation regarding the types of structures amenable to analysis than that offered by the orthotropic plate theory. As compared to the methods of finite element theory, the theory of beams supported by elastic foundations decreases the computer time by an order of magnitude, thus making the analysis particularly valuable as a design tool. This paper shows that the measurement of the grillage beam analysis based upon the elastic foundation concept can be further simplified by certain matrix transformations that uncouple the deflection equations. The problem has, in fact, been simplified to such an extent that many large grillages can be analyzed with the aid of a desk calculator. Whenever comparison with results obtained from finite element methods has been possible, it has been found that, for all practical purposes, complete correlation exists.
Cavitation Damage Experiments in a Rotating Disk Apparatus Especially With Regard to the Gas Content of Water
Authors: Hansen B. W. , Rasmussen R. E. H.
Published: January 2021

The experience obtained from earlier investigations, described in references [1,2],2 has been used in the construction of a new rotating disk apparatus, especially designed to give a high order of reproducibility and full control of the gas content of the water. The main object was to study what effect the gas content of the water has on cavitation damage.
Experimental Determination of Steady and Unsteady Loads on a Submerged Supercavitating Hydrofoil
Authors: Ransleben Guido E.
Published: January 2021

Measured spanwise distributions of steady-state and oscillatory lift and moment on a fully submerged supercavitating hydrofoil are presented. The foil had a rectangular planform of aspect ratio 5, and was excited in rigid-body rolling and pitching modes for the oscillatory tests. Considerable difficulty was experienced in the data reduction because of high noise levels, but a significant amount of data was recovered. All tests were made at a single angle of attack of 1 2 deg.
Theoretical and Experimental Study of Ship-Roll Stabilization Tanks
Authors: Chu W. H. , Dalzell J. F. , Modisette J. E.
Published: January 2021

This paper summarizes development of a quasi-linear theory for rectangular-type anti-rolling tank and presents results of the ensuing experimental investigation. Theoretical and experimental studies are compared. It was found that the initial theoretical method, although it reflects gross behavior of fluid in the tank and moments exerted on the ship therefrom, should be regarded as the foundation for a better understanding rather than as a design technique. Experimental findings indicate that the antiroll tank is a non-linear control element over its practical range of operation. Development of a nonlinear mathematical representation incorporating empirical results, as necessary, is recommended.
Low-Speed Controllability of Ships in Wind
Authors: Eda H.
Published: January 2021

Aerodynamic and hydrodynamic data for the Manner-class vessel, gathered in earlier experiments, were used to formulate a mathematical model representing the dynamic behavior of ships in wind. A digital computer was used to solve the eigenvalues of the system. Perturbation equations were linearized, with respect to equilibrium conditions, from nonlinear equations of motion. In addition, ship trajectory in certain wind conditions was examined by means of numerical solutions of the nonlinear equations of motion. Results indicate that the ship in bow wind tends, even without an autopilot system, to maintain its original course-with perturbation in yaw inducing yaw oscillations, the convergence of which depends upon the magnitude of relative wind velocity. It is shown that beam wind creates greater difficulties, although the use of an adequate autopilot increases the region of stability in wind of certain velocities (except in some conditions of relatively strong beam wind). An increase in rudder size is shown to improve controllability in wind significantly. Computations with and without the assumption of constant longitudinal speed indicate that the effect of surge motion on yaw and sway responses in wind is important, especially in beam wind.
Streamlines and Pressure Distribution on Arbitrary Ship Hulls at Zero Froude Number
Authors: Tuck E. O. , von Kerczek C.
Published: January 2021

A method is presented for computing the streamlines and the hydrodynamic pressure along the streamlines on a slender ship in steady forward motion at zero Froude number. The ship is represented by conformal mapping functions whose coefficients are polynomial functions of the longitudinal coordinate of the ship. The potential flow about the ship is obtained in terms of the coefficients of the surface equation of the ship and all flow quantities of interest are computed directly from these coefficients.
Bending, Buckling and Vibration of Orthotropic Plate-Beam Structures
Authors: Smith C. S.
Published: January 2021

A method is described of estimating elastic deflections and stresses in systems of interconnected rectangular orthotropic plates and single-direction beams, under distributed or concentrated lateral loads combined with compressive or tensile stresses applied either normal to or in the direction of the beams. The effects of initial deformation of beams and plates are included. Elastic buckling loads and modes and natural frequencies and modes of vibration may be computed. The methods described have been incorporated in a family of FORTRAN IV computer programs which are used to obtain a number of illustrative solutions, including:(/) deflections and stresses in an orthogonally stiffened, three-dimensional ship compartment; these are compared with results computed by an alternative finite element method; (//) buckling loads and modes and natural frequencies and modes of vibration for a typical deck structure; these are compared with results calculated by more approximate methods commonly used in design.
Stresses in Eccentric Stepwise Discontinuous Rings With Transition Section
Authors: Allentuch Arnold , Kempner Joseph
Published: January 2021

The stress distribution in a ring of nonuniform cross section under the action of a uniform radial line load is obtained. The solution is an approximation to the exact interaction problem of a reinforced circular cylindrical shell under hydrostatic pressure. The ring is fabricated in three segments; one segment, whose cross-sectional area varies according to a power function, connects two uniform segments. By a proper choice of parameter values the ring geometry can be reduced to two segments, one of uniform depth, the other of continuously varying depth. Several sets of parameters are chosen for numerical calculations. Within these sets only the length of the transition section changes. Thus an appraisal of the importance of the transition section in reducing the maximum stress is made. The stress distribution in a frame with different lengths of transition section is obtained.
Application of Lifting-Surface Theory to the Prediction of Hydroelastic Response of Hydrofoil Boats
Authors: Henry C. J.
Published: January 2021

In this report a theoretical procedure is developed for the prediction of the dynamic response elastic or rigid body, of a hydrofoil-supported vehicle in the flying condition— to any prescribed transient or periodic disturbance. The procedure also yields the stability indices of the response, so that dynamic instabilities such as flutter can also be predicted. The unsteady hydrodynamic forces are introduced in the equations of motion for the elastic vehicle in terms of the indicia I pressure-response functions, which are de rived herein from lifting-surface theory. Thus, the predicted vehicle-response includes the effects of three-dimensional unsteady flow conditions at specified forward speed. The natural frequencies and elastic modes of vibration of the vehicle and foil system in the absence of hydrodynamic effects are presumed known. A numerical procedure is presented for the solution of the downwash integral equations relating the unknown indicial pressure distributions to the specified elastic-mode shapes. The procedure is based on use of the generalized-lift-operator technique together with the collocation method.
Forces Exerted by Ice on Ships
Authors: Estrada H. , Ward S. R.
Published: January 2021

The factors affecting the strength of arctic sea ice are identified. Values are selected for the key parameters that determine ice strength. The selected values are based on a literature survey. The forces resulting from interaction of ice and hull are described in terms of the slope of the hull at the waterline and the coefficient of friction. The mechanism for ice failure is described and the effect of this analysis on hull design is discussed.
Experimental Determination of Steady and Unsteady Loads on a Surface Piercing, Ventilated Hydrofoil
Authors: Ransleben G. E.
Published: January 2021

Measured steady and unsteady section lift and moment coefficients at two spanwise locations on a surface-piercing ventilated hydrofoil are presented. The foil, of wedge cross section, was supported vertically, and submerged one chord length from the tip. Excitation in rigid-body rolling and pitching modes to the cantilevered foil produced the unsteady loads. All tests were made at a nominal angle of attack of 12 deg.
Elasto-Plastic Analysis of Uniform Grillages Under Lateral Load
Authors: Wah Thein
Published: January 2021

A method is presented for analyzing elastic-plastic grillages under arbitrary loads by finite difference calculus. The torsional stiffness of the beams is neglected. The introduction of two discontinuity functions representing the rotation at the plastic hinges permits a complete description of the structure from initial loading until collapse. The development of a collapse mechanism is signified by the vanishing of the determinant of the matrix of the equations determining the amount of rotation at the plastic hinges.
On Optimum Propellers With a Duct of Finite Length
Authors: Sparenberg J. A.
Published: January 2021

The efficiency of the optimum ducted screw propeller is calculated as a function of the clearance between the blades and the shroud and of the hub diameter. The bound vorticity on the blades and on the duct is discussed. Numerical results are given.
A Theoretical Contribution to the Wave-Resistance Problem of Ship-Bulb Combinations: Verification of the Negativeness of the Interaction Term
Authors: Kracht A. M.
Published: January 2021

In many cases vagueness exists concerning whether a bulb will reduce the wave resistance of a ship or not. In the present paper, by using linearized theory, it is shown that in a certain region of velocity the wave resistance of a ship-bulb combination is always smaller than or equal to the wave resistance of the ship without bulb.
A Linear Theory for Optimum Lifting-Surface Systems
Authors: Sparenberg J. A.
Published: January 2021

A linear theory is given for optimum lifting-surface systems working in an incompressible and inviscid fluid. These systems are assumed to carry out periodical motions. They deliver prescribed mean values of forces or moments at the cost of smallest possible energy losses. The concept of the ideal propeller is discussed.
Preliminary Design of Ship Lines by Mathematical Methods
Authors: Kuiper G.
Published: January 2021

A description is given of a mathematical representation of the ship's hull. The ship form can be given by a number of parameters, which are connected with the usual design parameters of a lines plan. Some qualitative design parameters such as U-or V-shaped sections can be formulated numerically. A design method is given which does not need more information than available at the preliminary design stage. Some results and variations are presented.
Comparison of Ship-Motion Theory and Experiment for Destroyer with Large Bulb
Authors: Smith W.E. , Salvesen N.
Published: January 2021

Experimental techniques for measuring pitch and heave motions for hull forms with large bulbous bows are investigated. It is found that free-running tests in regular small-amplitude waves give the most accurate results. A comparison of the pitch and heave amplitudes and phases obtained by the experiment and by the Korvin-Kroukovsky strip theory shows satisfactory agreement. It is concluded that with sufficiently accurate section representation, the strip theory can be used to predict head-seas motions not only for regular hull forms, but also for ships with bulbous bows and sonar arrays in small-amplitude waves.
Effective Flange Breadth of Stiffened Plates Under Axial Tensile Load or Uniform Bending Moment
Authors: Mansour A.
Published: January 2021

A plate reinforced with stiffeners is an important structural element in ships. In design procedures, often it is assumed that an effective flange of the plate together with the stiffener acts like a beam. In these cases, it is usual to assume that the breadth of the effective flange is some multiple of the thickness. Some analysis based on rational mechanics has been made in order to obtain the "actual" effective flange breadth under special cases of bending moments. Further investigations are still necessary to cover the wide variety of cases encountered in practice. A brief summary is given of the existing analysis and results and then extended to include some cases of practical importance.
Static Stresses on Wide-Bladed Propellers
Authors: McCarthy J. H. , Brock J. S.
Published: January 2021

Static stresses were obtained in laboratory experiments for a destroyer propeller having aerofoil blade sections and a supercavitating propeller having wedge-shaped blade sections, using specially constructed pressure chambers which allowed the blade faces to be loaded under air pressure. A new method of application of beam theory is presented which closely predicts the magnitude and distribution of radial stresses on the destroyer propeller blade. For the supercavitating propeller, neither the proposed beam theory method nor a particular computerized shell analysis can be considered entirely satisfactory for prediction of blade stresses.
Drag Reduction of Flat Plates with Slot Ejection of Polymer Solution
Authors: Granville Paul S.
Published: January 2021

The drag reduction due to polymer being emitted from a slot is analytically treated for the fourth stage for which the concentration boundary layer coincides with the momentum boundary layer.
Study of the Boundary Layer on Ship Forms
Authors: Webster W. C. , Huang T.T.
Published: January 2021

This paper presents a theoretical investigation of the development of the boundary layer about a ship. The "outer flow" conditions, including the streamlines and pressure distributions, are found from linearized, thin-ship theory using the method of Guilloton. Linearized, integral boundary-layer equations appropriate for three-dimensional turbulent flow are integrated numerically along the streamlines to determine the momentum thickness, the shape factor, and the angle of the boundary-layer flow to the outer flow. The results of computations for Series 60, block 0.60 and 0.80 are presented for various Froude numbers and ship lengths.
Vibration Equations for a Structure
Authors: Mott-Smith H. M.
Published: January 2021

The exact equations of vibrations of a dynamical system consisting of both continuous members and isolated masses are obtained by a new method employing Hamilton's variational equation. The method is quite general, and replaces the treatments by lumped-mass models in current use. It makes possible the calculation of wave solutions, which reveal new features of the nature of the motion. Comparison with the results from lumped-mass models shows the scope and limitations of these results. In some cases it makes possible the deduction of formulas for the stresses in structure members expressed directly in terms of the structural parameters, dispensing with all dynamical calculations. These statements are illustrated by examples.
A Wind Wave Co-Cumulative Spectral Model
Authors: Kottler Carl F.
Published: January 2021

A systematic investigation was made of the parameters chosen to define the Pierson-Moskowitz wind sea spectral model. The model was generalized and the form was extended to give a better fit of the data. Using the same sets of data as those selected by Pierson and Moskowitz for building their model, a least-squares fit of each set of the co-cumulative data gave a corresponding optimum set of parameters. These unique optimum sets of parameters yielded an eightfold decrease in the standard deviation. From this family of parameter sets, a co-cumulative spectral model was. developed to fix some of the parameters and relate the others to surface wind velocity. This modification and extension show that at least a twofold improvement in accuracy over the associated Pierson-Moskowitz co-cumulative model can be achieved.
On Ship Wave Patterns and Their Spectra
Authors: Tuck E. O. , Collins J. I. , Wells W. H.
Published: January 2021

The one dimensional and two dimensional spectra of a ship wave pattern have been derived. It is shown that the spectra have distinct signatures containing information on speed, direction, shape, size, and wave resistance of the ship. The speed and direction are readily determined but the relationship of the spectrum to other ship characteristics requires further investigation. Some examples of detailed wave patterns in the wake of a parabolic sided ship have been computed.
Effect of Shock Applied to a Ship’s Propeller
Authors: Mott-Smith H.M.
Published: January 2021

Using the exact differential equations of vibration for a ship's propeller-shaft system obtained in a previous paper, the response of the system to shock on the propeller is calculated and compared with the result obtained previously for an equal shock on the thrust bearing. The maximum force on this bearing is several times as great for the first case as compared with the second. The maximum displacement of the propeller with respect to the stern bearing is also calculated, and is found to depend greatly on the relative rates of propagation of waves of deformation in the shaft and in the ship.
On The Optimization of Shear Carrying Material of Large Tankers
Authors: Shama M. A.
Published: January 2021

The effect of longitudinal material distribution in a ship section, on shear stresses in and shear deformations of side shell and longitudinal bulkheads, is investigated and discussed. The investigation is concerned with large tankers having three longitudinal bulkheads and is carried out in the form of a parametric study. The results are given in terms of ship depth, thickness of side shell plating and the longitudinal vertical shear force of the main hull girder. An optimization procedure for calculating the optimum distribution of the shear carrying material of a hull girder is presented together with a numerical example. The calculated optimum distribution of the shear carrying material satisfies both strength and stiffness requirements. It is concluded that the relative values of the effective thicknesses of side shell and longitudinal bulkheads, as well as the transverse position of side longitudinal bulkheads, have a marked influence on the magnitude of the maximum shear stress and deformation in a ship section. It is also shown that an optimization procedure for the shear carrying material of large tankers could be achieved without violating the requirements of Lloyd's Register of Shipping Rules for 1968
Bow-Thruster Jet Flow
Authors: Beveridge John L.
Published: January 2021

Interaction between the ambient flow of a hull and bow-thruster inflow and outflow is examined theoretically and experimentally. Pressure distributions for duct inflow were derived by potential-flow techniques, and wind-tunnel pressure tests and flow-visualization experiments were conducted to determine the characteristics of duct outflow. Generalized and specific results are presented and discussed for two sizes of circular ducts operating over a range of ratios of free-stream velocity to jet velocity.
On the Computation of Wave Induced Bending and Torsion Moments
Authors: Ogilvie T. Francis
Published: January 2021

In the calculation of wave loads on a ship, one must consider the effects of both the incident waves and the diffraction waves (the latter being caused by the presence of the ship in the incident waves). In the ship-motions problem, Khaskind showed how one can do this without having to solve the diffraction-wave boundary-value problem. Khaskind's procedure is here extended to the calculation of structural loads on a ship. Two examples are discussed: (i) bending moment in the vertical plane of a ship in waves and (ii) torsion in the cross member of a catamaran. Many other applications are possible. In each case, it is necessary to solve a boundary-value problem, but it is generally much simpler than the diffraction problem.
A Note on the Nonstationary Actuator Disk
Authors: Sparenberg J. A.
Published: January 2021

The linear theory of the nonstationary actuator disk is derived by means of external force fields. The concept of the starting source or sink is discussed.
On the Nonlinear Theory of Orthotropic Plates
Authors: Mansour Alaa
Published: January 2021

Formulation of consistent equations for large deflections of orthotropic rectangular plates is presented. The plate is subjected to both uniform load perpendicular to its plane and edge compression. The resulting two-coupled fourth-order partial differential equations reduce, in the isotropic case, to yon Karman's fundamental equations. The equations are solved under two different sets of boundary conditions which occur frequently in ship structures. For numerical results, the solution is programmed and some results are obtained using IBM 360 Model 65. Distributions of deflections, membrane stresses, bending moments, etc. for an orthotropic plate are presented.
Flat-Plate Frictional-Drag Reduction with Polymer Injection
Authors: McCarthy Justin H.
Published: January 2021

A method is developed for prediction of frictional-drag reduction in high Reynolds number flows past smooth flat plates with polymer injection near the leading edge. Numerical results are given for water-Polyox WSR 301 solutions with either uniform concentration or injection.
Ship Rolling at Zero Speed in Random Beam Seas with Nonlinear Damping and Restoration
Authors: Vassilopoulos Lyssimachos
Published: January 2021

A theoretical method is developed for estimating the root-mean-square of nonlinear roll for surface ships at zero speed under the influence of random beam seas. The non-linearities considered include both "square-law" damping and a "Duffing-type" stiffness. An explicit relationship is derived for the rms nonlinear roll in terms of the linear roll variance and the ratios of nonlinear to linear damping and restoration coefficients. The method is illustrated by two examples stemming from earlier studies of similar problems.
Second-Order Theory of Oscillating Cylinders
Authors: Potash Roger L.
Published: January 2021

Two-dimensional cylinders of arbitrary shape undergo small-amplitude forced sinusoidal motion in sway, heave, and roll in or below the free surface of an infinitely deep ideal fluid. Equations for the theoretical fluid response to 'second-order' are derived and their solution formulated in terms of Fredholm integral equations. A numerical procedure is developed and applied to three surface-piercing cylinder sections. Graphs of force and moment acting on the cylinder as a function of nondimensional wave number k are presented for the pure motions and for combined sway and heave, sway and roll, and heave and roll. The results indicate the significance of second-order coupling forces and moments which result in the latter motion cases. Additionally, second-order response coefficients are shown to be important in the higher frequency range.
A Longitudinal-Cut Method for Determining Wavemaking Resistance
Authors: Moran D. D. , Landweber L.
Published: January 2021

A longitudinal-cut technique for computing the wave resistance of ship models moving in a towing tank is developed. The method uses finite-limit integrals of the wave profile along a line parallel to the ship motion. Solution of a set of simultaneous equations yields a set of coefficients which are in turn used in a series expression for wave resistance. This technique allows the wave resistance to be calculated from longitudinal-cut records of finite length, including multiple wave reflections from the walls of the channel. The accuracy of the method is verified by applying it to the wave system produced by a moving source distribution. A linear source distribution on the vertical plane of the ship midsection, and extending from the water surface downward, is used in this study. The computed wave resistance is compared with the known exact value for the source distribution. The numerical study indicated that the method predicted the wave resistance to within one percent of the exact value for almost all choices of Froude number, model length, and tank width. The applicability of the method was also verified for a Series 60, 0.60 block-coefficient model, 10 feet long.
Water Wave Singularities in a Prolate Spheroidal Coordinate System
Authors: Newman J. N.
Published: January 2021

Singular velocity potentials are derived which satisfy the linear free-surface boundary condition and appropriate initial condition or radiation condition, but which are singular in the same form as a spheroidal harmonic. Thus these singularities can be utilized to satisfy boundary conditions on submerged spheroids without integrating conventional point sources or dipoles over the body surface or axis, in an analogous manner to the use of spheroidal harmonics in an unbounded fluid. In addition to the general unsteady case, equations are derived for the special cases of steady forward motion and of sinusoidal time-dependence, either at zero or constant forward velocity of the spheroid. Wave-free singularities are derived for the case of zero forward speed, and applications to problems in wave resistance and in seakeeping are discussed briefly.
Sinkage and Trim in First-Order Thin-Ship Theory
Authors: Yeung Ronald W.
Published: January 2021

In first-order thin-ship theory, the sinkage and trim of a ship moving with constant speed into still water can be obtained from a pair of linear equations associated with force and moment. The right-hand sides of these equations are triple integrals of the Havelock source function over the undisturbed underwater profile. By approximating the hull form by a piecewise linear one, these terms may be taken to be composed of two distinct types of integrals whose values are calculated. Sinkage and trim for two mathematical and five Series 60 models have been calculated using these integrals. The results are compared with the corresponding experimental values. The agreement between theoretical and experimental values is considered satisfactory, especially for sinkage and for sufficiently small beam/length ratio.
The Application of Gegenbauer Polynomials to the Michell Integral
Authors: Michelsen Finn C.
Published: January 2021

Gegenbauer polynomials have been used to define the centerplane distribution of Havelock sources defining the ship in the Michell thin-ship theory. Orthogonality properties have been used to reduce the Michell integral to a double finite sum of coefficients defined in terms of the singularity distribution, the Froude number, and the length-draft ratio.
Extraction of Flow Energy by a Wing Oscillating in Waves
Authors: Wu Th. Yao-tsu
Published: January 2021

This paper attempts to investigate the possibility of extracting energy from surrounding flow by a two-dimensional hydrofoil oscillating through a gravity wave in water, or by an airfoil in gust. The greatest possible rate of energy extraction is obtained by the optimum mode of heaving and pitching of the hydrofoil, which is determined by the method of variational calculation of parameters. It is found that energy extraction is impossible if the incident flow is uniform, and becomes feasible only when the primary flow contains a wave component having a transverse velocity distribution normal to both the mean free stream and the wing span. When such waves of sufficiently large amplitude are present, not only flow energy but also a net mechanical power can be extracted from the surrounding flow.
Theory and Measurements of the Propeller-Induced Vibratory Pressure Field
Authors: Jacobs W. R. , Mercier J. , Tsakonas S.
Published: January 2021

A theory has been developed, based on lifting surface theory, for evaluation of the pressure field generated by an operating propeller in a nonuniform inflow field. In addition, an experimental procedure and a signal processing technique for measuring small pressure levels accurately have been established and utilized in an extensive experimental program. Theoretical results obtained by means of a computer program developed for the CDC 6600 high-speed digital computer agree well with those of experiments conducted at Davidson Laboratory and at the Naval Ship Research and Development Center. The difficulty of accurately establishing by measurements the decay of small pressures at points farther than one radius from the propeller precludes the possibility of determining the blade-frequency force exerted on a flat boundary by integrating the measured signatures. In contrast, integration of double the theoretical free-space pressure over the flat boundary appears to be a feasible and meaningful approach.
An Extension of Two-Dimensional Sail Theory
Authors: Tuck E. O. , Haselgrove M.
Published: January 2021

The two-dimensional sail theory of Thwaites is extended to account for nonrigid attachment of the trailing edge (leach) of the sail. This extension enables direct application to foresails (jibs), and possible application to mainsails. Results for sail shape and lift coefficient are presented which suggest a possible optimum length for jib sheets.
A Design Procedure for Large-Hub Propellers
Authors: Andrews James Bruce , Cummings Damon E.
Published: January 2021

A procedure is given for the design of propellers with large hubs. The hub is modelled by a line sink. A lifting-line propeller model with no hub far downstream is used for thrust, torque, and efficiency calculations. The circulation distribution from this wake propeller is moved up the hub streamlines to the propeller plane for the actual lifting-surface propeller blade design.
Buckling Problems in the Design of Fiberglass-Reinforced Plastic Ships
Authors: Smith C. S.
Published: January 2021

A study is made of the local and overall instability of single-skin FRP hulls stiffened by top-hat frames and girders under uniaxial and biaxial compression. Particular reference is made to transversely framed hulls, for which existing design methods are inadequate and in some respects unsafe. Approximate formulas and data curves are developed for evaluating the instability of flat panels with top-hat frames. Comparisons are made between approximate buckling solutions and more accurate folded-plate and finite-element solutions for typical FRP structures.
Integral Methods for Turbulent Boundary Layers in Pressure Gradients
Authors: Granville Paul S.
Published: January 2021

Shape parameter differential equations are developed for turbulent boundary layers in pressure gradients incorporating two-parameter velocity profiles. Energy and entrainment methods are included. Shear stress factors are explicitly developed for equilibrium and quasi-equilibrium conditions.
Directional Stability and Control of Ships in Waves
Authors: Eda Haruzo
Published: January 2021

The stability and oscillatory motions of ships (automatically steered and unsteered) in the horizontal plane were examined on a digital computer for the case of regular following seas. Available hydrodynamic data for Series 60 hull forms were used. Analysis of directional stability was made for the case of zero encounter frequency (i.e., the ship runs at high speeds equal to the wave celerity). The ship (which is hydrodynamically stable without automatic control in calm water) is directionally unstable in following seas except for the small region near the ascending node of the waves. Addition of automatic control can give the ship directional stability when it is located on the wave trough, but not when it is located on the wave crest. At relatively high frequency (i.e., at low speeds in following seas), the rudder and control system are almost incapable of reducing oscillatory motion. Violent rudder activity in following seas can be decreased by reducing the yaw-rate-gain control constant and by increasing the rudder-response-time constant.
The Wall Effect for Unsteady, Choked Supercavitating Flow
Authors: Kim Jong H.
Published: January 2021

A linear theory for the two-dimensional supercavitating flow past a flat hydrofoil heaving and pitching with small amplitudes in a choked tunnel is developed using the acceleration potential. It is supposed that the streamlines of the cavity always spring from the leading and trailing edges of the hydrofoil and that the hydrofoil is inclined at a small angle to the oncoming flow. Also the pressure in the cavity is assumed to be constant. Force and moment coefficients are calculated as functions of reduced frequency and the ratio of tunnel height to chord length. The pressure disturbances caused by the unsteady motion in a tunnel do not die out far upstream; these also depend on the chord-tunnel height ratio and reduced frequency.
The Wave Resistance of an Air-Cushion Vehicle in Steady and Accelerated Motion
Authors: Doctors Lawrence J. , Sharma Som D.
Published: January 2021

This paper deals with the theoretical wave resistance of an air-cushion vehicle (ACV) traveling over water of uniform finite or infinite depth, in steady or unsteady motion. Referring first to steady motion, it is shown that the unrealistic oscillations in the wave resistance curve at low Froude numbers found by previous workers can be eliminated by using a smoothed-out pressure distribution rather than one with sharp edges studied exclusively in the past. The main result of unsteady motion calculations is that the peak wave resistance in shallow water, even in moderately accelerated motion, is appreciably less than the corresponding steady-state value. An interesting feature of unsteady motion is that besides wave resistance there is another mechanism transferring energy to the free surface, which is here called the dynamic sustention power. Contrary to intuition, the wave resistance in unsteady motion over finite depth sometimes becomes negative at supercritical Froude numbers before finally vanishing at infinite speed.
On the Potential Theory of the Interaction of an Actuator Disk and a Body
Authors: Sparenberg J. A.
Published: January 2021

Actuator disks in the neighborhood of a rotationally symmetric body have been considered. The fluid is assumed to be incompressible and inviscid. The finite disturbances of the fluid by the body have been taken into account, and the theory is linearized with respect to the velocities induced by the actuator disk. The vorticity shed by the disk, its efficiency, and the force induced on the hull are discussed.
On Prediction of Extreme Values
Authors: Ochi Michel K.
Published: January 2021

This paper discusses the prediction of the extreme values of a stationary random process having an arbitrary bandwidth spectrum. Formulas to predict the extreme values are derived for a given number of observations and time by applying order statistics, and the effect of bandwidth of spectrum on the extreme values is discussed. The most probable extreme value and the extreme value for a preassigned probability of being exceeded are obtained. The estimation formulas are applied to predict the extreme value of the pitching motion and acceleration of a ship in irregular seas and waves generated in a towing tank. It is found that the extreme values observed in model experiments fall fairly well in the vicinity of the predicted most probable values. Theoretically, however, the chance that the extreme value will exceed the most probable value is rather high. Hence, the extreme value for a preassigned probability of being exceeded appears to be appropriate for ship (or marine structure) design consideration.
Free Vibrations of Circular Cylindrical Web-Stiffened Sandwich Shells
Authors: Ranlet David , Chen Youl-Nan , Kempner Joseph
Published: January 2021

An analysis of the free vibrations of simply supported and clamped, web-stiffened, circular, cylindrical sandwich shells is presented. The mathematical model formulated includes the effect of translatory and rotatory inertia in each layer of the sandwich, and treats the two face layers as thin shells in which the classical (Donnell) theory of shells applies. However, shear deformations are permitted in the core, which is treated as a layer of inhomogeneous, orthotropic material. In the analysis, the discrete nature of the webs is maintained, except for the inclusion of an average secondary shear modulus induced by the bending of the webs and faces. The effect of smearing-out, or averaging, a given web-stiffened core is also investigated. A Galerkin procedure is employed to determine the natural frequencies from a variational functional generated by means of Hamilton's principle.
Calculation of the Turbulent Boundary Layer on a Ship Hull at Zero Froude Number
Authors: von Kerczek C.
Published: January 2021

A turbulent boundary layer calculation scheme is presented which combines the Cumpsty-HeadSmith three-dimensional turbulent boundary layer calculation method, under the small cross flow approximation, with the Tuck-von Kerczek slender body potential flow at zero Froude number. A sample calculation for the Lucy Ashton double model conforming to the experiments of Joubert and Matheson is presented.
Elastic and Plastic Analysis of a Tanker Web Frame
Authors: Mansour Alaa , Jones Norman
Published: January 2021

Elastic and plastic limit analyses of a web frame of a 225,000-dwt tanker are presented. In the elastic range, three different methods are used to examine the behavior of the frame under the same loading conditions. Beyond the elastic range, plastic limit analysis is performed to investigate the collapse mechanisms and the corresponding collapse pressures. The results of these different approaches are discussed and compared.
An “Exact” Linear Lifting-Surface Theory for a Marine Propeller in a Nonuniform Flow Field
Authors: Tsakonas S. , Jacobs W. R. , Ali M. R.
Published: January 2021

The mathematical model used in previous Davidson Laboratory adaptations of linearized unsteady lifting surface theory to marine propellers has been revised by removing the so-called "staircase" approximation of the blade wake and replacing it by an "exact" helicoidal blade wake. A new numerical procedure and program based on the present model have been developed to evaluate the steady and unsteady blade loading distributions, which are used to determine the bearing forces and moments. Systematic calculations of these forces and moments for a series of propellers show better agreement on the whole with experimental measurements than did the earlier calculations for the same series. In addition, the chordwise loading distributions are much smoother than obtained previously. However, the quantitative improvement must be weighed against the considerable increase in computer time over the old method.
Frictional Resistance of Flat Plates in Dilute Polymer Solutions
Authors: Landweber L. , Poreh M.
Published: January 2021

For a flat plate moving in a dilute polymer solution, effects on boundary-layer characteristics, shear stress, drag reduction and maximum drag reduction are considered for polymers which satisfy the Meyer-Elata law. Results are derived from a model in which the velocity profiles satisfy the law-of-the-wall and a velocity-defect law, and the polymer has no effect in the range in which the latter law is valid. It is also assumed that the polymer affects the law of variation of the mixing length, and a family of velocity profiles representing this effect is adopted. This model then yields a curve of maximum drag reduction as well as a two-parameter family of curves of drag reduction, consequences of the nonoverlapping or overlapping of the two velocity-profile laws. The results are compared with those of Granville for drag reduction, and with the predicted curve of Virk-Granville and an experimental result of Levy and Davis for maximum drag reduction.
Minimum-Trajectory Pipe Routing
Authors: Wangdahl Glenn E. , Pollock Stephen M. , Woodward John B.
Published: January 2021

A dynamic programming method for routing pipe between two specified terminal points is developed and demonstrated. This method, modified to meet requirements of practical piping runs, could be an important contribution toward a totally computerized piping arrangement method.
Unstable Squat from Lateral Motion of Ships in Shallow Water
Authors: Tuck E. O.
Published: January 2021

The theoretical possibility of instability exists in two-dimensional or nearly two-dimensional flow involving ship sections in shallow water, whenever the clearance is very low. This squat instability, which causes the ship to hit the bottom, occurs only for speeds greater than a certain critical value which varies as the three-halves power of the clearance/water depth ratio. Some applications to lateral ship maneuvers, as in tug-assisted docking, are discussed.
Cross-Bispectral Analysis: Application to Ship Resistance in Waves
Authors: Dalzell J. F.
Published: January 2021

The objective of the present work has been to demonstrate by analyses of experimental data that a postulated quadratic functional polynomial model is a reasonable representation of the added ship resistance produced by waves. The evidence so far produced is fairly strong that this is so, and that the model shows considerable promise as a unifying concept for the analysis and interpretation of added ship resistance in random waves. In the course of the work cross-bispectral analysis methods were developed and applied to the derivation of or "identification" of the "added resistance operator" from data obtained in irregular waves. These methods appear to have further promise as a research tool, but, at their present stage of development, do not appear to be an efficient testing tool.
Statics and Dynamics of Elastic Shells with Cutouts —A Review
Authors: Pattabiraman J. , Ramamurti V. , Reddy D. V.
Published: January 2021

The purpose of this survey is to give a review of the methods and results of analytical and experimental investigations for stress concentrations in thin elastic shells subjected to static and dynamic loading. The increasing use of higher-strength materials in the design of pressure vessels, aircraft, ships, and nuclear reactors with high reliability necessitates more precise analyses in the regions of cutouts and concentrated loads.
Remark on a Semilinear Theory for Optimum Lifting-Surface Systems
Authors: Sparenberg J. A.
Published: January 2021

A semilinear theory for optimum lifting surfaces in an incompressible and inviscid fluid is discussed. The lifting surfaces or the bodies to which they can be connected may produce finite disturbance velocities. It is assumed however that only a small amount of vorticity per unit of time flows from the trailing edges.
A Numerical Investigation of the Ogilvie-Tuck Formulas for Added-Mass and Damping Coefficients
Authors: Faltinsen Odd M.
Published: January 2021

A numerical evaluation of the added-mass and damping coefficients in the heave and pitch ship-motion method of Ogilvie and Tuck (1969) is presented. A comparison with experiments shows good agreement.
Interactive Creation of Fair Ship Lines
Authors: Reed Arthur M. , Nowacki Horst
Published: January 2021

A procedure for the initial design of ship lines by means of interactive computer graphics from a display terminal is formulated and illustrated by a fairly elaborate pilot study. The emphasis of the paper lies on two essential aspects of the problem:The formulation of a systematic stepwise procedure for lines creation in the interactive graphics medium, andthe generation of underwater sections from given shape parameters by means of conformal mapping representation. Other features of the hull shape such as sectional area curve, design waterline, and deck contours are generated from polynomial influence functions.

The result of the interactive lines creation process is a mathematical definition of a fair ship hull closely approximating the hull form parameters specified by the designer.
A Simple Design Theory and Method for Bulbous Bows of Ships
Authors: Yim Bohyun
Published: January 2021

A simple bulb design theory and method to minimize wave resistance are presented for bulbous bow ships, which attempt to determine how large a bulb should be for a given parent ship and design speed, where the bulb should be located, and how it should be faired into the ship.
A Theoretical and Experimental Study on the Planform of Superventilated Wings
Authors: Tsen L. F. , Guilbaud M.
Published: January 2021

This study explores the influence of the aspect ratio, the taper ratio, and the sweepback on the flow over trapezoidal superventilated wings with a flat wetted lower surface. The flow is first calculated by a numerical method in the scope of the linearized supercavitating lifting-surface theory. The calculated wings are then made and tested in a water tunnel at zero cavitation number. The measured force and moment coefficients are compared with the prediction.