bluuebunny/crossref_metadata_2025 huggingface dataset:
Stresses Around Two Openings of General Shape
Authors: Dhir S. K.
Published: January 2021

A general method is presented for determining the stresses around two openings of any shape in a large plate of elastic isotropic material. The method is based on the complex variable approach of Muskhelishvili combined with the Schwarz successive approximation technique. Stresses are computed for the case of a small circular opening near a large square opening. The distance between the edges of the two openings is at least twice the diameter of the circular opening. The results are presented as stress concentration factors in contours of the size ratio of the two openings as a function of the distance between them. Several cases which frequently occur in ship construction are included.
Third-Order Interactions in Kelvin Ship-Wave Systems
Authors: Newman J. N.
Published: January 2021

This paper considers the possible existence of third-order resonant interactions in Kelvin ship-wave systems. Such interactions will generally occur when two discrete plane wave systems are present, but Phillips's criterion for third-order interactions is applied to the Kelvin pattern to show that there is no resonant interaction, except possibly along the cusp line. A more accurate analysis is then performed in the vicinity of the cusp line, using triple-integral solutions of the third-order free-surface condition, and it is shown that the resulting solutions are divergent on the cusp line, for large distances behind the disturbance. It is concluded that significant nonlinear interactions can occur on the cusp line, involving energy transfer among adjacent wave numbers.
On The Wave Resistance of Surface Effect Ships
Authors: Yim Bohyun
Published: January 2021

In an attempt to identify ways to reduce the peak wave resistance of surface effect ships, calculations of wave resistance are made for combinations of several singularity distributions with various parameters. Analyses are performed especially for the following components and parameters: various pressure planforms, the effect of sidewalls, the influence of sidewall camber, and the wave interference between the rectangular pressure planform with thin sidewalls and the front and rear skis. The result shows that, in general, the rectangular pressure planform is better than planforms of V-shaped bows and sterns. A gradual decrement of the sidewall displacement with the increasing Froude number is favorable, since not only the large buoyancy of sidewalls but also the low resistance helps the power reduction of SES for low-speed operations. Front and rear skis are helpful to reduce wave resistance for certain Froude numbers, although they may increase the drag for other Froude numbers. The camber of sidewall is not a good means for reducing the wave resistance of a rectangular pressure planform.
Wave Forces on Large Objects in the Sea
Authors: Milgram Jerome H. , Halkyard John E.
Published: January 2021

Three methods of finding wave forces on large, rigid axisymmetric stationary objects in the sea are examined. The problem is formulated in terms of an integral equation and the three methods are successive approximations, direct calculations by means of simultaneous algebraic equations, and use of Haskind's relations. The latter method is included as it offers a large saving of computational efforts for axisymmetric bodies. The applicability of the methods is studied from both the theoretical and applied points of view. Numerical results are given for submerged and floating spheres and for shapes comprising a vertical surface-piercing cylinder atop a sphere.
The Hydrofoil with Finite Cavity in a Solid-Wall Channel
Authors: Schot Steven H.
Published: January 2021

The asymmetrical fully cavitating linearized flow about an arbitrarily shaped slender hydrofoil placed anywhere in a solid-wall channel is considered as a doubly connected region problem. The method of solution involves conformal mapping and a generalization of the Plemeli formulas to doubly periodic functions. The velocity field is expressed in terms of Jacobi's that a functions with the nome q of these functions related directly to the cavity-length/channel-width ratio. Explicit results are obtained for a fully cavitating flat plate at small angles of attack in a midchannel position. For small q, simple wall effect correction terms are obtained for the cavity length and the lift coefficient as a function of cavitation number. These correction terms are correct up to and including third order in q and require no quadratures. For large values of the cavity-length/channel-width ratio (q close to unity) the asymptotic choked flow solution is used to compute the blockage cavitation number and the lift coefficient for the choked flow.
The Effect of Stiffener Size on Interframe Shell Instability of Ring-Reinforced Circular Cylinders
Authors: Ross C. T. F.
Published: January 2021

An investigation was made on three machine-stiffened steel models to find the effect of ring-stiffener size on the shell instability mode of failure. The increase in sizes of the stiffening rings showed only marginal increases in buckling pressures although the latter were all well in excess of the predictions of the von Mises formula.
Transverse Vibration of a Propeller Shaft
Authors: Mott-Smith H. M.
Published: January 2021

By use of the Hamiltonian method the complete set of partial differential equations is obtained for the transverse vibrations of a shaft with any number of elastically restrained bearings (intermediate and terminal) when the foundations of the bearings are subjected to independent preassigned shocks. A complete solution of these equations is given in modal form. The eigenvalues and eigen functions of frequency are obtained from a set of simultaneous matrix equations representing the propagation of boundary conditions from one bearing to the next.
Large Deflections of Rectangular Plates
Authors: Jones Norman , Walters R. M.
Published: January 2021

An approximate rigid, perfectly plastic analysis which retains the influence of finite deflections is presented herein for a uniformly loaded, fully clamped rectangular plate. This theoretical procedure provides reasonable engineering estimates of the permanent deflections of rectangular plates according to the recent experiments of Hooke and Rawlings on plates with aspect ratios in the range 1/3 ≤ β ≤ 1. The approximate method also predicts values which agree fairly well with the tests of Young on long rectangular plates β = 1/3), and for large permanent deflections gives similar values to the analysis by Greenspon when β = 1.
Three-Dimensional Planing at High Froude Number
Authors: Wang D. P. , Rispin P.
Published: January 2021

The steady motion of a planing surface of moderate aspect ratio at small angles of attack is considered. Linearized theory is used with a square-root type of pressure singularity representing the flow near the leading edge. An asymptotic solution for the pressure distribution on the planing surface at large Froude number (or small β, the inverse of the Froude number) is sought. The lowest-order term of the pressure distribution, obtained by setting β equal to zero, is found to be the same as the pressure distribution on the lower side of the corresponding thin wing. Higher-order terms in β are obtained by an iteration process. Explicit solutions are obtained to order β2 for rectangular planforms. Numerical results are calculated for rectangular flat plate planing surfaces of aspect ratios from 0.5 to 2.0. It is found that for large aspect ratios the lift coefficient is reduced by the gravity effect and for small aspect ratios it is increased, the dividing aspect ratio being about 1.5. The results compare reasonably well with experimental data.
On the Flow About a Spheroid Near a Plane Wall
Authors: Farell Cesar
Published: January 2021

The problem of incompressible potential flow about a prolate spheroid in axial motion parallel to a plane wall is considered and a solution free of any approximations, although not in closed form, is obtained. The added-mass coefficient for this motion is evaluated and the results are compared with an existing approximate solution. The expansion of harmonic functions of the form exp(αx +βy +γz) in a series of spheroidal harmonics, needed in the solution of the preceding problem and useful in general in the analysis of problems in potential theory in which spheroidal boundaries appear, is obtained.
The Representation of a Given Ship Form by Singularity Distributions When the Boundary Condition on the Free Surface is Linearized
Authors: Brard Roger
Published: January 2021

The inaccuracy of the usual representations of an actual ship hull, that is of a hull neither thin, nor flat, nor slender, seems to be one of the main causes of the discrepancy between the measured and calculated values of the wave resistance. It is shown in the first part of this paper that a line singularity distribution should be associated with the surface singularity distribution over the hull. In the second part, the order of magnitude of the contribution of the line singularity is evaluated in the particular case of a vertical, elliptical, infinite cylinder. It is considerably high when normal doublet distribution is used. It becomes of the first order at low Froude numbers in the case of a source distribution. The problem still requires extensive research in several directions outlined at the end of the paper.
Effect of Wake on Wave Resistance
Authors: Calisal Sander
Published: January 2021

Suction is applied to the boundary layer of a ship model designed to be of minimum resistance for a Froude number V/(Lg)1/2= 0.289. The total resistance with suction is measured and the wave resistance is calculated by a wave-survey method. For the design speed the wave resistance is observed to remain almost constant up to a certain suction value and then to increase linearly with suction. The remaining viscous resistance, calculated by subtracting the directly measured wave resistance from the total resistance, decreases by the application of suction to a value lower than the values given by ITTC 57 and Schoenherr curves.
Flutter of Supercavitating Hydrofoils-Comparison of Theory and Experiment
Authors: Song Charles C. S.
Published: January 2021

Unsteady flow due to harmonic oscillations of a two-dimensional supercavitating flat-plate hydrofoil in a free jet of finite width has been analyzed using first-order perturbation theory. The hydrodynamic loading coefficients thus obtained were used to study the hydroelastic instabilities: flutter and divergence. In conjunction with the analytical work, an experimental program was carried out using a free-jet water tunnel. Special attention was given to the influence of the free surfaces and the point of separation on the critical flutter speed. With proper interpretation of the location of the separation point near the leading edge, the theory and the experimental data were shown to be in fairly good agreement.
Numerical Prediction of Propeller Characteristics
Authors: Cummings Damon E.
Published: January 2021

A procedure is described for predicting the performance of a propeller numerically to within the accuracy of tunnel and open-water model tests. Given the geometry of the propeller, ship speed, wake fraction distribution and rpm, the thrust and torque characteristics are calculated. The procedure gives good results not only for "normal" propellers but also for such abnormal cases as a variable-pitch propeller operating at off-design pitches. The possibility exists of extension of the method for calculation of spindle torques, stresses, and cavitation inception.
Stresses Around Two Reinforced Openings of General Shape
Authors: Dhir S. K.
Published: January 2021

A general method is presented for determining the stresses around two openings of any shape in a large plate of elastic isotropic material. The two openings can have individual boundary reinforcements. The method is based on the complex variable approach combined with the Schwarz successive-approximation technique. As an illustration of the method, the stresses are computed for the case of a small circular opening near a large circular opening. The amounts of reinforcing material on these two openings were varied to determine the optimum reinforcement. Several cases that frequently occur in ship construction are included.
The Acceleration of an Air Cushion Vehicle Under the Action of a Propulsor
Authors: Doctors Lawrence J. , Sharma Som D.
Published: January 2021

This paper presents the solution for the motion of an air-cushion vehicle (ACV) starting from rest under the action of a propulsor of given thrust-speed characteristics. The wave resistance is based on linearized potential theory, while the aerodynamic drag components are assumed to be strictly quasi-steady. The problem is treated in two different ways: calculating the wave resistance in a truly unsteady manner, and on the simplified quasi-steady basis. The results show that the shape of the propeller characteristics has only a minor effect on the velocity pattern. However, the effect of overloading the ACV is shown to have crucial effects on its ability to surpass the critical depth hump. In this respect, the simpler quasi-steady calculations lead to unnecessarily pessimistic estimates of the acceleration margin. Under certain circumstances in relatively shallow water, the quasi-steady analysis would suggest that the ACV could not overcome the critical hump, while the more elaborate unsteady calculations show that it has indeed adequate power to reach its final cruising speed.
The Blockage Coefficient for Flow About an Arbitrary Body Immersed in a Channel
Authors: Taylor P. J.
Published: January 2021

Each cross section of a ship has a blockage coefficient which is uniquely dependent on its shape. A general numerical procedure is described for finding this coefficient when the cross section takes an arbitrary shape. Some asymptotic formulae, valid for a broad range of shiplike cross sections, are also derived for cases where the clearance below the ship is small.
Propeller Loading-Induced Velocity Field by Means of Unsteady Lifting Surface Theory
Authors: Jacobs W. R. , Tsakonas S.
Published: January 2021

An analysis based on the lifting surface theory has been developed for evaluation of the vibratory velocity field induced by the loading of an operating propeller in both uniform and nonuniform inflow fields. The analysis demonstrates that in the case of nonuniform flow the velocity at any field point is made up of a large number of combinations of the frequency constituents of the loading function with those of the space function (propagation or influence function). A numerical procedure has been developed adaptable to a high-speed digital computer (CDC 6600), and the existing program, which evaluates the steady and unsteady propeller loadings, the resulting hydrodynamic forces and moments, and the pressure field, has been extended to include evaluation of the velocity field as well. This program should thus become a highly versatile and useful tool for the ship researcher or designer.
On the Linear Theory of an Actuator Disk in a Viscous Fluid
Authors: Sparenberg J. A.
Published: January 2021

The linearized theory of an actuator disk working in an incompressible viscous fluid is given. The optimum radial thrust distribution is derived. This gives information about the optimum radial thrust distribution of a propeller in a turbulent wake. It is shown that the efficiency of an actuator disk is greater in a viscous medium than in an inviscid fluid.
A Note on the Resistance of Bodies of Revolution and Ship Forms
Authors: Matheson N. , Joubert P. N.
Published: January 2021

A simple so-called 'equivalent' body of revolution is proposed for reflex ship forms in an attempt to simplify calculation of the boundary layer over a ship's hull when there is no wavemaking. How­ever, exhaustive testing of one body of revolution did not produce a favorable comparison with re­sults for the corresponding reflex model. Gadd's recently proposed theory was used to calculate the boundary-layer development over the body of revolution. Reasonable agreement was obtained between the calculated and experimental results.
A Nonlinear Theory of Sloshing in Rectangular Tanks
Authors: Faltinsen Odd M.
Published: January 2021

A two-dimensional, rigid, rectangular, open tank without baffles is forced to oscillate harmonically with small amplitudes of sway or roll oscillation in the vicinity of the lowest natural frequency for the fluid inside the tank. The breadth of the tank is 0(1) and the depth of the fluid is either 0(1) or in-finite. The excitation is 0(ε) and the response is 0(ε1/3). A nonlinear, inviscid boundary-value problem of potential flow is formulated and the steady-state solution is found as a power series in ε1/3 correctly to 0(ε). Comparison between theory and experiment shows reasonable agreement. The stability of the steady-state solution has been studied.
Stresses in Marine Propellers
Authors: Ma James H.
Published: January 2021

A rational approach to the general solution of the propeller strength problem is established. A finite-element displacement model is utilized to predict the behavior of an elastic body having an arbitrary shape and subjected to prescribed loading. Solid elements in their general form are adopted. This formulation bypasses the constraints of simplified assumptions commonly employed by many classical plate and shell theories, and allows a more realistic approximation to the true structural configuration than is possible by most other conventional approaches. The application of the present procedure is simple and straight-forward. Good agreements with measured displacements and experimental stress data were obtained for a highly skewed blade as well as a supercavitating blade.
On the Role of Bow Friction in Icebreaking
Authors: Scarton Henry A.
Published: January 2021

The influence of frictional resistance on the icebreaking process is studied. A mathematical model is presented which gives expressions for the vertical force exerted on the ice by the bow plating of the ship and the force normal to the bow plating as a function of the horizontal thrust, bow angle, spread-angle complement, friction force direction, and coefficient of friction. To date, no other researcher has studied the most important effect of friction force directionality. Sample results are given for typical hull parameters. A new constraint criterion for use in icebreaker bow design is presented.
On the Shakedown Limit of a Ship’s Hull Girder
Authors: Jones Norman
Published: January 2021

A simple method for calculating the shakedown behavior of the hull girder of a ship or marine vehicle is presented herein. The requirements for shakedown demand allowable bending moments which are generally smaller than those necessary to " break the back of a ship."
Further Development of a Procedure for Determination of Wave Resistance from Longitudinal-Cut Surface-Profile Measurements
Authors: Tsai C.-E. , Landweber L.
Published: January 2021

The single-longitudinal-cut method of Moran and Landweber is refined both in the experimental techniques and the analytical procedures. Analytically, a method combining iteration and elimination is used, instead of matrix inversion, to solve the linear equations for the amplitude spectrum; the upper truncation point XT is held constant in the analysis of wave data; and the modified procedures are applied both to the symmetrical source distribution used by Moran as well as to an asymmetrical one. Similar results were obtained with the latter distribution. Experimentally, it was found that the results obtained with the single-longitudinal-cut procedure were sensitive to the lateral position of the cut. Consequently, a multiple-longitudinal-cut technique was developed, using three probes in parallel, with the data analyzed by the method of least squares. Applying the multiple-longitudinal-cut method to a family of four Series 60 models, consistent results among the 0.60-block models were obtained. Furthermore, the wave resistance was found to be essentially constant with respect to wave-record length for the 0.60-block geosims.
A Method of Computing Nonlinear Wave Resistance of Thin Ships by Coordinate Straining
Authors: Dagan G.
Published: January 2021

A systematical procedure is derived for determining the distribution of sources along the centerplane of a thin ship which generate a flow (and the associated wave resistance) satisfying the free-surface and body boundary conditions at second order. The method relies on a mapping of the flow domain onto a new domain by slightly straining the coordinates. The horizontal straining is selected such that the nonlinear solution should be easily derived from the first-order (Michell) solution in the strained domain. The results are shown to be similar to those obtained by Guilloton's method, but new features, such as the forward displacement of the bow singularities, are present.
The Theory of the Rayleigh Distribution and Some of Its Applications
Authors: Hoffman Dan , Karst Otto J.
Published: January 2021

The first part of the paper deals with the mathematical properties of the Rayleigh distribution, including but not limited to the density function, the moment generating function, the maximum likelihood estimator, confidence intervals, and the bivariate Rayleigh distribution. The second part deals with applications of the Rayleigh distribution to the analysis of the responses of marine vehicles to wave excitation. These applications are illustrated with regard to ocean waves, short-and long-term bending moment responses of a ship, and the "target problem" applied to the relationship between wind speed, wave height, and stress.
Stress Concentration Factors for Cutouts in Uniaxially Loaded Plates
Authors: Heller S. R.
Published: January 2021

The technical literature is briefly traced so as to identify comprehensive summaries of available data. The Inglis hypothesis, that the stress concentration factor for an equivalent ellipse can be used to estimate the stress concentration factor for a nonelliptic cutout, is shown to be valid provided the inclination of the semimajor axis to direction of uniform axial stress is taken into account. Means for determining inclination and half-length of cutout are illustrated.
Unsteady Lifting-Surface Theory for Ship Screws: Derivation and Numerical Treatment of Integral Equation
Authors: van Gent W.
Published: January 2021

In an early stage of studies concerned with lifting-surface theory for ship screws, the Netherlands Ship Model Basin initiated the development of a numerical solution of the mathematical model. To achieve this, a rigorous method was followed consisting of separation of regular and singular parts of the kernel of the integral equation, preparation of numerical procedures for integration of the regular parts, and analytical integration of the singular parts. The general solution includes the steady load due to blade geometry in uniform flow, the unsteady load in nonuniform flow, and the unsteady load due to propeller vibrations. The pressure distribution in the chordwise direction is represented by a series of linear combinations of Chebyshev polynomials. In this paper an account is given of this method of solution.
Simulation of Maneuvering Characteristics of a Destroyer Study Ship Using a Modified Nonlinear Model
Authors: Brown Samuel H. , Alvestad Reidar
Published: January 2021

This paper describes an analog computer maneuvering simulation of a destroyer study ship. The mathematical model used includes the ship propulsion machinery dynamics and the ship equations of motion. The model couples the ship propulsion dynamics equations with nonlinear maneuvering equations. The power plant representation consists of a simplified mathematical model of a General Electric LM2500 gas turbine engine and is primarily an engine mapping of engine torque versus engine speed using fuel flow. rate as a parameter. The simulation is used to accurately predict slow transients in ship speed during maneuvers resulting from slow increases in the fuel flow rate to the gas turbine. The advantage of the modified model presented in this paper over those not including propulsion dynamics is that it permits simulations of the effects of maneuvering on the propulsion plant.
Design of Transverse-Plane Bulkheads in Tankers
Authors: Carlsen Carl Arne , Kavlie Dag
Published: January 2021

A program system, INDETS, for computer-aided design of tanker structures has been developed. The system, which is the result of a joint effort of the Norwegian Institute of Technology, Trondheim, and the Aker Group, Oslo, is considered an effective tool for practical design. A design module of INDETS for tanker transverse-plane bulkheads is presented. The girder system is analyzed by a three-dimensional frame model including the surrounding structure as substructures. Two optimization methods, the Stress Ratio Technique and the Sequential Unconstrained Minimization Technique, are applied. A number of parametric variations on topology have been performed, and the depth and breadth have been varied to derive curves for estimating the weight of bulkheads at the preliminary design stage. As a conclusion, a simple-formula is presented.
A Validation Study of the Mixed-Foil Concept for High-Speed Hydrofoils
Authors: Wang D. P. , Shen Young T.
Published: January 2021

A hydrodynamic validation study of the concept of the mixed foil has been conducted. A mixed foil is a streamlined hydrofoil equipped with a flap or other device which, above a certain speed, can be activated so as to change the flow around the foil into a supercavitating flow. At take-off and at moderate speeds, a mixed foil is operated as a subcavitating foil; at high speeds, it is operated as a supercavitating foil. During high-speed operations, a reduction in the wetted planform area of a mixed foil is proposed. The present study produces a design outline for the mixed foil and identifies essential problems which should be studied in the future. The analysis is illustrated by using hydrofoils with plano-convex sections. The lift-to-drag ratios at takeoff and at 45-knot and 83-knot cruising speeds are obtained.
Dynamical Theory of Potential Flows with a Free Surface: A Classical Approach to Strip Theory of Ship Motions
Authors: Wang S.
Published: January 2021

The application of the dynamical theory to problems involving a solid body moving in an unbounded medium of inviscid and incompressable fluid is well known in classical hydrodynamics. The distinctive feature of this method is that the fluid and the body together are treated as one dynamical system and the description of the problem requires only one single source of information, the kinetic energy of the fluid resulting from the motion of the solid body. In this paper, the application of this classical method to floating-body problems is presented. In particular, the method is applied to derive the dynamic coefficients in the equations of ship motion following the strip-theory approximation. Formulas for the added-mass and dampling coefficients are obtained, and the differences as compared with those used in the latest version of strip theory are discussed.
Comments on Hess: “On the Problem of Shaping an Axisymmetric Body to Obtain Low Drag at Large Reynolds Numbers”
Authors: Goldschmied F. R. , Parsons J. S. , Goodson R. E.
Published: January 2021

The title paper deals with a classical problem and it invites several comments to fully explore its technical impact.
On a Rectangular Pressure Distribution of Oscillating Strength Moving Over a Free Surface
Authors: Chen Hsao-Hsin
Published: January 2021

Through the application of linearized water-wave theory, a solution of the free surface due to the disturbance of a moving, oscillatory pressure distribution of rectangular form is obtained. Such a solution provides the basis for formulating the wave resistance of the moving pressure distribution just cited, as well as the hydrodynamic coefficients of a captured-air bubble of rectangular footprint in heave motion. Numerical methods are developed to compute the aforementioned resistance and hydrodynamic coefficients, the numerical examples of which are also presented. Of special interest is the occurrence of negative effectivemass at low frequencies for the two forward speeds considered in the present work. Another interesting feature is the hydrodynamic instability and the negative damping that occurs in the low-frequency range when the Froude number is very high.
Forced Vibrations of Thin, Elastic, Rectangular Plates with Edges Elastically Restrained Against Rotation
Authors: Susemihl E. A. , Laura P. A. A.
Published: January 2021

Polynomial coordinate functions and the Galerkin method are used to determine the response of a thin, elastic, rectangular plate with edges elastically restrained against rotation and subjected to sinusoidal excitation. It is shown that when the flexibility coefficients approach infinity (simply supported edge conditions) the calculated results practically coincide with the exact solution in the case of a square plate when four terms of the expansion are used. Dynamic displacement and bending moment amplitudes are tabulated for different length-to-width ratios, flexibility coefficients, and frequency values.
Forces and Moments on a Ship Moving in a Shallow Channel
Authors: Beck Robert F.
Published: January 2021

The method of matched asymptotic expansions is applied to the problem of a ship moving with constant velocity in a channel of rectangular cross section. The depth of the channel is presumed small so that a linearized shallow-water solution is developed. The ship is assumed to be slender and is replaced in the outer region by a distribution of sources and vortices. As in earlier theories for slender bodies translating in shallow water, the source strength is proportional to the change in cross-sectional area of the ship. An integral equation must be solved to find the vortex strength. Using the source and vortex strengths, expressions are developed for the side force, yaw moment, sinkage, and trim. Numerical results are presented which show good agreement with experimental results.
On the Edge Singularity of an Actuator Disk with Large Constant Normal Load
Authors: Schmidt G. H. , Sparenberg J. A.
Published: January 2021

In this paper some aspects of the nonlinear potential theory of actuator disks are considered. A rather general formulation of the problem for a prescribed load on a curved surface is given. For the special case of constant normal load and no incoming velocity the singular behavior of the flow at the edge of the disk is discussed.
Calculation of Attached or Partially Separated Flow Around Airfoil Sections
Authors: Milgram Jerome H.
Published: January 2021

Two-dimensional airfoil theory is developed for incompressible flow, for which most aspects of the solution are found in a "mapped plane." Although the airfoil contour has large slopes in the physical plane when the airfoil has a round leading edge, the slopes in the mapped plane are small and uniformly approach zero as the airfoil thickness and camber ratios are made to approach zero by an affine transformation on the airfoil shape. Because of the small slopes in the mapped plane, a perturbation series is appropriate there. A relatively unified theory is given for attached and partially separated (trailing-edge separation) flows. The results of calculations by this theory are compared with the results of other theories and with measurements. The attached-flow theory is shown to be especially appropriate for thin marine propeller sections with blunted leading edges. Some new data on the pressure distribution across the wake at the trailing edge of an airfoil in partially separated flow are presented.
Numerical Calculation of Second-Order Wave Resistance
Authors: Hong Young S.
Published: January 2021

The wave resistance due to the steady motion of a ship was formulated in Lagrangian coordinates by Wehausen [1].2 By introduction of an iteration scheme the solutions for the first order and second order3 were obtained. The draft/length ratio was assumed small in order to simplify numerical computation. In this work Wehausen's formulas are used to compute the resistance numerically. A few models are selected and the wave resistance is calculated. These results are compared with other methods and experiments. Generally speaking, the second-order resistance shows better agreement with experiment than first-order theory in only a restricted range of Froude number, say 0.25 to 0.35, and even here not uniformly. For larger Froude numbers it underestimates seriously.
Wake-Source Theory
Authors: Brard Roger
Published: January 2021

Twenty-five years ago or so, Tulin recommended that the viscous resistance of ship models be determined by means of wake-survey measurements. Such a method had been imagined by Betz for estimating the drag of wing profiles. The extension of Betz's method to three-dimensional flows required many refinements. The present paper is intended to found the theory on a firm base. Rigorous formulas have been established for deeply submerged bodies and also for surface-ship models. But, in the latter case, wakesurvey measurements do not suffice; the energy lost by the wake in generating waves should also be determined. This is not yet possible. Therefore the estimates of the viscous resistance of a surface ship model are liable to a systematic error.
Wave Pattern Measurements Using a Half-Ship Model
Authors: Bellows Gerald E.
Published: January 2021

This report describes an investigation of the wave pattern of a half-ship model. Using a 5-ft (1.6 m) ship model that has been cut in half along the vertical centerline plane and by towing this half model very close to one wall of the model tank, a wave pattern corresponding to that produced on one side of a symmetric ship model is obtained. The longitudinal-cut method is used to measure the wave pattern. Comparisons of the wave resistance of the half model and whole model are given. It is apparent from these that the results are in agreement for distances from the wall of less than 3 in. (76 mm). These results show that the length of a longitudinal cut before reflection occurs can be doubled by using this procedure rather than towing a conventional ship model in the center of the tank. This is especially useful for tests of high-speed hull forms.
Sway Added-Mass of Cylinders in a Canal Using Dual-Extremum Principles
Authors: Bai Kwang June
Published: January 2021

This paper describes a finite-element method based on the dual extremum principles. As an application of the dual-extremum principles, the upper and lower bounds of the added mass of two-dimensional cylinders in a canal are computed for the zero-and infinite-frequency limits. Specifically, the upper and lower bounds of the added mass of a rectangular section, a triangular section, a circular section, and a Lewis-form section at the center of a rectangular canal are computed. The added mass is also computed for a rectangular section at off-center locations in a canal. Present numerical results are compared with previous results obtained by the hypercircle method [1].
In-Line and Transverse Forces on Cylinders in Oscillatory Flow at
High Reynolds Numbers
Authors: Sarpkaya Turgut
Published: January 2021

This paper presents the results of an extensive experimental investigation of the in-line and transverse forces acting on smooth and sand roughened circular cylinders placed in oscillatory flow at Reynolds numbers up to 1.5 × 106, Keulegan Carpenter numbers up to 100, and relative roughnesses from 1/800 to 1/50. The drag and inertia coefficients have been determined through the use of the Fourier analysis and the least-squares method. The transverse force (lift) has been analyzed in terms of its maximum, semi peak-to-peak, and root-mean-squarevalues. In addition, the frequency of vortex shedding and the Strouhal number have been determined. The results have shown that (a) for smooth cylinders, all of the coefficients just cited are functions of the Reynolds and Keulegan-Carpenter numbers, particularly for Reynolds numbers larger than about 20 000; (b) for rough cylinders, the force coefficients also depend on the relative roughness k/D and differ significantly from corresponding to the smooth cylinder; and that (c) the use of the frequencyparameter' D2/vT and the roughness Reynolds number Umk/vallows a new interpretation of the present as well as the previously obtained data.
Minimum-Weight Design of Stiffened Cylinders Under Hydrostatic Pressure
Authors: Simitses G. J. , Aswani M.
Published: January 2021

A methodology is developed by which one may design a stiffened cylinder of specified material, radius and length such that it can carry safely a given hydrostatic pressure with minimum weight. The solution is accomplished in two stages. First, design charts based on a simplified formulation of the objective function are obtained. Second, these design charts are used to evaluate the design variables. Such an approach enables the designer to introduce needed changes or avoid interaction of failure modes by paying the least weight penalty. Design examples are presented and the results are compared with those obtained by other investigators.
Theory for Absorption of Wave Power by a System of Interacting Bodies
Authors: Budal K.
Published: January 2021

Wave power absorption by a system of interacting bodies is analyzed within linear theory. A general expression for the wave power absorbed by the system, in terms of far-field velocity potentials, is derived. The optimum power absorption by a system of identical bodies from a plane incident wave is obtained. The theory is applied to various configurations of bodies oscillating in one or two modes. It is shown that the interaction between properly spaced bodies may raise the absorbed power per body by a substantial factor. It is also demonstrated that a single row of oscillating bodies may absorb 50 percent of the incident power if the bodies are operated in one mode and 100 percent if operated in two modes.
Some Extensions of the Classical Approach to Strip Theory of Ship Motions, Including the Calculation of Mean Added Forces and Moments
Authors: Loukakis Theodore A. , Scfavounos Paul D.
Published: January 2021

The application of the dynamical theory to the problem of a ship moving with constant forward speed on a free surface has been extended to include the exciting forces in oblique regular waves. As a result, it has become possible to derive a new formulation for the equations of motion, for a ship moving with five degrees of freedom. The application of the same theory has yielded formulas for the calculation of the mean added resistance and drift force in oblique regular waves and the calculation of all mean forces and moments for the forced oscillations of a ship in calm water.
Automatic Control of Underway Replenishment Maneuvers in a Random Sea
Authors: Alvestad Reidar
Published: January 2021

This paper describes a hybrid computer simulation of two ships performing replenishment operations in random seas. Such operations present collision hazards due to the nonlinear interaction forces and moments which result from close proximity maneuvering while underway. Maneuvers are simulated to demonstrate automatic controller performance during station-keeping, station-changing, and the approach and breakaway phases of typical underway replenishment (UNREP) operations. Results indicate that automatic control should be considered as a possible solution to the UNREP collision avoidance problem.
A Note on the Determination of Cavitation Nuclei Distributions by Holography
Authors: Gates E. M. , Bacon J
Published: January 2021

The purpose of this brief note is to describe the holographic technique and the equipment used to determine nuclei distributions in a water tunnel. Some of the resulting distributions are presented and compared with those of other investigations.
Vibrations of Orthogonally Stiffened Panels
Authors: Madsen Niels FI.
Published: January 2021

A general numerical method for the determination of natural frequencies and modes of vibration for orthogonally stiffened panels is presented. The panel is considered as an assembly of prismatic beams and plate strips rigidly connected along their longitudinal edges and transversely stiffened by beams of varying cross section. The modes of vibration are approximated by linear combinations of the analytically calculated modes of vibration for the prismatic panel, resulting from neglecting the transverse stiffening and assuming simple end supports. For the transverse stiffening, the effects of shear deflection, axial deformation, and St. Venant torsion are taken into account. As a practical example, the natural frequencies of a deep girder in a tanker have been calculated.
Static and Dynamic Analyses of the LSES Hull Structure
Authors: Hananel A. S. , Dent E. J. , Philips E. J. , Chang S. H.
Published: January 2021

To avoid the conservativeness in the large surface-effect ship hull design which results from simplifying assumptions in the stress analysis, the hull structure was analyzed as a three-dimensional elastic body. The NASTRAN finite-element program, level 15.0, was selected for use in this analysis as the most suitable program available. A finite-element model representing the true hull stiffness was used in obtaining the internal load and displacement distributions. The inertia effect of the ship masses was included with each set of static loads. This was done by using the Static Analysis with Inertia Relief solution included in NASTRAN. The stress redistribution around cutouts in the hull was treated in a separate study. The interaction between hull and deckhouse was investigated by attaching a model of the deckhouse onto the hull model, and then solving for the appropriate load conditions. The natural frequencies were obtained using a reduced finite-element model of both the hull and hull/deckhouse combination. A new technique was developed for determining the dynamic stresses and their proper superposition on the static stresses.
A Numerical Nonlinear Method of Sloshing in Tanks with Two-Dimensional Flow
Authors: Faltinsen Odd M.
Published: January 2021

A numerical method for the study of sloshing in tanks with two-dimensional flow is presented. The solution satisfies the exact nonlinear free-surface conditions. To avoid difficulties with transients, artificial damping is introduced. Comparison with a linear analytical solution, derived in this publication, shows that the numerical method gives reasonable results. Comparison with an approximate nonlinear analytical method, derived earlier by the author, indicates that the artificial damping leads to difficulties in special cases.
Computation of the Hydrodynamic Forces Induced by General Vibration of Cylinders
Authors: Webster William C.
Published: January 2021

The hydrodynamic pressures created by the arbitrary deformation around the girth of a two-dimensional section are computed in a form suitable for finite-element structural analysis. The computations are based on the panel method developed by Frank (1976) for determining the hydrodynamic forces on rigid sections. In this method the section is approximated by straight-line segments on each of which source singularities of constant strength are distributed. The source strengths are determined by matching the kinematic boundary condition at the center of each panel. Frank's method is extended to treat nonrigid-body deformations of an infinite cylinder, including deformations which are also periodically varying in the longitudinal direction. The results show that these hydrodynamic pressures are quite dependent on the shape of the deformation pattern and are extremely sensitive to the longitudinal periodicity.
Dynamic Variational Principles for Discontinuous Elastic Fields
Authors: Dökmeci M. Cengiz
Published: January 2021

Various forms of variational principles are derived for the three-dimensional theory of elastodynamics. The continuity requirements on the fields of stresses or strains and/or displacements are relaxed through Friedrichs's transformation. Thus, the generalized forms of certain types of earlier variational principles' are systematically constructed using a basic principle of physics. The variational principles derived herein are shown to generate, as the appropriate Euler equations, the complete set of the governing equations of linear elastodynamics, that is, the stress equations of motion, the strain displacement relations, the mixed natural boundary conditions, the constitutive equations, the natural initial conditions, and the jump conditions. Similarly, generalized variational principles are established for the nonlinear theory of elastodynamics, for the incremental motions in linear elasticity, and for an elastic Cosserat continuum, as well.
The Diffraction Forces for a Ship Moving in Oblique Seas
Authors: Troesch Armin Walter
Published: January 2021

The diffraction problem of a fixed slender ship moving in incident waves is formulated. The waves are assumed to be of the same order as the beam of the ship and are from an oblique heading. The boundary value problem is linearized with respect to wave amplitude and solved by the method of matched asymptotic expansions. The oscillating forward-speed potential is solved to two orders of magnitude. The first order is just the zero-speed case while the second-order problem involves solving a boundary-value problem with a nonhomogeneous free-surface condition. The solution to this second-order problem is given in terms of three auxiliary potentials, each satisfying a separate part of the boundary conditions. For zero forward speed, the sectional exciting force is calculated and compared with the commonly used integrand of the Khaskind relations. The two give different values, but when integrated over the hull both show the same total exciting force. The pressure distribution on an ore carrier for both zero forward speed and an abbreviated form of the forward-speed case is given and compared with experiments.
Influence of Surface Irregularities on Cavitation Performance
Authors: Arndt R.E.A. , Holl J.W. , Bohn J.C. , Bechtel W.T.
Published: January 2021

The problem of surface finish and its influence on cavitation inception is reviewed in terms of both theoretical aspects and practical implications. A field study indicates that the roughness problem may be brokendown into two categories, namely, isolated asperities and distributed roughness. All the available data for isolated asperities are collated into a single equation involving Reynolds number and relative roughness height. The effects of distributed roughness are linearly proportional to the local skin friction coefficient. New data are presented for slots and wire screen roughness. The use of the collated data is illustrated by several examples.
Memory Effects in Deepwater Maneuvering
Authors: Scragg Carl A.
Published: January 2021

This paper discusses the error introduced into maneuvering predictions by the use of a set of linearized equations of motion which ignore memory effects. After incorporating certain improvements into the impulse-response technique for the determination of hydrodynamic coefficients, experiments were conducted to measure a complete set of the coefficients. Maneuvering predictions were then made using two different sets of linearized equations of motion, one of which included memory effects and one which excluded memory effects. It was determined that significant errors occurred only during the initial phase of the maneuver, and that memory effects could be safely ignored for most deepwater maneuvering problems.