bluuebunny/crossref_metadata_2025 huggingface dataset:
An Analysis of the Quadratic Frequency Response for Added Resistance
Authors: Dalzell J. F. , Kim C. H.
Published: January 2021

The objective of the present work was to extend existing hydrodynamic theory for ship resistance added by waves to include time-dependent fluctuations, so that the so-called "quadratic frequency response function" for added resistance could be computed and compared with previously obtained experimental estimates. The concept of a quadratic frequency response function follows from the (nonphysical) theory for the general functional polynomial input-output model which was utilized in the previous experimental work. It was hoped that the present work, by providing a physical model, would either lend credibility to the previous work or expose its shortcomings. In the event, the present work appears to have accomplished both. Analytical and experimental estimates of the quadratic frequency response function are in good qualitative agreement, and in fair quantitative agreement. Most of those experimental estimates which appeared in the previous work to be of at least slightly dubious statistical merit have been discredited. Since it was these marginal experimental estimates which gave rise to the speculation that the quadratic frequency response function was inordinately complicated, the present work indicates that the function is merely, moderately complicated. There seems reasonable evidence that it is feasible to make hydrodynamic estimates of the quadratic frequency response function required for prediction of nonlinear fluctuations of resistance in random seas.
Wing Sections for Hydrofoils—Part 1: Symmetrical Profiles
Authors: Eppler Richard , Shen Young T.
Published: January 2021

NACA 16-series wing sections have been extensively applied to U.S. hydrofoil craft. However, this series of wing sections was developed around 1940. Since then new airfoil sections have been continuously investigated both theoretically and experimentally. By means of recently developed methods of calculation for boundary-layer and profile theory, it is possible to determine, in a simple way, profiles with fixed characteristics of pressure distributions and to carry out boundary-layer calculations. Three classes of new wing sections with improved hydrodynamic characteristics in terms of cavitation inception have been successfully developed. It is shown that each series of profiles has its own merit. The choice of a wing section can be made only when the operational requirements of the craft are specified.
Momentum Theory of a Propeller in a Shear Flow
Authors: Goodman Theodore R.
Published: January 2021

The momentum theory of moderately loaded propellers has been generalized to account for the effects of shear in the oncoming stream. A condition to determine the distribution of thrust for optimum efficiency is derived which generalizes a condition derived by Betz for a propeller in a uniform flow. This condition leads to a nonlinear integral equation, and a computer program has been developed for solving it. Results for a propeller of a given radius in particular wakes at different Reynolds numbers are presented and discussed.
A Model of an Axisymmetrical Ducted Propeller with Zero Tip Clearance
Authors: George Monir F.
Published: January 2021

This paper is concerned with the case of a propeller working inside a symmetrical duct of finite length, zero thickness, zero camber and zero tip clearance. The propeller is modeled by the well-known Lerbs lifting-line theory while its radial circulation distribution is represented by a double Fourier series which allows for a nonzero circulation to occur at the blade tip. At the same time the duct circulation is considered to vary axially and circumferentially, which results in a system of longitudinal vortex filaments shed from each point on the duct surface. A comparison is made between the present method and the more sophisticated Tachmindji potential theory and the agreement is very good. Comparison is also made between the ducted and free-running (open) propeller.
An Extended Linearized Inverse Theory for Fully Cavitating Hydrofoil Section Design
Authors: Parkin Blaine R. , Fernandez Joe
Published: January 2021

A new design theory for fully cavitating hydrofoils is based upon a linearized inverse theory of two-dimensional cavity flows at arbitrary cavitation number. The cavity surfaces are assumed to originate at the leading and trailing edges of the wetted surface. This paper reviews and completes the basic theory, which leads to a parametric design technique. In the resulting design procedure, one specifies the design lift coefficient, the cavitation number and the upper cavity thickness at two points along the profile chord. A prescribed pressure distribution shape is also selected. These quantities determine the profilelesgn, which consists of the upper cavity and wetted surface contours, the design angle of attack, the cavity length, the drag coefficient, the moment coefficient and the lift-to-drag ratio. The chief new feature of the third design procedure is that the designer can now prescribe two points on the cavity surface instead of one as heretofore. Although the designer must observe certain constraints when he specifies these two values of cavity thickness, the new procedure is still found to be more general and more flexible than design procedures studied previously.
Hydrodynamic Trends from a Generalized Design Procedure for Fully Cavitating Hydrofoil Sections
Authors: Parkin Blaine R. , Fernandez Joe
Published: January 2021

An extended design procedure for fully cavitating hydrofoils is based upon a linearized inverse theory of two-dimensional cavity flows at arbitrary cavitation number. The cavity surfaces are assumed to originate at the leading and trailing edges of the wetted surface. This paper completes the basic theory and gives detailed examples obtained from the resulting parametric design technique. In this procedure, one specifies the design lift coefficient, the cavitation number and the upper cavity thickness at two points along the profile chord. A prescribed pressure distribution shape is also selected. These quantities determine the profile design, which consists of the upper cavity and wetted surface contours, the design angle of attack, the cavity length, the drag coefficient, the moment coefficient and the lift-to-drag ratio. The method also includes off-design calculations in accordance with the direct theory of cavity flows, which determines the flow states for which interference can occur between the upper surface of the cavity and the upper nonwetted surface of the profile. The hydrodynamic performance of specific "point designs" is also given by these direct calculations. The chief new feature of the generalized design procedure is that it gives a designer the ability to prescribe two points on the cavity surface instead of one as heretofore. Although certain constraints must be observed by the designer when specifying these two values of cavity thickness, the third procedure is found to be more general and more flexible than design procedures studied previously. The necessary constraints are incorporated in the computer logic for the method. The fact that linearized theory is used tends to limit the applicability of the method to conceptual design and feasibility studies. The computer program for the procedure has been found to be economical and well suited for its intended purpose.
Lateral Forces on a Ship Approaching a Vertical Wall: A Theoretical Model
Authors: Hess Felix
Published: January 2021

This paper deals with the unsteady hydrodynamic problem of a ship approaching a vertical wall on an oblique course. The ship is considered as a slender body with a trailing edge. The sway force and yaw moment acting on the ship are computed for various water depths and heading angles. The main result of this theoretical study is that generally the force is directed toward the wall and the moment tends to turn the bow away from the wall.
On the Velocity Induced by a Vortex Elliptic Cylinder
Authors: George Monir F.
Published: January 2021

Exact analytic expressions are presented for the induced velocity components at any field point due to a single vortex ellipse and due to a vortex elliptic cylinder of uniform strength with a finite and a semi-infinite length. The elliptic cylinder is assumed to deviate very little from the reference circular cylinder. Comparison is made between the derived expressions and those due to a semi-infinite vortex circular cylinder, and sample calculations are presented. This investigation has a direct application to the case of nonaxisymmetric annular aerofoils of elliptic cross sections.
A Comparison of Theoretical and Experimental Pressure Distributions on Bodies of Revolution
Authors: Smits A. J. , Law S. P. , Joubert P. N.
Published: January 2021

A wide range of experimental pressure distributions along axisymmetric bodies was compared with the results of Landweber's potential flow calculation method. Apart from certain viscous effects, some discrepancies were found, and it is shown that blockage corrections are of the right order to account for these discrepancies. The calculation method was also used to show that the pressure distribution over the nose of the body is largely independent of the tail shape, and vice versa.
Ship Centerplane Source Distribution
Authors: Miloh T. , Landweber L.
Published: January 2021

A procedure for calculating the irrotational flow about a double ship model, by solving a Fredholm integral equation of the first kind for a centerplane source distribution, is described. The special problems of determining the curve in the centerplane bounding the source distribution and of smoothing sharply peaking inte-grands, to improve the accuracy of discretization of the integral equation, are treated. Application to ellipsoids, for which the results of the calculations can be compared with an exact solution, and to a ship form with parabolic lines, for which experimental data are available for comparison, indicate that satisfactory accuracy can be obtained by the method. A justification for using a centerplane distribution is that, as is shown, a line integral which appears in the higher-order solution for the flow about a ship form at nonzero Froude numbers can be avoided with such a distribution.
A Linear Theory of Springing
Authors: Skjørdal Svein O. , Faltinsen Odd M.
Published: January 2021

A linear slender-body theory of springing is derived. The wave excitation loads are calculated by a generalization of the short-wavelength theory of Faltinsen. A Green's function approach is used to find the pressure distribution. Numerical results are compared with experimental results of Wereldsma and Moeyes. The "forced-motion loads" are obtained by a generalization of the Ogilvie and Tuck approach for forced heave and pitch motions. Discrepancies with other methods are discussed. Numerical results of springing are presented.
An Experimental Investigation of Wall Effects on Supercavitating Hydrofoils of Finite Span
Authors: Maixner Michael R. , Leehey Patrick
Published: January 2021

A geometrically similar family of three half-span, elliptical-planform, supercavitating hydrofoils was tested in the M.I.T. variable-pressure water tunnel. Lift, drag, moment, tunnel speed, ambient pressure, cavity pressure and cavity length were measured for attack angles from 8 to 21 deg and a variety of ambient pressure settings. For the small and medium foils, it was sufficient to correct only for the effect on downwash of the images of the trailing vortices. The large foil data, however, required further correction; the corrected force and moment data for the large foil plotted slightly lower than did the data for the two smaller foils, while the cavity length data for the large foil indicated cavity lengths significantly larger than theoretical predictions or the cavity length data for the two smaller foils. Existing two-dimensional corrections may be used to bring the force data for the large foil into close agreement with the force data for the two smaller foils, but no correction factors exist for the cavity length data.
Leading-Edge Flutter of Supercavitating Hydrofoils
Authors: Brennen C. , Oey K. T. , Babcock C. D.
Published: January 2021

This paper presents the results of experiments and analysis of the phenomenon of leading-edge flutter which has been observed to occur for supercavitating hydrofoils. The experiments confirmed the existence of such a single-degree-of-freedom flutter involving chordwise bending and indicated that for long, natural (or vapor-filled) cavities the reduced flutter speed, UF/ωFc, was in the range 0.15 to 0.23. Secondary effects observed were the variation with the angle of attack (a minimum flutter speed occurred at 10 deg) and with a foil mass ratio. Shorter cavities typically yielded lower flutter speeds due to a complex interaction between the bubble collapse process occurring in the cavity closure region and the unsteady hydrodynamic load on the foil. Finally, a relatively simple theoretical analysis for supercavitating hydrofoils with elastic axes aft of midchord is presented. This linear analysis yields reduced flutter velocities somewhat lower than those observed.
Ship Vibrations in Random Seas
Authors: Chen Yung-Hsiang
Published: January 2021

A general analysis of ship dynamics in random seas is presented. The analysis covers the steady-state wave-induced response and the transient-state slam-induced (whipping) response. Wave-induced response includes both the rigid-body modes (seakeeping) and the hull flexural modes (springing). The strip theory by Salvesen, Tuck, and Faltinsen is used to determine the hydrodynamic forces. The ship structure is idealized by finite beam elements with the lumped-parameter system. The normal-mode approach is used to calculate the vibration characteristics and dynamic responses. Statistics of both wave-induced loads and responses are characterized by zero-mean Gaussian processes. By spectral analysis, the wave-induced responses can be predicted for a ship moving in random seas. The slamming impacts as the input to the ship are treated as a nonstationary filtered Poisson process. The output slam-induced (whipping) response process can be determined by passing such a nonstationary process through the time-invariant ship system or by using a Markov process. Two ship examples are studied. The 1000-ft (305 m) Great Lakes ore carrier Stewart J. Cort is used for the calculation of the wave-induced response, and the 525-ft (160 m) SS Gopher Mariner is used for the calculation of the slam-induced (whipping) response.
Simple Calculation of Sheltering Effect on Ship-Wave Resistance and Bulbous Bow Design
Authors: Yim B.
Published: January 2021

The sheltering effect on the ship wave resistance is treated by the free-surface pressure distribution inside the ship. The theory is developed and the numerical values of wave resistance are obtained for parabolic and sinusoidal hulls. The corrected wave resistance is shown to be reduced more than 20 percent from the Michell's wave resistance even for a Wigley hull with beam-length ratio 0.1. However, the humps and hollows of wave resistance still remain with the magnitude closer to the experimental results. The optimum volume of bulb for sinusoidal ships is also shown to be reduced from 7.6 percent to 18 percent of the values without sheltering effect for the range of Froude numbers from 0.15 to 0.35.
Some Comments on Certain Idealized Variance Spectra of the Seaway Currently in Fashion
Authors: St. Denis Manley
Published: January 2021

The purpose of this note is to offer some comments on the variance spectra of seaways of the type which includes, among others, the Pierson-Moskowitz, Bretschneider and International Ship Structures Congress spectra, and on related aspects which enter into the prediction of the short-term statistics of a steady seaway. More specifically, the intent is to bring out an inconsistency which, even if not necessarily serious, is, nevertheless, present when the variance spectrum describing the seaway contains the factor T3 or or-5, where T and ω are, respectively, spectral period and frequency. A partial solution is suggested which, although as yet wanting in accuracy because of the paucity of supporting experimental data, removes the inconsistency and yields somewhat more plausible outputs. However, there still remains a point to be clarified with respect to the so called spectral width parameter ϵ.
Sway, Roll, and Yaw Motion Coefficients Based on a Forward-Speed Slender-Body Theory—Part 2
Authors: Troesch Armin Walter
Published: January 2021

A comparison between theory and experiment is given for the roll-sway, sway-yaw added-mass, and damping coupling coefficients. The theory was derived by Troesch (1980), who followed an approach similar to that given by Ogilvie and Tuck (1969) for the heave and pitch coefficients. The experiments were presented by the Society of Ship Research of Japan in 1976.
Nonlinear Theory of Ship Maneuvering
Authors: Guo Chorng-Lin S.
Published: January 2021

A nonlinear theory of ship maneuvering, based upon the hydrodynamics of arbitrary small motions superimposed upon a constant forward speed, is developed. The problem is formulated as an initial-value problem for the velocity potential expanded in perturbation series in two parameters, ɛs and ɛm, representing the ship thinness or slenderness and its motion, respectively. The various potentials are found as solutions of integral equations constructed using the time-dependent Green function and they exhibit, therefore, memory effects. Then the complete rigid-body equations of motion of the ship are adjoined, resulting in a set of integro-differential equations for the motions. Numerical calculations for the determination of the kernel functions and coefficients occurring in the ship maneuvering equations, by slender-body theory that still includes the forward-speed effect, are made in both time and frequency domains. Complete space-time hydrodynamic force functions for Series 60 Cb = 0.60 have been calculated. Comparison between computed results and existing experimental data shows generally satisfactory agreement.
Analysis of the Torsional Response of the SL-7 Hull Structure by Use of the Finite-Beam Technique and Comparison with Other Techniques
Authors: Westin Hakan
Published: January 2021

A technique for analyzing a nonprismatic beam girder by subdividing it into a number of prismatic finite-beam elements, abbreviated herein as the FB-technique, is used for torsional analysis of the SL-7 containerships hull structure. Comparison with earlier model tests and finite-element (FE) calculations is done and in general a close agreement with the results obtained earlier is found.
An Analysis of the Quadratic Frequency Response for Lateral Drifting Force and Moment
Authors: Kim C. H. , Dalzell J. F.
Published: January 2021

Results of calculations are given for lateral drifting forces acting on a cylinder and a Series 60 hull derived by a new procedure involving application of the quadratic frequency response function (QFRF) and the close-fit method for flows induced by hull sections in the near field. The near-field solutions are required by the QFRF in order to obtain the nonlinear (second order) interaction effects in the presence of dual waves. This method yields the mean drifting force consisting of four components of which the relative wave-elevation term is dominant, whereas the Bernoulli quadratic term is secondary. A mathematical discontinuity of the drifting force in the neighborhood of a high frequency is investigated by applying a modified Green's function. Mean drifting forces for two forms have been calculated and the results compared with available analysis and model data. A fairly complete quadratic frequency response function for lateral drifting forces in the bifrequency domain was computed for the Series 60, CB = 0.6 ship at 60-deg heading. The computed results are presented in a three-dimensional view accompanied by a detailed discussion of the characteristic behavior.
Nonlinear Analysis of Slow Drift Oscillations of Moored Vessels in Random Seas
Authors: Roberts J. B.
Published: January 2021

A theoretical model is proposed for a moored vessel, with nonlinear restoring forces, responding to random waves. The model takes into account the nonlinear nature of the relationship between wave elevations and wave forces. Fokker-Planck equations are derived for the distribution of the amplitude response of the vessel. By simplifying these equations, with the introduction of a white noise approximation for the force process, an expression is obtained for the stationary amplitude distribution. The accuracy of this approximate result is assessed by a comparison with corresponding digital simulation estimates.
Design of Laterally Loaded Plating—Uniform Pressure Loads
Authors: Hughes Owen F.
Published: January 2021

An explicit formula is presented for the design of welded steel plates subjected to uniform lateral pressure, on the basis of a designer-specified level of acceptable permanent set, including that due to welding. The formula is derived from a combination of theoretical and experimental studies and shows good agreement with experimental results. For the convenience of designers the formula is also given in the form of design curves. The paper also delineates the areas of application of this and other formulas for laterally loaded plating. In brief, the paper shows that for static and quasistatic loads the formula derived herein is more accurate than formulas based on either the pseudo-elastic or the rigid-plastic approach. As the load becomes more dynamic the rigid-plastic approach becomes more appropriate, and for high-speed impact loads the rigid-plastic approach is best. For quasistatic loads, such as slamming, the formula presented herein is somewhat conservative while the rigid-plastic formulas are somewhat optimistic. A similar formula for concentrated loads (such as wheel loads) will be presented in a subsequent paper.
From Bulbous Bow to Free-Surface Shock Wave—Trends of 20 Years’ Research on Ship Waves at the Tokyo University Tank
Authors: Inui Takao
Published: January 2021

Trends of 20 years' research on ship waves at the Tokyo University Tank since 1960 are briefly sketched. Stress is focused on the importance of dialogues between man and nature. The process of these dialogues is exemplified by some typical cases, including the development of bulbous bows and the finding of free-surface shock waves. Wave-pattern pictures are shown to be indispensable for the initial stage of the di alogues, while wave contours and velocity-field measurements serve well in the second stage. The current wave analysis and wake survey may be the third. The relationship between "wavebreaking" and the "free-surface shock wave" is also discussed.
Linearized Stern Flow of a Two-Dimensional Shallow-Draft Ship
Authors: Schmidt G. H.
Published: January 2021

Using a linearized theory we investigate the flow at the stern of a two-dimensional ship. The ship is assumed to be infinitely long in the upstream direction. A method for the location of the point of separation is described. An explicit expression is derived for the amplitude and phase of the wave in the wake. Then, conditions on the shape of a stern which leaves no wave in the wake are given. Some of the results may be applicable to bow-flow as well.
Application of a Discrete Vortex, Source Distribution Model to Propeller Cavitation
Authors: Frydenlund O. , Persson B.
Published: January 2021

A linearized theory for the calculation of cavitation on a propeller in homogeneous flow is presented. The method enables a direct solution of the equations describing sheet cavitation on a propeller blade to be obtained without resorting to intermediate solutions of the fully wetted case. Good agreement is found between the computed extent of cavitation and the extent found in model experiments. The method shows a substantial improvement compared with other prediction methods where the determination of the cavity extent is based on the pressure distribution for the noncavitating case. Also shown is a comparison between computed and measured cavity shapes.
Strength of Bottom Plating of Yachts
Authors: Joubert P. N.
Published: January 2021

There are no studies available dealing directly with pressures on the bottom plating of yachts. By analyzing the loads required to deform the bottom plating, it is possible to gain some idea of the values of these pressures. Seven cases of yachts which suffered either deformations or failures are examined. It is concluded that bottom pressures experienced by yachts of 40 ft overall length when beating to windward in a gale may be as large as 80 psi.
A Correlation of Various Impact Properties of ABS Grade CS Steel
Authors: Opoku Justin , Arbiter William
Published: January 2021

Results of a study to evaluate the impact properties of ABS Grade CS steel are presented. Twelve plates of the material from seven different heats and of two different thicknesses were tested by drop weight, dynamic tear, and Charpy V-notch impact testing. The nil-ductility temperatures of the plates ranged from —57 to —34°C (—70 to —30°F). The plates showed considerable anisotropy in impact properties due to microstructural directionality. It has been found that empirical correlations exist between impact data obtained from transverse specimens of the various tests.
A Boundary-Element Method for Slamming Analysis
Authors: Geers Thomas L.
Published: January 2021

A boundary-element method for treatment of the fluid-structure interaction in slamming analysis is described. The method emphasizes simplicity and efficiency, so that the analyst may devote most of his computational resources to the analysis of the structure. Numerical results for a number of rigid-impactor problems are compared with analytical solutions and experimental data, and procedures for the finite-element analysis of flexible impactors are discussed.
Optimal Performance of Ships Under Combined Power and Sail
Authors: Letcher John S.
Published: January 2021

A simplified hydrodynamic and economic model is developed to describe the operation of a ship equipped with both sails and engine. In the range of light-to-moderate winds in which use of the engine is likely to be economical, the vessel is described by a characteristic speed, a characteristic fixed-cost rate, and five dimensionless parameters (four hydrodynamic, one economic). The model includes simultaneous optimization of three control variables: sail lift, throttle setting, and course angle; optimal setting of variable draft devices can be included optionally. Although no analytic solutions are attained, the simultaneous equations expressing minimization of cost per mile made good are set up, and a general algorithm is given for numerical solution of these problems. As an illustrative example, numerical values are worked out for the 30,000-dwt square-rigged bulk cargo ship from the 1975 University of Michigan study.
Effect of Parametric Excitation on Ship Rolling Motion in Random Waves
Authors: Roberts J. B.
Published: January 2021

An equation of motion for uncoupled ship rolling motion in irregular seas is considered in which parametric excitation, arising from the time dependence of the restoring moment, is included. It is shown that, when the damping is light, the method of stochastic averaging can be applied to yield an approximate Markov model for the rolling motion. Appropriate Fokker-Planck equations are given from which some simple expressions for the stationary response distribution are derived. For the case of linear damping it is found that the motion is unstable if the damping factor is sufficiently small. The inclusion of a quadratic damping term in the equation of motion is shown to limit the unstable motion predicted by the linear theory. Explicit expressions for the distribution of the roll response are derived for the case of combined linear and quadratic damping. The case of purely parametric excitation is considered in some detail.
Shock-Excited Vibrations with Application to the Slamming Response of a Flexible Ship to a Regular Wave Packet
Authors: Suhir Ephraim
Published: January 2021

Deterministic and probabilistic approaches to the problem of transient and steady-state linear oscillations of a one-degree-of-freedom system, subjected to repetitive shock loads, are developed. The case of the slamming response of a flexible ship hull to a regular wave packet is used to illustrate and to compare both techniques. It is concluded that the probabilistic approach is the more realistic when choosing guidelines for prediction and standardization of overall ship strength with consideration of slamming.
Optimal Self-Propulsion of a Deformable Prolate Spheroid
Authors: Miloh T.
Published: January 2021

The problem of self-propulsion of an elongated deformable body moving in an infinite medium of inviscid fluid is considered in some detail. A prolate spheroid is chosen as a model shape, and a particular deformation pattern which maximizes the Froude efficiency is sought. The Froude efficiency in this context is defined by the ratio of the kinetic energy of the body to the total kinetic energy of the system comprising the body and the fluid. It is demonstrated that a body can propel itself from rest in a persistent manner even for a periodic surface deformation with zero mean which preserves both the volume and the location of its centroid. Under these constraints the induced forward velocity of the body is of 0(ε2) where ε is the amplitude of the deformation velocity. It is also demonstrated that for a persistent self-propulsion to exist the body should develop a large degree of skewness, resulting from the interaction between the two deformation components—one with fore-and-aft symmetry and one without. It is also essential that the symmetric and asymmetric deformation components should be out of phase.
Curve Fit and Form Design Procedure Using Rotated Parabolas
Authors: Myrianthis C.
Published: January 2021

A method for curve fitting and form design using rotated second-order polynomial segments is presented. The segments, which are referred to axes of common origin but different rotation, are generated to connect known adjoining data points with slope conditions imposed where necessary. The use of second-order polynomials precludes the possibility of oscillations and it is shown how the number of data points required for any segment is related to the requirements imposed at the segment. The resulting smooth curve fit can represent a wide variety of shapes within the overall curve and permit the presence of discontinuities. The method is thus versatile and flexible and can be used for form design purposes. Applications of the method are given using a digital computer program. Future development and elaboration are discussed and reference is made to interactive applications.
Prediction of Steady and Unsteady Loads and Hydrodynamic Forces on Counterrotating Propellers
Authors: Tsakonas S. , Jacobs W. R. , Liao P.
Published: January 2021

Linearized unsteady-lifting-surface theory has been applied in the study of counterrotating propeller systems with equal or unequal number of blades operating in uniform or nonuniform inflow fields when both units are rotating with the same rpm. The mathematical model takes into account as realistically as possible the geometry of the propulsive device, the mutual interaction of both units and the three-dimensional spatially varying inflow field. The propeller blades lie on a helicoidal surface of varying pitch, have finite thickness and arbitrary planform, camber and sweep angle. The inflow field of the after propeller is modified by taking into account the effect of the race of the forward propeller, so that potential and viscous effects of the forward propeller are incorporated. These additional effects play an important role in determining the unsteady loading of the after propeller. This, together with some refinements introduced in the numerical procedure, has brought the theoretical results into better agreement with experiments. A computer program has been developed adaptable to a high-speed digital computer (CDC 6600-7600, Cyber 176) for counterrotating systems of equal and unequal number of blades, in uniform flow, for comparison with existing experiments.
Design of Laterally Loaded Plating—Concentrated Loads
Authors: Hughes Owen
Published: January 2021

In the design of plating subject to lateral loading, the principal load effect to be considered is the amount of permanent set, that is, the maximum permanent deflection in the center of each panel of plating bounded by the stiffeners and the crossbeams. The present paper is complementary to a previous paper [1]2 which dealt with uniform pressure loads. It first shows that for design purposes there are two types of concentrated loads, depending on the number of different locations in which they can occur; single location or multiple location. The hypothesis is then made that for multiple-location loads the eventual and stationary pattern of plasticity which is developed in the plating is very similar to that for uniform pressure loads, and hence the value of permanent set may be obtained by using the same formula as for uniform pressure loads, with a load parameter Q that is some multiple r of the load parameter for the concentrated load: 0 = rQP. The value of r is a function of the degree of concentration of the load and is almost independent of plate slenderness and aspect ratio. The general mathematical character of this function is established from first principles and from an analysis of the permanent set caused by a multiple-location point load acting on a long plate. The results of this theoretical analysis provide good support for the hypothesis, as do also the relatively limited experimental data which are available. The theory and the experimental data are combined to obtain a simple mathematical expression for r. A more precise expression can be obtained after further experiments have been performed with more highly concentrated loads. Single-location loads produce a different pattern of plasticity and require a different approach. A suitable design formula is developed herein by performing regression analysis on the data from a set of experiments performed with such loads. Both methods presented herein, one for multiple-location loads and the other for single-location loads, are valid for small and moderate values of permanent set and can be used for all static and quasistatic loads. Dynamic loads and applications involving large amounts of permanent set require formulas based on rigid-plastic theory. Such formulas are available for uniform pressure loads and were quoted in reference [1]. A formula for single-location loads has recently been derived by Kling [4] and is quoted herein.
Increase of Warping Rigidity in Open Sections of a Containership by Stiffening Plates
Authors: Pan Yong Hao , Lu Sung Y.
Published: January 2021

Distributions of warping stress and deformation of modules with open-section and longitudinal stiffening plates were determined by a finite-element program. Eleven models of various stiffnesses and configuration but under the same torsional moment were studied. The loading and overall hull size are close to a containership of 38 000-ton loading capacity. The prismatic thin-walled beam analysis was performed on a model to compare the results from the finite-element approach. It has been found that the warping rigidity can be effectively increased by installing plates along the axis of the ship. The maximum warping stresses, which are usually found at the hatch corners of the wing boxes, are evaluated and compared.
Application of Finite-Element Method to Interstiffener Buckling in Submersible Cylindrical Hulls
Authors: Rajagopalan K. , Chettiar C. Ganapathy
Published: January 2021

A finite-element procedure for the determination of buckling pressure of thin-walled cylindrical shells used in ocean structures is presented. The derivation of the elastic and geometric stiffness matrices is discussed in detail followed by a succinct description of the computer program developed by the authors during the course of this study for the determination of the buckling pressure. Particular attention is paid to the boundary conditions which strongly influence the buckling pressure. Applications involving the interstiffener buckling in submersible hulls and cylindrical shells with stepwise variation in wall thickness are considered and the results compared with the solutions and procedures available in the literature.
On the Shape of Post-Welding Deformations of Plate Panels in Newly Built Ships
Authors: Antoniou A. C. , Lavidas M. , Karvounis G.
Published: January 2021

The paper presents the results of an investigation carried out on nearly 700 plate panels in newly built ships and marine structures to establish the actual deformation shape of the panels, due to welding. The ultimate purpose of the research was to describe the deformation by a two-dimensional Fourier series, examine the statistical distribution of the Fourier series coefficients, and relate the coefficients to the principal welding or geometrical parameters. In view of the influence of the buckling mode component on the strength characteristics of the plate, a statistical relationship between the maximum welding distortion and the magnitude of the primary buckling mode component has been obtained, and limiting values of welding deformations, based on the primary buckling mode component, have been suggested.
The Diffraction of Free-Surface Waves by a Slender Ship
Authors: Sclavounos P. D.
Published: January 2021

A linear theory is presented for the scattering of small-amplitude monochromatic and unidirectional free-surface waves by a ship fixed at its mean advancing position. In an inner region close to the ship the hull geometrical slenderness is used to justify a quasi-two-dimensional approximation of the flow. The method of matched asymptotic expansions is then introduced to enforce the compatibility of the inner solution with the three-dimensional solution in the far field. The theory is shown to be uniformly valid for all wavelengths of practical interest and all angles of wave incidence. In the short-wavelength limit, existing theories are recovered and the singularity that is present in the limit from oblique to head incidence is removed. Computations are included for the pressure and the sectional exciting force distributions, the wave elevation, and the vertical exciting force and moment in head and bow waves on a prolate spheroid.
A Numerical Solution of Two-Dimensional Deep Water Wave-Body Problems
Authors: Nestegard A. , Sclavounos P. D.
Published: January 2021

A numerical technique is presented for the solution of deep water linear and time-harmonic wave-body-interaction problems in two dimensions. A mathematical boundary of circular shape surrounding the body is introduced in the fluid domain, thus defining two flow regions. A multipole expansion valid in the outer region is then matched to an integral representation of the solution in the inner region which is obtained by applying Green's theorem and by using the fundamental logarithmic singularity as the Green function. The method applies both to surface-piercing and submerged bodies. Numerical results are presented for the forced oscillations of three surface-piercing ship-like sections of regular shape. No irregular frequencies are encountered. Comparisons with existing numerical methods are made to test the accuracy and emphasize the computational efficiency of the present approach.
Vibration Force Reducer—and a New Approach to Ship Vibration
Authors: Ojak W.
Published: January 2021

The main reasons for excessive vibrations commonly occurring in modern ships are hydrodynamic pressures due to a cavitating propeller. These types of vibrations are difficult and time-consuming to evaluate, and expensive to suppress. More than 20 years of practical experience with different ships investigated by the author have resulted in a novel approach to the problem of ship vibrations. From the shipyard viewpoint it would be very convenient and desirable to have some simple mechanical means for the abatement of ship vibrations. It is the author's conclusion that it is possible to build such a simple and practical device. The device, which this paper describes, is referred to as the Vibration Force Reducer (VFR). It could be installed on a ship if required, and by a simple process of VFR tuning the undesirable ship vibrations can be minimized for any given rpm.
Wave-Induced Hull Vibrations: An Experimental and Theoretical Study
Authors: Troesch Armin W.
Published: January 2021

The results of an experimental and theoretical study investigating the main hull girder vibrations of Great Lakes bulk carriers are presented. The source of the excitation is considered to be the incident waves. The emphasis of the work is to understand the hydrodynamic aspects of ship springing. Theoretical calculations based upon a short-wavelength assumption compare well with experiments.
Double-Precision Evaluation of the Oscillatory Source Potential
Authors: Newman J.
Published: January 2021

A table with double-precision accuracy is constructed for the three-dimensional source potential which occurs in the case of harmonic motion with zero forward-velocity beneath a linearized free surface. To facilitate the numerical integration, the source potential is expressed as the sum of a finite integral and of Bessel and Struve functions. Romberg quadrature is used to evaluate the finite integral, and the Bessel and Struve functions are evaluated by backward recursion.
A Note on the High-Frequency Limits of a Floating Body
Authors: Greenhow Martin
Published: January 2021

High-frequency limits of an oscillating body without forward speed are examined. Some previously known yet unexploited formulas based on the Kramers-Kronig relations are applied to Hulme's results for a heaving and swaying sphere in the free surface to give the high-frequency limit and asymptotic behavior of the added mass coefficients.
Theory and Application of Stage-by-Stage Evaluation for Steam Turbine State-Line
Authors: Latorre Robert , Mourelatos Zisimos , Nikolaidis Efstratios
Published: January 2021

A theoretical model of a steam turbine is formulated based on idealized Curtis and reaction stages to obtain expressions for a stage-by-stage evaluation of the turbine state line. Using typical stage geometries and corrections a computer program was developed to size the turbine and evaluate its state line at design conditions. A comparison of the heat balance made with the stage-by-stage state line and the standard heat balance is presented. For the design case of 30 000 shp it is shown that the differences in the heat balance calculation results are within ±0.5 percent.
Temperature Distribution During Plate Bending by Torch Flame Heating
Authors: Moshaiov A. , Latorre R.
Published: January 2021

The flame bending of metal hull plates involves a complex thermoplastic process. In order to investigate the thermoplastic behavior it is first necessary to determine the time-varying temperature field in the plate. In this paper the temperature distribution during flame bending of a plate is studied using a distributed heat source moving along the plate surface at a constant speed. The temperature distribution is determined by the numerical solution of the partial differential equation describing the heat conduction in the plate as the distributed heat source passes. The equation is solved using the finite-element program ADINAT in the transient analysis mode. A number of results are presented to illustrate the transient behavior of the temperature near the plate edge as well as the quasi-steady-state temperature distribution. The results are shown to be in qualitative agreement with published experimental data. Additional studies are presented to clarify the influence on the temperature distribution from different material parameters, torch parameters and plate thicknesses. The point heat source expression was modified following Iwasaki's approach [4]. The temperature distribution calculated from this modified expression is shown to be in agreement with the numerical results.
Forward-Speed Vertical Wave Exciting Forces on Ships
Authors: Sclavounos P. D.
Published: January 2021

Expressions are derived for the heave and pitch exciting force and moment on a ship advancing in waves. They are obtained in the form of an integral over the ship axis of the outer source strength of the reverse-flow radiation problem multiplied by the value of the incident-wave velocity potential. Their performance is tested for two slender spheroids. Comparisons are made with predictions obtained from a three-dimensional numerical solution at zero speed—the expression common to strip-theory programs which uses the ship hull as the integration surface—and the direct solution of the diffraction problem.
Waveless Free-Surface Pressure Distributions
Authors: Broeck J.-M. Vanden , Tuck E. O.
Published: January 2021

Linear and nonlinear studies are made of two-dimensional free-surface flows under gravity, in which a disturbance is caused to an otherwise uniform stream by a distribution of pressure over the free surface. In general, such a disturbance creates a system of trailing waves. There are special disturbances that do not, however, and some categories of such disturbances are discussed here. This work has potential applications to design of splashless ship bows.
Response to “Comments on the Low-Aspect-Ratio Unsteady Propeller Force Theory of N. A. Brown”
Authors: Brown Neal A.
Published: January 2021

A commentary has been recently published [1] (2) on the validity of the low-aspect-ratio (LAR) approximate method for the analysis and design of propellers working in spatially nonuniform inflows, as presented at " Propellers '81" [2] by the present author. In that paper the estimation method was developed upon a power series representation of the inflow harmonic distribution over the radial extent of the screw disk. In order to facilitate the method for the convenience of the user, a conversion to an inflow representation in terms of a series of orthogonal Legendre polynomials was tendered, and a set of precomputed coefficients, central to the method, were recast by the use of an intuitive algorithm. The main body of the paper contained formulations for the LAR methods in terms of these Legendre polynomial representations of the inflow.
Effect of Change of Load Direction on SCF for Optimized Quasi-Square Hole in Isotropic Plates
Authors: Naik N. K. , Rajaiah K.
Published: January 2021

Determination of optimum quasi-square hole shape with minimum stress concentration in isotropic plates under uniaxial inplane loading is an important engineering problem in ship design. For such an optimized hole, the tensile and compressive boundaries are respectively having constant stress values. It should be noted that optimized shapes apply only to the loading conditions and specified geometric constraints. In actual practice, if the load axis for the optimized hole is tilted, the stress concentrations on the hole boundary will be increased. It is observed that the load axis tilt angle β can be as large as 11 deg on tensile region and 17 deg on compressive region before the load axis tilting negates the gain due to hole shape optimization for uniaxial tensile loading compared with a circular hole.