bluuebunny/crossref_metadata_2025 huggingface dataset:
A Practical Method for the Rational Design of Ship Structures
Authors: Hughes Owen F. , Mistree Farrokh , Žanic Vedran
Published: January 2021

A practical, rationally based method is presented for the automated optimum design of ship structures. The method required the development of (a) a rapid, design-oriented finite-element program for the analysis of ship structures; (b) a comprehensive mathematical model for the evaluation of the capability of the structure; and (c) a cost-effective optimization algorithm for the solution of a large, highly constrained, nonlinear redesign problem. These developments have been incorporated into a program called SHIPOPT. The efficiency and robustness of the method is illustrated by using it to determine the optimum design of a complete cargo hold of a general-purpose cargo ship. The overall dimensions and the design loads are the same as those used in the design of the very successful SD14 series of ships. The redesign problem contains 94 variables, a nonlinear objective function, and over 500 constraints of which approximately half are non-linear. Program SHIPOPT required approximately eight minutes of central processing unit time on a CDC CYBER 171 to determine the optimum design.
The Use of Jet Injection to Produce Uniform Velocity in a High-Speed Water Channel
Authors: Millward A. , Nicholson K. , Preston J. H.
Published: January 2021

The paper describes a high-speed recirculating water channel which has been developed so that the flow in the working section is uniform and the water surface is flat and horizontal over a wide speed range, including the critical Froude number related to channel depth. The working section is 1.37 m wide, 0.84 m deep, and the speed can be varied from 0.03 m/s to 6.1 m/s, corresponding to a Froude number range of 0.01 to 2.12. A surface injection system has been developed to offset the momentum defect at the free surface caused by the boundary layer growing on the upper surface of the enclosed contraction. It is concluded that a surface injection system is necessary for the successful operation of any future water channel with an enclosed contraction.
Effect of Ship Stern Asymmetry on Propulsion Efficiency
Authors: Piskorz-Nalecki J.W.
Published: January 2021

The tendencies to reduce ship resistance and thus obtain fuel economy at a given speed and to reduce ship dimensions are more and more evident in the shipbuilding world. One of the ways of increasing propulsion efficiency is the use of asymmetric stern shapes. This paper presents proposed asymmetric stern shapes and results of model testing of two hulls with identical dimensions and block coefficients. The results of the detailed investigations show the differences in water velocity distribution and water flow characteristics for a propeller operating in two different wakes. It can be concluded that the author's idea of stern asymmetry gives positive results. The investigations are continuing in order to determine to what extent asymmetric stern shapes can be used in practice.
Some Experiments on Artificially Roughened Lucy Ashton Geosims
Authors: Smits A.J. , Matheson N. , Joubert P.N.
Published: January 2021

A mirror-image model of the Lucy Ashton was covered with two different "mesh-type" roughnesses and tested in a wind tunnel. Total drag and velocity profile measurements are presented. Total drag results are also given for a normal Lucy Ashton model with the same roughness mesh tested in a towing tank. The influence of roughness on the wave drag component was found to be small, implying that the "interdependence" of wavemaking and viscous resistance is small. The importance of considering roughness as a local parameter is demonstrated, and the roughness function results agree well with the fully developed turbulent pipe flow results of Perry and Abell, even though the ship boundary-layer outer flow did not follow any recognized wake function.
Continuous Digital Simulation of the Second-Order Slowly Varying Wave Drift Force
Authors: Oppenheim B. W. , Wilson P. A.
Published: January 2021

A discussion is given on practical aspects of digital representation in time of the slowly oscillatory second-order wave drift force from a known force spectrum. The emphasis is placed on the computational efficiency and on the suitability of the simulation to a numerical integration of an equation of motion using a variable integration step size, where the force acts as the excitation of motion. The effect of approximating the original spectrum by a white spectrum is discussed. A sensitivity analysis is made to the range of frequencies of the spectra. The force time record is obtained by first generating at equal time intervals a discrete time series which possesses the desired random characteristics, and then by extending the discrete series into a continuously available digital record using a sin(x)/x-type interpolation. Various numerical tests are illustrated with plots. Superiority of the fast Fourier transform over the cosine series is demonstrated in terms of the spectral contents preservation.
Discus Buoy Stability and the Spectrum of Steep Waves
Authors: Nath John H. , Chester Theodore , Bunney Robert E. , Brooks David M.
Published: January 2021

Thick discus buoys are used in the ocean as platforms from which oceanographic and meteorological measurements are made and reported to shore. The stability of these buoys is sensitive to steep breaking waves, and a few have capsized in the ocean from large breaking waves. This occurrence can be simulated in laboratory scale-model studies. Generally, in the laboratory, the buoys will not capsize for a breaking wave that is small relative to buoy diameter. The problem is predicting the probability of capsizing for engineering planning purposes. This paper describes how first approximations can be made from a combination of laboratory scale-model testing of buoy capsizings in random waves, a few reported occurrences of buoy capsizings in the open ocean, and the statistics of ocean waves. An estimate of the joint probability density distribution function of a wave steepness parameter and a wave height parameter is made from buoy motion measurements. It is found that in the northeastern Pacific Ocean the wave climate is quite severe and includes a large percentage of relatively large breaking waves. Under such circumstances, buoy diameters of 10 m have a relatively low reliability. The reliability increases rapidly as buoy diameter increases.
Large-Amplitude Motion of an Elongated Body in Shallow Water
Authors: Miloh Touvia , Hauptman Aharon
Published: January 2021

A large-amplitude motion of a body of revolution in shallow water is analyzed by assuming the bottom to be even and the Froude number to be large enough for the velocity potential to vanish on the undisturbed free surface. First, the classical Kirchhoff-Lagrange equations of motion are extended to the case of time-dependent added-mass and inertia coefficients. The hydrodynamical force and moment acting on the body are expressed in terms of these coefficients together with their partial derivatives with respect to the generalized coordinates of the body. It is demonstrated how these expressions can be applied for the case of a prolate spheroid maneuvering in shallow water, where useful analytical expressions for the hydrodynamical coefficients are also obtained. By employing the concept of "equivalent spheroid" it is also shown that these results are universal in the sense that they may serve as useful approximations for arbitrary smooth bodies with axial symmetry. The hydrodynamical coefficients are given as a product of two terms, one which depends on the geometry of the body and the second on the relative position of the body with respect to the free surface. Both analytical and graphical solutions for these two functions are presented herein and it is also suggested how these can be used for a large-amplitude motion of nonspheroidal bodies of revolution.
Spectral Theory of Water Waves
Authors: Magnuson Allen H.
Published: January 2021

Spectral theory is applied to elemental water wave problems for a compressible liquid. Compressibility is introduced primarily to facilitate the spectral representation. Two basic representations are developed. The first (Havelock) expansion is derived from a vertical (z) spectral integration while the second modified Fourier form or Fourier-Bessel form comes from the lateral (x or r) spectrum. Both representations are interrelated by analytic continuation in the spectral space, and are shown to be consistent with existing results when compressibility is suppressed.
An Analysis of Heave Added Mass and Damping of a Surface-Effect Ship
Authors: Kim C. H. , Tsakonas S.
Published: January 2021

The analysis presents a practical method for evaluating the added-mass and damping coefficients of a heaving surface-effect ship in uniform translation. The theoretical added-mass and damping coefficients and the heave response show fair agreement with the corresponding experimental values. Comparisons of the coupled aero-hydrodynamic and uncoupled analytical results with the experimental data prove that the uncoupled theory, dominant for a long time, that neglects the free-surface effects is an oversimplified procedure. The analysis also provides means of estimating the wave elevation of the free surface, the escape area at the stern and the volume which are induced by a heaving surface-effect ship in uniform translation in otherwise calm water. Computational procedures have been programmed in the FORTRAN IV language and adapted to the PDP-10 high-speed digital computer.
Hydro-Acoustics of a Cavitating Screw Propeller; Far-Field Approximations
Authors: Noordzij L. , van der Kooij J.
Published: January 2021

To predict the far-field radiated noise of a cavitating screw propeller, acoustic tests have to be performed on model scale. In this paper the far-field approximation of the sound pressure of the cavitating screw propeller is derived. The conditions for which the sound pressure, as obtained on model scale, can be considered to be the far-field sound pressure, and the resulting frequency range, are discussed.
Theoretical and Experimental Buckling Loads of Imperfect Spherical Shell Segments
Authors: Odland Jonas
Published: January 2021

Buckling experiments with spherical shell segments subjected to three different axisymmetric loading conditions are described. Initial shape imperfections were measured so that the experimental results could be compared with theoretical predictions for imperfect shells. Relevant theoretical solutions including classical buckling and initial postbuckling are therefore reviewed. Due to the inherent irregular nature of the imperfections, a comparison is not straightforward. It was necessary to define the amplitude of an"equivalent" regular imperfection pattern. Because there is no rigorous justification for this approach, the experiments can neither verify nor invalidate the initial postbuckling theory, but there is no doubt that very important characteristics of the shells were predicted qualitatively correctly. According to classical linearized theory, the buckling stress should be approximately Independent of loading condition, but experiments as well as initial postbuckling analyses revealed that the critical principal stress for imperfect shellsmay well vary by a factor of 2 to 3 depending on the ratio between the principal stresses. Experimental results for a spherical shell subjected to an inward point-load were found to be in very good agreement with theoretical large-deflection analysis. Bifurcation from the axisymmetric condition associated with small loads was observed. As predicted by initial postbuckling theory, the bifurcations were found to be stable.
Five Years of Numerical Naval Ship Hydrodynamics at DTNSRDC
Authors: Salvesen Nils
Published: January 2021

In 1974 the Numerical Naval Ship Hydrodynamics Program was established at the David W. Taylor Naval Ship Research and Development Center. The objective of the program is to develop new numerical methods which can be used to evaluate those hydrodynamic performance characteristics which cannot be satisfactorily predicted by traditional methods. In this paper, the accomplishments during the first five-year period (1974–1979) are discussed. During this initial period, the effort was devoted entirely to naval ship free-surface problems. Several successful methods have been developed for solving fully three-dimensional ship-motions, ship-wave-resistance and local-flow problems using linearized free-surface boundary conditions. Numerical methods have also been developed for unsteady and steady two-dimensional problems where the exact free-surface conditions are satisfied. These new numerical methods are more accurate than the conventional computational methods and they can be used to analyze several naval free-surface problems which previously could only be investigated experimentally. It is concluded that the Numerical Naval Ship Hydrodynamics Program should include consideration of all areas in naval ship hydrodynamics where it is believed that the application of advanced numerical techniques and computers can result in better solution techniques.
Bending Moments and Shear Forces in Ships Sailing in Irregular Waves
Authors: Jensen J. Juncher , Pedersen P. Terndrup
Published: January 2021

This paper presents some results concerning the vertical response of two different ships sailing in regular and irregular waves. One ship is a containership with a relatively small block coefficient and with some bow flare while the other ship is a tanker with a large block coefficient. The wave-induced loads are calculated using a second-order strip theory, derived by a perturbational procedure in which the linear part is identical to the usual strip theory. The additional quadratic terms are determined by taking into account the nonlinearities of the exiting waves, the nonvertical sides of the ship, and, finally, the variations of the hydrodynamic forces during the vertical motion of the ship. The flexibility of the hull is also taken into account. The numerical results show that for the containership a substantial increase in bending moments and shear forces is caused by the quadratic terms. The results also show that for both ships the effect of the hull flexibility (springing) is a fair increase of the variance of the wave-induced midship bending moment. For the tanker the springing is due mainly to exciting forces which are linear with respect to wave heights whereas for the containership the nonlinear exciting forces are of importance.
On Optimum Screw Propellers with End Plates, Inhomogeneous Inflow
Authors: Klaren L. , Sparenberg J. A.
Published: January 2021

The optimization of a screw propeller acting in an inhomogeneous flow is considered by means of linearized potential theory. Numerical results are given with respect to the influence of end plates on the optimum circulation distribution in the case of rotationally symmetric inhomogeneous inflow.
Determination of Maneuvering Properties in Shallow Water by Impulse Response Techniques
Authors: Loeser Douglas J.
Published: January 2021

This work presents the results of a systematic investigation of the effects of shallow water, forward speed, and block coefficient on maneuvering properties. Stability derivatives are experimentally determined using a recently developed impulse procedure. The determination of the stability derivatives at zero frequency is examined. Experimental results are compared with similar results from regular motion tests. Numerical computation of ship maneuvers in shallow water using the experimentally determined motion derivatives gives a qualitative description of the effects of shallow water and depth.
Polynomial Approximations to Mooring Forces in Equations of Low-Frequency Vessel Motions
Authors: Oppenheim B. W. , Wilson P. A.
Published: January 2021

Multivariate polynomial approximations are considered to the coupled nonlinear mooring forces acting on a vessel moored with multileg moorings. The objective is to yield explicit forms of equations of the low-frequency vessel motions, since the exact mooring forces are known numerically only. Such forms could then be used for analytical solutions of the equations of motion. It is shown that the polynomials lack sufficient generality and accuracy for this purpose, and hence solution of the problem can be considered only by the exact method.
Preliminary Design of Mooring Systems
Authors: Triantafyllou Michael S.
Published: January 2021

The preliminary design of mooring systems is formulated by separating the quasi-steady solution from the dynamic solution. A multiple time-scale expansion provides the appropriate equations, which are nonlinear for the quasi-steady part and linear space varying for the dynamic part. The fast dynamic solution consists of a fast varying and a slowly varying part with respect to space. An asymptotic solution is obtained by using the WKB method for the fast part, while an approximate expression is derived for the slow part. The resulting solution is simple and can be used to determine the dynamic behavior of complex systems, while permitting an extensive parametric search and the use of spectral techniques. This formulation leads to rational measures of the dynamic performance which, combined with cost considerations obtained from the static solution, permit an optimal selection of the system parameters. An example demonstrates the features of this methodology.
Development of a Numerical Method for the Calculation of Power Absorption by Arrays of Similar Arbitrarily Shaped Bodies in a Seaway
Authors: Duncan James H. , Brown Clinton E.
Published: January 2021

A computational procedure is developed using first-order hydrodynamic theory to predict the motions and power absorption from arrays of similar three-dimensional buoys. The buoy shape and the number and placement of the buoys may be arbitrarily selected. The program provides for waves of selected frequency and direction or combinations thereof by simple superposition; thus, the effects on energy absorption of wave energy spectral distributions or short-crestedness can be analyzed. The computer model has been validated by comparison of its results with published analytically derived power optimal solutions for five buoys in a linear array. The program provides the power output of each buoy in the array with the associated motions in six degrees of freedom. The limited number of cases studied has provided the interesting result that identical buoys in an array tend to absorb wave energy at rates close to those of optimized systems for which buoy amplitude and phasing would have to be controlled.
Comments on Vaughan: “The Tearing Strength of Mild Steel Plate”
Authors: Woisin G.
Published: January 2021

The title paper [1] 2 has been of great interest in view of similar tests, with simple metal plates, conducted in 1966 by the author's company [2, 8]. We offer the following comments on Mr. Vaughan's paper.
A Three-Dimensional Nonlinear Large-Deflection Model for Dynamic Behavior of Risers, Pipelines, and Cables
Authors: Bernitsas Michael M.
Published: January 2021

A comprehensive nonlinear model for the dynamic behavior of marine risers, cables, and pipelines has been developed. Large three-dimensional lateral oscillations are modeled in the local principal, osculating and rectifying planes. Longitudinal extensional oscillations in the local tangential direction are also taken into account. The derived model shows the significance of three-dimensional bending effects and the contribution of the nonlinear terms. Lateral and longitudinal oscillations are coupled due to the curvature and geometric torsion of the centerline of the structure. The model also shows the effects of the external hydrostatic and the internal mud static pressure forces—which are integrated exactly along the structure—on the structure's tensile and bending rigidity.
Stability of Fishing Vessels with Water on Deck: A Review
Authors: Storch Richard L. , Çaglayan Ibrahim
Published: January 2021

A thorough literature survey of research into the effect of water on deck on fishing vessel stability revealed that four predominant analysis techniques have been employed. The first, a static approach, is used to judge vessel stability by predicting the pseudo-static angle of heel, the heel angle about which the vessel rolls when water is trapped on deck. The second approach is a dynamic one in which the equation of motion in roll is written and the water on deck is treated as a roll-inducing moment. The third approach employs probabilistic analysis to determine the likelihood of having water on deck, usually presented as a function of freeboard and sea state. A hydrodynamic analysis, applied in the research of Dillingham, models the geometry of the water on deck as a function of time and inputs the resulting forces and moments as an exciting term in the roll motion equation, assuming linear motions. The hydrodynamic approach represents a significant advancement in understanding the phenomenon and is a logical point from which to initiate further research efforts.
Stability Analysis of Ring-Stiffened Shells of Revolution
Authors: Subbia J. , Natarajan R.
Published: January 2021

A finite-element formulation is presented for the stability analysis of ring-stiffened shells of revolution using linear bifurcation buckling theory. Critical pressures and mode shapes in both general instability mode and interframe buckling mode have been obtained using this formulation. Three different boundary conditions have been studied and their effect on the stability characteristics is reported. A sophisticated theoretical model has been evolved to treat the external hydrostatic pressure as a follower force. Critical pressures for cylinders with internal and external stiffening are compared.
On the Jet Curtain Over Water
Authors: Tselnik D. S.
Published: January 2021

The problem of two planar or two-dimensional jets of nonviscous, incompressible, weightless fluid flowing from two nozzles installed symmetrically with respect to a vertical axis onto the surface of an immobile heavy liquid is considered. The flow pattern represents a simple model of a jet curtain of an air-cushion vehicle. The complete theoretical solution to the problem is found—in a thin-jet approximation and under the assumption that the height of the nozzles with respect to the undisturbed surface of the liquid is fixed. The special case of a single nozzle is also considered. Some experimental observations of an air jet flowing from an individual slotted nozzle onto a water surface are presented, and an explanation of the flow mechanism is proposed for the vertical nozzle. In essence, the corresponding process of flow has to be random.
A Note on the Application of Response Cross Spectra
Authors: Hutchison Bruce L.
Published: January 2021

A method is developed which permits easy evaluation of the response spectral moments and response statistics for any response process (for example, motion, force, stress, etc.) which can be stated as a linear combination of known response processes represented by a base cross spectral moment matrix. The method is shown to apply equally to response processes excited by unidirectional and directional wave spectra. An example calculation is included to illustrate the application of the technique. The method developed exhibits a high degree of computational efficiency and should therefore be useful for data base construction and systematic seakeeping series presentation. Due to the computational efficiency of the technique outlined in this note, many problems that presently require a high-speed computer could be performed with an electronic calculator.
A Consistent Hydrodynamic Theory for Moored and Positioned Vessels
Authors: Triantafyllou Michael S.
Published: January 2021

The motion of a moored, or positioned, vessel under the influence of waves can be decomposed into a large-amplitude, slowly varying part and a small-amplitude, fast varying part. A consistent theory can be formulated, therefore, based on a multiple time scale expansion, together with an amplitude expansion of the general governing equations. The existing theory of ship motions remains unchanged within the present approach, while the equations of drift motion can be obtained separately from the fast dynamics, in a straightforward manner. It is shown that if the slow motion flow is modeled as inviscid and irrotational, its potential is of first order and satisfies linear boundary conditions. Also, the second-order force calculation is not influenced by the slow motions. The rolling motion of a moored vessel is studied as an example of the concepts introduced.
Turbulence Stimulation and the Initial Boundary-Layer Development on Two Ship Forms
Authors: Smits A.J.
Published: January 2021

Inappropriate tripping devices may either not promote transition effectively or cause significant distortion of the initial boundary-layer development. By reexamining data for reflex geosims of Lucy Ashton and a small 0.80-CB tanker it is shown that this distortion can readily occur. To compare the boundary-layer development near the bow of a ship model under different test conditions the relative position of the virtual origin must remain constant. The concept of a virtual origin is considered using an approximate form of the momentum integral equation and it is found that locating the virtual origin is a highly ambiguous process, and therefore it becomes difficult to decide if the virtual origin remains constant or not. To compare and extrapolate total drag results, a correction for the virtual origin position is usually applied. For two widely different ship forms it is shown that the total skin friction coefficient is relatively insensitive to a poor estimate of the virtual origin position and an inappropriate choice of stimulator.
Irrotational Flow Within the Boundary Layer and Wake
Authors: Landweber Louis
Published: January 2021

Expressions are derived for centerplane source distributions which generate an irrotational flow field about a laterally symmetrical body that matches that exterior to the boundary layer and wake. Results are given for two-dimensional bodies and thin-ship forms. Pressure distributions at the wall of a two-dimensional body are determined for the flow in the boundary-layer region with and without vorticity. The difference between the pressure coefficients is shown to be principally proportional to the product of the surface curvature of the body by the sum of the displacement and momentum thicknesses.
A Stochastic Theory for Nonlinear Ship Rolling in irregular Seas
Authors: Roberts J. B.
Published: January 2021

By a combination of averaging techniques with the theory of Markov processes, an approximate theory is developed for the rolling motion of a ship in beam waves. A simple expression is obtained for the distribution of the roll angle, and is tested by a comparison with a set of digital simulation estimates due to Dalzell. Good agreement is obtained over a realistic range of damping values.
A Time-Dependent Green Function and Sway Added Mass of a Rectangular Cylinder at Zero Frequency
Authors: Chung Y.K.
Published: January 2021

The order of passage to the limit in double limiting processes in a sway added-mass problem in water of finite depth is reversible and the double limit is finite. The author considers a two-dimensional rectangular cylinder floating in water of finite depth and oscillating in sway motion. When its frequency and depth-draft ratio approach zero and unity, respectively, the problem involves double limiting processes. The case for frequency first and then draft in the processes has been studied by Flagg and Newman [1]2. Here the reverse order is considered, namely, draft first and then frequency, and examine the limiting value analytically. Then reversibility of the order is discussed. For this purpose, a time-dependent Green function is employed. Green's function, in particular, may be convenient to use, for it can handle an arbitrary motion of the body. A system of linear integral equations in the limit is obtained. The kernel of the integral equation, when the draft tends to the depth of water, can be written as an eigenfunction expansion. Hence, the system of equations can be examined in a simple way. Lastly, it is shown that the present method using the time-dependent Green function indeed satisfies the radiation condition.
Comments on Jacobs and Tsakonas: “Propeller Loading-Induced Velocity Field by Means of Unsteady Lifting Surface Theory”
Authors: Goodman Theodore R.
Published: January 2021

In the cited paper (2) a formula is given for the lth Fourier component of the velocity potential of an N-bladed propeller [equations (9) and (10) of the paper], (2). The total velocity potential is then, of course, given by the sum of all the components.
Explicit Approximations for Calculating Potential Flow About a Body
Authors: Noblesse F. , Triantafyllou G.
Published: January 2021

Several explicit approximations for calculating nonlifting potential flow about a body in an unbounded fluid are studied. These approximations are shown to be exact in the particular cases of flows due to translations of ellipsoids, and they are compared with the exact potential for two-dimensional flows about ogives in translatory motions. Two approximations, given by formulas (31) and (32) in the conclusion, appear to be of particular interest for practical applications, and they can be extended to free-surface flow problems, for example, ship wave resistance, and radiation and diffraction of regular waves by a body.
Blade Pressure Distribution for a Moderately Loaded Propeller
Authors: Tsakonas S. , Breslin J.P. , Jacobs W. R.
Published: January 2021

A new theoretical procedure has been developed modifying the existing analysis for a marine propeller operating in a nonuniform inflow field by considering the radially varying mean wake and mean propeller induction. In addition, the selection of a new reference surface around which the perturbation analysis is developed is based on the nonlinear form of the Bernoulli equation together with an appropriate kinematic condition existing at the propeller operational condition. A flow field closer to the propeller operating condition is achieved thereby and the linear theory requirement of small perturbation quantities is reinforced. The approach is thus applicable to moderately to heavily loaded propellers immersed in the stronger wakes of hulls of large block coefficient, although it can be used for lightly loaded propellers as well.
Static and Dynamic Buckling of Pressure-Loaded, Ring-Stiffened Cylindrical Shells
Authors: Simitses G. J. , Sheinman I.
Published: January 2021

The analysis of imperfect, stiffened, thin circular cylindrical shells, subjected to suddenly applied pressure, is presented. Moreover, a solution scheme for the complete (including post-limit point behavior) static analysis is described. The concept of dynamic stability is discussed for suddenly loaded structures. In addition, a fairly complete review of the reported works on the subject is presented. Results are presented for a ring-stiffened geometry. These include critical dynamic loads, critical static loads (limit point loads), as well as minimum post-limit point loads.
On Sculling Propulsion by Two Elastically Coupled Profiles
Authors: Sparenberg J. A. , de Vries J.
Published: January 2021

The sculling propulsion of two profiles which are coupled by an elastic hinge is considered. The leading profile carries out a prescribed motion. The motion of the second profile is induced by the hinge and by the fluid pressures. This profile regains part of the kinetic energy left behind by the first one. Numerical results are given.
Experimental and Theoretical Hydrodynamic Forces on a Mathematical Model in Confined Waters
Authors: Cohen Stuart B. , Beck Robert F.
Published: January 2021

Experimental results are given for a mathematical hull form tested in shallow water. The side force and yaw moment acting on the model due to a yaw angle, the presence of canal walls, and the interaction with another stationary mathematical shape are presented. Comparisons with linearized theories are made and, in general, found to be good.
A Note on the Evaluation of the Wave Resistance of Two-Dimensional Bodies from Measurements of the Downstream Wave Profile
Authors: Duncan James H.
Published: January 2021

As a body moves horizontally at constant speed in the proximity of a free surface it experiences a resistance due to the generation of waves. In two-dimensional cases the determination of this resistance from properties of the wave train has been the subject of several investigations. The linear theory was first presented by Lord Kelvin [1] 2 and later by Havelock [2] and Lamb [8]. Wehausen and Laitone [4] have derived an exact resistance formula in terms of the vertical distribution of velocity in the waves and the downstream surface height profile. This formula was later evaluated by Salvesen and von Kerczek [5] using third-order Stokes wave theory.
Low-Reynolds-Number Turbulent Boundary Layers in Zero and Favorable Pressure Gradients
Authors: Smits A. J. , Matheson N. , Joubert P. N.
Published: January 2021

This paper reports the results of an extensive experimental investigation into the mean flow properties of turbulent boundary layers with momentum-thickness Reynolds numbers less than 3000. Zero pressure gradient and favorable pressure gradients were studied. The velocity profiles displayed a logarithmic region even at very low Reynolds numbers (as low as Rθ = 261). The results were independent of the leading-edge shape, and the pin-type turbulent stimulators performed well. It was found that the shape and Clauser parameters were a little higher than the correlation proposed by Coles [10], and the skin friction coefficient was a little lower. The skin friction coefficient behavior could be fitted well by a simple power-law relationship in both zero and favorable pressure gradients.
The Representation of Ship Hulls by Conformal Mapping Functions: Fractional Maps
Authors: von Kerczek C.
Published: January 2021

The method for analytically representing ship hulls by conformal mapping functions of the cross sections and lengthwise polynomial interpolation of the mappings, which was developed by von Kerczek and Tuck [1], has found useful applications to ship hydrodynamics (see references [2] and [3]) as well as ship design [4]. In both such applications, however, there have been two major criticisms of this type of representation of the underwater portion of the ship hull. The first criticism concerned the occurrence of undesirable waviness in the longitudinal direction of the cross sections of the ship. This waviness is due to fitting high-degree polynomials to very slowly varying data. This defect of the surface representation can be removed easily by abandoning the polynomial interpolation and substituting some form of spline interpolation. It has been found that interpolation by simple Hermite cubic splines works very well. Such modifications of the lengthwise interpolation scheme are well known and need no elaboration.
Measurements in the Near-Wake Region of a Slender, Self-Propelled Model at Pitch or Yaw
Authors: Schetz J. , Lee H. , Kong F.
Published: January 2021

An experimental investigation of the near-wake region of a slender, propeller-driven model at pitch or yaw was undertaken in the Virginia Tech low-turbulence wind tunnel. The control surfaces on the model were set to render the model in equilibrium for the case with model pitch. The vehicle design was such that the vertical control surfaces were insufficient to achieve an equilibrium condition with the model at yaw. This is neither unusual nor undesirable, since such a vehicle can turn freely and there is little desire to operate in a straight line at yaw. A yaw-head probe was used for mean flow measurements, and a hot-wire anemometer with a normal, single wire or an X-wire served to obtain turbulent flow characteristics. The control surfaces were found to have mainly local influences on the flow field. In the pitch case, good symmetry was exhibited on both mean and turbulent flow quantities, but the lack of complete, all-directional equilibrium in the yaw case prevented the achievement of symmetry.
Simulation Analysis of Steering Control During Underway Replenishment
Authors: Brown Samuel H. , Dimmick Joseph G.
Published: January 2021

Underway replenishment (UNREP) operations have always been a difficult maneuver, and are accomplished by manual control of U.S. Navy ships, using the most experienced personnel. The probability of collision during UNREP increases with decreasing distance between the ships. The David W. Taylor Naval Ship Research and Development Center has recently completed an exploratory development program to define and analyze the control parameters affecting the dynamic interactions between ships during UNREP, resulting in definition of some of the requirements for a prototype ship separation and sensing and control system. The UNREP control problem was simulated on a hybrid computer using analytical models of two identical Mariner-class ships, including consideration of nonlinear maneuvering equations, ship interaction forces and moments, regular waves, severe first-and second-order irregular waves, oblique seaway, time-sampled separation measurements, and low-pass filters. Assumed sensor inputs to the controller were longitudinal and lateral separation, lateral separation rate, relative yaw, relative yaw rate, and rudder angle. Results of the simulation indicate that first-order irregular-wave excitations dominate the UNREP rudder control problem in severe sea states. Use of either automatic or quickened (display-aided) manual control was found to be feasible, but additional work is needed to define the capabilities and limitations of quickening in this application, and to redesign the controller, using modern control theory techniques.
Two-Dimensional Unsteady Planing Surface
Authors: Bessho Masatoshi , Komatsu Masahiko
Published: January 2021

The two-dimensional unsteady problem of a flat planing surface is analyzed based on airfoil theory. The present analysis treats the effect of the time-varying wetted length on the added mass and damping coefficient. When the reduced frequency becomes very small, the change in wetted length approaches the displacement of the intersection of the planing surface and the undisturbed water surface. In the limiting case of zero frequency, the wetted length change reduces to zero. It is noted that the damping coefficient by the present analysis indicates the negative value in the very small reduced frequency, as Ogilvie and Bessho predicted previously in their theories derived from the different points of view.
A Second-Order Theory for the Potential Flow About Thin Hydrofoils
Authors: Kennell Colen , Plotkin Allen
Published: January 2021

This research addresses the potential flow about a thin two-dimensional hydrofoil moving with constant velocity at a fixed depth beneath a free surface. The thickness-to-chord ratio of the hydrofoil and disturbances to the free stream are assumed to be small. These small perturbation assumptions are used to produce first-and second-order subproblems structured to provide consistent approximations to boundary conditions on the body and the free surface. Nonlinear corrections to the free-surface boundary condition are included at second order. Each subproblem is solved by a distribution of sources and vortices on the chord line and doublets on the free surface. After analytic determination of source and doublet strengths, a singular integral equation for the vortex strength is derived. This integral equation is reduced to a Fredholm integral equation which is solved numerically. Lift, wave drag, and free-surface shape are calculated for a flat plate and a Joukowski hydrofoil. The importance of free-surface effects relative to body effects is examined by a parametric variation of Froude number and depth of submergence.
Cavitating Flow Near the Apex of a Plane Delta Wing
Authors: Kida Teruhiko , Take Takanori
Published: January 2021

The problem of cavitating flow past the apex of an infinite sector, that is, "the delta-wing problem," is treated. This problem is just an inner problem in the sense of the method of matched asymptotic expansions, and the present study might be very important in leading to large increases in the accuracy of collocation methods for cavitating wings with pointed apexes.' A solution of Laplace's equation for this problem, that is, the velocity potential, involves rv where r is the distance from the apex and v is a parameter depending on the angle of the sector. The numerical values of v for various apex angles in the lowest approximation are obtained by Taylor's approximate method. In the special case where the apex angle is x, the first and second eigenvalues are obtained theoretically as m + 1/4 and m + 3/4, respectively, where m is an integer. From a physical insight, it is seen that the second eigenvalue is very important in the cavitating flow.
Convergence of a Sequence of Slender-Ship Low-Froude-Number Wave-Resistance Approximations
Authors: Noblesse Francis
Published: January 2021

Convergence of the sequence of slender-ship low-Froude-number wave-resistance approximations /"/, n > 0, obtained as a particular case of the slender-ship theory of wave resistance recently proposed by the author, is proved for the special case of ship hulls in the form of vertical cylinders with elliptical waterlines. Specifically, it is shown that we have where b is the thickness (beam/length) ratio of the cubical cylinder, Fis the Froude number, and r lf(b,F) is the Guevel-Baba-Maruo-Kayo low-Froude-number wave-resistance approximation associated with the exact zero-Froude-number (double-hull) potential. Vertical elliptical cylinders thus have the remarkable property that the ratio iipj{b,F)/rpp(b,F) is independent of the Froude number, that is, depends only on the thickness ratio of the cylinder.
Optimal Ship Forms for Minimum Total Resistance
Authors: Hsiung Chi-Chao , Shenyan Dong
Published: January 2021

A numerical scheme is developed by using the "tent" function to compute the hull surface area and then the ship frictional resistance in a quadratic form in terms of ship offsets. Combining with the wave resistance, a total ship resistance formula is derived in a standard quadratic form. With a set of linear-inequality constraints, the optimal solution of ship offsets for minimum total resistance can be obtained by applying a quadratic programming method to the problem. Computations have been carried out for three conditions which have exactly the same constraints as those required to obtain the optimal forms for minimum wave resistance shown in an earlier work [1].3 The optimal forms found for minimum total resistance also have either bow or midship bulbs. The new optimal bulbs have a relatively small size, higher vertical slope to the baseline, and less curvature at the tip of the bulb.
Plastic Reserve Strength of Rectangular Plates
Authors: Chu Ching-Yuan , Vorus William S.
Published: January 2021

An upper-bound functional which attains its minima at collapse of thin laterally loaded plates is formulated. A general collapse pattern for various thin plate problems is constructed in terms of a set of unknown parameters. An appropriate mathematical programming algorithm is applied to search for the correct parameters in the minimization procedure. Rectangular plates under uniform load are treated specifically. The least upper-bound solutions for rectangular plates with various boundary conditions are calculated. The corresponding elastic solutions are also calculated. From these elastic and plastic solutions the reserve strength of the plate beyond its elastic load capacity is predicted.
Turbulence Measurements Near the Stern of a Ship Model
Authors: Löfdahl Lennart , Larsson Lars
Published: January 2021

An experimental investigation in which Reynolds stress profiles were measured in the thick three-dimensional turbulent boundary layer at the stern of a ship model has been carried out. The measurements were performed using a specially developed hot-wire technique in which the mean velocity component perpendicular to the surface was considered. A large number of results are given in diagrams, and an error estimation for the different Reynolds stresses is presented. Efforts have been made, when positioning the measured turbulence profiles, to enable future development of calculation methods based on these results. The measured profiles have revealed a strong influence of streamline convergence (divergence) on the Reynolds stresses. Also, the effects of wall curvature are of importance, and since most parts of the investigated region have a convex curvature the average level of the stresses is reduced.
Improvement of the Performance of a Waterjet by Means of Polymeric Additives—Experimental Investigation
Authors: Pallabazzer Rodolfo
Published: January 2021

An experimental investigation was carried out to test the possibility of improving the propulsive performance of waterjets by the introduction of polymeric macromolecules in water solution. Four pumps were tested either in closed and open circulating loops or in a static waterjet plant. It was clearly demonstrated that polymeric dilute solutions of Polyox WSR-301 always produced an increase of pump head, static thrust and efficiency, together with shaft power reduction. Improvements up until 20 percent could be obtained. On the basis of the distribution and of the weight of the losses inside the pump, an interpretation of the effect is given together with a suggestion for a more simple method to obtain it.
Ray Theory and Kelvin Wave
Authors: Chung Yong Kwun
Published: January 2021

The paper illustrates how to get the pattern of waves generated from a point source in ray theory. A few examples of the wave patterns are shown when the point source accelerates and decelerates.
Hamilton’s Principle, Lagrange’s Method, and Ship Motion Theory
Authors: Miloh Touvia
Published: January 2021

Lagrange's equations of motion, describing the motion of several bodies on or below a free surface, are here derived from Hamilton's variational principle. The Lagrangian density is obtained by extending Luke's principle to the wave-radiation problem, and the hydrodynamical loads on the bodies are expressed in terms of the Lagrangian density and its derivatives with respect to the generalized coordinates of the bodies. First we consider a forced harmonic oscillation without a forward speed and then we discuss the case of the same oscillatory motion superimposed on arbitrary steady motion. In both cases we employ Lagrange's method to derive the transfer functions between the generalized forces and the amplitudes of the harmonic motions, in terms of added mass, damping, and the hydrostatic restoring coefficients. The case of a steady forward motion, for which the transfer function is already known, is obtained as a particular case of the general solution.
Comments on the Low-Aspect-Ratio Unsteady Propeller Force Theory of N. A. Brown
Authors: Schneider Steven P. , Biaisdell Gregory A. , Nelson David M.
Published: January 2021

A paper written by N. A. Brown [1], (3) develops an approximate formula for the prediction of the unsteady force on a propeller blade in terms of a theory based on a representation of the inflow field by a power series. This formula is then intuitively changed to one based on a representation of the inflow field in terms of Legendre polynomials. We here use the orthogonality of Legendre polynomials to demonstrate that this intuitive step is incorrect. Our further work is then discussed. The notation of the original paper is used.