bluuebunny/crossref_metadata_2025 huggingface dataset:
Extreme Values of Waves and Ship Responses Subject to the Markov Chain Condition
Authors: Ochi Michel K.
Published: January 2021

This paper discusses the effect of statistical dependence of the maxima (peak values) of a stationary random process on the magnitude of the extreme values. A theoretical analysis of the extreme values of a stationary normal random process is made, assuming the maxima are subject to the Markov chain condition. For this, the probability distribution function of maxima as well as the joint probability distribution function of two successive maxima of a normal process having an arbitrary spectral bandwidth are applied to Epstein's theorem for evaluating the extreme values in a given sample under the Markov chain condition. A numerical evaluation of the extreme values is then carried out for a total of 14 random processes, including nine ocean wave records, with various spectral bandwidth parameters ranging from 0.11 to 0.78. From the results of the computations, it is concluded that the Markov concept is applicable to the maxima of random processes whose spectral bandwidth parameter, ɛ, is less than 0.5, and that the extreme values with and without the Markov concept are constant irrespective of the e-value, and the former is approximately 10 percent greater than the latter. It is also found that the sample size for which the extreme value reaches a certain level with the Markov concept is much less than that without the Markov concept. For example, the extreme value will reach a level of 4.0 (nondimensional value) in 1100 observations of the maxima with the Markov concept, while the extreme value will reach the same level in 3200 observations of the maxima without the Markov concept.
Calculation of Propeller-Excited Whirling Critical Speeds
Authors: Woytowich Richard
Published: January 2021

This paper presents a calculation method, suitable for manual calculation or use with a small, desk-top calculator, for estimating the propeller-excited whirling critical speed of a shafting system. The method is especially adaptable to use with a small programmable calculator. Based on a two-support model of the propeller and tailshaft similar to that used in earlier whirling calculations, this method "brackets" the natural frequency by first assuming the forward end of the tailshaft to be simply supported, then repeating the calculation, assuming the forward end to be fixed. This gives an upper and lower limit on the natural frequency. The actual natural frequency is estimated by interpolation between these two values. The proposed calculation method includes propeller gyroscopic and inertia effects, as well as shaft mass effects. Entrained water may also be taken into account. Comparisons between the results of the proposed hand calculation and the results of other well-known methods of whirling analysis are presented for a typical vessel shafting system. Extensions of the proposed calculation to include the effects of the line shafting and the sterntube bearing stiffness are also presented.
Dynamic Plastic Response of Cylindrical Shells Under Gaussian Impulse
Authors: Ramu S. Anantha , Iyengar K. J.
Published: January 2021

The determination of the inelastic response of cylindrical shells under general impulsive loads is of relevance to marine structures such as submarines, in analyzing their slamming damages. The present study is concerned with the plastic response of a simply supported cylindrical shell under a general axisymmetric impulsive load. The impulsive load is assumed to impart an axisymmetric velocity to the shell, with a Gaussian distribution along the longitudinal axis of the shell. A simplified Tresca yield condition is used. The shell response is determined for various forms of impulses ranging from a concentrated impulse to a uniform impulse over the entire length of the shell. Conclusions about the influence of geometry of the shell and the spatial distribution of impulse on the plastic behavior of cylindrical shells are presented.
Propeller and Vane Wheel
Authors: Grim Otto
Published: January 2021

The vane wheel is a freely rotating device installed on the propeller shaft behind the propeller to provide additional thrust at no increase in power. The wheel, which is larger in diameter than its companion propeller, functions as a turbine by using the otherwise-wasted propeller slipstream to generate the extra thrust. This paper describes a series of tests performed at the Hamburg Ship Model Tank to compare the efficiency of the vane wheel arrangement with other propulsion units, including a conventional propeller, contrarotating propeller, and propeller with fixed guide mechanism. The Appendix provides a mathematical analysis of the performance of the various units investigated. Preface: For many years I had the great pleasure to live near Georg Weinblum, to work with him, and to receive his advice. After he retired I became his successor at Hamburg University. In 1938 I had met Georg Weinblum for the first time; in 1952 — after his return from the United States — for the second time, and after that we met regularly. He encouraged me to write my thesis and to work as a scientist. He always took a great interest in promoting young people and in awakening their enthusiasm for science. Many young people have had this experience and think of him with gratitude. Due to the founders' intentions, the memorial lecture should deal with a subject which belongs to naval architecture and which serves its development. I have chosen the subject, Propeller and Vane Wheel, which I presented for the first time to the German Society of Naval Architecture (Schiffbautechnische Gesellschaft) in 1966. I take this opportunity to discuss the subject again, and to a different extent, because I believe that the purpose of this work is really important and can be achieved without any difficulty in the present situation, where the search for new ideas with regard to the saving of energy has become an urgent necessity.
A Note on the Design of Wake-Adapted Propellers
Authors: Dyne Gilbert
Published: January 2021

Problems associated with the design of wake-adapted propellers are illustrated by results obtained from a simple propeller and wake model. It is shown that the widely used approach of the vortex theory gives much-too-low induced axial velocities at the inner radii of the propeller, which results in too-low blade pitch ratios. The reason for this is that no regard is paid to the fact that the vorticity of the approaching flow is changed by the propeller. If this changing vorticity is introduced in the vortex theory, its shortcomings are eliminated. An effect of the improvement is that the effective wake at the propeller plane differs from the nominal wake. The difference depends upon the propeller load. The propeller is shown to have a leveling effect on a nonuniform axisymmetric nominal wake.
On the Frictional Damping of the Rolling of a Circular Cylinder
Authors: Myrhaug Dag , Sand Ivar Øyvind
Published: January 2021

The frictional damping of the rolling motion of a circular cylinder is nonlinear. Although negligible at full scale, it may be important in model scale. The damping force is calculated using Fourier analysis of the frictional force on the surface of a cylinder with a vertical axis executing simple harmonic oscillations about its axis. Calculations of the velocity profile in the fluid near the oscillating cylinder, needed for the calculations of the frictional force, are carried out in the laminar and turbulent case using the boundary-layer approximation. For Reynolds shear stress modeling, the mixing length concept of Prandtl and an analogy to van Driest's model are used. The resulting nonlinear partial differential equation of the parabolic type is solved numerically using the Du Fort-Frankel explicit finite-difference scheme.
Sway, Roll, and Yaw Motion Coefficients Based on a Forward-Speed Slender-Body Theory—Part 1
Authors: Troesch Armin Walter
Published: January 2021

The added-mass and damping coefficients for sway, roll, and yaw are formulated for a ship with forward speed. The theory is similar to that given by Ogilvie and Tuck (1969) for the heave and pitch coefficients of a slender ship. Numerical results are presented for the cross-coupling coefficients.
Corrosive Liquid Effects on Cavitation Erosion
Authors: Okada Tsunenori
Published: January 2021

An experimental Investigation of the effects of corrosive liquids on the cavitation erosion of steels is presented. The macro-effects are described in terms of the weight loss, which is increased by the presence of the corrosive liquids. The micro-effects are discussed from photographs of the test surface showing the characteristic effects of the mechanical impact from the collapsing bubbles and the corrosive action on the material. The effects of the corrosive liquid on the fatigue strength of the material are also discussed.
Comment on Oppenheim and Wilson: "Continuous Digital Simulation of the Second-Order Slowly Varying Wave Drift Force”
Authors: Kaplan Paul
Published: January 2021

The title paper [1] 2 is intended to provide a method for simulating (via digital computation) the second-order slowly varying wave drift force acting on a ship in waves. The Oppenheim and Wilson method is based upon obtaining a digital time history representation when using known information about the power spectrum of this drift force. The main concern indicated in their paper is the requirement to provide the drift force time history for use in a digital simulation of a moored floating vessel which makes use of a variable time step integration technique. The necessity for obtaining such disturbing forces in the proper form when applying a variable time step integration technique is well understood, in view of similar experience using such variable time step integration procedures in different simulation studies covering both high-frequency and relatively low-frequency motion phenomena (for example, [2, 8]).
Turbulent Boundary Layers on Bodies of Revolution
Authors: Smits A.J. , Joubert P. N.
Published: January 2021

Turbulent boundary-layer flow over two arbitrary bodies of revolution was investigated by comparison with the flow over a two-dimensional wing-like body. For each body of revolution this wing" was first shaped to copy the body of revolution pressure distribution and then modified to have the same longitudinal curvature. The results were interpreted in terms of the effects of the extra rates of strain associated with longitudinal curvature and lateral divergence. These effects could be distinguished reasonably clearly and the experimental results should prove useful for testing calculation methods. Comparison with the calculations of Bradshaw et al [8, 9] shows that there occurs a strong interaction between the extra rates of strain due to convex curvature and divergence and that the implied simple summation of these two effects cannot be justified.
Added Moment of Inertia of Rolling Ship Sections
Authors: Hsu P. P. , Landweber L.
Published: January 2021

An expression for the added moment of inertia of a ship section rolling at low frequency at a free surface, in terms of the coefficients of the Laurent series of the function which maps the given section into a circle, has been derived. The method is applied to the two-parameter family of Lewis forms and the results are presented as a family of curves which gives the coefficient of the added moment of inertia as a function of the thickness ratio and the section-area coefficient of a form. A second application is to a square section, for which the Laurent expansion is an infinite series.
Computer Method for Forced Torsional Vibration of Propulsive Shafting System of Marine Engine With or Without Damping
Authors: Wu Jong-Shyong , Chen Wen-Hsiang
Published: January 2021

In the preliminary design of a propulsive shafting system, the additional (vibratory) stress due to torsional vibration is one of the important factors that must be considered in addition to the mean stress induced by the steady torque. In this paper, existing information concerning shaft design is reviewed; procedures formerly performed by slide rule, diagrams, and tabulations are formulated; and, based on the induced formulas, computer programs are developed. For an engine either two cycle or four cycle, single cylinder or multicylinder, and for a shafting system either undamped or damped (inner or outer or both inner and outer), it is required only to change the input data to obtain the desired data for various order numbers of torsional vibrations due to various firing orders of the cylinders. The output data include the natural frequencies and the corresponding mode shapes of the torsional vibrations, the amplitudes of twisting angles, and the vibratory stresses of the shafts. The reliability of the induced formulas and the developed computer programs has been confirmed by agreement between the computer output and existing information.
Flexible Wedges in Supercavitating Flow
Authors: Millett Kellie M. , Green Theodore
Published: January 2021

A linear theory is developed to model the steady supercavitating flow about a very slender wedge which can deform under the pressure distribution associated with the flow. The resulting static wedge deformation, drag, and cavity length show physically reasonable changes from previous work where the wedge is not allowed to bend to accommodate the flow, and suggest that the model can be adapted with confidence to more realistic and complex flows. One result of interest is that, with increasing cavitation parameter, a drag maximum is encountered, associated with deformation and consequent area reduction of very flexible wedges.
Stochastic Theory of the Slamming Response of Marine Vehicles in Random Seas
Authors: Mansour A. E. , Lozow J.
Published: January 2021

A stochastic theory is developed for the dynamic response of marine vehicles to slamming loads in random seas. Based on slamming observations and records, the slams are temporally represented as a train of Poisson impulses of random intensity occurring at random time intervals. Modal analysis is used to derive the impulse response and system functions of the marine vehicle. The probability density functions, spectral densities, autocorrelation functions, and other relevant statistics of both the input slams and the output vehicle response are developed and discussed. Special attention is given to the bending moment response. A numerical example is given in the last section in order to illustrate the application of the presented theory.
Plastic Collapse of Orthotropic Plates
Authors: Christodoulides John C. , de Oliveira Joao G.
Published: January 2021

A yield criterion for thin orthotropic shells expressed in terms of generalized stresses is first derived. This yield criterion is based on the yield criterion proposed by Hill for anisotropic continua and it is consistent with all the assumptions usually adopted in the technical theory of shells. As an example of application of this criterion the collapse of perfectly plastic rectangular orthotropic plates subjected to a uniform lateral pressure is studied using the Theorems of Limit Analysis.
A Slender-Ship Theory of Wave Resistance
Authors: Noblesse Francis
Published: January 2021

A new slender-ship theory of wave resistance is presented. Specifically, a sequence of explicit slender-ship wave-resistance approximations is obtained. These approximations are associated with successive approximations in a slender-ship iterative procedure for solving a new (nonlinear integro-differential) equation for the velocity potential of the flow caused by the ship. The zeroth, first, and second-order slender-ship approximations are given explicitly and examined in some detail. The zeroth-order slender-ship wave-resistance approximation, r(0) is obtained by simply taking the (disturbance) potential, ϕ, as the trivial zeroth-order slender-ship approximation ϕ(0) = 0 in the expression for the Kochin free-wave amplitude function; the classical wave-resistance formulas of Michell [1]2 and Hogner [2] correspond to particular cases of this simple approximation. The low-speed wave-resistance formulas proposed by Guevel [3], Baba [4], Maruo [5], and Kayo [6] are essentially equivalent (for most practical purposes) to the first-order slender-ship low-Froude-number approximation, rlF(1), which is a particular case of the first-order slender-ship approximation r(1): specifically, the first-order slender-ship wave-resistance approximation r(1) is obtained by approximating the potential ϕ in the expression for the Kochin function by the first-order slender-ship potential ϕ1 whereas the low-Froude-number approximation rlF(1) is associated with the zero-Froude-number limit ϕ0(1) of the potentialϕ(1). A major difference between the first-order slender-ship potential ϕ(1) and its zero-Froude-number limit ϕ0(1) resides in the waves that are included in the potential ϕ(1) but are ignored in the zero-Froude-number potential ϕ0(1). Results of calculations by C. Y. Chen for the Wigley hull show that the waves in the potential ϕ(1) have a remarkable effect upon the wave resistance, in particular causing a large phase shift of the wave-resistance curve toward higher values of the Froude number. As a result, the first-order slender-ship wave-resistance approximation in significantly better agreement with experimental data than the low-Froude-number approximation rlF(1) and the approximations r(0) and rM.
In-Duct Viscous Flow Pressure Distribution on a Body with Boundary-Layer Control
Authors: Lauchle Gerald C.
Published: January 2021

It is well known that the static pressure distribution of an axisymmetric body operating within the boundaries of a duct such as a wind tunnel or water tunnel test section is altered from that observed in a free stream because of solid blockage and horizontal buoyancy effects. Because potential-flow solutions can account only for the solid blockage, an auxiliary analysis must be performed to account for the viscous (horizontal buoyancy) effects. One such analysis has been performed by the present author [1],2 where it was assumed that boundary-layer development occurred in a natural zero-pressure-gradient-like manner over the test body and duct walls. In this paper, a modification of that analysis is presented which permits analysis of bodies with boundary-layer control. In addition to the theoretical formulation, a numerical example is presented to illustrate the effect on the pressure distribution of a 0.318-m-diameter (1.043 ft) body with surface suction operating in a 1.22-m-diameter (4.00 ft) duct.
Effect of Freestream Radial Velocity Component on Hydrodynamic Analysis of Propellers
Authors: Brockett Terry
Published: January 2021

For wake fields with circumferential averages that include a small radial component, an additional termarises in the mathematical model used for design or performance prediction of propellers that has been previously overlooked. This term arises from the boundary condition that the blade is impenetrable and is a function of only geometry and the inflow radial velocity component. This simple additional term is shown to be important for the example considered, leading to a variable change in camber and a pitch reduction.
Bow Flow and Added Resistance of Slender Ships at High Froude Number and Low Wave Lengths
Authors: Faltinsen Odd M.
Published: January 2021

Flow around a slender ship bow at high Froude number and regular incident head sea waves is analyzed by matched asymptotic expansions. The near-field solution implies solving a two-dimensional Laplace equation with complete linear free-surface conditions. A solution technique with fundamental sources and dipoles is used. The solution technique is tested with good results for transient forced heave oscillation of a circular cylinder and for steady flow around a wedge. Comparisons with other numerical and experimental results for steady bow flow around a Wigley hull and a Series 60, Cb = 0.6 model show partly satisfactory results. The theoretical model for unsteady flow around a ship bow is used to calculate added resistance on a slender ship in high Froude number and incident regular head sea waves of low wave lengths. Experimental results for added resistance at low wave length for a cargo ship with Cb = 0.61 are not in complete agreement with the theoretical predictions.
Preliminary Numerical Study of a New Slender-Ship Theory of Wave Resistance
Authors: Chen C. Y. , Noblesse F.
Published: January 2021

Results of various numerical calculations of wave resistance designed to evaluate the new slender-ship approximations obtained in Noblesse [1]3 are presented. Specifically, three main wave-resistance approximations are evaluated and studied. These are the zeroth-order slender-ship approximation r(0), which is compared with the classical approximations of Hogner and Michell; the first-order slender-ship low Froude-number approximation rIF(1), which is shown to be practically equivalent: to the Guevel-Baba-MaruoKayo low-Froude-number approximation rIF; and the first-order slender-ship approximation r(1), which is evaluated for the Wigley hull and compared with existing experimental data, corrected for effects of sinkage and trim, and with numerical results obtained by using the theory of Guilloton, the low-speed theory, and Dawson's numerical method. The approximations r(1) and rIF(1) are obtained by taking the velocity potential in the Kochin free-wave amplitude function as the first-order slender-ship potential Φ(1) and its zero-Froudenumber limit Φ0(1) respectively. A major difference between the potentials Φ(1) and Φ0(1) resides in the wave potential ΦW(1) that is included in Φ(1), but is ignored in the zero-Froude-number potential Φ0(1). It is shown that the wave potential ΦW(1) may not be neglected in comparison with the potential Φ0(1) and in fact has a remarkable effect upon the wave resistance. In particular, the wave potential ΦW(1) causes a very large phase shift of the wave-resistance curve, which results in greatly improved agreement with experimental data.
Study of Prismatic Planing Model Spray and Resistance Components
Authors: Latorre Robert
Published: January 2021

The results of a study of prismatic planing model spray and resistance components are presented. The calculated total resistance values are shown to be in good agreement with the measured resistance. The features of the whisker spray and spray blister are discussed along with an experimental technique using wide-beam prismatic models for measuring the spray thickness. A derivation based on energy considerations of the prismatic planing hull pressure resistance component and the spray thickness is presented. The spray thickness values calculated from this formulation are in qualitative agreement with the measured spray thickness. The frictional resistance component obtained from the resistance measurements indicated an extensive laminar flow on the planing model bottom. An acetanilid film was sprayed on the planing model bottom which tripped the laminar-turbulent transition. The CF-values estimated from the acetanilid film pattern were found to be 75 to 90 percent of the CF-values estimated from the corresponding resistance tests.
Comparison Between Theoretical Predictions of Wave Resistance and Experimental Data for the Wigley Hull
Authors: Chen C. Y. , Noblesse F.
Published: January 2021

A number of theoretical predictions of the wave-resistance coefficient of the Wigley hull are compared with one another and with available experimental data, to which corrections for sinkage and trim are applied. The averages of eleven sets of experimental data (corrected for sinkage and trim) and of eleven sets of theoretical results for large values of the Froude number, specifically for F 0.266, 0.313, 0.350, 0.402, 0.452, and 0.482, are found to be in fairly good agreement, in spite of considerable scatter in both the experimental data and the numerical results. Furthermore, several sets of theoretical results are fairly close to the average experimental data and the average theoretical predictions for these large values of the Froude number. Discrepancies between theoretical predictions and experimental measurements for small values of the Froude number, specifically for F = 0.18, 0.20, 0.22, 0.24, and 0.266, generally are much larger than for the above-defined high-Froude-number range. However, a notable exception to this general finding is provided by the first-order slender-ship approximation evaluated in Chen and Noblesse [1],3 which is in fairly good agreement with the average experimental data over the entire range of values of Froude number considered in this study.
Two-Dimensional Sails in Inviscid Flow
Authors: Jackson P. S.
Published: January 2021

This paper develops a general method for two-dimensional inviscid flow about flexible membranes (sails), and presents some general results for a single sail and for two sails interacting. The method is iterative, requiring successive calculations of pressure on a given shape and shape under a given pressure, and is easily extended to more complicated problems..
On the Squat of a Ship
Authors: Naghdi P. M. , Rubin M. B.
Published: January 2021

The problem of the squat of a "two-dimensional" ship is solved using a nonlinear steady-state solution of the differential equations of the theory of a directed fluid sheet. Particular attention is focused on the prediction of the sinkage and trim of the ship, and the results for a model ship qualitatively agree with available experimental data. Specifically, the solution presented here predicts the experimentally observed dependence of the sinkage and trim on the equilibrium depth of the water (regarded here as an incompressible, inviscid fluid), and predicts a nonzero drag for subcritical ship speeds (corresponding to the values of depth Froude number F < 1). The solution also exhibits certain detailed features of the sinkage curves which apparently were not observed in the experiments mentioned above. In this connection, additional relevant experiments are suggested.
A Simple One-Dimensional Theory for Air-Supported Vehicles Over Water
Authors: Tuck E. O.
Published: January 2021

Established theories for the aerodynamics of wings in extreme ground effect are generalized to allow the ground plane to be a free surface of water, on which the pressure is hydrostatic. The resulting free-surface disturbance increases the net lift force, if the trailing edge is the closest point to the undisturbed free surface, and if the (squared) Froude number based on the trailing-edge height is less than the water/air density ratio.
An Experimental and Theoretical Study on Cavitating Cascades and Their Application to Cavitating Propellers
Authors: Furuya Okitsugu , Maekawa Shin
Published: January 2021

In order to develop an analytical tool for predicting the off-design performance of supercavitating propellers over a wide range of operating conditions, a lifting-line theory was combined with a two-dimensional supercavitating cascade theory. The results of this simple method provided fairly accurate predictions for the performance at fully developed cavitating conditions. It was indicative that the fully developed supercavitating (s/c) propellers had strong cascade effects on their performance, and also that the three-dimensional propeller geometry corrections could properly be made by the lifting-line theory. However, the predicted performance with this propeller theory showed a significant deviation from experimental data in the range of J's larger than Jdesign, where partially cavitating conditions are expected to occur. Effort was then made on improving the prediction capability of the above propeller theory at partially cavitating (p/c) conditions. A new nonlinear partially cavitating cascade theory was then developed to provide a proper 2-D loading basis under such conditions. Two-dimensional cascade experiments were then conducted to prove the accuracy of the p/c and s/c cascade theories. The measured forces and flow observations obtained in these experiments shed a new light on the relationship between the forces and cavitation numbers at small angles of incidence. Corrected lift and drag forces were then used in the propeller program. The calculated results for KT and KQ with the new force data successfully correlated with the experimental data, now covering a large J-range where the partially cavitating conditions exist.
Wing Sections for Hydrofoils—Part 3: Experimental Verifications
Authors: Shen Young T.
Published: January 2021

Lifting surfaces such as hydrofoil wings or propeller blades will encounter periodic variations in angle of attack when operated in waves or in nonuniform ship wakes. Undesirable leading-edge sheet cavitation is a common occurrence on hydrofoils and marine propellers. To effectively avoid or delay leading-edge sheet cavitation it is necessary to develop a lifting surface able to tolerate large variations in angle of attack without cavitation. Based on a profile design theory, a series of hydrofoil sections having large cavitation-free bucket widths was developed and presented in previous papers, Part 1 and Part 2. The present paper provides the experimental verification. Profile YS-920 was selected as representative of the series and was tested in a high-speed water tunnel. The measured cavitation inception characteristics and force data of YS-920 were compared with the theoretical predictions. Additionally, they were compared with the measured cavitation and force data of the widely used NACA 66 (MOD) and NACA 16–309 wing sections to show the advantages of using a newly developed hydrofoil section to delay or avoid cavitation.
A Formulation for the Shear Coefficient of Thin-Walled Prismatic Beams
Authors: Bhat Shankaranarayana U. , Oliveira Joao G. de
Published: January 2021

A formulation for the shear coefficient of arbitrary monosymmetric thin-walled cross sections is proposed. The derivation uses integrated or average displacements and rotation, and the effect of Poisson's ratio is taken into account. In contrast to earlier formulations in which three-dimensional stress and displacement distributions for solid sections should first be assumed, the present approach applies directly to thin-walled cross sections. The theory is also valid in the case where the cross section contains several closed cells, and this requires the definition of compatibility conditions which take Poisson's effect into account. Some simple examples are given, which show that the shear coefficient increases by a few percent when Poisson's effect is considered, in a manner similar to what happens with open or single cell sections.
Roll Motion of a Ship in Random Beam Waves: Comparison Between Theory and Experiment
Authors: Roberts J. B. , Dacunha N. M. C.
Published: January 2021

The results of an experimental study of a ship rolling in random beam waves at zero speed are presented. The experiments were conducted in a large wave tank using a 1:20 scale model of the fisheries protection vessel Sulisker. By digitally processing the roll response measurements, obtained over long periods of time, estimates of the probability distribution of the roll peak amplitudes were obtained and compared with some corresponding theoretical predictions. The theory was found to give good agreement with the experimental findings for four different wave elevation spectra. In particular, the experimentally observed deviation from the Rayleigh distribution at high peak amplitudes was correctly predicted by the theory. This deviation is largely due to the pronounced nonlinear character of the roll damping.
Estimation of Nonlinear Ship Roll Damping from Free-Decay Data
Authors: Roberts J. B.
Published: January 2021

A common method of assessing the damping present in ship rolling motion is to perform a free-decay experiment, in which, in the absence of waves, the ship is given an initial roll amplitude and then released. By processing the resulting decaying, oscillatory trace it is possible to estimate quantitatively the degree of damping, even when this is nonlinear. In this paper an approach to the estimation of nonlinear damping is proposed which involves the use of a cubic spline interpolation of the peak amplitudes, followed by a parametric identification procedure. This method is first applied to some simulation data and then to some real free-decay data, obtained from a scale model of a ship, with various initial conditions. The experimental data are analyzed using two alternative parametric forms, that is, linear-plus-quadratic and linear-plus-cubic damping. A principal advantage of the proposed technique is that, because nonlinearities in the restoring moment are properly accounted for, it is not limited to small angles of roll. Thus it can be applied to free-decay data relating to very large initial roll amplitudes.
Optimal Blade Design for Windmill Boats and Vehicles
Authors: Blackford B. L.
Published: January 2021

This paper discusses the theoretical problem of designing the optimal windmill blade for use on windmill boats and vehicles, sailing at any angle with respect to the wind. The analysis shows that the optimal design for this application is considerably different from that for a conventional stationary windmill. A theoretical comparison is given between the net forward thrusts produced by such a windmill thruster and an airfoil sail, for all sailing directions. The comparison shows that a windmill thruster should be superior to a sail for boat speeds of half windspeed or lower, and vice versa for boat speeds higher than half windspeed. Experimental results from a 4-m catamaran boat, using a 4-m-diameter wind turbine, and from a wheeled vehicle, using a 1.2-m-diameter wind turbine, have been obtained. The boat achieves an upwind speed of about 50 percent of the wind speed and the vehicle achieves about 100 percent, in agreement with theory.
Post-Buckling Analysis of Heavy Columns with Application to Marine Risers
Authors: Kokkinis Theodore , Bernitsas Michael M.
Published: January 2021

The post-buckling behavior of heavy tubular columns following static instability under the combined action of weight, tension/compression at the top, and fluid static pressure forces in the gravity field is studied. A two-dimensional nonlinear small-strain large-deflection model of the column is derived, consisting of an integrodifferential equilibrium equation and two end rotation conditions. The equation of equilibrium is discretized using a finite-element method. An approximate solution valid in the neighborhood of the bifurcation point and an incremental solution are used to determine the secondary equilibrium path. The results of both methods are corrected by Newton-Raphson iteration. Conditions for unstable initial post-buckling behavior and existence of limit points on the secondary equilibrium path are presented. The numerical solution is applied to the problem of the elastica and is found to be in good agreement with the analytical solution. The secondary equilibrium path for a 500-m-long (1640 ft) marine drilling riser is calculated for two sets of boundary conditions and various values of the drilling mud density. The effect of the drilling mud density and the boundary conditions on the riser's post-buckling behavior is discussed.
Torsional Buckling of Columns by the Lyapunov Method
Authors: Akeju T. A. I.
Published: January 2021

The paper presents an application of Lyapunov's direct method to torsional and torsional-flexural buckling of columns. A metric space and a Lyapunov functional are proposed for each of the problems. Making use of Zubov's stability theorem and appropriate eigenvalue inequalities, the functionals yield the expressions for the buckling loads for simple and fixed supports. Of particular interest is the relative ease with which the expressions are derived, especially in the torsional-flexural buckling case, where it has not been necessary to seek the roots of the traditional cubic equation which governs the critical loads of the member.
Flexure of Polygonal Plates with Circular Holes
Authors: Wah Thein
Published: January 2021

A procedure is developed for determining the stresses in a polygonal plate with a circular hole. Classical plate theory is assumed. The boundary conditions are satisfied exactly term by term. Numerical results are given.
Mixing-Length Formulations for Turbulent Boundary Layers Over Arbitrarily Rough Surfaces
Authors: Granville Paul S.
Published: January 2021

Mixing lengths are formulated for turbulent boundary layers over arbitrarily rough surfaces from both the van Driest and the Rotta procedures. The associated eddy viscosities and the associated turbulent kinetic energies and turbulent dissipation rates are also formulated.
Added Mass of Two Cylinders
Authors: Venkatesan S. K.
Published: January 2021

Expressions for the classical added-mass coefficients have been calculated for the case of two arbitrary circular cylinders using the dipolar coordinate system. These are then applied to calculate the three nonzero added-mass coefficients of two identical circular cylinders in terms of constants of Jacobian elliptic functions. A calculation procedure is also evolved for the case of two circular cylinders of different radii. Finally, these results are extended to the case of twin cylinders of arbitrary shape using a certain family of conformal mappings.
A Lifting-Line Equivalent Profile Method for Propeller Calculations
Authors: Politis G. K.
Published: January 2021

The theoretical shortcomings of Lerbs' equivalent profile method are discussed and a novel equivalent profile method, using lifting-line theory, is presented. Details of the iteration scheme necessary for the solution of the resulting nonlinear problem are given. The problem of the equivalent radius is rationally formulated and uncertainties are shown to exist concerning the choice of the equivalent radius and the approximate relations for the efficiency and the power loading coefficient. The test results of five model propellers, with different geometric characteristics, are used in an extensive sensitivity-analysis procedure to demonstrate the good behavior of the proposed lifting-line equivalent profile method. A corresponding sensitivity analysis of Lerbs' equivalent profile method shows poor behavior with respect to changes in the equivalent radius, especially for non-constant-pitch propellers. The new method can easily be applied to wake-adapted propellers.
A Note on Ice Scaling
Authors: Jones Norman
Published: January 2021

A new dimensionless number is introduced in this note for the behavior of ice when the influence of gravitational and fracture, or cracking, forces are important. It appears likely that these forces should be scaled correctly when modeling the breaking of ice around offshore platforms and artificial islands and the cracking of ice fields around icebreaker bows.
Nonlinear Stability Analysis of Ship Towed by Elastic Rope
Authors: Bernitsas Michael M. , Kekridis Nikos S.
Published: January 2021

The course stability of a towed vessel is traditionally assessed using local linear analysis of a time-independent system of a ship towed by an inelastic towline. In this work a method is developed for studying the global stability of a nonlinear time-dependent model of the horizontal plane motions of a ship towed by a nonlinear elastic rope. First, the critical points of the corresponding autonomous system are found in the phase space and their nature is determined by local analysis. Then the global behavior of the trajectories in the phase space is predicted on the basis of the local analysis results. The results of the stability analysis are verified by comparison with the solution of the model by simulation. A barge, a tanker and a Mariner, with markedly different course stability characteristics, towed by two different elastic ropes are used to illustrate the method.
On Optimum Sculling Propulsion
Authors: Potze W.
Published: January 2021

Using a semilinear and two-dimensional theory, the highest possible efficiency is considered for sculling propellers consisting of two wings, the interaction of which is taken into account. The force and pitching moment acting on each wing and the power needed to move the wings are determined. The influence of the variation of a number of parameters is calculated.
Effect of a Simulated Free Surface on the Wake of a Slender Body
Authors: Mitra P. , Neu W. , Schetz J.
Published: January 2021

Turbulent flow measurements were performed in the wake of a slender axisymmetric body in the presence of a flat plate strut and an image plane crudely representing the "rigid lid" approximation to a free surface. The tests were performed in a wind tunnel at a nominal Reynolds number of 6.0 ⨯ 105. A Yawhead probe was used for the mean flow measurements, and a Constant Temperature Anemometer System with an x-wire probe was used to obtain the turbulent flow characteristics. The presence of the image plane was found to increase the velocity defect and the static pressure as the image plane was approached. A redistribution among the various components of velocity fluctuations was noted near the image plane. The transverse component was enhanced at the expense of the normal component. The image plane also was found to influence the magnitudes and radial spread of turbulence intensities and Reynolds stresses. Some interactions between the wake of the axisymmetric body and that of the plate strut were observed. Overall, the mean velocities and the turbulence quantities indicated symmetry about the image plane throughout the wake.
On the Numerical Radiation Condition in the Steady-State Ship Wave Problem
Authors: Jensen Peter Schjeldahl
Published: January 2021

The waves created by a thin ship sailing in calm water are examined. The velocity potential of the ship in the zero Froude number case is known and the additional potential due to the waves is calculated by the Green function technique. The simple Green function corresponding to the Rankine source potential is used here. Two major problems exist with this method. In the Neumann-Poisson boundary-value problem- probably the first iteration toward a full nonlinear solution to the ship wave problem _it is necessary to impose a radiation condition in order to get uniqueness. This problem is related to the second one, which arises due to the existence of eigensolutions. The two-dimensional situation is here analyzed first, thereby easing the three-dimensional analysis. A numerical scheme is constructed and results for the twodimensional waves generated by a submerged vortex and for the three-dimensional waves due to the Wigley hull are presented.
On Radiated and Scattered Waves from a Submerged Elliptic Cylinder in a Uniform Current
Authors: Mo A. , Palm E.
Published: January 2021

The two-dimensional radiation problem and diffraction problem are discussed for submerged elliptic cylinders when a current is present. It is shown that the impact of the current on the wave amplitudes and wave forces is large. The singularity in the problem, corresponding to a wave traveling upstream with a group velocity equal to the speed of the current, is examined. As expected, this singularity influences the motion strongly. It is found, however, that the amplitudes and forces remain finite.
Note on Vortex Control in Simulated Sail-Hull Interaction
Authors: McGinley Catherine B.
Published: January 2021

An experiment was performed in an attempt to use vortex "unwinders" to reduce or remove the horseshoe vortex that arises from the sail-hull intersection on submersibles. Although studies of the flow downstream of this sail-hull intersection show that the vortex can be reduced, removal of the vortex may have an adverse affect on the downstream wake region since the horseshoe or necklace vortex contributes to wake diffusion. Another approach to the horseshoe vortex problem is suggested whereby the vortex generated by the sail-hull intersection is initially augmented to aid in wake diffusion and subsequently removed downstream by appropriately placed unwinders.
Unsteady Linearized Lifting-Surface Theory in the Presence of a Free Surface
Authors: Leclerc J. , Salaun P.
Published: January 2021

A new lifting-surface theory is developed for the computation of three-dimensional hydrodynamic pressures on thin structures in the presence of a free surface. Two interesting cases are treated: the steady case and the supercritical unsteady case. The theory is linearized and the problem is reduced to the solution of an integral equation where the unknown function is the pressure difference between the elements of the structure and the right-hand side the angle of attack. Forces and moments are presented in both the steady and unsteady cases. This theory allows the analysis of flutter and the study of steady drag and of the turn of ships.
Application of the Cyclic Strain Approach to the Fatigue Failure of Ship Structural Details
Authors: Fricke Wolfgang , Paetzold Hans
Published: January 2021

The cyclic strain approach is useful for determining the fatigue life of notches strained in the elastic-plastic region. Examples are the flame-cut edges of cutouts in the ship steel structure. After the description of the cyclic stress-strain behavior of the usual mild steel, the individual elements of the approach are described: the probability distribution of load amplitudes, the relationship between load and local elastic-plastic strain, the relationship between the damage parameter and fatigue life, and finally the damage accumulation law. The approach is illustrated by two examples of longitudinal/transverse web intersections. In the first, the predicted life is confirmed by experimental results. The second example shows the approach for complicated load combinations. It is hoped that this paper will contribute to sound and crack-free ship structural details, particularly if unusual loads are applied to well-tried details or if simplified designs are introduced.
Analysis of Wave-Induced Horizontal-and-Torsion-Coupled Vibrations of a Ship Hull
Authors: Wu Jong-Shyong , Ho Chian-Sen
Published: January 2021

The natural frequencies and mode shapes of the horizontal-and-torsion-coupled vibrations of a ship hull with large hatch openings were investigated using the finite-element method; the dynamic behavior of the ship hull due to excitation of regular waves was studied by means of the Newmark direct integration method. In order to determine the property matrices of the entire ship hull, the hull was considered a nonuniform free-free beam composed of various open-and close-sectioned thin-walled tubes. Then the elemental mass matrix and stiffness matrix of each beam segment were derived based on the relationship between the kinetic energy and the nodal velocities and on that between the potential energy and the nodal displacements of each beam segment, respectively. The assembly of the elemental mass matrices and stiffness matrices will give the overall property matrices of the entire ship hull. In the forced vibration analysis, attention was paid to the influence of the responses of the heading angle, ship speed, and some key parameters relating to the structural properties. Also considered in this study were the effects of warping torsion, shear deformation, rotatory inertia, shear center and centroid, which are not concurrent, and the shear centers of various cross sections that are not collinear.
The Mechanics of the Flame Bending Process: Theory and Applications
Authors: Moshaiov Amiram , Vorus William S.
Published: January 2021

The flame bending process can be most useful in the present effort to automate the plate bending process in shipyards. To achieve this goal, the complicated thermo-elastic-plastic behavior of the plate during the process must be understood. A review of the past analytical research efforts reveals that these attempts have been restricted to beam bending. Here a theory for the thermo-elastic-plastic plate bending is developed. Furthermore, using a boundary element method as a solution technique, the difference between the mechanics of beam bending versus plate bending is shown. Recommendations for future work are given.