bluuebunny/crossref_metadata_2025 huggingface dataset:
Distribution Functions of Mass Properties: A Tool for Naval Architecture
Authors: Birbanescu-Biran Adrian
Published: January 2021

Dynamic sea load calculations require the lumping of the ship into a number of mass sections. For each such section, its mass, center of gravity and some components of its tensor of inertia must be calculated. Previously, this problem was solved by tedious methods. This paper presents a general method of calculating these data out of a database containing the mass data of all ship items. The method is based on the notion of distribution functions of mass properties. It is shown that two types of mass distribution functions can be used for representing all possible distributions. These functions are the step mass distribution and the second-degree mass distribution functions. Distribution functions of moments and moments of inertia can be calculated from the mass distribution functions by analytic integration and/or multiplications. The distribution functions are also an easy means of calculating the mass properties of a jumboized ship, starting from the data of the original ship.
The Elastic-Softening Failure of Floating Beams
Authors: Xirouchakis Paul C.
Published: January 2021

The solution is presented for an infinite elastic-softening floating beam under a point load. The response depends on two nondimensional parameters: the negative stiffness coefficient that characterizes the descending part of the moment-curvature curve, and the nondimensional softening region half-length. The solution exhibits two important features that the elastic-perfectly plastic solution does not show. First, in certain ranges of parameters, the elastic-softening beam has a clearly defined maximum load carrying capacity. Second, in some other ranges of parameters, the elastic-softening beam has a minimum load or residual strength. The beam stiffens up upon further deformation due to the reactions of the water foundation. Critical softening parameters are calculated that separate stable from unstable behavior.
Evaluation of the Wavelike Disturbance in the Kelvin Wave Source Potential
Authors: Baar J. J. M. , Price W. G.
Published: January 2021

This paper discusses the numerical evaluation of the characteristic Kelvin wavelike disturbance trailing downstream from a translating submerged source. Mathematically the function describing the wavelike disturbance is expressed as a single integral with infinite integration limits and a rapidly oscillatory integrand. Numerical integration of such integrals is both cumbersome and time-consuming. Attention is therefore focused on two complementary Neumann-series expansions which were originally derived by Bessho [1].2 Numerically stable algorithms are presented for the accurate and efficient evaluation of the two series representations. When used in combination with the Chebyshev expansions for the nonoscillatory near-field component which were recently obtained by Newman [2], the present algorithms provide an effective solution to the numerical difficulties associated with the evaluation of the Kelvin wave source potential.
Theory of Radar Backscatter from Short Waves Generated by Ships, with Application to Radar (SAR) Imagery
Authors: Milgram Jerome H.
Published: January 2021

In calm conditions, synthetic aperture radar (SAR) ship wake images have the form of a bright "V," typically with a half-angle between 2 and 5 deg. The images sometimes persist for many miles behind the ship and are more likely to be obtained if the ship is traveling close to the azimuth direction of the radar than if it is traveling close to the range direction. Here it is shown that Bragg scattering from ship-generated diverging waves is consistent with observed images. Methods of calculating radar scattering cross sections for "idealized" conditions are developed and examples from their use are presented.
Structural Simplification of Jack-Up Rig and Its Dynamic Responses in Regular Waves
Authors: Wu Jong-Shyong , Chang Cuann-Yeu
Published: January 2021

This paper is composed of two main parts: simplification of leg structure of the jack-up rig, and dynamic analysis of the entire rig due to excitation of regular waves. First, the legs of spatial beamlike lattice with rigid joints are replaced by the equivalent beams through application of the theory of static condensation and the principle of virtual work. Then the equations of motion of the entire rig are derived based on the simplified mathematical model, and the natural frequencies and mode shapes are sought by the Jacobi method. Finally, the dynamic behavior of the hinged rig and fixed rig operating in four kinds of water depths (and hence effective leg lengths) and wave heights is studied by means of the mode superposition technique. The phase angles between responses of the legs and the influence on responses of support conditions at the seabed, wave attack angle, and damping ratio are the key points of the investigation.
Splashless Ship Bows with Stagnant Attachment
Authors: Madurasinghe M. A. D.
Published: January 2021

Flow around a two-dimensional semi-infinite theoretical model of a ship bow is investigated with the aim of deriving a bow shape which possesses the desirable property of "splashlessness." There is numerical evidence that such flows can exist only for special body geometries. The flows of interest in this study possess a stagnation point at the attachment point and demand underwater bodies of a bulbous type, in order to be splashless. The nature of the solutions is discussed, giving analytical evidence, and a numerical scheme is then presented. The variation in the bulb shape and size with Froude number is discussed in detail.
On the Motion of a Slender Body Submerged Beneath Surface Waves
Authors: Wilmott P.
Published: January 2021

A slender axisymmetric body is submerged beneath a regular train of waves on an inviscid, incompressible, infinitely deep fluid. Using the method of matched asymptotic expansions, the velocity potential in the neighborhood of the body is calculated, thus determining the mean second-order vertical force when the body is permitted to respond to the exciting forces and moment but is otherwise moving with constant forward speed and depth beneath a head sea. To stablilize the body motion, the effects of a hydrofoil placed on the body axis are included. Several examples are computed showing the dependence of mean vertical force on body velocity.
The Motions of SWATH Ships in Waves
Authors: Fang Ming-Chung
Published: January 2021

Strip theory for a single running ship is applied to predict the coupled motions of smallaterplane area twin-hull (SWATH) ships, with and without speed, in waves. The hydrodynamic coefficients, in cluding the interactions between two hulls, are analyzed in a twodimensional manner and an integral equation method is utilized. To obtain the exciting force the three-dimensional diffraction potential is temporarily maintained during the derivation and finally replaced by the two-dimensional one. Neglecting the surge motion, five modes motions are obtained. The validity of the present theoretical prediction of SWATH motions is well confirmed by the existing model experimental results even in a following sea at high speed. Artificial damping due to the fin and viscosity is tested and found to give improvement in the resonant region of motion.
Computation of Viscous Flow Around Propeller-Shaft Configurations
Authors: Stern F. , Kim H. T. , Patel V. C. , Chen H. C.
Published: January 2021

A viscous-flow method for predicting propeller-hull interaction is validated by detailed comparisons with available experimental data for the relatively simple case of propeller-shaft configurations. The steady-flow results are in excellent agreement with the data and show that the present procedures are able to accurately predict many details of the flow field. The dependence of the flow field on propeller loading, including the formation of the hub vortex, is accurately simulated. Also, the robustness of the solution procedure is demonstrated by performing calculations for off-design (large-loading) conditions. The unsteady-flow calculations, which simulate the fanning action of a rotating finite-bladed propeller and which show reasonable agreement with certain general aspects of the experimental data, point out the difficulties of accurately resolving the complex blade-to-blade flow.
Multiple Resonances, Responses, and Parametric Instabilities in Offshore Structures
Authors: Wu Xiong-Jian , Wang Yigong , Price W. G.
Published: January 2021

Based on a functional analysis approach, time history effects are introduced into the representation of the fluid forces associated with offshore structures operating at shallow draft, shallow submergence and/or having a multihull construction, etc. A general linear theory is developed illustrating the pattern of behavior expected in the structure when performing a free decay motion or a forced motion excited by sinusoidal waves. It is shown that even in a simple one-degree-of-freedom mathematical model describing the behavior of an offshore structure, multiple natural frequencies and resonances may be exhibited in the responses. These features are examined and the investigation extended to assess the possibility of multiple parametric instabilities arising in the motions. For this purpose, the mathematical model is slightly modified to include a specific sinusoidal time-dependent term—as is common in a Mathieu type analysis—and conditions determined allowing motion instabilities to occur. This is confirmed by simple numerical examples.
A Numerical Modeling of Ship Bow Waves
Authors: Calisal S. M. , Chan J. L. K.
Published: January 2021

A two-dimensional numerical wavemaker model is used to predict the three-dimensional bow wave pattern caused by a wedge-shaped model moving at constant velocity. Solutions with linear and nonlinear free-surface conditions agree well with the experimental result. A formula derived from dimensional analysis is proved to be a good approximation of the numerical solution based on the linear formulation. A wave splashing phenomenon is predicted at high velocity by the nonlinear theory. The numerical results are compared with the analytic and experimental results reported by Ogilvie [1].2 The improvements given by the nonlinear formulations are observed to be in the correct direction.
Dynamics of Continuous-Mode Icebreaking by a Polar-Class Hull—Part 1: Mean Response
Authors: Ettema Robert , Stern Frederick , Lazaro Javier
Published: January 2021

Results are presented from an ice towing-tank study conducted in order to document the relationships between icebreaking pattern, resistance, and hull motions for a Polar-Class icebreaker model hull moving continuously through sheets of level ice. Two sets of experiments were conducted: for one, the hull was free to pitch, heave, and undergo limited roll (free hull); for the other, the hull was restrained from motions (fixed hull). For each condition, the hull was towed at the same range of speeds through urea-ice sheets of similar properties (thickness, strength, etc.). Measurements were made of resistance as well as motions and restraining forces and moments for the free-and fixed-hull conditions, respectively. The temporal records were analyzed to yield values of their mean and standard deviation and spectral densities. In Part 1 of this two-part paper, the experimental equipment and procedures are described and the values of the mean and standard deviation for both conditions are compared and related to observed patterns of icebreaking. It was found that the mean resistance was larger for the free hull than the fixed hull. For both conditions, mean resistance increased with the square of ice-sheet thickness. The relationship between mean resistance and hull speed was linear for the fixed hull, but not for the free hull, which was characterized by a larger and similar slope at low and high speeds, respectively, than for the fixed hull. The speed range at which the slope changes coincides with that at which the motions are maximum. This correlation indicates that the ice-induced hull motions of the free hull are responsible for its increased resistance over that of the fixed hull. Also, two leading prediction methods ("SPLICE " and "Milano ") are evaluated through comparisons with the measurements. Part 2 (to appear in a later issue) will examine spectral densities with regard to the natural frequencies of hull motions and frequencies associated with the icebreaking pattern to determine the dominant cycles of resistance and motions.
A Submerged Body with Zero Wave Resistance
Authors: Tuck E.O
Published: January 2021

A slender body consisting of a submerged finned spheroid is shown to have zero wave resistance at a design speed, and lower resistance than either the spheroid alone or the fin alone in a range of speeds around design speed
On the Radiation and Diffraction of Surface Waves by Submerged Spheroids
Authors: Wu G. X. , Taylor R. Eatock
Published: January 2021

The problem of wave radiation and diffraction by submerged spheroids is analyzed using linearized three-dimensional potential-flow theory. The solution is obtained by expanding the velocity potential into a series of Legendre functions in a spheroidal coordinate system. Tabulated and graphical results are provided for added mass and damping coefficients of various spheroids undergoing motions in six degrees of freedom. Graphs are also provided for exciting forces and moments corresponding to a range of incoming wave angles.
Slow-Drift Motions of a Moored Two-Dimensional Body in Irregular Waves
Authors: Faltinsen Odd M. , Zhao Rong
Published: January 2021

Weak points in the traditional way of analyzing slow-drift motion are discussed. A theory consistent to second order in wave amplitude and first order in slow-drift velocity for the slow-drift motion of a structure is presented. The interaction between the waves and the local quasi-steady flow due to the slow-drift velocity is incorporated. A new numerical procedure to solve the first-and second-order problem is presented. Generalized Haskind relations for the first-order excitation force and the force due to the second-order potential are derived.
Note on an Accurate Turbulent Velocity Profile for Use at Ship Scale
Authors: Grigson Christopher
Published: January 2021

Determinations of von Karman's constant and of B0 in the law of the smooth wall are compared and the considerable disagreement is explained. One determination, however, unique in its nature, seems definitive. A turbulent velocity profile equation with revised constants and a modified wake term is fitted with high precision to measurements above Rn = 107. Calculations which employ the profile lead to planar drag coefficients about 5 percent larger at full scale than those predicted by the 1957 International Towing Tank Conference (ITTC) line.
Cushioning of Slamming Impact by Elastomeric Layers
Authors: Ando Samon
Published: January 2021

The effectiveness of layers of elastomeric materials bonded to the undersurface of rigid plates in cushioning their impact on calm water was investigated under two-dimensional conditions. It was shown that an elastomeric layer of optimal modulus of elasticity could significantly reduce the slamming forces on flat bottoms falling vertically on a water surface. An elastomeric layer tended to increase the slamming force on wedge-shaped bottoms, but the magnitudes of maximum impact forces on wedge-shaped bottoms either with or without an elastomeric layer were considerably smaller than those values for the flat bottom under identical drop conditions and diminished sharply with increasing deadrise angle.
Three-Dimensional Effects in Ship Relative-Motion Problems
Authors: Beck Robert F. , Loken Arne E.
Published: January 2021

The total relative motion between a ship and the sea surface, including the effects of the ship motions, the incident waves, the diffracted waves, and the radiated waves, is discussed. The radiated and diffracted wave components are calculated using the theory of Salvesen, Tuck, and Faltinsen (1970) with the zero-speed potentials determined by fully three-dimensional calculations. Comparisons with experiments and other theoretical calculations for a simple mathematical hull form are given. The proposed theory shows significant improvement over slender-body theory for the diffraction component and is equal to or better than strip theory for the radiation component.
Theory and Application of a Bi-Metal Ring-Stiffened Cylinder Under External Pressure
Authors: Moshaiov A. , Joelson E. R.
Published: January 2021

Ring-stiffened pressure vessels have historically been constructed of one material only (for example, steel); this is especially true in naval submarines. Existing codes for the design of pressure vessels subjected to external pressure such as ASME and the British Standard BS5500 refer explicitly to unimetal designs only where the stiffening rings and the shell are made of one material only. Bi-metal structures are not accommodated in the design codes. A bi-metal structure would have one type of metal for the shell plating and another type for the ring stiffeners, possibly differing both in Young's modulus and material yield stress. An analytical study of the axisymmetric elastic deformations and stresses in a bi-metal ring-stiffened cylindrical shell under external hydrostatic pressure is given. A closedform solution to the governing differential equation for the bi-metal case is obtained and compared with the uni-metal case. A parametric study is conducted by varying the Young's moduli ratio for the shell and stiffeners of a typical design. Trends in the vessel's critical collapse pressure, shell deflection, and principal stresses are analyzed and the significance of different failure criteria is examined. An approach for modifying current uni-metal design methodologies to accommodate bi-metal structures is suggested. Preliminary comparisons of resulting bi-metal designs with "equivalent" uni-metal designs indicate that a bi-metal pressure hull can have significant advantages. Finally, recommendations for further research studies are made.
Investigation of Effective Bending and Shear Stiffness of Thin-Walled Girders Related to Ship Hull Vibration Analysis
Authors: Senjanovic Ivo , Fan Ying
Published: January 2021

Application of beam theory in flexural vibration analysis of thin-walled girders is extended for the high-frequency domain by introducing the concept of effective values of beam parameters, that is, cross-sectional moment of inertia, shear area, mass, and mass moment of inertia. Formulation of these parameters is based on equivalence of deformation energy and inertia work, respectively, for a considered structure and its beam model, resulting in the same values of their natural frequencies. For illustration, the natural vertical vibration of a simply supported pontoon has been considered, where it was possible to obtain the analytical solution due to sinusoidal mode shapes. The effective values of cross-sectional moment of inertia and shear area show significant variation in frequency domain. Transfer of effective values of beam parameters, determined for simply supported structure, in the case of other boundary conditions is suggested, based on equal mode wavelengths, and checked for the free pontoon. The results show very low discrepancies compared with a three-dimensional finite-element model solution, so this procedure may be applied generally, as well as to the problem of ship hull vibration. In conclusion, the possibility of calculating the values of effective parameters for multicell ship cross sections, utilizing the theory of folded structure and the finite-element method, is pointed out.
Experimental Study of Diesel Engine Cycle-to-Cycle Variation—Part II: Correlation of Ignition Delay and Cylinder Pressure Variation
Authors: Soonnadum M. , Latorre R. , Charnews D.
Published: January 2021

Marine diesel engine excitation can occur from the cycle-to-cycle variation in the engine output. The cycle-to-cycle variation in maximum cylinder pressure is often used to represent this variation. Recent tests indicate a poor correlation between the variation in maximum pressure and variation in pressure impulse (PI). This paper summarizes the results of systematic experiments to determine the cycle-to-cycle variation in maximum cylinder pressure, ignition delay (ID), and corresponding ignition pressure in a single-cylinder test diesel engine at various rpm and compression ratios. Comparisons show that there is a high correlation between the cycle-to-cycle variation in ID and PI. Consequently, the variation in the ignition delays should be used instead of the maximum pressure.
On the Nonlinear Analysis Methodologies for Thin Spherical Shells Under External Pressure with Different Finite-Element Codes
Authors: Boote Dario , Mascia Donatella
Published: January 2021

Submersible structures consist merely of simple and double curvature thin-walled shells. For this kind of structure, collapse occurs due to the combined nonlinear action of buckling and plasticity of material. Load-carrying capacity may then be assessed mainly by two approaches: experimental investigations and step-by-step numerical procedures. In nonlinear analyses, the results obtained are influenced by the magnitude of the load increment adopted. Solution procedures are then required in order to choose adequate parameters for material failure description as well as elastic nonlinearity. The aim of this paper is to carry out a suitable numerical procedure whose reliability does not depend on the finite-element code adopted.
Comment on Ross: “Design of Dome Ends to Withstand Uniform External Pressure”
Authors: Nandakumar C. G. , Rajagopalan K.
Published: January 2021

The instability pressure for a spherical cap that is used as the end closure for the submarine hull is found to be less than that of a cylindrical shell hull. Hence the new proposal for substituting an inverted dome in lieu of the spherical cap for the end closure is eminently worthwhile.
On Optimum Large-Amplitude Sculling Propulsion by Wings of Finite Span
Authors: Potze W.
Published: January 2021

The efficiency of sculling propellers consisting of one or two wings is considered by means of a linearized theory. The thickness and finite span of the wings and their interaction are taken into account. The influence of the viscosity of water on the efficiency is investigated. For a prescribed mean value of thrust and amplitude of the motion of the wings the optimum frequency is determined such that the efficiency is maximum. Numerical results are given in the case that the wings move with "optimum" angles of incidence.
Diffraction Waves About an Advancing Wedge Model in Deep Water
Authors: Miyata Hideaki , Kanai Makoto , Yoshiyasu Noriaki , Furuno Yohichi
Published: January 2021

The diffraction of regular waves by advancing wedge models is studied both experimentally and numerically. The nonlinear features of diffracted waves are visualized by wave pattern pictures and the formation is analyzed by the grid-projection method. The experimental observation indicates that the diffracted waves have a number of nonlinear characteristics similar to shock waves due to the interaction of incident waves with the advancing obstacle in the flow-field caused by the advancing motion. Bow waves of both oblique type and normal detached type are observed at remarkably lower Froude numbers than in the case of a ship in steady advance motion. Their occurrence systematically depends on the Froude number and the wedge angle. The numerical simulation of this phenomenon by a finite-difference method shows approximate agreement with the experimental results.
A Study on Delaminated Cylinders Subjected to Hydrostatic Pressure
Authors: Marshall J. G. , Moshaiov A.
Published: January 2021

In the maritime field composite materials offer several advantages over conventional metallic substances, especially for the construction of deep diving vessels. Such vessels, however, may suffer reduced buckling strength whenever structural defects such as delamination exist. An experimental study has been carried out to explore the delamination buckling in composite cylinders subjected to hydrostatic pressure. The experiments consist of a series of tests on chopped strand glass fiber cylinders. The buckling pressures are obtained for varying delamination sizes and positions. The results of the experiments are shown to follow the theoretically predicted trends.
Numerical Simulation of Nonlinear Free-Surface Flows Generated by a Heaving Body of Arbitrary Cross Section
Authors: Venkat N. Kolluru , Spaulding M. L.
Published: January 2021

A two-dimensional potential-flow model is employed to predict the wave and flow fields generated by wedge, circular, and semicircular cylinders and ship-shaped bodies in forced heaving motion. The case of a wedge penetrating still fluid at constant velocity is also studied. The model solves the potential flow equation, including the full nonlinear free-surface boundary conditions on a boundary-fitted coordinate system. The model equations are solved using a second-order finite-difference technique with a modified Euler method for the time domain and a successive over relaxation procedure for the spatial domain. Model predictions for the force coefficients and phase angles and the associated hydrodynamic mass and damping coefficients of the heaving bodies are generally in good agreement with available analytic theories and data for the dimensionless frequency range, 0
A Theoretical Approach to Bow Deck Wetness of a High-Speed Ship
Authors: Takagi Ken , Niimi Akihiro
Published: January 2021

A theoretical study of the phenomenon of deck wetness is presented and effects of the flare shape are discussed. It is shown that two-dimensional (2D) self-similar flow is applicable to the analysis of deck wetness on the assumption of long wavelength and high Froude number. The 2D self-similar flow which includes effects of the deck is calculated by an analytical method. Calculated results are compared with experimental results obtained at the limit of long wavelength, that is, in still water. Calculated results are used to determine the most suitable flare angle, and it is shown that increased flare is more effective than a knuckle to reduce bow deck wetness.
Computations of Ship Stern and Wake Flow and Comparisons with Experiment
Authors: Patel V. C. , Chen H. C. , Ju S.
Published: January 2021

A numerical method for the solution of the Reynolds-averaged Navier-Stokes equations has been employed to study the turbulent shear flow over the stern and in the wake of a ship hull. Detailed comparisons are made between the numerical results and available experimental data to show that most of the important overall features of such flows can now be predicted with considerable accuracy.
Application of Boundary Integral Method to Continuous Plate Structures
Authors: Moshaiov A. , Vitooraporn C.
Published: January 2021

Ship hulls are composed of complex plate structures. Such structures can be analyzed by analytical as well as numerical methods. Here it is demonstrated that boundary integrals can be used to analyze such structures by a seminumerical method. Boundary integrals have been used for analyzing single plate bending problems, and only recently have attempts been made to extend their use to complex plate structures. In this paper the Direct Boundary Integral Method for bending of thin elastic plates is extended to analysis of the continuous plate structures. The concepts of compatibility and equilibrium conditions along the common boundary have been imposed in conjunction with a boundary element formulation for each panel. Several examples of loading conditions are presented and compared with analytical solutions. The excellent agreement achieved illustrates the effectiveness of the extended formulation.
Statistical Analysis of Failure Time Distributions for Great Lakes Marine Diesels Using Censored Data
Authors: inözü B. , Perakis A. N.
Published: January 2021

Field-censored failure data collected from six identical Colt-Pielstick PC2-400 Great Lakes marine diesel engine components are analyzed. Appropriate censored lifetime data analysis techniques are presented and applied to obtain the probability density function (PDF) parameter estimates for the entire population when only a portion of that population has failed. Weibull and exponential PDF parameters are evaluated for seven components—namely, cylinder pistons, heads, jackets, liners and O-rings, connecting rod bearings, fuel cams, and turbochargers. Reliability and hazard functions for these items are presented and discussed. It is shown that the exponential model is inappropriate for these items.
Sum-and Difference-Frequency Wave Loads on a Body in Unidirectional Gaussian Seas
Authors: Kim M. H. , Yue Dick K. P.
Published: January 2021

When nonlinear effects are included in the diffraction of waves by a large body, there are, at second order, interactions at the sums and differences of the component frequencies of the incident waves. In this paper, the complete deterministic and stochastic solutions of second-order (sum-and difference-frequency) wave loads in unidirectional Gaussian waves are considered. The deterministic result, namely the wave force quadratic transfer function (QTF) in bichromatic incident waves, is complete in the context of second-order diffraction theory in that all the relevant components including those due to the exact second-order potentials are obtained. Statistical properties of second-order wave excitations are then investigated using the QTF results and a two-term Volterra series model. For illustration, the exact second-order force spectra and probability distributions for the simple geometry of a truncated vertical cylinder are obtained and compared with those based on a number of existing approximation methods. It is found that second-order exciting force variances and probability of extreme values may be significantly underestimated by existing approximation methods.
Roll Reduction by Rudder Control for Two Ships During Underway Replenishment
Authors: Fang Ming-Chung
Published: January 2021

A theoretical method for analyzing roll reduction by rudder control for ships during underway replenishment is developed. The basic idea is that, when the rudder is operating, yaw and roll moments will be generated that affect the rolling motion. This idea has been proven to be valid for a single ship running in waves and, therefore, is also applied in the present paper. Using the well-developed strip theory for two ships advancing in waves, a better set of gain coefficients for roll reduction by rudder control can be predicted a priori. From the present results, it is found that suitable rudder control indeed can reduce rolling motion especially at the resonance frequency. The results obtained by the present method can offer some valuable information for a roll-reducing autopilot. Rudder control therefore can be considered as another tool for reducing rolling motion while two ships are executing underway replenishment at sea.
Journal of Ship Research First and Second-Order Wave Effects on a Submerged Spheroid
Authors: Lee C. H. , Newman J. N.
Published: January 2021

Computations are presented for the linearized force and moment acting on a submerged slender spheroid in regular waves, the resulting pitch and heave motions, and the second-order mean force and moment. These numerical results, which are based on the use of a three-dimensional panel code, are compared with the approximations based on slender-body theory. The accuracy of the slender-body approximation is relatively good for the first-order forces and body motions, but substantial errors are revealed for the second-order mean drift force and pitch moment. Unlike the approximate result, the more correct numerical prediction of the mean pitch moment is non-zero, and generally acts in the bow down direction in head seas. To explain this result it is shown that the wave elevation directly above the spheroid increases in amplitude from bow to stern, thus causing a greater upward force on the afterbody relative to the forebody.
A Review of the Kelvin Ship Wave Pattern
Authors: Chung Yong Kwun , Lim Jin Soo
Published: January 2021

This paper finds that the Kelvin ship wave induced by a moving pressure point consists of a single system of divergent waves but that there are infinitely many different Kelvin wave patterns for a submerged point source.
Analysis of the Flow Around Supercavitating Hydrofoils with Midchord and Face Cavity Detachment
Authors: Kinnas Spyros A. , Finer Neal E.
Published: January 2021

In this work, first the linearized supercavitating hydrofoil problem with arbitrary cavity detachment points is formulated in terms of unknown source and vorticity distributions. The corresponding integral equations are inverted analytically and the results are expressed in terms of integrals of quantities which depend only on the hydrofoil shape. These integrals are computed numerically, in an accurate and efficient way, to produce cavity shapes and pressure distributions on the foil and cavity. The effect of the cavity detachment points on the shape of the cavity and the foil pressure distribution is investigated. An inviscid flow criterion for the cavity detachment point is derived for the case where the cavity detaches in front of the trailing edge on the pressure side of the hydrofoil. Finally, the accuracy of the linearized cavity theory is assessed for different foils and flow conditions, by analyzing the produced cavity shapes with a nonlinear panel method.
Forces on Surface-Piercing Propellers with Inclination
Authors: Vorus William S.
Published: January 2021

The well-established methodology developed for calculating the forces on fully submerged subcavitating propellers (Lewis [1]2) is applicable to surface-piercing propellers with similar accuracy. These general formulas are herewith adapted specifically to evaluation of the steady lateral force and moment set on surface-piercing propellers, which may be inclined relative to the stream direction. The fully submerged inclined-propeller case is included as a specialization of the formula. Predictions are compared with the traditional thinking on the effects of inclination and propeller geometric characteristics, such as blade rake, on boat performance attributes, such as steering torque and running trim.
Numerical Simulation of Unsteady Laminar Flow Over Vibrating Bodies (Planar Flow)
Authors: Venkat N. Kolluru , Spaulding Malcolm
Published: January 2021

A model is developed to simulate two-dimensional laminar flow over an arbitrarily shaped body, a part of which is subjected to simple harmonic motion. The vibration amplitude ratio, Ho, and the Reynolds number, Re, are maintained at 0.1 and 1000, respectively. The Strouhal number, St, is varied in the range 0.0 ≤ St ≤ 1.0. The computer code is tested for the flow in a square cavity and also over a flat plate. The friction and pressure coefficients over the vibrating portion of the body are determined. Fast Fourier Transforms are performed on the time series data of these coefficients. For low-frequency vibrations (low Strouhal number) the pressure and friction coefficients match the steady-state results for flow over a sinusoidal bump. A small-amplitude pressure wave generated by the oscillating plate propagates downstream with the flow. For high-frequency vibrations (high Strouhal number) the pressure and friction coefficients over the vibrating portion of the body deviate from the steady-state results and a high-amplitude pressure wave propagates downstream. The pressure at one chord length upstream is also affected. As St increases, the flow becomes highly nonlinear and higher harmonics appear in the downstream flow. Subsequent analysis indicates that the nonlinearity is controlled by the term v(Əu/Əy).
Modified Strip Model for Analyzing the Line Heating Method-Part 2: Thermo-Elastic-Plastic Plates
Authors: Moshaiov Amiram , Shin Jong Gye
Published: January 2021

A modified strip method is developed for analyzing the process of plate forming by the line heating method. The idea has been presented in Part 1 for analyzing elastic plates, and it is extended here to simulate approximately the transient thermo-elastic-plastic plate bending. Two cases are discussed. First, the case of uncoupled thermo-elastic-plastic plate is studied illustrating the use of a modified strip model. Second, generalized coupled governing equations for the thermo-elastic-plastic modified strip are derived and discussed. The results, with the use of a regular strip model, indicate a qualitative error in comparison with the use of a plate model, whereas with the use of a modified strip model a qualitative agreement is reached. Finally, suggestions for future research work are given.
Nonlinear Local Analysis of Steady Flow About a Ship
Authors: Noblesse F. , Hendrix D. M. , Kahn L.
Published: January 2021

A nonlinear local analysis of the steady potential flow at a ship bow and stern, and more generally at any point along a ship waterline, is presented. The hull boundary condition and the nonlinear kinematic and dynamic free-surface boundary conditions are satisfied exactly, at the actual position of the free surface, in this analysis. The bow-flow analysis shows that the free surface at a ship bow is tangent to the stem. This theoretical result appears to agree with existing experimental measurements of steady bow waves of the Wigley hull. Simple analytical expressions defining the fluid velocity at the bow and the stern, and more generally at any point along the wave profile, in terms of the elevation of the free surface at the corresponding point are also given. These analytical expressions and the available experimental measurements of wave profiles along the Wigley hull show that the velocity of the flow disturbance due to this hull is fairly small compared to the hull speed everywhere along the wave profile except in very small regions around the bow and the stern, where the total fluid velocity is nearly equal to the hull speed in magnitude but directed vertically. Nonlinearities therefore appear to be quite important, although only in very small regions surrounding a ship bow and stern. A genuine nonlinear method of calculation must then be able to represent the very rapid variation in the direction of the fluid velocity occurring within small regions around a ship bow and stern. In particular, a sufficiently fine discretization is required in these regions.
Analysis of Straight-Line Motion of Towed Ships
Authors: Papoulias Fotis Andrea
Published: January 2021

The problem of dynamic loss of stability in steady towing of a surface ship is considered. The two coordinates of the towing point and the towline length are the main bifurcation parameters. Bifurcation theory techniques are used in order to compute equilibrium and periodic solutions. The results are confirmed by numerical integrations. It is shown that both linear and nonlinear analyses are required to thoroughly understand, predict, and evaluate the system dynamic response.
Low-Aspect-Ratio Flat Ship Theory for Moderate Froude Numbers
Authors: Cole S. L.
Published: January 2021

Low-aspect-ratio flat ship theory models ships whose dimensions satisfy draft << beam <<length. This paper systematically derives the inner and outer linearized problems for moderate Froude number potential flow past such a ship and their solutions. These solutions are matched through an intermediate region. It is found that the leading-order term for the wave resistance for moderate speed low-aspectratio flat ship theory is the same as found in slender ship theory for ships with equivalent cross-sectional areas. Flat ship theory, however, predicts singularities in the flow along the outside of the ship's leading edge which are not present in slender ship theory. A simple example demonstrating these spurious singularities is worked out.
Discussion on Boote and Mascia: "On the Nonlinear Analysis Methodologies for Thin Spherical Shells Under External Pressure with Different Finite-Element Codes"
Authors: Galletiy G.D. , Blachut J.
Published: January 2021

The accurate prediction of the collapse pressures of thin, doubly curved elastic-plastic shells subjected to external pressure is important in many applications—not least to the occupants of submarines! As is well known, initial geometric imperfections can, in many shells, result in a substantial decrease in the shell's buckling resistance. In their paper, the authors (Boote and Mascia) discuss one imperfect hemispherical model which they analyzed with the help of two general purpose finite-element codes (MARC and ANSYS). The authors do not discuss the use of simpler programs for analyzing these shells [for example, BOSOR 5; Bushnell (1976)][Galletly etal (1987) or other work which has been published on the subject]. We have a number of comments on the subject paper, and these are given below.
Effects of Emulsified Fuel on Combustion in a Four-Stroke Diesel Engine
Authors: Harbach James A. , Agosta Vito
Published: January 2021

While the use of emulsified fuel in diesel engines has been an area of much research interest in recent years, the promising results reported in laboratories have not been easy to reproduce in commercial practice. Many of these studies have only measured external effects such as fuel consumption and exhaust emissions. A single-cylinder research engine was operated with water/diesel fuel oil and hydrous ethanol/diesel fuel oil emulsions of varying percentages. Crank angle, cylinder pressure and injector lift were recorded electronically over 50 engine cycles, permitting calculation of the mean and standard deviation of key combustion parameters. The results showed decreased fuel consumption and increased ignition delay, peak cylinder pressure and maximum cylinder pressure rise rate for emulsion operation. While the standard deviation data showed little change in cycle-to-cycle variation for wateremulsion operation, increases of over 200 percent were measured for operation at ethanol amounts over 20 percent.
On the Theory of Potential Flow About a Ship Advancing in Waves
Authors: Noblesse Francis , Hendrix Dane
Published: January 2021

This study considers the three-dimensional potential flow due to a ship advancing with constant average speed in a train of regular waves. A modified integro-differential equation for determining the velocity potential on the mean position of the hull surface is obtained, and a solid theoretical basis for obtaining a numerical solution of the equation via a panel method is developed following the approach used by Kochin more than 50 years ago. In short, the approach is essentially based on a Fourier representation of the solution of a modified integro-differential equation. This approach circumvents the fundamental difficulties associated with the numerical evaluation of the Green function and its gradient, and their subsequent integration over the panels used to approximate the hull surface of a ship.
Application of Process Analysis Method to the Solution of 2-DNonlinear Progressive Gravity Waves
Authors: Liao S. J.
Published: January 2021

Based on continuous mapping, a kind of analytical method for nonlinear problems, namely, the Process Analysis Method, is described and used to solve two-dimensional nonlinear progressive gravity waves. Solutions at the fourth order of approximation are obtained and compared with Stokesian waves. In contrast to the perturbation expansion method, the Process Analysis Method is independent of small or great parameters and therefore can solve nonlinear problems without small or great parameters.
Development of a Component-Based Scaling System for Ship-Ice Model Tests
Authors: Colbourne D. B. , Lever J. H.
Published: January 2021

This paper presents the development and verification of a method for conducting and scaling ice resistance model tests based on division of the total resistance into three components. It is shown that each of these components is subject to a separate scaling law. A comprehensive literature review traces development of the concept of independent components in icebreaking resistance and covers development of nondimensional scaling parameters. A system of analysis and presentation is developed based on nondimensional parameters unique to each of the identified components. A set of experiments was carried out on a highly simplified full form model to verify the proposed experimental procedure. Data from these experiments demonstrate the excellent data collapse which can be achieved using the developed nondimensional presentation.
Further Contributions to the Theory of Peripheral Jets in Ground Proximity
Authors: Tselnik David S.
Published: January 2021

A number of plane inviscid jet flow problems of interest in hydrodynamics require the use of elliptic functions theory. Generally speaking, finding the general solution to a problem in terms of elliptic functions is not a complicated task. However, finding solutions as rapidly convergent infinite series or as sound asymptotic formulas is often not as easy, and special ways of treatment may prove to be necessary. In parallel with solving the problem of peripheral jets, the author's earlier paper (1985) proposed some such ways of treatment. In the present paper, a new method of treatment is proposed (and used);this approach may be of help in studies where the methods of elliptic functions theory have to be used.
Dynamic Characteristics of a Submerged, Flexible Cylinder Vibrating in Finite Water Depths
Authors: Ergin A. , Price W. G. , Randall R. , Temarel P.
Published: January 2021

This paper presents experimental data and theoretical predictions of the dynamic characteristics (natural and resonance frequencies, mode shapes) of a flexible cylinder vibrating in air and at fixed positions below a free surface in water of finite depth. The flat-ended, thin cylindrical shell of overall length 1284 mm, external radius 180 mm, thickness 3 mm is made of mild steel. In the experiments, the shell was tethered (i) at 0.21, 0.23, and 0.68 m depths below the free surface in water of depth 1.6 m and (ii) at 0.25, 1.5, and 3.5 m depths in 4 m of water. The resonance frequency data recorded provide measures of the influences of free surface, cylinder position, rigid boundary, water depth, etc. occurring in the fluid-structure interaction process. The theoretical predictions are derived from a three-dimensional hydroelastic mathematical model which, through the calculations of the generalized fluid loadings, accounts for the influence of free surface and rigid boundaries, position of submerged cylinder, neutral buoyancy or, as in the present case, with tethers and buoyancy effects. An extensive comparison of results is included. The experimental restrictions of water depth, cylinder position, etc. and the fluid-structure interactions are assessed and illustrated through the calculated resonance frequency values.