bluuebunny/crossref_metadata_2025 huggingface dataset:
A Computer-Based Method for the Preliminary Design of Ships
Authors: Lyon Tim D. , Mistree Farrokh
Published: January 2021

Traditionally, the preliminary ship design process involves satisfying each design requirement sequentially, modifying the dimensions and repeating the process until all requirements are met. This approach neglects the interaction between the major design requirements (such as the effect of stability on deadweight), resulting in an acceptable instead of an optimal design. In order to achieve the most efficient and effective design, a multiple-objective optimization technique has been used. In the past, multiple-objective problems could be solved only in the linear domain using goal programming techniques. The proposed preliminary design optimization model involves a mix of linear and nonlinear goals and constraints and has been solved by a new method (see references [8, 9]). Five comprehensive examples are used to demonstrate the effectiveness of the method and to provide a basis for comparison with other published work. This is believed to be the first application of nonlinear goal programming in this field. The computer-based method proposed is new and makes an important contribution toward the automation of the preliminary design process.
Statistical Analysis of Second-Order Response of Marine Structures
Authors: Naess Arvid
Published: January 2021

A theoretical method is presented for estimating the response statistics of a marine structure that can be modeled as a second-order dynamic system subjected to a stationary, Gaussian sea. The method is particularly suitable for predicting extreme responses. The problem formulation expresses the response in terms of a second-order Volterra series, that is, including a linear and a quadratic term. For this response process the mean upcrossing frequency is found and asymptotic expressions are established that can be used to obtain closed-form solutions to the extreme-value problem.
Seakeeping Characteristics of a Drifting Vessel
Authors: Sellars Frank
Published: January 2021

This paper describes investigation of the roll response of a ship drifting broadside to the waves. Results of experiments with a modified Mariner-type cargo ship model free to roll, sway, heave, and pitch showed broadside drift caused a 20 percent increase in resonant roll amplitude. Calculation results for roll in beam seas with broadside drift confirmed that an increase in resonant roll amplitude is expected. These results are different from previous model tests which showed a reduction in roll when drift occurred. These previous tests had sway restrained and the effect of model test sway restraint on roll has been considered herein. It is concluded that sway restraint has a significant effect on roll.
Effect of the Second-Order Potential in the Slow-Drift Oscillation of a Floating Structure in Irregular Waves
Authors: Aranha J. A. P. , Pesce C. P.
Published: January 2021

The slow-drift phenomenon is important when the waves are irregular and the sea spectrum has a relatively narrow band. In this paper an expression is derived for the low-frequency force due to the second-order potential. This expression is the leading-order contribution in the wave spectrum bandwidth and can be exactly determined without computing the second-order potential. It is shown that this effect is of importance when the water depth is relatively shallow or the typical wave period relatively long.
A Note on the Extreme Wave Load and the Associated Probability of Failure
Authors: Mansour A. E.
Published: January 2021

Introduction and background - The probability distribution of the peak process of a stationary random process with zero mean was first determined by Rice [1]. 2 Following his basic derivation, Longuet-Higgins [2] and Cartwright and Longuet-Higgins [3] evaluated various wave statistics, first for a narrow-band Gaussian process, then extended the results for a Gaussian process of any spectral width.
Hydrodynamic Effects of Fixed Obstacles on Ships in Shallow Water
Authors: Davis A. M. J.
Published: January 2021

The uniform-slender-body theory is adapted to provide first-order estimates of the lateral force and yaw moment experienced by a slow moving vessel in the presence of vertical-sided obstacles. The resulting numerical procedure, which involves only the recursive calculation of coefficients and evaluation of integrals, yields results which demonstrate the considerable hazards to be faced in safely maneuvering the vessel past piers and islands or alongside channel walls.
Two-Dimensional Analysis on the Lateral Drifting Force Between Two Floating Structures
Authors: Fang M. C. , Kim C. H.
Published: January 2021

An analytical procedure for evaluating the lateral drifting forces between two structures by the near-field method is presented. The velocity potentials, including the hydrodynamic interactions, are evaluated by a two-dimensional sink-source technique. This method yields the mean drifting force consisting of four components of which the relative wave elevation term is dominant, whereas the Bernoulli quadratic term is secondary. The phenomena of negative drifting force have been found in the study, which are consistent with the standing wave or negative added mass. The near-field method clearly reveals the effects of the behavior of the response motions such as heave and roll resonances, although it seems to be complicated at first and difficult to use. It is also found that the hydrodynamic interactions between two bodies cannot be neglected. The near-field solutions are required for the further analysis of the quadratic frequency responses function in order to obtain the nonlinear (second order) interaction effects in the presence of dual waves.
Three Indirect Methods for the Drag Characterization of Arbitrarily Rough Surfaces on Flat Plates
Authors: Granville Paul S.
Published: January 2021

Three indirect methods for characterizing the drag of an arbitrarily rough surface on a flat plate are derived or rederived from the similarity laws of turbulent shear flows. These are:the well-known procedure using displacement thickness;the probably not-so-well-known procedure using total drag; anda proposed new procedure using only the freestream velocity and a local shear stress. The classical indirect procedure for pipe flow is also derived to show a commonality with the flat-plate methods.
An Equivalent 3-D Method for Analyzing Orthogonally Stiffened Plate Structures
Authors: Cho Kyu Nam , Vorus William S.
Published: January 2021

A new three-dimensional method is proposed for analyzing orthogonally stiffened grillage structures. The method is based on earlier work related to bridge decks. The relationship between system displacement and loads is described mathematically, and matrices are developed to examine the shear compatibility between plate and beam elements. The paper concludes with a comparison between deflections obtained by several different procedures and the proposed model.
The Surface Singularity Method Applied to Partially Cavitating Hydrofoils
Authors: Uhlman James S.
Published: January 2021

The surface singularity or boundary integral method is formulated numerically for the problem of the fully nonlinear potential flow past a partially cavitating hydrofoil. An iterative scheme is employed to locate the cavity surface. Upon convergence the exact boundary conditions are satisfied on all portions of the foil cavity boundary. The effects of hydrofoil section thickness and camber on cavity volume are investigated. The results are compared with those generated by a numerical linear theory, which includes the effect of section thickness, and with Tulin and Hsu's "short cavity" theory. Both section thickness and camber are shown to have significant effects on cavity volume.
The Full-Scale Viscous Drag of Actual Ship Surfaces and the Effect of Quality of Roughness on Predicted Power
Authors: Grigson Christopher
Published: January 2021

The hydrodynamic roughness functions of hull surfaces are surveyed. Δu+ is given for many different coated surfaces; all the surfaces have different topographies and all have roughness functions of different shapes which reveal that the quality of the roughness is as important as height in the generation of drag. The variety of these functions demonstrates that the viscous drag cannot be predicted without the use of the actual Au+ of the surface of interest. The planar drag coefficients of some of the hull surfaces are given as curves of CFR(Rn) and of ΔO(Rn). The behavior of ΔC with speed is compared with that deduced from careful trials, and is fully compatible with it. It is not compatible, however, with that of the ITTC formulae for AC, and the scientific foundations of the formulae are studied and found unsatisfactory. The influence of surface quality, hitherto not taken into account in predicting performance, could easily explain the relatively large errors in the statistics of predicted trial power. Shipbuilders need to measure the functions ΔU+ of their new hull surfaces and to acquire a data bank connecting their methods of finishing their hulls with Δu+.
The Limiting Values of Added Masses of a Partially Submerged Cylinder of Arbitrary Shape
Authors: Athanassoulis G. A. , Kaklis P. D. , Politis C. G.
Published: January 2021

Using Schwarz's integral formula, new series expressions are obtained for the low-and high-frequency limiting values of the added-mass tensor of partially submerged cylinders of arbitrary shape, including nonsmooth and non-symmetric ones. These series contain the Fourier coefficients of simple geometric quantities of the body contour, and their rate of convergence is controlled by geometrical parameters reflecting the smoothness of the double-body contour. Alternative expressions of a more usual form, in terms of the conformal mapping coefficients of the body contour, are also presented. The off-diagonal elements of the limiting added-mass tensors as well as the low-frequency added moment of inertia for nonsymmetric sections are apparently given for the first time. As an application, closed-form expressions for the limiting added-mass coefficients of an extended-Lewis family of ship sections are obtained. Numerical results are also presented for an extended-Lewis, a rectangular, and three ogival sections. The convergence of the frequency-dependent elements of the added-mass tensors towards their limiting values is also discussed in detail, and it is numerically illustrated for a heeled ship-like section.
The Wake of Self-Propelled and Over-Thrusted Slender Bodies Near a Simulated Free Surface
Authors: Neu W. , Mitra P. , Schetz J.
Published: January 2021

Measurements were performed in the turbulent wake of a propeller-driven axisymmetric body with a plane of symmetry. A flat plate strut was attached to the upper surface of the axisymmetric body, giving a configuration like that of a SWATH-type ship, with the free surface replaced by the plane of symmetry. All mean flow and turbulent flow parameters were measured at three streamwise stations. The measurements were performed for the self-propelled condition and 100 percent over-thrust condition. In the far wake, the center of the wake was found to migrate towards the plane of symmetry. Some interactions were noted between the wakes of the propeller-driven axisymmetric body and that of the flat plate strut—yielding lower axial velocities, higher turbulence intensities and larger static pressure changes compared to regions free of such interference. Comparisons of these effects in the self-propelled case, 100 percent over-thrust case and a previous unpropelled case are given. Spectral measurements were also performed in both near-wake and far-wake regions.
Parametric Identification of Nonlinear Ship Roll Motion from Forced Roll Data
Authors: Gawthrop P. J. , Kountzeris A. , Roberts J. B.
Published: January 2021

A method of estimating the parameters in a nonlinear, single-degree-of-freedom model of ship roll motion is described. It is shown that the "linear-in-the-parameters" nature of the model allows formulation of a relatively simple, and computationally very efficient, estimation procedure, based on a recursive, linear least-squares algorithm. The method is applied to the case of forced roll, where the roll moment excitation can be accurately determined. The general nature of the estimation scheme allows the combining of data from a sequence of experiments with sinusoidal forcing of varying frequency, and also allows the use of data arising from a nonsinusoidal forcing moment. In the latter case all the required parameters in the ship motion model can be estimated from a single test. The technique is illustrated by applying it to both digitally simulated data (where the parameters are known, a priori) and to real data, obtained from a model ship. In the latter case the parameter values obtained by the proposed method are shown to agree well with estimates obtained by alternative, independent methods.
Vibrations and Waterborne Noise on Fishery Vessels
Authors: Ojak W.
Published: January 2021

The Food and Agricultural Organization of the United Nations granted a fellowship to the author to study, at several European ship research institutes, the problem of noise generation and propagation on fishery vessels. He later took part in the design of the fishery research vessel Prof. Siedlecki, which included the implementation of a series of antivibration and antinoise precautions. This paper compares vibration and noise levels on two fishery research vessels—the conventional RV G.O.Sars and RV Prof. Siedlecki. The paper is divided into two parts. In the first part, mechanical vibrations of the elastically supported propeller are dealt with and conditions for minimum vibration response are determined. In the second part, structural vibrations in the ships and noise propagation from the ships to the water are described. The paper concludes with data on structural vibrations and waterborne noise propagation. This paper, and the paper published in the June 1984 issue of JOURNAL OF SHIP RESEARCH [1],2 completes the author's approach to propeller vibrations.
General Dynamic Shape Functions and Stiffness Matrix of Timoshenko Beam and Their Application to Structure-borne Noise on Ships
Authors: Chen Yung-Hsiang
Published: January 2021

The general dynamic shape functions and stiffness matrix of a Timoshenko beam are derived and used to establish the stiffness equations for an entire structural system. All the effects of rotary inertia of the mass, shear distortion, mass and structural dampings, axial force, elastic-spring and dashpot foundation are included in this formulation. These stiffness equations can then be easily modified to account for the influences from the concentrated dynamic properties. Both the low-and high-frequency dynamic responses are discussed generally, with special emphasis on the latter case. The problem of structure-borne noise on ships is also studied as an example for application.
Ship Wave Modification by a Surface Current Field
Authors: Griffin Owen M.
Published: January 2021

One potential contribution to the formation of the narrow-V patterns observed remotely in the wakes of surface ships is discussed. This is the interaction between the ship-generated waves and a surface current pattern in the ship's wake. This surface current field in turn is primarily a manifestation of the turbulent wake caused by the passage of the ship itself. It can be shown by means of relatively simple theoretical arguments that such an interaction can lead directly to a V-wake pattern which is included within a smaller angular region than that of the classical Kelvin waves produced by the steady motion of a surface ship in still water. Predictions of V-wake patterns are obtained which are in qualitative agreement with some of the recently observed ship wakes.
Autonomous Oscillations, Bifurcations, and Chaotic Response of Moored Vessels
Authors: Papoulias Fotis A. , Bernitsas Michael M.
Published: January 2021

The dynamic behavior of single-point mooring (SPM) systems under time-independent external excitation is analyzed. The time evolution of the corresponding dynamical system is described in a six-dimensional phase space. Bifurcation sequences of state equations are studied and parameter values at which the response of the SPM changes radically are identified. Analysis of stability and instability domains of the system reveals regions of operationally hazardous response. It is shown that an SPM system under time-independent environmental excitation may not stay in a position of static equilibrium. It may start oscillating either periodically or even in a random way depending on the dimension of the attracting set in the phase space, which in general may be noninteger. This explains the large-amplitude slow motions of SPM systems, in the horizontal plane, occasionally observed in practice and often attributed to time-dependent excitation from wave drift forces. Based on these results, rational design decisions can be made for selection of the principal SPM geometric parameters in order to improve the system operability.
Closed-Form Spectral Fatigue Analysis for Compliant Offshore Structures
Authors: Chen Y. N. , Mavrakis S. A.
Published: January 2021

Spectral fatigue analysis frequently has been applied to welded joints in steel offshore structures. Although, on the theoretical basis, the spectral formulation holds certain advantages over other formulations such as the discrete, design wave type of analysis, numerical methods developed on that basis generally suffer from the shortcomings of lack of precision and high computational cost. This paper synthesizes the uncertainties resulting from modeling errors that are regarded heretofore as unavoidable in an analysis. Such errors are traced to the approximations introduced in handling of wave data, in numerical integration of the response power spectra, and in the integration that leads to the determination of cumulative fatigue damage. To each of these sources of modeling error, a transparent, closed-form method is proposed which not only eliminates the potential errors but, surprisingly, improves the computational efficiency many times. The sensitivity of fatigue damage upon the variability of the shape parameter due to variability of wave environment for the so-called simplified analysis utilizing an idealized mathematical long-term probability density function (for example, the Weibull distribution) is also discussed.
The Surface Singularity or Boundary Integral Method Applied to Supercavitating Hydrofoils
Authors: Uhlman James S.
Published: January 2021

The surface singularity or boundary integral method is formulated numerically for the problem of the fully nonlinear potential flow past a supercavitating flat-plate hydrofoil. An iterative scheme is employed to locate the cavity surface. Upon convergence, the exact boundary conditions are satisfied on the foilcavity boundary. The predictions of the nonlinear model are compared with those generated by linear theory and with experimental data. In contrast to the results for the partialy cavitating case, the predictions of the linear theory for supercavitating flat-plate hydrofoils are seen to be excellent.
A Study of a Heaving Vertical Cylinder in a Towing Tank
Authors: Çalisal S. M. , Sabuncu T.
Published: January 2021

The effects of tank walls on experimentally measured hydrodynamic coefficients are of concern to researchers. In this numerical study of heaving vertical cylinders in a towing tank, the nonresonant, linear potential flow around a heaving cylinder in a towing tank has been formulated. The method used is based on a matching technique and on Graf's addition theorem. The calculations suggest that "blockage" or "wall effect" is more pronounced in shallow water tanks. A resonant frequency ω, corresponds to the frequency of a wave with a wave length equal to the width of the tank. For frequencies higher than ωr hydrodynamic coefficients are very close to infinite domain values for large values of the ratio of the tank beam to the cylinder radius. For frequencies less than ωr blockage correction to the hydrodynamic coefficients is necessary.
Analysis of Deformation Distribution of Different Points of Hull Cross Section
Authors: Nassef Ismail
Published: January 2021

The main objective of this work is to obtain deformations of different points of a hull cross section. Such deformations are impossible to determine using the theory of strength approach. For this purpose, elastic theory methods are applied. The resulting equations have excess terms studying the distribution effect of material of the cross section. An application of the resulting equations is presented with an evaluation of the difference between the traditional and the author's results.
Axisymmetric Viscid-Inviscid Interaction by a Frozen Vorticity Approximation
Authors: Hoffman Gilbert H.
Published: January 2021

A numerical solution procedure capable of a high degree of automation is presented for calculating the flow field associated with viscid-inviscid interaction on a body of revolution. The method makes use of ideas from asymptotic triple deck analysis of the trailing-edge problem. A simpler problem is solved in which two layers are postulated, an outer inviscid, rotational layer ("frozen vorticity") which largely governs the pressure in the trailing-edge region, and an inner turbulent layer which is modeled in a simple manner. These two layers are patched at a fixed distance from the wall and wake centerline rather than asymptotically matched. The method allows the viscid-inviscid interaction solution to be obtained by computer in four iterations, none of which require any user intervention. A high degree of automation is achieved in the computer code because of three factors:the solution cycle is very stable,all calculations use a common streamwise grid, andinformation is transferred to successive stages of the calculation by computer-generated files. Numerical solutions are presented for three bodies and the results compared with published experimental data.
Prediction of Heat Leakage Through Fish Hold Wall Sections
Authors: Wang De-qian , Kolbe Edward
Published: January 2021

Heat transfer through hold wall sections was investigated to improve prediction of heat leakage through fish hold boundaries of steel fishing vessels in the range of 14 to 32 m (45 to 105 ft). A finite-difference heat-transfer model was developed and eight fish hold wall sections representative of a 14 m (45 ft) boat were tested using the "guarded hot box" technique (ASTM C 236-80). Good agreement was obtained between the predicted and tested results. By applying the model, design curves of wall sections representative of typical West Coast steel vessels are presented.
Dynamics of Continuous-Mode Icebreaking by a Polar-Class Hull—Part 2: Spectral Analysis
Authors: Stern Frederick , Ettema Robert , Lazaro Javier
Published: January 2021

Part 2 of this two-part paper presents additional results from an ice towing-tank study of a Polar-Class hull for two conditions: 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). Measurements were made of resistance as well as motions and restraining forces and moments for the free-and fixed-hull conditions, respectively. In Part 1, the values of the mean and standard deviation for both conditions are compared and related to observed patterns of icebreaking. In Part 2, the spectral densities are examined with regard to the natural frequencies of hull motions and frequencies associated with icebreaking pattern to determine the dominant cycles of resistance and motions. A series of experiments was conducted to determine values of zero-speed natural frequencies and added-mass and damping coefficients for ice-covered conditions. The presence of an ice sheet significantly reduces the natural frequencies and increases the added-mass and damping coefficients. It was found that hull motions and icebreaking pattern determined the dominant cycles of resistance for the free hull. Icebreaking frequency, the frequency of individual breaking events, was significant only for thin ice such that significant heave and pitch did not occur. When w b was less than the natural frequencies of coupled heave and pitch amid ice, w the dominant frequency of resistance and motions occurred at integral fractions of usually b/2. The frequencies, (b/n, are associated with the icebreaking pattern, that is, cyclic manner by which hull trim changed as the hull broke and cleared a track through an ice sheet. When b equaled or exceeded to„, the dominant frequency of resistance coincided with The fixed hull responded at higher frequencies than the free hull, usually at u>0. Also, available full-scale data are shown to be in reasonable agreement with the present results for the free hull. Lastly, the principal conclusions of the overall study are summarized and the implications of the present work with regard to the development of prediction methods are discussed.
Experimental Study of Diesel Engine Cycle-to-Cycle Variation—Part I: Analysis of Cycle-to-Cycle Cylinder Pressure Variation
Authors: Chayangkura C. , Latorre R. , Charnews D.
Published: January 2021

With the increased use of marine diesel engines, engine-induced vibration has become an important problem. The vibration is caused by engine output variation, which has not been fully documented. In this paper the results of an analysis of the cycle-to-cycle variation in the cylinder pressure of a single-cylinder diesel test engine are presented. Data covering tests with different compression ratio settings and speeds are analyzed in terms of (a) cycle-to-cycle variation in maximum cylinder pressure Pmax and (b) cycle-to-cycle variation in the combustion work, denoted PI. Special tests are made to validate the data acquisition and data reduction system. The validation shows that the cylinder pressure measurements from the test engine run as a spark-ignition engine are in good agreement with published results. Analysis of the diesel engine test measurements show that the coefficient of variation in the diesel engine cylinder pressure is smaller than the spark-ignition engine value. These results also show there is relatively little correlation between the cycle-to-cycle coefficient for variation of the maximum pressure and the corresponding variation in the combustion work, PI.
Flow Structure Near the Bow of a Two-Dimensional Body
Authors: Grosenbaugh Mark A. , Yeung Ronald W.
Published: January 2021

Flow near a blunt ship's bow is experimentally investigated by studying the flow in front of horizontal, surface-piercing cylinders. A bore-like structure develops at the bow of a cylinder when it is immersed in a uniform stream. Observations indicate that the leading edge of this bow wave coincides with a point at which the main flow separates from the free surface. Experimental measurements of the location of the wavefront and the slope of the free surface at the wavefront are in fair agreement with existing theoretical predictions. Power spectra of the time records of the bow-wave elevation show a characteristic oscillation frequency at Froude numbers above a critical value. The bow-wave oscillation is a function of the cross-sectional shape of the two-dimensional body, the draft, and, to a lesser extent, the flow velocity. The inception of the oscillation depends on the Reynolds number, but the characteristic frequency is governed by inertial and gravitational forces.
Boundary-Layer Effects on Wave Resistance of a Ship Model
Authors: Shahshahan Ali , Landweber Louis
Published: January 2021

The wave-resistance coefficients of a Wigley ship form have been calculated by the Michell integral, using the Michell thin-ship centerplane distribution, a slender-body hull-surface distribution, and a slender-body centerplane distribution. These calculations have been carried out for two different cases:wave-resistance calculation without the effects of the boundary layer and wake, andcalculations including these effects. Results have been compared with the residuary resistance and the "measured" wavemaking resistance, obtained as the difference between the measured total and wake-survey resistances.
Numerical Study of Wall Influence on Boundary-Layer Transition for Two-Dimensional NACA 16-012 and 4412 Hydrofoil Sections
Authors: Latorre R. , Baubeau R.
Published: January 2021

One of the difficulties in hydrofoil model tests is the relatively low Reynolds number of the test piece and the presence of the test section walls. This paper presents the results of systematic calculations of the potential flow field of NA 4412 and NACA 16-012 hydrofoil in a test section with wall-to-chord ratios h/c -1.0. The corresponding boundary-layer calculations using the CERT calculation scheme are presented to show the influence of the nearby walls on shifting the location of the boundary-layer laminar-turbulent separation as well as turbulent separation. By introducing an effective angle of attack, it is possible to obtain close agreement in the calculated and measured suction side pressure distortion as well as the locations of the boundary-layer separation and transition.
Effect of Heavy Weather Maneuvering on the Wave-Induced Vertical Bending Moments in Ship Structures
Authors: Soares C. Guedes
Published: January 2021

Statistical data are collected so as to quantify the probability of occurrence of voluntary course changes in heavy weather as well as their dependence on significant wave height and on ship heading. Decision rules are established about when and how to change course, on the basis of the analysis of operational data and of interviews with experienced shipmasters. A Monte Carlo simulation is performed so as to determine how an omnidirectional distribution of initial headings is changed by voluntary course changes depending on the significant wave height. Finally, the effect of the nonuniform distribution of headings on the mean wave-induced vertical bending moment is calculated. It is shown that although heavy weather maneuvering eases the ship motions, it can increase the wave-induced bending moments and thus increase the probability of structural failure.
Vibration and Buckling of a Thin-Walled Dome Under External Water Pressure
Authors: Ross C. T. F. , Johns T.
Published: January 2021

The paper describes an investigation into the vibration and buckling of two similar thin-walled hemiellipsoidal prolate domes under external water pressure.
On the Influence of Choice of Generator Lines on the Optimum Efficiency of Screw Propellers
Authors: de Jong K. , Sparenberg J. A.
Published: January 2021

The optimum efficiency of a screw propeller, with or without end plates, depends on the geometry of the generator lines of blades and end plates. Quality numbers of propellers have been calculated for a variety of generator lines. The shape of the planform of end plates is discussed in order to minimize their viscous resistance.
Discussion on Grosenbaugh and Yeung: “Flow Structure Near the Bow of a Two-Dimensional Body”
Authors: Gadd G. E.
Published: January 2021

A note on surface tension effects on breaking bow waves - In their interesting recent paper [1], Grosenbaugh and Yeung show that the forward extent of a breaking bow wave in front of a two-dimensional body can be significantly affected by the addition of surfactants to reduce surface tension. However, although they note that contaminants such as dust can also affect the surface flow, they appear to be unaware of the possibility that dynamic effects on surface tension, particularly when surfactants are present, may play an important role, as discussed in reference [2]. As shown by Davies [3], surface films can damp eddies at a free surface of a turbulent liquid. The mechanism is due to the so-called Marangoni effect; that is, where a surface film is locally stretched, the surface contaminant concentration is momentarily reduced, leading to an increase in surface tension which tends to contract the local surface region again. This is why a soap bubble is so much more stable than one formed in pure water. Similarly, upwelling flows associated with turbulence at a water surface cause local stretching and contraction which will tend to be opposed by the presence of the surface contaminant.
An Investigation of Liquid Sloshing in Toroidal Containers
Authors: Modi V. J. , Welt F.
Published: January 2021

Liquid sloshing within torus-shaped partially filled containers is studied both analytically and experimentally, The potential flow model in conjunction with the boundary-layer correction is used and the perturbation method applied to solve for the nonlinear free surface equation. The pressure and damping forces exerted by the fluid on the solid walls are derived and compared with the results of the experimental program. Nonlinear phenomena involving the case of resonant coupling between the first and second liquid sloshing transverse modes at large container diameter ratios and low liquid heights are thoroughly investigated as they yield large damping ratios. The energy dissipation characteristics are particularly attractive at low frequencies generally encountered in a marine environment. The concept is likely to be useful for the design of stabilizers for buoys, ocean drilling platforms, and ships.
The Numerical Modeling of Ship Motions and Capsizing in Severe Seas
Authors: de Kat Jan O.
Published: January 2021

A numerical model has been developed to determine the large-amplitude motions of a steered vessel subjected to severe wave conditions, including those that may lead to capsizing. The model was used to identify different modes of capsizing, and to study relevant mechanisms and conditions. In this paper emphasis is placed on the theoretical aspects. The nonlinear model combines both potential and viscous flow effects, where integrations are carried out in the time domain over the instantaneous free surface; first-order memory effects are taken into account, and the free surface can be irregular, Some new results are presented concerning statistical properties relevant to the simulation of random following or quartering seas.
A New Approach to Linear Buckling of Thin Circular Cylindrical Shells
Authors: Vendhan Chiruvai P. , Bhattacharyya Subroto Kumar
Published: January 2021

Adopting an end-problem approach to static displacement equations of thin circular cylindrical shells, a type of coupled eigenvalue problem is developed which integrates the eigenvalue problem of bending as well as that of linear buckling. This is shown to provide an alternative mathematical criterion of linear bifurcation buckling. In addition, it provides new insight into the nature of Saint Venant effects. Numerical illustrations for an isotropic shell are worked out to demonstrate the structure of the proposed eigenvalue problem.
Ship Lines Using Convexity-Preserving Rational Cubic Interpolation
Authors: Clements John C.
Published: January 2021

A convexity-preserving, twice continuously differentiable, piecewise rational cubic interpolant f to offset data S = {(xj,yj)|j = 1, …, n; Δj2 ≠ 0; xj+1 > xj} is defined in terms of "tension" parameters τj, j = 1, …, n - 1 and the end conditions f"{x,) = f"(x„) = 0. The condition f"(xj)Δj2≥ 0, j = 2…..n -1 imposed on f is both necessary and sufficient to ensure that the interpolant preserves the local convexity/concavity properties of the set S. An algorithm for generating f is given and applied to the generation of ship lines from design station offset data. The specific advantages of this interpolant are its smoothness, simplicity, speed of computation and convexity-preserving properties.
Analytical Determination of the Critical Load of Delaminated Plates
Authors: Moshaiov Amiram , Marshall James
Published: January 2021

The presence of a delamination in a composite material may cause early buckling which could lead to structural collapse. Earlier studies have shown the effect of the delamination length both experimentally and numerically on the critical load of a laminated plate. In this paper an analytical study is performed involving the length of the delamination and its location, resulting in a characteristic equation for the buckling. The closed-form analytical solution for the critical bad agrees well with published numerical results which use both a Rayleigh-Ritz and a finite-element approach.
Modeling of Flow Around a Marine Propeller Using a Potential Based Method
Authors: Maitre T. A. , Rowe A. R.
Published: January 2021

A nonlinear method is presented for calculating potential flow around lifting bodies. The perturbation potential is taken to be unknown at the surface of the body while its value is fixed inside the body. This method is particularly well suited to cases of thin structures. It is applied to calculate the flow around a noncavitating marine propeller for which several difficulties are examined and solutions proposed: problem of the Joukowski condition, problem of propeller mesh, wake description. The influence of the hub and the calculated wake on numerical results is analyzed.
Computation of Viscous Flow Around Propeller-Body Configurations: Iowa Axisymmetric Body
Authors: Stern F. , Toda Y. , Kim H. T.
Published: January 2021

Further validation of a viscous-flow method for predicting propeller-hull interaction is provided through detailed comparisons with recent experimental data for the practical configuration of the Iowa axisymmetric body. Modifications are made to the k-ε turbulence model and wall functions for axisymmetric bodies. Close agreement is demonstrated between the calculations and the data, which supports the conclusion that the present procedures can accurately simulate the steady part of the combined propeller-hull flow field. However, the present extensive comparisons also point out the critical role of turbulence modeling and detailed numerical treatments. Also, comparisons are made with Huang's inviscid-flow method. Although both methods show similar trends, there are some important differences; for example, Huang's method predicts reduced propeller loading and larger axial velocities in the propeller plane near the body surface and propeller tip. Near the propeller tip, the present method exhibits a velocity defect region, which is absent in Huang's method. In consideration of the greater rigor of the present method, such differences imply that viscous effects play an important role in propeller-hull interaction even for the relatively simple case of an axisymmetric body and should be accounted for in the design procedures of wake-adapated propellers. However, part of the differences may be due to some of the present detailed numerical treatments, which indicate the need for continued refinement of comprehensive methods, such as the present one, and more detailed experimental information for validation purposes.
Ricochet Off Water of Spherical Projectiles
Authors: Miloh T. , Shukron Y.
Published: January 2021

The oblique water-entry problem of a spherical projectile is analytically analyzed with special reference to the ricocheting phenomena of the object off a free surface. Under the assumption of large impact velocity, the Kelvin-Kirchoff-Lagrange equations of motion are formulated in terms of the various time-dependent added-mass coefficients and their time derivatives. The actual trajectory of the sphere below the free surface is obtained by integration of these equations, and a critical value for the projectile incident angle (ricochet) is obtained in terms of the initial Froude number and the specific density of the solid. It is demonstrated that for infintely large Froude numbers this solution reduces to the well-known empirical expression for the critical angle of a sphere in oblique water-entry.
Calculation of the Rise and Pitch of a Three-Dimensional Low-Aspect-Ratio Flat Ship
Authors: McComb Todd
Published: January 2021

Using low-aspect-ratio flat ship theory, this paper defines a procedure to determine the position of a hull which is in equilibrium at some "fast" speed in terms of a given hull shape for the same hull at rest. This procedure is then used to find the equilibrium flow past a moving ship, when given the shape of the hull at rest. The method is then extended to find the hull configuration at various speeds based on either the configuration in the static case or at some other equilibrium speed, leading to a calculation of drag versus speed. Some general formulas and some simple examples are given.
On the Planar Translation of Two Bodies in a Uniform Flow
Authors: Guo Zhi , Chwang Allen T.
Published: January 2021

The general planar translation of two bodies of revolution through an inviscid and incompressible fluid is considered. The moving trajectories and the hydrodynamic interactions are computed based on the generalized Lagrange equations of motion, including the effects of solid constraints, external forces in the plane of motion, and a uniform stream in any direction parallel to the plane of motion. In a relative coordinate system moving with the stream, the kinetic energy of the fluid is expressed as a function of six added masses due to motions parallel and perpendicular to the line joining the centers of two bodies. Analytical solutions of added masses in series form are obtained for the motion of two spheres. A new iterative formula based on the analysis of velocity potentials around each body is developed for added masses and their derivatives with respect to the separation distance due to the transverse motion. The method of successive images and Taylor's added-mass formula are applied to determine the added masses and their derivatives due to the centroidal motion. These results are compared with the numerical solution of added masses computed by the boundary-integral method and the generalized Taylor added-mass formula. The integral equations, in terms of surface-source distributions on both surfaces, are modified for obtaining accurate numerical solutions. Numerical results are given for several practical engineering problems.
Similarity-Law Analysis and Turbulence Modeling for Riblet Drag Reduction
Authors: Granville Paul S.
Published: January 2021

A complete similarity-law analysis is developed for riblet drag reduction which results in a flat-plate drag formula. As an example, a design chart is developed for a particular riblet configuration from its empirical drag characterization. The riblet drag characterization is applied to turbulence modeling such as an eddy-viscosity formula and the k-ε method.
A General Theory for the Coupling Between Thickness and Loading for Wings and Propellers
Authors: Kinnas Spyros A.
Published: January 2021

The incompressible, inviscid flow around a generally shaped wing in arbitrary inflow is analyzed as a perturbation expansion, with respect to wing thickness, superimposed on the zero thickness lifting-surface problem (also called the mean camber surface problem). The first-order term in that expansion is shown that can also be treated as a lifting-surface problem with the inflow normal to the lifting surface given as the sum of two velocities. The first of those velocities is the one induced by the wing thickness source distribution and is non-zero in the case of a non-planar wing or in the case of a propeller. The second velocity is due to the coupling between wing loading and thickness and is given as a function of the zero thickness vorticity distribution and the wing thickness distribution. The presented method, though applicable to general shape wings (without any assumptions on the magnitude of wing twist or camber) in arbitrary inflow, is shown to reduce to previous methods of evaluating the coupling between thickness and loading for two-dimensional foils and planar wings in uniform inflow. Finally, the presented method is applied for several wing and propeller blade geometries and the results are shown to be in very good agreement with those from applying an existing potential based panel method.
The Rankine Topping Cycle Revisited
Authors: Woodward John B.
Published: January 2021

Cascaded thermodynamic machines are familiar in marine engineering, even if the word "cascade" is not common currency in that field. The author refers to the almost universal practice of exhausting the working fluid (air) of a diesel engine into a gas turbine (the turbocharger, usually), followed by exhausting of that working fluid into a heat exchanger that energizes the working fluid (water) of yet another turbine. If the same practice is to be described in terms of the respective power cycles, we would probably say that the cascade consists of a Rankine cycle topped by a Brayton cycle which is in turn topped by a diesel cycle. In similar fashion, recognized nomenclature might describe the diesel component as the "topping cycle," and the Rankine as the "bottoming cycle." The topping/bottoming nomenclature usually implies two different working fluids, so that the Brayton cycle might be described as a subpart of the topping cycle.
On Useful Shapes of Rigid Wings for Large-Amplitude Sculling Propulsion
Authors: Sijtsma P. , Sparenberg J. A.
Published: January 2021

If a wing of finite span moves through an incompressible and inviscid fluid, it will in general experience a resistance force, or equivalently, it leaves vorticity behind. We wonder if there are shapes of wings, which can move in a nontrivial way without leaving vorticity behind? We consider rigid, flat wings, hence without thickness and without curvature. Then we find, by numerical means, that wing shapes exist which can move tangentially to an arbitrary cylindrical surface without leaving vorticity behind. In fact, when we prescribe a chordlength distribution along the span, a unique wing shape with this property seems to exist. Such a resistanceless motion can be used as a base motion in the theory of sculling propulsion.
Feature Extraction from B-Spline Marine Propeller Representations
Authors: Patrikalakis Nicholas M. , Bardis Leonidas
Published: January 2021

This paper presents accurate algorithms for the extraction of gross geometrical features of marine propeller blades represented in terms of B-spline surfaces. These features have important hydrodynamic function and include specifically the camber surface, the section thickness function, pitch, rake, skew, chord length, maximum thickness, maximum camber of the section and leading edge. The approximation of the camber surface, on which most of the remaining features are based, is an intricate problem relying on an extension of the concept of a Brooks ribbon and requiring the solution of a complex system of nonlinear differential equations, developed for the problem at hand, and a sophisticated error evaluation scheme. The above features provide an alternate abstract representation of propeller blades useful in geometric design through lofting and fairing processes, in idealization for hydrodynamic and structural dynamic analyses and in verification of the quality of a manufactured blade. Furthermore, the derivation of these design features provides an alternate shape interrogation method for propeller blades, which is more intuitive for propeller designers in comparison with existing surface interrogation techniques.
Induced Effects on Propeller Inflows: Harmonics of Effective Wakes
Authors: Breslin John Pershing
Published: January 2021

A theory for the effects of the coupling of propeller inductions with radial and tangential shears in ship wakes is developed from linearized Euler equations. The main purpose is to determine the harmonics of effective wake by use of the given nominal wake. The analysis begins with a model in which the shears are neglected for propeller-induced velocities in spatially nonuniform flows. This demonstrates that the desired temporal mean components are due to both steady and unsteady blade loadings. This behavior also applies when the shear or vorticity are included. The field pressure with shear must satisfy a modified-Helmholtz equation having a parametric function of the reciprocal of the given axial wake velocity. A solution is found in terms of integrals for a class of shear flows whose parameters can be calculated from the given wake. The theory is found to be inapplicable at small radii for the case examined because of nonlinear effects. A possible alteration is outlined to compensate for this. Some tentative conclusions are drawn.