bluuebunny/crossref_metadata_2025 huggingface dataset:
The Generalized Image Model—An Application to the Design of Ducted Propellers
Authors: Kinnas Spyros A. , Coney William B.
Published: January 2021

The problem of the potential flow in the vicinity of two distinct bodies A and B, subject to a given inflow, is addressed. The flow field around B is analyzed by distributing singularities on its boundary. It is shown that in the presence of body A those singularities correspond to the modified source and dipole which satisfy the boundary condition on A, including the Kutta condition at its trailing edge. The generalized images of the singularities on B with respect to body A are defined as the difference between the modified and the free space sources or dipoles. The generalized image method is then applied to the design of ducted propellers. The propeller is modeled with lifting lines and the flow around it is analyzed as if the propeller were open. The duct is accounted for by taking as inflow to the lifting lines the flow inside the duct in the absence of the propeller and by pairing each of the lifting line vortex horseshoes I . . I with its generalized image with respect to the duct. The generalized image is determined by evaluating the flow around the duct in the presence of each of the vortex horseshoes by employing a potential based boundary element method. The optimum circulation distribution of the propeller inside the duct is determined by employing a discrete nonlinear optimization technique in order to maximize the propulsive unit efficiency. The effect of the main parameters of the problem on the optimum propeller circulation and the propulsive efficiency is shown with some examples.
Optimum Circulation Distributions for a Class of Marine Propulsors
Authors: Coney William B.
Published: January 2021

A new method for determining the optimum circulation distributions for both single- and multiple-stage marine propulsors is developed. The lifting-line model for the propulsor is first discretized with a vortexlattice. Variational calculus is then applied to this discretized problem. The result is a general procedure for determining optimum circulation distributions. This procedure can be readily extended to increasingly complex combinations of interacting lifting lines. The propeller lifting-line, vortex-lattice model is described in some detail. Circulation optimization equations for a propeller are derived. The equations are shown to recover traditional results for both light and moderate propeller loading, as well as for wake adapted propellers. Optimization equations for the torque limited case are presented. The vortex-lattice model for multiple stage propulsors is described and the optimization equations are derived. Examples of optimum circulation distributions for contrarotating propellers, a vane-wheel propulsor, and a propeller with pre-swirl stator are presented.
Hydrodynamic Forces and Motions of a Cylinder Near a Vertical Wall
Authors: Lewandowski Edward M.
Published: January 2021

A method for the evaluation of the hydrodynamic forces and moment on a cylinder, located near a vertical wall in water of finite depth, in regular waves, is presented. The method is applied to the simple case of a circular cylinder. The motions of the cylinder and the mean lateral drift force due to the waves are also evaluated. The presence of the wall is shown to have a pronounced effect on the added-mass and damping coefficients of the cylinder in a certain frequency range; the mean lateral force may become negative (directed toward the incident waves) in this range. A simple physical explanation for the results is provided.
Hydroelasticity and Wave Loads for a Full-Form Ship with Shallow Draft
Authors: Dong Yan Qiu , Lin Weixue
Published: January 2021

A shallow-draft full-form ship is a particular type of ship with a breadth-to-draft ratio higher than is conventional. To investigate the characteristics of such full forms in response to hull vibrations induced by waves, a special computer program based on the hydroelasticity theory of ships has been developed. In addition, an experimental investigation using a segmented elastic-keel model of the ship has been carried out in order to verify the theoretical calculations. It is found from calculation of the wave loads that the dynamic responses of this specific hull form cannot be accurately predicted by strip theory. It is concluded therefore that hydroelasticity theory should be used in the design of the hull structure.
The Icebreaking Problem in Two Dimensions: Experiments and Theory
Authors: Valanto Petri
Published: January 2021

Model experiments on the transient response of a floating ice sheet to an advancing icebreaker were carried out in two dimensions in order to provide information on the actual icebreaking phenomenon associated with ships advancing in level ice. The response consists of two parts:the dynamic bending of the ice sheet to flexural failure; andthe rotation of the broken ice slab until the slab is parallel to the bow plate of the advancing vessel.

A theoretical approach to calculate the transient response of the floating ice sheet is presented. The theory is based on the assumption of potential flow with a relatively complicated boundary condition on the ice sheet-fluid surface. The numerical solution is based on an initial-value approach. The kinematic and dynamic boundary conditions on the ice sheet-fluid boundary are used to advance the solution in time. The predicted results are compared to the experimental ones to evaluate the validity of the theoretical assumptions made. In most cases close agreement between experiments and theory is demonstrated. Together with the experiments, the numerical model developed is able to clarify several physical phenomena contributing to icebreaking resistance at the waterline of a vessel advancing in level ice.
On the Hydrodynamics of Vertically Oscillating Planing Hulls
Authors: Troesch Armin W.
Published: January 2021

This paper is concerned with the various modeling assumptions associated with planing boat dynamics and hydrodynamics when the hulls are traveling at low to moderate planing speeds. In particular, experimental results of the time-dependent behavior of the wetted length, amplitude dependence of the restoring force matrix, and amplitude and frequency dependence of the hydrodynamic inertia and damping matrices are presented. The experiments were conducted with prismatic hulls of varying speeds, length/beam ratios, and trim angles. Suggestions are made with respect to the physical modeling of the different terms in the equations of motion thus providing guidance to researchers interested in applying modern methods of dynamical systems analysis to planing dynamics. Significant nonlinear effects are identified in the restoring force matrix and relatively smaller ones in the added mass and damping matrices.
Properties of Finite-Difference Operators for the Steady-Wave Problem
Authors: Letcher John S.
Published: January 2021

A feature of most implementations of Dawson's boundary-integral method for steady free-surface flows is the use of upstream finite-difference operators for the streamwise derivative occurring in the linearized free-surface boundary condition. An algebraic analysis of a family of candidate operators reveals their essential damping and dispersion error characteristics, which correlate well with their observed performance in two-dimensional example flows. Some new operators are found which perform somewhat better than Dawson's, but the general outlook for accurate results using difference operators is nevertheless bleak. It is shown that the calculation necessarily diverges as panel size is reduced, and a breakdown at higher speeds is also inevitable. More promise appears to lie in satisfying the radiation condition by several alternative ways, which are briefly discussed.
Effects of Waves on the Wake of a Surface-Piercing Flat Plate: Experiment and Theory
Authors: Stern F. , Choi J. E. , Hwang W. S.
Published: January 2021

Results are presented from a towing-tank experiment conducted in order to document the effects of waves on the wake of a surface-piercing body. A unique, simple model geometry is utilized which makes it possible to isolate and identify the most important features of the wave-induced effects. Measurements were made for three wave-steepness conditions: zero, medium, and large. The effects of the waves for the latter two conditions are shown to be significant. In particular, the variations of the external-flow pressure gradients cause acceleration and deceleration phases of the streamwise velocity component and alternating direction of the crossflow, which results in large oscillations of the displacement thickness and wake centerplane velocities as compared to the zero-steepness condition. Remarkably, the wake displays a greater response, that is, a bias with regard to favorable as compared to adverse pressure gradients. The measurements are compared and close agreement is demonstrated with results from Reynolds-averaged Navier-Stokes calculations. Additional calculations are presented, including laminar-flow results, which aid in explicating the characteristics of the near and intermediate wake, the periodic nature of the far wake, and wave-induced separation. Previously, experimental and computational results were presented for the boundary-layer region.
Dynamics and Bifurcations of Pursuit Guidance for Vehicle Path Keeping in the Dive Plane
Authors: Papoulias Fotis A.
Published: January 2021

The problem of dynamic interactions between an orientation control law and pure pursuit guidance law for dive plane response of underwater vehicles is analyzed. A complete stability analysis is performed in order to evaluate regions of stable vehicle operations. It is shown that loss of stability can occur in either a static or dynamic way. In the first, a linearly increasing path deviation is observed, whereas in the second the loss of stability is accompanied by the generation of self-sustained oscillatory motions around the commanded path. Nonlinear analysis reveals the occurrence of both static and Poincaré-Andronov-Hopf bifurcations. Numerical experiments support the analytic predictions of the bifurcation analysis.
Lofting and Fabrication of Compound-Curved Plates
Authors: Letcher John S.
Published: January 2021

The fabrication of plates with compound curvature (nonzero Gaussian curvature) from initially flat sheet material necessarily involves some degree of in-plane plastic strain. A basically geometric theory is presented for modeling and controlling this process, leading to a quantitative description of both the strain distribution required to achieve the compounding, and the relationship between points and curves on the curved surface and the flat material. The theory thus provides accurate methods for lofting (expansion or plane development) of curved plates, as well as quantitative control of the compounding process. Several methods of numerical solution are presented, with illustrative examples.
Modern Nonlinear Dynamical Analysis of Vertical Plane Motion of Planing Hulls
Authors: Troesch Armin W. , Falzarano Jeffrey M.
Published: January 2021

When operating in a seaway, high-speed planing hulls exhibit strong nonlinearities. This paper investigates the vertical plane dynamic stability and response associated with such craft. Explicit expressions for the hydrodynamic forces are developed and modern methods of dynamical systems analysis are applied. An illustrative example is given in which the forced and unforced motions are examined. Parameter studies relating to the following topics are made: the onset of porpoising, the magnitude of motions while porpoising, and forced motions due to regular waves. It is found that while nonlinear effects can reduce the response over that predicted by linear theory, these same effects can also be responsible for sudden extreme behavior. The method described here is another tool that designers and operators can use to provide a more comfortable and safer vessel performance.
A Boundary Element Method for the Analysis of the Flow Around 3-D Cavitating Hydrofoils
Authors: Fine Neal E. , Kinnas Spyros A.
Published: January 2021

The three-dimensional steady cavitating hydrofoil problem is treated in nonlinear theory by employing a low-order potential-based boundary element method. The cavity extent and shape are determined for given cavitation number by satisfying the three-dimensional kinematic and dynamic boundary conditions on the hydrofoil surface beneath the cavity and on the portion of the wake sheet overlapped by the cavity. A unified discretization and algorithm is developed to predict the occurrence of general cavity planforms, including partial cavitation, supercavitation, and mixed partial/supercavitation. The cavity planform is determined iteratively by searching for the planform which corresponds to a closed cavity at all spanwise locations. Cavity shapes predicted by the present method, applied in two dimensions, are compared to the converged nonlinear cavity shapes and are found to differ only slightly for a range of foil thicknesses and angles of attack. The accuracy of the 3-D method is gaged by satisfying Green's formula, subject to a kinematic boundary condition, on a modified foil consisting of the union of the original foil and the cavity predicted by the present method. Comparing the resulting pressure distribution to the pressure distribution from the present method shows that the dynamic boundary condition is satisfied to within acceptable accuracy.
Experimental Study of Diesel Engine Cycle-to-Cycle Variation—Part IV
Authors: Orianto Mohamad , Latorre R. , Charnews D.
Published: January 2021

Marine diesel engine excitation can occur from the cycle-to-cycle variation in the engines output. The cycle-to-cycle variation in maximum cylinder pressure (P,,=,) is often used to represent this variation. Earlier studies examined the correlation between the cycle-to-cycle variation in the maximum cylinder pressure (Pm~), pressure impulse (PI), and ignition delay (ID), for the case of constant injection setting. Recent studies showed the injection timing strongly affects the cycle-to-cycle variation. This paper summarizes the results of systematic experiments to determine cycle-to-cycle variation for a single-cylinder diesel test engine and extrapolation to estimate the cycle-to-cycle variation in a 12-cylinder 925-hp diesel propulsion engine. Comparison of the extrapolated and measured results shows reasonable agreement.
Oscillatory Third-Order Perturbation Solutions for Sums of Interacting Long-Crested Stokes Waves on Deep Water
Authors: Pierson Willard J.
Published: January 2021

Oscillatory third-order perturbation solutions for sums of interacting long-crested Stokes waves on deep water are obtained. A third-order perturbation expansion of the nonlinear free boundary value problem, defined by the coupled Bernoulli equation and kinematic boundary condition evaluated at the free surface, is solved by replacing the exponential term in the potential function by its series expansion and substituting the equation for the free surface into it. There are second-order changes in the frequencies of the first-order terms at third order. The waves have a Stokes-like form when they are high. The phase speeds are a function of the amplitudes and wave numbers of all of the first-order terms. The solutions are illustrated. A preliminary experiment at the United States Naval Academy is described. Some applications to sea keeping are bow submergence and slamming, capsizing in following seas and bending moments.
Inverted Pendulum Stabilization of Submarines in Free Positive Buoyancy Ascent
Authors: Papoulias Fotis A. , McKinley Brian D.
Published: January 2021

The problem of steady-state vertical ascent of a submarine with excess buoyancy is analyzed. All possible vertical plane solutions are computed and their stability is established in both in-plane and out-of-plane perturbations. Divergence of trajectories, sensitivity of solutions to initial conditions, and stable inverted pendulum configurations are shown to exist for certain ranges of parameters.
On Combination of Slamming-and Wave-Induced Responses
Authors: Hansen P. Friis
Published: January 2021

Attempts to solve the combination problem of the low-frequency wave-induced bending and the high frequency slamming induced bending moments in ships have so far been based on a Poisson pulse train model for the occurrence of the slamming impacts. Embedded in the Poisson pulse model is the assumption that the time of occurrence and the intensity of a slamming impact are independent of the corresponding quantities of the previous impact. This assumption is not valid because the periodic character of the ship motion tends to concentrate the slamming impacts in clusters. Further, the times of occurrence of the slamming impact and the wave-induced stress peaks are highly correlated. Slamming impact usually generates the first peak of a compressive (sagging) slamming stress in the deck, as the wave-induced stress passes from hogging to sagging. The magnitude of the wave-induced and slamming-induced stress peaks, however, tends to be slightly negatively correlated. The work in the present paper is based on the so-called Slepian model process. This is a non-Gaussian and nonstationary process that gives a complete description of the original ergodic Gaussian process after an arbitrary upcrossing into a critical interval. By use of the Slepian model process, the joint distribution of the wave amplitude and the frequency is established at the occurrence of maximum slamming response within a cluster of slamming impacts. Thereafter the response is calculated for regular sinusoidal waves at selected wave amplitudes and frequencies. Response statistics are obtained by weighing the calculated response by the probability densities of the various pairs of wave amplitude and frequency.
Cross Track Error and Proportional Turning Rate Guidance of Marine Vehicles
Authors: Papoulias Fotis A.
Published: January 2021

The problem of turning rate guidance and control of marine vehicles is considered. Feedback with feed forward rudder control is used to deliver a specified turning rate for the vehicle, while a guidance law is employed to create the necessary sequence of turning rate commands which would allow convergence to a desired geographical path. Two different guidance schemes are presented and analyzed, namely, cross track error and proportional turning rate guidance. Stability conditions are computed explicitly, while nonlinear analysis techniques illustrate the significance of design parameters on the final system response that cannot be inferred from linearized stability results.
Effects of Impulse Duration and Combined Impulse-Hydrostatic Pressure on Buckling Stability of Cylindrical Structures
Authors: Pegg N. G.
Published: January 2021

Cylinders are primary components of civilian and naval marine structures and may be subject to impulsive loads that can induce a dynamic buckling response. This paper presents a comparative nonlinear finite-element numerical study of the effects of impulse time duration on the dynamic buckling response of a cylinder. The case of combined hydrostatic and impulsive pressures is also investigated to study the effects of an impulsive load on the buckling stability of a submerged cylinder. Dynamic buckling behavior is established by monitoring the nonlinear growth of initial shape imperfections in the finite-element models. The results show that the predominant harmonics and amplitudes of response are affected by the time duration of the pulse, tending towards the static buckling response with increased pulse duration. The combined hydrostatic and impulsive pressures produce significantly greater buckling deformations than either produce on their own, indicating that design against buckling stability, where impulsive loads are possible, should not consider the static and dynamic components independently.
On a Consistent Linearized Theory of the Wave-Making Resistance of Ships
Authors: Bessho Masatoshi
Published: January 2021

There are few discussions on the uniqueness in the theory of the wave-making resistance of ships. Moreover, a line integral term, singularity distribution around a periphery of the waterplane area, appearing in the theory casts a shadow on the uniqueness of the boundary-value problem. There is only one well-known consistent theory, that is, the two-dimensional theory of planing on the water surface in which a line integral term does not appear explicitly. In this theory, the sinkage and trim vary with speed and also the wetted length changes to fulfill Kutta's condition. However, in a usual displacement ship, having a nearly vertical stem, the wetted length could not vary as in the planing ship. In the present paper, introducing a new singularity just before the bow, we try to obtain a consistent linearized theory for a displacement ship. We solve numerically the boundary value problem, investigating the properties of solutions and then calculate the sinkage and trim when a barge is running freely or is being towed without any external force or moment except a towing force. Then, it is found that this free-running barge becomes unstable over the speed Fr = 0.61 regardless of the bottom shape. The resistance consists of three components, namely, the wave-making, the spray, and the water head resistance. The former two components are well known and the last one is a component introduced and named so here temporarily. This component resembles a wave-breaking resistance but we have no direct explanation.
Structural Reliability Analysis of Marine Diesel Engine Shafting Systems: An Equivalent Stationary Process Approach to the Level Crossing Problem
Authors: Lyridis Dimitrios V. , Perakis Anastassios N. , Parsons Michael G.
Published: January 2021

This paper is concerned with the level crossing problem of a stress above some limit. The problem arises when the structural reliability of a diesel engine shafting system is examined. The first excursion failure probability is derived for the case that the stress on the shaft is a one-frequency cyclostationary random process. A new method is introduced where the cyclostationary random process is replaced with an equivalent stationary one, defined to have an envelope process with the same upcrossing rate as the envelope of the original cyclostationary process. Both processes are assumed to have the same probability of upcrossing a specific threshold. The agreement between this approach, which results in an analytical expression, and the "exact," computationally time-consuming "Markov approach" presented in earlier work is excellent.
Cutting of a Longitudinally Stiffened Plate by a Wedge
Authors: Paik Jeom Kee
Published: January 2021

The aim of this study is to obtain test data for longitudinally stiffened steel plates which are quasistatically cut by a rigid wedge, idealizing the deck or bottom platings in ship collision or grounding, and also to derive an empirical formula relating the absorbed energy and cutting length. A series of tests for longitudinally stiffened high-tensile steel plates is conducted, varying several factors, namely plate thickness, plate aspect ratio, angle/shape of wedge tip and property of stiffeners. A total of 50 specimens with thicknesses in the range of 3.4 to 7.8 mm and wedge angles of 15, 30, 45, and 60 deg, including one unstiffened and two horizontally stiffened plate specimens, were tested. The importance of each parameter and its effect on the cutting response are investigated. By dimensionless analysis of the test results obtained here, the energy absorbed while a longitudinally stiffened plate is cut by a wedge is expressed as a function of cutting length, yield stress, equivalent plate thickness, and wedge angle. Incorporation of dynamic effects into the static formula is suggested. A comparison of the proposed solutions with the previous formulas or drop-hammer test results is made.
A New Concept of the Effective Shear Modulus for a Plate Buckled in Shear
Authors: Paik Jeom Kee
Published: January 2021

A new concept of the effective shear modulus is suggested for describing stiffness and strength of a plate in edge shear. This concept has quite similar advantages to the effective width, which has been recognized as an efficient approach for analysis of the post-buckling behavior of thin-walled members in compression. The theoretical background of the new idea is described, and based on results of the series analysis an empirical formula of the effective shear modulus for a simply supported rectangular plate is derived taking into account initial deflection effects. Using this formula, an ultimate shear strength formula of a plate is also suggested. The validity of the proposed formula is checked by comparison with the numerical results. It is concluded that the proposed idea will be quite useful if an effective shear modulus formula is successfully developed.
A Statistical Assessment of the Stochastic Modeling of Torsional Vibratory Loads in Internal Combustion Engines
Authors: Lyridis Dimitrios V. , Parsons Michael G. , Perakis Anastassios N.
Published: January 2021

A statistical assessment of the stochastic modeling of torsional vibratory loads in internal combustion engines is performed, based on (temperature) factory testbed data, for each cylinder of four 16-cyl Colt-Pielstick PC2V type engines at various speeds. Several statistical tests are carried out to examine the hypothesis that the random variables describing the cylinder-to-cylinder variability in marine diesel engine shafting systems are independent and identically (normally) distributed, as assumed in previous work of the authors and other researchers. It is concluded that these assumptions cannot be rejected. Finally, point estimators are derived for the coefficient of variation of the cylinder-to-cylinder variability, and their values are compared to the values proposed elsewhere, which are found to be rather high.
Emulsification Characteristics of Marine Fuel Oils with Water
Authors: Lin Cherng-Yuan , Lin Chein-Ming , Chen Cheh-Skiung
Published: January 2021

The effects of water-to-oil ratio, surfactant content, stayed time, and homogenizing speed on the emulsification characteristics of emulsion activity, emulsion stability, and mean micro-water-droplets diameter for a light distillate fuel oil and a heavy residual fuel oil are experimentally investigated. It is revealed that after centrifuging, the emulsion of the distillate fuel separates into four distinct layers from top to bottom of a test tube. Also, an emulsion of the distillate fuel oil emulsified with surfactant Span 20 is shown to have more fluctuating variations of emulsion activity and mean diameter of water droplets with homogenizing speed. A saturated state of the emulsion with the surfactant addition appears as the surfactant content = 1.5 to 2.0%. Higher surfactant content than 2% is shown to deteriorate the emulsification characteristics of these fuel oils. In addition, the residual fuel oil is found to have better emulsification characteristics in comparison with the distillate fuel oil.
An Experimental Investigation of Burning Droplets of Emulsified Marine Fuel Oils with Water
Authors: Lin Cherng-Yuan , Lin Chein-Ming , Cheng Che-Shiung
Published: January 2021

An experimental investigation is presented of the influences of emulsification of marine fuel oils A and C with water on the micro-explosion phenomenon and combustion characteristics of a burning droplet. The amount of surfactant and water-to-oil ratio by volume in the emulsion are varied to observe the variations of ignition delay, flame length, time required to attain the maximum flame length, duration as well as intensity of micro-explosion, flame appearance, and overall burning time. The measurements show that the emulsification effects on the combustion of marine fuel oils A and C are different. A droplet of C-oil emulsion is shown to be influenced by the addition of water and surfactant more significantly. The micro-explosion phenomena of droplets of A-and C-oil emulsions are seen to occur after and before their ignition, respectively. In addition, separate combinations of water and surfactant content exist for these fuel oils to achieve better emulsification effects on combustion. Droplets of emulsions with W/O = 15/85, E% = 2% for fuel oil A and W/O = 25/75, E% = 1% for fuel oil C are found to have the most violent droplet-disruption phenomenon and the longest flame length.
A Simplified Method to Estimate Longitudinal Deformations of Built-up Beams Due to Welding and Heating
Authors: Jang Chang Doo , Seo Seung II
Published: January 2021

When fabricating built-up beams, longitudinal deformations occur and they impede further work because of fabrication errors. For straightening of the deformations, heating of web plate is necessary. To fabricate built-up beams automatically, control of the deformations is needed, based on precise estimation of longitudinal deformations due to welding and heating. In this paper, to estimate the longitudinal deformations of welded beams, a simplified one-dimensional thermal elasto-plastic analysis method is proposed. Using this method, deformations due to welding and heating can be calculated efficiently and accurately. From the calculated results the phenomena that other researchers neglected were found, and experimental results verified the calculated ones. Simple formulas proposed in this paper can be easily used to control longitudinal deformations.
Prediction of Steady Propeller Performance with a Nonlinear Slipstream and Boundary-Layer Effect
Authors: Liu You-Hua
Published: January 2021

Both slipstream deformation and viscous effects are factors that affect the performance of a rotating marine propeller but neither of them has been properly treated in most of the current lifting-surface methods and surface panel theories. With the introduction of a partial roll-up wake model that is flexible to various cases of propeller geometry and loading condition, this paper presents a vortex-lattice method that can improve propeller performance prediction especially at heavy loading conditions. Some observations on the calculation of the blade leading-edge suction force and how to deduct it to account for the viscous drag increasing are given. The scale effect of propeller performance can be readily predicted by the quasi-three-dimensional boundary-layer calculation presented in this paper. Some patterns of the limiting streamlines on blade surfaces are also illustrated and compared with experimental results.
Wavemaking Resistance of a Group of Submerged Spheres
Authors: Wu G. X.
Published: January 2021

The hydrodynamic problem associated with a group of submerged spheres moving with the same constant speed (or stationary spheres in a uniform current) is analyzed based on the linearized velocity potential theory. There is no restriction on the submergences and radii of the spheres, or on distances between the spheres. The solution is obtained by using the multipole expansion method. The results are obtained for resistances, lifts, and attraction forces between the spheres. The horizontal forces are also compared with the far-field equations derived in this paper and excellent agreement has been found.
Numerical Algorithms for Slender Bodies with Vortex Shedding and Density Stratification
Authors: Wong Haw L. , Çalisal Sander M.
Published: January 2021

The correct prediction of the hydrodynamic performance of ships is an important factor in hull form design. This paper presents efficient numerical algorithms for the calculation of the hydrodynamic forces acting on slender ships. "Parabolized" slender-body theory, generalized to accommodate oblique forward ship motion, transforms a three-dimensional ship wave potential problem into a series of two-dimensional wave-maker problems in the ship frame. The computation starts at the bow section and progresses by marching in steps along the ship length. The application of this procedure for handling surface and interfacial waves created by a prolate spheroid in a density stratified flow is given; results are compared with published experimental results. The parabolized formulation, with the nonlinear free-surface conditions, is used for calculating the wave pattern and wave resistance of a Wigley hull at zero angle of incidence and at an angle of incidence of ten degrees. A hybrid boundary-element, discrete vortex procedure is used to calculate the potential flow. The strength of the vortices and their development is obtained as a part of solution. The numerical results are compared with published experimental and numerical results.
Dynamic Instability in Quartering Seas: The Behavior of a Ship During Broaching
Authors: Spyrou K. J.
Published: January 2021

The dynamic stability of ships encountering large regular waves from astern is analyzed, with focus on delineating the specific conditions leading to the uncontrolled turn identified as broaching. The problem's formulation takes into account motions of the actively steered or controls-fixed vessel in surge-sway-yaw-roll with consideration of Froude-Krylov and diffraction wave excitation. Dynamical analysis of surf-riding is carried out for the general case of quartering waves, exploring the route periodic motions—surf riding, loss of stationary stability, turn, capsize. Steady-state and transient analysis is carried out in the system's multidimensional state-space in order to identify all existing limit sets and locate attracting domains. Broaching from periodic motions is also a part of the investigation.
Ideal Cycle Evaluation of Steam Augmented Gas Turbines
Authors: Woodward John B.
Published: January 2021

A wide range of air-standard Brayton and modified-Brayton power cycles are evaluated to determine their second-law efficiencies and their volume flows per unit output. A cycle with reheating is chosen for further analysis on the basis of its potential for high efficiency through exploitation of its exhaust availability (exergy) and its low volume rates. This exploitation can be had either through a conventional Rankine bottoming cycle, or through injection of the bottoming cycle steam into the Brayton turbine. The Rankine bottoming cycle is superior with respect to second-law efficiency; the cycle augmented by injected steam is superior with respect to volume flows. Examination of irreversibilities illuminates the reasons for the better efficiency of the Rankine bottoming cycle alternative.
The Computer-Aided Functional Design of a Marine Propeller
Authors: Dekanski C. W. , Bloor M. I. G. , Wilson M. J.
Published: January 2021

An existing propeller geometry is represented mathematically using a method for computer-aided design known as the partial differential equation (PDE) method. Using this method of surface design ensures that the propeller blade is completely defined and controlled by a small set of design parameters. This geometry may be analyzed using a panel method to obtain the flow past the blade, and a performance measure, in this case the efficiency of the propeller, is obtained. Functional design of the propeller is achieved by allowing the design parameters to change. Altering the design parameters will affect the efficiency, and hence the set of design parameters which gives a propeller geometry of maximum efficiency is sought. This is achieved automatically through a numerical optimization routine which alters the design parameters. The advantage of this approach is that complex geometries may be represented in terms of a small parameter set which enables the effective implementation of the optimization routine. Constraints may also be imposed to maintain feasible designs. In the case considered the usual design constraints to delay and restrict the onset of cavitation are imposed. However, additional requirements, requiring in themselves substantial analysis, such as strength of the blade, may be considered.
Dynamic Positioning of Ships Using a Planned Neural Network Controller
Authors: Li Ding
Published: January 2021

Dynamic positioning of vessels is a technique which uses ship-mounted propellers and lateral thrusters commanded by a control system to maintain a desired position in the horizontal plane as closely as required. The environmental disturbing forces are those due to wind, waves and current. Heretofore, control systems basing on the PID principle have been used. This paper continues the authors' earlier work on a new kind of neural network control system which has several advantages, among them a versatile objective function which is adaptive to the need of the operator (more precision or more savings in power) and a completely feed-forward control which is self-adaptive to changes in environmental forces, including nonlinear wave drift forces. Emphasis in this paper is placed on the quality of control, which is improved by including a velocity term besides the position term in the objective function. The performance is effectively enhanced. The station-keeping problem is generalized to include moving the ship by neural-net control to a new target position if required. Computer simulations were carried out with satisfying results.
Detailed Bow-Flow Data and CFD for a Series 60 CB = 0.6 Ship Model for Froude Number 0.316
Authors: Stern F. , Longo J. , Zhang Z. J. , Subramani A. K.
Published: January 2021

The bow flow of the Series 60 CB = 0.6 ship model is reinvestigated using both experiments and computational fluid dynamics (CFD). More detailed bow-flow data are obtained by taking measurements of the wave elevation with a point gauge very near the bow. In the CFD, the bow flow is resolved in more detail by using the real bow geometry instead of the simplified vertical zero-thickness bow used in previous studies, which requires a much finer grid in the bow region. The experiments and CFD are briefly described; results are presented; and discussions are made concerning comparisons of the new and old CFD solutions with the extended data regarding the wave profile and elevation at the bow, the thin film and beads (i.e. attached spray sheet and bow vortices), and the stagnation effects.
Two-Dimensional Unsteady Planing
Authors: Ulstein Tore , Faltinsen Odd M.
Published: January 2021

An analytical and numerical study of two-dimensional unsteady planing of a flat plate is presented. The immersion of the plate is assumed small; hence, the spray at the leading edge is represented by a square root singularity. The analogy to airfoil theory is used and the hydrodynamic problem is solved in the time domain. The time-varying wetted-length change due to the water flow is accounted for by a generalized Wagner approach. The present theory is verified by comparison with an analytical solution by Sedov (1940) for water entry of a planing plate and with the linear frequency domain solution by Bessho & Komatsu (1984) for a heaving planing plate.
Estimation of Ultimate Longitudinal Bending Moment of Ships and Box Girders
Authors: Rahman M. K. , Chowdhury M.
Published: January 2021

The paper describes a methodology of computing the ultimate value of the longitudinal bending moment at any cross section of a ship or box girder. The cross section has been discretized into stiffened panels (one stiffener with its associated effective plating). The limit states for these panels, both tensile and compressive, are modeled in an appropriate manner. Since the ultimate strength of the girder section is largely governed by the behavior of the panels under compression, the authors have paid special attention in modeling the collapse as well as post-collapse behavior of these panels. A new stress-strain relationship is also introduced. The complete procedure has been coded into a FORTRAN program and tested against a number of box girder models and an actual ship for which the true behavior was known. The results obtained from the proposed program appear to be quite satisfactory. Good correlation was also found when compared with the results obtained by more complex and rigorous analytical methods.
On Quasi-Static Crushing of a Stiffened Square Tube
Authors: Paik Jeom Kee , Chung Jang Young , Chun Min Sung
Published: January 2021

The aims of this study are to obtain experimental data on the crushing of stiffened square tubes, and to develop a simple analytical expression for predicting the mean crushing strength of stiffened plates making up a plated structure. A series of axial crushing tests in a quasistatic condition was carried out on thin-walled square tubes which were composed of four identical panels. Specimens with longitudinal and/or transverse stiffeners, including unstiffened specimens, were tested, varying dimensions of plate and stiffener. The effective crushing length and the mean crushing strength of the test specimens were investigated. It was concluded that a longitudinally stiffened plate could reasonably be replaced by an unstiffened plate with equivalent plate thickness. Based on this approach, a simple expression for the effective crushing length and the mean crushing strength of stiffened plates was derived.
Numerical Solution of a Hydrofoil Moving Near an Interface
Authors: Wu G. X. , Miloh T. , Zilman G.
Published: January 2021

The problem of a hydrofoil moving near an interface of two fluids of different densities is analyzed. An iteration scheme is proposed which imposes the boundary conditions on the body surface and on the interface alternately. The numerical solution is obtained by using the linearized theory and a Glauert-type expansion for the vortex distribution. Results are provided for various cases with different densities and different speeds.
Geometric Modeling for Fully Nonlinear Ship-Wave Interactions
Authors: Celebi M.S. , Beck R.F.
Published: January 2021

Using the desingularized boundary integral method to solve transient nonlinear water-wave problems requires the solution of a mixed boundary value problem at each time step. The problem is solved at nodes (or collocation points) distributed on an ever-changing body surface. In this paper, a dynamic node allocation technique is developed to distribute efficiently nodes on the body surface. A B-spline surface representation is employed to generate an arbitrary ship hull form in parametric space. A variational adaptive curve grid generation method is then applied on the hull station curves to generate effective node placement. The numerical algorithm uses a conservative form of the parametric variational Euler-Lagrange equations to perform adaptive gridding on each station. Numerical examples of node placement on typical hull cross sections and for fully nonlinear wave resistance computations are presented.
Tearing Resistance of Advanced Double Hulls
Authors: Bracco Mark D. , Wierzbicki Tomasz
Published: January 2021

This paper studies the cutting by a wedge of advanced double hull (ADH) small-scale models. A total of six cutting experiments were performed with six different wedge geometries. Complex deformation patterns observed in the damaged specimens were simplified to obtain a closed-form upper bound for the steady-state cutting force. The ADH steady-state cutting force solution varied from 6% above to 12% below the experimental mean steady-state force. The absolute average error is 5%.
Propeller Wake Sheet Roll-up Modeling in Three Dimensions
Authors: Pyo Sangwoo , Kinnas Spyros A.
Published: January 2021

An algorithm for predicting the complete three-dimensional vortex sheet roll-up is developed. A higher order panel method, which combines a hyperboloidal panel geometry with a bi-quadratic dipole distribution, is used in order to accurately model the highly rolled-up regions. For given radial circulation distributions, the predicted wake shapes are shown to be convergent and consistent with those predicted from other methods. Then, a previously developed flow-adapted grid and the three-dimensional wake sheet roll-up algorithm are combined in order to estimate the propeller loading/trailing wake interaction. The complete wake geometry is determined by the method without the need of any experimental information on the shape of the wake. Predicted forces and tip vortex trajectories are shown to agree well with those measured in experiments.
A Numerical Method for Mean Drift Forces Acting on a 3-D Body Under Wave and Current
Authors: Lee Tzung-hang , Sun Bo-qi
Published: January 2021

Under the assumptions of potential theory, small-amplitude motion, small steady disturbance and low current speed, the problem is simplified and then a form of Green function of the simplified equation is derived. For ease of numerical calculation, following the idea of Huijsmans & Hermans (1985), the Green function is expended into an oscillating source G0 at zero forward speed and a correction term G1 to take into account low forward speed. Then the expressions for G0 and G1 are derived. It is shown that these expressions have good numerical calculation performance. To test the present method, it is applied to a hemisphere and a half submerged ellipsoid.
A Moving Boundary Finite Element Method for Fully Nonlinear Wave Simulations
Authors: Greaves D. M. , Borthwick A. G. L. , Wu G. X. , Taylor R. Eatock
Published: January 2021

The interaction of steep waves with surface ships and submarines may be simulated efficiently using a moving boundary finite element method. Here, unstructured hierarchical meshes are generated by triangularizing an underlying quadtree grid which adapts at each time step to follow the free surface. A potential flow theory finite element solver, developed by Wu & Eatock Taylor (1994,1995), is used to solve the two-dimensional nonlinear free surface problem in the time domain. Numerical results are presented for the following cases: standing waves in a rectangular tank; standing wave interaction with a fixed surface piercing rectangular body; and wave interaction with fixed submerged horizontal circular cylinders in a rectangular container. The results show encouraging agreement with analytical and alternative numerical schemes.
Dynamic Instability in Quartering Seas—Part III: Nonlinear Effects on Periodic Motions
Authors: Spyrou K. J.
Published: January 2021

The loss of stability of the horizontal-plane periodic motion of a steered ship in waves is investigated. In earlier reports we referred to the possibility of a broaching mechanism that will be intrinsic to the periodic mode, whereby there will exist no need for the ship to go through the surf-riding stage. However, about this point the discussion was essentially conjectural. In order to provide substance we present here a theoretical approach that is organized in two stages: Initially, we demonstrate the existence of a mechanism of parametric instability of yaw on the basis of a rudimentary, single-degree model of maneuvering motion in waves. Then, with a more elaborate model, we identify the underlying nonlinear phenomena that govern the large-amplitude horizontal ship motions, considering the ship as a multi-degree, nonlinear oscillator. Our analysis brings to light a very specific sequence of phenomena leading to cumulative broaching that involves a change in the stability of the ordinary periodic motion on the horizontal plane, a transition towards subharmonic response and, ultimately, a sudden jump to resonance. Possible means for controlling the onset of such undesirable behavior are also investigated.