bluuebunny/crossref_metadata_2025 huggingface dataset:
Wave Reduction by S-Catamaran at Supercritical Speeds
Authors: Chen Xue-Nong , Sharma Som D. , Stuntz Norbert
Published: January 2021

The S-catamaran is a catamaran with twin hulls that are slightly curved in an S-form and arranged at a mean yaw angle but mirror symmetric to their common longitudinal centerplane. Theoretical studies (Chen & Sharma 1997, Chen 1997) show that by proper choice of the sectional area curve, separation, curvature, and yaw the waves generated by the component hulls cancel each other at a supercritical design speed, and consequently the wave wake and wave resistance can be substantially reduced. Theoretically, an almost complete elimination of the waves would be conceivable for an S-catamaran. To verify this theory, a model experiment with an S-catamaran was recently carried out in the VBD. The S-catamaran (Chen & Sharma 1997) was designed to have the same length and displacement as the VBD model series M601, which was developed and tested much earlier in the VBD by Heuser (1973). Despite certain deviations from the ideal form for practical reasons, the wave resistance of the new curved-yawed-hull catamaran with and without skeg was numerically found to be less than that of an equivalent straight-unyawed-hull catamaran by 50% and 30%, respectively. Now, the new design, albeit without skeg, has been validated by a model experiment. In comparison with a reference catamaran of the series M601, up to 28% wave-resistance reduction was achieved in the experiment, although not in the originally designed configuration but at a reduced yaw angle found by trial and error.
Influence of Trapped Air on the Slamming of a Ship
Authors: Takagi Ken , Dobashi Junya
Published: January 2021

We describe a theoretical approach to a distorted plate penetrating calm water surface as a flow model of the water impact in rough seas. Further simplifications are employed so that the structure of ship is modeled by a tandem mass and spring system and a sequence of circular hollows is used as a bottom shape of the body instead of the surface shape of short crested waves. The results show that the model-scale ship experiences much larger stress at the local structure because of the influence of trapped air. Some results for the full-scale ship show that the three-dimensional effect, that is, the shape of sea surface deformation, is dominant for the cushioning of the impact force, and the trapped air affects some of this effect according to the magnitude of P and the natural period of the local structure.
Effect of Fracture on Crushing of Ship Structures
Authors: Abramowicz W. , Simonsen B. C.
Published: January 2021

This paper is concerned with loads and energy absorption during crushing of ship structures. Particular focus is on the effect of fracture of welds or parent material on the energy absorption of typical structural subassemblies of ships during deep collapse. The paper presents experiments and theories on the crushing response of typical strength elements. The theories are derived for an infinitely ductile material response and then consistently modified to include the effect of fracture. Theoretical formulas are compared with results of large-scale experiments performed at the Technical University of Denmark. The experimental series included 24 × and T aluminum and steel specimens scaled according to geometrical similarity and with a plate thickness varying between 2 and 20 mm. Theories and experiments demonstrate that the effect of fracture may be very significant for the loads and energy absorption in axial crushing of typical ship structural components. This effect of fracture has been neglected in previously published studies of bow crushing mechanics.
Efficient and Simplified Time Domain Simulation of Nonlinear Responses of Ships in Waves
Authors: Gu XueKang , Shen JinWei , Moan Torgeir
Published: January 2021

In this paper, a nonlinear time-domain strip theory is developed to predict nonlinear vertical ship motions and structural responses in severe waves. The effects of bottom impact, bow flare slamming, and green water on bending moments have been simulated. The flexible modes of the ship hull girder are accounted for by a Timoshenko beam theory. To validate the predicted responses, a model test was conducted for a ship with large bow flare and low bending rigidity, in both regular and irregular waves. The agreements between the calculated results and the model test are fairly good. The coupling effect between higher-order harmonic and the whipping components of vertical bending moments are verified by numerical calculations. Comparative studies with test and other theoretical results are also carried out for an S-175 containership with two kinds of bow flare forms. The causes of whipping and the variance in theoretical results are discussed. The good performance and high efficiency will make it possible to use the theory and its code for direct calculation of nonlinear bending moments in a long-term period and to develop a rule formula of design wave loads in the future.
Investigation of Ship Structural Vibration and Underwater Radiation Noise
Authors: Zou Chun-Ping , Chen Duan-Shi , Hua Hong-Xing
Published: January 2021

Underwater radiation noise is a very important factor for most ships, such as fishing boats, warships, and so forth. The magnitude of its energy depends on the vibration of the hull in contact with water. The vibration of the hull caused by the power plant, while the vessel is cruising, is the dominant source of underwater radiation noise, which is the subject of our investigation. In this paper, the coupled finite element/boundary element method is used to investigate ship structural vibration and underwater radiation noise. The finite element method (FEM) is employed to analyze modes and vibration responses of an entire ship for different kinds of excitations in consideration of fluid-structure interaction. The boundary element method (BEM) is used to analyze the underwater radiation noise. A FEM model is first constructed by using 30 geometric parameters and five kinds of finite elements. Then, the reduced matrix method is used to eliminate the local modes in order to obtain the overall bending and torsional modes of the ship. Last, vibration displacements of the hull are treated as the velocity boundary condition of BEM to calculate underwater radiation noise. Numerical results show thatthe calculated sound-pressure levels of underwater radiation noise are in a good agreement with experimentally measured results;although the vibration isolator is used, the propulsion diesel engine is the dominant source of the underwater radiation noise among all machines in the engine room and the maximum sound-pressure levels increase as the sailing speed of the ship increases;the underwater radiation noise of the ship with gearbox excitation is greater than that of the ship with diesel generator set excitation, which should be noticed by the ship designers during the design stage.
Application of a Boundary Element Method in the Prediction of Unsteady Blade Sheet and Developed Tip Vortex Cavitation on Marine Propellers
Authors: Lee Hanseong , Kinnas Spyros A.
Published: January 2021

Most marine propellers operate in nonaxisymmetric inflows, and thus their blades are often subject to an unsteady flow field. In recent years, due to increasing demands for faster and larger displacement ships, the presence of blade sheet and tip vortex cavitation has become very common. Developed tip vortex cavitation, which often appears together with blade sheet cavitation, is known to be one of the main sources of propeller-induced pressure fluctuations on the ship hull. The prediction of developed tip vortex cavity as well as blade sheet cavity is thus quite important in the assessment of the propeller performance and the corresponding pressure fluctuations on the ship hull. A boundary element method is employed to model the fully unsteady blade sheet (partial or supercavitating) and developed tip vortex cavitation on propeller blades. The extent and size of the cavity is determined by satisfying both the dynamic and the kinematic boundary conditions on the cavity surface. The numerical behavior of the method is investigated for a two-dimensional tip vortex cavity, a three-dimensional hydrofoil, and a marine propeller subjected to nonaxisymmetric inflow. Comparisons of numerical predictions with experimental measurements are presented.
Effect of Initial Deflection Shape on the Ultimate Strength Behavior of Welded Steel Plates Under Biaxial Compressive Loads
Authors: Paik Jeom Kee , Thayamballi Anil Kumar , Lee Jae Myung
Published: January 2021

The shape of weld-induced initial distortion in steel plates bounded by support members is normally very complex. It must be recognized that it is not only the magnitude of initial distortion, but also its shape that can significantly affect the plate collapse behavior. In this paper, some typical plate initial deflection shapes are selected from measurements for merchant ship plating between stiffeners. The influence of such initial deflection shapes on the ultimate strength behavior of steel plates subjected to biaxial compression as well as uniaxial thrust is then investigated applying nonlinear finite element analyses. It is confirmed that an initial deflection shape that approximates the buckling mode, with its maximum amplitude selected to be the same as the measured maximum initial deflection, is a good representation for the purposes of somewhat pessimistic evaluation of the ultimate strength of plating between stiffeners under biaxial compression as well as under uniaxial compression. Also, it appears that the influence of initial deflection shape on the plate collapse behavior under predominantly transverse axial compression or biaxial compression can be quite different from that under predominantly longitudinal axial compression. As another contribution, the ultimate strength interaction relationship of plating under biaxial compressive loads is presented. The results and insights developed from the present study are summarized.
Experimental Investigation of the Nonlinear Effects on the Statistics of Vertical Motions and Loads of a Containership in Irregular Waves
Authors: Fonseca N. , Guedes Soares C.
Published: January 2021

The paper presents the results of an experimental investigation of the nonlinear effects on the vertical motions and loads on a containership model advancing in irregular waves. The experimental data are compared with numerical results from a nonlinear time domain strip method. The tests were carried out in a seakeeping tank using three sea states with significant wave heights of 4.2 m, 6.1 m, and 9.9 m, thus including very severe conditions. The measured responses include the absolute and relative motions, vertical accelerations, and cross-sectional loads at midship and ¼ Lpp from the forward perpendicular. The statistics of the experimental records demonstrate partly the nonlinear behavior of the responses, especially of the structural loads. The probability distributions of the positive and negative peaks show that the heave and pitch motions are only slightly asymmetric and their distributions compare well with the Rayleigh distribution. The vertical loads present distributions of peaks that are highly asymmetric and deviate from the Rayleigh distribution. Comparisons between simulated results and experimental data show that the numerical model is able to represent the nonlinear characteristics of the responses.
Development of a Control-Oriented Model of the Vertical Motions of a Fast Ferry
Authors: Esteban Segundo , Giron-Sierra Jose M. , de Andres-Toro Bonifacio , de la Cruz Jesus M.
Published: January 2021

As a main part of a research study on the control of active flaps and a T-foil of a high-speed ferry, a control-oriented model of vertical motions of the ship has been developed. The objective of the control is to improve comfort, decreasing the impact of heave and pitch motions. We have experimental data from a towing tank institution and simulations with PRECAL. The model is based on a decomposition of the physic phenomena into two main aspects: the coupling of the ship with distance between waves and the dynamics of a semisubmerged mass. The model can be handled with MATLAB-SIMULINK, which is useful for studying control strategies. The model shows good agreement (model validation) with the experimental and simulated data for regular and irregular waves. The article shows a methodology, based on MATLAB tools, for obtaining control-oriented models from computer-aided design (CAD)–based programs. That means that the control-oriented model can be derived from the ship design, even before the ship is built.
Performance Prediction of Surface-Piercing Propellers
Authors: Young Yin L. , Kinnas Spyros A.
Published: January 2021

A three-dimensional low-order boundary element method is presented for the performance prediction of surface-piercing propellers. The negative image method is used to account for free surface effects. Detachment locations of ventilated cavities are searched for iteratively using a modified smooth detachment condition. Results from parametric studies and validations with experimental measurements are shown.
New Approach to the Suction Force at the Leading Edge of a Profile With Zero Thickness
Authors: Sparenberg J. A. , de Jager E. M.
Published: January 2021

This paper considers the suction force at the leading edge of a profile with zero thickness in an incompressible and inviscid fluid flow. The theory is linear, and the approach to the suction force is from the innerside of the profile. It is shown that the suction force can be considered as an "integral" over a delta function of Dirac situated at the nose of the profile. An application of the method is given to show that in the linear theory a nonslotted periodically moving profile that does not shed free vorticity cannot yield a nonzero mean thrust.
Numerical Modeling of Nonlinear Interactions Between Ships and Surface Gravity Waves, Part 1: Ship Waves in Calm Water
Authors: Lin Ray-Qing , Kuang Weijia , Reed Arthur M.
Published: January 2021

This paper presents a pseudo-spectral model for nonlinear ship-surface wave interactions. The algorithm used in the model is a combination of spectral and boundary element methods: the boundary element method is used to translate physical quantities between the nonuniform ship surface and the regular grid of the spectral representation; the spectral method is used throughout the remainder of the fluid domain. All possible wave-wave interactions are included in the model (up to N-wave interactions for the truncation order N of the spectral expansions). This paper focuses on the mathematical theory and numerical method of the model and presents some numerical results for steady Kelvin waves in calm water. The nonlinear bow waves at high Froude numbers from the pseudo-spectral model are much closer to the experimental results than those from linear ship wave models. Our results demonstrate that the pseudo-spectral model is significantly faster than previous ship wave models: with the same resolution, the CPU time of the pseudo-spectral model is orders of magnitude less than those of previous models. Convergence speed of this model is ANLogN instead of BN2, where N is the number of unknown (note that the N for the traditional boundary element method may be significantly larger than the N for the pseudo-spectral method for the same quality solution). A and B are CPU time requirements in each time step for our model and others, respectively.
A Probabilistic Model of Flooding Loads on Transverse Watertight Bulkheads in the Event of Hull Damage
Authors: Bhattacharya Baidurya , Basu Roger , Srinivasan Sanjay
Published: January 2021

Watertight bulkheads (WTBs) are crucial to ship survivability in the event of hull damage. Current design standards for WTBs are empirical and prescriptive in nature. However, damage-causing events and damaged ship response exhibit significant variabilities and uncertainties. Hence, the design and assessment of WTBs should be performed in a probability-based format. This paper outlines, as an essential input to reliability analysis, the development of a physically based probabilistic model of transverse WTB loads. Poisson arrival is assumed for damage events, and the maximum life-time load effect envelope on the WTB in damaged condition is derived. The emphasis of this paper is on the probabilistic modeling of loads; hence, simple phenomenological expressions of load components are used to underline the cause and extent of randomness in WTB loads. A response surface type approach is suggested for determining ship-specific model parameters. A large RO/RO vessel with side shell breach below the waterline is used for illustrating the application of the proposed methodology; randomness is considered in ship hydrostatic properties, damage location, length of breach, occurrence and duration of damage events, the environment, curve fitting, and modeling errors. Probabilistic estimates of the maximum load components are obtained through Monte Carlo simulations. These are compared with available code-prescribed design values.
Measurement of Response Amplitude Operators for an 86 m High-Speed Catamaran
Authors: Davis M. R. , Watson N. L. , Holloway D. S.
Published: January 2021

Radar observations of encountered wave profile and measurements of vessel motions have been used to derive motion response amplitude operators, and the results are compared with predicted motion responses. Data were collected from an INCAT Tasmania built ferry while on delivery between Australia and England. It has been found that the predicted motions using a time domain method are consistent with those observed with respect to the increase of response with vessel speed and the decrease of response for seas encountered from the beam directions. Peak heave and pitch response amplitude operators were measured and computed at up to 2.5 and 1.8, respectively, at high speed in head seas. Conventional low-speed frequency domain motion analysis was found to give smaller predicted responses at somewhat higher frequency than the high-speed time-domain motion analysis. Significantly larger rolling motions were measured than predicted, and it appears that the action of the steering system may contribute substantially to in-service rolling.
Time Domain Computation of the Wave-Making Resistance of Ships
Authors: Kara F. , Vassalos D.
Published: January 2021

The Ship Stability Research Centre, Department of Naval Architecture and Marine Engineering, The Universities of Glasgow and Strathclyde, Scotland, UKA linearized three-dimensional potential flow formulation in time domain is applied to calculate wave-making resistance of ships in calm water. Steady-state perturbation potentials for resistance are obtained as the steady-state limit of the surge radiation impulse response function using the transient free surface source distribution over the body surface. Five different vessels are used to validate the present numerical approximation. The results, including steady-state wave-making resistance, sinkage force, trim moment, and wave profile along the waterline, are compared with other published numerical and experimental results.
RANS Computational Fluid Dynamics Predictions of Pitch and Heave Ship Motions in Head Seas
Authors: Weymouth Gabriel David , Wilson Robert Vance , Stern Frederick
Published: January 2021

This work extends the previous effort in unsteady Reynolds averaged Navier-Stokes (RANS) simulations developed by the ship hydrodynamics group of the University of Iowa Iowa Institute of Hydraulic Research to the capability to predict pitch and heave motions of ships with forward speed in regular head seas. The simulations are performed with CFDSHIP-IOWA, which is a general-purpose, multiblock, high-performance parallel computing RANS code. Numerical verification studies in space and time demonstrate convergence for nearly all variables. The modified Wigley hull form experimental data presented in Journee (1992) are compared with simulation results over a range of Froude numbers, wavelengths, and wave amplitudes and found to give accurate results, with uncertainties less than 2%. Viscous ship motions characteristics are investigated by decomposing the full nonlinear problem into the forward speed diffraction and pitch and heave radiation problems, in the manner of strip theory. Comparisons between the current viscous RANS solutions and those from experiments, strip theory, and nonlinear potential flow simulations show the RANS method to predict damping and added mass coefficients with a high degree of accuracy.
High-Fidelity Models and Multiobjective Global Optimization Algorithms in Simulation-Based Design
Authors: Peri Daniele , Campana Emilio F.
Published: January 2021

This work presents a simulation-based design environment for the solution of optimum ship design problems based on a global optimization (GO) algorithm that prevents the optimizer from being trapped into local minima. The procedure, illustrated in the framework of multiobjective optimization problems, makes use of high-fidelity, CPU-time-expensive computational models, including a free surface-capturing Reynolds-averaged Navier Stokes equation (RANSE) solver. The optimization process is composed of a global and a local phase. In the global stage of the search, a few computationally expensive simulations are needed for creating analytical approximations(i.e., surrogate models) of the objective functions. Tentative designs, created to explore the design space, are then evaluated with these inexpensive approximations. The more promising designs are then clustered and locally minimized and eventually verified with high-fidelity simulations. New exact values are used to improve the surrogate models, and repeated cycles of the algorithm are performed. A decision maker strategy is finally adopted to select the more interesting solution, and a final local refinement stage is performed by a gradient-based local optimization technique. A key point in the algorithm is the introduction of the surrogate models for the reduction of the overall time needed for the objective functions evaluation and their dynamic evolution and refinement along the optimization process. Moreover, an attractive alternative to adjoint formulations, the approximation management framework (AMF), based on a combined strategy that joins variable fidelity models and trust region techniques, is tested. Numerical examples are given demonstrating both the validity and usefulness of the proposed approach.
Unsteady Wake Alignment for Propellers in Nonaxisymmetric Flows
Authors: Lee Hanseong , Kinnas Spyros A.
Published: January 2021

A low-order boundary element method is applied to predict the trailing wake geometries shedding from hydrofoil and marine propellers in steady and unsteady flows, as well as the vortex motions of the classical lifting line problem with elliptic loading distribution. In order to prevent the numerical instability near the vortex roll-up region, a tip vortex with finite core size is introduced at the end of the vortex line (or at the tip of the wake sheet in the case of a three-dimensional problem), and the induced velocities are evaluated at the displaced control points instead of the actual control points on the vortex (or wake) panels. Green's integral equation with boundary conditions is formulated based on the perturbation potential and solved for the potentials on the lifting bodies and the tip vortex surface. The three-component velocities on the tip vortex surface are computed by numerically differentiating the solution potentials, and the induced velocities on the wake surface are directly determined from the integral equation derived from analytical differentiation of Green's integral equation. The new geometries of the vortex line or the trailing wake as well as the location of the tip vortex core center are then determined by aligning them to the flow so that the force-free condition is satisfied on the wake. The method is applied for the two-dimensional and three-dimensional problems, and validated with experiments and other numerical methods in terms of tip vortex trajectory and blade forces.
Reminiscences of My Early Career in Waves
Authors: Ursell F.
Published: January 2021

My first research project was on water waves, and it began in June 1944, nearly 60 years ago. Since then, there have been big changes in our subject and in the practice of research, and it may be of interest to recall the situation as it was during my early career. Everything was on a small scale and involved few people. Engineers used the slide rule, the drawing board, and model experiments using the towing tank. Applied mathematicians showed how solutions could in principle be calculated, but actual numerical calculations were very slow; the most powerful aids were electromechanical calculating machines, or analogue calculators, or special finite-difference graphical methods, such as relaxation, which do not work for waves. There was no reason for engineers and mathematicians to collaborate closely.
Reminiscences and Reflections: Ship Waves, 1950–2000
Authors: Tulin Marshall P.
Published: January 2021

The last 50 years have seen remarkable progress in our understanding of ship waves, as well as many other scientific topics in ship hydrodynamics. Here is a historical narrative, written from a very personal perspective, about ship waves in this period, with technical details, which I hope will stimulate the interest of the younger readers. It shows how a life in research can be very exciting and personally rewarding through the pursuit of scientific challenge with others.
Second-Order Diffraction in Short Waves
Authors: Newman J. N.
Published: January 2021

Asymptotic approximations are derived for the second-order potential and the result-ing pressure forces acting on fixed vessels in monochromatic or bichromatic incident waves. These approximations are based on the short-wavelength assumption, with respect to the first-order incident waves. Comparisons are made with computations based on the second-order panel code WAMIT, to indicate the domains where the approximate results are useful.
Lifting Surfaces With Circular Planforms
Authors: Tuck E. O. , Lazauskas L.
Published: January 2021

A general lifting surface computer program is used for the special case where the planform is a circle, in order to compare lift and pitching moment with semianalytic solutions.
A Generalized Wagner Method for Three-Dimensional Slamming
Authors: Faltinsen O. M. , Chezhian M.
Published: January 2021

Impact between the water and ship, that is, slamming, can cause important global and local effects. A numerical method has been applied to predict water entry loads on three-dimensional bodies. The problem is solved as an initial value problem using the boundary element method. The Green second identity is used to represent the velocity potential as a distribution of Rankine sources and dipoles over the body surface and free surface. The problem is stepped up in time using the information from the boundary conditions. The kinematic free-surface condition is used to determine the intersection between the body surface and free surface at each time step. The exact body boundary condition is used, whereas the dynamic free-surface condition, φ = 0, is approximated on to a horizontal line and not on the exact free-surface profile. The approach presented by Zhao et al (1996) for two-dimensional water entry problems was extended to arbitrary three-dimensional bodies in this presented work. An idealized shape, which consists of cylindrical mid-body and hemispherical ends, was studied. The wetted body surface is calculated with great detail and is considered to be more important than the free-surface elevation away from the body. Drop tests have been carried out to verify and validate the numerical simulation. The effect of the angle between the free surface and the body surface has also been studied. The agreement between theory and experiments is good, and the effect of three-dimensionality is documented. The presented computational method is found to be robust for engineering use and computationally less demanding. The experimental results for vertical force have a strong oscillatory nature, and this has been analyzed using a simplified hydroelastic model. The hydroelastic model gives reasonable representation of the dynamic oscillations found in the vertical force. Reasons for the observed deviations between the numerical and the experimental results are documented. Recommendations for conducting drop tests with minimal dynamic effects are also presented.
The Application of Numerical Methods for the Solution of Some Problems in Free-Surface Hydrodynamics
Authors: Bulgarelli U. P.
Published: January 2021

The aim of this contribution is to present some of the recent developments achieved at INSEAN in the context of accurate and robust algorithms for the solutions of the system of partial differential equations governing complex free-surface flows. The paper addresses several problems of relevant interest in naval hydrodynamics, for example, sloshing, water on deck, microscale breaking waves, bow-stern flows, ship waves, steady and unsteady ship flows. Each problem is solved through the most appropriate numerical method, which is selected on the basis of the approximations that can be done for the particular problem and of the kind of result that the analysis has to provide. Numerical methods adopted involve classical boundary element approaches, smoothed particle hydrodynamics, heterogeneous domain decomposition techniques, level-set methods, steady and unsteady Reynolds averaged Navier-Stokes equations. Validation versus experimental data are presented. Comparisons among different numerical approaches are also established in a few cases with the aim of highlighting their limits and/or capabilities.
Ship Motion Computations Using a High Froude Number Time Domain Strip Theory
Authors: Holloway D. S. , Davis M. R.
Published: January 2021

High-speed strip theories are discussed, and a time domain formulation making use of a fixed reference frame for the two-dimensional fluid motion is described in detail. This, and classical (low-speed) strip theory, are compared with the experimental results of Wellicome et al. (1995) up to a Froude number of 0.8, as well as with our own test data for a semi-SWATH, demonstrating the marked improvement of the predictions of the former at high speeds, while the need to account for modest viscous effects at these speeds is also argued. A significant contribution to time domain computations is a method of stabilizing the integration of the ship's equations of motion, which are inherently unstable due to feedback from implicit added mass components of the hydrodynamic force. The time domain high-speed theory is recommended as a practical alternative to three-dimensional methods. It also facilitates the investigation of large-amplitude motions with stern or bow emergence and forms a simulation base for the investigation of ride control systems and local or global loads.
Experimental and Numerical Investigation Into the Effects of Initial Conditions on a Three Degree of Freedom Capsize Model
Authors: Lee Young-Woo , McCue Leigh , Obar Michael , Troesch Armin
Published: January 2021

The dynamics and hydrodynamics of ship capsizing include strong nonlinearities, transient effects, and physical phenomena that have not been fully identified or studied. This paper presents a study of some of the various mechanisms associated with this extreme behavior. A quasi-nonlinear three degree of freedom numerical model is employed to examine the effects of initial conditions on the ultimate state of a box barge model. The numerical results are then used to provide structure and understanding to otherwise seemingly inconsistent and ambiguous experiments.
Reliability-Based Inspection of Corroded Ship-Type FPSO Hulls
Authors: Sun Hai-Hong , Soares C. Guedes
Published: January 2021

This paper proposes a time-variant probabilistic corrosion model derived from a database with 157 thickness measurement records of 140 tankers. Incorporating the corrosion model in a time-dependent reliability method and referring to a required limit of safety level, a reliability-based inspection planning is proposed for ship-type floating production, storage, and offloading units (FPSOs) based on corrosion renewal criteria that account simultaneously for thickness reduction, hull girder ultimate strength, stiffened panel buckling strength, and plate ultimate strength
Nonlinear Ship–Wave Interaction Model, Part 2: Ship Boundary Condition
Authors: Lin Ray-Qing , Kuang Weijia
Published: January 2021

One of the main problems in modeling ship-wave hydrodynamics is solving for the forcing (pressure) at the ship boundary. With an arbitrary ship, singularities occur in evaluating the velocity potential and the velocities on the hull. Inaccuracies in the evaluation of the singular terms in the velocity potential result in discretization errors, numerical errors, and excessive computational costs. In this paper we present a new approach to evaluating the pressure on a ship: evaluating the pressure in the ship normal vector coordinate system. The main advantage of this approach is that p is a smooth function in the ship normal vector coordinate system, enabling us to obtain accurate results very efficiently (i.e., with much less CPU time) without encountering numerical difficulties arising from possible singularities.
Strongly Nonlinear Phenomena in Ship Hydrodynamics
Authors: Landrini Maurizio
Published: January 2021

This paper was presented as the 2003–2004 Georg Weinblum Memorial Lecture by Dr. Maurizio Landrini of Istituto Nazionale per Studied Esperienze di Architettura Navale (INSEAN, the Italian Ship Model Basin). Tragically, Maurizio was killed in an accident on June 26, 2003, before he could give the lecture. The lecture was presented in memoriam by Dr. Emilio F. Campana, a friend and colleague at INSEAN. The paper was finished by coresearchers and friends at INSEAN. The present paper is focused on the analysis of nonlinear phenomena in the naval context. The work is split into two parts. In the former, state-of-the-art numerical techniques handling nonlinear free-surface flows are analyzed. Related advantages and shortcomings are discussed through mutual verifications and comparisons with experiments for prototype cases. In the latter, practical problems relevant for ship hydrodynamics, where nonlinear phenomena play a major role, are studied. More in detail, water-on-deck, sloshing, and bow and stern ship breaking wave phenomena are attacked by means of both numerical and experimental techniques, and the main features connected with nonlinear mechanisms are identified.
Nonlinear Parametric Rolling in Regular Waves: An Approximate Analytical Solution for the Response Curve in the Region of First Parametric Resonance
Authors: Bulian Gabriele
Published: January 2021

An approximate analytical solution for the parametric roll response curve in the first parametric resonance zone is presented. Comparisons between analytical predictions and results obtained by means of numerical time domain simulations are performed in order to check the accuracy of the method. The use of a highly nonlinear 1.5-DOF model allows the disclosure of the presence of fold and pitchfork bifurcations. The method can be a simple and good aid both in the early design stage and for experimental planning. As an exercise showing the capabilities of the analytical methodology, the influence of damping parameters on the roll response is analyzed for a roll-on/roll-off (RO/RO) Pax.
Flow Beneath a Ship at Small Underkeel Clearance
Authors: Gourlay Tim
Published: January 2021

This article looks at the case of a large, flat-bottomed ship, such as a bulk carrier, moving in close proximity to a flat sea floor. It is shown that the flow beneath the ship can be modeled as a shear flow between two parallel plates, one of which is moving. The resulting flow can be represented using laminar Couette flow at low Reynolds numbers (possible at model scale) or the very different turbulent Couette flow at high Reynolds numbers (full scale). Implications of these flow models on squat and viscous resistance are discussed.
A Note on the Development of a Nonlinear Axisymmetric Reentrant Jet Cavitation Model
Authors: Uhlman James S.
Published: January 2021

The boundary integral method is formulated for the problem of the fully nonlinear, axisymmetric potential flow past a body of revolution. A model is devised for the exact formulation of the reentrant jet cavity closure condition. It is demonstrated that the solution obtained is essentially independent of the length selected for the jet. Results obtained using the reentrant jet cavity closure model are compared with those obtained using the Riabouchinsky-type cavity closure model used by Uhlman (1987, 1989) and with experimental results. The agreement between the two cavity closure models is seen to be excellent, with the Riabouchinsky wall results deviating only slightly at short cavity lengths. The agreement of the reentrant jet model with the experimental data is also excellent, although the addition of the viscous component of drag is seen to be required for cavitating cones of sufficiently small half-angle.
New Generic Equation for Interaction Effects on a Moored Containership Due to a Passing Tanker
Authors: Varyani K. S. , Vantorre M.
Published: January 2021

In order to improve the formulation of moored-passing ship interaction forces and moments in the mathematical model of a ship maneuvering simulator, a comprehensive captive model test program was carried out and a theoretical calculation method was developed. At present, semiempirical approaches, resulting in an estimation of forces and moments in the horizontal plane caused by hydrodynamic interaction on a moored ship due to a passing ship, are not available in literature. The present research intends to enhance the theoretical approach by validating the calculated peak forces and moments with experimental data. The numerical method is subsequently applied to generate a systematic database for the development of a new set of generic formulae for estimating the effect of passing vessels on moored ships in the equations of motion for surge, sway, and yaw applied in maneuvering and moor-ing simulators.
Assessing the Probability of the Dynamic Capsizing of Vessels
Authors: Ayyub Bilal M. , Kaminskiy Mark , Alman Phil R. , Engle Allen , Campbell Bradley L. , Thomas William L.
Published: January 2021

Current naval vessel design requirements for reduced signature may drive industry toward unconventional hull forms, such as the tumblehome, for some vessels. There is a critical need to develop a system-based approach to intact and damaged dynamic capsize assessment that addresses risk identification and mitigation strategies, such as design methodologies, onboard "smart systems" for operator guidance, real-time seaway monitoring for critical conditions, monitoring extreme seaway ship handling trainers, and probability-based tools for risk assessment. Development of a system-based approach will also improve ship safety and allow the development of unconventional ship designs that rely on a variety of systems, including inherent design characteristics for minimizing intact and damaged dynamic capsize risk. Avail-ability of new intact and damaged dynamic capsize design methods and risk mitigation technologies will benefit both industry and the US Navy by breaking through the barrier of empirical methodologies for stability assessment currently in use. In this paper, an innovative method for computing the probability of dynamic capsizing of vessels is provided. The computation can be based on numerical simulation data or experimental data. In this paper, the method is illustrated using numerical simulation data applied to a hypothetical vessel. The suggested method utilizes the time to capsizing as a primary random variable for assessing the resulting time-dependent probability. The method utilizes models from reliability analysis based on life data, including the Kaplan-Meier technique, and would enable engineers to examine the run duration of tests, plan future tests including test repetition needs, and interpolate and predict capsizing probabilities under operational conditions that are not tested. In addition, the method could offer a basis for developing a system-based approach to assessing intact and damaged stability, navigation guidance procedures, and future risk-based navigation systems that include the initial design of hull forms, navigation procedures including human factors, and stability criteria. The method developed in this paper is presented using numerical simulation results for one vessel for the purpose of illustration. The illustration of the method starts with computing the time-dependent capsizing probabilities under various operational conditions of speed, heading, and random wave characteristics, called operational cells. Then probability distributions were fitted to the data and used for prediction purposes to gain additional insights, make observations, and draw conclusions for additional work. The case study results also produced recommendations for future work.
A Time-Domain Iteration Method for Acoustic Scattering Problems
Authors: Kao Jui-Hsiang , Kehr Young-Zehr
Published: January 2021

This paper presents a new time-domain iteration method for computing multifrequency scattering waves from underwater obstacles. The equations are expressed in some forms relative to the retarded time, and the solution of scattering potential can be computed by an iteration process in which the boundary condition on each panel is naturally satisfied. Thus, the present method can treat the scattering problem of geometries with multiple sharp edges. In addition, the numerical inaccuracy due to time interpolation is minimized by using a Fourier series, and the results can robustly converge to correct values by setting zero initial scattering potentials. Several cases of a half sphere in different frequency ranges and one of multifrequency were tested by the present method. The results of all these cases agree with those reached by a frequency-domain boundary element method (BEM). In addition, a case with multiple sharp edges is also tested. The converged results can be obtained by the present method, but not by the BEM. Moreover, the present method is more computationally efficient, especially for the multifrequency case.
A Combined Control System With Roll Reduction and Track Keeping for the Ship Moving in Waves
Authors: Fang Ming-Chung , Luo Jhih-Hong
Published: January 2021

In this paper, a hydrodynamic numerical model with a combined control system is developed to simulate a ship steering in waves. The combined control system includes the PD controller and the sliding mode controller. By way of the rudder operation, the PD controller integrated with a line-of-sight (LOS) guidance system is used to control the track keeping, whereas the sliding mode controller is mainly chosen to reduce the roll motion. Different heading angle, wave height, wavelength, and initial speed are selected to investigate the combined control ability of the autopilot system. From simulation results, we find that this combined control system indeed works well, either for the ship roll motion reduction or for the ship track keeping in waves.
Marine Diesel Engine Fault Diagnosis by Using an Improved Hilbert Spectrum
Authors: Li Hongkun , Zhou Peilin , Ma Xiaojiang
Published: January 2021

Vibration signal analysis is a useful method for recognizing the pattern of a machine's working condition. However, it is difficult to recognize nonstationary and nonlinear vibration signal patterns satisfactorily with the traditional Fourier spectrum method. This paper introduces a novel time-frequency distribution method: an improved Hilbert spectrum (HS) for nonstationary vibration signal analysis, that is, applying a wavelet packet de-noise method as a preprocess of the HS. The HS is developed according to instantaneous frequency analysis by using a new kind of signal analysis method called empirical mode decomposition (EMD), which is highly accurate in analyzing various nonstationary and nonlinear signals. Due to a self-adaptive decomposition process, noise has a great effect on the accuracy of the EMD process and the corresponding HS. This has limited the application of the HS on real vibration analysis. In this study, a wavelet packet de-noising technique is employed as a preprocessing to improve the signal-to-noise ratio and the accuracy of the HS. Experimental data of a marine diesel fuel injection system are used to evaluate the improved methodology for system pattern recognition and fault diagnosis.
An Experimental Investigation Into the Performance of a Flush Water-Jet Inlet
Authors: Brandner P. A. , Walker G. J.
Published: January 2021

An experimental investigation of the flow within a generic flush type water-jet inlet has been carried out to identify the principal flow features and provide a basis for development of computational fluid dynamics (CFD) models. Tests were performed in a cavitation tunnel with the model inlet fitted to the test section ceiling, and effects of thickening the ingested tunnel wall boundary layer were investigated. The model was fitted with a range of instrumentation to investigate the ramp pressure distribution and boundary layer development, lip incidence, and pump face flow properties. Observations of lip and duct cavitation inception and behavior were also made. The results showed the inlet performance to be generally improved with the ingestion of a thicker boundary layer. The thickened boundary layer significantly reduced ramp boundary layer separation and distortion of flow at the notional pump face. However, a greater range of lip incidence occurred with the thickened boundary layer with consequent greater likelihood of lip separation and cavitation occurrence. Ideal lip incidence and pump face flow uniformity occurred at flow parameters significantly different from those for ideal pump face pressure recovery. Large developed cavities on the inlet lip were observed for a range of conditions typical of conventional high-speed vessel operation.
Empirical Force Laws for the Prescribed Dynamic Uplift of a Floating Plate
Authors: Vasileva Irina V. , Dempsey Kevin M.
Published: January 2021

An infinite thin plate floating on an ideal fluid of finite depth is subjected to a concentrated dynamic uplift force. For a specified upward displacement, the uplift force potential is the solution of a Volterra integral equation of the first kind and of convolution type. In this paper, empirical force laws for the prescribed dynamic uplift of a floating plate are derived for two canonical problems.