bluuebunny/crossref_metadata_2025 huggingface dataset:
Three-Dimensional Solution for the Diffraction Problem of a Submerged Body in Waves
Authors: Fang Ming-Chung , Su Sen-Xi
Published: January 2021

The paper presents a panel method to evaluate the diffraction problem on a submerged body moving beneath the free surface in regular waves. In the process of numerical calculation, the 1/r term in the potential function is treated by the method submitted by Hess & Smith (1964) with three ways for the integration, and the pulsating source terms due to the free surface effect are solved by using four different series expansions and an integral representation submitted by Telste & Noblesse (1986). With such derivation, the numerical computing techniques become available to calculate the wave exciting force for a submerged body advancing in regular waves at constant speed. Besides, the effect of the steady potential is also considered in the paper. The replacement of the double integration by a single integral in terms of a complex exponential integral is made in the derivative of the steady potential. The source strength on panels is solved efficiently by applying the Gaussian elimination method incorporated with the partial pivoting technique. Results obtained by the present technique are compared with the other methods and good agreement is found. The effect of steady flow is generally small, but it still cannot be neglected in some cases, especially for the slender body in oblique waves. It is also found that using the present technique incorporated with a suitable body mesh distribution can lead to more satisfactory results.
A Numerically Efficient Method for Analysis of Very Large Articulated Floating Structures
Authors: Garrison C. J.
Published: January 2021

A method is presented for evaluation of the motion of long structures composed of interconnected barges, or modules, of arbitrary shape. Such structures are being proposed in the construction of offshore airports or other large offshore floating structures. It is known that the evaluation of the motion of jointed or otherwise interconnected modules which make up a long floating structure may be evaluated by three dimensional radiation/diffraction analysis. However, the computing effort increases rapidly as the complexity of the geometric shape of the individual modules and the total number of modules increases. This paper describes an approximate method which drastically reduces the computational effort without major effects on accuracy. The method relies on accounting for hydrodynamic interaction effects between only adjacent modules within the structure rather than between all of the modules since the near-field interaction is by far the more important. This approximation reduces the computational effort to that of solving the two-module problem regardless of the total number of modules in the complete structure.
Design for Manufacturing Using B-Spline Developable Surfaces
Authors: Chalfant Julie S. , Maekawa Takashi
Published: January 2021

A developable surface can be formed by bending or rolling a planar surface without stretching or tearing; in other words, it can be developed or unrolled isometrically onto a plane. Developable surfaces are widely used in the manufacture of items that use materials that are not amenable to stretching such as the formation of ducts, shoes, clothing and automobile parts including upholstery and body panels (Frey & Bindschadler 1993). Designing a ship hull entirely of developable surfaces would allow production of the hull using only rolling or bending. Heat treatment would only be required for removal of distortion, thus greatly reducing the labor required to form the hull. Although developable surfaces play an important role in various manufacturing applications, little attention has been paid to implementing developable surfaces from the onset of a design. This paper investigates novel, user friendly methods to design complex objects using B-spline developable surfaces based on optimization techniques. Illustrative examples show the substantial improvements this method achieves over previously developed methods.
Analytical Expressions for Stability and Bifurcations of Turret Mooring Systems
Authors: Garza-Rios Luis O. , Bernitsas Michael M.
Published: January 2021

The eight necessary and sufficient conditions for stability of turret mooring systems (TMS) are derived analytically. Analytical expressions for TMS bifurcation boundaries where static and dynamic loss of stability occur are also derived. These analytical expressions provide physics-based means to evaluate the stability properties of TMS, find elementary singularities, and describe the morphogeneses occurring as a parameter (or design variable) or group of parameters are varied. They eliminate the need to compute numerically the TMS eigenvalues. Analytical results are verified by comparison to numerical results generated by direct computation of eigenvalues and their bifurcations. Catastrophe sets (design charts) are constructed in the two-dimensional parametric design space to show the dependence of design variables on the stability of the system. The TMS mathematical model consists of the nonlinear horizontal plane—surge, sway and yaw—fifth-order, large drift, low speed maneuvering equations. Mooring lines are modeled quasistatically by catenaries. External excitation consists of time independent current, steady wind, and second-order mean drift forces.
A Simple Method of Investigation of the Froude Number Effect on Lifting Flows About Ships
Authors: Ba M. , Guilbaud M.
Published: January 2021

Lifting effects on steady flows around ships for various values of the Froude number are investigated using a lifting surface method for zero thickness bodies with the steady wave resistance Green's function. To obtain very short computational times, the Fourier integrals are computed using a Romberg method with a given precision after interchanging the space and Fourier integrations. With this simple computing scheme, an efficient method for the prediction of lifting effects has been achieved. Computations have been led at various Froude numbers for sailing boats with yaw and heel angles, and for rudders, with and without simulation of the interaction with the hull. Simulation of some upstream flows, uniform and nonuniform, are also investigated.
Spraying Experiments with a Model Stern Trawler
Authors: Chung K. K. , Lozowski E. P. , Zakrzewski W. P. , Gagnon R. , Thompson T.
Published: January 2021

With a view to formulating vessel spraying and icing models, 22 spraying experiments were performed in the IMD/NRC towing tank using a 1:13 scale model of the stern trawler MT Zandberg. Neglecting the effect of wind drag on the spray droplet trajectories, an empirical spray flux equation for the scale Zandberg was derived, based on a statistical analysis of the spraying data. Using Froude number scaling, this model-scale equation was transformed into a full-scale spray flux equation. This spraying study shows that the total spray flux generated during ship/wave collisions depends on ship speed (Vs) and significant wave height (H1/3) according to V3⅓, H7⅓ while the spray flux distribution over the foredeck varies exponentially with longitudinal distance. Using this full-scale spray flux equation, a spray trajectory model, taking wind drag effects into account, was subsequently developed.
A Three-Dimensional Time-Dependent Icing Model for a Stern Trawler
Authors: Chung K. K. , Lozowski E. P.
Published: January 2021

A full-scale spray flux equation has been derived for ship-generated spray using spraying data obtained from model-scale experiments. Using this equation, droplet trajectory modeling, and spray mass continuity, a full-scale spraying model, which includes the effect of wind drag, has been developed for the stern trawler Zandberg. This spraying model has been incorporated into an icing model for the same vessel. A three-dimensional grid cell mesh is superimposed on the surface of the ship so that the local spray flux and icing rate on each grid cell can be calculated using the combined spraying and icing models. The disappearance of the Blue Mist II is used as a case study to illustrate the performance of the icing model. Under these severe icing conditions with off-head winds, the model predicts an icing rate of more than 13 tonnes per hour for the Zandberg, and the ice distribution is highly asymmetrical. This ice loading is the most dangerous condition for the ship's stability.
A Finite-Depth Unified Theory for the Linear and Second-Order Problems of Slender Ships
Authors: Kim Yonghwan , Sclavounos Paul D.
Published: January 2021

In this paper an extension of the unified slender-body theory is introduced to solve the finite-depth seakeeping problem of a slender ship. The far-and near-field behaviors of the velocity potential in finite depth are introduced, and a new kernel of the integral equation is derived for the heave and pitch motions of a slender ship at zero speed. The kernel of the integral equation is expressed in a series form which makes the integral equation easy to solve. Based on the present theoretical background, computations were carried out, and the hydrodynamic coefficients and motion RAOs were obtained. The computational results are compared with WAMIT, and a nice agreement is shown. The present method is extended to the computation of the second-order mean drift forces and moment in infinite and finite depth. Motion RAOs of sway, roll and yaw are obtained using strip theory, and the drift forces using the far-field momentum equations. The results show favorable agreement with WAMIT. Using the drift forces, the wave drift damping matrix is obtained for infinite depth. Aranha's formula is applied, and the damping coefficients are compared with the existing data. The present study shows that unified theory is an efficient and accurate design tool for slender ships.
Monte Carlo Simulations of Nonlinear Ocean Wave Records with Implications for Models of Breaking Waves
Authors: Pierson Willard J. , Jean-Pierre Azed
Published: January 2021

A Monte Carlo method for simulating nonlinear ocean wave records as a function of time is described. It is based on a family of probability density functions developed by Karl Pearson and requires additional knowledge of the dimensionless moments of a postulated nonlinear wave record, which are the skewness and kurtosis. A frequency spectrum is used to simulate a linear record. It is then transformed to a nonlinear record for the chosen values of the skewness and kurtosis. The result is not a perturbation expansion of the nonlinear equations that describe unbroken waves. It yields a simulated wave record that reproduces the chosen values for the skewness and, if needed, the kurtosis of a wave record so that the statistical properties are modeled. A brief history of the development of the linear model, presently in use, is given along with a survey of wave data that show the variability of the nonlinear properties of wave records. The need for a nonlinear model of waves for naval architecture, remote sensing and other design problems is shown. This method cannot provide any information on whether a particular wave will break. Some of the recent results on breaking waves and "green water" are reviewed. The possibility that this method can be extended based on the concept of a "local absorbing patch" is described.
Yawing of Turret-Moored Monohull Vessels in Response to Regular Waves
Authors: Liu F. , Brown D. T. , Fang J.
Published: January 2021

This paper considers the yawing behavior of a turret-moored floating production and storage vessel in regular waves. Experimental results are presented from regular wave tests performed on a model in a square wave basin indicating the vessel taking up yaw offsets of large amplitude in waves of specific frequency. The measured data are compared with results from second-order diffraction analysis and indicate that it is likely that the yawing behavior is caused by nonlinear potential loading.
Effect of Memory on the Stability of Spread Mooring Systems
Authors: Kim Boo-Ki , Bernitsas Michael M.
Published: January 2021

The importance of including the hydrodynamic memory effect in modeling and analysis of spread mooring systems (SMS) is assessed based on the design methodology for mooring systems developed at the University of Michigan. The memory effect is modeled by the hydrodynamic radiation forces expressed in terms of added mass at infinite frequency and convolution integrals of impulse response functions. The convolution integrals, which are explicit functions of time, are converted to autonomous excitation by the method of extended dynamics. For a given SMS configuration, nonlinear stability and bifurcation theory are used to produce catastrophe sets in the parametric design space separating regions of qualitatively different system dynamics. This approach reveals the complete picture of nonlinear phenomena associated with system dynamics and eliminates the need for extensive simulations. Catastrophe sets are developed in several parametric design spaces, providing fundamental understanding of the memory effects on SMS nonlinear dynamics. The mathematical model is based on the slow-motion maneuvering equations in the horizontal plane, including hydrodynamic memory effect and third-order quasi-steady hydrodynamic forces. Mooring lines are modeled by synthetic fiber ropes attached to surface terminals and deep-water catenary chains with touchdown and nonlinear drag. Environmental loads consist of time-independent current, wind, and mean wave drift forces.
Some Improvements and Comparisons in the Solution of the Neumann-Kelvin Problem
Authors: Marr G. , Jackson P.S.
Published: January 2021

This paper extends previous work by Baar & Price, Newman, and Doctors & Beck for the calculation of the Kelvin source and its derivatives and their use in a panel method for predicting wave drag. Particular attention is paid to the accuracy and convergence of the Baar & Price approach, complementing the study of these aspects of their own method made by Doctors & Beck. It is shown that the two methods provide consistent results for various numerical tests, for submerged bodies and for the Wigley hull. However, Baar & Price's own results for the Wigley hull, which compared well with experiments, could not be duplicated. The study removes to some extent numerical inaccuracies as a postulated source of the theory's difficulties, leading to the conclusion that the Neumann-Kelvin theory as it is currently understood does not give satisfactory wave resistance results for idealized ship hullforms.
Prediction of Oil Outflow in the Case of a Ship-Ship Collision Based on Energy Considerations
Authors: Samuelides Manolis
Published: January 2021

The work reported herein aims at the development of a methodology for the assessment of the behavior of tankers when involved in a ship-ship collision. It may be applied for the comparison of the behavior of tankers with different tank arrangements and it further accounts for differences in the structural configuration and scantlings. The proposed methodology is based, on the one hand, on the results of an analysis of damage cases expressed in terms of oil outflow versus collision energy and, on the other hand, on the distribution function of collision energy. These relationships are combined to obtain the distribution function of the oil outflow. The use of the methodology to investigate the influence of a stringer plate in a double-hull tanker illustrates its applicability and potential.
Performance Simulation of Marine Diesel Engines with SELENDIA
Authors: Chesse P. , Inozu B. , Roy P. , Tauzia X. , Hetet J. F.
Published: January 2021

This paper describes a diesel engine simulation code, named SELENDIA, jointly developed by EcoleCentrale de Nantes, France, and the University of New Orleans. The adopted models for steady-state and transient response simulation are briefly introduced in addition to various validation results. The capabilities of the code are illustrated by a study regarding the transient response of a sequentially turbocharged marine diesel engine as well as the simulation of engine performance under extreme conditions and the investigation of engine pollutant emissions.
Damping Coefficients for Extreme Rolling and Capsize: An Analytical Approach
Authors: Spyrou K. J. , Thompson J. M. T.
Published: January 2021

A method to identify the law of roll motion decay from extreme angles is presented based on perturbations of the elliptic-type solutions of the corresponding Hamiltonian system. Restoring polynomials up to the 7th order are considered. It is shown that the decay law can be expressed in closed form for up to quintic restoring. The method should be especially useful for deriving linear and nonlinear roll damping coefficients in the context of ship capsize investigations where the large amplitude behavior, near to the angle of vanishing stability, needs to be taken into account.
CFD Calculation of Sinkage and Trim
Authors: Subramani Anil K. , Paterson Eric G. , Stern Fred
Published: January 2021

A computational fluid dynamics (CFD) code for surface-ship boundary layers, wakes, and wave fields is extended by incorporating into it the capability of predicting sinkage and trim. The method is described and results are presented for the naval combatant FF1052 and the Series 60, Cg = 0.6 parent hull. Resistance, sinkage and trim, and wave profile on the hull are compared between the calculations and the experimental data. The trends in the data are predicted correctly and there is also good quantitative agreement overall between the calculations and the data.
SWATH Ship Motion Simulation Based on a Self-Tuning Fuzzy Control
Authors: Chiou Shan-Chin , Fang Ming-Chung
Published: January 2021

A time simulation technique using the self-tuning fuzzy control algorithm is applied to control stabilizing fins to reduce the pitch motion of the SWATH ship in longitudinal regular waves. A back-propagation-based fuzzy controller using the gradient descent method is presented and incorporated with the previous mathematical model to simulate the SWATH ship motion. The effects of surge force and viscous force are included. Basically the fuzzy controller consists of five parts:fuzzifier,rule base,database,inference engine, anddefuzzifier.

The calculations of the corresponding hydrodynamic coefficients at each time step follow the simplified technique developed before, which needs only one set of initial input data of the ship configuration. After comparing with the results using the static fuzzy controller, we find that the self-tuning fuzzy controller appears to be more practical and more efficient for operating stabilizing fins while the ship speed is high. Therefore, the fuzzy control with self-tuning algorithm developed here may offer a more efficient way to control fins of the SWATH ship and can also be regarded as a good basis for future studies in irregular waves.
Longitudinal Cut Method Revisited: A Survey on Main Error Sources
Authors: Lalli F. , Di Felice F. , Esposito P. G. , Moriconi A. , Piscopia R.
Published: January 2021

Some of the main error sources in wave pattern resistance determination were investigated. The experimental data obtained at the Italian Ship Model Basin (longitudinal wave cuts concerned with the steady motion of the Series 60 model and a hard-chine catamaran) were analyzed. It was found that, within the range of Froude numbers tested (0.225 ≤ Fr ≤ 0.345 for the Series 60 and 0.5 < Fr < 1 for the catamaran) two sources of uncertainty play a significant role: (i) the presence of a wave pattern generated by the air pressure disturbance, related to the carriage motion, and (ii) the unsteadiness of the free-surface flow (precision error). The importance of these effects increases, of course, with the model speed. The propagation of experimental errors in the wave resistance determination by the longitudinal cut method was next examined: within the elaboration of measured wave cuts experimental uncertainties are shown to be significantly damped. The wave resistance coefficient can be obtained therefore, with reasonable accuracy, from the measurement uncertainty point of view. Moreover, the errors related to wave cut truncation, as well as to probe transverse location, typical of the longitudinal cut method, were estimated. Systematic tests were performed by means of a numerical approach, which allows one to compare the wave resistance evaluated by the longitudinal cut method (applied in this case to the computed wave pattern) with the value obtained by pressure integration on the hull. As a result, the longitudinal cut method can be applied without introducing any severe limitation for the ratio b/L (tank width over model length), provided the wave cuts are measured at a proper transverse distance.
Development and Assessment of a Nonlinear Wave Prediction Methodology for Surface Vessels
Authors: Wyatt Donald C.
Published: January 2021

A numerical method for the prediction of steady nonlinear ship waves and their dependence on hull geometry is developed and assessed. The method employs desingularized Rankine singularities and Havelock singularities in an iterative boundary-integral solution procedure. The Fortran code incorporating this methodology, Das Boot, is tested on three validation cases and applied to a surface combatant hull form. Nonlinear wave elevation predictions for the case of a moving pressure pulse show a 0.988 correlation with a validated fifth-order spectral prediction. Nonlinear wave elevation predictions for a Series 60 hull form show a 0.974 correlation with model-scale wave elevation data. A nonlinear transom stern boundary condition is implemented. Stern wave predictions employing this model are shown to agree with an analytic two-dimensional solution. Initial predictions for a naval surface combatant incorporating a transom stern geometry show encouraging correlation, 0.81, with model-scale tank test data.
The Generation and Propagation of Ship Internal Waves in a Generally Stratified Ocean at High Densimetric Froude Numbers, Including Nonlinear Effects
Authors: Tulin Marshall P. , Yao Yitao , Wang Pei
Published: January 2021

A nonlinear theory for internal wave generation and propagation is derived here for slender ships traveling at high densimetric Froude number (Fh >> 1) in water of small density variation. It is based on an asymptotic equation for the evolution of the internal wave vorticity generated under the ship by a known inviscid ship flow and then self-propagating in the wake. In its numerical implementation, arbitrary pycnoclines and slender ship hulls may be used, and boundary conditions on the ship hull are satisfied; the free surface is treated here as rigid, although this may be relaxed. The theory has been implemented by a suitable numerical method and numerous simulations have been carried out. The results have been compared with earlier OEL experiments. In the near field, emphasis is given to a triple-lobe pattern in the pycnocline, an upwelling along the centerline of motion with a trough on either side, forming close behind the ship. Two distinct types of triple lobes are identified:dominant central lobe and very weak troughs, and;weak central lobe and dominant troughs.

The former (a) is shown to result in linear propagation into the far field. The latter (b) results in far-field patterns preceded by a deep trough whose propagation is nonlinear. The comparisons of both simulated trends and actual amplitudes with measurements are good, surprisingly so considering the small scale of the experiment and the asymptotic nature of the theory. The effect of the turbulent wake on the internal waves in the experiments is restricted to a very narrow region behind the ship; the bulk of the wave pattern including the leading waves seem unaffected. Simulations show that under certain conditions of stratification, triple-lobe patterns with abnormally large troughs are generated and lead to strong nonlinear effects; these deep troughs propagate sidewards to large distances aft (over 40 ship lengths) with slow decay, and result in much larger surface currents and strain rates than in the normal case. Correspondingly, fast waves of depression, which decay slowly, were discovered through the simulation of two-dimensional initial value problems, where the initial area of depression was significantly less than required of a true soliton; these "quasi-solitons" are briefly studied here.
Hydroelastic Analysis of a Simple Oscillator Impacting the Free Surface
Authors: lafrati A. , Carcaterra A. , Ciappi E. , Campana E. F.
Published: January 2021

The coupling between the hydrodynamic and elastic forces arising when a simple oscillator impacts the free surface is considered. The system is a two-mass oscillator, the lower mass being wedge-shaped, free falling on the free surface. Attention is devoted to a parametric investigation of the maximum of both hydrodynamic and elastic forces induced by the impact. The study is performed by a simplified theoretical model and by a numerical simulation of the fluid-structure interaction. The theoretical model suggested here provides an efficient tool for the computation of the hydrodynamic and elastic forces and of the corresponding maxima as a function of some parameters such as deadrise angle of the wedge, entry velocity, spring stiffness, and the masses. In particular, a closed-form expression for the critical value of the spring constant leading to the maximum elastic response is achieved as a function of the other parameters. Numerically, a panel method is adopted to solve the boundary integral formulation for the velocity potential. A suitable model is introduced to deal with the flow singularity at the intersection point between the free surface and the body contour. Time histories of the hydrodynamic and elastic forces are computed for different values of the spring stiffness and are compared with the corresponding results provided by the simplified theoretical model. The comparison shows that, despite the strong assumptions, the theoretical model allows a good estimate of the system critical condition.
On the Simulation of Amplified Bow Waves Induced by Motion in Head Seas
Authors: Wu M. , Tulin M. P. , Fontaine E.
Published: January 2021

The prediction of bow wave amplification for a ship navigating in head seas is achieved by means of the 2D +t nonlinear slender-body theory. High-resolution numerical simulations show the development of spray sheets along the hull. For conditions of navigation severe enough, the thick jets rise and top the deck level, leading to the possibility of deck wetness. The overall capabilities of the method of calculation are demonstrated through a systematic study for a frigate. Continuous time domain pictures of the flow as the bow enters the incoming waves are presented. The relationship between the incoming wave parameters and the sequence of probable events (deck wetness, slamming, …) that occurs in the bow region is studied, leading to predictions of both the onset and strength of probable deck wetness, as well as forefoot emergence and possible slamming events. The probability of deck wetness in the numerical simulation is confirmed by model experiments. Results are summarized in charts that allow critical evaluation of a given design (see Figs. 8 and 9), including the nonlinear dynamic rise of the water elevation, experienced as a spray sheet along the hull of critical importance for predicting the probable onset of deck wetness. These charts would seem extremely useful in the design phase, and it is our major purpose here to bring the possibility of computing them with the 2D+t method to the attention of naval architects.
Rapid Estimation of Near-and Far-Field Wave Wake from Ships and Application to Hull Form Design and Optimization
Authors: Day Alexander H. , Doctors Lawrence J.
Published: January 2021

A method is presented by which the wave wake generated by a ship may be repeatedly calculated very rapidly. The method is based on linear thin-ship theory, using the idea of elemental tent functions as building blocks to represent the hull, which have previously been applied in the context of resistance minimization. This approach allows much of the calculation to be carried out in advance, with the results stored in a database. Issues of convergence, accuracy, and storage strategy are discussed. In order to demonstrate the application of the approach to preliminary design optimization, an illustrative study is carried out in which hull forms for monohull and catamaran vessels are optimized in the sense of minimizing the maximal wave height along a series of longitudinal cuts. The effect of the transverse location of the cuts on the resulting hull forms is found to be quite substantial, especially for the catamarans; the performance of the vessels optimized to reduce wave height at one transverse location may be quite suboptimal at another location, illustrating the difficulty of choosing an appropriate specification for low-wash vessels.
Estimation of Response Amplitude Operators for Ships via the Circular-Hyperbolic Decomposition
Authors: Suleiman B. M. , Fahey S. O’F. , Nayfeh A. H. , Hajj M. R.
Published: January 2021

The frequency-domain analysis is commonly used to determine ship-motion characteristics, such as transfer functions and Response Amplitude Operators (RAOs). The Discrete Fourier Transform (DFT) has been the most widely used technique to conduct such an analysis. Nevertheless, application of the DFT is not always desirable because of leak-age. This problem cannot be eliminated unless the frequency content of a signal is known and all frequency components are rational multiples of each other. In this paper, we apply a recently developed closed-form decomposition technique, called the circular-hyperbolic decomposition (CHD), to estimate the RAOs of coupled heave and pitch motions using evenly sampled discrete ship-motion data. We show the advantages of the new technique over the DFT when leakage is present. We also introduce enhancements to the CHD in terms of a decimation parameter and a generalization for multiple signals. The results show that it is a promising technique.
Tip Vorticity Reduction and Optimization of Lifting Surfaces
Authors: Sparenberg J. A.
Published: January 2021

In linearized optimization theory, lifting surfaces, moving in an inviscid and incompressible fluid, shed tip vorticity of which the strength has infinite square-root singularities. Here we discuss that an optimization procedure can be coupled to constraints so that the strength of the shed vorticity remains bounded along the wing span.
Redesign of Cylindrical Shells by Large Admissible Perturbations
Authors: Alzahabi Basem , Bernitsas Michael M.
Published: January 2021

Structural redesign is the process of finding a new design that satisfies a set of performance requirements starting from a poorly performing design. Structural redesign is formulated as a two-state problem where the baseline design exhibits undesirable response characteristics and the objective design satisfies the design requirements. A LargE Admissible Perturbations (LEAP) methodology is developed to formulate and solve the problem of structural redesign of cylindrical shells for modal dynamics. First, the nonlinear perturbation equations of cylindrical shells for modal dynamics are derived relating the baseline to the unknown objective design. The redesign problem is formulated as an optimization problem. Next, an algorithm is developed to solve the nonlinear problem and to identify a locally optimal design that satisfies the given modal dynamics specifications. The developed LEAP algorithm calculates incrementally without trial and error or the repetitive finite-element analyses the structural design variables of the objective design. Numerical applications of cylindrical shell redesign for modal requirements are used to verify the methodology and test the algorithm. The developed methodology identifies incompatible frequency requirements where solutions cannot be achieved. Further, systematic redesign applications show that even for strip uniform shells, modes are linked, making satisfaction of multiple frequency objectives impossible.
Hull Form Optimization by Shift and Deformation of Ship Sections
Authors: Markov N. E. , Suzuki K.
Published: January 2021

A technique for reducing ship wave resistance is presented. It is based on a single B-spline patch which approximates the hull surface. A selected specific change of the B-spline coefficients resembles a smooth shift of the ship sections in the longitudinal direction. An unconstrained Davidson-Fletcher-Powell (DFP) optimization procedure controls the changes. The wave resistance is evaluated by a higher-order Rankine source panel method. The numerical results, shown for Series 60 and the Hamburg Test Case (HTC) containership, prove that the method is appropriate for preliminary hull form design.
An Adjoint Formulation for Shape Optimization in Free-Surface Potential Flow
Authors: Ragab Saad A.
Published: January 2021

This paper is a step towards the application of automatic shape optimization techniques to the hydrodynamic design of marine vehicles. The flow is assumed to be irrotational and free-surface conditions are linearized. Several objective functionals of relevance to free-surface flow are proposed, and adjoint formulations for the determination of their gradients are derived. The accuracy of the gradient using the adjoint formulations has been verified by comparisons with direct calculations using second-order finite differences. The method is then used to obtain an optimal solution to the inverse problem for a three-dimensional body submerged near a free surface, and to design a minimum wave resistance body.
Control of Rolling in Ships by Means of Active Fins Governed by a Fuzzy-Logic Controller
Authors: Liut Daniel A. , Hughes Owen F. , Mook Dean T.
Published: January 2021

A fuzzy-logic controller is designed to govern the motion of fins in order to reduce roll motion in ships. The controller is trained by a moment-matching procedure. This procedure is also adapted to generate the fuzzy-logic rules by means of a clustering algorithm. The ship motion simulation is done by means of the program LAMP (Large Amplitude Motion Program), which can simulate the motion of a ship in a seaway. To model the fins we use a program called FINS, which is based on an unsteady vortex-sheet approach. Results are shown that prove the efficiency of the method, with average motion reductions up to 29% of the original values.
Rankine and Fourier-Kochin Representation of Near-Field Ship Waves
Authors: Noblesse Francis
Published: January 2021

New fundamental analytical representations of the near-held potential how that corresponds to a given how at a surface bounding a potential-how region are given for three classes of free-surface hows in deep water: diffraction-radiation of regular water waves by an offshore structure, steady ship waves, and time-harmonic ship waves (diffraction-radiation with forward speed). These near-held how representations, called Rankine and Fourier-Kochin representations, define the how in terms of distributions of Rankine singularities and Fourier-Kochin distributions of elementary waves over the boundary surface and its intersection with the mean free surface. The Rankine and Fourier-Kochin near-held how representations involve only simple ordinary functions. These how representations extend the previously given Fourier-Kochin representations of waves.
Pitch-Heave Dynamics of a Segmented Skirt Air Cushion
Authors: Graham T.A. , Sullivan P.A.
Published: January 2021

The formulation and experimental validation of a mathematical model of the nonlinear pitch-heave dynamics of an uncompartmented, segmented skirt cushion system for an air cushion vehicle are described. This system relies on surface contact to attain static stiffness in pitch and roll. The formulation includes a dynamic model of the lift air system, the effect of segment flexibility on effective cushion capacitance and on hovergap, and hysteretic skirt-surface contact forces. Predictions of linear stability and of nonlinear response to pitch disturbances are made for two skirt materials, the first generating considerable hysteresis in pitch stiffness, and the second having much greater extensibility but negligible hysteresis. These predictions are compared with experimental results obtained from a 900 kg test model. The basic structure of the system's stability characteristics are correctly predicted; this includes a nonlinear pitch-heave instability associated with coupling between pitch and heave motion, and with the modulation of the cushion volume by pitch motion. However, there remain unaccounted sources of cushion damping. This and other factors, such as sensitivity of the predicted results to the flexure of the panels that form the model air supply plenum, make close quantitative agreement between theory and experiment difficult to achieve.
An Inverse Hull Design Problem in Optimizing the Desired Wake of a Ship
Authors: Chen Po-Fan , Huang Cheng-Hung
Published: January 2021

An inverse hull design problem for optimizing the shape of the after hull based on the desired wake distribution is solved using the Levenberg-Marquardt Method (LMM) and the commercial code SHIPFLOW. The desired wake distribution on a propeller plane can be obtained by modifying the existing wake distribution of the parent ship. The surface geometry of the ship is generated using the B-spline surface method, which enables the shape of the hull to be completely specified with only a small number of parameters (i.e., the control points). The advantage of calling SHIPFLOW as a subroutine in the present inverse calculation lies in that many difficult but practical hydrodynamic problems regarding ship design can be solved under this construction. The validity of the present 3-D inverse hull design problem for the after hull of a ship is justified based on the numerical experiments. Results show that optimal hull form can always be obtained based on the required wake distributions.
Green Function Solutions for the Transient Motion of Water Sections
Authors: Holloway D. S. , Davis M. R.
Published: January 2021

A time-domain boundary element method based on a Green function solution is derived for two-dimensional motions in the presence of a free liquid surface. Particular attention is given to the numerical evaluation of the required Green functions with regard to accuracy and speed of solution by choice of a computational algorithm appropriate to the domain of particular computations. The method is validated with reference to analytic solutions for submerged and floating cylinders in steady, transient and periodic motion. The intended application of the method is in the computation of wave response of slender ships at high Froude number by a fixed frame strip theory where the Green function obviates the necessity to panel the free surface with elements.
Joint Distributions of Successive Wave Crest Heights and Successive Wave Trough Depths for Second-Order Nonlinear Waves
Authors: Wist Hanne T. , Myrhaug Dag , Rue Håvard
Published: January 2021

Joint distributions of successive wave crest heights and successive wave trough depths for nonlinear waves are presented. Two different approaches are used in order to derive the probability distributions. The first method includes the effect of second-order Stokes-type nonlinearity on successive wave statistics in finite water depth, and the second method is a parametric model only for crest heights based on second-order simulations. The theoretical distributions are compared with observed wave data obtained from field measurements in the central North Sea.
Sloshing in Rectangular and Cylindrical Tanks
Authors: Sames Pierre C. , Marcouly Delphine , Schellin Thomas E.
Published: January 2021

To validate an existing finite volume computational method, featuring a novel scheme to capture the temporal evolution of the free surface, fluid motions in partially filled tanks were simulated. The purpose was to compare computational and experimental results for test cases where measurements were available. Investigations comprised sloshing in a rectangular tank with a baffle at 60% filling level and in a cylindrical tank at 50% filling level. The numerical study started with examining effects of systematic grid refinement and concluded with examining effects of three-dimensionality and effects of variation of excitation period and amplitude. Predicted time traces of pressures and forces compared favorably with measurements.
Free Vibration Analysis of Orthotropic Circular Cylindrical Shell Under External Hydrostatic Pressure
Authors: Xuebin Li , Yaju Chen
Published: January 2021

An analysis is presented for the free vibration of an orthotropic circular cylindrical shell subjected to hydrostatic pressure. Based on Flügge shell theory, the equations of free vibrations of an orthotropic circular cylindrical shell under hydrostatic pressure are obtained. For shear diaphragms at both ends, the resulting characteristic equations about pressure and frequency are given. These two parameters are calculated exactly. The effect of the shell's parameters (L/R, h/R) and material properties on the free vibration characteristics are studied in detail. Differences between Love-Timoshenko, Donnell equations and that of the Flügge theory are examined as well.
On Three-Dimensional Solutions of Drift Forces and Moments Between Two Ships in Waves
Authors: Fang Ming-Chung , Chen Gung-Rong
Published: January 2021

A far-held approach solving the lateral drift forces and moments between two ships in regular waves is adopted. The velocity potentials for diffraction and radiation based on a 3-D-source distribution technique are obtained. Using the Telste & Noblesse algorithm with a series expansion technique for the principal value integral solves the numerical solutions for corresponding Green functions and their derivatives. One pair of ship models is used for numerical calculations and a 2-D method based on the near-held approach is also included for comparisons. Generally the results obtained by the present technique indicate that the interaction effects between two ships have a profound influence on the drift forces and moments, and the direction of incident waves plays an important role. The results also show that the values predicted by the 2-D method are always very much overestimated because of the trapping energy between two ships. Therefore, the 3-D method prediction model developed here is regarded as more physically reasonable than the 2-D one.
Fatigue Damage of Structural Joints Accounting for Nonlinear Corrosion
Authors: Garbatov Y. , Rudan S. , Soares C. Guedes
Published: January 2021

Analysis of the influence of corrosion on the stress concentration factors of typical ship structural details is presented. While traditionally constant stress concentration factors are adopted, it is proposed here to use time-varying stress concentration factors, which result from the progress of corrosion in the structure. Three-dimensional finite-element models are adopted to obtain the detailed stress distribution at different times. Linear and nonlinear models of the effects of corrosion wastage on the plate thickness reduction are considered and stress concentration factors and fatigue damage are calculated as a function of time. It is concluded that the stress concentration factors have a nonlinear dependency with the time and this leads to a significant difference of the fatigue damage of structural components subjected to corrosion as compared with the traditional predictions.
Bifurcation Analysis of Ship Steering in Canals
Authors: Papoulias Fotis A. , Kapasakis Panos E.
Published: January 2021

The problem of ship steering in canals and confined waters is analyzed with emphasis on stability and bifurcation analysis. The classical maneuvering equations of motion augmented with a model for ship-canal interaction are used to model open-loop dynamics. Coupling of a control law and a guidance scheme with appropriate time lags is employed to model the essential dynamics of a helmsman. The complete system is analyzed using both linear and nonlinear techniques in order to assess its stability under finite disturbances. The results indicate that for certain regions of parameters, limit cycle oscillations may develop that could compromise system stability and safety of operations.
A Model for the Simulation of Steady Spilling Breaking Waves
Authors: Muscari R. , Di Mascio A.
Published: January 2021

A numerical model for the simulation of two-dimensional spilling breaking waves is described. The model is derived from Cointe and Tulin's theory of steady breakers (Cointe & Tulin 1994), although some important changes have been introduced in order to obtain a stable algorithm when coupled with steady-state Reynolds averaged Navier-Stokes equations (RANSE) solvers. In particular, the shape of the breaker and its relation with the following wave height differ from the original model, and moreover, additional conditions for the tangential stress and the turbulent viscosity are proposed. The model has been implemented in a RANSE code, developed for the study of ship flows, through a modification in the free-surface boundary conditions below the breaker. This yields a simple but effective way to reproduce the breaker influence on the underlying flow. The algorithm was used for the simulation of the flow past a submerged hydrofoil. The numerical results are compared with the experimental data by Duncan (1983).
Reliability-Based Specification of Welding Distortion Tolerances for Stiffened Steel Panels
Authors: Elsayed Tarek , Mansour Alaa
Published: January 2021

The purpose of this study is to analytically derive a simple and reasonably accurate expression for the maximum allowable unfairness tolerance of longitudinally stiffened panels in ship structures. The stiffened panels under consideration are typical of those found in the deck, bottom, or side shell of longitudinally stiffened ships. They are assumed to be under still water and wave-induced loads, resulting in predominantly compressive loads. A plate-stiffener combination model is used as representative of the stiffened panel. Ultimate strength is determined based on a strut approach taking into account the effects of initial stiffener deflection and welding residual stresses in the stiffener. A series of stiffener reliability analyses relative to the ultimate failure strength of the stiffener for varying proportions of column slenderness ratios is carried out. Based on the computed results, a simple expression for predicting the maximum allowable unfairness tolerance of the stiffener is derived. The developed expression, expressed in terms of the stiffener slenderness ratio, can be useful for the assessment of fairness limits of plating with frames, or as a design guideline in ship structures during construction.
Maneuvering of Surface Vessels Using a Fuzzy Logic Controller
Authors: Cao Yusong , Lee Tzung-hang
Published: January 2021

A fuzzy logic controller is developed for maneuvering control of surface vessels. The fuzzy controller uses a vessel's heading, yaw rate, distance from a reference point, and the velocity of the vessel relative to the reference point as inputs to generate the control outputs. The control outputs include rudder angle, increase in propeller thrust, and lateral bow thrust. The design of the fuzzy controller is simple and does not require a mathematical modeling of the complicated nonlinear system. The core of the fuzzy controller is a set of fuzzy associative memory (FAM) rules that correlate each group of fuzzy input sets to a fuzzy output set. A FAM rule is a logical if-then type statement based on one's sense of realism, experience, and expert knowledge. The effectiveness and robustness of the fuzzy controller are demonstrated through the numerical time-domain simulations of path tracking and dynamic positioning of a Mariner-class hull with use of nonlinear maneuvering equations of motions.