bluuebunny/crossref_metadata_2025 huggingface dataset:
An Inverse Geometry Design Problem in Optimizing Hull Surfaces
Authors: Huang Cheng-Hung , Chiang Cheng-Chia , Chou Shean-Kwang
Published: January 2021

The technique of the inverse design problem for optimizing the shape of a bow from a specified pressure distribution is presented. This desired pressure distribution can be obtained by modifying the existing pressure distribution of the parent ship. The surface geometry of the ship is generated using the B-spine surface method which enables the shape of the hull to be completely specified using only a small number of parameters (i.e. control points). The technique of parameter estimation for the inverse problem is thus chosen. Results show that the accuracy of the final desired ship form depends on the number of polygons used in 6-spline surface fitting; only when enough polygons are used can the good final geometry that was calculated based on a given pressure distribution be obtained.
On the Simultaneous Design of Blade and Duct Geometry of Marine Ducted Propulsors
Authors: Yiu K. F. C. , Zangeneh M.
Published: January 2021

In ducted propulsor design for marine vessels, due to the strong interaction between the duct and the propeller blades, it is very important to design the duct and the blade geometry simultaneously. Here, a three-dimensional inverse design method is presented to take this into consideration. The method is based on three-dimensional potential flow; however, the effect of the inlet shear flow and the resulting rotational flow is also modeled via the Clebsch formulation. The duct profile is designed to achieve a target velocity distribution while the blade geometry is computed to attain a desired mass-flow rate and a certain circulation distribution. The method is applied to the design of three generic ducted propulsors with a 7-bladed contrarotating configuration.
A Systematic Approach to Modeling Nonlinear Multi-DOF Ship Motions in Regular Seas
Authors: Chen Shyh-Leh , Shaw Steven W. , Troesch Armin W.
Published: January 2021

The modeling and dynamics of nonlinear, large-amplitude motions of vessels in regular beam seas are studied. By using a wave-fixed coordinate system, a three-degree-of-freedom ship model which contains roll, sway, and heave motions is obtained. This model systematically includes various factors that contribute to ship motions. After nondimensionalization and rescaling, it is transformed into a form that is amenable to analysis that takes advantage of various time scales in the problem. This analysis provides a systematic reduction of the full system to a single-degree-of-freedom (DOF) dynamics problem in which roll is dominant. The analysis is based on invariant manifold theory of dynamical systems, and allows one to account for coupling to the quasi-static heave dynamics and the sway velocity. Numerical simulations of a model for a typical fishing vessel are presented and demonstrate that the traditional single DOF roll model represents approximately the dynamics on a special subset—an invariant manifold—of the higher dimensional state space of the full three-DOF model. This work points the way towards a systematic means of modeling general, large-amplitude motions of vessels in a variety of sea states.
Numerical Implementation, Validation, and Marine Applications of an Energy Finite Element Formulation
Authors: Vlahopoulos Nickolas , Garza-Rios Luis Octavio , Mollo Christopher
Published: January 2021

The Energy Finite Element Analysis (EFEA) offers an improved solution to the established Statistical Energy Analysis (SEA) for simulating the vibration of large-scale structures. A theoretical overview and comparison of the two methods is presented first. The main aspects of a numerical EFEA implementation are discussed. A published marine application is analyzed, and comparison of the results offers an initial validation of the EFEA. Numerical models for a fishing boat are generated for both methods and utilized for further comparison between the two formulations. The applicability of the EFEA in the marine field is demonstrated and its benefits are discussed.
Response Characteristics of Serially Connected Semisubmersibles
Authors: Riggs H. R. , Ertekin R. C.
Published: January 2021

One design for a mobile offshore base is to link serially as many as five large semisubmersibles to form a platform long enough to support large aircraft. This paper investigates the linear, wave-induced response characteristics of serially-connected semisubmersibles. A major motivation of this study is to understand more completely the forces required to link semisubmersible modules. The impact of connector strategy and damping on the response, especially the connector forces, is investigated, and the response "modes" which contribute to the connector forces are evaluated in detail. It is shown that the response characteristics can be impacted significantly by the connection strategy, and that connector damping can be a significant source of energy loss when compared to radiation damping. The wet natural frequencies and normal modes are also determined and used to explain the response characteristics of different connection strategies. Although the analyses are based on a specific semisubmersible design, the results provide insight on how other systems of connected semisubmersibles would likely behave.
The Effect of the Steady Flow Potential on the Motions of a Moving Ship in Waves
Authors: Fang Ming-Chung
Published: January 2021

A three-dimensional method to analyze the motions of a ship running in waves is presented, including the effects of the steady-flow potential. Basically, the general formulations are based on the source distribution technique by which the ship hull surface is regarded as the assembly of many panels. The present study includes three algorithms for treating the corresponding Green function:the Hess & Smith algorithm for the part of simple source I/r,the complex plane contour integral of the Shen & Farell algorithm for the double integral of steady flow, andthe series expansions of the Telste & Noblesse algorithm for the Cauchy principal value integral of unsteady flow.

The study reveals that the effect of steady flow on ship motions is generally small, but it still cannot be neglected in some cases, especially for the ship running in oblique waves. The effect also depends on the fore-aft configuration of the ship. The results predicted by the present method are found to be in fairly good agreement with existing experiments and other theories.
Absorbed Energy in Ship Collisions and Grounding—Revising Minorsky’s Empirical Method
Authors: Pedersen P. Terndrup , Zhang Shengming
Published: January 2021

Minorsky's well-known empirical formula, which relates the absorbed energy to the destroyed material volume, has been widely used in analyses of high-energy collision and grounding accidents for nearly 40 years. The advantage of the method is its apparent simplicity. Obviously, its drawback is that the absorbed energy does not depend on the arrangement of the structure, the material properties, and the damage mode. The purpose of the present paper is to establish a new simple relation between the absorbed energy and the destroyed material volume, which can be used as a design tool for analysis of ship collisions and grounding. The developed expressions reflect the structural arrangement, the material properties, and different damage patterns. The present method is validated against a large number of existing experimental results and detailed numerical simulation results. Applications to full-scale ship grounding accidents, the bottom raking damage to tankers and the bottom damage distribution for high-speed vessels are also presented. The proposed method may be considered as an improvement of the classical Minorsky method.
Numerical Analysis of 2-D and 3-D Cavitating Hydrofoils Under a Free Surface
Authors: Bal Sakir , Kinnas Spyros A. , Lee Hanseong
Published: January 2021

A method which models two- or three-dimensional cavitating hydrofoils moving with constant speed under a free surface is described. An integral equation is obtained by applying Green's theorem on all surfaces of the fluid domain. This integral equation is divided into two parts:the cavitating hydrofoil problem, andthe free-surface problem.

These two problems are solved separately, with the effects of one on the other being accounted for in an iterative manner. The cavitating hydrofoil surface and the free surface are modeled with constant strength dipole and source panels. The source strengths on the free surface are expressed in terms of the second derivative of the potential with respect to the horizontal axis by applying the linearized free-surface conditions. The induced potential by the cavitating hydrofoil on the free surface and by the free surface on the hydrofoil are determined in an iterative sense. In order to prevent upstream waves the source strengths from some distance in front of the hydrofoil to the end of the truncated upstream boundary are enforced to be equal to zero. No radiation condition is enforced at the downstream boundary or at the transverse boundary. The method is applied to 2-D and 3-D hydrofoil geometries in fully wetted or cavitating flow conditions and the predictions are compared with those of other methods in the literature.
Chines-Dry Planing of Slender Hulls: A General Theory Applied to Prismatic Surfaces
Authors: Breslin John P.
Published: January 2021

The ultimate goals of this two-part study are the advantages and de' ciencies of application of camber to dry-chine, stepped-planing forms. The present paper is limited to the correlation of a relatively new theory with existing data to qualify it for use in a later paper which will predict the hydrodynamic characteristics of practical forms without and with cambers. Following a brief account of the pertinent literature, a mathematical model is developed via slender-body theory. It is a generalization of M. P. Tulin's (1957) seminal analysis of flat, cambered, delta-wing waterplanes to include deadrise, together with a departure from the oversimpli' ed Wagnerian (1932) theory ' rst introduced by Vorus (1996). It is an independent, less complicated development which con'rms Vorus's result for his special case of straight-sided wedges. Detailed comparisons of all the hydrodynamic coefficients with data from model tests of prismatic hulls show that this theory is superior to that of Wagner. A very simple formula for maximum pressures is shown. Comparisons with the extensive theories of Zhao and Faltinsen are discussed. The theory is justi' ed for extension to more pragmatic forms within the scope of the theory.
Design Optimization of Ship Hulls via CFD Techniques
Authors: Peri Daniele , Rossetti Michele , Campana Emilio F.
Published: January 2021

Numerical shape optimization of a tanker ship hull has been carried out with the aid of computational fluid dynamics (CFD) techniques and experimentally verified. The choice of a specific objective function is based on the needs of the user. In the present study, total resistance and wave pattern have been used either separately or linearly combined. In the optimization process, three different algorithms have been tested, coupled together with a CFD flow solver. A perturbation surface has been used to modify the shape of the hull, allowing for a sharp reduction of the number of design variables. Accordingly, with different objective functions and geometrical constraints, several new optimized shapes of the bulb of a tanker ship have been automatically obtained. Among them, two optimized models have been built and tested, in the INSEAN towing tank, against the original design. In both cases the measured data have confirmed the success of the optimization process.
Kelvin and V-like Ship Wakes Affected by Surfactants
Authors: Zilman Gregory , Miloh Touvia
Published: January 2021

Synthetic aperture radar (SAR) ship wake images in light wind and calm sea conditions frequently appear in the form of a bright V with a half-angle of 2 to 3 deg. Sophisticated and conflicting explanations of this phenomenon, based on the Bragg scattering mechanism, have been proposed. There is a belief that the narrow V-wake is not a part of the Kelvin wake. An alternative approach, which is not generally accepted, suggests that short divergent Kelvin waves may contribute to the V-wake imaging although these waves are mixed with unsteady surface waves generated by the ship-induced turbulence. Ship-generated divergent waves contaminated by surfactants and their radar backscattering cross section are studied. The hull of the ship is represented by a single layer of hydrodynamic singularities. The Green function of a point source moving below a free surface covered by surfactants is derived. A closed-form asymptotic solution for the far ship wave wake is obtained. It is used to calculate analytically the corresponding radar backscattering cross section. The radiative, viscous, and surfactant-induced decay of the V-wake brightness along the V-arms is discussed. The theoretical results are compared against available experimental data.
Numerical Modeling of the Water Flow Around Ship Hulls
Authors: Rigby S.G. , Nicolaou D. , Sproston J.L. , Millward A.
Published: January 2021

A numerical method based on potential-flow theory using Rankine sources has been developed for the prediction of the flow past ship hulls. For purposes of validation, the method has been applied initially to the known analytical solution of flow past a sphere submerged in an infinite fluid. It was confirmed that a significant improvement could be obtained over the original method of Hess and Smith by projecting the collocation points back onto the actual surface of the sphere with additional smaller gains using submergence of the panels below the body surface. The method was then extended by the introduction of a free-water surface boundary condition and used to calculate the wave resistance of a Wigley hull for higher Froude numbers, up to 1.0. Raven's correction to Dawson's original formulation was included and evaluated. It was found that the correction made only a small difference to the calculated wave resistance. The results of the present work were seen to agree closely with experimental data for residual resistance up to a Froude number of approximately 0.65 but then give slightly lower values for higher Froude numbers. The difference was attributed primarily to the method of deducing the experimental values of the residual resistance from the total resistance where the frictional resistance had been based on the static wetted surface area.
Limit State of Torsion of Ship Hulls with Large Hatch Openings
Authors: Hu Yuren , Chen Bozhen
Published: January 2021

The limit state of torsion of ship hulls with large hatch openings is studied. A method to determine the distribution of the plastic shear flow on the hull cross section in the limit state by using the lower-bound theorem is presented together with the corresponding linear programming problem. The limit torsional moment of the hull cross section is obtained based on the distribution of the shear stress in the limit state. Three example limit states for typical containerships of different sizes with large hatch openings are calculated. The calculated limit torsional moments are compared with the design values of wave torque calculated by using the equations given by main classification societies in their rules. A rough estimate of the safety margin is obtained. The results show that for large containerships, it is necessary to pay attention to the safety with respect to torsion. The present method can serve as an effective tool in structural reliability analysis of ships with large hatch openings when the failure mode of torsion is taken into account.
Model-Scale/Full-Scale Correlation in Open Water and Ice for Canadian Coast Guard “R-Class” Icebreakers
Authors: Spencer Don , Jones Stephen J.
Published: January 2021

CCGS Pierre Radisson, one of the R-Class icebreakers Model-scale data from the National Research Council of Canada, Institute for Marine Dynamics' water and ice towing tanks for the Canadian Coast Guard's R-Class icebreaker are compared with previous model tests and, more importantly, with three sets of full-scale ice trials data collected in 1978, 1979 and 1991. In open water, good agreement between model-and full-scale was found for bollard tests, and for self-propulsion tests provided a roughness allowance of 0.0008 was used. In ice, good correlation was found with the 1978 tests when the ship was new and there was little snow cover, using a model hull/ice friction coefficient of 0.05. Good agreement with the later tests, 1979 and 1991, was also obtained with somewhat higher model/ice friction coefficients of 0.055 and 0.065. This is attributed to a deteriorating, and hence rougher, full-scale ship hull surface. The model tests showed that a change in friction coefficient from 0.03 to 0.09 causes a doubling of the delivered power. For the full-scale ship, it is suggested that relatively inexpensive localized hull maintenance in the shoulder area, where ice jamming occurs and hence hull/ice friction is important, could improve performance and reduce the chance of structural damage.
Effect of Gas Forces on Parametrically Excited Torsional Vibrations of Reciprocating Engines
Authors: Pasricha M. S.
Published: January 2021

In the past the effects of ignoring the variable inertia characteristics of reciprocating engines on the accuracy of torsional vibration calculations were considered to be negligible. The associated secondary resonances tended to be dismissed by most engineers as interesting but of no importance. The situation changed in recent years, since there was evidence of the existence of the secondary inertia effects, which could have contributed to a number of otherwise inexplicable crankshaft failures in large multi-cylinder marine diesel engine systems. In view of these facts, a mathematical model is derived with key nondimensional parameters for the analysis of the effect of gas forces on the motion of the variable inertia system. The complex waveform responses are examined in detail within the range of speeds of engine rotation at which adverse effects are known to have occurred in practice. The effects on the parametrically excited motion of the system are investigated at a particular speed of the crankshaft rotation due to the action of external excitations with respect to changes in phase angle and inertia ratio. It is shown that under certain circumstances, interaction of secondary resonance effects with the excitations can be serious for torsional vibration. General comments on Draminsky's work in the light of present investigations are included.
A Quasi-Explicit Hydrodynamic Model for the Dynamic Analysis of a Moored FPSO Under Current Action
Authors: Simos A. N. , Tannuri E. A. , Pesce C. P. , Aranha J. A. P.
Published: January 2021

In an earlier work Leite et al (1998) developed a heuristic hydrodynamic model, based on the shrtwing theory, for the horizontal current forces on an FPSO system. The proposed model was quasi-explicit in the sense that it depends on the ship's main dimensions and on only three hydrodynamic coefficients, namely, the friction coefficient Cf for head on incidence, the drag coefficient CY for a cross-flow, and the related yaw moment coefficient lCY. As discussed in Leite et al (1998), these coefficients could even be estimated from the ITTC friction curve and from Hoerner's sectional results, which would then turn the hydrodynamic model explicit. The model has been tested against experimental results for the horizontal force coefficients, obtained both at IPT and at the Marin wave tank, and it has also been confronted with bifurcation experiments for a turret configuration realized at IPT. The agreement rendered good results in all cases tested. The heuristic approach has now been extended to incorporate the yaw velocity terms while preserving the quasi-explicit feature of the original model. The main purpose of the work herein is to present such a development together with some experimental validation. Using Froude scaling of different ships in distinct ballast conditions, the horizontal forces and moment in the yaw rotating tests were measured at IPT and at Marin and compared with those predicted by the heuristic model, the observed agreement again being fair enough. In an accompanying paper in this issue, the derived mathematical model is tested against experiments that emulate a single-point mooring of a tanker ship in order to disclose the model's ability to cope with the main dynamic features of the fishtailing instability problem.
Experimental Validation of a Quasi-Explicit Hydrodynamic Model: Fishtailing Instability of a Single-Point Moored Tanker in Rigid-Hawser Configuration
Authors: Tannuri E. A. , Simos A. N. , Leite A. J. P. , Aranha J. A. P.
Published: January 2021

The extended hydrodynamic model derived in Simos et al (2001), where the yaw velocity terms have been incorporated to the model proposed by Leite et al (1998) while preserving its quasi-explicit feature, is used here to study some typical dynamic problems of moored ships, specifically the fishtailing shtailing instability that may occur in a single-point mooring (SPM) system. Since the intention was to check the hydrodynamic model, the hawser was assumed rigid to avoid the complex dynamics that may occur when the actual hawser slackens and the obtained results were confronted with experimental ones, obtained at the IPT wave tank. The agreement is very good in the sense that not only the limit-cycle amplitudes are compatible but also the time series are very similar. For the VLCC model in ballasted condition (40%) the fishtailing shtailing instability occurs only for a relatively high current velocity and some Froude effect is then detectable. Using results from the static bifurcation experiment an ad hoc correction is proposed for such effect, showing a relatively close agreement between experiments and the theoretical model. This Froude effect correction is, however, not relevant for an actual SPM system subjected to a usual ocean current.
Bow Wave Dynamics
Authors: Waniewski T. A. , Brennen C. E. , Raichlen F.
Published: January 2021

Experimental studies of air entrainment by breaking waves are essential for advancing the understanding of these flows and creating valid models. The present study used experimental simulations of a ship bow wave to examine its dynamics and air entrainment processes. The simulated waves were created by a deflecting plate mounted at an angle in a supercritical free-surface flow in a flume. Measurements of the bow wave geometry at two scales and also for a bow wave created by a wedge in a towing tank are presented. Contact line and bow wave profile measurements from the different experiments are compared and demonstrate the similarity of the flume simulations to the towing tank experiments. The bow wave profile data from the towing tank experiments were used to investigate the scaling of the wave with the flow and the dependence on geometric parameters. In addition, surface disturbances observed on the plunging wave are documented herein because of the role they play in air entrainment. The air entrainment itself is explored in Waniewski et al (2001).
A Stochastic Stillwater Response Model
Authors: Friis-Hansen Peter , Ditlevsen Ove
Published: January 2021

In this study a stochastic field model for the stillwater loading is formulated where the statistics (mean value, standard deviation, and correlation) of the sectional forces are obtained by integration of the load field over the relevant part of the ship structure. The objective of the model is to establish the stochastic load field conditional on a given draft and trim of the vessel. The model contributes to a realistic modeling of the stochastic load processes to be used in a reliability evaluation of the ship hull. Emphasis is given to container vessels. The formulation of the model for obtaining the stochastic cargo container load field is based on a queuing and loading policy that assumes containers are handled by a first-come-first-serve policy. The load field is assumed to be Gaussian. The ballast system is imposed to counteract the angle of heel and to regulate both the draft and the trim caused by the possible uneven distribution of the cargo load and the bunker load over the system. Stability is not explicitly accounted for. Finally, the calculated second moment statistics of the sectional forces in a container vessel in a full load condition are reported. The obtained statistics for the maximum stillwater bending moment is compared to statistics from available regression formulas. It is found that the suggested model predicts a coefficient of variation of the maximum stillwater bending moment that is a factor of two to three times lower than that obtained by use of the regression formula. It turns out that an important parameter of the stochastic cargo field model is the mean number of containers delivered by each customer.
Free-Surface Effects of Yacht Appendages
Authors: Jackson P.S. , Marr G.
Published: January 2021

This paper uses a panel method based on Kelvin sources and doublets to explore the interactions between the free surface and yacht hull appendages. The emphasis is on understanding the physical origins of the kinds of effects observed in tank tests and in trying to confirm or improve the methods used to predict these effects. Three kinds of interaction are explored, the first being the effect of Froude number, heel and leeway on sideforce, the second being the subsequent effects of residuary resistance due to appendages, and the third being the change in wave drag associated with the presence of a ballast bulb at zero heel and leeway.
Water Entry of a Wedge with Finite Deadrise Angle
Authors: Faltinsen O. M. , Wu Jin
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.
Hydrodynamic Characteristics of Wings in Circular Motion
Authors: Segal Zelik
Published: January 2021

Hydrodynamic characteristics of wings in circular motion are determined at present very approximately, as a rule, according to the solution of the problem on streamlining the wing by a small curvature nonviscid potential. However, in some practical cases the radius of the wing trajectory is of the same order of magnitude as the wing chord. That is why there is a necessity for a more correct determination of wing hydrodynamic characteristics, accounting for the relatively large curvature of the wing trajectory and the and viscosity. This paper presents a description and results of our theoretical and experimental investigation of the hydrodynamic characteristics of wings in a wide range of relative radiuses of their motion.
Enhanced Heat Transfer with Swirl Duct Under Rolling and Pitching Environment
Authors: Chang S. W. , Zheng Y.
Published: January 2021

A detailed experimental investigation of heat transfer in a square duct fitted with twisted tape under a rolling and pitching environment is described, with particular reference to the heat transfer augmentation of shipping machinery. This study focuses on the development of an experimental procedure and methods for data processing, the parametric analysis and a selection of measurements that illustrate the manner by which the swinging forces and buoyancy interactively affect the local heat transfer. The swinging Coriolis force and buoyancy influence to a considerable extent the forced convection heat transfer in the swirl duct. Although enhancing the buoyancy level increases the heat transfer as the swirl duct rolls or pitches, the swinging Nusselt number is initially reduced relative to the stationary condition at the weak swinging oscillation, but tends to recover as the swinging force increases. The synergistic effects of harmonic and nonharmonic rolling and pitching oscillations reduce the heat transfer. Hot spots could develop in a swirl duct due to the slow rolling and/or pitching motions if the effect of the swinging oscillations on the heat transfer is not adequately considered. An empirical correlation has been developed for both single-axis and compound swinging conditions which permits the interactive effect of swinging Coriolis and buoyancy forces on forced convection to be quantified and which provides an evaluation of the local heat transfer in a swinging swirl duct.
Analytical Expressions of Capsize Boundary for a Ship with Roll Bias in Beam Waves
Authors: Spyrou K.J. , Cotton B. , Gurd B.
Published: January 2021

We have considered Melnikov's method for assessing ship safety against capsize in beam waves when there is some steady heel due, for example, to beam wind loading. For a generic restoring lever parameterized with respect to the degree of lever asymmetry ("bias") we have derived closed-form relationships characterizing capsizability and linking the critical wave-slope, the amount of bias, and the damping. Qualitative differences in the safe basin characteristics are identified, which depend on whether the bias is small or large. A critical look into the accuracy of the Melnikov formulas is also presented for nearly symmetric and for strongly asymmetric rolling, based on comparisons with numerical predictions.
Resistance Reduction by Increased Beam for Displacement-Type Ships
Authors: Çalisal S. M. , Gören Ö. , Danisman D. Bülent
Published: January 2021

The resistance of a conventional hull with a parallel middlebody was compared with its modified version having no parallel middlebody. The modified hull was obtained by parabolizing the waterlines, that is, by extending the waterlines continuously about the middlebody, which results in an increased beam and elimination of shoulders. Numerical and experimental results suggest that there could be a significant reduction in the ship's EHP by parabolizing the waterlines at modest Froude numbers. Also, a theoretical justification based on Michell's integral is presented.
An Algorithm for Optimized Design of Maneuvering Experiments
Authors: Sutulo S. , Soares C. Guedes
Published: January 2021

Properties of an adjusted version of Mitchell's algorithm for synthesis of D-optimized experimental designs for response estimation were studied numerically for a third-order polynomial linear regression model widely used in ship maneuvering. Numerical experiments for 2, 3, and 4-factor cases were conducted for different numbers of levels in the classic full-factorial plan used as a set of candidate points. Selection of the runs to be included in the design under construction was made after an exhaustive search. Initial designs were obtained with the pseudo-random or quasi-random generation. A method of assembling an optimized design with the given degree of redundancy is proposed. An important conclusion is that relatively coarse grids can be used for discretizing the factor space that can facilitate substantially the synthesis of the designs without any significant loss of quality.
Nondimensionalized Relationship Between Heating Conditions and Residual Deformations in the Line Heating Process
Authors: Shin Jong Gye , Lee Jang Hyun
Published: January 2021

The nature of a line heating process is very complex since a variety of factors affects the amount of residual deformation. A linear relationship between input and output parameters, which has been derived from simple experiments, is successively used. This relationship, however, is very limited since it does not include important parameters and the line heating process is not linear. A rigorous approach is presented here in an attempt to obtain new relationships between input parameters and final deformations during the line heating process. The residual deformations are investigated by using a thermal elastic-plastic analysis based on finite-element analysis (FEA). Experiments are carried out in order to verify the validity of the FEA results. The nondimensional input parameters are then determined by the dimensional analysis. The relationships between the input parameters and the residual deformations are developed by using multi-variate analysis (MVA) and multiple-regression methods. The final form of the relationships is nonlinear and includes relevant information.
Steady Hydrodynamic Analysis of Planing Surfaces
Authors: Savander Brant R. , Scorpio Stephen M. , Taylor Robert K.
Published: January 2021

The objective of this work is to continue to develop rationally based tools for hydro-dynamic analysis of three-dimensional planing surfaces. The small craft naval architect is in need of a computationally efficient method to analyze planing surfaces allowing for sufficient sensitivity to hull geometric details. Planing surface analysis first received attention during the early part of the 20th century. This development was associated with flying boat applications. Von Karman (1929) and Wagner (1932) are considered the first researchers to develop rational models for planing surface analysis. The work contained herein is derived from the extension of Tulin (1957) originally by Vorus (1996) and later by Savander (1997). The model developed allows for general variation in deadrise in both the transverse and longitudinal directions. Hence, buttock line curvature is included in the formulation. The chine beam of the hull can vary longitudinally. Fundamental theoretical and numerical enhancements have been made to Vorus (1996) and Savander (1997). The current model is compared with constant and variable velocity 2-D impact experiments, prismatic planing model tests, Savitsky (1964) prismatic planing model, and deepwater Series 62 model test results (Clement & Blount 1963). The comparisons in many cases are excellent, especially at high Froude number. The comparisons illustrate the utility of the method. Problematic areas are presented and topics for further research are suggested.
Multidisciplinary Design Optimization of a Naval Surface Combatant
Authors: Peri Daniele , Campana Emilio F.
Published: January 2021

Whereas shape optimal design has received considerable attention in many industrial contexts, the application of automatic optimization procedures to hydrodynamic ship design has not yet reached the same maturity. Nevertheless, numerical tools, combining together modern computational fluid dynamics and optimization methods, can aid in the ship design, enhancing the operational performances and reducing development and construction costs. This paper represents an attempt of applying a multidisciplinary design optimization (MDO) procedure to the enhancement of the performances of an existing ship. At the present stage the work involves modeling, development, and implementation of algorithms only for the hydrodynamic optimization. For a naval surface combatant, the David Taylor Model Basin (DTMB) model ship 5415, a three-objective functions optimization for a two-discipline design problem is devised and solved in the framework of the MDO approach. A simple decision maker is used to order the Pareto optimal solutions, and a gradient-based refinement is performed on the selected design.
Wind Tunnel Tests on Flow Characteristics of the KRISO 3,600 TEU Containership and 300K VLCC Double-Deck Ship Models
Authors: Lee Sang-Joon , Kim Hak-Rok , Kim Wu-Joan , Van Suak-Ho
Published: January 2021

The flow characteristics in the stern and near-wake region of two ship models, the Korea Research Institute of Ships and Ocean Engineering (KRISO) 3,600 TEU containership (KCS) and the KRISO 300K very large crude oil carrier (VLCC) (KVLCC), were investigated experimentally. The double-deck ship models were installed in a subsonic wind tunnel. The freestream velocity was fixed at Uo = 25 m/s, and the corresponding Reynolds numbers based on the model length (Lpp) were about 3.3x 106 and 4.6x 106for the KCS and KVLCC models, respectively. The spatial distributions of mean velocity components and turbulence statistics, including turbulence intensities, Reynolds shear stresses, and turbulent kinetic energy, were measured using a hot-wire anemometer. For both ship models, the stern flow and near-wake show very complicated three-dimensional flow patterns. The longitudinal vortices formed in the stern region dominantly influence the flow structure in the near-wake region. In the region of main longitudinal vortices, the mean velocity deficits and all turbulence statistics have large values, compared with the surrounding flow. As the flow moves downstream, the turbulence statistics increase and have maximum values at the after-perpendicular (AP) plane and then decrease gradually due to the expansion of the shear layer. For the KVLCC model, the spatial distributions of mean velocity components and turbulence intensities behind the propeller plane clearly show hook-shaped contours. These experimental results, especially the turbulence statistics, can be used not only to understand the flows around modern practical hull forms but also to validate the computational fluid dynamics codes and turbulence models. The complete experimental data set is available on the website (http://www.postech.ac.kr/me/efml/data).
Numerical Modeling of Supercavitating Propeller Flows
Authors: Young Yin L. , Kinnas Spyros A.
Published: January 2021

A three-dimensional boundary element method is used for the numerical modeling of supercavitating propellers subjected to nonaxisymmetric in†ow. The method has been developed in the past for the prediction of unsteady sheet cavitation for conventional propellers. To allow for the treatment of supercavitating propellers, the method is extended to model the separated flow behind trailing edges with nonzero thickness. The convergence of the method is studied. Results from numerical validation, as well as comparisons of predictions with experimental measurements, are provided.
Benchmarking of Computational Fluid Dynamics for Ship Flows: The Gothenburg 2000 Workshop
Authors: Larsson Lars , Stern Frederick , Bertram Volker
Published: January 2021

The Gothenburg 2000 was an international benchmark workshop for computational fluid dynamics applied to ship flows. Test cases were three modern hull forms. One case without a free surface focused on turbulence modeling, whereas wave prediction was of interest for the other two. Of the free-surface cases, one had an operating propeller. For the first time, verification and validation procedures were an integral part of such benchmark efforts in ship flows. The workshop showed that free-surface waves may now be well predicted also away from the hull. There is a general improvement in the computation of the stern flow thanks to better turbulence modeling, but there is still room for improvement. Full-scale viscous flows may be computed without numerical difficulties. Verification and validation procedures should be applied for uncertainty analysis, and there is a discussion of the uncertainty in the predicted integral quantities in the paper. Further detailed conclusions and recommendations are also given based on the comparison of extensive standardized plots of the comparative computations and evaluation of the integral quantities.
Hybrid Reliability Predictions of Single and Advanced Double-Hull Ship Structures
Authors: Lua James , Hess Paul E.
Published: January 2021

A hybrid approach based on the combination of the Monte Carlo simulation (MCS) technique and the first-order reliability method (FORM) is developed to quantify the small probability of failure of a hull girder under longitudinal bending. The ultimate strength (ULTSTR) bending solver, developed by the U.S. Navy, is integrated with the hybrid probabilistic analysis framework. Different from the conventional approach, where the probability distribution of the hull capacity is preassumed, the probability distribution of the ultimate bending strength is determined by propagation of the uncertainties associated with hull geometric and material property parameters into ULTSTR via a small number of Monte Carlo simulations. The FORM-based solution module is then applied in the reduced random variables space to compute the probability of failure. Both the computational efficiency and numerical accuracy of the hybrid approach are demonstrated through its application to a Navy frigate, designated Ship A. The validated hybrid approach is then applied to a Navy combatant, designated Ship B, in both its single-and double-hull configurations. The reliability results reveal the benefit in using the advanced double-hull configuration, assuming its design load is the same design load encountered by the corresponding single hull during its service life.
A NURBS Panel Method for Three-Dimensional Radiation and Diffraction Problems
Authors: Kim Booki , Shin Yung S.
Published: January 2021

A B-spline panel method is developed to solve a boundary integral equation for three-dimensional potential flow problems. In particular, a nonuniform rational B-spline (NURBS) surface is introduced to accommodate a precise geometric description of a given body. For the unknown (potential) description over the surface, uniform B-spline basis functions are used. A collocation approach is adopted for numerical computations, and influence coefficients are evaluated in a robust manner over the surface defined by NURBS. Convergence characteristics of the present method have been investigated in the numerical experiments on the unbounded problem of a sphere, the radiation problem of a floating hemisphere, and the diffraction problem of a submerged spheroid. It is shown that the numerical results are in excellent agreement with analytical solutions in all cases considered. It is concluded that the NURBS panel method is superior to existing panel methods in geometric description of body surface, and convergent solutions can be achieved rapidly with a small number of panels.
Coupling of Sloshing and Ship Motions
Authors: Rognebakke Olav F. , Faltinsen Odd M.
Published: January 2021

The coupled effect between ship motions and sloshing is studied. Two-dimensional experiments of a hull section containing tanks filled with different levels of water excited in sway by regular waves have been conducted. Steady-state results are obtained for the sway amplitude. Even if violent sloshing occurs in the tanks, the steady-state motion is almost linear and sinusoidal with the frequency of the linear incident waves. This implies that higher-order harmonics of the sloshing force are filtered out by the system. Simulations of the modeled case are performed using a linear and a nonlinear sloshing model and mainly assuming linear external flow. For steady-state motion, a convolution formulation does not improve the results relative to using constant coefficients in the equation of motion. However, in order to properly model the transient behavior in an irregular sea, a convolution formulation must be included. The treatment of the retardation function for the external problem is discussed in detail. A good agreement between experiments and computations is reported. The calculated coupled motion is sensitive to the damping of the sloshing motion in a certain frequency range where the coupled sloshing and ship motions cause resonant ship motions. A quasilinear frequency domain analysis is used to explain this by introducing the sloshing loads as a frequency dependent spring.
Optimum Ship Steering-Stabilization Control
Authors: Whalley R. , Ebrahimi M.
Published: January 2021

The problem of ship steering-stabilization control is outlined. A constant-speed, openwater, warship model relating the yaw and roll angle to input changes on the rudder and stabilizer fins is presented. The coupled nature of the model is demonstrated and simple open-loop precompensation is proposed. Analysis, followed by closed-loop design procedures, which induce desired dynamic characteristic s, are invoked. Optimum minimum control effort regulation is achieved via regenerative feedback. The penalty costs incurred when operating under suboptimum conditions are commented upon.
Comparison Between Numerical Computations and Experiments for Seakeeping on Ship Models With Forward Speed
Authors: Maury C. , Delhommeau G. , Ba M. , Boin J. P. , Guilbaud M.
Published: January 2021

The recent progress of computers and numerical algorithms enables us today to use the translating and pulsating Green function in panel methods for seakeeping calculations. Two different methods of calculations of this function, its derivatives and their integrations over panels or segments, are briefly presented and have been introduced into the seakeeping codes Aquaplus developed at Ecole Centrale de Nantes and Poseidon at Laboratoire d'Etudes Aerodynamiques (LEA), Centre d'Etudes Aerodynamiques et Thermiques (CEAT). Both codes interchange the Fourier and boundary integrals on panels or waterline segments, the last part being performed analytically. These methods have been used to compute flows around Wigley or Series 60 model ships. To check the numerical results, an experimental setup has been developed at the CEAT that measures forces and moments on a model in forced harmonic oscillations of pitch or heave. Tests have been performed in the recirculating water channel of Ecole Centrale de Nantes on two L = 1.2 m Series 60 models of CB = 0.6 and 0.8 block coefficients. Unsteady wave patterns have been recorded using a resistive wave probe. The experimental results are compared with the numerical ones.
Experimental Investigation of the Nonlinear Effects on the Vertical Motions and Loads of a Containership in Regular Waves
Authors: Fonseca N. , Soares C. Guedes
Published: January 2021

The nonlinear vertical responses of a containership advancing in regular waves are investigated experimentally. The paper presents the results of an experimental program carried out in a seakeeping tank with a model of the ITTC S-175 containership in head regular waves. All the wave frequency ranges of interest were tested, and for each wave frequency several wave amplitudes were used ranging from small to large amplitude. In this way the influence of the wave amplitude on the nonlinear characteristics of the responses was assessed. The measured responses include the absolute and relative motions, vertical accelerations, and cross-sectional loads at midship and ¼ Lpp from the forward perpendicular. Strong nonlinear effects were detected, especially on the loads, which can be identified by the variation of the transfer function with the wave amplitude, the asymmetry of the time histories, and the presence of higher harmonics.