bluuebunny/crossref_metadata_2025 huggingface dataset:
Turbulence Effects on the Design and Performance of Low-Drag Keels
Authors: Vijgen P. M. H. W. , van Dam C. P. , Obara C. J.
Published: January 2021

Achievement of laminar boundary-layer flow over the keel of sailing yachts offers great potential for increased boat speed resulting from the reduction in viscous drag. The intensity and the spectral energy distribution of small-scale turbulence in the upper layer of the ocean can have a large effect on the extent of laminar flow and, hence, the drag reduction. A detailed summary and interpretation is provided of measured turbulent intensities and length scales in the upper ocean. An analysis is given of the effect of small-scale turbulence on boundary-layer transition and profile drag for two laminar-flow foils at zero and moderate leeway angles. Using the modified en-transition criterion it is shown that the level of small-scale oceanic turbulence is an important parameter in the design of a laminar-flow foil. At high turbulence levels, the foil with a more forward location of the minimum-pressure point generates less drag than the foil with a more aft location of the minimum-pressure point at the same flow conditions.
Numerical Study on a Viscous Flow with Free-Surface Waves About a Ship in Steady Straight Course by a Finite-Volume Method
Authors: Miyata Hideaki , Zhu Ming , Watanabe Osamu
Published: January 2021

A finite-volume method is developed and applied to a flow about a ship. It employs an explicit timemarching procedure with the sub-grid scale turbulence model without using the wall-function on the body surface. The averaging treatment is on a much smaller level than the method so far used. The curvilinear grid system is fitted not only to the hull surface but also to the free-surface, which is deformed by the wave motion. The comparison between simulated and measured results shows quite excellent agreement in the waves and marginally satisfactory agreement in the wake distribution. The simulated results reveal some interesting features of the flow, such as the systematic formation of the longitudinal vortices, the generation of vortices in the vicinity of the free-surface, and the complicated interaction of vortices near the after end of a ship.
Time Simulation of Water Shipping for a Ship Advancing in Large Longitudinal Waves
Authors: Fang Ming-Chung , Lee Ming-Ling , Lee Chwang-Kuo
Published: January 2021

The technique of time-domain numerical simulation for the occurrence of water shipping on board in head waves is presented. The nonlinear effects of the large-amplitude motion are treated. These nonlinear factors include the effect of large wave amplitude, large ship motion, the change of hull configuration below the free surface and the nonlinear resultant wave. Therefore, the variation of the potentials and the hydrodynamic coefficients for a ship at each time step must be carefully treated. While handling the determination of the instantaneous wave surface around the ship hull, the complete incident, diffracted, and radiated wave system is used rather than the incident wave only. The complexity of the ship speed effect on the related terms is also treated at each time step, especially for the radiation problems. An experimental setup is also designed to measure the motion response and the relative motion, and comparisons are made. The results show excellent agreement and the validity of the theory is confirmed. The successful development of the present technique can be extended to analyze the dynamic stability, capsize phenomena, and ship motion in irregular waves
Parameterization of Directional Spectra and Its Influence on Ship Motion Predictions
Authors: Graham Ross , Juszko Barbara-Ann
Published: January 2021

An approach to parameterizing directional spectra proposed by Hogben & Cobb based on a combination of the Ochi & Hubble 6-parameter spectrum and the Longuet-Higgins et al cos2p model is adopted for a study of directional parameterizations and their influence on ship motion predictions. Two schemes for evaluating the directional spreading parameters are assessed in terms of their ability to reproduce highly resolved measured directional spectra, and the best approach, termed the 10-parameter spectrum, is adopted. The applicability of the 10-parameter spectrum to hindcast spectra is investigated, and acceptable fits obtained for 93% of the spectra considered. An evaluation of the ability of the hindcast model to reproduce the measured spectral data is also made. In general, it is found that the differences between the hindcast spectra and associated 10-parameter fits are significantly smaller than the differences between the hindcast spectra and the field data, and it is concluded that the 10-parameter spectrum is a suitable basis for developing statistical descriptions of directional wave climates. The effects of directional parameterization on ship motion predictions are investigated by computing the ship responses as a function of heading for sample hindcast spectra, and the associated 10-parameter and Bretschneider 2-parameter spectra. The responses calculated using the 10-parameter spectrum are found to be in better agreement with the hindcast results than those obtained with the Bretschneider 2-parameter spectrum, with a significant improvement in modeling accuracy in the case of bi-modal spectra. The potential advantages of incorporating the 10-parameter spectrum in future operability analyses of flight operations is examined by comparing the head-to-wind roll response computed using hindcast spectra with that predicted using 10-parameter and Bretschneider spectra.
Response Analysis and Operating Limits of Crane Ships
Authors: Schellin T.E. , Jiang T. , Östergaard C.
Published: January 2021

Results are presented of a recent research project with the objective of quantitatively predicting the dynamic response of crane ships during lifting operations offshore. For this purpose, a mathematical simulation model was developed. This model considers the elasticity and damping of the hoisting rope assembly and includes bi-angular swing of the hook load coupled with hull motions. The nonlinear, time-domain motion equations comprise effects of gravity, buoyancy, hydrodynamic reactions, viscous drag, wave excitation, and the mooring system. The mathematical model was verified by comparing calculated system response with corresponding measurements from scale-model tests. To derive transfer functions of system response, the dynamic motion equations were linearized about the system's equilibrium state. The dynamic behavior of a shear-leg crane barge and a semisubmersible crane vessel was investigated and operational limits were specified. Based on these limits, obtaining the crane ships' probability of successfully performing a heavy lift was demonstrated.
On the Nonlinear Dynamics of Pursuit Guidance for Marine Vehicles
Authors: Papoulias Fotis A.
Published: January 2021

A theoretical analysis of the nonlinear dynamic phenomena involved in pure pursuit guidance of marine vehicles is performed. Nomoto's model (Crane et al 1989) is used to provide the basis for the main vehicle turning lag. Results obtained in closed-form expressions demonstrate the existence of bifurcations to periodic solutions. The center manifold of the system is evaluated to within a third-order approximation. Third-and fifth-order expansions are utilized in order to provide information on limit cycle existence and stability. Recommendations regarding the appropriate selection of control design parameters are provided.
Evaluation of the Wave-Resistance Green Function: Part 3— The Single Integral Near the Singular Axis
Authors: Clarisse J.-M. , Newman J.N.
Published: January 2021

The single integral part of the wave-resistance Green function is considered near its singular axis. Completing the work of Ursell (1988) an asymptotic expansion is proposed that is valid in the vicinity of the source when this lies on or near the free surface. For the complementary region away from the singular axis an improvement of Bessho's (1964) convergent series is also obtained. Numerically, both expres¬sions along with previous results guarantee fast and accurate evaluations of the single integral within two wavelengths downstream of the source. For larger distances downstream, the result of Ursell (1988) is shown to be still valid within bounded distances of the singular axis. Hence the single integral can be evaluated analytically or numerically in a whole neighborhood of its singular axis.
A Numerical Study of the Hydrodynamic Forces Developed by a Marine Rudder
Authors: Willis C. J. , Crapper G. D. , Millward A.
Published: January 2021

The flow around a ship's rudder has been modeled using the vortex lattice method. The technique has been used to study the forces, particularly the side force, developed by the rudder in uniform and nonuniform flow. The model was extended to include the effect of a plate above the rudder in order to simulate the hull. A final part of the work was a study of the effect of the deadwood ahead of therudder. The results obtained from the calculations have shown that a small side force can be created if the rudder is placed symmetrically along the propeller axis when the gap between the top of therudder and the hull is not large. In addition, it was found that a side force could be generated by the proximity of the rudder to the deadwood.
Numerical Evaluation of Free-Surface Green Functions
Authors: Ponizy B. , Noblesse F. , Ba M. , Guilbaud M.
Published: January 2021

A very simple and efficient method for computing the nonoscillatory near-field terms in the expressions for the Green functions, and their gradients, for wave diffraction/radiation by an offshore structure and steady ship waves in deep water is presented. The Green functions are decomposed into three terms corresponding to simple (Rankine) singularities, wave fields, and nonoscillatory near-field (local) flow components. The method which is presented for approximating the latter nonoscillatory near-field components is based on the use of a coordinate-transformation and a function-transformation. The coordinate-transformation maps the unbounded domain of definition of the Green function into a finite domain (unit square or cube) of transformed coordinates. The function-transformation expresses the near-field components, which are singular at the origin, in terms of functions that are regular everywhere. Proper coordinate and function transformations reduce the problem of approximating singular functions in unbounded domains into that of approximating smoothly varying functions within finite domains. The latter task can be accomplished in a number of ways, including the use of linear table interpolation presented in the study.
Solution Branching and Dive Plane Reversal of Submarines at Low Speeds
Authors: Papoulias Fotis A. , Riedel Jeffery S.
Published: January 2021

The problem of multiple steady-state solutions in the dive plane of submarines under depth control at low speeds is analyzed. This phenomenon occurs regardless of the particular means used for depth control, manual or automatic, and linear or nonlinear. It is shown that the primary bifurcation parameter is a Froude-like number based on the vehicle speed and metacentric height. Generic solution branching is shown to occur below a critical Froude number. Singularity theory techniques are employed to quantify the effects that various vehicle geometric properties and hydrodynamic characteristics have on steady-state motion. It is demonstrated that a comprehensive bifurcation study provides a systematic and effective way of predicting the phenomenon of dive plane reversal at low speeds. A complete characterization of the parameters in the problem, both in deep water and at periscope depth, is achieved through the organizing center of the pitchfork singularity.
Probability-Based Ship Structural Safety Analysis
Authors: Mansour A. E. , Hovem L.
Published: January 2021

This paper provides a demonstration on the use of probability-based ship structural safety analysis and enumerates the benefits in comparison with traditional methods. Reliability techniques are developed to determine safety levels of existing vessels, taking into consideration uncertainties in loads, strength and calculation procedures. Ultimate, serviceability and fatigue limit states are developed and applied to an existing tanker. The corresponding load models are examined and, in some instances, further developed. Safety indices associated with yielding, buckling, and fatigue are calculated. Conclusions are drawn regarding the benefits and drawbacks of using probability-based ship safety analysis. This paper provides a demonstration on the use of probability-based ship structural safety analysis and enumerates the benefits in comparison with traditional methods. Reliability techniques are developed to determine safety levels of existing vessels, taking into consideration uncertainties in loads, strength and calculation procedures. Ultimate, serviceability and fatigue limit states are developed and applied to an existing tanker. The corresponding load models are examined and, in some instances, further developed. Safety indices associated with yielding, buckling, and fatigue are calculated. Conclusions are drawn regarding the benefits and drawbacks of using probability-based ship safety analysis.
Modeling Issues Related to the Hydrodynamics of Three-Dimensional Steady Planing
Authors: Lai Canhai , Troesch Armin W.
Published: January 2021

A three-dimensional numerical model using vortex lattice methods is developed to solve the steady planing problem. This paper examines assumptions related to high-speed planing hydrodynamics, including those used by two-dimensional slender-body theories. Emphasis is placed upon the investigation of various modeling issues such as the zero pressure condition on the free surface and the treatment of the flow off the chines. Numerical results including hydrodynamic forces and pressure distributions are presented and compared with experiments. A simple model to include the effect of gravity in the near field is also examined. The models described here can be incorporated into design methodologies for predicting the hydrodynamic force and moment acting on planing hulls with general shape.
Effect of Hull Discretization on Steady Free-Surface Flow Calculations
Authors: Hendrix Dane , Noblesse Francis
Published: January 2021

Steady free-surface potential flow about a mathematically defined hull form is considered. The flow is defined using the slender-ship approximation. The hull form is approximated by means of flat triangular panels within which the source strength is piecewise constant. Convergence of the computed velocity potential, wave profile, and lift, moment and drag with respect to hull discretization (size and aspect ratio of panels) is evaluated.
Highly Nonlinear Rolling Motion of Biased Ships in Random Beam Seas
Authors: Jiang Changben , Troesch Armin W. , Shaw Steven W.
Published: January 2021

Recent developments in dynamical systems analysis are applied and extended to the study of highly nonlinear ship rolling motion and capsizing in random beam seas. Damping and wave excitation moments are dealt with as perturbations since they are relatively small compared with inertial effects and hydrostatic righting moments. There is no restriction on the restoring moment due to hydrostatic loads, and bias effects are included. Safe and unsafe areas are defined in the phase plane of the unperturbed system model to distinguish the qualitatively different ship motions of capsize and noncapsize. Capsize events are represented by solutions passing out of the safe region. The probability of such an occurrence is studied using the Melnikov function and the concept of phaseflux rates. Expressions for the phase space flux rate are derived and evaluated by numerical integration. The correlation of phase space flux and capsize is investigated through extensive simulation. It is shown that these analytical tools provide reliable, predictive information regarding the likelihood of a vessel capsize in a given sea state.
Hydrodynamic Memory Effect on Stability, Bifurcation, and Chaos of Two-Point Mooring Systems
Authors: Chung Jin-Sug , Bernitsas Michael M.
Published: January 2021

The stability properties of two-point mooring systems governed by their slow horizontal motions are studied theoretically. The often-neglected memory effect due to hydrodynamic wave loads change—in some cases critically—the stability boundaries in the system design space. The third-order maneuvering equations and a nonlinear elastic spring model are used to describe the dynamics of the moored vessel and the mooring lines, respectively. The resulting model accurately represents a two-point mooring system and can be used for stability analysis in the sense of Lyapunov. The stability charts of mooring systems with memory effects exhibit considerable differences from systems without memory in local regions of bifurcation diagrams. Further, the pattern of these changes of stability boundaries varies with the hydrodynamic properties of the moored vessel and/or the environmental conditions. The findings of this study suggest that the number of influencing design parameters can be much more than the present stability theory of dynamical systems can handle. They prove, however, that neglecting the memory effect may result in selecting unsafe configurations of two-point mooring systems.
Interaction Equation for the Collapse of Tankers and Containerships Under Combined Bending Moments
Authors: Gordo J. M. , Soares C. Guedes
Published: January 2021

The ultimate collapse of the midship section of tankers and container ships under combined vertical and horizontal bending moments is determined by an approximate method. That accounts for the load shortening contribution of each plate and stiffener assembly, thus being able to construct the moment-curvature relation for the hull girder. The method is applied to study five tankers and six container ships and the results are used to define an interaction formula proposed to account for the combination of the load effects for design purposes.
A Twisted Rudder for Reduced Cavitation
Authors: Shen Young T. , Jiang Chen W. , Remmers Kenneth D.
Published: January 2021

A rudder operating behind a propeller can experience large onset flow angles along the rudder span. At a given speed, the maximum rudder angle before cavitation is substantially higher in turning to one direction than to the opposite side. At high speeds, rudders can experience severe surface cavitation, even at zero degree rudder deflection angle. Observation from full-scale trials and dry dock inspection of a surface ship combatant show that rudder cavitation is a real problem in terms of ship operation and maintenance. It is shown in this paper that cavitation inception and erosion problems associated with the existing fleet rudders can be avoided or reduced by using the concept of a twisted rudder. A fleet rudder can be twisted along its span to align the incoming flow. The twisted rudder model has been designed, fabricated, and tested in the Navy's Large Cavitation Channel (LCC). Two-component Laser Doppler Velocimetry (LDV) was used to measure the field velocity and inflow angles in the propeller slipstream. A dynamometer and a series of pressure taps were used to measure rudder lift, drag and pressure distributions on the rudder surface. To evaluate the effect of twist angles on rudder performances, a full-scale rudder, designated the non-twisted rudder, has also been fabricated and tested back-to-back in the LCC with the twisted rudder for direct comparison. The advantages of using a twisted rudder to improve cavitation performance are presented in this paper.
Theoretical and Experimental Study on the Ultimate Strength of Corrugated Bulkheads
Authors: Paik Jeom K. , Thayamballi Anil K. , Chun Min S.
Published: January 2021

The objectives of the present study are to obtain experimental data on collapse strength of steel corrugated bulkhead models and also to develop a simple analytical formulation for ultimate strength useful in the design of corrugated bulkheads under static lateral pressure. Collapse tests on nine mild steel corrugated bulkhead models having five bays of corrugations are carried out, varying the corrugation angle, the plate thickness and the type of loading (axial compression and/or lateral pressure). Using the test data, the characteristics of the collapse mechanism for corrugated bulkheads are investigated. For purposes of rapid first cut estimates of strength, a new and simple analytical formulation for predicting the ultimate strength of corrugated bulkheads under hydrostatic pressure is derived based on an assumed stress distribution over the corrugation cross section at the ultimate limit state. The modeling error associated with the new formulation is established by comparing its predictions with the experimental results. The development of ultimate strength based design guidelines and the effect of design parameters such as the corrugation angle on ultimate strength of a corrugated bulkhead are then discussed. All experimental information and strength data are tabulated, which is a benefit in itself.
Local Buckling of Stiffeners in Ship Plating
Authors: Paik Jeom Kee , Thayamballi Anil K. , Park Young Eel
Published: January 2021

The aim of the present study is to analytically investigate the characteristics of local buckling of the stiffener web in the stiffened panels under uniaxial compressive loads. A plate-stiffener combination model is used as representative of the stiffened panel. The elastic buckling condition for the stiffener web is analytically derived by solving the characteristic value problem involving the governing differential equation under the corresponding loading and boundary conditions. A series of analyses of stiffener web buckling strength for varying proportions of plating and web/flange is carried out. Based on the computed results, a basic investigation of stiffener web buckling is made. Closed-form approximate expressions for predicting the buckling strength of the stiffener web are derived taking into account the influence of rotational restraints at the plate-stiffener web connection and stiffener web-flange intersections. Design considerations for potentially preventing buckling of the stiffener web are then discussed. The computed basic results for the stiffener web buckling coefficient are documented.
Time-Domain Analysis of Large-Amplitude Vertical Ship Motions and Wave Loads
Authors: Fonseca N. , Soares C. Guedes
Published: January 2021

The vertical motions and wave induced loads on ships with forward speed are studied in the time domain, considering non-linear effects associated with large amplitude motions and hull flare shape. The method is based on a strip theory, using singularities distributed on the cross sections which satisfy the linear free surface condition. The solution is obtained in the time domain using convolution to account for the memory effects related to the free surface oscillations. In this way the linear radiation forces are represented in terms of impulse response functions, infinite frequency added masses and radiation restoring coefficients. The diffraction forces associated with incident wave scattering are linear. The hydrostatic and Froude-Krylov forces are evaluated over the instantaneous wetted surface of the hull to account for the large amplitude motions and hull flare. The radiation contribution for wave loads is also obtained in the time domain using convolution to account for the memory effects related to the free surface oscillations. Results of motions and wave loads for the S175 container ship are presented and analyzed. The results from the present method are compared with linear results.
Nonlinear Heave Dynamics of an Air Cushion Vehicle Bag-and-Finger Skirt*
Authors: Chung J. , Sullivan P. A. , Ma T.
Published: January 2021

The flexible skirt system used almost exclusively on large amphibious air cushion vehicles such as the U.S. Navy's 150 tonne landing craft is the bag-and-finger skirt, but little information on its dynamical properties is available in the journal literature. The present paper describes results of an analysis of the nonlinear heave dynamics of a simplified configuration chosen specifically to allow formulation from first principles The skirt mass is lumped in the fingers, with the bag being modeled as a combination of massless inelastic membranes and links. Airflow processes are assumed quasi-steady, and the bag-and-cushion volumes are modeled as lumped pneumatic capacitances. The modulation of cushion air escape by skirt-surface contact is also included. The numerical results show that nonlinear effects occur at wave input amplitudes expected to be encountered in practice. At a given frequency, input amplitude increase causes jumps in heave response, period doubling, and chaos. Furthermore, results for two typical configurations show resonance at frequencies at which humans are most sensitive. One solution to this problem may be to reduce skirt mass The paper concludes with a discussion of issues requiring further investigation.
Numerical Simulation Method for Flows About a Semi-Planing Boat with a Transom Stern
Authors: Orihara Hideo , Miyata Hideaki
Published: January 2021

A new simulation method based on computational fluid dynamics (CFD) is developed for a semiplaning boat with a transom stern in unsteady motion. The time-dependent Reynolds-averaged Navier-Stokes (RANS) equation is discretized by the finite-volume method and solved by the MAC-type solution algorithm, The free-surface treatment in this study is based on the density function method. The motion of the boat is simultaneously solved by combining the equation of the motion of the boat with the flow computation, and the effect of the boat motion is implemented by the moving grid method in the flow computation. Simulations for two types of practical high-speed boats are performed in the Froude number range from 0.5 to 1.0 and the results are compared with experimental ones. It is demonstrated that this method can simulate both the flow about the boat and the running attitude in free-to-run condition with a sufficient degree of accuracy and that it can be used as an effective tool for the development of hull form of practical high-speed boats.
Nonlinear Kinematic Analysis of the Deformation of Plates for Ship Hull Fabrication
Authors: Shin Jong Gye , Ryu Cheol Ho
Published: January 2021

Curved plates in a ship's hull are fabricated by mechanical or thermal processes, such as roller bending and line heating methods. The formation of curved plates is a process in which, from the point of view of mechanics, permanent bending and/or in-plane strains are applied to flat plates. Only bending strains are applied to single curvature shells, while in-plane strains, in addition to bending strains, need to be applied in order to form double curvature shells. In-plane strains, however, are known to be small and, thus, can be neglected. The mechanics of plate bending is different from the production of plate bending. In the mechanics of plate bending, an initial configuration of a plate is given, along with boundary and loading conditions. The deformed shape can then be calculated. In the production of plate bending, however, only the final deformation shape is given and the initial configuration is unknown. Loading conditions must also be determined. This paper presents rigorous formulations of a kinematic problem for the production of plate bending. Nonlinear kinematic analysis with and without initial imperfections is employed in order to include in-plane strains. An algorithm is suggested to determine an initial configuration from given surface data. Numerical examples show that the in-plane strain must not be negligible and, rather, plays an important role in the determination of heating paths in the line heating method.
Disturbance During Steady and Unsteady Motion of a Two-Dimensional Pressure Distribution
Authors: Okita Noriaki , Sahin Iskender , Hyman Mark C.
Published: January 2021

A two-dimensional study of flow due to a moving pressure distribution in subcritical Froude numbers over finite-depth water was conducted by a linearized ideal flow approach. A numerical integration algorithm was developed to evaluate the analytical solution given by Cauchy principal-value integrals. The surface elevation, bottom pressure profiles, and wave resistance were computed as functions of speed and water depth. The calculated results agreed well with published values.
Measurement of Global Loads on a Full-Scale SES Vessel Using Networks of Fiber Optic Sensors
Authors: Jensen A. E. , Taby J. , Pran K. , Sagvolden G. , Wang G.
Published: January 2021

A method for measurement of global loads on a vessel, using strain measurements from a network of strain sensors and extensive Žnite-element analyses (FEA) with idealistic load cases, is presented. The sensors are attached at carefully selected locations at a cross section amidships, where the most signiŽcant loads have their maximum values. The Žnite-element (FE) strain values are used in precalculations to reduce the computational effort to solve a set of linear algebraic equations in real time. The method has been successfully tried out on the full-scale surface effect ship (SES) KNM Skjold (47 m, 270 tons, and 50 knots) instrumented with a network of Žber optic Bragg strain sensors. The seakeeping tests were performed in the North Sea (1999) in sea states 3, 5, and upper 6. Other parameters that were varied during the test program were the heading, forward speed, and on/off-cushion. The loads measured during the tests were the sagging/hogging moment, the horizontal bending moment, and the longitudinal twisting moment. The measured loads were compared with respective dimensioning loads based on DNV rules (HSLC) (1996). The results showed that when the vessel is subjected to bow flare slamming impacts, the sagging moment exceeded the DNV dimensioning value by a factor of 1.6, indicating that the HSLC rules do not provide conservative global loads when these extreme events occur. However, the peak loads were well within the design limits.
Application of Contour Line Method to Estimate Extreme Ship Hull Loads Considering Operational Restrictions
Authors: Baarholm Gro Sagli , Moan Torgeir
Published: January 2021

This paper is concerned with estimating the response value corresponding to a return period, say 100 years. In principle, this response needs to be obtained by combining the response in all the sea states. The response for a given sea state, specified by the significant wave height, Hs, and the peak period, Tp, can be obtained in the frequency domain for the linear response. Time domain simulation is required to obtain the nonlinear response, and long time series are required to limit the statistical uncertainty in the simulations. Especially in the latter case, it is crucial to introduce ways to improve the efficiency in the calculation. A method to determine the long-term extremes by considering only a few short-term sea states is outlined. The sea states have a certain probability of occurrence and are identified by a contour line in the (Hs TJ-plane. This will make possible practical estimation of the extreme loads the vessels are exposed to.
A Numerical Study on Sloshing Flows Coupled with Ship Motion—The Anti-Rolling Tank Problem
Authors: Kim Yonghwan
Published: January 2021

A computational study on the sloshing problem coupled with ship motion in waves is introduced. The ship motion excites the sloshing flow in the ship's liquid cargo, and the slosh-induced forces and moments affect the ship motion in return. This study applies a numerical method to solve the coupling problem of the ship motion and sloshing flow. In particular, it concentrates on the anti-rolling tank, which has the most significant coupling effects of two problems. The three-dimensional sloshing flow has been simulated using the finite-difference method, while the ship motion has been obtained using a time-domain panel method. At each time step, the instantaneous displacement, velocity and acceleration of ship motion have been applied to the excitation of liquid motion, and the corresponding slosh-induced forces and moments have been added to the wave-induced excitation. The computational model is a modified S175 hull, and the computational results have been compared with the experimental data of a supply vessel. Although the two hull forms are not identical, the numerical result for the modified S175 hull shows the same trend of the roll RAOs with experimental data when the anti-rolling tanks are considered. Therefore, the numerical method introduced in this study is expected to be very useful in observing the coupling effects of sloshing and ship motion problems.
A B-Spline Higher-Order Panel Method Applied to Two-Dimensional Lifting Problem
Authors: Lee Chang-Sup , Kerwin Justin E.
Published: January 2021

A higher-order panel method based on B-spline representation for both the geometry and the solution is developed for the solution of the flow around two-dimensional lifting bodies. The influence functions due to the normal dipole and the source are separated into the singular and nonsingular parts; then the former is integrated analytically, whereas the latter is integrated using Gaussian quadrature. Through a desingularization process, the accuracy of the present method can be increased without limit to any order by selecting a proper numerical quadrature. A null pressure jump Kutta condition at the trailing edge is found to be effective in stabilizing the solution process and in predicting the correct solution. Numerical experiments indicate that the present method is robust and predicts the pressure distribution around lifting foils with far fewer panels than existing low-order panel methods.
An Experimental Investigation on Bow Water Shipping
Authors: Barcellona Marco , Simos Maurizio , Greco Marilena , Faltinsen O.M.
Published: January 2021

The water on deck caused on a restrained ship model without forward speed in head waves is studied experimentally by using a transient test technique. A single water-shipping event is induced by the wave packet, and the severity of the interaction is controlled by the wave-packet steepness. Three different bow geometries are considered. Two of them are analytical hull forms, and the last is the ESSO-Osaka tanker. The models are equipped with a transparent-material deck to study the flow-field evolution by image analysis. A vertical wall is placed at a certain distance from the forward perpendicular to mimic the presence of deck structures. Velocity of the shipped water along the deck, pressure field on the deck, and horizontal impact force on the wall are measured. The main fluid-dynamic aspects of the green-water phenomenon are highlighted. For the tested cases, water shipping starts always with the free surface exceeding the freeboard, plunging onto the deck, and forming complex cavities entrapping air inside. The geometry of the air cavity depends on the hull form and the wave steepness. Then the water propagates along the deck. In general, the water front is strongly three dimensional because of the water entering along the deck contour. The interaction of the shipped water with the vertical structure consists of impact, run up-run down cycle, and backward plunging of the water onto the deck, still wetted. The evolution of the pressure field follows that of the water front. Pressure peaks are associated with the impact against the vertical wall, and by the backward plunging of the water on the deck, at the end of the run up-run down cycle of the water. It is shown that both these stages can be of importance from the structural point of view. I am sad to report that Maurizio Landrini was killed in a motorcycle accident on June 26, 2003. Maurizio was an outstanding marine hydrodynamist who had been selected as the 2003 Georg Weinblum Lecturer. He was born on March 2, 1963, and earned his Ph.D. degree in Theoretical and Applied Mechanics at the University of Rome. Except for short periods as a visiting researcher at the Ocean Engineering Laboratory, University of California, Santa Barbara, and the Department of Marine Technology, Norwegian University of Science and Technology, he worked his entire career at INSEAN, the Italian Ship Model Basin. He has authored or coauthored over 80 papers. He was a personal friend and innovative researcher with whom I have spent many hours discussing hydrodynamics. He will be greatly missed in the marine hydrodynamics community. Robert F. Beck