bluuebunny/crossref_metadata_2025 huggingface dataset:
Numerical Simulation of Motions of Two-Dimensional Floating Bodies
Authors: Sen D.
Published: January 2021

A potential-flow numerical model is described for time-simulation of motions of two-dimensional floating bodies subjected to an oncoming wave train. The model is fully nonlinear in that no assumptions of smallness either in wave steepness or in body motions are made. The basic algorithm is based on a boundary integral formulation and time-stepping of the nonlinear free-surface constraints in an Eulerian frame of reference. Simple techniques are devised to overcome numerical instability problems that are encountered in the proposed method. The simulation time can be extended over several periods of steady-state oscillations depending on the size of the computational domain. Several illustrative results simulating large heave and roll motions as well as drifting of a rectangular body are presented and discussed. The numerical predictions are also evaluated against model tests which include several nonnegligible nonlinear phenomena, and the agreement is encouraging.
Study of Planing Hydrodynamics Using Strips of Transversely Variable Pressure
Authors: Cheng Xiaoming , Wellicome J. F.
Published: January 2021

A pressure strip method is developed for the prediction of hydrodynamic forces acting on planing hulls moving on the surface of calm water. Within the frame of linearized potential flow theory, the presence of a planing surface is represented by an assemblage of strips of transversely variable pressure placed on the mean free surface. The unknown pressure distribution on each strip is represented by a sine series with unknown coefficients which are determined by solving an integral equation relating the pressure distribution to the free-surface elevation underneath the planing hull. Numerical solutions are obtained for the planing of 3-D flat plate and three basic profiles of 2-D planing surfaces, which are taken as the extreme cases of large-aspect-ratio 3-D planing surfaces. The results are compared with experimental data and good agreement is achieved.
A Localized Finite-Element Method for the Nonlinear Steady Waves Due to a Two-Dimensional Hydrofoil
Authors: Bai Kwang June , Han Jae Hoon
Published: January 2021

An application is described of the localized finite-element method to a steady nonlinear free-surface flow past a submerged two-dimensional hydrofoil at an arbitrary angle of attack. The earlier investigations with the linear free-surface boundary condition have shown some disagreement between the computed results and the experimental measurements for the cases of shallow submergence. The aim of this paper is to investigate the effect of the nonlinear free-surface condition for the cases where the linear results show disagreement with the experimental measurements. The computational method of solution is the localized finite-element method based on the classical Hamilton's principle. In the present study, a notable step is introduced in the matching procedure between the fully nonlinear and the linear subdomains. The numerical results of wave resistance, lift force, and circulation strength are presented. The computed pressure distributions on the hydrofoil and wave profiles are shown and compared with the experimental measurements and also with the linear computational results. The present computed results show better agreement with the experimental results. In some cases, however, a difficulty in the convergence of the iterative solution procedure was experienced. This difficulty in the convergence may be due to the limit of the range of the existence of the true solution in potential-flow formulation.
Viscous Flow Around Marine Propellers Using Boundary-Layer Strip Theory
Authors: Hufford Gary S. , Drela Mark , Kerwin Justin E.
Published: January 2021

This paper presents a method to analyze the viscous flow around marine propellers using boundary layer strip theory. A state-of-the-art two-dimensional boundary-layer formulation is coupled to a state-of-the-art perturbation potential panel method used in marine propeller flow analysis. The coupling procedure is applied along strips of the blade where two-dimensional boundary-layer flow is assumed. For this paper these strips were assumed to be constant radial strips of the blade. The resulting method is applied to a conventional marine propeller and comparisons to experiments are given. Results include the global quantities of thrust, torque, and efficiency and the local strip quantities of displacement thickness and section drag coefficient. The resulting comparisons, showing the applicability of the method to conventional marine propellers, are quite good.
Bifurcation of Static Equilibrium of a Semisubmersible in Waves
Authors: Aranha J. A. P. , Pinto M. O.
Published: January 2021

This paper reviews the phenomenon of the steady tilt of a semisubmersible from the point of view of the theory of bifurcation. The problem is similar to that of the buckling of an elastic structure, with the wave amplitude playing the role of the critical load. Depending on the wavenumber, the bifurcation can be "subtle," as in the case of a Euler beam, or "catastrophic," as in the case of shells and arches. Experimental results on a simplified submerged structure show very good agreement with the theoretical prediction from the viewpoint of second-order wave theory.
Kelvin Wakes and Wave Resistance of Cruiser-and Transom-Stern Ships
Authors: Nakos D. E. , Sclavounos P. D.
Published: January 2021

The steady wave patterns, Kelvin-wake spectra and wave resistance of several realistic ship hulls are computed by a Rankine panel method. Wall-sided as well as transom-stern ships are studied over a broad range of Froude numbers and the importance of enforcing a Kutta-type condition of smooth flow detachment at the transom stern is demonstrated. The lack of numerical damping in the solution scheme permits the reliable prediction of the Kelvin wake far from the ship and allows its use in the evaluation of the free wave spectrum. The wave resistance is evaluated by pressure integration as well as momentum conservation and the merits of the latter method are discussed.
Reduction of Hull Whipping in Slamming by Active Control System
Authors: Hsueh Wen-Jeng , Lee Ya-Jung
Published: January 2021

The reduction of hull girder whipping in slamming by an active control system is investigated. Under the consideration of hull flexibility, a mathematical formulation is developed for the whipping of a hull, subject to slamming, and including an active vibration control system consisting of a tuned mass and hydraulic servo system. Using the optimal theory, the control law of the active system is determined. In addition, a closed-loop estimator is introduced to estimate the distribution of hull motion, which is required to compute the actuator output of the active system. Finally, a numerical example of an application to a 205-ton high-speed craft is described. The results show that the whipping will be reduced significantly. The whipping acceleration and induced stress in particular are reduced more than 95% within 2 sec by this scheme.
Computation of Viscous Flow Around Propeller-Body Configurations: Series 60 CB = 0.6 Ship Model
Authors: Stern F. , Kim H. T. , Zhang D. H. , Toda Y. , Kerwin J. , Jessup S.
Published: January 2021

Validation of a viscous-flow method for predicting propeller-hull interaction is provided through detailed comparisons with recent extensive experimental data for the practical three-dimensional configuration of the Series 60 CB = 0.6 ship model. Modifications are made to the k-e turbulence model for the present geometry and application. Agreement is demonstrated between the calculations and global and some detailed aspects of the data; however, very detailed resolution of the flow is lacking. This supports the previous conclusion for propeller-shaft configurations and axisymmetric bodies that the present procedures can accurately simulate the steady part of the combined propeller-hull flow field, although turbulence modeling and detailed numerical treatments are critical issues. The present application enables a more critical evaluation through further discussion of these and other relevant issues, such as the use of radial-and angular-varying body-force distributions, the relative importance of turbulence modeling and grid density on the resolution of the harmonics of the propeller inflow, and three-dimensional propeller-hull interaction, including the differences for the nominal and effective inflows and for the resulting steady and unsteady propeller performance. Also, comparisons are made with an inviscid-flow method. Lastly, some concluding remarks are made concerning the limitations of the method, requirements and prognosis for improvements, and application to the design of wake-adapted propellers.
Harmonic Analysis of Nonlinear Oscillations of Cubic Dynamical Systems
Authors: Senjanovic I.
Published: January 2021

Cubic dynamical systems are of great interest in marine technology. The state of the art concerning ship rolling and vessel mooring is described. Time-domain simulation is an indirect and unreliable way to determine harmonic response characteristics of nonlinear systems; frequency-domain analysis is therefore preferable. Numerical methods for deterministic and random oscillations are approximate. In order to establish a general sophisticated method, the well-known harmonic balance method is extended to polyharmonic excitation and improved to operate completely in the frequency domain. Special recurrent and simultaneous algorithms are given for the case of monoharmonic and polyharmonic excitation and multi-and single-valued response respectively. Subharmonic oscillations are analyzed using the general method. Random oscillations are treated as a set of periodic responses caused by the same excitation spectrum and different phase angles. Illustrative examples are chosen from marine technology practice. Principal, superharmonic and subharmonic response spectra are analyzed. The importance of further research which would cover other nonlinear effects by harmonic analysis is pointed out.
Tensile Behavior of Local Members on Ship Hull Collapse
Authors: Paik Jeom Kee
Published: January 2021

A number of methods for hull collapse analysis have been developed, taking into account buckling and yielding, but the importance of necking and ductile-fracture behavior has been disregarded. In this paper, a simplified model for steel members is formulated for modeling necking and ductile-fracture behaviour. The model is incorporated into the previous ISUM units which have been developed, considering buckling and yielding. Application to analysis of the progressive collapse behavior for a 1/3-scale frigate test hull in the sagging condition is demonstrated, and tensile behavior of local members on hull collapse is discussed.
Shock-Wave Damage of Ring-Stiffened Cylindrical Shells
Authors: Fatt Michelle S. Hoo
Published: January 2021

A solution methodology for the nonlinear plastic response of the central bay of a ring-stiffened cylindrical shell subject to shock-wave loading is presented. The solution is based on a simple structural model that uses an analogy between a cylindrical shell and a string-on foundation in which ring stiffeners are modeled as lumped masses and springs. By requiring dynamic equilibrium within the central bay of the shell, one may reduce the problem to solving an inhomogeneous wave equation for which the motion of the ring stiffener is introduced into one of the boundary conditions of the string. The initial-boundary-value problem is solved by using a modified Galerkin approximation. The mode shape used to describe the local or bay deformation in the Galerkin approximation is determined from the experimental profile of an actual damaged shell. A Galerkin approximation not only yields a simple solution for the transient deformations of the shell, but it also has an advantage over an exact solution in that it can be easily extended to shells subject to asymmetric pressure loading with arbitrary time variation. The Galerkin solution is shown to approach two extreme cases of dynamic loading for the exponentially decaying pressure load: impulsive loading and static loading. A final deformed profile of the shell is obtained by using the concept of plastic unloading waves. The solution for the transient deflection is a stepping stone to the evaluation of strains and is therefore important in establishing a failure criterion for the shell. The analytical results presented herein may therefore be instrumental in establishing design criteria for prevention of failure of the ring-stiffened shell.
Hydrodynamic Forces on a Submerged Sphere Undergoing Large Amplitude Motion
Authors: Wu G. X.
Published: January 2021

The hydrodynamic problem of a sphere submerged below a free surface and undergoing large amplitude oscillation is investigated based on the velocity potential theory. The body surface boundary condition is satisfied on its instantaneous position while the free-surface boundary condition is linearized. The solution is obtained by writing the potential in terms of the multipole expansion.
Heave Stiffness of an Air Cushion Vehicle Bag-and-Finger Skirt
Authors: Sullivan P. A. , Charest P. A. , Ma T.
Published: January 2021

The heave stiffness of a bag-and-finger flexible skirt air cushion is investigated analytically and experimentally. The investigations use a two-dimensional section of the skirt confined between end-plates and moving in heave. This simplified geometry facilitates analysis involving a minimum of empiricism. Experiments show that the airflows, including leaks between fingers and at the end-plates, can be modeled as orifice-like. The analysis assumes that the fingers can be modeled as rigid massless bodies. Three models of the bag, based on combinations of massless inelastic membranes and rigid links, are investigated. The predictions and experiments are in good agreement and show that modest geometry changes can have large effects on heave stiffness. It is suggested that these simple skirt models can provide useful insights into the dynamics.
On the Determination of Density Profiles in Stratified Seas from Kinematical Patterns of Ship-Induced Internal Waves
Authors: Avital E. , Miloh T.
Published: January 2021

The aim of this paper is to propose a method for determining the dispersion relation of a highly stratified medium from measured geometrical patterns of ship-generated internal waves. This is a first step towards devising a practical method for calculating the density distribution of a stratified fluid from the detectable free-surface kinematic signature of the induced internal wake, by using some optical or remote sensing means. We assume that the body which causes the wake moves with a constant velocity along a circular trajectory. By applying the constant-phase method, we derive an explicit solution for the wake crest lines. Then, for an infinitely large ship's turning radius (straight course), a closed-form expression for the dispersion relation versus wake geometry is obtained. A similar approximate form is also obtained for a circular course. Some numerical simulations are presented, and the applicability of the proposed method is demonstrated for several realistic thermocline distributions, measured in lakes and seas.
A Comparative Study on the Combustion Characteristics of Burning Droplets of Marine Fuel Oils
Authors: Lin Cherng-Yuan , Pan Tze-Chin , Cheng Che-Shiung
Published: January 2021

An experimental study conducted on a single oil droplet suspended on a quartz filament is carried out to investigate the effects of droplet size and heating time on the combustion characteristics of marine fuel oils. Fuel oils A and C, which approximate ASTM Nos. 2 and 6 fuel oils, respectively, are considered in this study primarily due to their frequent applications in marine power plants. The properties of these fuels are widely different; marine diesel fuel oil A is a distillate oil of miscible multi-components while heavy fuel oil C is known as a residual oil containing considerable amounts of immiscible matter. The combustion phenomena are observed by cinematography. The results show that the influences of droplet size and heating time on the combustion characteristics of flame length, flame appearance, soot, ignition delay, and overall burning rate vary for these two fuel oils to a significant extent. The reasons for these variations are discussed.
Fatigue Life and Reliability of Randomly Excited Structures
Authors: Cai G. Q. , Yu J. S. , Lin Y. K.
Published: January 2021

An improved stochastic model is used to investigate the fatigue failure of a structural or machine component under random excitations. The failure is treated as a classic first-passage event in which a dominant crack grows to the critical length. Two specific improvements are made over previous analyses in that the critical crack length is treated properly as an absorbing boundary for the crack growth process, and that the correlation among the successive stress cycles which induce the crack growth is taken into account. Analytical and numerical results are given of the probability density and statistical moments of the fatigue life, and of the reliability function in the case of the Gaussian stress process.
Instability of Cup-Cylinder Compound Shell Under Uniform External Pressure
Authors: Khan Raisuddin , Uddin Wahhaj
Published: January 2021

Instability of compound cup-end cylindrical shells under uniform external pressure is studied. Nonlinear differential equations governing the large axisymmetric deformations of shells of revolution which ensure the unique states of lowest potential energy of the shells under a given pressure are solved. The method of solution is multisegment integration, developed by Kalnins and Lestingi, for predicting the mode of buckling and the critical pressure of these compound shells. Results show that, when simple cylindrical and spherical shells which develop the same membrane stress under pressure are used as a compound cup-end cylindrical shell, buckling takes place in the cylinder portion, near the cup-cylinder junction, at loads a few times higher than the buckling load of conventional dome-cylinder shells.
A Numerical Optimization Technique Applied to the Design of Two-Dimensional Cavitating Hydrofoil Sections
Authors: Mishima Shigenori , Kinnas Spyros A.
Published: January 2021

A numerical nonlinear optimization technique is applied to the systematic design of two-dimensional partially or supercavitating hydrofoil sections. The design objective is to minimize the hydrofoil drag for given lift and cavitation number. The hydrodynamic analysis of the cavitating hydrofoil is performed in nonlinear theory, via a low-order potential-based panel method. The effects of viscosity are taken into account via a uniform friction coefficient applied on the wetted foil surface. The total drag, lift, cavitation number, and other quantities involved in the imposed constraints, are expressed in terms of quadratic functions of the main parameters of the hydrofoil geometry, angle of attack, and the cavity length. The optimization is based on the method of multipliers by coupling the Lagrange multiplier terms and the penalty function terms. The robustness and convergence of the method are extensively investigated, and the results are compared with those from applying other design methods.
Hydrodynamics of a Body Moving Over a Mud Layer-Part II: Added-Mass and Damping Coefficients
Authors: Zilman G. , Kagan L. , Miloh T.
Published: January 2021

A ship cross section undergoes periodic oscillations in a finite water layer, overlaying a mud layer. The upper fluid is considered to be inviscid, and the mud is modeled as a Newtonian liquid. The section contour is replaced by a distribution of wave sources with unknown strength, satisfying a corresponding boundary integral equation. Its kernel is expressed through a newly derived Green function. The numerical solution of the integral equation allows evaluation of the added-mass and damping coefficients. Specific computations pertaining to Lewis forms show a drastic dependence of the added-mass and damping coefficients on the mud thickness and density.
Optimization of Bow Plating for Icebreakers
Authors: Brown Peter W. , Jordaan Ian J. , Nessim Maher A. , Haddara Mahmoud M. R.
Published: January 2021

The objective of the work reported here is to ensure that ice-capable ships are both safe and economical. It is largely based on research conducted over the past two decades. The present methodology allows the designer to calculate a bow plating thickness which will resist local ice loads and be cost-effective. Full-scale data for the MV Canmar Kigoriak and USCGC Polar Sea were ranked, curves were fitted through the tail of each data set, and a Type I extreme probability distribution was derived for each data set. The Canmar Kigoriak data were then subdivided based on contact area and a simulation was performed to derive the load distributions on subregions of the instrumented panel, termed subpanels. On the basis of this analysis, a local ice load model was validated and is used in the subsequent analysis. To evaluate the strength of the bow plating, three limit stages (three-hinge collapse, permanent set, and membrane collapse) are considered. Statistical distributions for each of the input parameters are established. The probability of failure is calculated for each limit state corresponding to a range of plate thicknesses, frame spacings, and annual numbers of impacts, using First Order Reliability Method software. Plate thickness is optimized for minimum cost. Minimum safety levels for permanent set and membrane collapse are also specified. The objective function considers costs due to construction, aesthetics, repair, and replacement. An empirical expression for the expected annual cost of damage is developed. Optimum plating thicknesses are specified. Costs associated with lost use of the vessel or increased steel weight can also be specified.
An Empirical Formula to Estimate the Resistance of a Convoy in a Restricted Waterway
Authors: Marchal J.L.J. , Shen Y.-D. , Kicheva D.
Published: January 2021

An examination of the literature produced very few references related to the subject of estimating the resistance of a convoy navigating in a waterway of limited cross section. This paper reports the findings of one such study—a joint research project undertaken by Belgium's University of Liege and the Bulgarian Ship Hydrodynamics Centre. A polynomial is presented here for evaluating the total resistance of a convoy moving in a restricted waterway. The resistance was found to depend on Froude number and on the relative dimensions (length, width and depth) between the convoy and the channel. The results obtained by the suggested polynomial are compared with those obtained by the other three existing empirical methods.
Technical Note: Evaluation of Surface-Ship Resistance and Propulsion Model-Scale Database for CFD Validation
Authors: Longo J. , Stern F.
Published: January 2021

An evaluation is performed of the surface-ship model-scale database for computational fluid dynamics validation with regard to current status and future requirements. The specific emphasis is on data of relevance to resistance and propulsion and validation of Reynolds-averaged Navier-Stokes computer codes. The data were evaluated relative to criteria and requirements developed for geometry and flow, physics, and computational fluid dynamics validation as well as past uses. Conclusions are made with regard to the available data and past uses, and recommendations are offered for future uses of the available data and future data procurement.
Wave-Drift Damping of a 200 kdwt Tanker
Authors: Prins Henk J. , Hermans Aad J.
Published: January 2021

Drift forces and wave-drift damping are calculated for a 200 kdwt commercial supertanker. The timedependent equations are solved by a numerical algorithm developed by Prins & Hermans (1994a). Agreement of the drift forces with towing-test measurements is reasonably good; agreement of the wave-drift damping with extinction tests is very good. The agreement with the wave-drift damping resulting from towing-test measurements is less convincing. This is due to errors in the measurements caused by the fact that towing tests involve small differences between large quantities.
Linear and Nonlinear Hydroelastic Analysis of High-Speed Vessels
Authors: Wu MingKang , Moan Torgeir
Published: January 2021

A linear formulation of ship hydroelasticity is presented. Appropriate body boundary conditions of flexible modes are obtained and the hydroelastic version of high-speed strip theory is established. A nonlinear time-domain simulation method is also presented. The total response is decomposed into linear and nonlinear parts. The linear part is evaluated using appropriate linear potential-flow theory and the nonlinear part comes from the convolution of the impulse response functions of linear ship-fluid system and the nonlinear hydrodynamic forces. Four high-speed vessels with different ship lengths but with similar body plan and internal structural arrangement are used as examples. The calculations of midship bending moments are carried out at different forward speeds and head sea states. The results show that the hydroelastic effect in linear extreme responses is insignificant and that the hydrodynamic damping plays a leading role in the flexible modes when the dynamic amplification of ship hull becomes important. The results also indicate that strong nonlinearity is the most prominent feature of high-speed vessels even in the moderate sea state and must be taken into account. The nonlinear influences are more remarkable in ships at large Froude numbers than in those at small ones, and more important in sagging moment than in hogging moment.
A Flat Cylinder Theory for Vessel Impact and Steady Planing Resistance
Authors: Vorus William S.
Published: January 2021

This work has been motivated by the need for an alternative hydrodynamic theory to apply in analysis of impact loads on typical sections of vessels operating in waves, as well as for the closely analogous hydrodynamics of steady planing in calm water. A theory is needed which is computationally practical, but also physically sound, and incorporating the needed level of sensitivity to detail in the driving physical variables. A new theory believed to achieve this objective is proposed herewith. It can be viewed as a rational compromise between direct numerical inversion of the relatively exact governing equations, which is not presently possible to the needed level of generality, and the simple asymptotic theories evolved from the original work of Herbert Wagner (1932). The single solution field of the exact formulation is retained in the proposed theory; this is versus separate near and far fields of the asymptotic methods. The major reduction of the exact equations exercised here is the specification of uniform first-order geometric linearity; this is also an implicit characteristic of the Wagner class of asymptotic theories. All boundary conditions are satisfied on the horizontal axis in the limit of flatness. But the proposed theory retains the hydrodynamic nonlinearity of the exact formulation; the transverse flow perturbation is retained in the axis boundary conditions to consistent order. As contour flatness is approached and geometric linearity is more and more closely achieved, the transverse contour velocity becomes increasingly larger. The achievement of uniform geometric linearity in the flatness limit is therefore accompanied by uniform hydrodynamic nonlinearity. This is not recognized in the asymptotic theories, where the far field is linear both geometrically and hydrodynamically. The reduction of the exact formulation to an axis satisfaction of the boundary conditions allows much of the geometric inversion imbedded within the initial value problem to be performed analytically. Thus the outer numerical time integration of the system is in terms of stable algebraic formula, resulting in algorithms that are reliably computable on standard computing equipment. Discretization of the general theory for numerical analysis is proposed. The analysis procedure developed is applied to a number of cases of generalized flat cylinder impact. This is in the interest of demonstrating both its utility and its value in providing new insight into the very complex character of impact hydrodynamics.
Steady Waves and Forces About a Yawing Flat Plate
Authors: Landrini M. , Campana E. F.
Published: January 2021

An analysis of the flow about a free-surface-piercing yawed plate in steady drift, or in steady turning motion, is presented. The problem is studied by means of an inviscid rotational flow model, based on an integral representation for the velocity field in terms of source and surface vorticity distributions. The related integral equations are numerically solved by coupling a source panel technique together with the vortex lattice method for treating the surface vorticity integrals. The free surface conditions are linearized with respect to the double model lifting flow, and the vortex shedding has been modeled in a simple but effective manner. A special effort has been put in the validation of the present approach by comparing the obtained results with several experimental data and previous numerical computations. The keel vortex shedding, as was expected by virtue of the low draft-to-length ratio typically encountered in naval architecture, has been found crucial for the prediction of the hydrodynamic forces on a maneuvering ship.
On the Second-Order Wave Radiation of an Oscillating Vertical Circular Cylinder in Finite-Depth Water
Authors: Gören Ömer
Published: January 2021

A vertical circular cylinder which is in periodic oscillatory motion with small amplitudes in finite depth is considered. The usual assumptions necessary for the potential flow stand valid in the present study. A classical perturbation procedure is employed to solve the nonlinear problem through the second-order. According to the solution method presented, the fluid domain is separated into interior and exterior regions in which boundary-value problems (BVP) are decomposed into two BVPs each having one nonhomogeneous boundary condition. A nonhomogeneous second-order free-surface condition is treated by means of a modified form of Weber's integral theorem. Eigenfunction expansions are used for homogeneous solutions. Thus, to conclude the solution, the exterior and interior solutions are then matched on the common boundary. Numerical results are given for a heaving vertical circular cylinder. Wave field analysis around a vertical cylinder shows that the second-order wave pattern is typically dominated by the second-order wave number related to the second-order dispersion relation. The procedure also satisfies the conditions at infinity through the second-order.
Reliability of Maintained Ship Hulls Subjected to Corrosion
Authors: Soares C. Guedes , Garbatov Y.
Published: January 2021

A time-variant formulation is presented to model the degrading effect that corrosion has on the reliability of ship hulls. The effect of corrosion is represented as a time dependent decrease of plate thickness that affects the midship section modulus. One repair policy was considered and the example results showed the effect of plate replacement when its thickness reached 75% of the original thickness. The example results also illustrated how the limit value of the thickness in the repair criteria influences the reliability and the decision about repair actions. This is also shown for the effect of different corrosion rates and allowable stresses.
Numerical Analysis of Structure of Free-Surface Shock Wave About a Wedge Model
Authors: Miyata Hideaki , Kanai Akihiro
Published: January 2021

Detailed characteristics of the free-surface shock wave (FSSW) are numerically studied for the case of waves generated about a wedge model. The MAC-type finite-difference solution method called TUMMAC-VIII is employed. The density function method is used for implementation of the nonlinear free-surface condition in the framework of a rectangular coordinate system. The computed results show that the wave front angle varies systematically and that the shock condition is fulfilled in the thin layer near the free surface, which is one of the most typical characteristics of the FSSW. Some important mechanisms of wave breaking accompanied by the FSSW, such as overturning of wave front, vortex generation and energy dissipation, are also approximately simulated.
Nonlinear Reaction Forces on Oscillating Bodies by a Time-Domain Panel Method
Authors: Berkvens P. J. F. , Zandbergen P. J
Published: January 2021

An outline of a time-domain boundary integral equation method (with second-order accuracy) for bodies floating on a fluid is given. It includes the full nonlinear dynamics of a potential flow with a free surface. To validate the method, a partially immersed body is forced to oscillate at a small amplitude for each of three modes. Relevant components of the reaction force on the body are integrated separately, thereby enhancing the accuracy of the hydrodynamic coefficients determined from this force signal. Linear frequency-domain results in a range of frequencies agree well with the present ones for the square, excellently for the circle. Nonlinear fluid-body interaction is simulated for a vertically oscillating square with amplitudes up to 80% of its draft. The force dependence on the motion amplitude provides a confirmation of second-order theory. Furthermore, the triple-frequency force component shows a pronounced cubic dependence on the amplitude.
Generalized Harmonic Analysis of Nonlinear Ship Roll Dynamics
Authors: Peyton Jones J. C. , Cankaya I.
Published: January 2021

Algebraic expressions are presented which enable the harmonic balance equations to be written down directly in terms of the coefficients of a general nonlinear ship roll equation, without restriction on the number of harmonics considered. The rolling response is then readily computed, as illustrated by an investigation of the resonant modes of ships with angle-dependent cubic damping, or quintic terms in the righting moment. Details are also given of the validation process, showing how simulation time can be reduced by an appropriate choice of initial conditions.
Dynamic Instability in Quartering Seas—Part II: Analysis of Ship Roll and Capsize for Broaching
Authors: Spyrou K. J.
Published: January 2021

In earlier studies we have analyzed the phenomena which can generate loss of ship controllability in astern seas. In this paper we examine how the yaw instability associated with broaching can lead to roll instability and ship capsize. The dynamic effects responsible for capsize during the forced turn of broaching do not have their origin in the customary roll equation but are the result of interactions with other motions of the ship. Stability studies based solely on the roll equation are thus clearly inappropriate for this case where a multidimensional approach is deemed necessary. After presenting the theoretical background we set out a multi-degree method of global analysis which is based on transient maps. We apply this method to clarify how capsize occurs during the escape from surf-riding and also during transients from arbitrary initial condition of the ship. Our study establishes the connection between speed, heading, automatic control parameters and capsize. The proposed method can be useful in the context of a design methodology for minimizing the risk of ship capsize in astern seas.
Three-Dimensional Transient Behavior of Towed Marine Cables
Authors: Vaz M. A. , Patel M. H. , Witz J. A.
Published: January 2021

A numerical solution is presented for the three-dimensional transient motion of a marine cable towed by a vessel that can arbitrarily change speed and direction on the horizontal plane of the water surface. The solution is obtained by dividing the towed cable into η straight rigid elements. The translational and rotational motion of each element is described by its elevation and azimuth angles. The equations of force and moment equilibrium and the geometric compatibility relationships for each element are used to form a system of 2n ordinary differential equations which are solved numerically using the Runge-Kutta method. In order to illustrate the solution, a range of results are presented for cable tension and towed cable motions as the towing vessel carries out turning maneuvers.
Reliability and Uncertainty Evaluation for Longitudinal Bending of Hull Girders of Surface Ships
Authors: Chao Ru-Jen , Ayyub Bilal M.
Published: January 2021

Structural reliability and uncertainty assessment of hull-girder bending of surface ships requires the consideration of the following three aspects:structural strength,loads, andmethods of reliability analysis.

A methodology was developed to assess the reliability of hull girders subjected to extreme bending moments. The methodology is based on ultimate strength assessment of hull-girder bending using an incremental strain compatibility method. Two reliability assessment methods—(1) advanced second moment (ASM) method, and (2) Monte Carlo simulation (MCS) method with variance reduction techniques—were employed for structural reliability assessment of hull-girder bending of surface ships. This study demonstrates the structural reliability evaluation of hull-girder bending of ships (1) by considering its strength parameters as random variables, and (2) by considering a non-closed performance function using both reliability methods. This technique can also be applied to a closed-form expression of the performance function. Utilizing such a methodology, ultimate strength and loads for hull-girder bending can be developed individually as modules, and then combined into a non-closed form in a performance function. Simulation methods are also used to assess the uncertainty in hull girder strength due to uncertainties in basic random variables. Examples using the ASM and MCS methods for reliability assessment are also presented.
Dynamic Elastic/Viscoplastic Response of Hull Plating Subjected to Hydrodynamic Wave Impact
Authors: Caridis P. A. , Stefanou M.
Published: January 2021

A numerical simulation of the response of a flat plate subjected to hydrodynamic wave impact is presented. The formulation is based on a time domain solution of the large deflection plate equations using a finite difference mesh. The material behavior is elastic/viscoplastic, following the classical Perzyna model, and the procedure is validated against a series of model collision experiments. The correlation results were found to be good and the procedure was subsequently used to predict the response of plating subjected to wave impact loads, characterized by a steep rise to a maximum pressure followed by an exponential decay. A comparison with an analytical model was conducted and following this a parametric study of the characteristics of the pressure pulse was carried out. The paper concludes with a study of the effect of multiple wave impacts. It was found that, even though individual impacts may not cause rupture, a small number of these may lead to rupture of the plating, provided the maximum pressure is large enough.
Experiment and Viscous Flow Analysis on a Partially Cavitating Hydrofoil
Authors: Brewer Wesley H. , Kinnas Spyros A.
Published: January 2021

A partially cavitating hydrofoil experiment is performed at the MIT Variable Pressure Water Tunnel. Velocities are measured along a rectangular control surface surrounding the hydrofoil, in the boundary layer region, as well as in the proximity of the cavity surface. The cavity detachment and reattachment points are measured for several values of the cavitation number. The forces are evaluated from the measured velocities via momentum flux integrations. The measurements are compared with the numerical results from a nonlinear, inviscid cavity flow analysis method, coupled with a boundary layer solver.
Impulsive Motion of a Wide Torus Submerged Below a Free Surface
Authors: Tyvand Peder A.
Published: January 2021

The impulsively starting motion of a torus submerged horizontally below a free surface is studied analytically, using a small-time expansion. The torus is assumed wide, i.e., the torus radius is much larger than its initial submergence depth. A quasi-two-dimensional theory is applied. Its accuracy is checked by comparing the first-order surface elevation with slender-body theory. The hydrodynamic force and torque are investigated in the first three orders of the small-time expansion. The ratio between the cross-section radius and submergence depth is arbitrary (between 0 and 1). The general motion of the torus consists of all six degrees of freedom. Special emphasis is put on the five different leading-order nonlinear interactions that may occur between these modes: surge/heave, surge/roll, sway/roll, heave/roll, and roll/yaw. These leading-order nonlinear interactions give rise to zeroth-order forces and torques. The leading-order gravitational effects are investigated.
Resistance Optimization of Displacement Vessels on the Basis of Principal Parameters
Authors: Day Alexander H.
Published: January 2021

The genetic algorithm (GA) has been used to optimize hullforms with respect to their total resistance. The hulls are represented in a parametric manner using a small number of variables, such as length, beam, and draft—as well as other geometric characteristics, including the length of parallel keel and draft at the bow and stern. Constraints may be applied both to these variables and to other parameters. Results are shown for both monohulls and catamarans, in cases for which the constraints are largely inactive, for a large range of displaced volumes and forward speeds. These illustrate the hulls generated in the extreme case in which resistance is the only factor of interest. An important characteristic of the results is the fact that the variations of the optimal principal dimensions are generally not continuous with respect to the speed, although the resistance itself is usually continuous. That is, it is possible that a small change in speed may demand an entirely different optimal hullform.
Time-Domain Hydroelasticity Theory of Ships Responding to Waves
Authors: Xia Jinzhu , Wang Zhaohui
Published: January 2021

A time-domain linear theory of fluid-structure interaction between floating structures and the incident waves is presented. The structure is assumed to be elastic and represented by general separation of variables, whereas the fluid is described as an initial boundary value problem of potential free surface flow. The general interface boundary condition is used in the mathematical formulation of the fluid motion around the flexible structure. The general time-domain theory is simplified to a slender-body theory for the analysis of wave-induced global responses of monohull ships. The structure is represented by a nonuniform beam, while the generalized hydrodynamic coefficients can be obtained from two-dimensional potential flow theory. The linear slender body theory is generalized to treat the nonlinear loading effects of rigid motion and structural response of ships traveling in rough seas. The nonlinear hydrostatic restoring force and hydrodynamic momentum action are considered. A numerical solution is presented for the slender body theory. Numerical examples are given for two ship cases with different geometry features, a warship hull and the S175 containership with two different bow flare forms. The predicted results include linear and nonlinear rigid motions and structural responses of ships advancing in regular and irregular waves. The results clearly demonstrate the importance and the magnitude of nonlinear effects in ship motions and internal forces. Numerical calculations are compared with experimental results of rigid and elastic material ship model tests. Good agreement is obtained.
Influence of Reciprocating Motion on Heat Transfer Inside a Ribbed Duct with Application to Piston Cooling in Marine Diesel Engines
Authors: Chang S. W. , Su L. M.
Published: January 2021

This paper presents the results of an experimental study aimed at investigating the effect of reciprocating motion on the heat transfer for the flow inside a square ribbed enclosure. This flow configuration was a modification of the modern cooling system within a reciprocating piston of a marine heavy diesel engine. Initially, the heat transfer characteristics for the ribbed duct flow were examined and validated by comparing the present data with the relevant publications. Significant heat transfer enhancements detected from the nonreciprocating forced convection tests suggested the potential for heat transfer improvement using ribbed coolant channel. For the shaking effect on the cooling performance of the ribbed enclosure, a heat transfer impediment near which the thermal boundary layers were initiated was found when the reciprocating force was relatively low. Further increase of the reciprocating force or the level of heating power enhanced heat transfer. At the highest reciprocating speed tested, the heat transfer could be increased to a level about 145% of the equivalent stationary case. This study clarified that the circular ribs could be added inside the cooling passages in order to improve the cooling performance of the piston.
Interaction Between Two Closely Spaced Azimuthing Thrusters
Authors: Brandner Paul , Renilson Martin
Published: January 2021

To assist in predicting the performance of omni-directional propelled vehicles a series of experiments has been conducted to measure the interaction between two closely spaced ductedazimuthing thrusters. The thrusters were tested below a shallow draft ground board in a towing tank at a spacing of approximately 2 propeller diameters. Measurements were made of forces acting on a single thruster for a range of operating conditions and similarly on two thrusters for a range of relative positions. The results show that forces from the trailing thruster are heavily affected by interaction, particularly due to impingement of the race from the leading thruster, where as forces from the leading thruster remain essentially unaffected despite its proximity to the trailing thruster. A semi-empirical mathematical model suitable for simulation of omni-directional vehicle dynamics is presented. The model is based on the trajectory of the race from the leading thruster derived from momentum considerations with additional empirical relations to account for other more minor flow effects. Comparison of the predicted and measured results show satisfactory agreement.
Nonlinear Ship Motions
Authors: Huang Yifeng , Sclavounos Paul D.
Published: January 2021

A nonlinear numerical method has been developed to compute motion responses for a ship traveling in steep ambient waves. The method is based on an approximate theory and is an extension to a well-established linear time-domain numerical method. The nonlinear solution is found to be greatly improved over the classical linear and quasi-nonlinear solutions, in comparison to experimental measurements for conventional commercial ships. Through this study, it is also demonstrated that the free surface hydrodynamic nonlinearities are at least as important as, if not more than, the hydrostatic and Froude-Krylov nonlinearities. Stability, consistency and convergence for the nonlinear method are also addressed.