bluuebunny/crossref_metadata_2025 huggingface dataset:
A Simple Method for Predicting the Grounding Strength of Ships
Authors: Wang Ge , Ohtsubo Hideomi , Liu Donald
Published: January 2021

Although the destructive effects of grounding accidents are understood, very few tools are available that can be used by designers to evaluate a ship's strength in grounding accidents. This paper proposes a simple method to predict the strength of a ship's bottom during the process of grounding. A ship's hull is characterized by structural members that are periodically arranged along the ship length. As a result, the internal resistance force developed during grounding is in a sense periodic in the longitudinal direction. For the main structural members of the ship bottom, the following four primary failure modes are considered in this paper: the stretching failure of transverse structures, denting, tearing and concertina tearing failure of bottom plates. The calculation formulas for these identified failure modes are assembled to construct the prediction method for bottom strength. The proposed method is verified by checking the predictions against a series of large-scale grounding experiments and an actual grounding accident. The attractiveness of the method developed is that it makes possible the prediction of the strength of a ship hull in the event of grounding using hand calculation.
Wave-Current Interaction with a Large Three-Dimensional Body by THOBEM
Authors: Kim D. J. , Kim M. H.
Published: January 2021

The effects of uniform steady currents (or small forward velocity) on the interaction of a large three-dimensional body with waves are investigated by a time-domain higher-order boundary element method (THOBEM). The current speed is assumed to be small so that the viscous effects and the steady wave system generated by currents are insignificant. Using regular perturbation with two small parameters є and δ associated with wave slope and current velocity, respectively, the boundary value problem is decomposed into the zeroth-order steady double-body-flow problem at 0(δ) with a rigid-wall free-surface condition and the first-order unsteady wave problem with the modified free-surface and body-boundary conditions expanded up to O(eδ). Higher-order boundary integral equation methods are then used to solve the respective problems with the Rankine sources distributed over the entire boundary. The free surface is integrated at each time step by Adams-Bashforth-Moulton method. The Sommerfeld/Orlanski radiation condition is numerically implemented to absorb all the wave energy at the open boundary. To solve the so-called corner problem, discontinuous elements are used at the intersection of free-surface and radiation boundaries Using the developed numerical method, wave forces, wave field and run-up, mean drift forces and wave drift damping are calculated.
Numerical Water Tunnel in Two and Three Dimensions
Authors: Choi Jin Keun , Kinnas Spyros A.
Published: January 2021

The flow of a propeller inside of a tunnel is addressed. A numerical method is developed in which the flow inside the tunnel is treated via a potential based panel method. First, the method is applied to the two-dimensional flow of a hydrofoil inside of a tunnel. The total and the perturbation potential formulations are developed, and solved via a direct and an iterative method. The results from both formulations and solution schemes are found to converge very fast with the number of panels and truncated tunnel length. Then, the perturbation potential formulation is applied to the analysis of the flow of a propeller inside a tunnel. The propeller problem and the tunnel problem are solved separately, with the effects of one on the other being accounted for in an iterative manner. The equivalent unbounded flow velocity is calculated and compared with that predicted by Glauert.
The Forward Speed Diffraction Problem
Authors: Korsmeyer F. T. , Bingham H. B.
Published: January 2021

This paper examines the theory and computational methods behind predicting the linear unsteady motion of a ship with steady forward speed in waves. The focus is on the wave exciting force impulse-response function as computed via the transient free-surface Green function. The linear equation of motion for a ship in waves was first written in a rational form, using the concept of the impulse-response function, by Cummins (1962). Some years later King et al (1988) added the corresponding wave exciting force in its appropriate convolution form. We extend this work by clarifying the definition of the impulsive incident wave in following seas, and show it to be easily computable. Continuing truncated calculations towards infinite time becomes especially important in following waves, and the method suggested by Bingham et al (1994) is employed here. A novel filtering scheme is also introduced to prevent short wave contamination of the solution. These developments allow calculations in following waves to be presented for the first time using this approach. The integral equation formulation of the linear seakeeping problem is reviewed in some detail, and the relevant equations derived. Transient Haskind relations for bodies with forward speed are also derived although, like their frequency-domain counterparts, these are only approximate. Computed, first-order exciting forces and response-amplitude operators for real ship geometries, in head and following seas, are presented that demonstrate the usefulness of the transient approach for the diffraction problem.
Asymmetric Vessel Impact and Planing Hydrodynamics
Authors: Xu Lixin , Troesch Armin W. , Vorus William S.
Published: January 2021

The paper proposes a two-dimensional theory for asymmetric impact problems of vessels with arbitrary geometry. The interaction of two body sides is incorporated into the hydrodynamic impact model. Following Vorus's (1996) flat-cylinder theory, two types of flow models are established for cases of small and large asymmetry. The distinguishing difference between the two types is whether the flow is attached or separates at the keel on the first instances of impact. General solutions for such nonlinear boundary value problems are determined by solving the singular integral equations, while free-vortex shedding (jet-spraying) is carried out through a time-marching procedure. Initial conditions are derived from basic solutions of flat-sided contours with constant impact velocity. The method of discrete vortices is then applied to the prediction of slamming loads (including both lifting force and restoring moment) on typical two-dimensional sections of vessels with flat or nearly flat bottoms. Calculated results of both flow types, i.e., small and large asymmetry, are presented for various hull contours with constant or variable impact velocity. This approach also provides the foundation for future work involving traverse dynamic stability analysis of high speed planing hulls
Joint Distribution of Successive Wave Periods Revisited
Authors: Myrhaug Dag , Rue Håvard
Published: January 2021

A joint distribution of successive wave periods is presented. First, the analysis includes comparisons between observed wave data and an empirical as well as theoretical distributions of wave period. Secondly, a joint distribution of successive wave periods based on a best fit of a Weibull distribution to the wave period distribution is developed. Comparisons are made with observed wave data as well as with the previous approach of Myrhaug & Rue (1993). It appears that the revised approach is in better agreement with the data.
Cavitating Propeller Experiment (CAPREX III): Measurement and Prediction of Tunnel Pressures
Authors: Kinnas Spyros A. , Kimball Richard W. , Choi Jin-Keun
Published: January 2021

This paper first describes Phase III of the CAvitating PRopeller Experiment (CAPREX) performed at MIT's variable pressure water tunnel. The three components of the screen-generated nominal wake inflow were measured using an LDV system. The unsteady pressure field on the upper tunnel wall for the first three blade harmonics was also measured in a 5 × 5 grid above the propeller tip, for various propeller cavitation conditions from fully wetted to supercavitating. Then, a recently developed numerical method which models the flow of a cavitating propeller inside a tunnel is used for the calculation of the pressures on the tunnel walls. The effects of a time-varying blade cavity source and of the flexibility of the tunnel walls are included in the calculation. Lastly, the amplitudes of the first blade harmonics of the predicted pressures are compared directly with those measured in the experiment.
A B-Spline Based BEM for Unsteady Free-Surface Flows
Authors: Landrini M. , Grytøyr G. , Faltinsen O. M.
Published: January 2021

Fully nonlinear free-surface flows are numerically studied in the framework of the potential theory. The problem is formulated in terms of boundary integral equations which are solved by means of an arbitrary high-order boundary element method based on B-Spline representation of both the geometry and the fluid dynamic variables along the domain boundary. The solution is stepped forward in time either by following Lagrangian points attached to the free surface or by a less conventional scheme in which evolution equations for the B-Spline coefficients are integrated in time. Numerical examples for inner and outer free-surface flows are shown. The accuracy of the numerical solution is assessed either by checking mass and energy conservation or by comparing with reference solutions. Good results are generally obtained. Extended use of the developed algorithm to more applied problems in the context of naval hydrodynamics is now under development.
Cavitating Propeller Analysis Including the Effects of Wake Alignment
Authors: Kinnas Spyros A. , Pyo Sangwoo
Published: January 2021

Various wake alignment techniques which have been developed in the past for the analysis of non-cavitating propellers in uniform inflows are reviewed and some of them are extended in the case of cavitating flows subject to inclined inflows. The effect of the inclined trailing wake geometry on the predicted cavities and blade forces is found to be significant. Predicted open flow characteristics and unsteady forces acting on the blades of an inclined shaft propeller are compared with those predicted by other methods, as well as with those measured in experiments.
Linear Hydroelastic Analysis of High-Speed Catamarans and Monohulls
Authors: Hermundstad Ole Andreas , Aarsnes Jan Vidar , Moan Torgeir
Published: January 2021

A linear method for hydroelastic analysis of high-speed vessels is presented. It is based on a modal approach and represents a generalization of the high-speed strip theory of Faltinsen & Zhao (1991a). Hydrodynamic interaction between the hulls of catamarans is properly accounted for by utilizing symmetry. It is demonstrated how an integral theorem can be utilized to find the hydrodynamic force for general mode shapes. Theoretical predictions of ship motions and sectional forces and moments are compared with experimental data for a flexible high-speed catamaran model in regular waves. The influences of hull interaction and the application of the integral theorem are demonstrated.
Heat Transfer of Impinging Jet and Ribbed-Duct Flows with System Reciprocation
Authors: Chang S. W. , Su L. M. , Yang T. L.
Published: January 2021

This paper describes an experimental investigation of heat transfer for impinging jet and ribbed duct flows under system reciprocation which focuses on the variable reciprocating effects on these two flow systems for piston cooling application. The experimental data reconfirmed the unsteadiness of reciprocating flow which led to the local temporal heat transfer variations when both test sections reciprocated. For impinging jet flow, reciprocation did not modify the fundamental physics that facilitated heat transfer, but the local instantaneous heat transfer could be improved or impeded by reciprocation, depending on the Reynolds number and reciprocating frequency. For reciprocating ribbed duct flow, the fundamental heat transfer was considerably modified from the nonreciprocating situation so that the distribution of heat transfer along the ribbed surface evolved toward a wavy-like pattern from the nonreciprocating zigzag pattern when the reciprocating frequency or Reynolds number increased. Comparing these two reciprocating systems at high mass flow rate and high reciprocating frequency showed a higher spatial-time averaged heat transfer level for ribbed duct flow while the reciprocating impinging jet flow provided better cooling performance when the Reynolds number or reciprocating frequency was relatively low Therefore, the ribbed duct and impinging jet flows might be suitable for piston cooling of high-and low-speed engines respectively.
Reliability of Corrosion Protected and Maintained Ship Hulls Subjected to Corrosion and Fatigue
Authors: Guedes Soares C. , Garbatov Y.
Published: January 2021

A formulation is presented for the assessment of the reliability of a ship hull with respect to failure of the longitudinal members as a result of fatigue and corrosion. The model allows for the existence of multiple cracks and it accounts for the crack growth process. The midship section modulus is described by a stochastic process A new model is presented for the effect of corrosion, which is a time-dependent process with two stages. In the first one, there is no corrosion due to the existence of coating protection. Upon failure of the protection system, general corrosion decreases plate thickness and affects the midship section modulus. The inspection is modeled as a random process. One repair policy is considered in the example, which consists of plate replacement when its thickness reaches 75% of the original thickness. The time-dependent degrading effect of corrosion and crack growth are modeled as a random process also. The reliability is predicted by a time variant formulation and the effects of maintenance actions in increasing the reliability are shown. The sensitivity of the reliability estimates with respect to several parameters is also studied. The formulation has been applied to a tanker.
Transient Free-Surface Hydrodynamics Using Rational Approximation of the Green’s Function
Authors: Damaren Christopher J.
Published: January 2021

Rational approximations in the frequency domain are developed for the source function of linear free-surface hydrodynamics using the recently uncovered fourth-order ordinary differential equation (ODE) satisfied by the time-domain source function. The radiation problem for a floating body in deep water is formulated using a source plus wave-free potential expansion for the fluid. The inherent rational dependence on frequency of the wave-free potentials as well as the source approximation are used to develop a system of constant-coefficient ODE's for the radiation impedance which can be used to develop the motion of the body in a simple manner. The technique is applied to the heaving motion of a floating sphere with good results. The application to more general body geometries is explored by formulating the frequency-domain problem using the variational principle of Chen and Mei and exploiting its polynomial dependence on frequency.
Water Entry of a Wedge by Hydroelastic Orthotropic Plate Theory
Authors: Faltinsen Odd M.
Published: January 2021

Water entry of a hull with wedge-shaped cross sections is analyzed. The stiffened platings between two transverse girders on each side of the keel are separately modeled. Orthotropic plate theory is used. The effect of structural vibrations on the fluid flow is incorporated by solving the two-dimensional Laplace equation in the cross-sectional fluid domain by a generalized Wagner's theory. The coupling with the plate theory provides three-dimensional flow effects. The theory is validated by comparison with full-scale experiments and drop tests. The importance of global ship accelerations is pointed out. Hydrodynamic and structural error sources are discussed. Systematic studies on the importance of hydroelasticity as a function of deadrise angle and impact velocity are presented. This can be related to the ratio between the wetting time of the structure and the greatest wet natural period of the stiffened plating. This ratio is proportional to the deadrise angle and inversely proportional to the impact velocity. A small ratio-means that hydroelasticity is important and a large ratio means that hydroelasticity is not important.
Computational Fluid Dynamics of Four-Quadrant Marine-Propulsor Flow
Authors: Chen Bin , Stern Frederick
Published: January 2021

Computational fluid dynamics results are presented of four-quadrant flow for marine-propulsor P4381. The solution method is unsteady three-dimensional incompressible Reynolds-averaged Navier-Stokes equations in generalized coordinates with the Baldwin-Lomax turbulence model. The method was used previously for the design condition for marine-propulsor P4119, including detailed verification and validation. Only limited verification is performed for P4381. The validation is limited by the availability of four-quadrant performance data and ring vortex visualizations for the crashback conditions. The predicted performance shows close agreement with the data for the forward and backing conditions, whereas for the crashahead and crashback conditions the agreement is only qualitative and requires an ad hoc cavitation correction. Also, the predicted ring vortices for the crashback conditions are in qualitative agreement with the data. Extensive calculations enable detailed description of flow characteristics over a broad range of propulsor four-quadrant operations, including surface pressure and streamlines, velocity distributions, boundary layer and wake, separation, and tip and ring vortices. The overall results suggest promise for Reynolds-averaged Navier-Stokes methods for simulating marine-propulsor flow, including offdesign. However, important outstanding issues include additional verification and validation, time-accurate solutions, and resolution and turbulence modeling for separation and tip and ring vortices.
Hydroelastic Response of a Floating Mat-Type Structure in Oblique, Shallow-Water Waves
Authors: Ertekin R. Cengiz , Kim Jang Whan
Published: January 2021

The linear, Level I Green-Naghdi (GN) theory is developed to study the hydroelastic behavior of a rectangular airport or runway whose draft is "small" and which floats in a near-shore area. The new theoretical and numerical model uses the linear, shallow-water wave equations of the GN type for the fluid dynamics and the thin-plate theory for the structural dynamics. The governing equations are matched at the juncture boundary and the resulting partial differential equations are solved by the boundary-integral-equation method, and the finite-difference method is used for discretizing the boundary conditions at the edges of the plate. The method devised here is proven to be very efficient in a parametric study of the hydroelastic response of a mat-type floating runway in regular, oblique waves. The main parameters varied in the problem are the stiffness, length and beam of the mat. The deflections of the mat are calculated for various incoming wave frequencies and heading angles in water of "shallow" depth. The results are compared with the available experimental data and numerical calculations by others. The mean drift loads on the mat are also calculated by following Maruo's far-field method.
Reliability-Based Allowable Unfairness Tolerances for Unstiffened Plates
Authors: Mansour Alaa , Elsayed Tarek
Published: January 2021

A procedure and a simple formula have been developed for determining the maximum allowable plating unfairness tolerance in ship panels. The formula is based on reliability assessment of strength of unstiffened plates having initial imperfections. Plate ultimate strength is determined by taking into account the effects of initial deflections and residual stresses. A series of plate reliability analyses relative to the ultimate strength failure, for varying plate unfairness, and aspect and slenderness ratios, is carried out. Based on the computed results, a simple expression for predicting the maximum allowable unfairness tolerance of the plate is derived. The developed expression, described in terms of the plate slenderness ratio, can be useful for the assessment of unfairness limits of plating between frames in ship structures.
Life-Cycle Fatigue Reliability of Ship Structures: A Proposed System
Authors: Petinov Sergei V.
Published: January 2021

Fatigue damage of structural details in essence may be attributed to the consequences of the traditional approach of securing the reliability of structures when the design and maintenance are provided by different groups of experts with different principles and different professional training. Progress may be achieved when the whole life-cycle reliability of a structure is provided uniformly in the design and service cycles. A series of actions and appropriate fatigue models composing an automated system to aid in the design and maintenance of ship structures is proposed. Considering the existing and feasible actions, attention is focused on the fatigue design and post-fabrication assessment of fatigue properties at critical locations.
Partially Cavitating Hydrofoils: Experimental and Numerical Analysis*
Authors: Pellone Christian , Maître Thierry , Briançon-Marjollet Laurence
Published: January 2021

The numerical modeling of partially cavitating foils under a confined flow configuration is described. A complete study of previous numerical models highlights that the presence of a turbulent and two-phase wake, at the rear of the cavity, has a nonnegligible effect on the local pressure coefficient, the cavitation number, the cavity length and the lift coefficient; hence viscous effects must be included. Two potential methods are used, each being coupled with a calculation of the boundary layer developed downstream of the cavity. So, an "open cavity" numerical model, as it is called, was developed and tested with two types of foil: a NACA classic foil and a foil of which the profile is obtained performing an inverse calculation on a propeller blade test section. On the other hand, under noncavitating conditions, for each method, the results are compared with the results obtained by the Navier-Stokes solver "FLUENT." The cavitating flow configurations presented herein were carried out using the small hydrodynamic tunnel at Bassin d'Essais des Carènes [Val de Reuil, France]. The results obtained by the two methods are compared with experimental measurements.
Inertia Effects on Pulsed Propulsion: Application to the Study of a Hydro-Propulsor
Authors: Mariaux G. , Peube J. L. , Gervais Y.
Published: January 2021

The marine propulsion systems that exist at the moment rely on the product creating an almost continuous flow in which the mechanical energy is given to the liquid in a continuous fashion. Here we study an original seawater propulsor in which the mechanical energy is provided to the liquid by the alternative displacement of a fluid contact surface. The produced flow is channeled towards the back of the vehicle that has to be propelled by a system of valves, in order to create an average positive thrust. These valves are free, so their operation is linked with the flow resulting from the interaction between the surface and the fluid contained within the mechanism. The mode of surface displacement clearly shows the discontinuous character of the transmission of the mechanical energy from the engine to the fluid as well as the unsteady flow produced. Therefore we have developed a model which permits study of the technical and geometrical characteristics, the particular flow sizes (pressure and velocity), and the performance of the propulsion system (thrust and efficiency). Three basic parameters allow study of the evolution of the performance of the device in correlation to its geometry. Moreover, we show that it's possible to make the flow almost continuous by increasing the internal fluid mass of the mechanism considerably.
Experimental Investigation of Propeller Wake Evolution by Means of LDV and Flow Visualizations
Authors: Stella A. , Guj G. , Di Felice F. , Elefante M.
Published: January 2021

An experimental investigation of the propeller wake has been performed in a cavitation tunnel using LDV and flow visualizations. The objective is the hydrodynamic and geometrical characterization of the wake flow field and its downstream evolution features. Implications of the physical aspects for wake modeling are also highlighted. The viscous blade wake, originating in the boundary layer on the blade surfaces, the trailing vortex sheets, due to the radial gradient of the bound circulation, as well as the turbulence distribution are identified at the trailing edge and followed. The near-wake geometry is quantitatively determined describing the progressive bending of the blade wake sheets, the slipstream contraction and the tip vortex trajectory. Furthermore, the effects of turbulent diffusion and viscous dissipation, which cause a rapid space-broadening of the velocity gradients in the trailing-edge wake, are examined. Insights into the viscous interaction between blade flow and roll-up process in the tip region are also proposed. Finally, the onset and development of the slipstream instability leading to the breakdown of the vortices system in the far wake are studied also by means of visualizations in incipient cavitating flow conditions.
A Study on Sensitivity of Maneuverability Performance on the Hydrodynamic Coefficients for Submerged Bodies
Authors: Sen Debabrata
Published: January 2021

Based on a constant-coefficient dynamic model, a study was made to determine the influence of various hydrodynamic coefficients on the predicted maneuverability quality of submerged bodies. Two types of geometries were considered, a submarine and an axisymmetric slender geometry. For the submarine, the equations of motion used were the revised standard submarine equations (Feldman 1979) while for the latter geometry a dynamic model was developed. From computer simulation of a few selected definitive maneuvers based on these two different dynamic models for the two geometries, the sensitivity of the simulated trajectory on changes in different coefficients was found. The results quantified in form of sensitivity values are presented. It is found that the typical measures from the maneuvers do not depend significantly on most of the nonlinear coefficients. The coefficients having significant effects on the trajectories are found to be the linear damping coefficients for the submarine and the linear inertial force coefficients for the axisymmetric body.
Ultimate Strength and Effective Width Formulations for Ship Plating Subject to Combined Axial Load, Edge Shear, and Lateral Pressure
Authors: Paik Jeom Kee , Thayamballi Anil K. , Kim Bong Ju
Published: January 2021

The aim of the present study is to develop closed-form formulations for the ultimate strength of simply supported steel plating subject to a combination of longitudinal axial load, edge shear, and lateral pressure. The post-weld initial imperfections (initial deflections and residual stresses) are included in the strength formulations as parameters of influence. By solving the equilibrium and compatibility governing differential equations of large-deflection plate theory, the membrane stress distribution inside the plating under axial and lateral pressure loads is formulated in closed form. The ultimate strength formulation for plating under axial load and lateral pressure is then derived under the assumption that the ultimate limit state is reached if the plate edges yield. An empirical formula for the plate ultimate shear strength is suggested based on numerical FE solutions. A relevant ultimate strength relationship between axial load and edge shear is then proposed by combining the two sets of the ultimate strength formulations. As another contribution, the effective width formulation for plating under combined axial compression and edge shear which allows for the shear lag effect caused by lateral pressure as well as the influence of post-weld initial imperfections is developed. The validity of the proposed ultimate strength formulations is shown by comparing with experimental results and nonlinear finite-element analyses. Modeling uncertainty of the developed plate ultimate strength formula against the experimental and numerical results is studied in terms of bias and coefficients of variation.
An Experimental Investigation of Cavitation Inception and Development on a Two-Dimensional Hydrofoil
Authors: Astolfi J.-A. , Leroux J.-B. , Dorange P. , Billard J.-Y. , Deniset F. , de La Fuente S.
Published: January 2021

The cavitation inception (and desinent) angles at given cavitation numbers, the velocity distribution, and the resulting pressure coefficient, together with the sheet cavity lengths developing on a hydrofoil surface, have been investigated experimentally for a Reynolds number ranging between 0.4 × 106 and 1.2 × 106. It is shown that the cavitation inception (and desinent) angle decreases progressively when the Reynolds number increases and tends to be close to the theoretical (inviscid) value when the Reynolds number is larger than 0.8 × 106. The magnitude and the position of the minimum surface pressure coefficient, inferred from the velocity distribution measured at the leading edge, were shown to be dependent upon the Reynolds number as well. An investigation of the cavitating flow velocity field upstream of the cavity and on the cavity surface showed that the pressure in the cavity was very close to the vapor pressure. The detachment location of the cavity was found to occur very close to the leading edge (at about one hundredth of the foil chord for both Re = 0.4 × 10® and Re = 0.8 × 106). The length cavities measured from flow visualizations exhibited a sudden change for a Reynolds number passing from 0.7 × 106 to 0.8 × 106 with a given angle of incidence (α= 6 deg) and cavitation number (σ = 1.3). Photographs of the sheet cavity show that the cavity length can be inferred also from the extent of the region for which the pressure coefficient is close to the cavitation number. It was shown to have the values l/c 0.03 for Re = 0.4 × 106 and l/c ~ 0.06 for Re = 0.8 × 10® and σ = 1.8 with the latter value very close to the value obtained from flow visualizations. Photographs of the cavity show that the increase of the cavity length is coupled to the migration, towards the leading edge, of a transition point on the cavity surface when the Reynolds number increases.
Ship Waves in a Stratified Fluid
Authors: Radko Timour
Published: January 2021

The far-field asymptotics of the linear waves excited by a moving object are obtained for a fluid consisting of n density layers (n is arbitrary). The structure of the perturbations of free surface and density interfaces is analyzed as a function of the depth of the object and its velocity. The amplitudes of different types of waves are compared. The present model also confirms and generalizes the features of the ship waves that were known previously only for the cases of one-layer and two-layer fluids.
Prediction of Non-Axisymmetric Effective Wake by a Three-Dimensional Euler Solver
Authors: Choi Jin-Keun , Kinnas Spyros A.
Published: January 2021

A fully three-dimensional Euler solver, based on a finite volume approach, is developed and applied to the prediction of the effective wake for propellers subject to non-axisymmetric inflows. The method is coupled with an existing lifting-surface vortex-lattice method for the analysis of unsteady cavitating propeller flows. The results are validated against analytical solutions from actuator disk theory. The effect of the grid parameters on the results (circumferential average and amplitudes of harmonics of the predicted effective wake) is found to be very weak. The predicted total velocity field correlates very well with that measured in propeller experiments.
The Maximum Sinkage of a Ship
Authors: Gourlay T. P. , Tuck E. O.
Published: January 2021

A ship moving steadily forward in shallow water of constant depth h is usually subject to downward forces and hence squat, which is a potentially dangerous sinkage or increase in draft. Sinkage increases with ship speed, until it reaches a maximum at just below the critical speed Here we use both a linear transcritical shallow-water equation and a fully dispersive finite-depth theory to discuss the flow near that critical speed and to compute the maximum sinkage, trim angle, and stern displacement for some example hulls.
Advanced Closed-Form Ultimate Strength Formulation for Ships
Authors: Paik Jeom Kee , Hughes Owen F. , Mansour Alaa E.
Published: January 2021

The aim of this paper is to develop an advanced ultimate strength formulation for ship hulls under vertical bending moment. Since the overall failure of a ship hull is normally governed by buckling and plastic collapse of the deck, bottom, and sometimes the side shell stiffened panels, it is of crucial importance to accurately calculate the ultimate strength of stiffened panels in deck, bottom and side shell for more advanced ultimate strength analyses. In this regard, the developed formulation is designed to be more sophisticated than previous simplified theoretical methods for calculating the ultimate strength of stiffened panels under combined axial load, in-plane bending and lateral pressure. Fabrication-related initial imperfections (initial deflections and residual stresses) and potential structural damage related to corrosion, collision, or grounding are included in the panel ultimate strength calculations as parameters of influence. All possible collapse modes involved in collapse of stiffened panels, including overall buckling collapse, column or beam-column type collapse (plate or stiffener induced collapse), tripping of stiffeners and local buckling of stiffener web, are considered. As illustrative examples, the paper investigates and discusses the sensitivity of parameters such as lateral pressure, fabrication-related initial imperfections, corrosion, collision and grounding damage on the ultimate strength of a typical Cape size bulk carrier hull under vertical bending.
Application and Verification of Deepwater Green Function for Water Waves
Authors: Chakrabarti Subrata K.
Published: January 2021

An efficient method for the numerical evaluation of the free-surface Green function for deep-water application was presented by Telste & Noblesse (1986) and again by Ponizy et al (1994). A FORTRAN code was include in their 1986 paper. The numerical method makes use of known mathematical functions. Numerical values of some of these mathematical functions were depicted, but no verification on the accuracy of the Green function routine in an application was given. The purpose of this paper is to compare their numerical values in the near-field and far-field regions with other similar computation for the infinite-depth Green function. The results of the infinite-depth Green function are also compared with the results from the finite-depth Green function that is more time consuming. Based on the accuracy of the various methods, the regions of application of the efficient deepwater Green function formulation and the effect of the water depth on the Green function are discussed. Any regions of inaccurate results are noted. Forces on submerged offshore structures and motions of the floating structures are determined using the lower-order panel method and these different Green function routines. The results on the motions of a semisubmersible in various water depths are compared and the accuracy of these routines in various regions is shown. The presented results will help the hydrodynamicist and designer to evaluate the suitable formulation and its regions of application for the accurate analysis and design of offshore structures.
Experimental Study on the Influence of Hull Spacing on Hard-Chine Catamaran Motions
Authors: Centeno R. , Varyani K. S. , Soares C. Guedes
Published: January 2021

An experimental program was performed with hard-chine catamaran models in regular waves. The distance between the demi-hulls of the models was changed to assess its effects on the wave-induced motions. The results allowed the study of some aspects related to catamaran motions, like the interference between the hulls and resonance frequencies. The experimental results are compared with calculations performed with a recently developed code based on a two-dimensional potential flow theory in which viscous forces are included through a cross-flow drag approach. The effect of the hull distance in the heave and pitch motion responses and the importance of the viscous forces in such hull configurations are shown.
An Investigation into the Self-righting of a Modern Racing Yacht in Waves
Authors: Renilson Martin , Tuite Andrew
Published: January 2021

Ocean sailing yachts can, and do, capsize from time to time, and so the safety of those who sail on them is linked directly to their ability to self-right once capsized. Current regulations used for racing yachts are based on statical concepts, which have been shown to be inappropriate (Renilson et al 2000). In order to gain an understanding of the dynamic factors involved, experiments were conducted on a 1/12.5 scale model of an ocean sailing yacht in waves in the towing tank at the Australian Maritime College. Two different experimental procedures were developed: Testing in a single breaking wave, and testing in steep irregular waves. Four variations of the limit of positive stability were tested, together with one condition which had a different roll radius of gyration, without water on board the model. In addition, two variations of the limit of positive stability were tested to represent the condition with 4000 kg of water on board. From the tests it was possible to conclude that, for the given yacht, if the limit of positive stability is decreased from 119 deg to 104.7 deg the yacht is much less likely to self-right under the action of waves, with or without 4000 kg of water on board.
Analysis of Global Load Effects in Catamarans
Authors: Heggelund Svein Erling , Moan Torgeir
Published: January 2021

Relevant stresses and deformations resulting from longitudinal bending and torsion are calculated for a 60 m catamaran by a global finite-element model. The results are compared with results from prismatic beam theory modified to account for the effect of wide flanges and significant window openings typical for a catamaran hull. It is found that the global stresses are predicted with a reasonable accuracy for the initial design stage. In the present case, the effect of warping on shear stress due to torsional loading is moderate and can be neglected. However, this effect is strongly dependent on the vessel design and can be important for a vessel with narrower hulls and a superstructure that is lower relative to the total height.
Implementation of Finite-Element Codes for the Simulation of Ship-Ship Collisions*
Authors: Servis Dimitris , Samuelides Manolis , Louka Tina , Voudouris Giorgos
Published: January 2021

The problem of ship collisions may well be considered one of the most complicated impact problems that contemporary engineering research is encountering. The structures involved are very large and include various structural elements. Thus, there is a large number of different modes of deformation that may occur, a fact that introduces a lot of parameters in the investigation of such problems. Finite-element analyses have been used over the past decade to solve several impact problems effectively. Though considerable success has been recorded in many research areas, such as the automotive industry, ship collision simulations still confront diffculties culties in providing reliable results. This paper attempts to determine the parameters that largely influence ship collisions and to provide tools and guidelines for the effective implementation of finite-element codes.
Prediction of Unsteady Effective Wake by a Euler Solver/Vortex-Lattice Coupled Method
Authors: Choi Jin-Keun , Kinnas Spyros A.
Published: January 2021

A fully three-dimensional Euler solver, based on a finite volume approach, is developed and applied to the prediction of the unsteady effective wake for propellers subject to non-axisymmetric inflows. The Euler solver is coupled with an existing lifting-surface vortex-lattice method for the computation of unsteady propeller flows. The coupled method is validated against the uniform inflow case, in which ideally the uniform flow should be recovered as the effective wake. The predicted total velocity field correlates very well with that measured in the water tunnel experiment. Lastly, the unsteady effective wake predicted by the present method is compared with the steady effective wake predicted by the authors' previous steady method.
Limit Loads for Laterally Loaded I-Section Beams With Consideration of Shear
Authors: Belenkiy L. , Raskin Y.
Published: January 2021

The paper examines an effect of shear forces on limit load for I-section beams carrying later alloads. The problem is solve don the basis of a physical model, which enables one to take into account the effect of a resistance of beam flanges to the plastic shears train in the web of the beam. The physical model for the evaluation of limit loads was veriŽed using nonlinear finite element analysis. An engineering technique for the calculation of limit loads for shiphull beams subjected to large shear forces was developed using this model. As illustrative examples, the paper shows the application of the proposed technique to obtain closed-form solutions for the prediction of limit loads.
Conceptual Hull Design Using a Genetic Algorithm
Authors: Lowe T. W. , Steel J.
Published: January 2021

A genetic algorithm is used to search the design variable space of a model ship hull for forms having specified values of various primary and secondary geometric parameters. A representative of each distinct cluster of the forms found is identified and presented as a candidate hull design having the required geometric characteristics. This could form the basis of a prototype conceptual design tool enabling the generation of hull forms satisfying specified requirements. The geometric parameters considered include the displacement, waterline length, waterline beam, and waterplane coefficient together with the locations of the centers of flotation and buoyancy. The hull surface is represented using the partial differential equation method, which permits a wide range of fair hull forms to be accessible using a relatively small number of design variables.
Experimental Investigation of the Flow Around a Fast Displacement Ship Hull Model
Authors: Olivieri A. , Pistani F. , Penna R.
Published: January 2021

The aim of the present paper is the description of the flow around a fast displacement shiphull model with particular attention on the mechanisms responsible for the generation of streamwise vertical structures along the hull boundary layer. The collected data contribute to a surface-ship resistance and propulsion model-scale database for computational fluid dynamics validation as part of an international cooperative project between Istituto Nazionale per Studied Esperienze di Architettura Navale (INSEAN), Iowa Institute of Hydraulic Research (IIHR), and David Taylor Model Basin (DTMB) on experimental and computational fluid dynamics and uncertainty assessment for a combatant geometry(Stern et al 2000). A cross validation of the present results has been carried out through the ones obtained at DTMB and IIHR. Uncertainty assessment of the results has been evaluated following the AIAA Standard S-071-1995.
Cyclostationary Random Vibration of a Ship Propeller
Authors: Jha Akhilesh , Nikolaidis Efstratios , Gangadhararn Sathya
Published: January 2021

A special class of nonstationary processes with periodically varying statistics, called cyclostationary (CS), is investigated. This process is encountered in many engineering problems involving rotating machinery, such as turbines, propellers, helicopter rotors, and diesel engines. The objective of this paper is to show that a CS model of the flow-induced excitation on a propeller can describe the physics of the problem more accurately than a traditional stationary model. The mean values of the hydrodynamic forces are calculated using the vortex panel method and the vortex theory of propellers. Considering the randomness in the axial and the tangential components of the wake velocity, we calculate the covariance matrix of the forces. This analysis shows that the hydrodynamic forces acting on the propeller are CS processes. Then we calculate the standard deviation (root mean square [RMS]) of the blade response. We show that the CS model predicts the timewise variation of the statistics of the excitation and the response (e.g., the RMS), including their peaks. A traditional stationary model cannot provide this information because it assumes constant statistics. Finally, a parametric analysis is performed to demonstrate the effects of the correlation structure of the velocity field behind a ship hull on the RMS of the blade deflection.
Calculation of Deep-Water Wash Waves Using a Combined Rankine/Kelvin Source Method
Authors: Janson Carl-Erik , Leer-Andersen Michael , Larsson Lars
Published: January 2021

This paper presents a method for computation of far-field wash waves in deep water. The method combines a nonlinear Rankine source method in an inner domain with a Kelvin source method for the far-field waves in an outer domain. Kelvin sources are distributed on a vertical matching wall, positioned at the outer edge of the inner domain. These sources are used to specify a boundary condition for the disturbance velocity potential on the matching wall. The boundary condition is used in the Rankine source solution of the inner domain. The size of the inner domain can be reduced in the transverse direction compared to a method using Rankine sources only, as the wave reflections at the edge of the inner domain are eliminated. Further, the far-field waves can be computed using the solution on the matching wall together with the Kelvin source distribution. The verification of the present method includes a comparison for a single Kelvin point source and a comparison to a Rankine source method at intermediate distances for the Wigley hull and for a catamaran. A grid dependence study for the position, size, and panel density on the matching wall is included for the Wigley hull. Computed and measured longitudinal wave cuts are compared for a catamaran both in the inner and the outer domain. Good agreement is obtained.
Weakly Singular Boundary-Integral Representations of Free-Surface Flows About Ships or Offshore Structures
Authors: Noblesse Francis , Yang Chi
Published: January 2021

The fundamental problem of determining the free-surface potential flow that corresponds to a given flow at the wetted surface of a ship or offshore structure is considered for diffraction-radiation of time-harmonic waves with forward speed and the special cases corresponding to zero forward speed or zero wave frequency. Boundary-integral representations that define the velocity potential in terms of functions that are no more singular than a Green function G are given. These boundary-integral representations are weakly singular in comparison to the classical boundary-integral representations of free-surface potential flows, which define the potential in terms of G and · G.