bluuebunny/crossref_metadata_2025 huggingface dataset:
System Identification for Nonlinear Maneuvering of Ships Using Neural Network
Authors: Rajesh G. , Rajasekhar G. Giri , Bhattacharyya S. K.
Published: January 2021

This paper deals with the application of nonparametric system identification to the nonlinear maneuvering of ships using neural network method. The maneuvering equations contain linear as well as nonlinear terms, and one does not attempt to determine the parameters (or hydrodynamic derivatives) associated with nonlinear terms, rather all nonlinear terms are clubbed together to form one unknown time function per equation, which are sought to be represented by neural network coefficients. The time series used in training the network are obtained from simulated data of zigzag and spiral maneuvers. The neural network has one middle or hidden layer of neurons and the Levenberg-Marquardt algorithm is used to obtain the network coefficients. Using the best choices for number of hidden layer neurons, length of training data, convergence tolerance, and so forth, the performances of the proposed neural network models have been investigated and conclusions drawn.
Wave-Induced Vibrations of an Axial-Loaded Immersed Timoshenko Beam Carrying an Eccentric Tip Mass with Rotary Inertia
Authors: Wu Jong-Shyong , Chen Chin-Tzu
Published: January 2021

Under the specified assumptions for the equation of motion, the closed-form solution for the natural frequencies and associated mode shapes of an immersed "Euler-Bernoulli" beam carrying an eccentric tip mass possessing rotary inertia has been reported in the existing literature. However, this is not true for the immersed "Timoshenko" beam, particularly for the case with effect of axial load considered. Furthermore, the information concerning the forced vibration analysis of the foregoing Timoshenko beam caused by wave excitations is also rare. Therefore, the first purpose of this paper is to present a technique to obtain the closed-form solution for the natural frequencies and associated mode shapes of an axial-loaded immersed "Timoshenko" beam carrying eccentric tip mass with rotary inertia by using the continuous-mass model. The second purpose is to determine the forced vibration responses of the latter resulting from excitations of regular waves by using the mode superposition method incorporated with the last closed-form solution for the natural frequencies and associated mode shapes of the beam. Because the determination of normal mode shapes of the axial-loaded immersed "Timoshenko" beam is one of the main tasks for achieving the second purpose and the existing literature concerned is scarce, the details about the derivation of orthogonality conditions are also presented. Good agreements between the results obtained from the presented technique and those obtained from the existing literature or conventional finite element method (FEM) confirm the reliability of the presented theories and the developed computer programs for this paper.
A Force Estimation Method for Viscous Separated Flow Over Slender Axisymmetric Bodies With Tapered Tails
Authors: Jeans Tiger L. , Holloway A. Gordon L. , Watt George D. , Gerber Andrew G.
Published: January 2021

A new impulse method for modeling the normal force distributions along slender axisymmetric bodies with tapered tails is presented. This method is based on a decomposition of the hydrodynamic impulse along the body into an inviscid, profile-dependent component and a viscous, profile-independent component. It is applicable to separated flows up to 30 deg of incidence. Model results for the normal force distributions, total normal force, and total moment on axisymmetric streamlined bodies with tapered tails are compared with computational fluid dynamics (CFD) simulations and experimental data up to a Reynolds number of 23 × 106 with good agreement. The model was also tested on a missile-shaped body and was found to be in excellent agreement with experimental results.
Partial Cavity Drag Reduction at High Reynolds Numbers
Authors: Lay Keary A. , Yakushiji Ryo , Makiharju Simo , Perlin Marc , Ceccio Steven L.
Published: January 2021

Air lubrication to reduce hull skin friction is an idea that originated more than a century ago. There are few implementations of this concept, and there are even fewer systematic investigations at high Reynolds numbers. To address this, an experimental investigation was performed at the W. B. Morgan Large Cavitation Channel that examined the drag-reducing effects of a ventilated partial cavity at high Reynolds numbers. The design was accomplished using both linear gravity wave theory and a two-dimensional inviscid numerical model via Fluent. The physical model was a 12 m long flat plate with a plenum on the bottom. The plenum was formed by an abrupt step near the nose and a long sloping reattachment region toward the rear. Air was injected from the aft face of the step to create a cavity approximately 17.8 cm deep. Friction loads, air flow, and cavity pressure were measured over a range of air fluxes and speeds near the cavity design speed of 3.4 m/s. Cavities were shown to be stable with respect to large changes in air flux and slow perturbations in tunnel speed and pressure. Stable cavities were produced that reduced the skin drag by more than 95% over the extent of the cavity, including the cavity closure.
Numerical Investigation to Predict Ship Squat
Authors: Debaillon P.
Published: January 2021

As empirical formulas do not succeed in predicting the ship squat with sufficient reliability, a numerical modeling system was developed. It is based on a three-model coupling to reproduce the physics of the phenomenon. The numerical modeling system was also used to set up a new formula. Finally, a comparison between measurements, empirical formulas, and the numerical modeling is made for three examples.
A Subjective Risk-Estimation Approach for Modeling Ship Hull Vibration
Authors: Godaliyadde D. , Phylip-Jones G. , Yang Z.L. , Batako A.D. , Wang J.
Published: January 2021

A subjective novel approach incorporating an evidential reasoning (ER) algorithm is developed to achieve the risk estimation of ship hull vibration (SHV). A hierarchical structure for SHV modeling (hazard identification model) is constructed using a combined qualitative and quantitative approach. The quantitative criteria are converted to the qualitative criteria by applying a rule-based quantitative data transformation technique to make use of ER. A mapping process is formulated to convert and quantify the qualitative criteria. Intelligent Decision System (IDS) software is used for synthesis in the hierarchical structure and to produce the risk-estimation results graphically. The results of this paper reveal that the ER is capable of producing the risk estimation of SHV.
RANS Simulations of Supercavity Flows
Authors: Pellone C. , Maître T. , Franc J. P
Published: January 2021

This work aims at evaluating the capacity and limitations of conventional Reynolds-averaged Navier-Stokes (RANS) techniques to numerically simulate supercavity flows. The configuration is that of a two-dimensional (2D) symmetrical supercavitating wedge investigated experimentally by Michel (1974). Mesh effect is studied in detail under noncavitating conditions. The computational grid is refined in the region where cavitation develops in order to accurately track the supercavity. The effect of tunnel height is also analyzed, and the height finally chosen was large enough to simulate an infinite flow-field. The cavitating flow is treated as a homogeneous mixture of variable density. To account for vaporization and condensation, an additional continuity equation for the vapor (or the liquid) is solved with an appropriate source term expressing mass transfer between the two phases. The effect of nuclei concentration on the vaporization rate and then on the development of the supercavity is investigated. Results obtained using two different RANS codes are compared. They are also compared with experimental data and with inviscid solutions including a nonlinear boundary element method. They concern in particular cavity length and shape, pressure distribution, and drag coefficient. Under unsteady conditions, a special attention is paid to the characteristic growth time of the supercavity following a sudden pressure drop, from noncavitating conditions.
Real-Time Strain Monitoring of a Navy Vessel During Open Water Transit
Authors: Nichols J. M. , Seaver M. , Trickey S. T. , Aktas E. , Scandell K. , Salvino L. W.
Published: January 2021

In this work we describe the installation of a real-time, fiber-optic strain monitoring system aboard a US Navy vessel undergoing sea trials. The system is lightweight, unintrusive, corrosion resistant, and provides dynamic strain response measurements from direct current (DC) up to 360 Hz. Also described are the data acquisition and subsequent analysis. The goals of the study were to demonstrate a fiber-optic strain monitoring system under real world conditions and to better understand the source of deck cracking above an area housing mission-critical components. The results of the two-day trial indicate that there exist large stresses in the deck plate during normal ship operation. Based on the results, it is clear that ship maneuvers, slewing of the radar located on the deck plate, and insolation-related effects are not the primary source of the observed stress.
Isothermal Jet Suction Through the Lateral Openings of a Cylindrical Funnel
Authors: Mishra Dipti P. , Dash Sukanta K. , Kishan P. Anil
Published: January 2021

This paper discusses the computation of air entrainment in to the louvers of a cylindrical funnel as a result of a high-velocity isothermal air jet placed inside the funnel having different lengths of protrusion and different funnel diameters. The experimental setup consists of a cylindrical Perspex tube with circular louvers cut around it. The flow through the nozzle is measured with a rotameter, and the velocity at the cylinder outlet is measured with a hot wire anemometer. The numerical simulation is carried out by solving the conservation equations of mass and momentum for the funnel with a surrounding computational domain so that the suction can take place at the louver entry. The resulting equations have been solved numerically using finite volume technique in an unstructured grid employing eddy viscosity based two-equation k-e turbulence model of Fluent 6.3. It has been found from the experiment and the CFD computation that there exists an optimum funnel diameter for which the mass ingress into the funnel is highest, and also there exists an optimum protrusion length of the nozzle that entrains maximum air flow into the funnel. For isothermal air suction the mass ingress into the funnel does not depend on the inclination of the funnel, whereas for low velocity and high temperature of the nozzle fluid the mass ingress in to the funnel depends on the inclination of the funnel. After a critical nozzle velocity (Gr/Re2 < 0.5), the mass ingress into the funnel does not again depend on the inclination of the funnel. An approximate relation for the entrance length of a sucking pipe has also been developed from the present CFD solution. The original contribution of the paper is the setting of a computational methodology for computing various conditions of suction flow in to a funnel while having the numerical confidence by comparing the CFD result with a small-scale experimental measurement in the laboratory.
Development of a Fatigue Model Useful in Ship Routing Design
Authors: Mao Wengang , Ringsberg Jonas W. , Rychlik Igor , Storhaug Gaute
Published: January 2021

In this paper, a simple fatigue estimation model, using only the encountered significant wave height, is used for predicting fatigue accumulation of a vessel during a voyage. The formulation of the model is developed based on the narrow-band approximation. It is assumed that the significant response range, hs, has a linear relationship with encountered significant wave height, Hs. The mean stress upcrossing frequency, fz, is represented by the corresponding encountered wave frequency, and it is expressed as a function of Hs. The capacity and accuracy of the model are illustrated by application on one container vessel's fatigue damage accumulation in an amidships detail, operating in the North Atlantic during 2008. For this vessel, all the necessary data needed in the fatigue model, and verification of it, was obtained by measurements. The results from the proposed fatigue model are compared with the well-known and accurate rainflow analysis. Influence of nonlinearities, for example, whipping, on fatigue damage predictions is also discussed.
Experimental and Numerical Study of Wave-Induced Load Effects of Open Ships in Oblique Seas
Authors: Zhu Suji , Wu Mingkang , Moan Torgeir
Published: January 2021

Open ships inherently possess low torsional rigidity because of their open deck structural configuration. Some of the structural failures for open ships are caused by wave-induced torsional moment in combination with other load components in oblique seas. Relatively few experimental results about horizontal bending and torsional moments in oblique seas have been published, however. Further, test data for vertical shear force and vertical bending moment in oblique seas are quite scarce. A backbone model has been recently tested by the Center for Ships and Ocean Structures (CeSOS) in the towing tank and ocean basin at the Marine Technology Center. The model consists of 15 box-shaped segments, in addition to bow and stern segments, which are interconnected by an aluminum beam on the top. Model tests in oblique seas without forward speed were first carried out to provide basic comparisons. Tests in head and oblique seas with speeds were then conducted in regular waves. Irregular wave tests were also carried out to assess the spectral responses and peak distributions of cross-sectional load effects. Load effects at 7 longitudinal positions were measured through strain gauges, including vertical shear force (VSF), vertical bending moment (VBM), horizontal bending moment (HBM), and torsional moment (TM). The motivation of this paper is to perform a benchmark study by comparing numerical predictions of different computer codes with these test results. The uncertainties in the experiments and the computer codes are discussed, and conclusions are presented at the end of this paper.
Numerical analysis of the effects on a floating structure induced by ship waves
Authors: Sun L. , Dong G.H , Zhao Y. P. , Liu C. F.
Published: January 2021

Ship-generated waves can make bad effects on offshore structures. A numerical model is presented for evaluating the forces exerted on a nearby floating structure by ship generated waves. The ship waves were modeled using Michell thin-ship theory (Wigley waves), the forces were computed using a boundary element method in the time domain, and the motions of the offshore structures were evaluated using the equation of motion of the floating body, and predicted using the fourth-order Runge-Kutta method. The numerical method was validated by comparing its results to those of frequency-domain methods reported in the literature. It was then applied to calculate the force of ship waves on a floating box. The ship's speed, dimensions, and distance were varied. The numerical results indicate some useful rules for varying these factors.
Ship Motion and Wave Radar Data Fusion for Shipboard Wave Measurement
Authors: Stredulinsky David C. , Thornhill Eric M.
Published: January 2021

Defence Research and Development Canada (DRDC) Atlantic has conducted many dedicated seakeeping and structural load trials on the Canadian Navy research ship CFAV Quest and on several Canadian Navy warships. Typically, wave buoys have been deployed to measure seaway wave characteristics; however, there has been an ongoing interest in evaluating shipboard wave measurement systems. These systems have some advantages over wave buoys for short-term trials and are needed for longer-term sea trials and to provide wave input data for tactical and real-time ship operator guidance systems. This paper presents some of our experiences with wave radar. In the last few years there have been significant advances in wave radar technology (systems that extract wave data from backscatter information contained in the video output of X-band navigational radar displays). Commercial "off-the-shelf" systems are now available. While there is evidence that these systems can provide reliable wave data from shore-based or stationary platform installations, it is DRDC's experience on a ship moving in waves, that wave radars can give good direction and frequency measurements but less reliable wave heights. DRDC has developed a method to improve shipboard wave height measurement through fusion of wave radar data with measured ship motion response data. This paper discusses the development of the wave data fusion process, validated through previous sea trial data, and presents the results of a recent demonstration of the approach during a sea trial conducted on CFAV Quest in November/December 2008.
Reduction of Hull-Radiated Noise Using Vibroacoustic Optimization of the Propulsion System
Authors: Caresta Mauro , Kessissoglou Nicole J.
Published: January 2021

Vibration modes of a submarine are excited by fluctuating forces generated at the propeller and transmitted to the hull via the propeller-shafting system. The low frequency vibrational modes of the hull can result in significant sound radiation. This work investigates reduction of the far-field radiated sound pressure from a submarine using a resonance changer implemented in the propulsion system as well as design modifications to the propeller-shafting system attachment to the hull. The submarine hull is modeled as a fluid-loaded ring-stiffened cylindrical shell with truncated conical end caps. The propeller-shafting system is modeled in a modular approach using a combination of mass-spring-damper elements, beams, and shells. The stern end plate of the hull, to which the foundation of the propeller-shafting system is attached, is modeled as a circular plate coupled to an annular plate. The connection radius of the foundation to the stern end plate is shown to have a great influence on the structural and acoustic responses and is optimized in a given frequency range to reduce the radiated noise. Optimum connection radii for a range of cost functions based on the maximum radiated sound pressure are obtained for both simple support and clamped attachments of the foundation to the hull stern end plate. A hydraulic vibration attenuation device known as a resonance changer is implemented in the dynamic model of the propeller-shafting system. A combined genetic and pattern search algorithm was used to find the optimum virtual mass, stiffness, and damping parameters of the resonance changer. The use of a resonance changer in conjunction with an optimized connection radius is shown to give a significant reduction in the low frequency structure-borne radiated sound.
Time Domain Prediction of Added Resistance of Ships
Authors: Kara Fuat
Published: January 2021

The prediction of the added resistance of the ships that can be computed from quadratic product of the first-order quantities is presented using the near-field method based on the direct pressure integration over floating body in time domain. The transient wave-body interaction of the first-order radiation and diffraction problems are solved as the impulsive velocity of the floating body by the use of a three dimensional panel method with Neumann-Kelvin method. These radiation and diffraction forces are the input for the solution of the equation of the motion that is solved by the use of the time marching scheme. The exact initial-boundary-value problem is linearized about a uniform flow, and recast as an integral equation using the transient free-surface Green function. A Wigley III hull form with forward speed is used for the numerical prediction of the different parameters. The calculated mean second-order added resistance and unsteady first-order impulse-response functions, hydrodynamics coefficients, exciting forces, and response amplitude operators are compared with experimental results.
Translational Added Mass of Axisymmetric Underwater Vehicles with Forward Speed Using Computational Fluid Dynamics
Authors: Mishra Virag , Vengadesan S.
Published: January 2021

This paper presents a computational fluid dynamics (CFD) approach to the calculation of translational added mass coefficient of axisymmetric underwater bodies in both longitudinal and transverse directions. The proposed method involves CFD simulations of accelerated as well as uniform flows past axisymmetric bodies based on Reynolds averaged Navier-Stokes (RANS) equations and makes use of the results of these simulations to obtain the inertia force acting on a body as a function of time. The translational added mass can be obtained from this inertia force history. Validation of the methodology is presented for the benchmark case of accelerated flow past sphere and infinitely long circular cylinder in cross-flow for which analytical solutions of the added mass problem are well known.
Verification and Validation of URANS Wave Resistance for Air Cushion Vehicles, and Comparison With Linear Theory
Authors: Bhushan S. , Stern F. , Doctors L. J.
Published: January 2021

Verification and validation of URANS wave-resistance predictions for straight-ahead and yawed air-cushion vehicles in calm deep and shallow water are performed. The nonlinear and linear theories are compared to explicate their trends for large cushion pressures, water depth, and cushion dimensions, and the nonlinear theory sinkage and trim trends are discussed. The grid-verification study shows monotonically converged solutions with averaged uncertainty of 4% and 10% for straight-ahead motion in deep and shallow water, respectively. URANS predictions agree with the experimental data to within 6% and 9% for straight-ahead deep and shallow water simulations, respectively. The smooth-edged cushion-pressure simulations predict lower resistance than the sharp-edged case, whereas no significant dependence is obtained for Reynolds number and turbulence modeling. URANS predicts attenuation in the resistance secondary hump as the cushion-pressure level increases. On the other hand, the linear theory does not account for the effect of cushion-pressure level. The linear and nonlinear theories compare within 4.5% for static cushion-pressure-to length ratios less than 0.025 and Froude number greater than 0.5 for both deep and shallow water. The nonlinear theory predicts the effect of water depth better than the linear theory, when compared with the experiments. Both the theories agree well in predicting the decrease in resistance with the decrease in cushion width. The nonlinear theory does not show unrealistically large resistance and side force for sharp-edged cushion pressure for yawed cases, as observed in the linear theory. However, both the theories compare well for the resistance and side-force predictions for the smooth-edged cushion pressure, where the results agree within 10% of the deep-water experimental data. The nonlinear theory predictions for the sinkage and trim are in good agreement with the experimental data, but sinkage is overpredicted and trim is underpredicted. URANS wave-elevation patterns display transverse and diverging waves, which compare well with the Kelvin waves for Froude number less than 0.6 and greater than 1.0, respectively. URANS predicts breaking waves for large cushion pressures for Froude number less than 0.6.
Experimental and Theoretical Analysis of Propeller Shaft Loads in Oblique Inflow
Authors: Amini Hamid , Steen Sverre
Published: January 2021

A series of model tests on an azimuth thruster model in oblique inflow conditions were performed for different heading angles and at different advance coefficients in pushing and pulling modes. Tests were performed in ventilating and non-ventilating conditions. A novel shaft dynamometer was used to measure all six component forces and moments on the propeller shaft. It was found that the propeller shaft lateral force and bending moment were quite large, and thus, the load at the shaft-bearing positions was about three times larger than when only the propeller weight was considered. The results also showed that oblique inflow due to steering gives higher bending loads than when the propeller is subject to ventilation in the straight-ahead condition. A basic blade element momentum method (BEMT) was used to predict the forces and moments on the propeller shaft in oblique flow conditions. Fairly good agreement was found between the BEMT results and the experimental results.
Ship Springing Response in Finite Water Depth
Authors: Vidic-Perunovic Jelena
Published: January 2021

The influence of water depth on the vertical wave induced bending moment acting on a hull has been studied. The deep-water second-order nonlinear hydroelastic strip theory, which is based on the relative motion concept, has been generalized to account for a finite water depth. Results for an analytical beam and for a tanker ship are presented and discussed. Short-term load predictions that account for a range of different sea states are given for a tanker ship. As seen from the present study, the effect of intermediate water depth may be a significant factor in calculations of ship springing response.
A Simple Verification Test for Nonlinear Flow Calculations Around a Ship Hull Steadily Advancing in Calm Water
Authors: Noblesse Francis , Wang Lijue , Yang Chi
Published: January 2021

Simple analytical relations that can readily be applied to verify a critical aspect of numerical predictions of fully nonlinear free-surface flows around ship hulls steadily advancing in calm water are given. The relations do not involve the flow field equations; that is, they are only based on the boundary conditions at the ship hull surface and at the free surface. These boundary conditions have a predominant influence on free-surface flows around advancing ship hulls. The analytical relations are exact for inviscid flows, and can be applied to numerical methods that solve either the Laplace equation (potential-flow methods) or the Euler flow equations (CFD Euler-flow methods). They provide a simple test to verify if numerical predictions given by nonlinear potential-flow or Euler-flow methods correctly satisfy the hull-surface and free-surface boundary conditions along the contact curve between the hull surface and the free surface. The relations might also be used to verify CFD methods that solve the RANS equations if they are applied at the edge of the viscous boundary layer. The analytical test can identify an inconsistency, which might point to a "method issue" related to a feature of a numerical method (e.g., a numerical-differentiation scheme) or an "implementation issue" in the implementation of the method (e.g., a poor discretization). For purposes of illustration, the test is applied to predictions of flows around the Wigley parabolic hull given by two CFD methods that solve the Euler equations with fully nonlinear boundary conditions at the free surface. This illustrative example demonstrates that the test can indeed be useful to identify numerical inaccuracies. The analytical relations can also be used to determine experimental values of the flow velocity at a ship wave profile that correspond to measurements of the wave profile.
Sail Aerodynamics: On-Water Pressure Measurements on a Downwind Sail
Authors: Maria Viola Ignazio , Flay Richard G. J.
Published: January 2021

Pressures on three horizontal sections of a downwind sail were measured for several wind directions and sail trims. The pressure distributions were compared with wind tunnel tests; similarities and differences were found, the latter as a result of the dynamic effects, which were not modeled in the wind tunnel. A pressure distribution at the head of the spinnaker resembling that from a delta wing was measured at an apparent wind angle of 120°.
Generalized Modes in Time-Domain Seakeeping Calculations
Authors: Tuitman Johan T. , Malenica Šime , van't Veer Riaan
Published: January 2021

The concept of "generalized modes" is to describe all degrees of freedom by mode shapes and not using any predefined shape, like rigid body modes. Generalized modes in seakeeping computations allow one to calculate the response of a single ship, springing, whipping, multibody interaction, etc., using a uniform approach. The generalized modes have already been used for frequency-domain seakeeping calculations by various authors. This article extents the generalized modes methodology to be used for time-domain seakeeping computations, which accounts for large-amplitude motions of the rigid-body modes. The time domain can be desirable for seakeeping computations because it is easy to include nonlinear load components and to compute transient response, like slamming and whipping. Results of multibody interaction, two barges connected by a hinge, whipping response of a ferry resulting from slamming loads, and the response of a flexible barge are presented to illustrate the theory.
Probabilistic Fire Safety Assessment of Passenger Ships
Authors: Themelis Nikos , Spyrou Kostas J.
Published: January 2021

A probabilistic framework is proposed for the assessment of passenger ship fire safety that is based on a structured generation of "design fires." The aim is to establish a rational and practical means for evaluating design selections (materials, geometry, sensors, and suppressors) that influence fire safety with reference to the implicit safety objectives attended by the current regulations. Thus, alternative design solutions could be evaluated more comprehensively. Fire growth intensity, restriction of heat release rate resulting from ventilation shortage, occurrence of flashover, and the final decay are key processes modeled in the current approach. They are interfaced with fire suppression triggered by detection. The effect of manual intervention is also assessed. An application is included based on uniform distributions of selected random parameters. Justification for the considered ranges is provided. The effect of assuming different probability distributions is considered. The methodology can be used for producing the probability of containment and extinguishment of fires as well as for judging the performance of an overall or partial ship design solution.
Uncertainty Analysis of Load Combination Factors for Global Longitudinal Bending Moments of Double-hull Tankers
Authors: Teixeira Angelo P. , Soares C. Guedes , Chen Nian-Zhong , Wang Ge
Published: January 2021

The present article aims at assessing the probabilistic characteristics of the load combination factors for global longitudinal bending moments of double-hull tankers. The calculations are performed based on a sample of oil tankers representative of the range of application of the Association of Classification Societies' (IACS)–Common Structural Rules (CSR) design rules. The article starts by reviewing the probabilistic models that have been proposed to model stillwater and wave-induced loads and their characteristic extreme values. Different load combination methods are also reviewed including an analytical method that provides the combined characteristic value of stillwater and wave-induced bending moments based on the Poisson assumption for upcrossing events and using the first-order reliability method in combination with the point-crossing method. The predictions of the different load combination methods are assessed on the basis of a sample of five oil tankers adopted during the IACS-CSR design rules development process. A parametric and an uncertainty propagation study are then performed to identify the range of variation and the probabilistic models of the load combination factors that are applicable to double-hull tankers.
Comparison of Measured Ship Squat with Numerical and Empirical Methods
Authors: Briggs Michael J. , Kopp Paul J. , Ankudinov Vladimir K. , Silver Andrew L.
Published: January 2021

The Beck, Newman and Tuck (BNT) numerical predictions are used in the Coastal and Hydraulics Laboratory (CHL) Channel Analysis and Design Evaluation Tool (CADET) model for predicting underkeel clearance (UKC) resulting from ship motions and squat. The Ankudinov empirical squat prediction formula has been used in the CHL ship simulator and was recently updated. The World Association for Waterborne Transport Infrastructure (formerly The Permanent International Association of Navigation Congresses, PIANC) has recommended several empirical and physics-based formulas for the prediction of ship squat. Some of the most widely used formulas include those of Barrass, Eryuzlu, Huuska, ICORELS, Romisch, Tuck, and Yoshimura. The purpose of this article is to compare BNT, Ankudinov, and PIANC predictions with measured DGPS squat data from the Panama Canal for four ships. These comparisons demonstrate that the BNT, Ankudinov, and PIANC predictions fall within the range of squat measurements and can be used with confidence in deep draft channel design.
A Quasi-three-dimensional Finite-volume Shallow Water Model for Green Water on Deck
Authors: Liut Daniel A. , Weems Kenneth M. , Yen Tin-Guen
Published: January 2021

A quasi-three-dimensional hydrodynamic model is presented to simulate shallow water phenomena. The method is based on a finite-volume approach designed to solve shallow water equations in the time domain. The nonlinearities of the governing equations are considered. The methodology can be used to compute green water effects on a variety of platforms with six-degrees-of-freedom motions. Different boundary and initial conditions can be applied for multiple types of moving platforms, like a ship's deck, tanks, etc. Comparisons with experimental data are discussed. The shallow water model has been integrated with the Large Amplitude Motions Program to compute the effects of green water flow over decks within a time-domain simulation of ship motions in waves. Results associated to this implementation are presented.
Wave Scattering of Spheroidal Bodies Below a Free Surface
Authors: Chatjigeorgiou Ioannis K. , Miloh Touvia
Published: January 2021

A new multipole expansion method based on Havelock's theorem is proposed for solving the hydrodynamic problem of a submerged spheroid moving below a (linearized) free surface. In particular, the Green's function thus derived can be used to determine the forces and moments exerted on an oscillating spheroid with forward motion (radiation and wave resistance) or a fixed spheroid in the presence of a monochromatic time-harmonic incident wave (diffraction). We present a solution for the diffraction problem, including some numerical simulations for the heave, sway, and surge forces as well as yaw moments acting on a prolate rigid spheroid (depending on its eccentricity) in the case of an oblique incident wave field.
A Method to Predict Rudder Stall Inception from Two-dimensional Airfoil Data
Authors: Hughes Michael J. , Shen Young T.
Published: January 2021

The behavior of the force on a rudder changes significantly after the inception of stall, requiring different mathematical formulae to compute rudder forces prior-and poststall. Determining the inception angle at which stall occurs is important for predicting the rudder force on a maneuvering ship. A method to compute the inception angle of stall on a rudder is presented in this article. The theoretical formulation is based on a flow similarity approach, which relates three-dimensional rudder stall inception with two-dimensional airfoil data. Rudders are low-aspect ratio wings, and the three-dimensional lift is based on the low-aspect ratio wing theory. The two-dimensional airfoil stall data are obtained from National Advisory Committee for Aeronautics (NACA) reports. The derived theory is first validated with wind tunnel data from foils with a NACA 0015 profile of aspect ratios 1, 2, and 3. The theory is also validated with data from foils with a NACA 0012 profile and an aspect ratio of 2, 3, and 6.
Experimental Study of Air Layer Sustainability for Frictional Drag Reduction
Authors: Jagdish Bhat Nikhil , Xian Brandon Tay Zhi , Kwee Tiaw Joo , Dev Arun Kr.
Published: January 2021

Frictional drag reduction by microbubbles is a promising engineering method for reducing ship fuel consumption, especially for large, slow steaming vessels. Total resistance can be broken down into frictional drag and form drag (also known as pressure drag or profile drag). Ship's hull form optimization is commonly to reduce the form drag of a ship. Another technique would be required to deal with the frictional (viscous) portion of the total resistance. One such technique that reduces the friction resistance is the air lubrication technique. This research looks at possible enhancement for the microbubbles drag reduction technique with the use of hydrophobic plates to trap and retain an air layer. The hydrophobic surface cannot sustain bubbles by itself. Laser-machined microstructure coupled with hydrophobic coatings allows the rapid formation of air layer rapidly and sustainability of the air layer is recorded. With extensive experimental studies, we have shown that an air layer can be entrained around a moving flat plate thereby reducing friction. This could pave the way for applying this technique around the wall of moving ship hulls thereby minimizing the viscous drag and reducing the shipping costs.
Modeling of Finite-span Ram Wings Moving Above Water at Finite Froude Numbers
Authors: Matveev Konstantin I.
Published: January 2021

Power-augmented ram wings can be used for very fast transportation of heavy cargo over water and relatively flat solid surfaces. This article describes a coupled aerohydrodynamic model for a ram wing in steady forward motion. Effects of a finite wingspan and finite Froude numbers are accounted for by the extreme ground effect theory for airflow and a linearized potential flow theory for water. Representative results showing the influence of several variable parameters of the vehicle geometry and operational regimes are demonstrated for a selected ram-wing configuration. The developed method can be applied for modeling of airborne lifting surfaces operating in the strong ground effect on a variety of fast marine craft.
Waterjet Propulsion and Thrust Deduction
Authors: Eslamdoost Arash , Larsson Lars , Bensow Rickard
Published: January 2021

The goal of this article is to describe and investigate the parameters that play a role in the waterjet-hull interaction. In general, these parameters can be split into sinkage, trim, and local flow variation from the bare hull to the self-propelled hull. Each of these parameters has in turn been split into components, which are estimated in relative size. For this purpose, a newly developed method for modeling waterjet-driven vessels is used. Knowing the magnitude of each single parameter separately helps to understand the physics behind the thrust deduction and may aid in the optimization of the hull/propulsor configuration.
Probabilistic Load Combination Factors of Wave and Whipping Bending Moments
Authors: Corak Maro , Parunov Joško , Guedes Soares C.
Published: January 2021

Extreme values of wave and whipping bending moments are important in structural design of large containerships. Since the extreme values of these two, partially correlated processes do not occur at the same time instant and even at the same environmental conditions, it is necessary to combine them by using probabilistic load combination methods. The correlation analysis between wave and whipping bending moments is performed and a practical method for calculation of the most probable load combination factor between considered bending moments is presented. Short-term load combination factors are calculated by reconstruction of the signal from the frequency domain solution. Results are validated by comparison with model test data of the 9400-TEU containership for various sea states and speeds and heading angles. Practical regression equations for estimation of the most probable short-term load combination factor are formulated. Regression equations are then used in the computation of the long-term distribution of combined bending moment. The procedure is demonstrated on the example of the two large containerships.
Numerical and Experimental Studies of Residual Stresses in Multipass Welding of High Strength Shipbuilding Steel
Authors: Fu Guangming , Gurova Tetyana , Lourenco Marcelo I. , Estefen Segen F.
Published: January 2021

The article contributes, through numerical simulation based on models calibrated by experimental results, to better estimate residual stresses and distortions in welded structures representatives of ships and offshore platforms considering welding procedures relevant to shipyard current practices. A multi-pass welding is carried out to investigate the residual stresses in laboratory tests. The temperature at several positions on a plate sample is recorded with thermocouples and residual stresses are measured using an x-ray diffraction technique. Finite element (FE) models are developed in this study and experimentally validated. The three dimensional (3D) moving Goldak's double-ellipsoidal heat source model is employed in the simulations. A Levenberg-Marquardt neural network algorithm is employed to determine the geometric parameters of the heat source model. The technique based on neural network is applied to dimension the heat source later employed in the thermal analysis using 2D FE model to reduce the computer time of the numerical simulation and to make it feasible for shipbuilding industry applications. The numerical results of temperature and residual stress distribution are correlated with the experimental measurements. Finally, the effects of preheat and interpass temperatures on the residual stresses are investigated using numerical simulation. The effects of the transient releasing temperature on the residual stresses are also discussed.
Slamming Kinematics, Impulse and Energy Transfer for Wave-Piercing Catamarans
Authors: Lavroff Jason , Davis Michael Richard
Published: January 2021

Wave slam on high-speed wave-piercing catamarans involves interaction between unsteady hydrodynamics and structural response. For this class of vessel, the period of whipping and the duration of slam loading are similar, and hydroelastic simulation in model testing is important. The high Froude number results in relatively large heave and pitch motions that influence slamming. The model tests carried out were intended to identify the most severe slams possible. Slam loads increase with wave height and forward speed, and peak slam loading was related most clearly to the maximum relative velocity between bow and water surface. The peak load mostly occurred after the time at which the center bow arched cross section would fill with displaced water when calculated on the basis of the hull cross-section movement relative to the encountered wave and before the top of the arch reached the undisturbed surface of the encountered wave. For a 112-m vessel with 2500 tonnes displacement slams in 5.4 m height, regular waves would reach a maximum force of 2115 tonnes weight with a duration of 1.14 seconds and an impulse of 918 tonne seconds. The energy imparted to structural deformation would reach 3.9 MJ at full scale, of which approximately 1.0 MJ would be transferred into structural whipping. The results obtained in these model tests are broadly consistent with the most severe slam loads observed during sea trials.
A Statistical Approach to Ship Fuel Consumption Monitoring
Authors: Bocchetti Dario , Lepore Antonio , Palumbo Biagio , Vitiello Luigi
Published: January 2021

The reduction of the environmental impact imposed by Kyoto Protocol and the growth of competitiveness imposed by the shipping market have urged shipping companies to pay increasing attention to ship energy efficiency improvement and CO2 emission reduction. According to the Ship Energy Efficiency Management Plan (SEEMP) recommended by the International Maritime Organization (IMO), the main scope of this article is in fact to overcome the deterministic limits of the monitoring systems installed in modern ships and support technical management in decision making based on large navigation databases. The proposed statistical approach is founded on a multiple linear regression and allows for both pointwise and interval predictions of the fuel consumption. At the end of each voyage, the model can be used to alert management for a possible change in ship performance in all those situations where the actual fuel consumption lies outside the prediction interval. Moreover, the model can also be utilized to quantify the contribution to the fuel consumption due to the hull and propeller fouling, which is particularly profitable for shipping companies and operators to claim for carbon credits after a specific improvement operation.
LES Applied to Ship Research
Authors: Mahesh Krishnan , Kumar Praveen , Gnanaskandan Aswin , Nitzkorski Zane
Published: January 2021

Numerical simulations using the Reynolds Averaged Navier-Stokes (RANS) methodology have been widely used to study fluid problems in a variety of fields including ship research. Although computationally cheap, RANS fails to predict the fluid behavior accurately in complex flow problems where the underlying physics is dominated by unsteady complex physical phenomena. This paper discusses the use of large eddy simulation (LES) to study such complex flow physics. The predictive capability of LES is demonstrated in three complex flow problems: crashback, cavitation, and hydro-acoustics, which are of particular interest to the ship community. LES results are shown to be in good agreement with experiments for the mean and root mean square values of flow quantities in all these cases.
A Study on Trim Optimization for a Container Ship Based on Effects due to Resistance
Authors: Sun Jianglong , Tu Haiwen , Chen Yongnian , Xie De , Zhou Jiajian
Published: January 2021

The objective of this paper is to perform trim optimization on a 4250-TEU container ship based on the influence of trim on the resistance by using computational fluid dynamics (CFD) in conjunction with towing tank tests. First, the International Towing Tank Conference (ITTC) procedures were applied to uncertainty analysis of CFD and the CFD procedure was further verified and validated through three representative resistance curves obtained by the tests. Next, a series of resistance curves in different conditions with varied drafts and trims were obtained by the CFD computations for the model to provide data source to analyze the influence of the trim on the resistance. Results indicate that the variation of wave-making resistance due to trim dominates that of the total resistance. Finally, the resistance data for the model were converted to the engine power of the real ship. At each speed, the response surface of engine power with respect to drafts and trims was constructed and thus a trim optimization program was developed. The real ship operated under the instruction of the trim optimization program can save energy and reduce emissions significantly.
Escort Tug Performance Prediction Using Computational Fluid Dynamics
Authors: Smoker Brendan , Stockdill Bart , Oshkai Peter
Published: January 2021

In this paper, we outline and validate a computational fluid dynamics (CFD) method for determining the hydrodynamic forces of an escort tug in indirect towing mode. We consider a range of yaw angles from 0° to 90° and a travel speed of 8 knots. We discuss the effects of scaling on prediction of flow separation and hydrodynamic forces acting on the vessel by carrying out CFD studies on both model and full-scale escort tugs performing indirect escort maneuvers. As the escort performance in terms of maximum steering forces is strongly dependent on the onset of flow separation from the hull and skeg of the tug, the model-scale simulations under-predict the maximum steering force by 12% relative to the full-scale simulations. In addition, we provide a method for converting the hydrodynamic forces of the CFD escort study into towline and thrust forces.