bluuebunny/crossref_metadata_2025 huggingface dataset:
Seakeeping Analysis of a High-Speed Monohull With a Motion-Control Bow Hydrofoil
Authors: Sclavounos Paul D. , Borgen Henning
Published: January 2021

The seakeeping performance is studied of a foil-assisted high-speed monohull vessel using a state-of-the-art three-dimensional Rankine panel method. The vessel is equipped with a bow hydrofoil acting as a passive heave and pitch motion-control device in waves. The formulation of the seakeeping of ships equipped with lifting appendages is developed, and the mechanisms responsible for the reduction of the heave and pitch motions of high- speed vessels equipped with hydrofoils are studied. The sensitivity of the heave and pitch motions on the longitudinal position of the hydrofoil is studied. It is found that the most efficient location for the hydrofoil is at the ship bow leading to a 50% reduction of the root mean square values of the heave and pitch motions in a Joint North Sea Wave Project (JONSWAP) spectrum. Several extensions of the analysis of the present paper are discussed. They include the reduction of the roll motion of high-speed vessels, the design of optimal active motion-control mechanisms, and the coupling of the hull form and lifting appendage design for high-speed monohull vessels.
Probabilistic Analysis of Nonlinear Wave Loads on Ships Using Weibull, Generalized Gamma, and Pareto Distributions
Authors: Wang Lihua , Moan Torgeir
Published: January 2021

The statistics of nonlinear wave- induced bending moment in ship hull girders in a short-term period is studied. Systematic probabilistic analysis is performed directly on wave load time histories for different ship types under various sea state and ship speed conditions. The order statistics concept and peak-over-threshold method are used for estimation of the extreme wave loads. The generalized gamma, generalized Pareto, and Weibull distributions are utilized for describing wave load peak values. The three distributions are evaluated and compared with respect to the shape parameters, goodness of fit of the models to the wave load data, and statistical uncertainty in the extreme estimates. Important features of the wave load statistics are also revealed.
Phase-Averaged Particle Tracking Velocimetry Measurements of Propeller Wake
Authors: Lee Sang-Joon , Paik Bu-Geun , Lee Choung Mook
Published: January 2021

The objective of the present paper is to apply an adaptive hybrid two-frame particle tracking velocimetry (PTV) technique for measuring the flow characteristics of turbulent wake behind a marine propeller with five blades. Compared to the conventional particle image velocimetry method, the hybrid PTV technique increases the spatial resolution and measurement accuracy significantly while reducing the computation time. For each of four different blade phases of 0, 18, 36, and 54 deg, 400 instantaneous velocity fields were measured. They were ensemble averaged to investigate the spatial evolution of the propeller wake in the region ranging from the trailing edge to a two propeller diameter (D) downstream location. The phase-averaged mean velocity fields show that the trailing vorticity and the viscous wake are formed by the boundary layers developed on the blade surfaces. The vorticity contours at each phase angle show that the tip vortices are produced periodically. The slipstream contraction occurs in the near-wake region up to about x= 0.5 D downstream. Thereafter the unstable oscillation occurs due to the separation of tip vortex from the wake sheet behind the maximum contraction point. As the tip vortex evolves downstream, its strength is reduced due to turbulent diffusion, viscous dissipation, and active mixing between tip vortices and adjacent wake flow. The technique presented here can be readily extended to investigate the nominal and effective wake distribution as well as the details of the flow field fore and aft of a rotating propeller behind a ship model.
Uncertainty Assessment for Towing Tank Tests With Example for Surface Combatant DTMB Model 5415
Authors: Longo Joe , Stern Fred
Published: January 2021

Uncertainty assessment methodology, procedures, and results are presented for most typical towing tank tests using a 3.048 m geosym of naval combatant DTMB model 5415, which is an established benchmark for computational fluid dynamics validation. The tests include resistance, sinkage and trim, wave profile, wave elevations, and nominal wake. The procedures are summarized and follow International Towing Tank Conference Quality Manual Procedures. The facility and measurement systems are briefly described, and detailed uncertainty assessment examples for each test are provided with descriptions of bias and precision limits and total uncertainties.
Forces Exerted on a Hovercraft by a Moving Pressure Distribution: Robustness of Mathematical Models
Authors: Zilman Gregory
Published: January 2021

The wave resistance, side force, and yawing moment acting on a hovercraft moving on the free surface of a heavy fluid is studied. The hovercraft is represented by a distributed excess pressure. Various types of pressure and bounding contours are considered. The sensitivity of the results to numerous uncertainties in the problem's physical parameters is investigated. It is found that constant pressure over a rectangular region moving with an angle of drift results in peculiar side force values. Several robust mathematical models of a moving hovercraft are proposed and analyzed.
A New Approach to Lifting Line Theory: Hub and Duct Effects
Authors: Mishkevich Victor G.
Published: January 2021

This paper deals with a new approach to lifting line theory in which the presence of a hub and/or duct is taken into account by introducing the generalized induction factors. The proposed mathematical model is built on the assumption that the hub and/or duct are simulated with infinite cylinders. The circulation distribution function is represented in the form of a series of orthogonal Jacobi polynomials that covers all cases that can occur in practical propeller design, including both zero and nonzero gap conditions. The integral equation of the lifting line theory is solved numerically by applying the highest accuracy quadrature formula for singular integrals. Propellers with optimum and arbitrary circulation distribution are considered. The proposed theory is intended to improve design of the near hub and duct blade sections, cavitation control, and integral propeller characteristics. Numerical results are presented for the purpose of comparison with different methods and to illustrate the developed approach.
Ultimate Strength of Stiffened Panels With Cracking Damage Under Axial Compression or Tension
Authors: Paik Jeom Kee , Satish Kumar Y. V.
Published: January 2021

The aim of the present paper is to investigate the ultimate strength characteristics of a longitudinally stiffened panel with cracking damage and under axial compressive or tensile loads. A series of nonlinear finite element analyses are undertaken with varying the size and location of cracking damage. A relevant theoretical model for predicting the ultimate strength of the stiffened panel with cracking damage is studied. The insights and results developed from the present study will be very useful for the ultimate limit state-based risk or reliability assessment of aging steel plated structures with cracking damage.
Simulation of Postwelding Distortion Control of Stiffened Hull Blocks by Line Heating
Authors: Jang Chang Doo , Nomoto Toshiharu , Ko Dae Eun , Ryu Hyun Su , Ha Yun Sok
Published: January 2021

The objective of this study is to develop an analysis method to predict the reduction of welding distortion of stiffened plates by line heating. The equivalent loading method, based on the inherent strain theory, was established to analyze the heat straightening of stiffened plates. The heat input for the analysis was obtained based on experimental temperature variation curves. Temperature distributions during two- line heating process were calculated by two-dimensional heat transfer analysis using the finite element method. The degree of restraints was estimated by combining the experimental data of simple specimen and unit loading analysis. Equivalent loads were obtained by integrating the inherent strains, which were determined from the highest temperature and the degree of restraint. Finally, the equivalent loads obtained were imposed, as applied loads, on the elastic analysis to predict the reduction of welding deformation in stiffened plates. If the basic experiments for several simple cases are carried out, the proposed method can be extended to the analysis of heat straightening of welding distortion of more complicated stiffened plates and ship hull blocks.
A Note on the Bernoulli Equation for Propeller Flows: The Effective Pressure
Authors: Kinnas Spyros A.
Published: January 2021

Steady or unsteady, wetted or cavitating, propeller flows are often treated via inviscid models, at given effective inflow (which accounts for the interaction of the vorticity in the inflow with the propeller). Once the velocity flow field is determined, the pressure distribution on the blades must be determined in order to evaluate forces and sheet cavity patterns. This note revisits the application of the Bernoulli equation to propeller flows. It is found that the concept of effective pressure, that is, a pressure that is different from that in the absence of the propeller, must also be introduced in some cases.
Capsizing Probability Prediction for a Large Passenger Ship in Irregular Beam Wind and Waves: Comparison of Analytical and Numerical Methods
Authors: Paroka D. , Umeda N.
Published: January 2021

This paper presents a comparison of capsizing probability of a large passenger ship using an analytical method and a numerical experiment in beam wind and waves. The analytical method uses Belenky's piece-wise linear approach, and the numerical experiment is based on the Monte Carlo method to realize both fluctuating wind and irregular waves with random phases. The effect of the gustiness is modeled by the Davenport spectrum. The result of the numerical experiment is verified by a two-sided statistical test with a confidence level of 0.05. Outcomes of both methods are compared for various sea states covering extremely severe sea states, severe sea states, and moderate sea states. As a result, it was pointed out that quality of predicted capsizing probability using numerical experiment increases when the number of realizations increase. Poisson process assumption in the analytical method seems to be a breakdown in extremely severe sea states, but it may be applicable in severe sea states, which the current weather criterion assumes. Numerical experiment for capsizing probability could be impractical in moderate sea states.
A Modified Static Equivalency Method for Roll-on/Roll-off Vessels
Authors: Pawlowski Maciej
Published: January 2021

A refined static equivalency method (SEM) for assessing damaged stability is presented, based on the accumulation of water on the vehicle deck of roll-on/roll-off (RO/RO) vessels. For each damage case, a critical water head on the vehicle deck can be calculated that causes the ship to heel statically to a point of no return. This static elevation is compared with the dynamic one, induced by waves, which has been obtained theoretically. This enables in turn the knowledge of the critical sea state, described by significant wave height Hs and calculating the factor s = F(Hs), essential in the new subdivision regulation, based on distribution of sea states at the moment of collision. The critical Hs for each damage case represents the capsizal resistance of damaged RO/RO vessels. The paper explores the theoretical boundary stability curve along with the uncertain zone and shows good agreement with the previous and new experimental results. Based on this analysis, new expressions for the critical relative wave height and critical sea state were derived. Manuscript received at SNAME headquarters April 2003; revised manu-script received December 2005.
Surface Ship Total Resistance Prediction Based on a Nonlinear Free Surface Potential Flow Solver and a Reynolds-Averaged Navier-Stokes Viscous Correction
Authors: Huan James C. , Huang Thomas T.
Published: January 2021

A fast turnaround and an accurate computational fluid dynamics (CFD) approach for ship total resistance prediction is developed. The approach consists of a nonlinear free surface potential flow solver (PShip code) with a wet-or-dry transom stern model, and a Reynolds-averaged Navier-Stokes (RANS) equation solver that solves viscous free surface flow with a prescribed free surface given from the PShip. The prescribed free surface RANS predicts a viscous correction to the pressure resistance (viscous form) and viscous flow field around the hull. The viscous free surface flow solved this way avoids the time-consuming RANS iterations to resolve the free surface profile. The method, however, requires employing a flow characteristic-based nonreflecting boundary condition at the free surface. The approach can predict the components of ship resistance, the associated wave profile around the hull, and the sinkage and trim of the ship. Validation of the approach is presented with Wigley, Series 60 (CB = 0.6), and NSWCCD Model 5415 hulls. An overall accuracy of ±2% for ship total resistance prediction is achieved. The approach is applied to evaluating the effects of a stern flap on a DD 968 model on ship performance. An empirical viscous form resistance formula is also devised for a quick ship total resistance estimate.
A Shell-Element–Based Elastic Analysis Predicting Welding-Induced Distortions for Ship Panels
Authors: Jung Gonghyun
Published: January 2021

A new numerical model, Q-Weld (Edison Welding Institute, Columbus, OH), which is a shell-element-based elastic analysis, is proposed for the prediction of the distortion induced in ship panels. Based on the results of the three-dimensional thermal-elastic-plastic analyses, it was found that the shell element-based model excluding the geometry of fillet welds and including only transverse and longitudinal plastic strains is valid without significant loss of accuracy. The developed Q-Weld predicts well-agreed distortions with the three-dimensional thermal-elastic-plastic analysis and demonstrates its potential in welding-induced distortion analysis, including buckling analysis.
Dynamics of a Ship Steering in Wind Revisited
Authors: Spyrou K. J. , Tigkas I. , Chatzis A.
Published: January 2021

An integrated numerical environment for the exploration and assessment of nonlinear ship dynamics has been developed. The potential is demonstrated through an investigation of controllability of a modern Ro-Pax in steady wind. An improved windloading module is coupled to a standard maneuvering model, and the combination is put through "continuation analysis" in order to determine the branching behavior and specific bifurcations governing system responses. The analysis unveils a complex dynamical structure that dictates the limits of the ship's course-keeping capability. The topology, in state-parameter space of self-excited yawing in head wind, the occurrence of which had been established from earlier research, is now clarified. Interesting interactions between stationary and periodic responses are reported. The effectiveness of active control in removing undesirable responses is also part of the analysis.
Reynolds-Averaged Navier-Stokes Simulations for High-Speed Wigley Hull in Deep and Shallow Water
Authors: Sakamoto Nobuaki , Wilson Robert Vance , Stern Frederick
Published: January 2021

Reynolds-averaged Navier-Stokes simulations and verification and validation studies for a high-speed Wigley hull in deep and shallow water are presented using CFD-SHIP-IOWA Version 4.00, which is a general-purpose ship hydrodynamics computational fluid dynamics code: single-phase level set free surface and k-w turbulence modeling; higher-order conservative discretization, embedded overset grids, advanced iterative solvers, and implicit coupling flow field and predicted motions numerical methods; and high-performance computing for message-passing interface (MPI)-based domain decomposition. The results are presented for low to high speed and deep to shallow water. The investigation is exploratory in nature using an idealized geometry and relatively coarse grids. Based on the verification and validation results, modifications for increased grid resolution at the bow for high speed and improved grid orthogonality for shallow water are made to obtain better solutions. The flow physics observations provide both integral and differential views of the highspeed and shallow-water flow fields, including resistance, pressure variation, wave pattern, boundary layer, and vortices.
Steady Flow Approximations in Three-Dimensional Ship Motion Calculation
Authors: Kim Booki , Shin Yung-Sup
Published: January 2021

When a ship advances at constant speed in waves, the steady flow interacts with the unsteady wave field generated by the ship's motion. The interaction between the steady flow and the unsteady wave field appears in so-called mj terms. The three different steady flow models, that is, free stream, double body flow, and steady wave flow, are considered for the realization of the mj terms. For completeness in a linear sense, the steady flow contributions are retained in a consistent manner in the expressions for the hydrodynamic and restoring forces, which can be derived from the integration of the linearized pressure over the mean wetted part of the hull surface. The steady trim and sinkage are also considered important in determining the mean wetted position. The numerical results are obtained using a three-dimensional panel method based on a translating and pulsating Green function approach. An efficient numerical method is applied for the accurate evaluation of the mj terms without deriving the second derivatives of the Green function. Numerical calculations have been made for a submerged sphere and a Wigley hull. It is found that the steady flow has strong influence on added masses and damping forces in heave and pitch at relatively low encounter frequencies, while its effect is not observed as significant in wave exciting forces. The importance of the steady flow effect is also pronounced in the peak values of heave and pitch motion responses. In comparison with semiana-lytical and experimental results, the double body and steady wave flows are found to be the proper choices for the steady flow approximation.
A Nonlinear Analysis Formulation for Bend Stiffeners
Authors: Vaz M. A. , de Lemos C. A. D. , Caire M.
Published: January 2021

Bend stiffeners are polymeric structures with a conical shape designed to limit the curvature of flexible risers and umbilical cables at their uppermost connections, protecting them against overbending and from accumulation of fatigue damage. Thus, they are of vital importance to deep water oil and gas production systems. This work develops a mathematical formulation and a numerical solution procedure for the geometrical and material nonlinear analysis of the riser/bend stiffener system considered as a beam bending model. The structures are separately modeled, which allows the numerical calculation of the contact force along the system arc length. The governing differential equations are derived considering geometrical compatibility, equilibrium of forces and moments, and nonlinear asymmetric material constitutive relations, which leads to a shift in the neutral axis position from the cross-section centroid. The eccentricity and the bending moment versus curvature relation for each cross section are numerically calculated and then expressed by a polynomial power series expansion. A set of four first-order nonlinear ordinary differential equations is written and four boundary conditions are specified at both ends. Once the global problem is solved, the contact force may be promptly calculated. A finite difference method is implemented in Fortran code to obtain the numerical solution. A case study is carried out where linear elastic symmetric and nonlinear elastic asymmetric constitutive models are compared and discussed. The results are presented for the riser/bend stiffener deflected configuration, angle, curvature, and contact force distribution. The results demonstrate that an accurate structural analysis of bend stiffeners depends on a precise assessment of the nonlinear asymmetric polyurethane property.
The Simulation of Ship Motions Using a B-Spline–Based Panel Method in Time Domain
Authors: Datta Ranadev , Sen Debabrata
Published: January 2021

In this paper, a B-spline-based higher-order method is developed for simulating three-dimensional ship motions with forward speed. The problem is formulated in time domain using a transient free surface Green function. The body geometry is defined by open uniform or nonuniform B-spline basis functions depending on the hull type, whereas the unknown field variables are described by open uniform B-spline basis functions. The collocation method is applied to discretize the integral equation and then solved for the unknown potentials and source strengths. Motion computations in head waves are carried out for three types of ship hulls: a mathematically defined Wigley hull, a typical containership (S175 hull), and a Series 60 hull. Results are obtained for regular and irregular waves and compared with available experimental and computational results. It is found that the results from the present method are in very good agreement with the published results, and in particular with experimental data. Long-duration simulations have also been carried out with an ordinary desktop PC (PIV with 512 MB RAM) to demonstrate the ability of the method to simulate motions over long periods without any visible deterioration using only modest computational resources.
High-Performance Partially Cavitating Hydrofoils
Authors: Kopriva Jim E. , Amromin Eduard L. , Arndt Roger E. A. , Wosnik Martin , Kovinskaya Svetlana
Published: January 2021

Partial cavitation reduces hydrofoil wetted area and friction, but usually with a significant drag penalty associated with unsteady cavity dynamics. A design concept for a high-performance partially cavitating hydrofoil that centers on the suppression of these oscillations by tuning the local pressure gradient in the region of cavity closure is described. The design algorithm is based on ideal fluid theory. An example of this design is the OK-2003 hydrofoil, which is derived from the NACA-0015 geometry. The concept is verified through water tunnel experiments. It is found that under partial cavitation, a two-dimensional hydrofoil exhibits up to a 100% increase in the lift-to-drag ratio compared to its noncavitating conditions. The substantial increase in this ratio relative to the ratio exhibited by the initial NACA-0015 hydrofoil remains significant within a 3 deg range of angle of attack and under a variation of cavitation number of about ±0.2. It was also found that this new hydrofoil design reduces hydrodynamic force pulsations under partially cavitating conditions to operational levels typical of noncavitating flow. In order to further verify the design benefits, the effects of cross flow have been studied with a swept hydrofoil of the same cross section. It was found that outstanding performance of the designed cavitating hydrofoil is retained with 15 deg sweep.
Computational Fluid Dynamics Validation for a Fin/Bulb/Winglet Keel Configuration
Authors: Werner Sofia , Pistidda Alessio , Larsson Lars , Regnstrom Björn
Published: January 2021

A wind tunnel test of an America's Cup keel model is used for validation of one Reynolds-averaged Navier Stokes (RANS) code and one potential flow/boundary layer code. The effects of grid size, stagnation point anomaly, and turbulence model on the RANS results are discussed. Various setups of the potential code are compared. The ability of both methods to predict forces and trends are shown. The errors of the RANS code are slightly larger than the experimental error, whereas the potential flow/boundary layer results are within the experimental uncertainty, provided that a correct panelization is used. A comparison of the experimental wake flow pattern to the one computed with RANS is presented. The k-w turbulence model is shown to give the best predictions of the wake.
Output-Only Analysis for Modal Parameters Estimation of an Elastically Scaled Ship
Authors: Coppotelli Giuliano , Dessi Daniele , Mariani Riccardo , Rimondi Marcello
Published: January 2021

The study of the ship structural response assumes an increasing importance as soon as the structures, characterized by much more lightness, are designed and built for faster vessels. This requisite implies a greater flexibility of the structures themselves, the elastic response of which has to be evaluated with accuracy in order to predict the dynamic behavior. In the present paper, a methodology for the identification of the modal parameters from the measurement of only the responses of a vibrating structure has been developed and applied to an elastically scaled model. This output-only technique is successfully applied to the segmented model of a real ship towed in the INSEAN linear basin. The broadband random excitation, provided by the loads exerted by an irregular sea pattern, induces a stochastic response of the model, which is monitored with accelerometers. The obtained results not only outline the parametric dependence of the modal properties on the ship speed, but also suggest a possible practical application of this technique for on-board structural monitoring and fatigue-life prediction.
Analysis and Prediction of Slamming-Induced Loads of a High-Speed Monohull in Regular Waves
Authors: Dessi Daniele , Mariani Riccardo
Published: January 2021

In recent years, an important trend in the shipbuilding industry has been the increase in the length and speed of high-speed crafts, thus demanding lighter structures. High-speed vehicles with their increased flexibility are more likely to be excited by impulsive loads, such as slamming, which has been extensively studied and discussed by the scientific community. Nevertheless, ship design still demands plain and reliable procedures (numerical and/or experimental) to evaluate the time-dependent global loads in structural dynamics. In this paper, the aim is to explore the possibility of combining the conservation of fluid momentum with the two-dimensional numerical estimation of the effective wetted length in order to improve the prediction of the impact loads without losing the simplicity and efficiency of analytical methods. In order to evaluate the prediction capability of the proposed formulation, the numerical computation of the slamming force is based on processing the model test data relative to the incoming waves and rigid-body motion, and the attained results are compared with the hydrodynamic force experimentally identified. The presented analysis is applied to the slamming tests in regular head waves of a segmented model, supported by an elastically scaled beam, of a fast ferry. By using the slamming load obtained with the theoretical model, the elastic response in terms of bending moments is computed and compared with that provided by direct measurement with strain gauges. Finally, the uncertainty analysis relative to both numerical and experimental results is performed.
Structural Reliability Analysis of Composite Advanced Sail for Virginia Class Submarine
Authors: Eamon Christopher D. , Rais-Rohani Masoud
Published: January 2021

A structural reliability model is developed for a large composite submarine sail structure. Random variables include material strength and stiffness properties as well as load. Limit states are formulated in terms of material strength parameters and buckling resistance. A series system reliability model that bases structural performance on first component failure is used. A total of 205 random variables and 117 limit states compose the structural system model. Most component reliability indices ranged from 3 to 7, with overall system failure governed by material in-plane shear with a reliability index of 1.84. A probabilistic sensitivity analysis determined that load and material strength were the most significant random variables, while material stiffness parameters were unimportant. Significant computational effort was saved by reducing the number of random variables to the most influential set. The effects of correlation and random variable probability distribution were explored. It was found that correlation has little effect on results, but probability distribution is significant. Recommendations are made to improve performance.
The Taming of the Shrew: Tailoring Freak Wave Sequences for Seakeeping Tests
Authors: Clauss Günther F.
Published: January 2021

If you want to build a ship, don't drum up people together to collect woodand don't assign them tasks and work but rather teach them to long for the endless immensity of the sea.___Antoine de Saint-Exupery (1900–1944)___The basic law of the seaway is the apparent lack of any law.___Lord Rayleigh___Based on the wave focusing technique for the generation of task-related wave packets, a new technique is proposed for the synthesization of tailored design wave sequences in extreme seas. The physical wave field is fitted to predetermined global and local target characteristics designed in terms of significant wave height, peak period, as well as wave height, crest height, and period of individual waves. The generation procedure is based on two steps: First, a linear approximation of the desired wave train is computed by a sequential quadratic programming method that optimizes an initially random phase spectrum for a given variance spectrum. The wave board motion derived from this initial guess serves as a starting point for directly fitting the physical wave train to the target parameters. The subplex method is applied to improve systematically a certain time frame of the wave board motion, which is responsible for the evolution of the response-related design wave sequence. The discrete wavelet transform is introduced to reduce significantly the number of free variables to be considered in the fitting process. Wavelet analysis allows the efficient localization of the relevant information on the electrical control signal of the wave maker in time and frequency domain. As the presented technique permits the deterministic generation of design rogue wave sequences in extreme seas, it is well suited for investigating the mechanism of arbitrary wave-structure interactions, including capsizing, slamming, and green water as well as other survivability design aspects. Even worst case wave sequences, such as the Draupner New Year wave, can be modeled in the wave tank to analyze the evolution of these events and to evaluate the response of offshore structures under abnormal conditions. This procedure is illustrated by investigations of an offshore lift operation, of the behavior of a semisubmersible and an FPSO in tailored freak waves as well as the analysis of ship capsizing in deterministic wave sequences at selected target positions.
Study on the Operating Process of an Underwater Diesel Engine
Authors: Cui Yi , Zhu Yilun , Deng Kangyao
Published: January 2021

A steady state and transient simulation model for an underwater diesel engine system, including governor, diesel engine, and pipe systems after turbine, is developed and verified. A two-phase flow of exhaust gas and water at the tail pipe is studied with three-dimensional fluid dynamics calculation. A water flooding criterion for an underwater engine is also given by these models and related experiments. Safe operation ranges of the engine are also studied. The histories of relative engine speed, pressure, and Froude number of the tail pipe exhaust gas under starting and stopping processes are studied. The Froude number of the tail pipe exhaust gas is an oscillating phenomena when the engine is starting, which is likely to cause sea water to flow backward into the tail pipe. The opening of the tongue valve must be controlled according to engine back pressure during the stopping process to prevent sea water flooding on the one hand and high back pressure on the other. The underwater diesel engine operating control strategy can be given on the basis of the research work.
Leonhard Euler and the Theory of Ships
Authors: Nowacki Horst
Published: January 2021

On April 15, 2007, the scientific world commemorated Leonhard Euler's 300th birthday. Euler's eminent work has become famous in many fields: mathematics, mechanics, optics, acoustics, astronomy, and geodesy, even in the theory of music. This article will recall his no less distinguished contributions to the founding of the modern theory of ships. These are not so widely known to the general professional public. In laying these foundations in ship theory, as in other fields, Euler was seeking "first principles, generality, order and above all clarity." This article will highlight those achievements for which we owe him our gratitude. There is no doubt that Leonhard Euler was one of the founders of the modern theory of ships. He raised many fundamental questions for the first time and through all phases of his professional lifetime devoted himself to subjects of ship theory. Thereby he gave a unique profile to this still nascent scientific discipline. Many of his approaches have been of lasting, incisive influence on the structure of this field. Some of his ideas have become so much a matter of routine today that we have forgotten their descent from Euler. This article will synoptically review Euler's contributions to the foundation of this discipline, will correlate them with the stages of Euler's own scientific development, embedded in the rich environment of scientific enlightenment in the 18th century, and will appreciate the value of his lasting aftereffects until today. The same example will serve to recognize the fertile field of tension always existing between Euler's fundamental orientation and his desire to make contributions to practical applications, which has remained characteristic of ship theory to the present day. Without claiming completeness in detail, this article aims at giving a coherent overview of Euler's approaches and objectives in this discipline. This synopsis will be presented primarily from the viewpoint of engineering science in its current stage of development.
Experiments of Two-Dimensional Transom Stern Flow
Authors: Maki Kevin J. , Troesch Armin W. , Beck Robert F.
Published: January 2021

Measurements of the free-surface behind a backward facing step are made using laser-induced fluorescence and a digital video camera. Tests are conducted for two Reynolds numbers and a range of Froude numbers. An edge detection algorithm is used to locate the free surface from the digital images, and the ensemble of images are used to calculate the mean and root mean square of the elevation. The results of amplitude, length, and steepness are determined from the mean profiles and compared to existing potential flow theories. It is found that the potential flow theories overpredict the real-fluid measured mean-wave amplitude. The experimentally determined wavelength is much shorter than the nominal length, and an existing stream function theory is implemented to explain how the viscous wake acts to shorten the steady wavelength.
An Experimental Examination of the 2D+T Approximation
Authors: Shakeri Mostafa , Maxeiner Eric , Fu Thomas , Duncan James H.
Published: January 2021

Measurements of contact line height and longitudinal wave profiles from experiments with a three-dimensional naval ship model and experiments using a 2D+T wave maker with motions approximating the three-dimensional hull form are compared. The shape and maximum height of the contact line in the bow region are nearly the same in the two experiments, and the distance downstream along the hull over which the two measurements agree increases with increasing Froude number, Fn = Um/√gLm, where Um is the ship model speed, g is the acceleration of gravity, and Lm is the ship model waterline length. The comparison of the longitudinal wave profile (wave cut) data from the two experiments shows fairly good agreement for wavelengths and amplitudes at the highest Froude number and the measurement position closest to the hull.
Heat Insulation Performance of Marine Structures
Authors: Lee Jen-Chieh , Chang Song-Kuo
Published: January 2021

The performance of heat insulation of marine structures is investigated using numerical simulation, Eurocode's formula calculation, and experimental measurement. Two popular fire protection materials of rock wool 60k (60 kg/m3) and ceramic fiber 80k (80 kg/m3) are chosen to show the requisite minimum thickness for marine structures to meet the regulation of IMO heat insulation A-class. Compared with the results of Eurocode's formula calculation and experimental measurement, the effectiveness of the heat insulation performance of marine structures, predicted from numerical simulation, can be demonstrated. The numerical simulation shows that the heat insulation performance of marine structures with fire protection material of ceramic fiber (25 mm) or rock wool (50 mm) meets the requirement of A-30 class. Though there is an obvious difference between the results from numerical simulation and experimental measurement during heating process, the fire protection materials combined with ceramic fiber (25 mm) and rock wool (25 mm) and under the condition of the ceramic fiber exposed to fire can still satisfy the requirement of a heat insulated A-60 class bulkhead.
Hydrostatic Stability of Compartmented Structures Supported by Air Cushions
Authors: Thiagarajan Krish P.
Published: January 2021

This paper presents theoretical formulations to evaluate the restoring moment of structures supported by air cushions at zero forward speed. The air cushion is assumed to be enclosed within a number of compartments that are open to sea. The height of the water plug within the compartments is thus an important parameter. The theory, developed from first principles, is verified against data from inclining experiments conducted on a nine-compartment air cushion supported structure at different drafts and water plug heights. The theory shows that the air cushion affects the stability in two conflicting ways: favorable decrease in the vertical center of gravity caused by the water plug effect and unfavorable enhancement of the internal free surface effect. The net effect on stability depends on the operating conditions as well as on the scale of the structure being considered. A correction factor for the metacentric height incorporating the air cushion effects is proposed.
Naval Ship Structures Exposed to Rocket Thermal and Pressure Loads
Authors: Mascia Donatella , Tuveri Maria L.
Published: January 2021

Effects of rocket launch on a naval ship structures located near a rocket gun are studied. Using a finite element thermal analysis, the temperatures along the thickness are determined and then applied to the structure to investigate the thermal stresses distribution. Stresses caused by time/space dependent pressure loads are investigated as well, using transient structural analysis.
A Direct Measurement of Wave Resistance by the Measurement of Wave Height on a Surface Patch
Authors: çalisal Sander M. , Sireli Mete E. , Tan Jeff
Published: January 2021

This paper explains a new procedure for the direct measurement of wave resistance from the measurement of ship-wave height on a patch of surface water near the hull. The optical instrumentation used and the newly developed method for numerical calculations are explained. Internal consistency tests and a comparison with well-known longitudinal wave height cut methods, LCM, are provided. This numerical procedure does not require any truncation correction and uses all of the data collected by an optical system described in the paper. This procedure could be more attractive to narrower tanks, as the requirement for tank beam to model length ratio for successful truncation correction b/L > 5 is removed. This formulation can also be used in connection with data collected by a series of wave probe records.
Model-and Full-Scale URANS Simulations of Athena Resistance, Powering, Seakeeping, and 5415 Maneuvering
Authors: Bhushan Shanti , Xing Tao , Carrica Pablo , Stern Frederick
Published: January 2021

This study demonstrates the versatility of a two-point, multilayer wall function in computing model-and full-scale ship flows with wall roughness and pressure gradient effects. The wall-function model is validated for smooth flat-plate flows at Reynolds numbers up to 109, and it is applied to the Athena R/V for resistance, propulsion, and seakeeping calculations and to fully appended DTMB 5415 for a maneuvering simulation. Resistance predictions for Athena bare hull with skeg at the model scale compare well with the near-wall turbulence model results and experimental fluid dynamics (EFD) data. For full-scale simulations, frictional resistance coefficient predictions using smooth wall are in good agreement with the International Towing Tank Conference (ITTC) line. Rough-wall simulations show higher frictional and total resistance coefficients, where the former is found to be in good agreement with the ITTC correlation allowance. Self-propelled simulations for the fully appended Athena performed at full scale using rough-wall conditions compare well with full-scale data extrapolated from model-scale measurements using the ITTC ship-model correlation line including a correlation allowance. Full-scale computations are performed for the towed fully appended Athena free to sink and trim and the boundary layer and wake profiles are compared with full-scale EFD data. Rough-wall results are found to be in better agree-ment with the EFD data than the smooth-wall results. Seakeeping calculations are performed for the demonstration purpose at both model-and full-scale. Maneuvering calculation shows slightly more efficient rudder action, lower heading angle overshoots, and lower roll damping for full-scale than shown by the model scale.
Efficient Method Based on Optimization and Simulation for the Probabilistic Strength Computation of the Ship Hull
Authors: Okasha Nader M. , Frangopol Dan M.
Published: January 2021

The accurate computation of the strength of a ship hull is vital for ensuring its reliability. Taking into account the uncertainties in the material properties and fabrication details requires a probabilistic approach for the determination of the strength of the ship hull. This study proposes an efficient approach for the determination of the probabilistic strength of the ship hull. First, a novel deterministic method for the fast and accurate calculation of the strength of the ship hull is presented. In this method, stresses in the hull section are determined using the constitutive models of the stiffened panels. These models take into account the various possible failure modes and initial imperfections. The ultimate strength is found by an optimization search algorithm. The method is shown to be as accurate as the rigorous incremental curvature method but with significantly less computational time. The method is then applied with a Latin-hypercube sampling simulation, and the output sample is tested against several potential distributions. The best-fit probability distribution of the ultimate strength of the ship hull is provided.
Analytical bow waves for fine ship bows with rake and flare
Authors: Noblesse Francis , Delhommeau Gérard , Queutey Patrick , Yang Chi , Kim Hyun Yul
Published: January 2021

The bow wave generated by a steadily advancing ship is considered for a family of fine ruled ship bows with rake and flare. This family of ship bows is defined in terms of four parameters: the ship draft D, the entrance angles a and a' at the top and bottom waterlines, and the rake angle 8. The corresponding bow wave similarly depends on four parameters: the draft-based Froude number F and the three angles a, a', and 8. An extensive parametric study, based on thin-ship theory, is performed to explore the variations of the water height Z0 at the ship stem X = 0, the location X0 (measured from the ship stem) of the intersection of the bow-wave profile with the mean free-surface plane Z = 0, and the bow-wave profile, with respect to the four parameters F, a, a', and 8. This parametric study extends the previously reported similar study of the height Zb of the bow wave and the location Xb of the bow-wave crest. These two complementary parametric studies yield simple analytical relations, which extend relations given previously for wedge-shaped ship bows without rake or flare. In spite of their remarkable simplicity, the analytical relations given here yield bow waves that are comparable to computational fluid dynamics (CFD) waves given by Euler-flow calculations. The analytical relations, which explicitly account for the influence of the four primary parameters F, a, a', and 8, can be used immediately—without hydrodynamic calculations—for ship design, notably at early design stages when the precise hull geometry is not yet known. The study also provides insight for ship bow design. Specifically, it suggests that a bow with positive rake and negative flare may be beneficial, and that a bulb located aft of the stem and integrated with the hull may be an advantageous alternative to a traditional bulb protruding ahead of the bow, in agreement with the results of a hull-form optimization analysis.
Investigation of Twin-Screw Naval Ships Maneuverability Behavior
Authors: Di Mascio Andrea , Dubbioso Giulio , Notaro Chiara , Viviani Michele
Published: January 2021

The problem of ship maneuverability has currently reached a significant consideration, both for merchant ships, with the adoption of IMO standards, and naval ships, with the production of various documents by NATO Specialist Teams. In literature, many works regarding maneuverability of single-screw slow/medium speed ships are present, while a lack of information about twin-screw ships (cruise ships, Ro/Ro ferries, mega yachts, naval vessels) exists. These ships are usually characterized by different hull forms and more complex stern configuration because of the presence of appendages such as kegs, shaft lines, and brackets, which can strongly affect maneuverability behavior. In this work various prediction methods, namely statistical regressions, system identification, and RANSE, are investigated to evaluate twin-screw naval vessels maneuverability behavior. Results of this analysis clearly evidence importance of stern appendages influence on maneuverability capabilities of this type of ship (including also nonlinear effects resulting from hull/appendage interactions).