bluuebunny/crossref_metadata_2025 huggingface dataset:
Comparative and Uncertainty Assessment of Design Criteria for Stiffened Panels
Authors: Assakkaf Ibrahim A. , Ayyub Bilal M.
Published: January 2021

Stiffened and gross steel panels (plates) are very important components in ship and offshore structures, and therefore they should be designed for a set of failure modes that govern their strength. They form the backbone of most ships' structure, and they are by far the most commonly used element in a ship. They can be found in bottom structures, decks, side shell, and superstructures. To evaluate the strength of a stiffened or gross panel element, it is necessary to review various strength-predicting models and to study their biases, applicability, and limitations for different loading conditions acting on the element. In this paper, strength limit states for various failure modes of ship panels are presented. For each limit state, commonly used strength models were collected from many sources for evaluating their limitations and applicability and to study their biases and uncertainties. Wherever possible, the different types of biases resulting from these models were computed. The bias and uncertainty analyses for these strength models are needed for the development of load and resistance factor design (LRFD) rules for stiffened and gross panels of ship structures. The uncertainty and biases of these models were assessed and evaluated by comparing their predictions with ones that are more accurate or real values. The objective of this paper is to summarize strength prediction models of stiffened and gross panels that are suitable for LRFD development for ship structures. Monte Carlo simulation was used to assess the biases and uncertainties for these models. Recommendations for the use of the models and their biases in LRFD development are provided.
High-Speed Trimaran Drag: Numerical Analysis and Model Tests
Authors: Mizine Igor , Amromin Eduard , Crook Leonard , Day William , Korpus Richard
Published: January 2021

A numerical technique for high-speed trimaran resistance calculation is developed. The technique is based on the modified viscous-inviscid interaction concept and quasi-linear theory of wave resistance (Amromin et al 1984). The key element of this technique, which is called modified quasi-linear theory (MQLT), is an account of Froude number influence on the ship trim, transom drag, and wetted surface. This influence leads to appearance of a drag component that significantly depends on both Reynolds number and Froude number. This component has been traditionally included in residuary drag in the model test data. The presented preliminary numerical results were obtained with simplifications of the boundary layer theory that are acceptable for slender hulls. Calculated drag is in sufficient accordance with results of model tests. The MQLT computations of boundary layers are also compared with the Reynolds averaged Navier-Stokes (RANS) calculations(one-equation turbulence model by Spalart and Allmaras 1992) at model and ship scale Reynolds numbers. An analysis of the model-ship scale correlation factor for high-speed slender hulls with transom sterns and diverse mutual position of the trimaran hulls is done.
Influence of Whipping on Long-term Vertical Bending Moment
Authors: Baarholm Gro Sagli , Jensen Jørgen Juncher
Published: January 2021

This paper is concerned with estimating the response value corresponding to a long return period, say 20 years. Time domain simulation is required to obtain the nonlinear response, and long time series are required to limit the statistical uncertainty in the simulations. It is crucial to introduce ways to improve the efficiency in the calculation. A method to determine the long-term extremes by considering only a few short-term sea states is applied. Long-term extreme values are estimated using a set of sea states that have a certain probability of occurrence, known as the contour line approach. Effect of whipping is included by assuming that the whipping and wave-induced responses are independent, but the effect of correlation of the long-term extreme value is also studied. Numerical calculations are performed using a nonlinear, hydroelastic strip theory as suggested by Xia et al (1998). Results are presented for the S-175 containership (ITTC 1983) in head sea waves. The analysis shows that whipping increases the vertical bending moment and that the correlation is significant.
Computational Fluid Dynamics–Based Optimization of a Surface Combatant
Authors: Tahara Y. , Stern F. , Himeno Y.
Published: January 2021

Computational fluid dynamics (CFD)-based optimization of a surface combatant is presented with the following main objectives:development of a high-performance optimization module for a Reynolds averaged Navier-Stokes (RANS) solver for with-free-surface condition; anddemonstration of the capability of the optimization method for flow- and wave-field optimization of the Model 5415 hull form.

The optimization module is based on extension of successive quadratic programming (SQP) for higher-performance optimization method by introduction of parallel computing architecture, that is, message passing interface (MPI) protocol. It is shown that the present parallel SQP module is nearly m(= 2k+ 1; k is number of design parameters) times faster than conventional SQP, and the computational speed does not depend on the number of design parameters. The RANS solver is CFDSHIP-IOWA, a general-purpose parallel multiblock RANS code based on higher-order upwind finite difference and a projection method for velocity-pressure coupling; it offers the capability of free-surface flow calculation. The focus of the present study is on code development and demonstration of capability, which justifies use of a relatively simple turbulence model, a free-surface model without breaking model, static sinkage and trim, and simplified design constraints and geometry modeling. An overview is given of the high-performance optimization method and CFDSHIP-IOWA, and results are presented for stern optimization for minimization of transom wave field disturbance; sonar dome optimization for minimization of sonar-dome vortices; and bow optimization for minimization of bow wave. In conclusion, the present work has successfully demonstrated the capability of the CFD-based optimization method for flow- and wave-field optimization of the Model 5415 hull form. The present method is very promising and warrants further investigations for computer-aided design (CAD)-based hull form modification methods and more appropriate design constraints.
Global Hydroelastic Response of Catamarans Due to Wetdeck Slamming
Authors: Ge Chunhua , Faltinsen Odd M. , Moan Torgeir
Published: January 2021

Global hydroelastic effects due to wetdeck slamming on a high-speed catamaran with forward speed in regular head sea waves are studied experimentally and theoretically. The elastic response is dominated by a two-node bending mode. Predictions of vertical shear forces, bending moments, and slamming force are in fair agreement. Experimental and theoretical error sources are discussed. An important uncertainty is associated with improper measurements of trim angles. The hydrodynamic model of the side hulls needs to be improved by considering hydrodynamic hull interaction.
A Nonlinear Mathematical Model for Ship Turning Circle Simulation in Waves
Authors: Fang Ming-Chung , Luo Jhih-Hong , Lee Ming-Ling
Published: January 2021

In the paper, a simplified six degrees of freedom mathematical model encompassing calm water maneuvering and traditional seakeeping theories is developed to simulate the ship turning circle test in regular waves. A coordinate system called the horizontal body axes system is used to present equations of maneuvering motion in waves. All corresponding hydrodynamic forces and coefficients for seakeeping are time varying and calculated by strip theory. For simplification, the added mass and damping coefficients are calculated using the constant draft but vary with encounter frequency. The nonlinear mathematical model developed here is successful in simulating the turning circle of a containership in sea trial conditions and can be extended to make the further simulation for the ship maneuvering under control in waves. Manuscript received at SNAME headquarters February 19, 2003; revised manuscript received January 27, 2004.
RANS Maneuvering Simulation of Esso Osaka With Rudder and a Body-Force Propeller
Authors: Simonsen Claus D. , Stern Frederick
Published: January 2021

A simplified potential theory-based infinite-bladed propeller model is coupled with the Reynolds averaged Navier-Stokes (RANS) code CFDSHIP-IOWA to give a model that interactively determines propeller-hull-rudder interaction without requiring detailed modeling of the propeller geometry. Computations are performed for an open-water propeller, for the Series 60 ship sailing straight ahead and for the appended tanker Esso Osaka in different maneuvering conditions. The results are compared with experimental data, and the tanker data are further used to study the interaction among the propeller, hull, and rudder. A comparison between calculated and measured data for the Series 60 ship shows fair agreement, where the computation captures the trends in the flow, that is, the flow structure and the magnitude of the field quantities together with the integral quantities. For the tanker, the flow study reveals a rather complex flow field in the stern region, where the velocity distribution and propeller loading reflect the flow field changes caused by the different maneuvering conditions. The integral quantities, that is, the propeller, hull, and rudder forces, are in fair agreement with experiments. No formal verification and validation are performed, so the present results are related to previous work with verification and validation of the same model, but without the propeller. For the validated cases, the levels of validation are the same as without the propeller, because the validation uncertainties, that is, the combined experimental and simulation uncertainties, are assumed to be the same for both cases. Based on this, validation is obtained for approximately the same cases as for the without-propeller conditions, but the comparison errors, that is, the difference between experiment and calculation, are different. For instance, the difference between computation and experiment for the ship resistance is generally larger with the propeller than without, whereas the opposite is the case for the rudder drag. Summarizing the results, the method shows encouraging results, and taking the effort related to modeling the propeller into account, the method appears to be useful in connection with studies of rudder-propeller-hull related flow problems, where the real propeller geometry cannot be modeled.
Numerical Analysis of the Influence of Above-Water Bow Form on Added Resistance Using Nonlinear Slender Body Theory
Authors: Kihara Hajime , Naito Shigeru , Sueyoshi Makoto
Published: January 2021

A nonlinear numerical method is presented for the prediction of the hydrodynamic forces that act on an oscillating ship with a forward speed in head waves. A "parabolic" approximation of equations called "2.5D" or "2D+T" theory was used in a three-dimensional ship wave problem, and the computation was carried out in the time domain. The nonlinear properties associated with the hydrostatic, hydrodynamic, and Froude-Krylov forces were taken into account in the framework of the slender body theory. This work is an extension of the previous work of Kihara and Naito (1998). The application of this approach to the unsteady wave-making problem of a ship with a real hull form is described. The focus is on the influence of the above-water hull form on the horizontal mean wave force. Comparison with experimental results demonstrates that the method is valid in predicting added resistance. Prediction of added resistance for blunt ships is also shown by example.
Propulsive Performance of a Twin-Rectangular-Foil Propulsor in a Counterphase Oscillation
Authors: Liu Pengfei
Published: January 2021

Analysis of propulsive thrust and efficiency of a finite aspect ratio, twin-foil counter- phase wing-in-ground (WIG) effect propulsor configuration is made using a time- domain panel method. Comparisons were made for the effects of number of foils (single versus double), aspect ratio, variable distance between two foils with fixed heave amplitude—that is, influence of interaction, and heave amplitude with fixed distance. In addition to the apparent advantage of propulsor dynamics equilibrium due to the cancellation of the side and vertical forces, results show that each foil of the twin-foil configuration, when close to each other to generate the WIG effect, has substantially higher thrust contribution than the single-foil propulsor under moderate to heavy load conditions (reduced frequency greater than 0.5). Due to the interaction of foils on each other, increase of thrust also produced a higher efficiency over the whole range of reduced frequencies examined. Findings also include the tendency of the thrust and efficiency due to both the fixed heave amplitude with varied distance between foil equilibrium position and fixed distance with varied heave amplitude. Twin-foil counterphase oscillating propulsors show an aerodynamic and hydrodynamic advantage for micro air vehicles (MAV) and autonomous underwater vehicles (AUV) over the single-foil configuration.
Unsteady Rollup Modeling for Wake-Adapted Propellers Using a Time-Stepping Method
Authors: Politis Gerasimos K.
Published: January 2021

An efficient method for predicting the unsteady wake contraction and rollup of a wake-adapted marine propeller is presented. The method is based on a Morino formulation of the unsteady propeller problem for an observer in an inertia— motionless—coordinate system. Thus, such problems as a propeller in inclined flow or a propeller performing any general motion (for example, heaving) can be directly simulated by the proposed method, as a by-product. The heart of the method is a time-stepping algorithm by which the dynamic evolution of the free wake is calculated in the time domain, satisfying the Helmholtz vortex theorems. The method has been applied to a number of steady and unsteady flow cases, and results are presented, showing that stable rollup wake patterns for a wide range of control parameters can be produced accompanied by good predictions for propeller forces and pressure
Dedication to Professor Touvia Miloh
Authors: Tulin Marshall P.
Published: January 2021

Those of us working in ship hydrodynamics are fortunate that the talents of Touvia Miloh were attracted to problems in our own field. This is evidently the influence of Professor Louis Landweber, his Ph.D. supervisor at the University of Iowa, who had spent half his career at the Taylor Model Basin as well as at Admiral Taylor's Experimental Model Basin at the Washington Naval Yard. Taylor was trained at the turn of the 19th century in Britain by Robert Froude, and Landweber was among the first Americans with decided analytical talent to work in ship hydrodynamics.
Mathematical Techniques for Linear Wave–Structure Interactions
Authors: Evans D. V.
Published: January 2021

It is difficult not to be impressed by the sheer range of Touviah Miloh's research output, and it is all the more remarkable that he has found the time to become a regular contributor to the Water Wave Workshops over many years. Each of his contributions is characterized by the application of powerful mathematical techniques coupled with a keen sense of the underlying physics of the problem under consideration. In the spirit of this approach, this paper offers a review of some of the mathematical techniques that have been employed to tackle a variety of classical linear water-wave problems involving fixed or floating structures, and that have provided analytical or semianalytical solutions capable of useful physical interpretation. It is appropriate at this point to refer to the excellent monograph on the same topic by Chris Linton and Phil McIver (2001), and there is inevitably some overlap in choice of problems and techniques. My choice is a personal one reflecting my own interests, and I would like to apologize in advance to those colleagues whose work is not mentioned in what follows, which is primarily based on contributions from descendants of the Ursell school, which have been so prominent at these Workshops from their inception.
Novel Grey Model for Diesel Engine Oil Monitoring
Authors: Chang Hui-Kuo , Kuo Hsing-Chia , Wang Yen-Zen
Published: January 2021

Electronic sensors and data processing systems are increasingly integrated with mechanical systems for continuous condition monitoring and early warning of pending failure. Various predictive algorithms have been applied to sensor data trends. Traditional grey algorithms have been highly useful for data trend prediction but suffer from serious overshoot at inflection points when applied to fluctuating data curves, that is, curves that cannot be accurately represented by a single grey exponential equation. This paper therefore presents an improved grey model (GM), a two-section residual grey model (2S-RGM), and demonstrates 2S-RGM by applying it to data trends in a marine engine oil quality monitoring system. 2S-RGM constantly evaluates data trends and seeks inflection points at which the curve is broken into separate sections, each being treated by an independent GM. 2S-RGM is tested using two sets of published marine diesel engine oil data, one ferrographic and one spectroscopic. Predictive results of 2S-RGM are compared to results of the same data sets applied to six other well-known predictive methodologies. It is demonstrated that 2S-RGM is significantly more accurate, with the additional benefit of avoiding the setup costs of earlier artificial-intelligence-based GM improvements.
An Approach for Reliability-Based Fatigue Design of Welded Joints on Aluminum High-Speed Vessels
Authors: Collette Matthew , Incecik Atilla
Published: January 2021

Fatigue cracks are an ongoing problem for aluminum high-speed vessels, and preventing fatigue cracks caused by wave loading is expected to be a significant challenge for future aluminum high-speed ferries and military vessels. To aid in this effort, a hot-spot fatigue design approach using first-order reliability methods (FORM) is constructed. Two different limit state functions are investigated, and the accuracy and consistency of the FORM method for the highly nonlinear fatigue limit state equations are evaluated through a comparison with Monte Carlo simulation results. The sensitivity of the resulting safety index to changes in the input variables, and their uncertainties, are presented graphically. The method is compared to existing design standards for four simple structural details.
Parametric Identification for Nonlinear Ship Maneuvering
Authors: Bhattacharyya S. K. , Haddara M. R.
Published: January 2021

A parametric identification method for the estimation of hydrodynamic derivatives embedded in the nonlinear steering equations for ship maneuvering in calm seas is presented. The models developed for identification involve determination of constant, "low-frequency" hydrodynamic derivatives. The method is robust, noniterative, and computationally light, and it requires no starting estimates. In this method, the time domain operations are converted to linear operations in the frequency domain. The responses of the ship in a few standard maneuvers have been simulated in the numerical examples, and the proposed method is applied to these data in order to estimate the hydrodynamic derivatives for a few "identifiable" combinations.
Large-Eddy Simulation of Spatially Developing Turbulent Wake Flows
Authors: Shi Shaoping , Celik Ismail , Smirnov Andrei , Yavuz Ibrahim
Published: January 2021

The feasibility of applying the large-eddy simulation (LES) technique in complex high Reynolds number flows has been studied. The focus of the study is on the spatially developing wake flows with an application to ship wakes. The bluff body that generates the wake is excluded from the computational domain. To make this possible, a new random flow generation technique (RFG) is used to provide the turbulent inflow boundary conditions as a function of time. The technique provides an instantaneous velocity field at the inlet boundary in conjunction with the prescribed mean flow field obtained either from RANS (Reynolds averaged Navier-Stokes) simulations or from experimental data. The combined LES-RFG procedure has been validated in previous publications in cases of a flat plate and a mixing layer. At the inflow boundary, turbulence characteristics, including the shear stresses, were reconstructed. The time averaged results showed good agreement with the experiments in the developing wake. The same procedure is used to simulate a ship wake (ship model DTMB 5512) in the near field of 1.5 ship cord length. The LES technique captured both spatial and temporal development of the large coherent structures that play an important role in the evaluation of bubble concentration in the ship wakes. These structures are usually smeared out in RANS simulations.
Design Sensitivity Analysis and Topology Optimization Method Applied to Stiffener Layout in Hull Structures
Authors: Ha Yoondo , Kim Woojong , Cho Seonho
Published: January 2021

A continuum-based design sensitivity analysis (DSA) method is developed for threedimensional Mindlin plate structures. The first-order variations of energy form, load form, and structural responses with respect to nonshape design variables are derived. An adjoint variable method is employed because of its computational efficiency, especially with respect to problems where there are many design variables but only a few performance measures. The developed DSA method is utilized with the topology optimization method by using a density approach, which yields an optimal structural layout for the required structural performances. For the numerical implementation, a finite element method, the developed DSA method, and a gradient-based topology optimization method are integrated into a unified and automated framework. The developed topology optimization method is applied to the numerical models of stringer and cargo hold to find the optimal layout of stiffeners. Comparing the existing and optimal designs, significant improvements in the displacement and Von Mises stress distributions are observed. The results show that the topology optimization method can be used as a useful tool for determining a suitable layout of stiffeners in the early stage of hull structural design.
Development of a Multifactor Regression Model of Ship Maneuvering Forces Based on Optimized Captive-Model Tests
Authors: Sutulo S. , Soares C. Guedes
Published: January 2021

The paper provides the results of model tests planned with an optimized experimental design method. Captive-model tests have been carried out according to such a design on a computerized planar-motion carriage with a model of a fast catamaran with five varying factors (drift angle, rate-of-yaw amplitude, sinkage, trim and heel angles) and with all six force/moment components measured at each run. The measured values were used after preprocessing for construction of polynomial regression models for all force components acting upon the catamaran's hulls. It is demonstrated that the optimized experimental design method allows rather complicated mathematical models for maneuvering hydrodynamics forces to be obtained from captive model tests at a reasonable level of effort.
Simple Analytical Expressions for the Height, Location, and Steepness of a Ship Bow Wave
Authors: Noblesse Francis , Hendrix Dane , Faul Lisa , Slutsky Jonathan
Published: January 2021

Dimensional analysis and other fundamental theoretical considerations (thin-ship limit, shallow-draft and deep-draft limits) are used, with bow-wave measurements for six wedge-shaped hull forms, to obtain simple analytical expressions that explicitly define the height, location, and steepness of the bow wave generated by a ship in terms of the ship speed, draft, and waterline entrance angle. These simple analytical expressions are in excellent agreement with the available experimental measurements for six wedge-shaped hull forms. Good agreement is also obtained for other ship-bow forms, especially if a simple procedure—illustrated for the Wigley hull and the Series 60 model—is used to define an effective ship draft and an effective waterline entrance angle.
Complete Identification of the Roll Equation Using the Stationary Random Roll Response
Authors: Haddara Mahmoud R.
Published: January 2021

A method is developed to predict the time series of the wave exciting moment per unit virtual mass moment of inertia using the stationary random roll response. The estimated variance and autocorrelation function of the excitation are compared with those obtained using numerically generated data. The agreement is excellent. The method was also applied to experimental data obtained using two ship models. The predicted autocorrelation function for the excitation was compared with the autocorrelation function of the wave height. The method predicts the form of the autocorrelation function accurately. The method lends itself to use aboard ships at sea without interrupting the mission of the ship. Results of this analysis can help in planning optimum ship routing.
Prediction of Sheet Cavitation on a Rudder Subject to Propeller Flow
Authors: Kinnas Spyros A. , Lee Hanseong , Gu Hua , Natarajan Shreenaath
Published: January 2021

This paper presents two numerical methods, a vortex lattice method (MPUF-3A) coupled with a finite volume method (GBFLOW-3D) and a boundary element method (PROPCAV), which are applied to predict time-averaged sheet cavitation on rudders, including the effects of the propeller as well as of the tunnel walls. The coupled MPUF-3A and GBFLOW-3D determines the velocity field due to the propeller within the fluid domain bounded by tunnel walls. MPUF-3A solves the potential flow around the propeller by distributing the line vortices and sources on the blade mean camber surface and determines the pressure distributions on the blade surface. GBFLOW-3D solves Euler equations with the body force terms converted from the pressure distributions on the blade surface and determines the total velocity field inside the fluid domain. The tunnel walls are treated as a solid boundary by applying the slip boundary condition, and the propeller blades are modeled via body forces. The two methods are solved iteratively until the forces on the blade converge. The cavity prediction on the rudder is accomplished via PROPCAV, which can handle back and face leading edge or mid-chord cavitation, in the presence of the three-dimensional flow field determined by the coupled MPUF-3A and GBFLOW-3D. The present method is validated by comparing the cavity shapes and the cavity envelope with those observed and measured in experiment and computed by another method.
Residual Strength and Survivability of Bulk Carriers After Grounding and Collision
Authors: Das Purnendu K. , Chuang Fang
Published: January 2021

The aim of this paper is to quantify the changes in the residual resistant capacity and corresponding failure probability, after collision and grounding, for both double-skin-side (DSS) and single-skin-side (SSS) bulk carriers. The residual strength after collision and grounding, as well as the residual torsional constant and shear strength, are investigated, based on the advanced analysis methods developed by the authors. Failure probability, of damaged DSS and SSS bulk carriers, is studied assuming the load effects obtained from the classification rules and American Bureau of Shipping (ABS) guideline, respectively. Finally, the survivability of DSS and SSS bulk carriers after damage is addressed.
Implication of Nonclassical Effects on Dynamic Response of Sandwich Structures Exposed to Underwater and In-Air Explosions
Authors: Librescu Liviu , Oh Sang-Yong , Hohe Jorg
Published: January 2021

A study devoted to the dynamic response of sandwich panels to underwater and in-air explosions is presented. The study is carried out in the context of a geometrically nonlinear model of sandwich structures featuring anisotropic laminated face sheets and a transversely compressible orthotropic core. The unsteady pressure generated by the explosion and acting on the face of the sandwich panel includes the effect of the pressure wave transmission through the core. Its implications on the structural time-histories as corresponding to the underwater and in-air explosions are put into evidence. The effects of the transverse core compressibility on dynamic response are highlighted. In this sense, one of its major implications is the possibility to capture interactively the global and local (wrinkling) dynamic response of the panel. It is shown that implementation of the structural tailoring technique in the face sheets can constitute an important mechanism for enhancing the dynamic load-carrying capacity of sandwich panels when exposed to blast pulses. Effects of the core, the composite architecture of face sheets, orthotropy of the material of the core, geometrical non-linearities, initial geometric imperfection, and the damping ratio are investigated, and their implications for the dynamic response are highlighted. The comprehensive structural model considered in conjunction with the time-dependent loads generated by the underwater and in-air explosions, and the results obtained in this context, are expected to contribute to a better understanding of the response behavior and to be instrumental toward a better design of these structures.
Simulating Ship Maneuvers in Deep and Coastal Waters
Authors: Ong Muk Chen , Lee Selina C. C. , Lim Arthur T. B. , Lo Edmond Y. M. , Tan Soon Keat
Published: January 2021

An engineering approach for simulating ship maneuvers in both deep and coastal waters taking into account effects of ambient current and wind was developed. The three degree-of-freedom rigid body equations of surge, sway, and yaw were numerically solved. A semiempirical approach was applied to determine the forces and moments arising from the propeller, rudder, current, wind, and wave making. Hydrodynamic calculations coupled with the slender body approximation were used to determine the wave-making resistances for arbitrary water depth. This approach was also adopted for determining the sway and surge added masses and yaw added moment. Computational fluid dynamics calculations were further used to determine the drag forces and the dependence with depth. Predictions of ship trajectories were compared with the field trial data of a full-size containership at design and ballast loading conditions in both deep and coastal waters. The comparison consisted of turning circle motion, zig-zag maneuvers, and actual sea voyage data, and yielded favorable agreement.
Multiobjective Optimization of a Containership Using Deterministic Particle Swarm Optimization
Authors: Pinto Antonio , Peri Daniele , Campana Emilio F.
Published: January 2021

The purpose of this paper is to show how the improvement of the hydrodynamics performance of a ship can be obtained by solving a shape optimization problem using the particle swarm optimization (PSO) technique. PSO has been recently introduced to solve global optimization problems and belongs to the class of evolutionary algorithms. In this paper, the basic stochastic algorithm is modified into a deterministic method, eliminating the randomized heuristic search. This algorithm has been then extended to deal with multiobjective problems by following the concept of subswarms and introducing a new strategy for the selection of the subswarm leaders. Two different versions of this strategy are illustrated and compared. Effectiveness and efficiency of the method proposed here are demonstrated by solving a set of algebraic multiobjective test problems, designed to represent a wide selection of possible shapes of the Pareto front. Comparisons with a well-known multiobjective genetic algorithm are also presented. Finally, the new method is used to reduce the heave and pitch motion peaks of the response amplitude operator of a containership advancing at fixed speed in head seas, subject to some real-life constraints. The results confirm the applicability of the developed approach to real ship design problems.
Constructive Neural Networks and Their Application to Ship Multidisciplinary Design Optimization
Authors: Besnard Eric , Schmitz Adeline , Hefazi Hamid , Shinde Rahul
Published: January 2021

This paper presents a neural network-based response surface method for reducing the cost of computer-intensive optimizations for applications in ship design. In the approach, complex or costly analyses are replaced by a neural network, which is used to instantaneously estimate the value of the function(s) of interest. The cost of the optimization is shifted to the generation of (smaller) data sets used for training the network. The focus of the paper is on the use and analysis of constructive networks, as opposed to networks of fixed size, for treating problems with a large number of variables, say around 30. The advantages offered by constructive networks are emphasized, leading to the selection and discussion of the cascade correlation algorithm. This topology allows for efficient neural network determination when dealing with function representation over large design spaces without requiring prior experience from the user. During training, the network grows until the error on a small set (validation set), different from that used in the training itself (training set), starts increasing. The method is validated for a mathematical function for dimensions ranging from 5 to 30, and the importance of analyzing the error on a set other than the training set is emphasized. The approach is then applied to the automated computational fluid dynamics-based shape optimization of a fast ship configuration known as the twin H-body. The classical approach yields a design improvement of 26%, whereas the neural network-based method allows reaching a 34% improvement at one fifth of the cost of the former. Based on the analysis of the results, areas for future improvements and research are outlined. The results demonstrate the potential of the method in saving valuable development cycle time and increasing the performance of future ship designs.
Note on the Time-Dependent Virtual Inertia of a Deforming Body “Translating” in an Unbounded Fluid
Authors: Sparenberg J. A.
Published: January 2021

The concept of virtual inertia of a body with a fixed shape translating in an ideal fluid can be used to describe the force needed to accelerate the body as well as the kinetic energy of the fluid. It is elucidated that this is not a useful possibility in general with respect to a body that has a time-dependent shape. However, for a restricted class of time-dependent shapes, which will be described, the accelerated "translation" of the body in a fluid can be treated analogously to the accelerated translation of a body with a fixed shape. Only bodies that do not shed vorticity are considered.
Parametric Generation, Modeling, and Fairing of Simple Hull Lines With the Use of Nonuniform Rational B-Spline Surfaces
Authors: Pérez F. L. , Clemente J. A. , Suárez J. A. , González J. M.
Published: January 2021

This paper deals with the use of a simple parametric design method applied to simple hull lines, such as sailing ship hulls and round bilge hulls. The described method allows the generation of hull lines that meet hydrodynamic coefficients imposed by the designer, obtaining more flexibility than with normal affine transformations of a parent hull. First, a wire model of the ship stations is made with the use of explicit curves. The method is completed with an automatic surface modeling of the previ¬ously generated offsets. The construction of spline curves and their application in the definition of ship lines are reviewed. Approximation of spline curves fitting the data on the stations is made, with special emphasis on the choice of parametrization, which is relevant to increasing the accuracy of the splines. B-spline surface modeling of the hull and the fairing process adapted to maintain certain ship characteristics are described. Some examples of the generation, lofting, and fairing process are pre¬sented.
Wave-Making Resistance of a Catamaran Hull in Shallow Water Using a Potential-Based Panel Method
Authors: Tarafder Md. Shahjada , Suzuki Kazuo
Published: January 2021

The aim of this paper is to investigate the influence of the water depth and the wave interference effects on the first- and second-order wave-making resistance of a catamaran hull using a potential-based boundary element method. Since the interior flow of each monohull of a catamaran is different from the exterior flow, both monohulls must be considered as lifting bodies. The pressure Kutta condition is imposed at the trailing edge of the lifting body to determine the dipole distribution, which generates required circulation on the lifting part. The effects of hull separation and water depth on the hydrodynamic characteristics of a catamaran hull are analyzed and the validity of the computer scheme is examined by comparing the wave resistance with others' numerical results. The present method could be a useful design tool for screening the suitable combinations of hull parameters and hull spacing at the preliminary design stage of a catamaran hull.
Numerical Study of Cavitation Inception Due to Vortex/Vortex Interaction in a Ducted Propulsor
Authors: Hsiao C.-T. , Chahine G. L.
Published: January 2021

Cavitation inception in a ducted propulsor was studied numerically using Navier-Stokes computations and bubble dynamics models. Experimental observations of the propulsor model and previous numerical computations using Reynolds-averaged Navier-Stokes (RANS) codes indicated that cavitation inception occurred in the region of interaction of the leakage and trailing tip vortices. The RANS simulations failed, however, to predict correctly both the cavitation inception index value and the inception location. To improve the numerical predictions, we complemented here the RANS computations with a direct Navier-Stokes simulation in a reduced computational domain including the region of interaction of the two vortices. Initial and boundary conditions in the reduced domain were provided by the RANS solution of the full ducted propulsor flow. Bubble nuclei were released in this flow field, and spherical and nonspherical bubble dynamics models were exercised to investigate cavitation inception. This resulted in a solution in much better agreement with the experimental measurements than the original RANS solution. Both the value of the cavitation inception index and the location of the cavitation inception were very well captured. The characteristics of the emitted acoustic signals and of the bubble shapes during a cavitation event were also computed.
Compressive Strength of Stiffened Plates With Imperfections: Simple Design Equations
Authors: Masaoka Koji , Mansour Alaa
Published: January 2021

The behavior and ultimate compressive strength of stiffened plates with imperfections have been investigated in this paper using a nonlinear finite element method. The imperfections considered consisted of initial deflection and residual stresses. Several types of initial deflections were investigated, including those that may initiate stiffener column buckling and stiffener tripping. Extensive parametric study was conducted in order to systematically determine the impact of these initial imperfections on the ultimate compressive strength of stiffened plates of various geometric properties and stiffener shapes. The objective of the study was to develop simple design equations for determining ultimate strength based on finite element parametric study. The developed algebraic equations reflect the impact of imperfections on ultimate strength. A Perry-Robertson type equation was developed to incorporate the influence of the imperfections. It was found that under certain conditions a hybrid type mode of failure was necessary to accurately represent the behavior of stiffened plates with imperfections, in addition to the usual plate and stiffener failure modes. It was also found that column buckling type initial deflection is the most important form of imperfection.
Wavelet Analysis of Loads on a Flexible Ship Model Traveling in Large-Amplitude Waves
Authors: Du Shuangxing , Hudson Dominic A. , Price W. Geraint , Temarel Pandeli , Chen Ruizhang , Wu Yousheng
Published: January 2021

This study describes an application of a Daubechies wavelet function to analyze measured ship model data. The records of a self-propelled, flexible model of the S175 containership moving in waves are analyzed by fast Fourier transform (FFT) and wavelet methods. It is shown that the high-frequency component of the recorded rigid body motions can be omitted without substantially affecting the main features of the data set relating to dynamic loads. The decomposition of the bending moment time history into low-and high-frequency components allows the time of impact occurrence and its amplitude to be easily detected. Such quantities provide important information for the development of generic and realistic transient impact (e.g., slamming, green water) force models for ships traveling in waves.
Closure of the Deep Wake Hollow of High-Speed Ships
Authors: Vorus William S.
Published: January 2021

Interest has developed in recent years in the length of the "wake hollow" downstream of high-speed vessels with blunt transom sterns. Past work has shown that this wake cavity appears to increase the effective length of a vessel, and thereby reduce its effective Froude number, with the result of a reduction in wave resistance. The research presented here is development and demonstration of a simple mathematical theory for the downstream wake closure characteristics of fully ventilated wakes of fast ships with transom sterns. The theory uses the linear thin body approximations with gravity in a formulation consistent with the thin body theory of wave resistance, although wave resistance is not dealt with here. The length of the wake hollow, or "trench," predicted is compared with recent experiments. Calculations of variation of the hollow length with transom shape and Froude number are presented.
Numerical Research on FPSOs With Green Water Occurrence
Authors: Zhu Renchuan , Miao Guoping , Lin Zhaowei
Published: January 2021

Green water loads on sailing ships or floating structures occur when an incoming wave significantly exceeds freeboard and water runs onto the deck. In this paper, numerical programs developed based on the platform of the commercial software Fluent were used to numerically model green water occurrence on floating structures exposed to waves. The phenomena of the fixed floating production, storage, and offloading unit (FPSO) model and oscillating vessels in head waves have been simulated and analyzed. For the oscillating floating body case, a combination idea is presented in which the motions of the FPSO are calculated by the potential theory in advance and computional fluid dynamics (CFD) tools are used to investigate the details of green water. A technique of dynamic mesh is introduced in a numerical wave tank to simulate the green water occurrence on the oscillating vessels in waves. Numerical results agree well with the corresponding experimental results regarding the wave heights on deck and green water impact loads; the two-dimensional fixed FPSO model case conducted by Greco (2001), and the three-dimensional oscillating vessel cases by Buchner (2002), respectively. The research presented here indicates that the present numerical scheme and method can be used to actually simulate the phenomenon of green water on deck, and to predict and analyze the impact forces on floating structures due to green water. This can be of great significance in further guiding ship design and optimization, especially in the strength design of ship bows.
Application of the IMO Maneuvering Criteria for Pod-Driven Ships
Authors: Woodward Michael D. , Atlar Mehmet , Clarke David
Published: January 2021

The fundamental objective of this paper is to make qualified assessment of the validity of the International Maritime Organization (IMO) maneuvering criteria "Resolution MSC.137(76)," when applied to pod-driven ships. The performance limits given by the criteria provide an adequate benchmark to compare all ships, regardless of propulsion type. However, the application of specific helm angle is less well defined as azimuthing pod drives, like any vectoring thrusters, can be turned to any helm angle, with no specific definition for the angle of maximum force. To address this problem, new methods for modeling the hydrodynamic reaction for both the ship hull and pod drive are identified. Then, a dedicated numerical tool is developed and simulation study conducted exploring systematic variation of applied helm angles with comparison of time-and frequency-domain responses. The study reaches the definitive conclusion that the criteria provides equivalent information about the maneuvering response of pod-driven ships as for conventionally propelled ships and can thus be applied directly.
Experimental and Numerical Studies on Ship Motion Responses Coupled with Sloshing in Waves
Authors: Nam Bo-Woo , Kim Yonghwan , Kim Dae-Woong , Kim Yong-Soo
Published: January 2021

This study considers the motion responses of floating bodies in waves coupled with sloshing-induced internal forces and their effects on sloshing-induced impact loads. The linear ship motion is solved using an impulse-response-function (IRF) method, while the nonlinear sloshing flow is simulated using a finite difference method. The considered models are a liquid natural gas floating production, storage, and offloading unit (LNG FPSO) with two partially filled tanks and a modified S175 hull with an antirolling tank. In the case of the LNG FPSO model, both numerical and experimental studies are carried out. Three degree-of-freedom motion responses are allowed in the presence of regular waves, and the measured response amplitude operators (RAOs) are compared with computational results. For the modified S175 hull, the computational results are compared with other existing computational results. It is observed that the present method provides a fair agreement with experimental and other numerical results, showing significant coupling effects on both motion responses and sloshing flows. The numerical study extends to the observation of pressure field inside the tanks, and a significant difference in internal pressure is also shown.
Optimal Short-Range Routing of Vessels in a Seaway
Authors: Dolinskaya I. S. , Kotinis M. , Parsons Michael G. , Smith R. L.
Published: January 2021

An investigation of the optimal short-range routing of a vessel in a stationary random seaway is presented. The calculations are performed not only in head seas but also in oblique waves. The evaluation of the added drag is performed by computing the time average wave force acting on the vessel in the longitudinal direction. Subsequently, the added drag is superimposed on the steady drag experienced by the ship as it advances in calm water. In this manner, the fastest path between the origin point A and the destination point B can be evaluated, taking into account operational constraints. To obtain the fastest path between two points, the underlying structure and properties of the maximum mean attainable speed are analyzed. This detailed analysis allows us to demonstrate the fastest path for the problem without any operational constraints to be a straight line. Subsequently, the solution is reevaluated for scenarios where the original optimal path violates at least one of the operability criteria considered. For that case, a fastest path is found to be a path consisting of one waypoint, that is, a two line segment path. In addition to providing a closed-form fastest-path solution for the case of no operational constraints, a bound is provided for travel time error for more general speed functions in the case where a straight line path is followed.