bluuebunny/crossref_metadata_2025 huggingface dataset:
Fatigue Reliability Based Design Optimization of Bending Stiffener
Authors: Yang Hezhen , Wang Aijun
Published: January 2021

A methodology for fatigue reliability based design optimization is proposed for the design of bending stiffener. Bending stiffener is employed to protect the upper connection of umbilical/flexible riser against damage from overbending. It is prone to cause fatigue failure due to the wave induced vessel motions. Therefore, its fatigue character has a great impact on the safety of oil and gas production and we should pay more attention to it. In addition, the fatigue analysis involves material, geometric, and loading uncertainties, hence the reliability analysis is performed for considering the influence of uncertain factors. In this work, the fatigue reliability based optimization involves the fatigue analysis and complex optimization algorithms the metamodel is used to reduce the computational cost. Threemetamodels are constructed by the optimum Latin hypercube method. Then, the optimum metamodel is selected for the optimization through the accuracy evaluation. The feasibility of the methodology is verified by a test case of beam. Finally, it is applied to the fatigue reliability based design optimization of bending stiffener. The results demonstrate that this methodology is rational and improves the fatigue reliability of bending stiffener. First, compared with deterministic optimization.
Welding Distortion Analysis of Hull Blocks using Equivalent Load Method Based on Inherent Strain
Authors: Kim Yong Tai , Kim Tae Jun , Park Tae Yoon , Jang Chang Doo
Published: January 2021

Welding deformation reduces the dimensional accuracy of ship hull blocks and decreases productivity due to the correction work. Prediction and minimizing of welding distortion at the design stage will lead to higher quality as well as higher productivity. Therefore, the development of an effective method to predict accurately the weld distortion of hull blocks considering the fabrication sequences is required. In the case of hull block welding work in shipyards, the welding process of curved stiffened plates has large amounts of workload. This paper suggests an efficient method for predicting the welding deformation of stiffened curved plates based on the inherent strain theory combined with the finite element method. The equivalent load was determined by integrating inherent strain components which are calculated in the vicinity of heat affected zone using the highest temperature and the degree of restraint. The welding distortion of curved stiffened panels under equivalent load are calculated by elastic analysis and compared with that by intensive elasto-plastic finite element analysis. It is verified that the proposed method has a high efficiency and accuracy.
Dynamic Viscoplastic Response of a Circular Plate Subjected to Underwater Shock
Authors: Zong Z. , Zhang Y. F. , Zhou L.
Published: January 2021

A structure subjected to underwater shock exhibits surprising dynamic behavior, different from the permanent plastic deformation of a structure subjected to air blast, due to the presence of complicated fluid-structure interaction (FSI) effect. Previous studies of a circular plate subjected to underwater shock indicate that there exist large discrepancies between theoretical and experimental results of plastic deformations. Herein we thus propose a new double-scale and double-phase (DSDP) FSI model for correct prediction of the dynamic plastic behavior of a circular plate subjected to underwater shock. Results obtained from this DSDP model are compared with several experimental tests, with excellent agreement observed. This model is believed useful for further implementation in those software programs that handle underwater explosion and its effects on marine structures.
Fatigue Life Assessment and Lifetime Management of Aluminum Ships Using Life-Cycle Optimization
Authors: Kwon Kihyon , Frangopol Dan M.
Published: January 2021

The development of aluminum ship structures has been promoted in the context of the rapid evolution of high-speed and light-weight vessels. Under the repeated and/or fluctuating application of stresses during voyages, fatigue damage of structural ship members is accumulated. For this reason, fatigue reliability analysis has to be conducted for assessing and predicting lifetime performance of aluminum ships. This assessment offers the opportunity to optimally perform the lifetime ship structural management planning. To allocate limited financial resources required to balance the lifetime reliability of ship structural details and the life-cycle cost, single-or multi-objective optimization can be used. The multi-objective optimization problem has several competing objectives such as:(minimizing the life-cycle maintenance cost,maximizing the fatigue reliability of details with welded attachments, andminimizing the fatigue damage. The S-N (stress vs. number of cycles) approach and available sea loading information are used to evaluate the time-dependent fatigue reliability. In this paper, the estimated fatigue reliability is incorporated into a life-cycle cost optimization problem to find the optimal inspection and repair interventions. The proposed approach is illustrated on an aluminum ship detail.
Validation of Potential-Flow Estimation of Interaction Forces Acting upon Ship Hulls in Parallel Motion
Authors: Sutulo Serge , Soares C. Guedes , Otzen Janne F.
Published: January 2021

The hydrodynamic interaction problem is of great importance for numerical ship handling simulators and at present, only a relatively simple potential double body panel method can be expected to supply estimates of interaction forces and moments in real time on commonly used hardware, without limitations on the hull shape, and on the mutual position and motion of the interacting bodies. Such a code was developed on the basis of the classic Hess and Smith method and proved to be fast enough to model interaction in real time when a moderate number of panels is used. In the present paper, results obtained with the potential code are validated against experimental data obtained in deep and shallow water towing tanks for the case of a tug operating near a larger vessel. All the tests corresponded to the steady regime and only cases with parallel center planes were considered here. The comparisons carried out for various discretization of the hulls provide useful information about natural limitations in breaking at too close lateral distances and about acceptable trade-off between the computational speed and accuracy. In addition, influence of the nonzero sway and yaw velocities is investigated numerically.
Prediction of Plate Bending by Multi Divisional Analysis in Induction Heating
Authors: Lee Young Hwa
Published: January 2021

Induction heating is more efficient for plate bending because of its easy operation and control of working parameters compared with heating by a torch. In this study, a more efficient method was proposed for the prediction of plate bending. The conventional analysis method using the axis symmetric coil model could not handle the varying temperature during the heating and forming process for curved plates with a convex, a concave, or a twisted curvature. The proposed method using some discrete divisions and steps in this study could overcome these difficulties and show more accurate, reasonable results of temperatures and deflections in flat or curved plates. This method is composed of multidisciplinary analyses such as an electro-magnetic analysis, a heat transfer analysis, and a deformation analysis based on inherent strain method and elastic deformation analysis.
Intelligent Quaternion Ship Domains for Spatial Collision Risk Assessment
Authors: Wang Ning
Published: January 2021

In this article, a novel ship domain model termed intelligent quaternion ship domain (IQSD) has been proposed by effectively considering ship maneuverability and human factors. Unlike previous ship domains, the proposed IQSD is much more dependable and flexible for navigators to make decisions. The key characteristics are as followsthe domain size is determined by the quaternion including 4 radii, i.e., fore, aft, starboard, and port, which sufficiently take factors affecting the domain (i.e., ship maneuverability, speeds and courses, etc.) into account;the domain shape is modeled by another parameter k, which makes the IQSD more flexible because the ship boundary could be not only linear or nonlinear, but also thin or fat; 3) furthermore, the navigator states including skill ability and physical and mental states have been effectively modeled by a fuzzy system, which determines the shape parameter, k. To reasonably relate the IQSD to potential applications, i.e., collision risk assessment, collision avoidance and trajectory planning, etc., a generalized IQSD (GIQSD) with fuzzy boundaries has been developed by using fuzzy sets. As a consequence, the GIQSD would become more practical and convenient for applications because uncertainty and fuzzy information has been merged into the GIQSD. Furthermore, concepts of longitudinal and lateral risk based on the GIQSD have been defined to estimate the spatial collision risk (SCR) for ships encountered. Finally, comprehensive simulations have been conducted on various encounter situations and comparative studies with typical ship domains have been intensively analyzed. Simulation results demonstrate that the IQSD is more effective and flexible than previous ship domains, and the intelligent SCR based on the GIQSD is reasonable and dependable.
A Wave Resistance Formulation for Slender Bodies at Moderate to High Speeds
Authors: Taravella Brandon M. , Vorus William S.
Published: January 2021

T. Francis Ogilvie (1972) developed a Green's function method for calculating the wave profile of slender ships with fine bows. He recognized that near a slender ship's bow, rates of change of flow variables axially should be greater than those typically assumed in slender body theory. Ogilvie's result is still a slender body theory in that the rates of change in the near field are different transversely (a half-order different) than axially; however, the difference in order of magnitude between them is less than in the usual slender body theory. Typical of slender body theory, this formulation results in a downstream stepping solution (along the ship's length) in which downstream effects are not reflected upstream. Ogilvie, however, developed a solution only for wedge-shaped bodies. Taravella, Vorus, and Givan (2010) developed a general solution to Ogilvie's formulation for arbitrary slender ships. In this article, the general solution has been expanded for use on moderate to high-speed ships. The wake trench has been accounted for. The results for wave resistance have been calculated and are compared with previously published model test data.
Numerical Solution of Body-Exact Problem in the Time Domain
Authors: Qiu Wei , Peng Hongxuan (Heather)
Published: January 2021

Motions of a floating body in waves are computed in the time domain by solving the body-exact problem with the panel-free method and exact geometry. In the present study, the body boundary condition is imposed on the instantaneous wetted surface exactly at each time step. The free surface boundary is assumed linear so that the time-domain Green function can be applied. The body geometry is represented by NonUniform Rational B-Spline surfaces. At each time step, the instantaneous wetted surface is obtained by trimming the entire body surface. With the panel-free method, the body-exact problems are solved without involving repanelization of the wetted hull surface at each time step. Validation studies have been carried out for a submerged sphere, a flared body, and a Wigley hull. The hydrodynamic forces on the submerged sphere undergoing large-amplitude motion were computed and compared with analytical solutions. For the flared body oscillating in a free surface and the Wigley hull in waves, numerical results were compared with experimental data and solutions by other numerical methods.
Estimation of Resistance and Self-Propulsion Characteristics for Low L/B Twin-Skeg Container Ship by a High-Fidelity RANS Solver
Authors: Sakamoto Nobuaki , Kawanami Yasutaka , Uto Shotaro , Sasaki Noriyuki
Published: January 2021

Reynolds-averaged Navier-Stokes simulations together with verification and validation studies for a low L/B twin-skeg container ship are carried out using SURF version 6.44, which is a high-fidelity RANS solver for ship hydrodynamics developed at the National Maritime Research Institute: single-phase level set free surface, Spalart-Allmaras/k-co turbulence, and body-force propeller models; finite volume discretization; and parallelized by openMPW for high-performance computing. At the beginning, simulation numerical uncertainty has been quantified for resistance and self-propulsion coefficients on the basis of the standard V&V procedure recommended by the International Towing Tank Conference. Then the resistance and self-propulsion simulations are carried out at several speeds ranging from low to medium Froude numbers. The overall results are encouraging in that the solver accurately predicts resistance and self-propulsion coefficients as well as velocity distribution at the propeller plane in comparison to the available experimental data. Further sophistications in computational method, especially in estimating self-propulsion coefficients, will lead the solver to be more practical and powerful design tool.
An Analytical Model to Predict the Bending Behavior of Unbonded Flexible Pipes
Authors: Dong Leilei , Huang Yi , Zhang Qi , Liu Gang
Published: January 2021

Analytical formulations are presented to determine the bending moment-curvature relationship of a helical layer in unbonded flexible pipes. Explicit expressions describing the variation of both bending stiffness and moment as a function of the applied curvature are given. The approach takes into account the nonlinearity of the response caused by the interlayer slip. The contribution of local bending and torsion of individual helical elements to the bending behavior of helical layers is included. Theoretical results for a typical unbonded flexible pipe using the nonlinear formulation for helical layers are compared with experimental data from the available literature. Encouraging correlations are found and the importance of the initial interlayer pressures is seen. The influence of local bending and torsion of individual helical elements on the bending behavior of the entire pipe is also evaluated. The results show that the inclusion of this local behavior significantly influences the full-slip bending stiffness.
Forward Speed Calm Water Roll Decay for Surface Combatant 5415: Global and Local Flow Measurements
Authors: Irvine Martin , Longo Joseph , Stern Frederick
Published: January 2021

Global and local flow measurements for forward speed calm water roll decay are performed in a towing tank for surface combatant model 5415 for both bare hull (BH) and bilge keel (BK) conditions. Roll motion is oscillatory with underdamped exponential decay and linear with respect to initial roll angles less than the average initial roll angle (9°). For larger mean roll angles (> 3°), damped natural frequency is a few percent below the hydrostatic natural roll frequency with larger values for BH than BK condition and increasing Froude number (Fr), whereas for smaller mean roll angles, it sharply increases toward the hydrostatic natural roll frequency. For larger mean roll angles, logarithmic decrement and linear damping linear increase with larger values for BK than BH condition and increasing Fr, whereas for smaller mean roll angles, they sharply increase. For increasing Fr, mean and initial roll angle averaged mean roll angle decreases by 50%; damped natural frequency increases by 6% with larger values for BH than BK condition; and logarithmic decrement/linear damping coefficient increase by a factor of three/four with larger values for BK than the BH condition. Logarithmic decrement and Himeno method linear damping coefficients are qualitatively similar. Nonlinear damping coefficient is two orders of magnitude smaller than linear damping coefficient. Roll reconstruction errors are smallest for Himeno with linear and nonlinear damping. The phase-averaged wave pattern and velocity and axial vorticity fields at x/L = 0.675 initially show larger amplitudes followed by oscillatory exponential decay. Alternating vortex pairs are shed from the bilge keel tip with damped magnitudes for decreasing mean roll angles. The local flow indicates lower frequencies and larger damping than the roll motion.
Hydrodynamic Study on Added Resistance Using Unsteady Wave Analysis
Authors: Kashiwagi Masashi
Published: January 2021

It is known that the added resistance in waves can be computed from ship-generated unsteady waves through the unsteady wave analysis method. To investigate the effects of nonlinear ship-generated unsteady waves and bluntness of the ship geometry on the added resistance, measurements of unsteady waves, wave-induced ship motions, and added resistance were carried out using two different (blunt and slender) modified Wigley models. The ship-generated unsteady waves are also produced by the linear superposition using the waves measured for the diffraction and radiation problems and the complex amplitudes of ship motions measured for the motion-free problem in waves. Then a comparison is made among the values of the added resistance by the direct measurement using a dynamometer and by the wave analysis method using the Fourier transform of measured and superposed waves. It is found that near the peak of the added resistance where ship motions become large, the degree of nonlinearity in the unsteady wave becomes prominent, especially at the forefront part of the wave. Thus, the added resistance evaluated with measured waves at larger amplitudes of incident wave becomes much smaller than the values by the direct measurement and by the wave analysis with superposed waves or measured waves at smaller amplitude of incident wave. Discussion is also made on the characteristics of the added resistance in the range of short incident waves.
Development of a Spectral Method and a Statistical Wave Model for Crack Propagation Prediction in Ship Structures
Authors: Mao Wengang
Published: January 2021

As a result of the wide use of high-tensile steel and the imperfect fabrication process in ship construction as well as some uncertainties in ship fatigue design, cracks could be initiated much earlier than expected. The presence of fatigue cracks greatly affects a ship's structural safety and serviceability. To ensure structural safety and perform reliable crack inspection and maintenance planning, it is important to know how fast cracks can grow in ship structures. In the current study, the principles of fracture mechanics are used for crack propagation analysis in ships. By taking into account the special properties of a ship's stress response, an efficient spectral method is proposed and validated for the prediction of crack propagation in ship structures. In this spectral method, structural stresses are assumed to be narrow-band Gaussian processes. Furthermore, for crack inspection and maintenance planning based on crack growth, it is essential to know the wave environments encountered in a ship's future operations. Therefore, a spatiotemporal statistical wave model based on both satellite and buoy measurements is briefly introduced. It is developed to generate wave environments along arbitrary ship routes. Finally, the deck longitudinal stiffener of a 2800TEU containership is used to demonstrate the application of the spectral method and the wave model for the prediction of crack propagation in ships. The route information and operating conditions are taken from full-scale measurements of this ship. In the case study, the scatter of crack propagation associated with the wave environments encountered is also investigated. The results from this investigation indicate possible potentials of crack inspection and maintenance optimization to enable more efficient ship operation.
On the Accurate Calculation of Effective Wake/Application to Ducted Propellers
Authors: Tian Ye , Jeon Chan-Hoo , Kinnas Spyros A.
Published: January 2021

A hybrid method that couples a potential flow solver with a Reynolds-Averaged Navier-Stokes (RANS) solver for calculating the effective wake of a propeller is proposed. Two improvements are addressed in this method:a conservative interpolation scheme that conserves the total forces when passing information from the potential flow solver to the RANS solver; anda novel option that evaluates the effective wake at the control points in the blade zone. The proposed method is first assessed in the case of an open propeller subject to uniform inflow and then applied to predict the performance of the ducted propellers under uniform inflow. The results of the numerical simulation are correlated with available experimental measurements.
Application of Volterra Series Analysis for Parametric Rolling in Irregular Seas
Authors: Moideen Hisham , Somayajula Abhilash , Falzarano Jeffrey M.
Published: January 2021

Parametric roll is a phenomenon in which there is a large rolling motion of a ship even when the ship is moving into head seas with no direct excitation. It is a nonlinear dynamic phenomenon of a ship rolling system with nonlinearities in the stiffness as well as the damping terms. Parametric roll of container ships in head seas is a relatively new problem, which has gained lot of importance after the catastrophic incidence of APL China in 1998. Analysis of parametric roll of container ships in regular head waves has been studied extensively. However, the ships do not encounter regular waves in the ocean. So, it is necessary to study how important parametric roll is in irregular seas. To study this, it is first important to model the variation of metacentric height in irregular waves, which is nonlinear as a result of the influence of underwater geometry and the motions of the ship in a seaway. In this work, the change of metacentric height (GM) in irregular waves has been modeled using a Volterra series approach. This transfer function for metacentric height (GM) is used to study parametric rolling of ships in irregular waves. Based on this study, roll motion sensitivity to the spectral peak period and significant wave height has been carried out.
On Fully Aligned Lifting Line Model for Propellers: An Assessment of Betz condition
Authors: Menéndez Arán David H. , Kinnas Spyros A.
Published: January 2021

We discuss the optimum propeller loading through the use of a lifting line model. Viscous terms are included through a drag-to-lift ratio, and a hub image model is implemented. Two types of trailing wake geometries are considered: one based on helical wakes, which are aligned at the blade (using the so-called "moderately loaded propeller" assumption), and a second one based on a full wake alignment model to represent more accurately the wake geometry and its effect on the efficiency of the propeller. A comparison of the efficiencies and the loading distributions obtained through both methods is presented as well as convergence and numerical accuracy studies. The accuracy of Betz condition according to both wake models is tested, and conclusions are drawn based on these results.
Performance Simulation of a Dual-Direction Ship in Level Ice
Authors: Tang Xiang , Riska Kaj , Moan Torgeir
Published: January 2021

The ice performance of a dual-direction ship is investigated through a numerical procedure developed to simulate the continuous-mode icebreaking in level ice. The effect of the propeller-hull-ice interaction for running astern is accounted for by applying the knowledge obtained from model tests to the numerical procedure. The numerical procedure is in turn used as a performance prediction tool to supplement the model test data to investigate the thrust deduction in ice.
Operational Modal Analysis for Dynamic Characterization of a Ro-Lo Ship
Authors: Orlowitz Esben , Brandt Anders
Published: January 2021

The dynamic characteristics of ship structures are becoming more important as the flexibility of modern ships increases, for example, to predict reliable design life. This requires an accurate dynamic model of the structure, which, because of complex vibration environment and complex boundary conditions, can only be validated by measurements. In the present paper the use of operational modal analysis (OMA) for dynamic characterization of a ship structure based on experimental data, from a full-scale measurement of a 210-m long Ro-Lo ship during sea trial, is presented. The measurements contain three different data sets obtained under different operating conditions of the ship: 10 knots cruising speed, 18 knots cruising speed, and at anchor. Natural frequencies, modal damping ratios, and mode shapes have been successfully estimated for the first 10 global modes. Damping ratios for the current ship were found within the range 0.9%–1.9% and natural frequencies were found to range from 0.8 to 4.1 Hz for the first 10 global modes of the ship at design speed (18 knots). The three different operating conditions showed, in addition, a speed dependency of the natural frequencies and damping ratios. The natural frequencies were found to be lower for the 18-knots condition compared with the two other conditions, most significantly for the vertical bending modes. Also, for the vertical bending modes, the damping ratios increased by 28%–288% when the speed increased from 10 to 18 knots. Other modes were not found to have the same strong speed dependency.
Submarine Maneuvers Using Direct Overset Simulation of Appendages and Propeller and Coupled CFD/Potential Flow Propeller Solver
Authors: Martin J. Ezequiel , Michael Thad , Carrica Pablo M.
Published: January 2021

This article presents two approaches to simulate maneuvers of a model radio-controlled submarine. In the direct simulation approach, rudders, stern planes, and propellers are gridded and treated as moving objects using dynamic overset technology. The second approach couples the overset computational fluid dynamics (CFD) solver and a potential flow propeller code, with both codes exchanging velocities at the propeller plane and wake, body forces, and propeller forces and moments, whereas rudders and stern planes are still explicitly resolved. It is shown that during the maneuvers, the range of advance coefficients does not deviate much from the design point, making a coupled approach a valid choice for standard maneuvering simulations. By allowing time steps about an order of magnitude larger than for the direct simulation approach, the coupled approach can run about five times faster. The drawback is a loss of resolution in the wake as the direct propeller simulation can resolve blade vortical structures. Open water propeller curves were simulated with both the direct propeller approach and the coupled approach, showing that the coupled approach can match the direct approach performance curves for a wide range of advance coefficients. Simulations of a horizontal overshoot maneuver at two approach speeds were performed, as well as vertical overshoot and controlled turn maneuvers at high speed. Results show that both CFD approaches can reproduce the experimental results for all parameters, with errors typically within 10%.
Stochastic Dynamic Analysis and Reliability of a Vessel Rolling in Random Beam Seas
Authors: Chai Wei , Naess Arvid , Leira Bernt J.
Published: January 2021

This article presents a four-dimensional (4D) path integration (PI) approach to study the stochastic roll response and reliability of a vessel in random beam seas. Specifically, a 4D Markov dynamic system is established by combing the single-degree-of freedom model used to represent the ship rolling behavior in random beam seas with a second-order linear filter used to approximate the stationary roll excitation moment. On the basis of the Markov property of the coupled 4D dynamic system, the response statistics of roll motion can be obtained by solving the Fokker-Planck equation of the dynamic system via the 4D PI method. The theoretical principle and numerical implementation of the current state of the art 4D PI method are presented. Moreover, the numerical robustness and accuracy of the 4D PI method are evaluated by comparing with the results obtained by the application of Monte Carlo simulation (MCS). The influence of the restoring terms and the damping terms on the stochastic roll response are investigated. Furthermore, based on the well-known Poisson assumption and the response statistics yielded by the 4D PI technique, evaluation of the reliability associated with high-level response is performed. The performance of the Poisson estimate for different levels of external excitations is evaluated by the versatile MCS technique.
Resistance Prediction on Submerged Axisymmetric Bodies Fitted with Turbulent Spot Inducers
Authors: Shen Young T. , Hughes Michael J. , Gorski Joseph J.
Published: January 2021

A method to predict bare hull ship resistance is presented in this article. Hull resistance is assumed to consist of friction drag and residual drag. The friction drag coefficient is represented by an equivalent flat plate coefficient multiplied by a form factor to incorporate effects of body geometry and boundary layer (BL) characteristics on drag. Theories of form factors including the effect of BL transition locations have been successfully derived. Form factors are shown to have a noticeable effect on body drag at high Reynolds numbers (Re) and a significant effect at model Re. Residual drag coefficient is obtained from model tests with application of scaling formulae to relate model scale residual drag coefficient to full scale drag coefficient. To address the issue of laminar flow on models in residual drag measurements, a new device termed a "turbulent spot inducer" is introduced in model tests. Finally, a new scaling formula to relate model scale residual drag coefficient to full scale residual drag coefficient with the flow on body surface partly laminar and partly turbulent is derived. It is shown that a traditional 1þK scaling method used in the marine industry is a special case of the newly derived residual drag scaling formula.
Ship-to-Ship Interaction during Overtaking Operation in Shallow Water
Authors: Yuan Zhi-Ming , Kellet Paula , Incecik Atilla , Turan Osman , Boulougouris Evangelos
Published: January 2021

Hydrodynamic interaction continues to be a major contributory factor in marine casualties and hazardous incidents, in particular, in the case of overtaking operations. The situation becomes even worse when the overtaking operation occurs in shallow and narrow channels, where the interaction can cause the vessels to collide and, in one case has caused the capsizal of the smaller vessel with loss of life. The aim of this article is to propose a methodology, as well as to discuss the development of a numerical program, to predict the ship-to-ship interaction during overtaking operations in shallow water. Since the vessels involved in this study have different forward speeds, an uncoupled method will be used to solve the boundary value problem. The in-house multibody hydrodynamic interaction program MHydro, which is based on the 3D Rankine source method, is used and extended here to investigate the interactive forces and wave patterns between two ships during an overtaking operation. The calculations given in this article are compared with model test results as well as published computational fluid dynamics (CFD) calculations. Very satisfactory agreement has been obtained, which indicates that the proposed methodology and developed program are successfully validated to predict the hydrodynamic interaction between two ships advancing in confined waters. The discussions also highlight the speed effects.
A Study of Propeller Operation Near a Free Surface
Authors: Li Yuwei , Martin Ezequiel , Michael Thad , Carrica Pablo M.
Published: January 2021

This paper presents a study of the effects of the interaction of the free surface with a marine propeller operating close to it, including the effects of depth and cross flow. Extensive simulations using the naval hydrodynamics computational fluid dynamics solver REX were conducted to study the open water characteristics, transient blade loads, and flow behavior of propeller 4661, with comparison to fully submerged experimental data at 0° and 30° shaft inclination with respect to the incoming flow. Deeply submerged computations and experiments show that the cross flow results in an increase in thrust and torque and lower efficiency relative to uniform inflow. Near the surface, computations show that effects on thrust and torque increase more dramatically as the propeller load increases. Furthermore, the presence of the free surface breaks the symmetry resulting in highest blade force losses when the blade is near top dead center. As the propeller approaches the surface, the amplitude of the higher harmonics of blade force increases. A demonstration calculation for a self-propelled submarine sailing deep and near the surface shows that operating closer to the surface results in higher propeller loads and lower efficiency.
A Panel Method with a Full Wake Alignment Model for the Prediction of the Performance of Ducted Propellers
Authors: Kinnas Spyros A. , Fan Hongyang , Tian Ye
Published: January 2021

An improved perturbation potential-based panel method is applied to model the flow around ducted propellers. One significant development in this method is the application of full wake alignment scheme in which the trailing vortex wake sheets of the blades are aligned with the local flow velocity by also considering the effects of duct and duct wake. A process of repaneling the duct is simultaneously introduced to improve the accuracy of the method. The results from the improved wake model are compared with those from a simplified wake alignment scheme. At the same time, full-blown Reynolds-averaged Navier-Stokes (RANS) simulations are conducted via commercial solvers. The forces, i.e., thrust and torque, on the propeller predicted by this panel method under the improved wake alignment model show good agreement both with experimental measurements, a hybrid method developed by the Ocean Engineering Group of University of Texas at Austin, and the full-blown RANS simulations. Moreover, predicted pressure distribution on the blades and duct are compared among the various methods.
Tomographic-PIV Survey of the Near-Field Hydrodynamic and Hydroacoustic Characteristics of a Marine Propeller
Authors: Felli Mario , Falchi Massimo , Dubbioso Giulio
Published: January 2021

This article deals with a pioneering application of tomographic particle image velocimetry (tomographic PIV) for the hydrodynamic and hydroacoustic analysis of a marine propeller. The hydrodynamic study was mainly focused on the topological analysis of the propeller wake characteristics in the near field based on the vorticity field and on the tilting and stretching terms of the vorticity transport equation. Hydroacoustic analysis concerned the use of tomographic PIV in combination with the Powell's acoustic analogy. Tomographic PIV proved to be a valid tool for the detailed quantitative reconstruction of the complex vortex topology in the propeller wake and provided an accurate description of the source terms of the Powell's analogy. In particular, it was shown that the tip vortex perturbation represents the dominant nonlinear contribution to the radiated far-field noise in non-cavitating flow conditions.
Sample Selection Method for Ship Resistance Performance Optimization Based on Approximated Model
Authors: Chang Haichao , Cheng Xide , Liu Zuyuan , Feng Baiwei , Zhan Chengsheng
Published: January 2021

Approximated model instead of computational fluid dynamics tool is utilized for performance analysis in hull form optimization process, which can save time significantly. Sample selection is the central issue of approximated model building. This article focuses on the sample selection method and the application of approximated model in hull form optimization. Latin hypercube sampling and uniform design are compared. The uniform design based on genetic algorithm approach is proposed. The radial basis function interpolation method is used for hull surface automatic modification. An approximated model using a neural network for ship resistance performance is established. The stem profile's optimization for the Korea Research Institute of Ships and Ocean Engineering (KRISO) container ship is completed. The results show that hull form optimization based on the approximated model can significantly improve optimization efficiency and is practical for engineering design.
A Hybrid Empirical-Numerical Method for Hydroelastic Analysis of a Floater-and-Net System
Authors: Ma Leixin , Hu Ke , Fu Shixiao , Moan Torgeir , Li Runpei
Published: January 2021

Because of scale effects and inappropriate hydrodynamic models, the nonlinear hydroelastic response of net cages used for fish-farming cannot be analyzed precisely with traditional model testing or combinations of finite element methods (FEMs) and load models. In this study, an innovative hybrid method is proposed to determine the hydroelastic response of full-scale floater-and-net systems more accurately. In this method, the net for the fish cage was vertically and peripherally divided into similar interconnected sections with different hydrodynamic parameters, which were assumed to be uniformly distributed over each section. A model of a typical section was subjected to various towing velocities, oscillation periods, and amplitudes in a towing tank to simulate the potential motions of all sections in the net under various currents, waves, and floater movements. By analyzing the measured hydrodynamic force from this test section, a hydrodynamic force database for a typical net section under various currents, waves, and floater motions was built. Finally, based on an FEM, the modified Morison equation and the hydrodynamic force database, the hydroelastic behavior of the full-scale fish cage was calculated with an iterative scheme. It is demonstrated that this hybrid method is able to produce correct hydroelastic response for both steady and oscillatory flows. The hydroelastic response of a two-dimensional example of a full-length net panel with steady currents and floater oscillations was studied in detail.
An Extended Verification and Validation Study of CFD Simulations for Planing Hulls
Authors: De Luca Fabio , Mancini Simone , Miranda Salvatore , Pensa Claudio
Published: January 2021

In the context of marine application of computational fluid dynamic (CFD), it is well known that the numerical simulations of planing craft are significantly less reliable than that of displacement ships. For this reason, it is important to perform a comprehensive approach to the verification and validation (V&V) methodology and procedures for simulating CFD planing craft. In the first part of this paper, an assessment of the accuracy and effectiveness of different simulation setups and techniques for planing craft is performed. In the second part, the results of the V&V study are reported for three different hull models at four Froude numbers (Fr). The Unsteady Reynolds-Averaged Navier-Stokes code results were validated using benchmark experimental data obtained for three hull models characterized by systematic variation of the length to beam ratio. Grid independence, iteration, and time-step convergence analysis for response variables (resistance coefficients, wetted surfaces, and dynamic trim angles) were conducted using the main error and uncertainty estimation methods available in the literature. The same procedures were followed for the profiles of the wave patterns. The results showed that there was improved reliability of the numerical simulation of the planing craft in terms of the errors and uncertainties, related to the predictions of resistance, running attitude, and wave pattern. The results of the V&V study highlighted the fact that modeling of the planing
Extreme Value Statistics of Large Container Ship Roll
Authors: Gaidai Oleg , Storhaug Gaute , Naess Arvid
Published: January 2021

The paper describes a method for prediction of large container ship extreme roll angles occurring during sailing in harsh weather. Rolling is coupled with other ship motions and exhibits highly nonlinear behavior. Risk of losing containers due to a large roll is primary concern for ship transport. Because of non-stationarity and complicated nonlinearities of both waves and ship motions, it is a considerable challenge to model such a phenomenon. In case of extreme motions, the role of nonlinearities dramatically increases, activating effects of second and higher order. Moreover, laboratory tests may also be questioned because of the scaling and the sea state choice. Therefore, data measured on actual ships during their voyages in harsh weather provide a unique insight into statistics of ship motions. The aim of this work is to benchmark state of art method, which makes it possible to extract the necessary information about the extreme response from onboard measured time histories. The method proposed in this paper opens up the possibility to predict simply and efficiently both short- and long-term extreme response statistics.
Analysis on the Performance of Deckwetness of Sandglass-type and Cylindrical Floating Bodies
Authors: Du Ya-zhen , Wang Wen-hua , Wang Lin-lin , Yao Yu-xin , Gao Hao , Huang Yi
Published: January 2021

In this paper, the influence of the second-order slowly varying loads on the estimation of deck wetness is studied. A series of experiments related to classic cylindrical and new sandglass-type Floating Production, Storage, and Offloading Unit (FPSO) models are conducted. Due to the distinctive configuration design, the sand glass type FPSO model exhibits more excellent deck wetness performance than the cylindrical one in irregular waves. Based on wave potential theory, the first-order wave loads and the full quadratic transfer functions of second-order slowly varying loads are obtained by the frequency-domain numerical boundary element method. On this basis, the traditional spectral analysis only accounting for the first-order wave loads and time-domain numerical simulation considering both the first-order wave loads and nonlinear second-order slowly varying wave loads are employed to predict the numbers of occurrence of deck wetness per hour of the two floating models, respectively. By comparing the results of the two methods with experimental data, the shortcomings of traditional method based on linear response theory emerge and it is of great significance to consider the second-order slowly drift motion response in the analysis of deck wetness of the new sandglass-type FPSO.
Appendage Drag Prediction on Submerged Axisymmetric Bodies
Authors: Shen Young T. , Hughes Michael J.
Published: January 2021

A new appendage resistance prediction method, which mitigates the technical issues with the existing test procedure, has been developed and presented in this paper. The primary aspects of the new method are 1) the Froude's equivalent flat plate friction drag concept extensively used in the marine industry will not be used in the present method, instead, an aerodynamic profile drag concept for resistance prediction is presented, 2) the turbulent stimulators extensively used in existing model appendage resistance tests will not be used in the proposed test procedure, which eliminates the need for high-speed tests and the problematic issue of estimating the parasitic drag associated with turbulence stimulators, 3) the important juncture vortex drag associated with appendages is considered, 4) the effective velocity entering the stern appendages on resistance is considered, 5) the new scaling formula to relate model profile drag and juncture vortex drag to full-scale appendage drag is developed and presented in this paper.
Hydrodynamic Characteristics of a Hydrofoil-assisted Amphibious Vehicle
Authors: Lee Seung-Jae , Lee Tae-il , Lee Jong-Jin , Nam Wonki , Suh Jung-Chun
Published: January 2021

For amphibious vehicles that are utilized in military services, high-speed ship-to-shore movement is an important requirement for enhancement of the operational capability in tactical environments. At high speeds, such a vehicle begins to sink at the stern, causing the bow to rise out of the water. Moreover, excessive trim has a deleterious effect on forward field of vision and powering performance. In this study, a hydrofoil was considered as a trim-control device to decrease the significant bow rise without compromising the performance. Experiments were conducted in a towing tank to investigate the running attitude and powering performance of a box-shaped amphibious vehicle at high speeds. Results for the hydrodynamic features show that a fixed hydrofoil under the stern of the vehicle successfully achieved an improved trim. It was also found that the interaction between the waterjet and hydrofoil can enhance the dynamic lift of the hydrofoil.
Numerical Simulation of Hydrodynamic Characteristics of Underwater Hull Cleaning Robot Using CFD Techniques
Authors: Chen Yan-Zhen , Hu Yi-Huai , Wang Tai-You , Munyao Elijah , Zhang Sheng-Long , Jiang Jiawei , Ma Cheng
Published: January 2021

In this article, an underwater hull cleaning robot model based on propeller thrust adsorption is established for near-wall conditions. By using a computational fluid dynamics method, which is proven feasible by comparing a calm water resistance simulation with its experimental data, the influence of floating body shape and wall distance on its hydrodynamic characteristics is studied. Then, the body force propeller model is used to analyze the interaction between the propeller flow field and the flow field around the underwater cleaning robot. Compared with the cuboid floating body, the results show that the streamlined appearance can greatly reduce front high-pressure area, the pressure drag between the front and rear ends, and the viscous resistance. Its drag coefficient is reduced by 11.5%. The presence of the hull will increase the pressure drag and viscous resistance of the underwater hull cleaning robot, which is similar to the "shallow water blockage effect" of a ship. For this model, the decrease in the wall distance results in a progressive increase in resistance and drag coefficient. As the wall distance is .15 m, the drag coefficient of the underwater hull cleaning robot increases by 4.55%, compared with the limitless water field. For the body force propeller model, the study indicates that when the flow velocity is constant, both the resistance in the forward direction and the adsorption force of the underwater hull cleaning robot increase with the increase in rotation speed of the propeller. The thrust propeller generates a higher increase in resistance and a lower increase in adsorption force compared with the adsorption of the propeller. When the rotation speed is constant, the resistance of the underwater hull cleaning robot increases, with the increase in the flow velocity, and the adsorption force of the underwater hull cleaning robot first decreases and then increases. Therefore, it must be fully considered that the significant influence of the hull and the propeller on the underwater hull cleaning robot can provide theoretical guidance for future related design and research.