bluuebunny/crossref_metadata_2025 huggingface dataset:
A Combination of Algebraic and Geometric Methods for Interface Capturing in Free Surface Flow
Authors: Kuhn John
Published: January 2021

Eulerian techniques for multiphase analysis of free surface flow use a phase fraction to track the volumetric amount of air and water in discrete computational cells. There is no explicit model for the free surface, but its location is implied by the phase fraction field. The effect of the free surface on the flow solution depends on a process known as interface capturing, which is used to solve an advection equation for the phase fraction. This equation can be solved using algebraic methods that are similar to those used for other advection problems, but numerical diffusion is a common difficulty. It destroys the sharpness of the transition in the phase fraction field across the air-water interface. Geometric reconstruction of the interface can be used to mitigate diffusion, but it is difficult to implement with most types of grids due to the complexity of finding intersections among discrete interfacial elements and the faces of computational cells. A new method is proposed in this work that is based on a combination of algebraic and geometric methods. The goal is to preserve the attractive aspects of each while avoiding the less attractive aspects. For example, the new method uses geometric bounds on interface position as a means of mitigating diffusion, but it does so without reconstructing the interface. This makes it relatively simple. A new time integration technique is also presented. It uses subcycles based on a time step limiter to facilitate rigorous mass conservation in multidimensional flow, in contrast to existing methods that are based on one-dimensional phase fraction limiters. Numerical convergence is assessed, and a finite difference flow solver is used to demonstrate the method for a variety of test cases.
Different Methods for Fatigue Assessment of T Welded Joints Used in Ship Structures
Authors: Crupi V. , Guglielmino E. , Risitano A. , Taylor D.
Published: January 2021

The aim of this work is the prediction of high-cycle fatigue behavior in welded joints, which represent regions of weakness in the ship structures. The traditional methods for fatigue assessment of welded joints have some limitations. Some new methods were recently developed by Taylor: the crack modeling method (CMM) and the theory of critical distances methods (TCD). Experimental tests were carried out to define the high-cycle endurance limits of aluminum T-shaped welded joints. Using data obtained from finite element analysis (FEA), the fatigue strength was evaluated according to the CMM and the TCD. Thermographic analysis was also carried out during the experimental tests to assess the high-cycle endurance limits of the welds by means of the Risitano method (RM). The previous methods were also applied to a specific case, fatigue in T joints containing a drilled hole at different angles, which allowed us to study a typical industrial design problem involving two different features. Good predictions were achieved using all the methods.
Identification of Nonlinear Ship Model Parameters Based on the Turning Circle Test
Authors: Casado Manuel Haro , Ferreira Ramón , Velasco F. J.
Published: January 2021

This work presents a contribution to solving the problem of identification of ship model parameters using the experimental results from a particular trial test. The innovation of this paper lies in the fact that for this identification purpose it is necessary to know only the turning radius that describes the ship during the performance of the turning test trial. A relatively complex nonlinear model of Norrbin has been chosen as a basis because it represents the ship's dynamics appropriately, as proven through experimental measurements obtained during the course change test. The proposed algorithm of identification of the four ship model parameters is based on an adaptive procedure and the backstepping theory. Another additional coefficient can be determined by an alternative procedure. The knowledge of the true values that characterize the dynamic of a ship is fundamental in the ship steering control that is carried out by autopilots. The simulation results show the suitability of the proposed procedure.
Dynamic Response Analysis and Comparative Study of Circular Cylindrical Shell Subjected to Radial Impact
Authors: Xuebin Li
Published: January 2021

Following Flu¨ gge's exact derivation for the buckling of cylindrical shells, the equations of motion for dynamic loading of a circular cylindrical shell under external hydrostatic pressure have been formulated. The normal mode theory is used to provide transient dynamic response for the equations of motion. The responses of displacements, strain, and stress are obtained for the area of impact, while those outside the area of impact are also calculated. The accuracy of normal mode theory and Timoshenko shell theory are examined in this paper.
Revised Approach to Khaskind’s Method to Calculate the Wave-Making Resistance Depending on the Sectional Area Curve of the Ship
Authors: Pascual E.
Published: January 2021

The use of Khaskind's method applied to calculate the wave-making resistance during the design of ship forms is a very interesting issue, as the curve of areas, the hull wetted surface, and the immersion of the center of buoyancy are the only necessary elements for calculation purposes. This paper shows the implementation of this method on several ships in order to optimize this resistance.
Modeling the Maneuvering Behavior of Container Carriers in Shallow Water
Authors: Delefortrie G. , Vantorre M.
Published: January 2021

Due to the expansion of the dimensions of container vessels, the available maneuvering space in harbor areas and their access channels is decreasing as waterway authorities are often unable to increase the channel dimensions at the same pace. The under keel clearance is an especially important parameter for ship maneuver-ability and controllability. After an overview of the shallow water effects on ship maneuvering, a new mathematical maneuvering model based on captive model tests is introduced. The mathematical model is valid in a large under keel clearance range and is applicable in four quadrants of forward speed: propeller rate combinations, drift angles, and yaw angles. The mathematical model has been validated by means of an independent set of captive model tests.
Ship Drag Reduction by Microalgal Biopolymers: A Feasibility Analysis
Authors: Gasljevic K. , Matthys E. F.
Published: January 2021

We have investigated the feasibility of using high-molecular-weight polysaccharides produced by marine microalgae to reduce the drag on ships and therefore to be able to reduce the needed propulsion power and fuel costs or, alternatively, to increase the ship speed. Experimental and analytical studies were used to answer four critical questions:How suitable are the biopolymers for drag reduction on ships?What is the needed polymer consumption rate at a given level of drag reduction?What is the achievable polymer production rate that can be achieved by the microalgae?What are possible modes of implementation of the proposed technology?

It is seen that in situ production of biopolymers by microalgae growing on the hull may be a possible approach to polymeric ship drag reduction. Production of biopolysaccharide off the ship and even harvesting it from the ocean are other possibilities. The use of biopolymers is naturally advantageous from an environmental point of view as well. Some comparison of biopolymers and synthetic polymers is also presented. Several technical issues remain to be investigated, but the information available suggests that biopolymers may be the best additives for drag reduction on ships.
Abnormal Wave-Induced Load Effects in Ship Structures
Authors: Soares C. Guedes , Fonseca N. , Pascoal R.
Published: January 2021

The paper presents an approach to determine the global load effects induced on shif structures by abnormal, freak, or episodic waves. It refers to the present procedure of determining extreme values of wave-induced responses, including the recent advances of adopting time series of wave elevation as reference design conditions t calculate the wave-induced structural loads on ships in heavy weather. It is show how this procedure can be extended to account for abnormal or episodic waves Reference is made to what is presently known about abnormal or freak waves showing that although it is possible to determine the loads induced by these wave in floating and fixed structures, the present knowledge about the probability of occurrence of these waves is not enough to allow a wave design criterion to be defined in a way consistent with the present probabilistic approaches. However, it is suggested that at the present stage of knowledge it is possible to determine the load induced by abnormal waves similar to ones that have been measured at various ocean locations and that are thus realistic; a method is described to perform such calculations. Although this information cannot replace the wave-induced loads calculated with the presently established procedures, it can serve as guidance for th design. An application example is presented of a containership subjected to a wav trace that includes an episodic wave that was measured during a severe storm in Central North Sea. The measured wave time history is modified in order to investigate the influence of the wave steepness on the induced vertical motions and loads. Th loads induced by the abnormal wave are compared for the first time with extreme values from long-term distributions.
Numerical Approaches for Hydroacoustic Analysis of Marine Propellers
Authors: Testa C. , Ianniello S. , Salvatore F. , Gennaretti M.
Published: January 2021

This paper is devoted to a theoretical and numerical hydroacoustic analysis of marine propellers. The use of the Ffowcs Williams-Hawkings equation is addressed and compared with a Bernoulli-based methodology, typically used in the naval context. A computational tool based on a boundary element formulation for the velocity potential is used to determine the hydrodynamic loads on the propeller blades. Then, both the Bernoulli and the Ffowcs Williams-Hawkings equations are used to evaluate the pressure far field. The role played by the incompressibility assumption is treated from theoretical and computational points of view; thus, some other numerical issues, concerning the wake modeling effects and the alternative methodologies, are discussed in order to assess the superiority of the acoustic analogy approach and to support its use for naval applications.
Performance Prediction of Newton-Rader Propellers
Authors: Young Yin L. , Liu Zhanke
Published: January 2021

In this work, a numerical method is presented for the hydrodynamic and hydroelastic analysis of Newton-Rader (NR) propellers (Newton & Rader 1961). The NR propellers are a well-known series of three-bladed propellers specifically designed, extensively tested, and well documented for high-speed crafts. The tests were conducted at the Vosper Cavitation Tunnel, and the propellers exhibit both face and back cavitation patterns (Newton & Rader 1961). The predicted fully wetted and cavitating performance agreed well with experimental measurements. The results indicate that the NR propellers can achieve high efficiency in both the fully wetted and cavitating regimes if the blades exhibit only back cavitation. However, significant reduction in efficiency was observed in all cases when face cavitation develops. The effects of varying blade area ratio on the hydrodynamic and structural performance are discussed. The importance of hydroelastic effects for both model-scale and full-scale NR propellers in uniform and wake inflow are presented.
Pitch and Heave Tests and Uncertainty Assessment for a Surface Combatant in Regular Head Waves
Authors: Irvine Martin
Published: January 2021

Towing-tank experiments of coupled pitch and heave motions are presented for a surface combatant advancing in regular head waves. The data include ballasting parameters, time histories, fast Fourier transform (FFT), Fourier series amplitudes, and pitch and heave transfer functions and phases for a range of speeds, wave steepnesses, and wave frequencies. The geometry is David Taylor Model Basin (DTMB) model 5512, which is a 1/46.6 scale geosim of DTMB model 5415 (DDG-51) with Lpp = 3.048 m. The experiments are performed in a 3.048 × 3.048 × 100 m towing tank equipped with a plunger-type wave maker. The test program is undertaken to provide a validation data set for unsteady Reynolds-averaged Navier-Stokes and other computational fluid dynamics (CFD) codes, including rigorous uncertainty assessment of the experimental results following standard procedures. Results indicate that the regular head waves are linear with second- and third-order magnitudes consistent with third-order Stokes waves. Pitch and heave responses and phases show expected trends for long and short wavelengths and are linear or Ak independent for all test conditions. Maximum response occurs for frequency of encounter equal to pitch and heave natural frequencies and Lpp / λ = 0.75. Under these conditions, an equation is derived that predicts the Froude number for maximum response as a function of ship geometrical coefficients.
The Rise of Water at a Ship Stem
Authors: Noblesse Francis , Delhommeau Gérard , Guilbaud Michel , Yang Chi
Published: January 2021

The height of water at the stem of a ship hull—with a nonbulbous wedge-shaped bow—that advances at constant speed in calm water is considered using two distinct methods:a theoretical-experimental approach in which elementary fundamental theoretical considerations (dimensional analysis and rudimentary asymptotic considerations in thin-ship, shallow-draft, and deep-draft limits) are used in conjunction with experimental measurements for simple hull forms and a rectangular flat plate towed at several yaw and heel angles; andthin-ship theory, that is, a fully analytical approach. Both of these two methods yield simple expressions that define the rise of water at a ship stem explicitly—ab initio and without calculations—in terms of the ship speed, draft, and waterline entrance angle. The theoretical-experimental expression and the thin-ship expression are in good agreement except at low Froude numbers and are also in reasonable agreement with experimental measurements.
Sinkage and Trim of a Fast Displacement Catamaran in Shallow Water
Authors: Gourlay Tim
Published: January 2021

A theoretical method is put forward for predicting the sinkage and trim of a fast displacement catamaran in shallow water. Special emphasis is placed on the trans-critical speed range, where sinkage and trim reach a maximum and the risk of grounding is at its highest. Results are condensed into simple formulas for estimating maximum sinkage and trim of a fast displacement catamaran through the transcritical speed range.
Ultimate Longitudinal Strength of Ship Hulls of Composite Materials
Authors: Chen Nian-Zhong , Soares C. Guedes
Published: January 2021

A progressive collapse analysis method is proposed to predict the ultimate longitudinal strength of ship hulls of composite materials. The load-average strain curve derived from a progressive failure nonlinear finite element analysis is adopted for representing the behavior of each stiffened composite panel forming a hull cross section. The bending moment of the ship hull under a prescribed curvature is achieved by integrating the reaction force of each stiffened panel over a hull cross section based on the load-average strain curves. The ultimate longitudinal strength of a ship hull is obtained from the moment-curvature relationship of the ship hull, which is established by imposing progressively increasing curvatures of a hull cross section. An all-composite ship is analyzed as an application.
Dynamic Positioning Thruster Near Wake Hydrodynamic Characteristics at Near Bollard Pull
Authors: El Lababidy Said A. , Bose Neil , Liu Pengfei , Walker Dan
Published: January 2021

The knowledge of the hydrodynamic characteristics and momentum effects of the flow of dynamic positioning (DP) thrusters are important factors in the design of structures around the DP thrusters and in improving DP system reliability. In the present study, the flow field around a DP thruster model was precisely measured in a cavitation tunnel using a two-component laser Doppler velocimetry (LDV) system. These experiments were carried out with and without a nozzle at three different axial planes up to 1.5 diameters downstream, and the results are presented here for a pitch/diameter ratio of 1.2 at near bollard pull operating conditions (J ¼ 0.4 and J ¼ 0.45). This paper shows and compares the results of the DP thruster near wake hydrodynamic and momentum characteristics when operating with and without a nozzle at two different low advance coefficient values.
Numerical Analysis of Ship-Generated Waves Action on a Vertical Cylinder
Authors: Dong G. H. , Sun L. , Zong Z. , An H. W. , Wang Y. X.
Published: January 2021

In this paper, the action of ship-generated waves on a nearby vertical cylinder is considered in pure theory. Intensive demands of modern sea transportation result in larger and larger ships. These ships generate high waves as they move in calm water. The ship-generated waves can travel long distances without much attenuation. They are so strong that they might cause damage to nearby marine structures (e.g., platforms, river banks, breakwaters, etc.). Therefore, it is necessary to evaluate the forces of ship-generated waves acting on nearby marine structures. The problem turns out to be composed of two problems: evaluation of waves generated by a moving ship (ship-wave problem) and evaluation of the action of ship waves on a cylinder (wave-action problem). Here the wave-action problem is computed in detail with a boundary element method in time domain. And the ship-wave problem is evaluated in the well-known Michell thin-ship theory. Thus, the problem posed in this paper is finally solved using numerical methods by combining the ship-wave and wave-action problems. The numerical analyses of the result are: The resultant forces and moments acting on the cylinder are surprisingly large, characterized by being highly oscillatory. The periods of the oscillations are proportional to ship speed. The actions of ship-generated waves on nearby structures are not negligible. This is a new factor necessary to be considered for design of both marine structures and ships. Meanwhile, the potential fatigue damage resulting from oscillations of the forces and moments should be considered, too.
Practical Evaluation of Steady Flow Resulting from a Free-Surface Pressure Patch
Authors: Noblesse Francis , Delhommeau Gérard , Yang Chi
Published: January 2021

The linearized potential flow resulting from a distribution of pressure that advances at constant speed along a straight path at the free surface of calm water, of effectively infinite depth and lateral extent, is considered. A practical method for evaluating the free-surface elevation caused by the moving free-surface pressure patch—which can be used to model steady flows of air-cushion vehicles, high-speed planing boats, surface-effect ships, and some types of hybrid ships—is given. The key ingredient of this method is a highly simplified analytical approximation to the local-flow component in the expression for the Green function associated with the classic Michell-Kelvin linearized free-surface boundary condition.
Naval Hull Form Multicriterion Hydrodynamic Optimization for the Conceptual Design Phase
Authors: Zalek Steven F. , Parsons Michael G. , Beck Robert F.
Published: January 2021

For a given set of ship design and operational criteria, there exists a trade-off between the ship's calm water powering performance and its seakeeping performance. Ship hulls that are designed for optimal powering performance can have poor seakeeping performance, and vice versa. It is typically not possible to obtain the global optimum for both of these objectives because of the competition between the powering and seakeeping performance functions and the design constraints. The set of globally nondominated solutions, or Pareto front, considering these competing criteria is searched for by navigating the multimodal search space using a multicriterion, population-based evolutionary algorithm optimization process. The optimization process uses a nontraditional objective function formulation that eliminates the need to tune the penalty function parameters for each new problem formulation and appears to provide a more thorough representation of the numerically approximated Pareto front. Results show that properly integrating this optimization process with the design criteria yields a set of hydrodynamically superior design solutions. The problem formulation and development is applicable to naval surface vessels and applied to a monohull frigate type example.
The Prediction of the Added Resistance for the Trimaran Ship With Different Side Hull Arrangements in Waves
Authors: Fang Ming-Chung , Wu Yi-Chin , Hu Deng-Kai , Lee Zi-Yi
Published: January 2021

In this paper, a second-order steady-state approach and a three-dimensional pulsating source distribution method are applied to derive the added resistance on a trimaran ship advancing in waves. The added resistance treated here is the secondorder steady-state hydrodynamic force, which can be expressed as products of the ship-motion responses, the radiation potential, diffraction potential, and the incident wave potential, and all related velocity potentials are in three-dimensional form. The steady flow potential is also included in the motion response calculation to investigate its effect on the added resistance. In order to validate the prediction method, the experiments for measuring the added resistance of a trimaran model in head waves were also handled in a National Cheng Kung University (NCKU) towing tank, and the related data are adopted to compare with the theoretical results. The comparisons show that the prediction results obtained in the paper generally agree well with experimental data; the validity of the prediction method applied here can be regarded as acceptable, and the effect of the steady flow potential on the added resistance of the trimaran ship can be neglected.
Robust Stress Check Formula of Lifting Padeye
Authors: Bo Zhou , Yujun Liu , Zhuoshang Ji
Published: January 2021

Lifting padeyes are widely used in the construction of offshore structures and ships. It has been shown that the traditional check method cannot reflect the realistic value and distribution of actual stress on the padeyes. A more accurate method for the padeye stress calculation is essential and important for promoting the safety of the padeyes. In this paper, a new check formula is proposed based on the analysis of deformation and external loads distribution on lifting padeyes. The results of finite element method and the solutions of traditional check formula and new check formula are compared. It is shown that, by applying the stress check formula derived in the paper, the value and the location of the dangerous stresses occurred can be evaluated easily and exactly. The safe reliability of structure design can be improved significantly.
Some Effects of Piston Friction and Crank or Gudgeon Pin Offset on Crankshaft Torsional Vibration
Authors: Guzzomi A. L. , Hesterman D. C. , Stone B. J.
Published: January 2021

The varying inertia associated with reciprocating mechanisms leads to nonlinear frequency coupling between rotational speed and an engine system's average torsional natural frequencies. This coupling can cause secondary resonance problems. Recent work by the authors has shown that piston-to-cylinder friction and gudgeon pin or crank offset can modify coupling behavior. These effects can be demonstrated by analysis of an engine's receptance function and through time simulations. This paper presents the derivation of a single-cylinder engine receptance in the presence of piston-to-cylinder friction. Simulations are then used to investigate some of the effects of piston-to-cylinder friction, offset, and excitation phase on the frequency content of the crankshaft velocity. Simulations indicate that nonlinear coupling is affected by these variables, which has implications for secondary resonance detection and prevention. The most significant finding is that stronger coupling behavior can occur when piston-to-cylinder lubrication breaks down.
Study on Mixed Pulse Converter (MIXPC) Turbocharging System and Its Application in Marine Diesel Engines
Authors: Cui Yi , Gu Hongzhong , Deng Kangyao , Yang Shiyou
Published: January 2021

In order to improve fuel efficiency and power density, the boost pressure of diesel engine is increasing continuously. The increase in boost level leads to some problems, such as lack of air under part load operating conditions, response delay during transient processes, and high mechanical and thermal load. In order to meet the high boost level demand, a new type of turbocharging system—mixed pulse converter (MIXPC) turbo-charging system for multicylinder diesel engines (from 4 to 20 cylinders) has been invented. A turbocharged diesel engine simulation model, based on one-dimensional finite volume method (FVM) and total variation diminishing (TVD) scheme, has been developed and used to design and analyze the MIXPC turbocharging system. The applications of MIXPC system in in-line 8- and 4-cylinder and V-type 16-cylinder medium-speed marine diesel engines have been studied by calculation and experiments. The results show that the invented MIXPC system has superior engine fuel efficiency and thermal load compared with original turbocharging systems.
Resistance of a Ship Undergoing Oscillatory Motion
Authors: Doctors Lawrence J. , Day Alexander H. , Clelland David
Published: January 2021

In this paper, we describe extensions to the research of Doctors et al. (Doctors, L. J., Day, A. H., and Clelland, D., 2008, Unsteady effects during resistance tests on a ship model in a towing tank, Journal of Ship Research, 52, 4, 263–273) and Day et al. (Day, A. H., Clelland, D., and Doctors, L. J., 2009, Unsteady finite-depth effects during resistance tests in a towing tank, Journal of Marine Science and Technology, 14, 3, 387–397) in which the oscillations in the wave resistance during the constant-velocity phase of a towing-tank resistance test on a ship model were measured and predicted, in the cases of relatively deep and relatively shallow water. In the current study, the ship model was towed with a harmonic velocity component superimposed on the usual constant forward velocity. This work constitutes a first step in the understanding of the unsteady hydrodynamics of a racing shell (rowing boat). We show here that the unsteady wave resistance varies considerably from the traditional (steady) average value. Indeed, the wave resistance is frequently negative during part of the oscillatory cycle. However, the general effect is an increase in the temporal mean value of the wave resistance; this suggests that every effort should be made to reduce the unsteadiness of the motion. We also demonstrate that the unsteady wave-resistance theory provides an excellent prediction of the measured effects summarized here. These predictions are often within a few percent of the measured values of the resistance.
Evaluation and Modification of a Robust Path Following Controller for Marine Surface Vessels in Wave Fields
Authors: Li Zhen , Sun Jing , Beck Robert F.
Published: January 2021

This paper evaluates a novel robust path following controller for marine surface vessels in wave fields. Because of complex wave structure interactions, most path following control designs neglect the wave impact at the design stage and rely on simulation or experiment to ensure the satisfactory performance in wave fields. In this paper, we first introduce a numerical test bed that combines the ship dynamics and wave effects on vessels to facilitate the model-base performance evaluation of path following control systems in wave fields. Then, a novel robust path following controller is described and its key features are summarized. Simulation results of the path following controller in the wave field are presented. Several issues, such as steady-state errors and rudder oscillations, have been identified, thereby motivating controller modification and gain retuning. Mitigating strategies for improving the controller performance are proposed and numerically evaluated. The simulation results show that the performance of the modified controller can be substantially improved in wave fields.
Time-Domain Simulations of Radiation and Diffraction Forces
Authors: Zhang Xinshu , Bandyk Piotr , Beck Robert F.
Published: January 2021

Large-amplitude, time-domain, wave-body interactions are studied in this paper for problems with forward speed. Both two-dimensional strip theory and three-dimensional computation methods are shown and compared by a number of numerical simulations. In the present approach, an exact body boundary condition and linearized free surface boundary conditions are used. By distributing desingularized sources above the calm water surface and using constant-strength flat panels on the exact body surface, the boundary integral equations are solved numerically at each time step. The strip theory method implements Radial Basis Functions to approximate the longitudinal derivatives of the velocity potential on the body. Once the fluid velocities on the free surface are computed, the free surface elevation and potential are updated by integrating the free surface boundary conditions. After each time step, the body surface and free surface are regrided due to the instantaneous changing wetted body geometry. Extensive results are presented to validate the efficiency of the present methods. These results include the added mass and damping computations for a Wigley III hull and an S-175 hull with forward speed using both two-dimensional and three-dimensional approaches. Exciting forces acting on a Wigley III hull due to regular head seas are obtained and compared using both the fully three-dimensional method and the two-dimensional strip theory. All the computational results are compared with experiments or other numerical solutions.
On the Physics of Vapor/Liquid Interaction During Impact on Solids
Authors: Yung T-W. , Sandström R. E. , He H. , Minta M. K.
Published: January 2021

Situations involving liquid impact on solid surfaces represent a class of mechanics that has broad practical application. In addition to the liquid and solid surface, most real applications occur in the presence of a vapor. This multiphase physics is complex, and the ambient vapor can have a major influence on the maximum impact pressure. While the ambient vapor is often ignored for its relatively low density, the experimental data in this paper illustrate that ambient vapor/liquid properties and their interaction during an impact event can alter maximum pressures by as much as 2 orders of magnitude. These experiments also provide a basis to demonstrate that the effect corresponds well to a dimensionless "Interaction Index" proposed in this paper. This index is a function of the ambient vapor and liquid properties that account for the degree of influence on the resulting pressure time history. The Interaction Index also provides an essential building block for scaling of experiments. The paper includes both a mathematical formulation and relevant physical test data. The results show that the Interaction Index performs remarkably well in physical tests over a broad range of vapor properties.
Current Capabilities of DES and LES for Submarines at Straight Course
Authors: Alin N. , Bensow R.E. , Fureby C. , Huuva T. , Svennberg U.
Published: January 2021

The flow around an axisymmetric hull, with and without appendages, is investigated using large eddy simulation (LES), detached eddy simulation (DES), and Reynolds averaged Navier Stokes (RANS) models. The main objectives of the study is to investigate the effect of the different simulation methods and to demonstrate the feasibility of using DES and LES on relatively coarse grids for submarine flows, but also to discuss some generic features of submarine hydrodynamics. For this purpose the DARPA Suboff configurations AFF1 (bare hull) and AFF8 (fully appended model) are used. The AFF1 case is interesting because it is highly demanding, in particular for LES and DES, due to the long midship section on which the boundary layer is developed. The AFF8 case represents the complex flow around a fully appended submarine with sail and aft rudders. An actuator disc model is used to emulate some of the effects of the propulsor for one of the AFF8 cases studied. Results for the AFF8 model are thus presented for both "towed" and "self-propelled" conditions, where as for the bare hull, only a "towed" condition is considered. For the AFF1 and the "towed" AFF8 cases experimental data are available for comparison, and the results from both configurations show that all methods give good results for first-order statistical moments although LES gives a better representation of structures and second-order statistical moments in the complex flow in the AFF8 case.
Safety Index of Fatigue Failure for Ship Structure Details
Authors: Wengang Mao , Rychlik Igor , Storhaug Gaute
Published: January 2021

One way to assess the uncertainty in fatigue damage analysis is to use a so-called safety index. In the computation of such an index, the variation coefficient for the accumulated damage is required. In this paper the expected fatigue damage and its coefficient of variation are firstly estimated from measured stress. Secondly, when suitable stress measurements are not available these are computed from models for damage accumulation and sea states variability. Stresses during the ship sailing period are regarded as the nonstationary, slowly changing, Gaussian processes, and hence damage accumulation, during encountered sea state, can be approximated by an algebraic function of significant wave height, ship speed, and heading angle. Further, the space time variability of significant wave height is modeled as a log normal field with parameters estimated from the satellite measurements. The proposed methods to estimate uncertainties in the damage accumulation process are validated using full-scale measurements carried out for a container vessel operating in the North Atlantic.
An Experimental Investigation into the Influence of Ramp-Mounted Vortex Generators on the Performance of a Flush Waterjet Inlet
Authors: Brandner P. A. , Dawson E. C. , Walker G.J.
Published: January 2021

The use of ramp-mounted vortex generators for reduction of pump face flow distortion within a generic flush type waterjet inlet has been investigated experimentally. Tests were performed in a cavitation tunnel with the model inlet fitted to the ceiling of the test section and an upstream boundary layer artificially thickened to 30° of the inlet duct diameter. A group of four delta-shaped vortex generators on the inlet ramp mounted symmetrically about the vertical center plane were tested at six streamwise locations and at two incidences. The vortex generators were oriented each side of the centerplane to produce corotating vortex pairs opposing the effects of the dominant secondary flow within the curved duct. The model inlet was fitted with a range of instrumentation to investigate the ramp pressure distribution, lip incidence, and pump face flow properties. Lip cavitation inception, and vortex generator cavitation inception and occurrence were also investigated. Pump face flow distortion within the bare duct flow, which was dominated by a total pressure/velocity deficit at the top of the disc, was significantly reduced by the addition of the vortex generators. Circumferential distortion improvements were assessed using a distortion parameter, harmonics of the velocity variation, and considerations of rotor blade incidence variation. The vortex generators were found to have little effect on local lip pressures and consequently lip cavitation inception; they also had a negligible effect on the duct pressure recovery. Cavitation occurrence on the vortex generators was found to present potential performance limitations at low cavitation numbers.
On the Influence of the Warping Shear Stress on the Hull Girder Strength
Authors: Campanile A. , Mandarino M. , Piscopo V.
Published: January 2021

In this paper a new theory is proposed for the shear stress evaluation; new relations have been obtained for the tangential stresses and the normal ones, generated by the shear force variability; a numerical method has been developed that gives the same values for the tangential stresses as the traditional shear stress theory and evaluates the normal stress field, by a Ritz variational procedure. A numerical application of the developed method is carried out for a bulk carrier, obtaining an appreciable redistribution of the r stresses, for the alternate holds loading condition, characterized by great values of the unit vertical shear.
Optimization of Ships’ Diagonal Ballast Water Exchange Sequence Using a Multiobjective Genetic Algorithm
Authors: Chen Jing , Lin Yan , Huo Junzhou , Zhang Mingxia , Ji Zhuoshang
Published: January 2021

Ballast water management and the method chosen to achieve it is a key issue and concerns key technologies in ship design. If the sequential exchange method is the chosen method, the sequence chosen to perform the exchange is very important and affects many aspects including ships' stability, structural strength, maneuverability, operational expenses and building cost, and so forth. In this paper, based on the multiple risk assessment criteria of the sequential method, the problem of finding a feasible and optimum exchange sequence is boiled down to a multiobjective combinatorial optimization problem with multiple nonlinear constraints. The diagonal exchange strategy was adopted, and the diagonal exchange mathematical model was built, taking into consideration the ship's intact stability, structural strength, trims, draughts, and bridge vision. In order to find a set of Pareto solutions, a multiobjective genetic algorithm (MOGA) was used. In the algorithm, a constraint-domination principle was adopted to handle the multiple constraints, and a nondominated sorting method was used to perform the selection of the Pareto solutions. Using the proposed mathematic model and the MOGA, a Pareto solution set that met all the design criteria could be efficiently and accurately obtained for the engineers to choose from within short running times. Compared with the traditional symmetrical exchanging method, the simulation results showed that the proposed method can produce more and better solutions with smaller trims, smaller bridge blind vision range, and better structural strength performances.
Nonlinear Surge Dynamics of a Ship in Astern Seas: “Continuation Analysis” of Periodic States with Hydrodynamic Memory
Authors: Spyrou Kostas J. , Tigkas Ioannis G.
Published: January 2021

Continuation analysis is performed for the coupled surge, heave, and pitch motions of a ship in steep following seas. The focus of the work is on the efficient elicitation of system dynamics related to the phenomena of nonlinear surging and surf-riding. Background material with several references can be found in Spyrou (1996a, 1996b, 1997, 2006). Main novel features of the current work are the inclusion of fluid memory effects within the framework of continuation analysis and the successful implementation of continuation for the periodic motions that correspond to the "overtaking waves" scenario. The entailed steps for realizing these goals are discussed in detail. Application is presented for a well-known ITTC ship.
A Method to Scale the Roughness of Submarine Nonskid Coatings on a Free-Running Model for Maneuvering Experiments
Authors: Shen Young T. , Hess David E.
Published: January 2021

A portion of the upper-deck surface of a submarine can be coated with roughness for crew safety when walking on the hull. The roughness factor for the nonskid coating on a full-scale submarine is very large, on the order of 400 under typical ship operation conditions. Boundary layer development, flow separation, cross-flow drag, hull surface pressure, and ship motion may be modified by the presence of this coating during turning maneuvers. Free-running model (FRM) submarines are routinely employed by the Naval Surface Warfare Center to characterize submarine maneuvering behavior, and the application of an appropriately sized nonskid coating to the model is required for fidelity of model maneuvering experiments. Three methods to scale the coating have been investigated, and conventional geometric scaling and wall shear velocity scaling methods were found to be inadequate. A new scaling method termed the momentum boundary layer thickness (MBLT) method has been developed. This method relates the cross-flow drag on the FRM with that on the full-scale vehicle. Boundary layer velocity profiles on an axisymmetric body at model and full-scale Reynolds numbers have been computed by a RANS code. Velocity profiles encountered by the full-scale nonskid coating are found to match well with those developed on the FRM with roughness sized using the MBLT method. The scaled roughness size compares favorably with two empirically determined roughness sizes that have been previously used on FRMs that have shown good correlation with full-scale maneuvering data.
Experience from SIMMAN 2008—The First Workshop on Verification and Validation of Ship Maneuvering Simulation Methods
Authors: Stern F. , Agdraup K. , Kim S. Y. , Hochbaum A. C. , Rhee K. P. , Quadvlieg F. , Perdon P. , Hino T. , Broglia R. , Gorski J.
Published: January 2021

The SIMMAN 2008 workshop was held in Copenhagen, Denmark in April 2008. The purpose of the workshop was to benchmark the prediction capabilities of different ship maneuvering simulation methods including systems- and CFD-based methods through systematic quantitative comparisons and validation against EFD data for tanker (KVLCC), container ship (KCS), and surface combatant (5415) hull form test cases. For the KVLCC test case, two stern shape variants named KVLCC1 and KVLCC2 giving different instability loops were included. Free model test data was compared with systems-based methods and CFD for specified free maneuvers. Some of the systems-based methods used provided PMM and CMT data, and two used CFD instead. CFD-based methods were used to simulate forced motions and were compared with PMM/CMT model test data. The submissions were blind in the sense that the benchmark model test data was not provided prior to the workshop, unless data was required as input to the simulation method. A total of 64 submissions were received for the free maneuver simulations, which included a wide range of the state-of-the-art methods in use today, such as PMM- and CMT-based methods, CFD based methods, system identification, neural network tools and various empirical methods. For the forced motion simulations a total of 16 submissions were received, comprising different CFD-based methods such as RANS, URANS, and DES. This paper gives an overview of hulls, model tests, test cases, submissions, comparison results as well as the most important observations and conclusions.
Ship Drag Reduction by Air Bottom Ventilated Cavitation in Calm Water and in Waves
Authors: Amromin Eduard , Karafiath Gabor , Metcalf Bryson
Published: January 2021

The goal herein is ship drag reduction by air bottom cavitation in the moderate range of Froude number Fr (0.4 < Fr < 0.65) in both calm water and in waves. A ship hull with a bottom niche terminating in a cavity locker/seal (suppressing cavity tail oscillations and reducing the air escape from the cavity) was designed using nonlinear ideal fluid theory. The wave impact on the cavity shape and drag reduction was estimated with a novel analytical approach that takes into account the air compressibility in the cavity and air entrainment by the water. The model drag was measured in the Naval Surface Warfare Center linear tow tank at different drafts in calm water and in waves. The baseline configuration was with the niche closed by a flat cover. The attained total drag reduction at 0.45 < Fr < 0.63 was up to 25%, whereas the air supply power was under 4% of the gain in the required propulsion power. The air cavity was stable in waves (up to sea state 5 for a 90 meter ship) and the effectiveness of drag reduction by cavitation in seaway was greater than in calm water due to smaller wave-induced additional drag of the ship with air bottom cavity. Two identical models were built and tested also as a seatrain. However, the percentage drag reduction due to cavity ventilation in the seatrain configuration was less than for a single hull. The need for fine tuning the air supply distribution between the hulls was found.
Time-Variant Redundancy of Ship Structures
Authors: Decó Alberto , Fragopol Dan M. , Okasha Nader M.
Published: January 2021

An efficient procedure for the computation of the redundancy of ship structures is presented. The changes in the redundancy due to corrosion section loss over time are also studied. Moreover, uncertainties associated with structural geometry, material properties, and loading, are accounted for. In order to calculate the redundancy index, the probability of failure of the first component and the probability of ultimate failure of the whole hull girder must be evaluated. The probability of failure is computed using a hybrid Latin Hypercube - second-order reliability method (SORM) technique. The deterministic analyses during the simulations are conducted using an optimization approach for computing the ultimate bending strength of the whole hull girder and the progressive collapse method for computing the first bending failure.
Corrosion-Dependent Ultimate Strength Assessment of Aged Box Girders Based on Experimental Results
Authors: Saad-Eldeen S. , Garbatov Y. , Guedes Soares C.
Published: January 2021

This paper presents a corrosion-dependent analysis of the ultimate strength analysis of aged box girders based on experimental results. Three multispan corroded stiffened box girders subjected to four-point vertical load are analyzed, idealizing the behavior of midship sections of full ships. The specimens have three levels of corrosion. Two corrosion-dependent formulas for assessing the ultimate strength as well as the ultimate bending moment of corroded structures are proposed. Using a time-dependent corrosion growth model, equivalent time-dependent formulations are developed. The effect of corrosion degradation on the residual stresses during the service life is also analyzed, and a regression equation for predicting the remaining residual stresses along the service life is proposed. Finally, a corrosion-dependent moment-curvature relationship has been developed accounting for the changes in geometrical characteristics and material properties of the tested box girders.
A Hydrodynamic Preliminary Design Optimization Framework for High Speed Planing Craft
Authors: Mohamad Ayob Ahmad F. , Mohamad Ayob Ahmad F. , Ray Tapabrata , Smith Warren
Published: January 2021

Ship design optimization in preliminary design stage aims to identify optimum vessel dimensions based on performance targets and design constraints simultaneously. Although vast amount of designs have been generated and evaluated since the application of optimization approaches to ship design, only a few of such designs have been built or "dissected" to gain a deeper understanding as to why such designs tend to be optimal. In this paper an optimization framework is introduced for the design of high speed planing craft, which consists of a geometry module, standard performance estimates, and a suite of state-of-the-art optimization algorithms. Single and multiobjective optimization problem formulations are solved using the framework. Designs identified through the process of optimization are further analyzed to uncover relationships among the design variables that lead to better designs. An important contribution of this paper is to illustrate the steps involved in deriving pseudo performance estimates and their utility in the context of preliminary design where such relationships can be effectively and efficiently used to sieve through a large number of designs.