bluuebunny/crossref_metadata_2025 huggingface dataset:
A New TOPSIS Methodology Based on Single-Valued Neutrosophic Numbers for Selection of Suitable Roll Stabilizer Type for Motor Yachts
Authors: Sener Bekir , Balin Abit , Yildiz Burak , Demirel Hakan
Published: January 2021

Selection of a suitable stabilization system for motor yachts is a challenging problem for both owners and designers. Also, this is a good sample of multicriteria decision-making problem that includes many criteria required to be assessed at the same time. The present work aims to propose an extended Technique for Order Preference by Similarity to Ideal Solution methodology based on single-valued neutrosophic numbers which represent the uncertainty of real-world applications. A questionnaire was applied to a group of experts who were asked to evaluate four different stabilizer alternatives according to the 15 criteria determined. Evaluations of the experts were analyzed through the proposed methodology, and results were presented and discussed.
Optimization of Ship Design within an Integrated Multimodal Transport System
Authors: Gkochari C. C. , Papanikolaou A. D.
Published: January 2021

A methodology for the optimization of ship design within a multimodal transport system, accounting for logistics, economics, and environmental issues, is presented and its application to a typical shortseashipping scenario is demonstrated. The introduced methodology reveals the benefits of a holistic scientific approach to the optimization of complicated transportation problems.
Performing Detailed Design Reviews of a US Navy Surface Combatant within an Integrated Data Environment
Authors: Grogan G. R. , Borthen J. L.
Published: January 2021

Between November 2006 and March 2009, the US Navy's first Zumwalt class guided missile destroyer, DDG 1000, underwent detailed design. According to a Government Accountability Office shipbuilding study in 2005, late changes to a ship's design is recognized as the primary factor contributing to increasing ship construction costs. Therefore, a strict detailed design review process was implemented for DDG 1000 that included improved computer-aided design tools and more efficient communication methods than previous ship detailed design efforts. The actual benefit of the design reviews of the ZUMWALT class will not truly be known until after the lead ship has been commissioned; however, the design reviews, along with the unprecedented involvement by stakeholders via an integrated data environment, have already proved to be an effective means for reducing the probability that setbacks will be encountered at the waterfront.
System Development and Applications of a Shipyard Layout Design Framework
Authors: Song Young Joo , Lee Dong Kun , Woo Jong Hun , Shin Jong Gye
Published: January 2021

Shipyard design and the equipment layout problem, which is directly linked to the productivity of ship production, is an important issue in the production planning of mass production of ships. In many cases, shipbuilding yard design has relied on the experience of the internal engineer, resulting in sporadic and poorly organized processes. Consequently, economic losses and the trial-and-error involved in such a design process are inevitable problems. In this paper, a checklist of major elements is defined in order to fine-tune the shipbuilding yard designing process. The input/ output data based on the simulation of a shipbuilding yard layout designing framework and methodology proposed in previous research is also defined. Initial architecture is executed to develop software that integrates all the relevant processes and designing tools. In this course, both user request and design data by the steps are arranged and organized in the proposed layout design template form. In addition, simulation is carried out based on the parent shipbuilding process planning and scheduling data of the ship product, shipbuilding process, and work-stage facilities that constitute the shipbuilding yard. In addition, design items are verified and optimized with a layout and equipment list that shows optimal process planning and scheduling effects. All of the content of this paper is based on the simulation-based shipbuilding yard layout designing methodology, while the initial architectural processes are based on object oriented development methodology and systems engineering methods.
A New Approach to Ship Repair Using CONWIP and Parts Kits
Authors: Rodzewicz Thomas C. , Potterton Jonathan H. , Lappe Katherine M. , Yezefski Brent C. , Singer David J.
Published: January 2021

The Constant Work in Process (CONWIP) system uses elements of push, pull, and parts kitting to reduce overall process times and minimize variability. The research presented in this paper introduces the CONWIP concept to ship repair through the completion of a discrete event simulation. The research demonstrates that a CONWIP approach to ship repair can improve drydock turnover for large classes of ships requiring similar repairs, such as the US Coast Guards Mission Effectiveness Project.
Practical Design Equations for Cold Roll Forming of Doubly Curved Hull Plates Using Line Array Roll Set
Authors: Shim Do-Sik , Yang Dong-Yol , Kim Kwang-Heui , Chung Sung Wook , Han Myoung Soo
Published: January 2021

The line array roll set (LARS) process, as one of many kinds of incremental forming processes, is a continuous process in which a flat metal plate is formed into a singly or doubly curved plate through successive passes of forming rolls. It was found that the curvature level of the formed plates in the previous study was well over the curvature required in shipyards. This fact shows that the LARS method has good potential for shipbuilding applications. A ship hull is composed of many curved plates with various double curvatures. Consequently, for the desired curvatures of target shapes, the bending radii must be determined considering the springback phenomenon. In the present study, design equations are proposed for engineering applications, particularly in relation to shipbuilding. For the development of design equations, the deformation of the plates is analyzed using some engineering assumptions. In addition, experimental coefficients are introduced to simplify the theoretical equations. The experimental coefficients are determined as the best fit for the experimental data using the least squares method, resulting in the derivation of design equations. It has been shown that the prediction from the design equation with the results from the experiments shows good agreement and can be used for practical applications.
Development of Distortion Modeling Methods for Large Welded Structures
Authors: Yang Y. P. , Castner H. , Kapustka N.
Published: January 2021

Two distortion modeling methods, mapping plastic strain and lump-pass modeling, were developed and validated for predicting distortion on large welded structures to reduce the computation time. The mapping plastic strain method requires two kinds of models, local models and a global model. The local models are analyzed to predict plastic strains, and the global model is analyzed by mapping the plastic strains to predict distortions. The lump-pass modeling method includes two kinds of analyses: a thermal analysis and a thermomechanical analysis. The thermal analysis is conducted to predict temperature history. The thermomechanical analysis is performed to predict distortion by inputting the predicted temperature history.
Kinetics of Electrocoagulation of Hexane Extractable Materials in Artificial Bilge Water Treatment
Authors: Rincon Guillermo J. , La Motta Enrique J. , Mickler Blake
Published: January 2021

Research on the electrocoagulation (EC) of hexane extractable materials (HEM) has been conducted at the University of New Orleans using a commercial bench-scale EC reactor. A series of EC experiments were performed using a synthetic emulsion with a HEM concentration of approximately 700 mg/L−1. It was confirmed that EC of HEM follows first-order kinetics, and kinetic constants of 0.0441 s−1 and 0.0443 s−1 were obtained from applying both the dispersion and tanks-in-series (TIS) models, respectively. In both cases, R2 was 0.97. Also, the TIS model indicated that each cell of the EC behaves as an independent continuous-stirred tank reactor.
Simulation-Based Work Plan Verification in Shipyards
Authors: Lee Dong Kun , Shin Jong Gye , Kim Youngmin , Jeong Yong Kuk
Published: January 2021

The productivity of a shipyard depends on how efficiently and systematically its limited resources are managed and used. Korean shipyards, the most competitive in the world, have developed and operate their own production management systems to attain high productivity, each of which reflects the unique characteristics of a specific company. Recently, research on simulation methods to enhance production management systems has been gaining popularity. Production management based on simulations rejects decision-making based on experience and intuition and values the establishment of improvement methods based on quantitative and concrete data. In this article, simulation is applied to the work plan as part of the production planning in shipyards. To this end, the work planning processes and planning systems are analyzed. Based on this analysis, a simulation model and application system are suggested. By using the results obtained in this study, it is expected that shipyards can construct cycles for establishing, simulating, and analyzing work plans, enabling the establishment of more precise production plans.
A Proposed Methodology for the Technoeconomic Evaluation of Energy Efficiency Retrofits: A Bulk Carrier Case Study
Authors: Tsereklas-Zafeirakis Angelos , Aravossis Konstantin , Gougoulidis George , Pavlopoulou Yanna
Published: January 2021

In light of the International Maritime Organization (IMO) directives on climate change and the continuous effort of shipping companies to reduce operating costs, this article proposes a methodology for the technoeconomic evaluation of energy efficiency retrofits. The aim of this article is to provide a management tool able to support the decision-making process of investing in energy efficiency methods. The introductory part briefly discusses the environmental problem caused by the gaseous pollutants as well as the regulatory framework that is going to seriously affect the bunker pricing in the near future. In the main part, a series of energy efficiency retrofits, suggested by IMO in the Ship Energy Efficiency Management Plan Annex, are presented with a view to applying them on a bulk carrier. The analysis focuses on the evaluation of these retrofits as potential investments from an owner's strategic point of view. The assessment takes into account major uncertainties of the data used through Monte Carlo simulations and conducts multicriteria analysis to include also nonfinancial criteria in the decision-making process.
A Hybrid 2.5-Dimensional High-Speed Strip Theory Method and Its Application to Apply Pressure Loads to 3-Dimensional Full Ship Finite Element Models
Authors: Zhao Chengbi , Ma Ming
Published: January 2021

As the three-dimensional (3D) finite element model (FEM) has become the de facto standard for ship structural design, interest in accurately transferring seakeeping loads to panel-based structural models has increased dramatically in recent years. In today's design practices, panel-based hydrodynamic analyses are often used for mapping seakeeping loads to 3D FEM structural models. However, 3D panel-based hydrodynamic analyses are computationally expensive. For monohull ships, methods based on strip theories have been successfully used in the industry for many years. They are computationally efficient, and provide good predictions for motions and hull girder loads. However, many strip theory methods provide only hull girder sectional forces and moments, such as vertical bending moment and vertical shear force, which are difficult to apply to 3D finite element structural models. Previously, the authors have proposed a hybrid strip theory method to transfer 2D strip theory-based seakeeping loads to 3D FEM. In the hybrid approach, the velocity potentials of strip sections are first calculated based on the ordinary 2D strip theories. The velocity potentials of a finite element panel are obtained from the interpolation of the velocity potentials of the strip sections. The panel pressures are then computed based on Bernoulli's equation. Integration of the pressure over the FEM wetted panels yields the hydrodynamic forces and moments. The equations of motion are then formulated based on the FEM. The method not only produces excellent ship motion results, but also results in a perfectly balanced structural model. In this article, the hybrid approach is extended to the 2.5D high-speed strip theory. The simple Rankine source function is used to compute velocity potentials. The original linearized free surface condition, where the forward speed term is not ignored, is used to formulate boundary integral equations. A model based on the Series-64 hull form was used for validating the proposed hybrid method. The motion response amplitude operators are in good agreement with VERES's 2.5D strip theory and with experimental results. Finally, an example is provided for transferring seakeeping loads obtained by the 2.5D hybrid strip theory to a 3D FEM.
Parametric Design and Multiobjective Optimization of Containerships
Authors: Priftis Alexandros , Papanikolaou Apostolos , Plessas Timoleon
Published: January 2021

The introduction of the energy efficiency design index (EEDI) and ballast water treatment regulations by the International Maritime Organization, the fluctuation of fuel price levels, along with the continuous endeavor of the shipping industry for economic growth and profits has led the shipbuilding industry to explore new and cost-efficient designs for various types of merchant ships. In this respect, proper use of modern computer-aided design/computer-aided engineering systems (CAD/CAE) extends the design space, while generating competitive designs with innovative features in short lead time. The present article deals with the parametric design and optimization of containerships. The developed methodology, which is based on the CAESES/Friendship-Framework software system, is demonstrated by the conceptual design and multiobjective optimization of a midsized, 6500-TEU containership. The methodology includes a complete parametric model of the ship's external and internal geometry and the development and coding of all models necessary for the determination of the design constraints and the design efficiency indicators, which are used for the evaluation of parametrically generated designs. Such indicators defining the objective functions of a multiobjective optimization problem are herein the EEDI, the required freight rate, the ship's zero ballast container box capacity, and the ratio of the above to below deck number of containers. The set-up multiobjective optimization problem is solved by use of the genetic algorithms, and clear Pareto fronts are generated. Identified optimal design proves very competitive compared with the standard containership designs in the market.
Model-Based Computational Shipyard Dynamics and Its Applications
Authors: Shin Jong Gye , Kim Youngmin , Jeong Yong-Kuk , Woo Jong Hun , Ryu Cheolho
Published: January 2021

A ship production system can be represented by various production factors and production management indicators. To manage such a system efficiently, a theory is required to analyze and predict its behavior. The theory should be able to fully express the relationships between production factors and production management indicators. For this purpose, computational shipyard dynamics was proposed by Kim et al. in the Journal of Ship Production and Design (2018). This methodology includes input variables, output variables, and key performance indicator (KPI) functionals, implemented as a simulation model. In this study, a rigorous approach to realize a model of a complex ship production system is presented by embodying previous research. A model-based ship production system theory is defined, which consists of production factors, production management indicators, and the relationships between them, called the simulation-based KPI functionals. The production factors are defined using a six-factor model, and the production management indicators are defined using KPIs that are already used in shipyards so that they are quantitatively measurable. To verify the proposed theory, it was applied to fabrication shop, panel block assembly line, and ship block logistics simulation cases, which are examples that are similar to the job shop, flow shop, and project shop cases, respectively.

Introduction

1.1. Background

Approximately 40% of shipyards worldwide have been closed over the last decade. The reasons for this are the economic recession and intense competition. Inefficiency in the production system is not a big problem in the marine shipping industry and offshore-plant-related industries when these industries are booming with high demands and sufficient funding. However, when crises approach, unrevealed problems emerge, and low productivity leads to catastrophes at shipyards.
A Study of Midship Bending Moments in Irregular Head Seas
Authors: Lewis Edward V.
Published: January 2021

In this article an exploratory study on behalf of the S-3 Panel of The Society of Naval Architects and Marine Engineers is reported, in which the statistical characteristics of model bending moments in irregular head seas have been predicted on the basis of the principle of linear superposition of responses to the component waves. It is shown that for the case of a T2-SEA1 tanker model, agreement between predicted and observed bending moments in irregular waves is reasonably good. The method is then applied to predicting the trend of bending moments with severity of sea and speed of ship.
Propellers in Nozzles
Authors: van Manen J. D.
Published: January 2021

The paper deals with the vortex system of the "screw + nozzle" propeller. The results obtained from systematic experiments with propellers in nozzles in which the length-diameter ratio of the nozzle, the number of blades, and the blade-area ratio of the propeller have been varied are discussed. In addition the results of experiments carried out for determining the optimum diameter of the nozzle system behind the ship are described. Explanatory comments on nozzle design are given, including diagrams for determining the radial inequality of the axial velocities in the nozzle and for making computations with regard to cavitation and strength. The influence of the clearance between blade tip and nozzle wall is discussed.
Energy Expressions and Differential Equations …. for Stress and Displacement Analyses of Arbitrary Cylindrical Shells
Authors: Kempner Joseph
Published: January 2021

Energy expressions and the related equilibrium equations and natural boundary conditions for the determination of the stresses in and displacements of uniform, thin-walled cylinders of arbitrary cross section loaded in an arbitrary manner by surface and edge forces and moments are presented. The derivations are based upon the Kirchhoff-Love assumptions of the classical theory of shells and are performed to within a degree of accuracy employed by Flügge in his derivation of the equilibrium equations applicable to circular cylindrical shells; hence, in terms of stress resultants, the exact, small-deflection equilibrium equations are obtained. Methods of simplification of the relations derived and of solution of the differential equations presented are indicated.
The Frictional Resistance and Turbulent Boundary Layer of Rough Surfaces
Authors: Granville P. S.
Published: January 2021

By means of the similarity laws of the turbulent flow in boundary layers, a general relation is developed for the frictional resistance of flat plates with arbitrary roughness from which logarithmic formulas are obtained for the specal cases of the fully rough regime, the quasi-smooth regime, and engineering roughness. Among other uses, this general relation permits for the first time a simple rational extrapolation to full-scale conditions of the frictional resistance of model plates covered uniformly with any irregular full-scale roughness encountered in practice. Furthermore, for calculations of turbulent boundary layers in pressure gradients on rough surfaces, relations are derived for the local skin friction and velocity-profile shape parameter in terms of momentum-thickness Reynolds number. Simplified relations also are derived for the velocity profile of the transitional sublayer in the vicinity of a rough surface.
Bulkhead Plating
Authors: Sellers M.L. , Evans J.Harvey
Published: January 2021

This paper reports an attempt to find satisfactory expressions for transverse bulkhead plating thickness in meaningful mathematical terms including all the most important parameters. In the investigations on which it is based, numerous theoretical solutions were used, some of which included the effects of membrane stresses and plastic behavior. These were related to the requirements of classification societies and other data representative of satisfactory service experience. The results are expressed as simple semiempirical formulations based on elasticity theory.
Lateral Force and Moment on Ships in Oblique Waves
Authors: Hu Pung Nien
Published: January 2021

A method for evaluating the exciting force and moment on surface ships as well as on fully submerged bodies in oblique waves is developed, based on the assumptions of long regular waves and slender bodies. The differential equation, together with the boundary conditions, for each component of the velocity potential is studied. Momentum theorems for slender-body sections are derived and applied to the evaluation of stripwise force and moment on bodies in the presence of a free surface. The result is found to be directly related to the added masses of the body sections. Lateral added masses of body sections in the presence of a free surface are investigated in detail and numerical values are presented for Lewis sections.
Static Performance Analysis and Experimental Investigation of the “Hydroskimmer” Air-Cushion Vehicle
Authors: Stoller Harold M.
Published: January 2021

An analysis is presented for the zero pitch static performance of a three-dimensional ground-effect machine with varying height nozzles based on "thick-jet" theory. Experimental data are presented for the static performance and stability behavior of the Bureau of Ships' Hydroskimmer Air Cushion Vehicle for a peripheral nozzle configuration with and without an interior nozzle. The analysis developed is used to compute the performance characteristics of the Hydroskimmer and comparison is made with zero pitch experimental results.
Three-Dimensional Approach to the Gust Problem for a Screw Propeller
Authors: Shioiri J. , Tsakonas S.
Published: January 2021

The unsteady lifting-surface approach is utilized for the hull-induced gust problem in the marine propeller case and the corresponding surface integral equation is solved under the Weissinger approximation. The applicability of the Weissinger method to the nonstationary flow case is studied. The kernel function is evaluated after some mathematical simplification. From numerical calculations of unsteady lift due to the gust, which are restricted to a four-bladed propeller of sector form blade with different blade-area ratios and various pitch-diameter ratios, conclusions are drawn as to the dependence of unsteady lift on such important parameters as the blade-area and pitch-diameter ratios, and the nature of the three-dimensional effects in the unsteady gust problem is clarified.
A Note on Short-Time Prediction of Ship Motions
Authors: Dalzell John F.
Published: January 2021

The prediction of aircraft-carrier, landing-ramp motions a short time into the future, is a problem of importance in that new or improved methods lead directly to increased safety and extended operational capability. This note presents a possibly different point of view of this problem and the results of some preliminary work which indicate that further study of the feasibility of this approach may be warranted.
Added Masses of Two-Dimensional Forms by Conformal Mapping
Authors: Landweber L. , Macagno M.
Published: January 2021

The Bieberbach method of mapping a plane section into a circle is found to converge too slowly for practical application when the number of terms of an assumed transformation series is increased. A modification of the procedure, in which, after a first mapping by the Bieberbach method into a nearly circular section, the latter is mapped into a much more nearly circular section by a second application of the method, is found to yield sufficiently accurate results. A FORTRAN program for computing mapping functions is presented. Motivation for this development is to make available a more accurate procedure than is presently used in ship-vibration calculations for obtaining the added masses of ship sections in horizontal or vertical vibration at a free surface.
The Effect of Air Compressibility in a First Approximation to the Ship Slamming Problem
Authors: Johnson Robert S.
Published: January 2021

It has been suggested that the high pressures exerted on the bottom of a ship's hull during slamming are developed in the air trapped between the hull and the water's surface. To test this hypothesis, the two-dimensional, unsteady problem of the flow of air, where compressibility is accounted for, between a rigid, flat-bottomed block falling towards a rigid plane, is solved using a numerical method. The computed pressures exceeded those found experimentally by Maclean [8],2 and it is concluded that the deformation of the water's free surface must be accounted for in order to obtain agreement with the experiment. To the author's knowledge, the numerical method, a modified version of Sauer's method of Near Characteristics, is applied here for the first time, and a maximum allowable time step, for this problem, is found by digital computer experimentation.
Pressure Stability of Orthotropic Prolate Spheroids
Authors: Becker Herbert
Published: January 2021

Through the use of general instability theory for doubly curved orthotropic shells, a mathematical relation was developed to predict external pressure buckling of stiffened prolate spheroids. The procedure was applied to two experiments which were found to be in fair agreement with theory. In general, the method is applicable to doubly curved shells with orthotropic material properties (composites) as well as geometric orthotropicity, and subject to arbitrary membrane stress fields. It is not limited to pressure alone. Furthermore, because of the closed form of the solutions to many problems, the procedure would be particularly useful for optimization purposes.
Effect of a Rotational Wake on the Wavemaking Resistance of an Ogive
Authors: Tatinclaux J.-C.
Published: January 2021

The rotational wake of a two-dimensional ogive in an unbounded fluid is simulated by a volume distribution of vertical line vortices. Expressions for the wave elevation and the wave resistance, including wake effect, are derived. It is found that, with the chosen vorticity, the wave resistance is from 10 percent larger to 35 percent smaller, depending upon the Froude number, than in the irrotational case. It is shown that, when the wave elevation ζ is expressed as the sum of its asymptotic form ζas and a quantity Z(ω;x,y) representing the local effect of the vorticity present in the vicinity of the transverse cut, Eggers' method for the determination of the wave resistance from surface-profile measurements is valid when applied to the asymptotic wave profile, i.e. to the quantity [ζ(x,y) – Z(ω;x,y)].
Sway Added-Mass Coefficients for Rectangular Profiles in Shallow Water
Authors: Flagg C. N. , Newman J. N.
Published: January 2021

This paper presents analytic and numerical results for the added-mass coefficients of two-dimensional rectangular cylinders, accelerating laterally in shallow water. The free surface is assumed rigid, corresponding to low-frequency oscillations in waves or low Froude number maneuvers in calm water. The effects of finite water depth are most significant for rectangles of large beam-draft ratio.
On the Wave Resistance of a Submerged Spheroid
Authors: Farell César
Published: January 2021

A solution to the problem of potential flow about a submerged prelate spheroid in axial horizontal motion beneath a free surface has been derived within the theory of infinitesimal waves, satisfying exactly the body boundary condition, and the wave resistance of the spheroid has been evaluated. The solution is in the form of a distribution of sources on the surface of the spheroid; the analysis yields an infinite set of equations for determining the coefficients of the expansion of the potential of the distribution in spheroidal harmonics. The difference between the present results for the wave resistance and those given by Havelock's approximation is found to be rather significant. Comparison with experimental wave resistance measurements obtained using the wake-survey technique shows agreement for Froude numbers between 0.35 and 0.40.
Wave Forces on a Stationary Platform of Elliptical Shape
Authors: Chen H. S. , Mei C. C.
Published: January 2021

Exciting forces and moments due to plane incident waves on a stationary platform are studied in this paper. The platform is a vertical cylinder with a finite draft and elliptical cross section. The mathematical solution to the diffraction problem is obtained on the basis of the linearized long wave approximation. Numerical results via Mathieu functions are presented for a shiplike body with beam-to-length ratio Various draft-to-depth ratios and angles of incidence are considered. Results have been checked with the limiting case of a circular cylinder for the long-wave length range. Aside from its own practical interest, the present theory provides a basis for comparison with other approximate theories of slender-body type and serves as a prelude to the corresponding calculations for arbitrary wavelengths.
On the Experimental Determination of the Resistance Components of a Submerged Spheroid
Authors: Farell César , Güven Oktay
Published: January 2021

Towing-tank measurements of the viscous resistance of a spheroid model by means of wake surveys together with total resistance measurements show that the proximity of the free surface greatly influences the viscous resistance, which becomes much larger than the deep-submergence resistance as the spheroid approaches the free surface. Wind tunnel measurements reveal a similar effect of a rigid wall on the viscous drag of a body. The values of the wave resistance obtained as the difference between the measured values of total resistance and viscous resistance are found to be in agreement, for the range of Froude numbers investigated, with the analytical results obtained neglecting viscous effects and linearizing the free-surface boundary condition, but satisfying exactly the boundary condition on the surface of the body.
Slamming Damage
Authors: Jones Norman
Published: January 2021

A relatively simple theoretical procedure for estimating the amount of damage (dishing) of the bottom plating of ships and marine vehicles during a severe slam is presented herein. The reasonable agreement between the theoretical predictions and the experimental results of Clevenger and Melberg is quite encouraging, while other scant evidence is cited which further corroborates the general procedure. However, it emerges from the various discussions that further experimental results on the slamming damage of plating is required before this or any other theoretical method can be widely accepted.
A Time-Domain Solution to the Motions of a Steered Ship in Waves
Authors: Pérez Leonardo Pérez y
Published: January 2021

The motions of a ship in waves are expressed as linear responses to arbitrary exciting forces by means of a convolution integral. Frequency-independent nonlinearities are considered to be part of the arbitrary forces. The method is used to numerically simulate the sway, roll, and yaw motions of a ship model in waves with nonlinear roll damping coefficient and an autopilot. The agreement of the simulation with experimental results is quite reasonable. This method is restricted neither to these modes of motion nor to these nonlinearities; it can be used for all six modes of motion and any frequency-independent nonlinearity.
Effect of Forcing Terms and General Characteristics of Torsional Vibrations of Marine Engine Systems with Variable Inertia
Authors: Carnegie W. D. , Pasricha M. S.
Published: January 2021

The torsional vibration phenomenon in the running gear of reciprocating engine systems is usually dealt with by considering a series of constant inertias connected by sections of massless shafting. Such a simplified model does not reproduce the exact dynamic characteristics of the actual system. In recent years several cases of marine crankshaft failures have been attributed to the phenomenon of secondary resonance, which is explained by the fact that the effective inertia of each slider crankmechanism varies about a mean value in relation to the position of the crank. When the variableinertia effect is allowed for, the equations of motion taking into account the effect are nonlinear. Assuming small displacements, the equations can be linearized to predict important characteristics of the motion. The motions in the form of complex wave forms are studied at different speeds of engine rotation and some of the wave form solutions are analyzed in the range of present investigations. Computer methods making use of numerical analysis processes, namely, the modifiedEuler's equations and the Runge-Kutta constants, have been applied in the investigations. A study of the effect on the motion of the system due to variation of inertia ratio is carried out at a particular speed of the crankshaft rotation; also investigated are the variations in the motions due to the action of external excitations with respect to changes in phase angle and inertia ratio. General comments on Draminsky's work in the light of the present investigations are included.
Comments on “Automated Optimal Design of Frame Reinforced, Submersible, Circular, Cylindrical Shells” by M. Pappas and A. Allentuch
Authors: Becker H.
Published: January 2021

Pappas and Allentuch in the title paper computerized the investigation of a minimum-weight, ring-stiffened, elastic circular cylindrical shell under external pressure and obtained results similar to those found by Gerard in closed form in 1961.
Transverse Vibrations of a Ship Hull in Ideal Fluid, Determined Through Variational Methods
Authors: Mišra Prayag Narayan
Published: January 2021

A direct formulation for analyzing the vibration characteristics of an arbitrary body and predicting the three-dimensional velocity potential is presented. It consists of forming the Lagrangian for a Timoshenko-beam fluid system and minimizing Hamilton's principal function by the Rayleigh-Ritz method. Due to the boundary condition, the minimizing sequence for vibration amplitude transforms the velocity potential into an associated sequence of Neumann boundary-value functions. These are expressed further in terms of another minimizing sequence and evaluated after minimizing the corresponding energy functionals according to the method of minimal surface integrals. The theory is applied to a simple body and the resulting vibration characteristics are found to be more accurate than previous theoretical estimates and closer to published experimental data. Finally, the feasibility of the procedure is outlined for a submerged ship hull, employing approximate methods of numerical quadrature.
A Review of Effective Plating for Use in the Analysis of Stiffened Plating in Bending and Compression
Authors: Faulkner Douglas
Published: January 2021

The review is divided into three main parts. The first is very brief and covers shear lag effects associated with stiffener plate bending. Part 2 concerns the behavior of unstiffened long plate elements (a ≥ b) in compression, which is referred to as effective ‘width’ effects. The concepts considered are maximum plate strength and how this is affected by initial distortion, normal pressure, and boundary conditions; stress distribution in plate elements before failure; and the "reduced effective width" concept for defining plate element stiffness, as required for use in stiffened-plate collapse theories. Final appraisal leads to recommendations based upon the equation advanced ten years ago for mean expected stress-free plate strength: σm/σο = (2/β) — (1/β2). It is used by the British Navy and has been recommended in Europe for box-girder bridge design. Part 3 concerns welding stress effects, and a critical strain theory is advanced for describing welded plate behavior in compression. The review has of course assessed appropriate test data, including a reappraisal from three full-scale destroyer tests. Some emphasis has been placed upon the statistical characteristics of the data, in order that this may help establish structural strength distributions for probabilistic approaches to ductile structural reliability. The paper ends with a brief historical review drawn from aeronautical, civil engineering and naval architectural sources, and a listing of the more important effective width formulas.
Hull Bending Moment Due to Ship Bottom Slamming in Regular Waves
Authors: Mansour A. , d'Oliveira J. M.
Published: January 2021

A review of the existing literature on the overall response of ships to bottom slamming is presented. A mathematical formulation of the vibratory bending moment due to bottom impact slamming in regular waves is then developed. The hydrodynamic problem concerning the definition of the loads is first discussed and a particular physical model is adopted for determining the hull vibratory behavior. Based on this formulation, a general computerized procedure leading to the time-history representation of the midship bending moment is developed. Finally, an illustrative example of application to a Mariner ship is described and the results are related to some available data.
Some Numerical Results on Wave Resistance of a Point Dipole
Authors: Lee Chuan
Published: January 2021

The distribution of singularities (that is, source, sink, and dipole) representing a ship's hull has played an important role in the study of wave resistance in naval hydrodynamics. Based on the theoretical wave resistance formula from linearized free-surface theory, six different wave resistance expressions in terms of three wave components along a longitudinal cut parallel to the ship's course are presented. To demonstrate the numerical accuracy of these wave resistance expressions, the analysis has been applied to the theoretical wave profiles generated by a submerged point dipole, and the results are compared with the known theoretical value.
Shear Stresses in Bulk Carriers Due to Shear Loading
Authors: Shama M. A.
Published: January 2021

A brief note is given on various components of the longitudinal vertical shearing force. The stillwater component is examined with particular emphasis on the effect of local cargo loading and the mechanism of shear load transmission. The main factors affecting the wave-induced and dynamic components are indicated and an approximate method is given for estimating the impulsive dynamic component. A method is then given for calculating the shear stress distribution over a typical section of a bulk carrier. The ship section is idealized by a simplified structural model comprising closed and open cells. The structural model retains all the geometrical properties of the original section. Two numerical examples are considered to examine the effect of ship section parameters on shear stress distribution. It is shown that:(i) High shear stresses may be developed in the side shell plating.(ii) The variation of ship section parameters has a negligible effect on the maximum shear stress and may have a significant local effect.(iii) The shear carrying capacity of a given ship section could be easily estimated. Alternatively, for a given shearing force, a "shear coefficient," representing shear capability, could be estimated.
Hydrodynamic Forces on Ships in Dredged Channels
Authors: Beck R. F. , Newman J. N. , Tuck E. O.
Published: January 2021

The problem to be treated here is that of steady longitudinal motion of a ship in a dredged channel, with specific attention to the prediction of sinkage and trim, and wave resistance. The dredged channel is idealized to be of rectangular cross section, and linearized shallow-water solutions are developed for the dredged or deep section, and for the two shallow regions alongside the channel. The ship is assumed slender, moving along the centerline of the channel, and is replaced by an equivalent source distribution, as in the earlier theories of Tuck for shallow water of constant depth. At the channel boundaries a matching of solutions is carried out, between the deep and shallow regions, and it is shown that the effects of the shallow regions can be replaced by a mixed boundary condition on the solution for the channel region. Calculations of the sinkage and trim and of the wave resistance are presented and discussed, for the cases where the channel region is subcritical and where the shallow regions are either subcritical or supercritical.
Wave Resistance and Wave Patterns of Thin Ships
Authors: Keller Joseph B. , Ahluwalia Daljit S.
Published: January 2021

The wave resistance R and wave height h(x, z) are evaluated asymptotically for small Froude number F = U(gL)−½ for a slender hull of any shape. Michell's theory for a thin ship of length L moving with constant speed U along a straight line is the starting point. It is found that asymptotically R and h depend only upon four properties of the ship—the slope of the hull and the slope of the profile curve of the hull at the waterline at bow and stern. Simple formulas are obtained for R and h in terms of these slopes. The wave pattern consists of four waves—a longitudinal and a transverse wave from the bow and a similar pair from the stern. Their phases are the same as those of Kelvin waves due to pressure points at the bow and stern, and they also decay with distance like cylindrical waves. However, their amplitudes have different angular variations from those of Kelvin waves.
On the Problem of Shaping an Axisymmetric Body to Obtain Low Drag at Large Reynolds Numbers
Authors: Hess John L.
Published: January 2021

This paper describes an attempt to design by analytic means a class of axisymmetric bodies having low drag in incompressible flow for the case where the boundary layer is fully turbulent over the entire body. The drag is to be made small solely by proper shaping of the body, and the drag coefficient to be minimized is that based on a reference area equal to the two-thirds power of the body's volume. Clearly the flow should be unseparated for low drag. A comparison of various drag-calculation methods shows that the Truckenbrodt formula, which expresses drag as an integral of a power of the potential-flow surface velocity, is sufficiently accurate, and this formula is adopted as the chief analytic tool. Among the consequences of this choice is that bodies with low drag at one Reynolds number have low drag at all. Drag performances of various types of bodies are compared, including those of " cavitation shapes" derived from a new inverse potential-flow program, it appears that there is a preferred range of fineness ratio from three to about seven. Two-dimensional optimization studies are carried out using an integral formula for drag analogous to that of Truckenbrodt. The principal conclusion is that for bodies having fineness ratios in the preferred range and having unseparated fully turbulent boundary layers the drag coefficient based on the two-thirds power of volume is not very sensitive to body shape, and thus that within these constraints no significant additional drag reduction can be obtained from shaping alone.
On the Maximum Thrust of Sails by Sailing Close to Wind
Authors: Sparenberg J. A. , Wiersma A. K.
Published: January 2021

The maximum thrust of sails when sailing close to wind is discussed. The influence of the gap between sails and hull and the influence of a reduction of the heeling force and the heeling moment on the maximum thrust are considered. Numerical results are given.
Analytical Determination of Slamming Pressures for High-Speed Vehicles in Waves
Authors: Stavovy Alexander B. , Chuang Sheng-Lun
Published: January 2021

An analytical method is proposed for determining wave impact "slamming" pressures on all types of ship hulls including advanced vehicles that may travel at speeds up to 100 knots and even higher speeds. The method is based on the Wagner wedge impact theory, the Chuang cone impact theory, and experiments performed at the David W. Taylor Naval Ship Research and Development Center. Determination of the impact pressure is based on the hypothesis that the impact velocity is equal to the relative velocity normal to the impact surface of the moving body and the wave surface. The proposed method has been verified by several model tests in waves and by actual ship trials of the catamaran USNS Hayes. Computer programs are included for the practical use of the method.
Blockage with a Free Surface
Authors: Newman J. N.
Published: January 2021

The occurrence of blockage, or a jump in the velocity potential between the upstream and downstream infinities, is well known for steady two-dimensional flow past a body in a rigid channel. This paper considers the analogous situation where there is a free surface, as in the wave resistance problem for submerged two-dimensional bodies in a fluid of finite depth. It is shown that blockage occurs in spite of the free surface, taking values which depend not only on the dipole moment but also upon the Froude number based on depth. The occurrence of blockage, in the present context, has a bearing primarily upon the correct formulation of far-field radiation conditions for steady flows with finite depth.
Comments on Hoffman and Karst: “The Theory of the Rayleigh Distribution and Some of Its Applications”
Authors: Dattatri J. , Shankar N. Jothi , Raman H.
Published: January 2021

Hoffman and Karst have recently reported, in the title paper, an excellent review of the Rayleigh distribution and some of its applications. They mention that for many ocean zones there is a lack of measured wave data. The primary purpose of this note is to supplement their conclusions with some additional measured ocean wave data. These data, from the west coast of India near Mangalore, where a new major port has recently been commissioned, were obtained over a period of 18 months during 1968–1969, using a frequency-modulated subsurface pressure-type recorder. The analysis of this data has been reported in an earlier paper [1]. 3 More recently, during 1974, some additional data were obtained using an accelerometer-type Wave Rider buoy. The data obtained from the subsurface recorder need to be modified to account for the pressure response and instrument factors, and considerable uncertainties are involved in this computation. On the other hand, the Wave Rider data need no such modifications and can be considered to be more representative of the sea state at the locality. As such, the surface recorder data (Wave Rider data) have been utilized mainly in the preparation of this note, and the subsurface recorder data are furnished for the purpose of comparison. The west coast of India is under the influence of the southwest monsoon during the months of June to September, when the prevailing strong winds cause heavy seas. During the nonmonsoon period, the Arabian Sea is practically calm, with long low swells. Hence the data used herein cover a wide range of conditions from the 'sea' to the 'swell.'