bluuebunny/crossref_metadata_2025 huggingface dataset:
Maximum Air Suction Into a Louvered Funnel Through Optimum Design
Authors: Mishra Dipti P. , Dash Sukanta K.
Published: January 2021

The rate of air suction into a louvered cylindrical funnel with lateral openings has been computed numerically by solving the equations of conservation of mass, momentum, and energy along with the two k-z turbulence closure equations. It was found that the air suction rate into a louvered funnel can be maximum for an optimum nozzle protrusion length into the funnel irrespective of the nozzle fluid temperature. There also exists an optimum funnel diameter (irrespective of the nozzle fluid temperature) and funnel height for which the air suction rate can be the maximum. Keeping the volume of the funnel constant, the shape of the funnel was changed to a frustum. It was found that an inverted frustum with a value of r1/r2 = 0.8 could suck the maximum amount of air compared to a cylindrical funnel of the same volume. The cylindrical sucking funnel has interestingly a much shorter entrance length compared to a simple pipe flow case with the same entrance Reynolds number. The entrance length for the sucking funnel is also a function of the nozzle fluid temperature, and a simple relation for the entrance length as a function of Ren and Tn/T∞ could also be developed for a sucking funnel. Numerical experiments were done for an inclined funnel to compute the mass suction into it. It was found that for Gr/Re2 ≤ 0.4 (where Gr is the Grashof number and Re is the Reynolds number) given by the funnel inclination had no effect on the rate of mass suction while for 0.4 < Gr/Re2 < 1 the funnel inclination had marginal influence. As the value of Gr/Re2 increased beyond 1 the influence of the funnel inclination on rate of mass suction was found to be significant.
Method to Control Unsteady Force of Submarine Propeller Based on the Control of Horseshoe Vortex
Authors: Zhihua Liu , Ying Xiong , Chengxu Tu
Published: January 2021

The submarine propeller works in the submarine wake with severe circumferential nonuniformity, which causes the hydrodynamic force to act on the blade. This results in severe oscillation with the rotation of the propeller and impairs the hydrodynamics and noise performance of the submarine propeller. The horseshoe vortex generated at the hull-appendages junctions of the submarine has important influence on wake uniformity. In the present study, the state of the submarine horseshoe vortex is analyzed and a new method of vortex control baffler is presented. The aim is to weaken the horseshoe vortex. Based on the wind tunnel experiment and numerical simulation on the submarine model, the vortex control baffler can decrease the strength of the submarine horseshoe vortex and improve the uniformity of the submarine wake. Vortex control bafflers adapted for the fully appended SUBOFF model are designed, and the unsteady force of three kinds of propellers functioned after the SUBOFF model is calculated numerically. The results show that although the skew angle and blade number are different, the amplitudes of the unsteady force acting on the blades of all three propellers decreased by 50% to 80% due to the effects of the vortex control baffler.
Estimation of Extreme Ship Response
Authors: Mao Wengang , Rychlik Igor
Published: January 2021

In practice the severity of ship response is measured by high quantiles of long-term distribution of the response. The distribution is estimated by combining the short-term distribution of the response with a long-term probability distribution of encountered sea states. The paper describes an alternative approach, the so-called Rice's method, based on estimation of expected number of upcrossings of high levels by stress during 1 year. The method requires description of long-term variability of the standard deviation, skewness, kurtosis, and zero upcrossing frequency of ship response. It is assumed that the parameters are functions of encountered significant wave height, heading angle, and ship speed. The relation can be estimated from the measured stresses or computed by dedicated software assuming rigid ship hull model. Then Winterstein's transformed Gaussian model is used to estimate the upcrossing rates of response during a sea state. The proposed method is validated using the full-scale measurements of a 2,800 TEU container ship during the first 6 months of 2008. Numerical estimation of 4,400 TEU container ship extreme of the extreme response for a 4400 TEU container ship illustrates the approach when no measurements are available.
The Effect of Sloshing in Tanks on the Hull Girder Bending Moments and Structural Reliability of Damaged Vessels
Authors: Jia Huirong , Moan Torgeir
Published: January 2021

The structural reliability analysis of damaged vessels has commonly been conducted by neglecting the effect of sloshing. In this paper, the coupled motion of the damaged vessel and sloshing is set up based on the assumption that the damaged tanks are of rectangular shape. The sloshing effects in tanks are modeled by a linear multimodal approach. Then the effect of sloshing in tanks on the hull girder bending moments and the failure probability are studied for an oil tanker in various damage conditions. It is concluded that in certain tank resonance conditions, sloshing effects cannot be neglected. In such cases sloshing damping plays an important role on the sloshing effects.
Aero-Hydrodynamic Aspects of Power-augmented Ram Wings
Authors: Matveev Konstantin I.
Published: January 2021

The subject of this article is the two-dimensional interaction of air and water flows under a power-augmented ram wing. The extreme ground effect theory is applied for the air flow, whereas the water flow is treated with a linearized model based on a method of hydrodynamic singularities. Calculated aerodynamic characteristics of power-augmented ram platforms and water surface deformations at moderate and high Froude numbers are presented for a horizontal plate with a flap, a trimmed plate without a flap, and an S-shaped profile. Additionally, plates in contact with water are modeled. The transition from airborne to waterborne states is accompanied by drastic variations of the lift and center of pressure. It is found that solutions can be nonunique when the plate trailing edge is very close to the water surface.
Unified Rotor Lifting Line Theory
Authors: Epps Brenden P. , Kimball Richard W.
Published: January 2021

A unified lifting line method for the design and analysis of axial flow propellers and turbines is presented. The method incorporates significant improvements to the classical lifting line methods for propeller design to extend the method to the design of turbines. In addition, lifting line analysis methods are developed to extend the usefulness of the lifting line model to allow generation of performance curves for off-design analysis. The result is a fast computational methodology for the design and analysis of propellers or turbines that can be used in preliminary design and parametric studies. Design and analysis validation cases are presented and compared with experimental data.
Parametric Generation of Planing Hulls with NURBS Surfaces
Authors: Perez-Arribas Francisco L. , Peter-Cosma Erno
Published: January 2021

This article presents a mathematical method for producing hard-chine ship hulls based on a set of numerical parameters that are directly related to the geometric features of the hull and uniquely define a hull form for this type of ship. The term planing hull is used generically to describe the majority of hard-chine boats being built today. This article is focused on unstepped, single-chine hulls. B-spline curves and surfaces were combined with constraints on the significant ship curves to produce the final hull design. The hard-chine hull geometry was modeled by decomposing the surface geometry into boundary curves, which were defined by design constraints or parameters. In planing hull design, these control curves are the center, chine, and sheer lines as well as their geometric features including position, slope, and, in the case of the chine, enclosed area and centroid. These geometric parameters have physical, hydrodynamic, and stability implications from the design point of view. The proposed method uses two-dimensional orthogonal projections of the control curves and then produces three-dimensional (3-D) definitions using B-spline fitting of the 3-D data points. The fitting considers maximum deviation from the curve to the data points and is based on an original selection of the parameterization. A net of B-spline curves (stations) is then created to match the previously defined 3-D boundaries. A final set of lofting surfaces of the previous B-spline curves produces the hull surface.
Experimental Investigation on Hydrodynamics of a Fish Cage Floater-net System in Oscillatory and Steady Flows by Forced Oscillation Tests
Authors: Fu Shixiao , Xu Yuwang , Hu Ke , Zhong Qian , Li Runpei
Published: January 2021

In this article, the hydrodynamic characteristics of a floater-net system in oscillatory and steady flows are investigated through forced oscillation experiments in a towing tank. The effects of Keulegan-Carpenter number, Reynolds number, and reduced velocity are studied. Also, hydrodynamic forces on the floater and net are compared in detail to analyze their respective contributions to the total drag force. The results indicate that in oscillatory flow, the added mass coefficient of the floater is larger than that of the floater-net system, whereas the drag coefficient is smaller. The proportion of the drag force exerted on the floating cylinder reaches its maximum in oscillatory flow and its minimum in steady current flow. In addition, the reduced velocity has a very clear influence on the hydrodynamic performance of the floater-net system; specifically, the drag coefficient in oscillatory flow becomes smaller as reduced velocity increases.
Bow and Stern Shape Integrated Optimization for a Full Ship by a Simulation-based Design Technique
Authors: Li Sheng-Zhong , Zhao Feng , Ni Qi-Jun
Published: January 2021

Advanced computational fluid dynamic (CFD) techniques and optimization algorithms are successfully integrated together into what is known as Simulation-based Design (SBD) techniques, which open a new situation for hull-form optimization design and configuration innovation. In this article, fundamental elements of the SBD techniques are described and crucial components are analyzed profoundly with a focus on breaking through key technologies as global optimization algorithms, hull geometry modification and reconstruction, and code integration. Then, combined with high-fidelity CFD codes (on Reynolds-averaged Navier-Stokes), an automatic hull-form design optimization framework is established. Based on that, the full ship (bulk carrier) is optimized by selecting the total resistance and the quality of propeller disk wake field as objective functions. The results show that the decrease of the total resistance is significant at the possible speed range with a reduction of approximately 5% taking into account gains of propulsion efficiency produced by the improvement of wake field, the comprehensive energy-saving effect will be further expanded. The example confirms the applicability of the developed SBD frame-work to the full ship design problems.
An Experimental Study on Tip Vortex Cavitation Suppression in a Marine Propeller
Authors: Park Sang-LL , Lee Seung-Jae , You Geuk-Sang , Suh Jung-Chun
Published: January 2021

Normally, tip vortex cavitation (TVC) is first observed at a certain location behind the tips of propeller blades. Therefore, TVC is important for naval ships and research vessels that require raising the cavitation inception speed to maximum possible values. The concepts for alleviating the tip vortex are summarized by Platzer and Souders (1979), who carried out a thorough literature survey. Active control of TVC involves the injection of a polymer or water from the blade tip. The main effect of such mass injection (both water and polymer solutions) into the vortex core is an increase in the core radius, consequently delaying TVC inception. However, the location of the injection port needs to be selected with great care to ensure that the mass injection is effective in delaying TVC inception. In the present study, we propose a semi-active control scheme that is achieved by attaching a thread at the propeller tip. The main idea of a semi-active control is that because of its flexibility, the attached thread can be sucked into the low-pressure region closer to the vortex core center. An experimental study using a scale model was carried out in the cavitation tunnel at the Seoul National University. It was found that a flexible thread can effectively suppress the occurrence of TVC under the design condition for a model propeller.
Empirical Equations for Planing Hull Bottom Pressures
Authors: Morabito M. G.
Published: January 2021

Recently there has been increasing interest in the fluid-structure interaction problem of planning hull bottom structure during slamming events. Significant work has been done in estimating the bottom pressures that occur during a slam and incorporating this into structural models of planing craft. In this article, empirical equations for the pressure distribution on prismatic planing hulls are developed, including both hydrostatic and hydrodynamic effects, deadrise variation, trim, and wetted length. The empirical method is based on relevant experimental measurements of planing hull bottom pressures that have been made over an 80-year period. This analysis may readily be extended to the impact problem by substitution of an equivalent planing velocity, which is discussed in the article. The end result is a closed form solution for bottom pressures on prismatic planing craft that can be rapidly calculated using a simple spreadsheet. The method is applicable for deadrise angles from 0 to 40, trim angles up to 30, and wetted lengths up to five beams. This wide range of parameters is significantly larger than most current models. The empirical method is modular, allowing for substitution of more accurate formulae as more data become available in the future.
Conditional Stochastic Processes Applied to Wave Load Predictions
Authors: Jensen Jørgen Juncher
Published: January 2021

The concept of conditional stochastic processes provides a powerful tool for evaluation and estimation of wave loads on ships and offshore structures. This article first considers conditional waves with a focus on critical wave episodes. Then the inherent uncertainty in the results is illustrated with an application where measured wave responses are used to predict the future variation in the responses within the next 5–30 seconds. The main part of the article is devoted to the application of the First Order Reliability Method for derivation of critical wave episodes for different nonlinear wave-induced responses. A coupling with Monte Carlo simulations is shown to be able to give uniform accuracy for all exceedance levels with moderate computational time, even for rather complex nonlinear problems. The procedure is illustrated by examples dealing with overturning of jackup rigs, parametric rolling of ships, and slamming and whipping vibrations.
Entrainment of Air at the Transoms of Full-Scale Surface Ships
Authors: Terrill Eric J. , Taylor Genevieve R.L.
Published: January 2021

We report on the results from a series of full-scale trials designed to quantify the air entrainment at the stern of an underway vessel. While an extremely complex region to model air entrainment due to the confluence of the breaking transom wave, bubbles from the bow, turbulence from the hull boundary layer, and bubbles and turbulence from propellers, the region is a desirable area to characterize and understand because it serves as the initial conditions of a ship's far-field bubbly wake. Experiments were conducted in 2003 from R/V Revelle and 2004 from R/VAthena II using a custombuilt conductivity probe vertical array that could be deployed at the blunt transom of a full-scale surface ship to measure the void fraction field. The system was designed to be rugged enough to withstand the full speed range of the vessels. From the raw timeseries data, the entrainment of air at speeds ranging from 2.1 to 7.2 m/s is computed at various depths and beam locations. The data represent the first such in-situ measurements from a full-scale vessel and can be used to validate two-phase ship hydrodynamic CFD codes and initialize far-field, bubbly wake CFD models.
Effect of Slam Force Duration on the Vibratory Response of a Lightweight High-Speed Wave-Piercing Catamaran
Authors: McVicar Jason John , Lavroff Jason , Davis Michael Richard , Thomas Giles
Published: January 2021

When the surface of a ship meets the water surface at an acute angle with a high relative velocity, significant short-duration forces can act on the hull plating. Such an event is referred to as a slam. Slam loads imparted on ships are generally considered to be of an impulsive nature. As such, slam loads induce vibration in the global hull structure that has implications for both hull girder bending strength and fatigue life of a vessel. A modal method is often used for structural analysis whereby higher order modes are neglected to reduce computational effort. The effect of the slam load temporal distribution on the whipping response and vertical bending moment are investigated here by using a continuous beam model with application to a 112 m INCAT wave-piercing catamaran and correlation to full-scale and model-scale experimental data. Experimental studies have indicated that the vertical bending moment is dominated by the fundamental longitudinal bending mode of the structure. However, it is shown here that although the fundamental mode is dominant in the global structural response, the higher order modes play a significant role in the early stages of the response and may not be readily identifiable if measurements are not taken sufficiently close to the slam location. A relationship between the slam duration and the relative modal response magnitudes is found, which is useful in determining the appropriate truncation of a modal solution.
Experimental Performance of a Novel Trochoidal Propeller
Authors: Roesler Bernard T. , Kawamura Malia L. , Miller Eric , Wilson Matthew , Brink-Roby Jonathon , Clemmenson Eric , Keller Matthew , Epps Brenden P.
Published: January 2021

In the quest for higher energy efficiency in marine transportation, a promising alternative marine propulsor concept is the trochoidal propeller. The authors have 1) designed and tested a novel trochoidal propeller using a sinusoidal blade pitch function and 2) created a theoretical model to describe the principal physics governing the operation of such propellers. The main results presented herein are measurements of thrust and torque, as well as the calculated hydrodynamic efficiency, for a range of absolute advance coefficients. The performance of the present sinusoidal-pitch trochoidal propeller is compared with prior cross-flow propellers, as well as a representative screw propeller. Although the efficiency of the present sinusoidal-pitch propeller exceeds that of prior cycloidal-pitch trochoidal propellers, it is slightly lower than the efficiencies of the other propellers considered. Model predictions show excellent agreement with the experimental data, which opens possibilities for future investigation and optimization of novel blade pitch motions.
Development of a Simplified Procedure for the Determination of the Ultimate Load and Associated Spindle Torque of Propeller Blades
Authors: Fischer Claas , Fricke Wolfgang , Junglewitz Andreas
Published: January 2021

Blade deflection observed in experiments regarding the ultimate strength of controllable pitch propeller blades does not agree with the one that is assumed in the load case for the blade failure load currently defined in the Polar Class Rules. The reason is that a failure of the blade tip due to large plastic deformation is not taken into account, but can occur in reality if the load is applied relatively close to the trailing edge of skewed propellers. The plastic blade deformation can be computed by numerical simulations using an elastic-plastic material curve. These simulations, however, are time consuming and, hence, unpractical in the daily design process of propeller blades. Therefore, a simplified approach to determine the ultimate load and the associated spindle torque of the blade is presented. It requires elastic finite element (FE) analyses with varying point of load application, geometrical data, and a simplified material curve. The critical blade section is determined from highly stressed locations found in the elastic FE analysis. Afterward, the ultimate bending moment which the section can carry is determined by assuming a linear strain distribution over the thickness and a definite limit strain on the pressure surface. This allows the stress distribution to be transferred directly from the material curve. The ultimate load is determined by integrating the stress distribution over the section thickness and along the chord length, the latter in a simplified way. The approach is supported by various numerical simulations showing the fundamental elastic-plastic behavior of propeller blades and their response due to superimposed bending and torsional loads. In conclusion, the ultimate strength is mainly controlled by bending loads and the approach considers a failure of the blade tip, leading to more realistic spindle torques compared to the approach in the Polar Class Rules.
Wet and Dry Transom Stern Treatment for Unsteady and Nonlinear Potential Flow Model for Naval Hydrodynamics Simulations
Authors: Mola Andrea , Heltai Luca , DeSimone Antonio
Published: January 2021

We present a model for the fast evaluation of the total drag of ship hulls operating in both wet and dry transom stern conditions, in calm or wavy water, based on the combination of an unsteady semi-Lagrangian potential flow formulation with fully nonlinear free-surface treatment, experimental correlations, and simplified viscous drag modeling. The implementation is entirely based on open source libraries. The spatial discretization is solved using a streamline upwind Petrov-Galerkin stabilization of an iso-parametric, collocation based, boundary element method, implemented using the open source library deal. II. The resulting nonlinear differential-algebraic system is integrated in time using implicit backward differentiation formulas, implemented in the open source library SUNDIALS. The Open CASCADE library is used to interface the model directly with computer-aided design data structures. The model accounts automatically for hulls with a transom stern, both in wet and dry regimes, by using a specific treatment of the free-surface nodes on the stern edge that automatically detects when the hull advances at low speeds. In this case, the transom stern is partially immersed, and a pressure patch is applied on the water surface detaching from the transom stern, to recover the gravity effect of the recirculating water on the underlying irrotational flow domain. The parameters of the model used to impose the pressure patch are approximated from experimental relations found in the literature. The test cases considered are those of the U.S. Navy Combatant DTMB-5415 and the National Physical Laboratory hull. Comparisons with experimental data on quasi-steady test cases for both water elevation and total hull drag are presented and discussed. The quality of the results obtained on quasi-steady simulations suggests that this model can represent a promising alternative to current unsteady solvers for simulations with Froude numbers below 0.35.
An Experimental Investigation of Ride Control Algorithms for High-Speed Catamarans Part 2: Mitigation of Wave Impact Loads
Authors: AlaviMehr Javad , Lavroff Jason , Davis Michael R. , Holloway Damien S. , Thomas Giles A.
Published: January 2021

High-speed craft frequently experience large wave impact loads due to their large motions and accelerations. One solution to reduce the severity of motion and impact loadings is the installation of ride control systems. Part 1 of this study investigates the influence of control algorithms on the motions of a 112-m highspeed catamaran using a 2.5-m model fitted with a ride control system. The present study extends this to investigate the influence of control algorithms on the loads and internal forces acting on a hydroelastic segmented catamaran model. As in Part 1, the model active control system consisted of a center bow T-Foil and two stern tabs. Six motion control feedback algorithms were used to activate the model-scale ride control system and surfaces in a closed loop system: local motion, heave, and pitch control, each in a linear and nonlinear application. The loads were further determined with a passive ride control system and without control surfaces fitted for direct comparison. The model was segmented into seven parts, connected by flexible links that replicate the first two natural frequencies and mode shapes of the 112-m INCAT vessel, enabling isolation and measurement of a center bow force and bending moments at two cross sections along the demi-hulls. The model was tested in regular head seas at different wave heights and frequencies. From these tests, it was found that the pitch control mode was most effective and in 60-mm model-scale waves it significantly reduced the peak slam force by 90% and the average slam induced bending moment by 75% when compared with a bare hull without ride controls fitted. This clearly demonstrates the effectiveness of a ride control system in reducing wave impact loads acting on high-speed catamaran vessels.
Ship Hull Fouling Estimation Using Shipboard Measurements, Models for Resistance Components, and Shaft Torque Calculation Using Engine Model
Authors: Fonteinos Michael I. , Tzanos Efstratios I. , Kyrtatos Nikolaos P.
Published: January 2021

This paper presents a method for hull condition estimation regarding fouling, by focusing on the increase of power demand over a period. Onboard recorded data from performance reports and noon reports of four Panamax bulk carriers identical sister ships were provided by a shipping company. In most cases, engine power onboard vessels is measured using a torque meter. Since torque measurements are generally considered of variable reliability and the required accuracy for the present study was high, the propeller shaft torque demand was calculated using an engine simulation software tuned for each specific engine and fed with recorded engine data. To distinguish the effect of fouling, wave-added resistance, air resistance, and calm water resistance were deducted from total ship resistance. Wave-added and air resistances were calculated using the STAwave-2 empirical method and Fujiwara regression formula, respectively. Calm water resistance was calculated using the FORMDATA systematic statistical series due to the lack of vessel's lines. The increase of resistance due to fouling was estimated through the increase of the Propeller Law coefficient (CPROP) and the Fouling Resistance coefficient (CFOUL), over a dry dock interval period.
Experimental Investigation of Roughness Effect on Ship Resistance Using Flat Plate and Model Towing Tests
Authors: Kiosidou Evangelia D. , Liarokapis Dimitrios E. , Tzabiras Georgios D. , Pantelis Dimitrios I.
Published: January 2021

Towing tests on a thin flat plate of 3-mm thickness and on a ship model in smooth and rough condition were performed and extrapolation to ship scale was attempted. A newly designed experimental setup was constructed for the examination of the thin plate. The experiments on smooth flat plate included examination of a series of trip wires for flow stimulation, among which the optimum was 1.3 mm. In rough condition, the plate was covered with sandpapers of 40 and 80 grit. Both calculated roughness functions exhibited Nikuradse behavior, verifying the validity of the experiments. The equivalent sand roughness height was 1.7 times the average sandpaper roughness, as calculated by the Schlichting diagram for sand-roughened plates. Both roughness functions indicated transitionally rough regime, except for the last two data of the rougher sandpaper that lay on the fully rough regime. The results were extrapolated to ship scale using Granville method. Extrapolation of smooth model results in ship scale revealed that the traditional Froude method predicts higher resistance coefficient compared to the International Towing Tank Conference (ITTC) 78 method. Rough model results were extrapolated to ship scale by applying a newly proposed extrapolation method, using Schlichting resistance formula for rough plates as the friction correlation line, according to Froude method and for two length scales, namely the plate and ship length. The two versions of the proposed extrapolation method provided an upper and lower limit for the predicted rough hull total resistance coefficient.
Geometric Modelling and Deformation for Shape Optimization of Ship Hulls and Appendages
Authors: Berrini Elisa , Mourrain Bernard , Roux Yann , Durand Mathieu , Fontaine Guillaume
Published: January 2021

The precise control of geometric models plays an important role in many domains such as computer-aided geometric design and numerical simulation. For shape optimization in computational fluid dynamics (CFD), the choice of control parameters and the way to deform a shape are critical. In this article, we describe a skeleton-based representation of shapes adapted for CFD simulation and automatic shape optimization. Instead of using the control points of a classic B-spline representation, we control the geometry in terms of architectural parameters. We assure valid shapes with a strong shape consistency control. Deformations of the geometry are performed by solving optimization problems on the skeleton. Finally, a surface reconstruction method is proposed to evaluate the shape's performances with CFD solvers. We illustrate the approach on two problems: the foil of an AC45 racing sail boat and the bulbous bow of a fishing trawler. For each case, we obtained a set of shape deformations and then we evaluated and analyzed the performances of the different shapes with CFD computations.
EFD and CFD Study of Forces, Ship Motions, and Flow Field for KRISO Container Ship Model in Waves
Authors: Wu Ping-Chen , Hossain Md. Alfaz , Kawakami Naoki , Tamaki Kento , Kyaw Htike Aung , Matsumoto Ayaka , Toda Yasuyuki
Published: January 2021

Ship motion responses and added resistance in waves have been predicted by a wide variety of computational tools. However, validation of the computational flow field still remains a challenge. In the previous study, the flow field around the Korea Research Institute for Ships and Ocean Engineering (KRISO) Very Large Crude-oil Carrier 2 tanker model with and without propeller condition and without rudder condition was measured by the authors, as well as the resistance and self-propulsion tests in waves. In this study, the KRISO container ship model appended with a rudder was used for the higher Froude number .26 and smaller block coefficient .65. The experiments were conducted in the Osaka University towing tank using a 3.2-m-long ship model for resistance and self-propulsion tests in waves. Viscous flow simulation was performed by using CFDShip-Iowa. The wave conditions proposed in Computational Fluid Dynamics (CFD) Workshop 2015 were considered, i.e., the wave-ship length ratio λ/L = .65, .85, 1.15, 1.37, 1.95, and calm water. The objective of this study was to validate CFD results by Experimental Fluid Dynamics (EFD) data for ship vertical motions, added resistance, and wake flow field. The detailed flow field for nominal wake and self-propulsion condition will be analyzed for λ/L = .65, 1.15, 1.37, and calm water. Furthermore, bilge vortex movement and boundary layer development on propeller plane, propeller thrust, and wake factor oscillation in waves will be studied.
Probability of Ship High-Runs from Phase-Space Data
Authors: Kontolefas Ioannis , Spyrou Kostas J.
Published: January 2021

A clustering scheme has been applied for capturing qualitatively different surge motion patterns in the phase space. The scheme enables the identification of "high-run" incidents as soon as such motions are triggered and while their phenomenology has not yet been well developed. A "high run" is a surf-riding-like behavior, appearing in irregular following seas. The concept of finite-time coherent sets is exploited for deriving estimates of the probability of high-runs. The method is verified by identifying independently the corresponding hyperbolic Lagrangian coherent structures; then, consistency is sought between the two approaches. An important feature of the method is that it does not rely on the use of some empirical criterion for the high-run threshold, such as one based on the exceedance of an arbitrary high-speed level. Despite its computational burden, the proposed scheme offers "objective" statistical information on a ship's high-run tendency that can be used for benchmarking simpler (approximative) probability calculation schemes.

1. Introduction

Current efforts to assess a ship's tendency for abnormal behavior in extreme seas are still limited from our inadequate grasp of the full variety of nonlinear ship motion phenomena that could be realized in an irregular seaway. A classification of these motion patterns would provide a sound basis for developing probabilistic calculation methods of ship operability and safety in extreme seas. A few recent research efforts in our group have been related to this target. In one case, it was endeavored to distinguish ship high-runs from ordinary surging, by engaging the concept of instantaneous wave celerity (Spyrou et al. 2014). In another, the derivation of a practical metric for the probability of high-run was pursued (Belenky et al. 2016). Also, high-run and broaching-to statistics were produced through a direct approach based on assigning prescriptive exceedance thresholds (Spyrou et al. 2016b). Moreover, the theory of surf-riding was extended for bichromatic waves, revealing some rather unexpected types of motion (Spyrou et al. 2018). Even richer phenomena could be conjectured for a multifrequency environment.
Air Entrainment and Surface Fluctuations in a Turbulent Ship Hull Boundary Layer
Authors: Masnadi Naeem , Erinin Martin A. , Washuta Nathan , Nasiri Farshad , Balaras Elias , Duncan James H.
Published: January 2021

Air entrainment due to turbulence in a free-surface boundary layer shear flow created by a horizontally moving vertical surface-piercing wall is studied through experiments and direct numerical simulations (DNS). In the experiments, the moving wall is created by a laboratory-scale device composed of a surface-piercing stainless steel belt that travels in a loop around two vertical rollers; one length of the belt between the rollers simulates the moving wall. The belt accelerates suddenly from rest until reaching constant speed and creates a temporally evolving boundary layer analogous to the spatially evolving boundary layer that would exist along a surface-piercing towed flat plate. We report cinematic laser-induced fluorescence measurements of water surface profile histories, cinematic observations and measurements of air entrainment events, and air bubble size distributions and motions. To complement the experiments, DNS of the temporally evolving turbulent boundary layer were conducted, considering both the air and water phases. Because of cost considerations, only a portion of the belt was simulated at a lower Reynolds number, keeping the Froude number, however, at the same levels as in the experiments. The results of the experiments and DNS are found to be in qualitative agreement and are used synergistically to explore the physics of the air entrainment process; quantitative agreement is not to be expected given the differences in setup and Reynolds numbers. In the experiments and DNS, the free-surface motion is found to consist of a region near the belt with fast-moving uncorrelated large-amplitude ripples and an outer region of small-amplitude propagating waves. Entrainment events similar to plunging breaking waves are found in the experiments, and these and other entrainment mechanisms are examined in detail in the DNS. The spatial distributions of bubble numbers and velocities are reported along with their diameter distributions.
An Energy Efficient Autopilot Design
Authors: Tréhin Mathilde , Laurent Johann , Kerhascoët Hugo , Rossi André , Diguet Jean-Philippe
Published: January 2021

In this paper, we propose a new control method for the next generation of sailboat autopilots. These new systems will need to manage more actuators to control the hydrofoils, which is going to significantly increase the energy requirements. So, this method is aware of the autopilot power consumption. It uses a model predictive controller to manage the actuators. This controller uses a dynamic model of the actuator, running in real time, to anticipate the future behavior of the system. Once the predictions are made, it determines the future control sequence to apply in order to follow the reference trajectory. To do so, it minimizes a cost function which takes into account two criteria: the precision of the system and the energy. With the proposed control method, skippers can focus on one or the other criterion depending on their goals and the boat's energy balance. We apply this method to one of the autopilot's subsystems, namely the rudder control. The electric actuator intervening in this control loop and the load representing the force opposed to its motion are modelled to design the control law. The first results of that method are compared with a standard autopilot. We increase by 40% the precision level and we are able to reduce the consumption by at least 20%. This work provides the first necessary components of a future autopilot that will control the whole appendages to a three-dimensional piloting. Moreover, this type of management is a first step towards possible fossil fuel-free sailboats.
Science of the 470 Sailing Performance
Authors: Masuyama Yutaka , Ogihara Munehiko
Published: January 2021

This paper holds a significant place in the Journal of Sailing Technology, as the very last publication of Prof. Masuyama, published posthumously, and co-authors by Dr. Ogihara. For many decades, Prof. Masuyama has been a very influential and respected member of the sailing yacht research community world-wide, holding the chairmanship of the Sailing Yacht Research Association of Japan for close to 20 years, and being involved with the Japanese America’s Cup Challenge. His expertise and academic research have impacted generations of researchers, and his work on high performance sails, sailing yachts and velocity prediction remains at the forefront of sailing technology. It is therefore with great honour that the Journal of Sailing Technology presents the very last insights of Prof. Masuyama into the sailing performance of the 470 Olympic class dinghy.
Hydrodynamic Design of Planing Hulls
Authors: Savitsky Daniel
Published: January 2021

The elemental hydrodynamic characteristics of prismatic planing surfaces are discussed and empirical planing equations are given which describe the lift, drag, wetted area, center of pressure, and porpoising stability limits of planing surfaces as a function of speed, trim angle, deadrise angle, and loading. These results are combined to formulate simple computational procedures to predict the horsepower requirements, running trim, draft, and porpoising stability of prismatic planing hulls. Illustrative examples are included to demonstrate the application of the computational procedures.
A Glimpse of Our Defense Posture
Authors: Forrest Matthew G.
Published: January 2021

Today, Defense is our Nation's business —defense in terms of a deterrent to others as well as in striking power to destroy their war-making capability
Sulfur and Sea Salt Attack of Turbine Blades
Authors: Dalton C.A.
Published: January 2021

Sulfur attack in aero engines and salt attack in marine engines are recurring problems. The effects, mechanism and prevention of sulfur attack in aero engines is discussed. The mechanism for sea salt attack on marine turbine blades is proposed and the results of tests designed to cure the trouble are presented. The treatment suggested is only a palliative and speculation on future work for greater protection is included.
A Program for an Investigation of the Rudder-Torque Problem
Authors: Schoenherr Karl E.
Published: January 2021

Panel H-10 (Controllability) of The Society of Naval Architects and Marine Engineers Technical and Research Program was requested to undertake an investigation of existing uncertainties in pre-calculating rudder torque and lateral force. In order to become quickly familiar with the subject and prospects therein, the Panel commissioned the author of this paper to survey the status of current knowledge of the subject and prepare a report of the findings. In particular, this report was to identify the most promising approaches for future work leading to an ultimate solution of the problem and to include technical descriptions of proposed programs for an exhaustive investigation, all of which are discussed in this paper.
Solution of Cavitation Problems in Pumps by Means of Model Air Testing
Authors: Pilarczyk K. , Rusak Vasil
Published: January 2021

This paper describes a case of rather unusual and severe cavitation in a double-suction centrifugal pump and the way the problem was corrected. The cavitation was demonstrated in a heavy erosion in the impeller blades while the performance of the pump did not show any signs of deterioration. The original design of the pump and the operating conditions were rather conventional with the available NPSH exceeding the recommended Hydraulic Institute Standard values. To solve this problem it was necessary to study, in detail, the velocity pattern at the impeller inlet. For this purpose, a wooden model of the pump suction nozzle was built and tested with air. A three-dimensional picture of the flow distribution in the impeller eye was obtained from this test indicating a considerable nonunlformlty in both the circumferential and the radial direction. This information led to the redesign of the impeller-inlet passage which ultimately eliminated the cavitation.
The Model-Ship Correlation Problem
Authors: Todd F. H.
Published: January 2021

The principal method of predicting ship horsepower is still by the use of scale models in a towing tank. However, the problem of the extrapolation of the data from model to ship is an extremely difficult one which is still not satisfactorily solved. This paper discusses the types of scale effect which arise in the interpretation of model resistance and propulsion data. It suggests that although satisfactory engineering solutions can be obtained by the use of gross overall correlation coefficients derived from a comparison of ship trial results with predictions from model tests, yet many unknown areas remain in our basic knowledge of how correctly to extrapolate model data. The need is emphasized for further experimental and theoretical work in the model field, to clear up such questions as blockage effects, turbulence stimulation, and the division of resistance into its several components, and for full-scale trials in which all the quantities measured on the model will also be measured on the ship. Such trials would give for the first time information on the scale effects on wake, thrust deduction, propeller open efficiency, and overall propulsive efficiency. Until we know the extent of such effects, we lack guidance as to where to look for further improvement in ship performance.
Design Improvements and Standardization of Propulsion Shafting and Bearings
Authors: Fielding Sterling A.
Published: January 2021

This paper presents a study of merchant ship propulsion shafting with emphasis on departing from present practice to explore the adaptability of certain design concepts, fabrication methods and materials which have been developed and utilized in related engineering fields. Application of torque-tube shafting, characterized by use of material, is considered for the slow-speed, high-torque line shaft system. For the propeller shaft the persistent fatigue failure problem is approached with a proposed change in the geometry of the shaft to obtain maximum reinforcement of the "weak links" in this component. To coordinate the work of multiple planning agencies to avoid needless variations in design details, standardization of size and shape of some items is suggested where a functional improvement or cost advantage appears attainable.
An Engineer’s Introduction to PERT Scheduling and Control
Authors: Honsinger Vernon C.
Published: January 2021

Program Evaluation and Review Technique (PERT) is a method of planning work, comparing status with schedule, and evaluating progress at all levels of management in order to better control a major, complex, engineering project. PERT/COST adds control of manpower and funds. Three time estimates—optimistic, most likely, and pessimistic—are combined to obtain an expected time for completing each activity. The PERT network shows interdependencies of activities. An important result of the PERT calculations is the determination of the critical and slack paths of the network.
Own or Charter A Suggested Method of Analysis for Oil Companies
Authors: Walsh W. R.
Published: January 2021

This paper describes a method whereby the economic advantages of ownership and period charters of oil tankers may be compared. It is hoped that this subject will be of interest to designers, engineers, and persons not directly engaged in operational matters. To this end, brief discussions of charter types, advantages of ownership or charters, operational equivalency and other factors are included. Normal economic analysis is shown to be misleading because it does not recognize the financing element inherent in the charter alternative. Because long-term charters involve a fixed series of noncancellable obligations on the company's earnings it is argued that they are equivalent to debt as far as the oil company's management is concerned. The company could promise the same payments to a creditor and receive lump-sum proceeds to finance ownership. Financing charges are removed from charters by capitalizing them at the oil company's cost of debt. The debt or purchase equivalent of the charter is thus determined and an equitable comparison with ownership can be made. The effect of charter length and type are examined by illustrative cases. The relevancy of the method to short-term charters is discussed and left as a matter of individual corporate policy.
Ring-Stiffener Parameters for Cylindrical Pressure Hulls With Circular Imperfections
Authors: Bodey Charles E.
Published: January 2021

Small manned submarines have ship characteristics and mission requirements which require special emphasis in design. Such vehicles are generally: (a) Limited in seakeeping ability, (b) limited in towing capability, and (c) limited in surface cruising range. They must therefore be designed with special consideration to launch and recovery by surface tenders. The cylindrical pressure-hull configuration leads to use of ring stiffeners to balance the buckling resistance to the yielding resistance. The ring stiffeners constitute a major element of such a structure. This discussion is focused on the ring-stiffener function. A preliminary design method based on a parametric ring section is suggested; and an example using this device is carried through as a specific exercise which is scaled to the problem of small submarine design. Consideration is given to factors such as corrosion allowance, beam curvature, and circular imperfections.