Search

The focus of this paper is the optimization of a ship propeller with regard to its acoustic emission, taking advantage of its flexible material. For this purpose, an optimization method is developed based on a partitioned approach for the simulation of the fluid-structure problem. A boundary element method is applied on the hydrodynamic side whilst the structural problem is solved via a finite element approximation. The approach is validated referring to the hydrodynamic performance of model propellers at different stiffness values. Two optimization approaches are applied. In the first approach, only the hydrodynamic part of the problem is simulated. The second approach considers the fully coupled fluid-structure interaction. The optimized propeller is simulated using a partially nonlinear model for sheet cavitation to evaluate the noise level. Finally, the results are compared with those of the reference propeller. [ABSTRACT FROM AUTHOR]

Wind propulsion systems (WPS) for commercial ships can be a key ingredient to achieving the IMO green targets. Most WPS installations will operate in conjunction with propellers and marine engines in a hybrid mode, which will affect their performance. The present paper presents the development of a generic, fast, and easy tool to predict the propeller and engine performance variation, along with the cost, as a function of the wind power installed in two operation conditions: fixed ship speed and constant shaft speed. Specific focus is directed toward showing generic trends and trade-offs that inform economic decision-making. To this end, a key feature of the presented work is the ability to assess the cost–benefit of both controllable pitch propellers and fixed pitch propellers (CPPs and FPPs). This provides advice on when, in terms of WPS installation size, it is worthwhile to install which kind of propeller. CPPs are found to be more suitable for newly built wind-powered ships (>70% wind power), while a conventional FPP is satisfactory for wind-assisted ships (<70% wind power) and retrofitted installations. The results for a 91,373 GT bulk carrier showed that a WPS unloads the propeller and the engine, which leads to an increase in the propulsive efficiency and a detrimental rise of the engine specific fuel oil consumption. However, propeller gains are found to be greater than engine losses, which result in extra savings. Thus, not only does a WPS save fuel and corresponding pollutant emissions, but it also increases the entire propulsive efficiency. [ABSTRACT FROM AUTHOR]

The objective of this paper is to predict the noise radiated from submarine propellers with different control surface types (the cross- and X-type). When the propellers are free from cavitation, such as those of submarines at a diving depth, the radiated noise dominate, due to unsteady propeller forces. A well-known submarine model (DARPA SUBOFF) is taken as the computing sample. Simulations for hydrodynamics, including stern wakes and unsteady propeller forces, are carried out by using CFD (Computational Fluid Dynamics) technology, and the results are compared with the experimental data. The accuracy of the predicted noise depends on the CFD results. Comparisons between the CFD results and the experimental data are in good agreement. The CFD results are treated as dipole strengths in the linear wave theory to predict the radiated noise caused by the unsteady forces of the propeller. It is found that, when the control surface is of the X-type, the propeller inflow is more uniform, and the radiated noise can be decreased by about 5 dB compared to the cruciform control surface. [ABSTRACT FROM AUTHOR]

The unsteady propeller forces of an underwater vehicle were numerically simulated using computational fluid dynamics to investigate the effects of the axial location of the stern planes. A benchmark study was undertaken using a three-bladed propeller; experimental results of the nominal inflow wake profile were analyzed and the unsteady propeller forces were measured. The numerical method was applied to predict the unsteady propeller forces in the SUBOFF model’s wake by varying the axial locations of the stern planes. Several remarks were made on the primary harmonics of the hull’s wakes and blade-rate propeller forces. [ABSTRACT FROM AUTHOR]

Ship maneuvring simulators are a useful tool for the design of inland waterways and for training of skippers. The realism of the maneuvring prediction is a key success factor. In this paper, a 6 DOF (degrees of freedom) maneuvring model is presented which is able to predict the maneuvring behavior of push convoys in different, rigidly connected configurations (number of barges, draft of the barges, and position of the pusher) and for different water depths. The coefficients of this maneuvring model have been determined based on captive model tests and the realism is exemplified with a number of fast time simulation runs, including the turning on the spot of a convoy by means of uncoupled control of rudders and propellers. Final validations were performed during real-time simulation runs with experienced skippers. [ABSTRACT FROM AUTHOR]

The transient performance of a direct-drive large two-stroke marine diesel engine, installed in a vessel operating in a seaway with heavy weather, is investigated via simulation. The main engine of the ship is equipped with a selective catalytic reduction (SCR) aftertreatment system for compliance with the latest International Maritime Organization (IMO) rules for NOx reduction, IMO Tier III. Because of limitations of exhaust gas temperature at the inlet of SCR systems and the low temperature exhaust gases produced by marine diesel engines, in marine applications, the SCR system is installed on the high-pressure side of the turbine. When a ship sails in heavy weather, it experiences a resistance increase, wave-induced motions, and a time-varying flow field in the propeller, induced by ship motions. This results in a fluctuation of the propeller torque demand and, thus, a fluctuation in engine power and exhaust gas temperature, which can affect engine and SCR performance. To investigate this phenomenon and take into account the engine-propeller interaction, the entire propulsion plant was modeled, namely, the slow-speed diesel propulsion engine, the high-pressure SCR system, the directly driven propeller, and the ship's hull. To simulate the transient propeller torque demand, a propeller model was used, and torque variations due to ship motions were taken into account. Ship motions in waves and wave-added resistance were calculated for regular and irregular waves using a 3D panel code. The coupled model was validated against available measured data from a shipboard propulsion system in good weather conditions. The model was then used to simulate the behavior of a Tier III marine propulsion plant during acceleration from low to medium load, in the presence of regular and irregular waves. The effect of the time-varying propeller demand on the engine and the SCR system was investigated. [ABSTRACT FROM AUTHOR]

In the preliminary design of a propulsion unit, the selection of propeller diameter is most commonly based on open water tests of systematic propeller series. The optimum diameter obtained from the propeller series data is, however, not considered to be representative for the operating conditions behind the ship, instead a slightly smaller diameter is often selected. We have used computational fluid dynamics to study a 120-m cargo vessel with an integrated rudder bulb-propeller hubcap system and a four-bladed propeller series, to increase our understanding of the hydrodynamic effects influencing the optimum. The results indicate that a 3-4% smaller diameter is optimal in behind conditions in relation to open water conditions at the same scale factor. The reason is that smaller, higher loaded propellers perform better together with a rudder system. This requires that the gain in transverse kinetic energy losses thanks to the rudder overcomes the increase in viscous losses in the complete propulsion system. [ABSTRACT FROM AUTHOR]

This study considers a blunt trailing-edged propeller operating both in a uniform and a nominal wake fields. Experiments are performed in the cavitation tunnel of Hyundai Maritime Research Institute. The effects of propeller rotation speed, tunnel flow speed, and blade sheet cavitation growth on the generation mechanism of the singing propeller are investigated. The cavitation, sound, and vibration characteristics related to the singing phenomena are measured by a hydrophone, amicrophone, an accelerometer, and a highspeed digital camera. The natural frequencies of propeller blades are predicted using a finite elementmethod and verified by both contact- and noncontact-type impacthammer tests in air and underwater conditions. The inflow speed and angle of attack for each section of the propeller blades are calculated using the Reynolds-averaged Navier-Stokes equation- based flow analysis. Using a detached eddy simulation, the vortex shedding patterns and their frequencies are calculated. The predicted vortex shedding frequencies are compared with the measured singing frequency and blade natural frequency for determination of consistency. Under cavitation-free regime, the vortex shedding frequencies are predicted for normalized blade radial positions of .8R and .9R. The computed values are close to the two blade natural frequencies and also consistent with the double singing phenomena in the cavitation tunnel test. For fully developed blade sheet cavitation condition, the vortex formation in the wake region is observed to be strongly influenced by the cavitation growth on the pressure side surface. Propeller singing is diminished with the continuous growth of cavitation and is finally locked-off. The significant variation of the flow-induced sound and vibration levels are also observed for the locked-in and the locked-off conditions. The singing occurrence location and frequency under uniform inflow condition are analyzed to investigate the generationmechanism of propeller singing. This study can be applied to the analysis of singing location and its frequency of a propeller operating in the hullwake, which changes the angle of attack according to the propeller rotation angle. [ABSTRACT FROM AUTHOR]

Ducted propellers are commonly used on naval vessels such as submarines and increasingly more in omnipresent autonomous underwater vehicles. Understanding the noise signature of these vessels is of critical importance from both detection and concealment perspective, but the detailed physics of how the tip of the propeller blade interacts with the boundary layer on the duct is not sufficiently well understood. The present study introduces a series of simulations in which tip vortices formed over finite-span lifting surfaces are investigated with the aim of better understanding interactions of tip-gap flow and its interaction with incident boundary layers on radiated noise. Particular attention is devoted to characterizing the nature of the incipient complex flow features and their effect on the force coefficients, surface pressure fluctuations. These reveal that variations of force coefficients with tip-gap height may be used as an early indicator of tip vortex being suppressed as the gap is reduced. Use of the λ2 criterion identifies the formation of strong coherent vortical structures in the tip-gap region. It is suggested that the interaction of these structures with the tip edges is likely to be an important source of noise, with a similar generation mechanism to trailing edge noise. Preliminary analysis of the acoustic signatures computed using the Ffowcs Williams-Hawkings acoustic analogy indicates high levels of directivity, with most of the noise being generated by the foil rather than the duct. The presence of substantial amounts of vorticity in the flow also suggests that accounting for the nonlinear quadrupole noise sources within the fluid might be necessary to fully describe the noise pattern developed. [ABSTRACT FROM AUTHOR]

This article introduces the composition and 12 operating conditions of a four-engine two-propeller hybrid power system. Through the combination of gearbox clutch and disconnection, the propulsion system has four single-engine operation modes, two double-engine parallel operation modes, and six PTI operation modes. Because the propulsion system has a variety of operating conditions, each operating condition has a form of energy transfer. As a result, its energy management and control are more complicated. To study the energy management and control strategy of a diesel- electric hybrid propulsion system, this work mainly studies the simulation model and sub-models of a diesel-electric hybrid propulsion system. In this study, MATLAB/SIMULINK software is used to build the diesel engine model, motor model, and ship engine system mathematical model. The test and analysis were carried out on the test bench of the diesel-electric hybrid power system. By comparing the theoretical value of the SIMULINK simulation model with the test value of the test bench system, the correctness of each sub-model modeling method is verified. On the one hand, research on the text lays a theoretical foundation for the subsequent implementation of the conventional energy management and control strategy based on state identification on the unified management and distribution of the diesel-electric hybrid power system. At the same time, energy management of the diesel-electric hybrid system is also carried out. Optimization research provides theoretical guidance. [ABSTRACT FROM AUTHOR]

TheDefense AdvancedResearch ProjectsAgency (DARPA) Suboff Submarine propelled by the Italian Ship Model Basin (INSEAN) E1619 propeller is extensively used in submarine validation studies. Although there are several numerical studies where the DARPA Suboff submarine is used in combination with E1619 propeller there are no experimental data available in open literature for the self-propulsion condition. In this article, the self-propulsion characteristics of the DARPA Suboff submarine model with INSEAN E1619 propeller obtained with experimental and numerical methods are presented and discussed bymeans of Taylorwake fraction, thrust deduction, hull efficiency, relative rotative efficiency, and propulsive efficiency. To experimentally investigate the submarine form, a self-propulsion experimental setup is designed and manufactured. Resistance and self-propulsion experiments are conducted in Istanbul Technical University Ata Nutku Ship Model Testing Laboratory. Resistance tests are carried out for three different speeds, and the results show good agreement with the published experimental results. Propulsion tests are conducted by using the load-varying selfpropulsion test method for constant speed and seven different propeller rotation rates. Rotational speed, thrust, and torque forces at self-propulsion point are investigated. For the numerical computations a commercial Computational Fluid Dynamics (CFD) code is used. Propeller open water characteristics and nondimensional velocities behind the propeller are calculated. Self-propulsion point of the submarine and propeller assembly is also solved numerically and the results are compared with the results obtained from the experiments, and it is seen that especially the propeller rate of revolution and thrust force are predicted with very good approximation. [ABSTRACT FROM AUTHOR]

This article presents an overview of the recent developments at Instituto Superior Técnico and Maritime Research Institute Netherlands in applying computational methods for the hydrodynamic analysis of ducted propellers. The developments focus on the propeller performance prediction in open water conditions using boundary element methods and Reynolds-averaged Navier-Stokes solvers. The article starts with an estimation of the numerical errors involved in both methods. Then, the different viscous mechanisms involved in the ducted propeller flow are discussed and numerical procedures for the potential flow solution proposed. Finally, the numerical predictions are compared with experimental measurements. [ABSTRACT FROM AUTHOR]

The acoustical performance of a counter-rotating marine propeller system is computed using the Ffowcs, Williams and Hawkings (FWH) algorithm. The solution procedures, where finite volume computational fluid dynamics calculations were exploited, was validated with a conventional propeller having experimental results (namely David Taylor Model Basin [DTMB] 4119). The large eddy simulation formulation and the sliding mesh technique are employed to build thrust and torque curves. Mesh dependency, turbulence model, and discretization schemes were all assessed to have repeatable and accurate results. Because the application under consideration involved inhomogeneous flow and blade interactions, DTMB 3684 and 3685 counterrotating propeller (CRP) models were used for comparisons. In terms of validation of numerical acoustics, the acoustical model evaluation study was first performed on a flow over a cylinder and a rain gutter model. The FWH approach produced good results for the spectrum at near-field and far-field locations. The performance of an inclined propeller, namely VP1304, in a noncavitating condition was investigated and the results were compared with the experiments conducted at the Potsdam Model Basin. Pressure pulses of this propeller in the cavitation tunnel were also attained and compared with experimental results. The amplitudes of the pressure fluctuations were in good agreement with the experimental data except for the weak third harmonics. Last, the generic form of the CRP system attached to an underwater vehicle body was considered to investigate the acoustic spectrum in terms of blade passing frequencies, interacted harmonics and radiated noise. [ABSTRACT FROM AUTHOR]

An operating propeller is the main source of vibration on the ship hull, especially on the stern. In this article, an improved numerical scheme is presented to predict the pressure fluctuations on the ship hull due to the unsteady sheet cavitation of a propeller. The calculated results are compared with the published results and experimental data carried out in the hydrodynamics and cavitation tunnel of Hamburgische Schiffbau-Versuchsanstalt to verify the improvement. The present method is based on a two-cycle iterating scheme which satisfies the boundary integral equation in time domain. The hull pressure fluctuations calculated by the first-cycle iterations are treated as the initial values for the second-cycle iterations. The solid angles of the elements will deviate from the standard value, .5, as the dramatic variation in geometry appears, and accumulate numerical errors in the calculating process. During the second-cycle iterations, a filter based on the solid angles on hull elements is proposed to minimize the iterating error. A container ship is treated as the computing sample in this study, and evidence is offered regarding the 16% improvement achieved by the present method. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The present study aimed to identify significant design parameters on the propeller open water efficiency and characteristics of the wake field of a propeller with propeller-boss-cap-fins (PBCFs), with special attention to hub vortex dynamics. A towed underwater stereoscopic particle image velocimetry system was used to measure the near wake fields of a five-bladed propeller and a PBCF model. Through model tests, it was confirmed that the disappearance of a low-pressure area behind a boss cap, i.e., a reduction of the hub vortex, was the dominant contribution to open water efficiency gains from PBCF rather than a decrease in net torque. Global force and wake fields were also measured in response to design parameter variations of PBCF, i.e., fin chord length, fin span height, pitch angle, and phase lag. In the cases of pitch angle and fin chord length variations, PBCF with a light loading configuration had better open water efficiency than the baseline PBCF. However, in the case of a short fin span height for light loading configuration, the hub vortex was not entirely prevented, and the total open water efficiency decreased. Under heavy loading configurations, excessive negative thrust and torque degraded the open water efficiency. Phase lag variations were less effective with respect to the open water efficiency than other design parameter variations. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

In the quest for higher energy efficiency inmarine 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. [ABSTRACT FROM AUTHOR]

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

High-fidelity, eddy-resolving, simulations of marine propellers are challenging due to the coexistence of moving and stationary elements within the computational box, as well as the need to accurately resolve the dynamics of wake structures such as the tip and hub vortices, which have an effect on the acoustic signature of underwater vehicles. Although an isolated propeller in open-water conditions can be simulated in a rotating reference frame, in a computation involving the body of an appended submarine, e.g., the relative motion needs to be properly treated. This increases the computational cost and reduces the accuracy/robustness of typical body-fitted approaches. In this work, an immersed boundary formulation is utilized to perform large-eddy simulations of a propeller in open-water conditions and in the presence of an upstream appendage at zero incidence. In such case, the requirement for the grid to conform to the moving body is relaxed--solution is locally reconstructed to satisfy boundary conditions--and efficient, conservative structured solvers can be used. This enables us to capture the detailed dynamics of the tip vortices and their footprint on the statistics of the wake. The influence of the upstream appendage is also assessed. [ABSTRACT FROM AUTHOR]

This article deals with a pioneering application of tomographic particle image velocimetry (tomographic PIV) for the hydrodynamic and hydroacoustic analysis of a marine propeller. The hydrodynamic study was mainly focused on the topological analysis of the propeller wake characteristics in the near field based on the vorticity field and on the tilting and stretching terms of the vorticity transport equation. Hydroacoustic analysis concerned the use of tomographic PIV in combinationwith the Powell's acoustic analogy. Tomographic PIV proved to be a valid tool for the detailed quantitative reconstruction of the complex vortex topology in the propeller wake and provided an accurate description of the source terms of the Powell's analogy. In particular, it was shown that the tip vortex perturbation represents the dominant nonlinear contribution to the radiated far-field noise in noncavitating flow conditions. [ABSTRACT FROM AUTHOR]

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

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/V Athena 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. [ABSTRACT FROM AUTHOR]

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

The ice performance of a dual-direction ship is investigated through a numerical procedure developed to simulate the continuous-mode icebreaking in level ice. The effect of the propeller-hull-ice interaction for running astern is accounted for by applying the knowledge obtained from model tests to the numerical procedure. The numerical procedure is in turn used as a performance prediction tool to supplement the model test data to investigate the thrust deduction in ice. [ABSTRACT FROM AUTHOR]

We discuss the optimum propeller loading through the use of a lifting line model. Viscous terms are included through a drag-to-lift ratio, and a hub image model is implemented. Two types of trailing wake geometries are considered: one based on helical wakes, which are aligned at the blade (using the so-called "moderately loaded propeller" assumption), and a second one based on a full wake alignment model to represent more accurately the wake geometry and its effect on the efficiency of the propeller. A comparison of the efficiencies and the loading distributions obtained through both methods is presented as well as convergence and numerical accuracy studies. The accuracy of Betz condition according to both wake models is tested, and conclusions are drawn based on these results. [ABSTRACT FROM AUTHOR]

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 semiactive control scheme that is achieved by attaching a thread at the propeller tip. The main idea of a semiactive 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. [ABSTRACT FROM AUTHOR]

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 highfidelity 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 framework to the full ship design problems. [ABSTRACT FROM AUTHOR]

A hybrid method that couples a potential flow solver with a Reynolds-Averaged Navier-Stokes (RANS) solver for calculating the effective wake of a propeller is proposed. Two improvements are addressed in this method: 1) a conservative interpolation scheme that conserves the total forces when passing information from the potential flow solver to the RANS solver; and 2) a novel option that evaluates the effective wake at the control points in the blade zone. The proposed method is first assessed in the case of an open propeller subject to uniform inflow and then applied to predict the performance of the ducted propellers under uniform inflow. The results of the numerical simulation are correlated with available experimental measurements. [ABSTRACT FROM AUTHOR]

To improve the stealth of a submarine, the sound power radiated from the hull can be reduced using active noise and vibration control. In this article, active control is applied to minimize hull excitation by propeller forces transmitted through the shaft. The dominant propeller axial force fluctuations are directly related to blade passage and the phase of the force is determined by the absolute angle of the propeller shaft. Because the propeller forces are deterministic, the application of feedforward control is appropriate. Numerical finite element/boundary element (FE/BE) models of a submarine have been developed to find the transfer functions. Different control strategies are investigated in which active control is applied to the propeller/shafting system and/or to the submarine hull. Active vibration control and discrete structural acoustic sensing based on the far-field radiated sound power were considered for development of the cost function. In addition, the performance of a system in which active control is combined with passive control using a resonance changer is investigated. It is shown that the combination of tuned control actuators and a resonance changer results in a significant reduction of radiated sound power. [ABSTRACT FROM AUTHOR]

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

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. [ABSTRACT FROM AUTHOR]

A series of model tests on an azimuth thruster model in oblique inflow conditions were performed for different heading angles and at different advance coefficients in pushing and pulling modes. Tests were performed in ventilating and nonventilating conditions. A novel shaft dynamometer was used to measure all six component forces and moments on the propeller shaft. It was found that the propeller shaft lateral force and bending moment were quite large, and thus, the load at the shaft-bearing positions was about three times larger than when only the propeller weight was considered. The results also showed that oblique inflow due to steering gives higher bending loads than when the propeller is subject to ventilation in the straight-ahead condition. A basic blade element momentum method (BEMT) was used to predict the forces and moments on the propeller shaft in oblique flow conditions. Fairly good agreement was found between the BEMT results and the experimental results. [ABSTRACT FROM AUTHOR]

Vibration modes of a submarine are excited by fluctuating forces generated at the propeller and transmitted to the hull via the propeller-shafting system. The low frequency vibrational modes of the hull can result in significant sound radiation. This work investigates reduction of the far-field radiated sound pressure from a submarine using a resonance changer implemented in the propulsion system as well as design modifications to the propeller-shafting system attachment to the hull. The submarine hull is modeled as a fluid-loaded ring-stiffened cylindrical shell with truncated conical end caps. The propeller-shafting system is modeled in a modular approach using a combination of mass-spring-damper elements, beams, and shells. The stern end plate of the hull, to which the foundation of the propeller-shafting system is attached, is modeled as a circular plate coupled to an annular plate. The connection radius of the foundation to the stern end plate is shown to have a great influence on the structural and acoustic responses and is optimized in a given frequency range to reduce the radiated noise. Optimum connection radii for a range of cost functions based on the maximum radiated sound pressure are obtained for both simple support and clamped attachments of the foundation to the hull stern end plate. A hydraulic vibration attenuation device known as a resonance changer is implemented in the dynamic model of the propeller-shafting system. A combined genetic and pattern search algorithm was used to find the optimum virtual mass, stiffness, and damping parameters of the resonance changer. The use of a resonance changer in conjunction with an optimized connection radius is shown to give a significant reduction in the low frequency structure-borne radiated sound. [ABSTRACT FROM AUTHOR]

A viscous/inviscid interactive (VII) approach is applied to predict the performance of hydrofoils and propellers with nonzero trailing edge thickness. The emphasis has been put on developing VII models for flow separation. The investigation starts from a two-dimensional (2D) hydrofoil. The current method uses an iterative scheme to find a nonlifting closing extension behind the trailing edge. Two kinds of schemes are applied for the iteration process: (1) a non-lifting extension with 1 or 2 degrees of freedom, in fully wetted condition and (2) an extension which is treated like a cavity surface, but with a nonconstant cavity pressure distribution. The results from these schemes are compared with those from a commercial RANS Solver (Fluent). Next, the current schemes using flap extensions are extended to three-dimensional (3D) propeller flows. The 3D models are developed so that all the span-wise strips of the propeller satisfy similar conditions to those used in 2D. A propeller with significant nonzero trailing edge thickness is analyzed, using several 3D models, and the results are compared with existing experimental data. [ABSTRACT FROM AUTHOR]

A subjective novel approach incorporating an evidential reasoning (ER) algorithm is developed to achieve the risk estimation of ship hull vibration (SHV). A hierarchical structure for SHV modeling (hazard identification model) is constructed using a combined qualitative and quantitative approach. The quantitative criteria are converted to the qualitative criteria by applying a rule-based quantitative data transformation technique to make use of ER. A mapping process is formulated to convert and quantify the qualitative criteria. Intelligent Decision System (IDS) software is used for synthesis in the hierarchical structure and to produce the risk-estimation results graphically. The results of this paper reveal that the ER is capable of producing the risk estimation of SHV. [ABSTRACT FROM AUTHOR]

The effects of the free surface on the flow around a rotating propeller were investigated experimentally in a circulating water channel by varying the propeller immersion depth. Instantaneous velocity fields were measured using a two-frame particle image velocimetry (PIV) technique at four blade phases. These fields were ensemble averaged to obtain the phase-averaged flow structure of both the inflow and the wake. The flow around the propeller was influenced by the propeller rotation speed, the loading on the blades, and the proximity of the propeller to the free surface. The boundary layers developed on the blade surfaces led to the formation of viscous wake at all immersion depths. As the propeller was moved closer to the free surface, the axial velocity within the slipstream decreased. Interaction between the tip vortices and the slipstream seemed to cause the tip vortices to follow an oscillating trajectory. The presence of the free surface greatly affected the wake structure, especially for the propeller immersion depth of 0.6 D. At small immersion depths, the free surface modified the tip and trailing vortices and the slipstream flow structure downstream of X/D = 0.3 in the propeller wake. The present study shows that wake modeling should consider the free surface effects to accurately predict propeller performance or cavitation at small propeller immersion depths. [ABSTRACT FROM AUTHOR]

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

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

An engineering approach for simulating ship maneuvers in both deep and coastal waters taking into account effects of ambient current and wind was developed. The three degree-of-freedom rigid body equations of surge, sway, and yaw were numerically solved. A semiempirical approach was applied to determine the forces and moments arising from the propeller, rudder, current, wind, and wave making. Hydro- dynamic calculations coupled with the slender body approximation were used to determine the wave-making resistances for arbitrary water depth. This approach was also adopted for determining the sway and surge added masses and yaw added moment. Computational fluid dynamics calculations were further used to determine the drag forces and the dependence with depth. Predictions of ship trajectories were compared with the field trial data of a full-size containership at design and ballast loading conditions in both deep and coastal waters. The comparison consisted of turning circle motion, zig-zag maneuvers, and actual sea voyage data, and yielded favorable agreement. [ABSTRACT FROM AUTHOR]

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