An efficient and robust approach to predict ship self-propulsion coefficients

Achieving a reliable and accurate numerical prediction of the self-propulsion performance of a ship is still an open problem that poses some relevant issues. Several CFD methods, ranging from boundary element methods (BEM) to higher-fidelity viscous Reynolds averaged Navier–Stokes (RANS) based solvers, can be used to accurately analyze the separate problems, i.e. the open water propeller and the hull calm water resistance. However, when the fully-coupled self-propulsion problem is considered, i.e. the hull advancing at uniform speed propelled by its own propulsion system, several complexities rise up. Typical flow simplifications adopted to speed-up the simulations of the single analysis (hull and propeller separately) lose their validity requiring a more complex solver to tackle the fully-coupled problem. The complexity rises up further when considering a maneuver condition. This aspect increases the computational burden and, consequently, the required time which becomes prohibitive in a preliminary ship design stage.The majority of the simplified methods proposed in literature to include propeller effects, without directly solve the propeller flow, in a high-fidelity viscous solver are not able to provide all the commonly required self-propulsion coefficients. In this work, a new method to enrich the results from a body force based approach is proposed and investigated, with the aim to reduce as much as possible the computational burden without losing any useful result. This procedure is tested for validation on the KCS hull form in self-propulsion and maneuver conditions.     

On the development of a small catamaran boat

Hull forms and hydrodynamic characteristics of small catamarans are studied. The results of model tests and numerical simulations are cross-examined to carefully investigate the shallow water behaviors of the boats as well as the influence of spacing between demi-hulls on the resistance characteristics. A 12 m long 9.77 ton class catamaran has been developed and several ships have already been produced and deployed as pleasure fishing boats along the west coast of the Korean peninsula. The boats are made of fiber-reinforced plastics and are equipped with a pair of 280 hp diesel engines and water jet propulsion systems. The maximum speed of a fully loaded catamaran exceeds 25 knot. The results of sea trials are compared with those predicted from the model tests.     

艏艉线型优化对船舶阻力性能的影响

为提高母型船阻力性能,以船体阻力性能为优化对象,基于改造母型船法,研究船舶球鼻艏以及船尾线型的改变对船舶阻力性能的影响.采用高度集成化的Tribon系统、可视化绘图软件Auto CAD及CFD(Computational Fluid Dynamics)通用前处理软件ICEM联合建模的方法来建立船体模型.通过模拟计算结果与实验值的对比分析,验证CFD技术在船舶阻力性能预报中的合理性和有效性.通过对比3种不同球鼻艏时的船体阻力得知:从阻力性能方面考虑,对于低速丰满型船舶选用普通型球鼻艏以及中高速船舶采用上翘型球鼻艏均可以获取较好地减阻效果.同时比较不同航速下尾部线型对船体总阻力的影响表明,选优后的方形尾在相同的航速下阻力低、消耗的功率小、形状效应小、黏压阻力和摩擦阻力也相对较小.     

Evaluation of manoeuvring coefficients of a self-propelled ship using a blade element momentum propeller model coupled to a Reynolds averaged Navier Stokes flow solver

The use of an unsteady computational fluid dynamic analysis of the manoeuvring performance of a self-propelled ship requires a large computational resource that restricts its use as part of a ship design process. A method is presented that significantly reduces computational cost by coupling a blade element momentum theory (BEMT) propeller model with the solution of the Reynolds averaged Navier Stokes (RANS) equations. The approach allows the determination of manoeuvring coefficients for a self-propelled ship travelling straight ahead, at a drift angle and for differing rudder angles. The swept volume of the propeller is divided into discrete annuli for which the axial and tangential momentum changes of the fluid passing through the propeller are balanced with the blade element performance of each propeller section. Such an approach allows the interaction effects between hull, propeller and rudder to be captured. Results are presented for the fully appended model scale self-propelled KRISO very large crude carrier 2 (KVLCC2) hull form undergoing static rudder and static drift tests at a Reynolds number of 4.6×10⁶ acting at the ship self-propulsion point. All computations were carried out on a typical workstation using a hybrid finite volume mesh size of 2.1×10⁶ elements. The computational uncertainty is typically 2–3% for side force and yaw moment.     

Experimental Investigation into the performance of the Axial-Flow-Type Waterjet according to the Variation of Impeller Tip Clearance

The tip clearance inside the duct from the tip of the impeller is very important to the performance of waterjet systems, which fact has been proven in the pump field. The tip clearance is especially important on the model scale because it is very difficult in manufacture to keep the tip clearance constant and minimally small along the inside of the duct. In the present study, a flush-type waterjet propulsion unit (duct, impeller, stator, and nozzle) was designed for an amphibious tracked vehicle. Two impellers of different inner diameter were designed and manufactured in order to investigate the gap effect. Resistance and self-propulsion tests with a 1/5-scale model were conducted in PNU towing tank. The flow rate at the nozzle exit, the static pressure at the various sections along the duct and also the nozzle, the revolution of the impeller, and the torque, thrust, and towing forces at various advanced speeds were measured. Based on these measurements, the performance was analyzed according to the ITTC 96 standard analysis method. Based on this analysis method, the full-scale effective and delivered power of the tracked vehicle was estimated according to the variation of tip clearance.     

Ice resistance measurements in ridges with IB APU in the Baltic sea

Ice ridges form a difficult obstacle for ice navigation. Despite this fact, the resistance of ships in ridges has been investigated very little.A trial was performed with the Finnish icebreaker APU (propulsion machinery power of 8·8 MW) in April 1974 in the Baltic, in order to measure its resistance in ridges.Most of the 11 ridges were so massive that the ship could not penetrate through them by a continuous mode, the ramming mode had to be used.When the ship was penetrating a ridge, its speed and the propeller revolutions were registered for determining the resistance. A doppler radar was used for measuring ship spped.In case the ship was stopped in the ridge it was extracted, reversed and accelerated for the next ram. The time history was registered for determining the ship's speed of advance.Before starting a test, the ridge profile above the water level was measured. This was simply done by using a levelling instrument.The main object of the test was to determine the ship's speed of advance. The results, i.e. ice resistance, ship speed and ridge characteristics were analysed on three levels: momentary values average values for rams and average values for a series of rams in one ridge.The test series presented in the article was the first one in full scale in which the speed of the advance of a ship moving by ramming was determined and the ridge profiles were mapped. The measuring system developed worked well. As results the tests gave data of the ship's resistance and of the ship's speed of advance in ridges.     

Material selection for the gas containment system of a compressed natural gas carrier fleet

In this work, the possible exploitation of fiber-reinforced composites in the context of maritime transportation of compressed natural gas (CNG) is investigated. In addition to a more conventional steel configuration, two different fiber materials, carbon and glass, are considered as construction materials for pressure vessels (PVs) to be stored on board ships, with thickness optimized by FEM analysis.The considered scenario is represented by the transportation of CNG from an offshore well to a terminal on shore. Fleets of ships carrying CNG in pressure vessels manufactured with the investigated materials are generated by means of a ship synthesis model (SSM) software and compared on the basis of technical and economical indicators.The choice of the construction material influences considerably the weight of the PVs, which represent a major item of total ship weight and reflects directly on the general transport performances in terms of resistance, seakeeping and reliability in the service. On the other hand, capital as well as operating expenditures are considerably affected by the choice. When exploring the design space, the ship synthesis model is able, at a preliminary stage of the design, to account for the various technical and economical aspects, their implications and relationships. Results are presented of computations carried out in a specific case, identified by the annual gas production and other characteristics of the well terminal and a cruising route for the ships. The comparison is carried out on the basis of the cost per transported unit of gas and of the percentage of success in the transportation process. The computations show that the choice of the PV material has a key influence on the results in terms of optimal number, dimensions and speed of the ships.     

On the propulsion quality of ships operating at restricted water depth

The propulsive efficiency of marine vehicles has been investigated from the point of view of the effect of restricted waters of the propulsion characteristics. Model tests have been performed for both single-screw and twin-screw vessels. Also optimum propulsion data for modern sea-going single-screw merchant ships operating in unrestricted waters are presented for the sake of general comparison.     

Some methods to obtain the added resistance of a ship advancing in waves

Added resistance in waves is an important part of ship dynamic due to its economical effect on ship exploitation. Can the ship sustain speed in a rough sea state? If not, this will produce delays and economical losses if added resistance is not taken into account in the propulsion design. There are not many simple methods to obtain the added resistance in waves of a ship, and the validity of the results is not always good enough for different ships. In this paper, some theories that can be used to predict the added resistance of a ship are studied and validated against seakeeping tests of some monohull models. Tests and results focus in head seas, which are the most severe for the added resistance. Experimental results are compared with numerical calculations and conclusions about the range of application of the presented theories are obtained.     

Hydrodynamics of an oscillating articulated eel-like structure

This study examines the hydrodynamic performance of a highly simplified eel-like structure consisting of three articulated segments with the two aft segments oscillating. A physical model was built and tested to determine the forces developed with the model stationary, to find the self-propulsion speed, and to explore the effect on hydrodynamic performance of different swimming patterns. It was found that hydrodynamic performance increases with increasing oscillation frequency; the highest forces when stationary, and the highest self-propulsion speeds were produced by swimming patterns in which the amplitude in the aft segment is larger than that in the forward segment, and in which the motion of the aft segment lags the forward segment.A simple semi-empirical model based on Morison’s equation was implemented to predict the hydrodynamic forces. This was shown to predict mean thrust well in cases in which the aft segment oscillates in phase with the forward segment, but less reliably when the phase difference between the segments increases. Force time histories are generally not well-predicted using this approach. Nonetheless, self-propulsion speeds are predicted within 30% in all cases examined.     

VLCC油船波浪增阻预报方法的实用修正

近年来随着船舶环保和营运性能要求更高,波浪增阻预报正变得越来越重要。由于存在假设和简化,势流理论方法的短波增阻预报精度差,而经验方法在不同船型中的适用性不强。以有航速VLCC船迎浪航行为例,考虑吃水和航速影响,对理论和半经验方法的波浪增阻结果进行验证和比较分析,并总结出适用特定船型的快速精确预报方法。理论方法基于水平线段移动脉动源的三维面元法求解速度势问题,进而采用三维船体辐射能量法得到船舶辐射增阻,基于二阶波浪力定常分量公式计算得到绕射增阻;经验方法采用ISO15016-2015推荐的STAWAVE2方法。通过分析辐射和绕射增阻占比,讨论了目前方法的适用范围,进而对半经验方法的修正系数进行了研究,给出了反映相似船型和航速特征的改进公式。     

深远海养殖工船最小推进功率研究

针对十万吨级深远海养殖工船在波浪中的阻力和运动响应开展了船模试验与模拟计算,并对其最小推进功率进行了校核。以试验流体力学（EFD）模型试验与模型尺度计算流体力学（CFD）模拟计算的结果进行对比作为方法验证,将实尺度CFD模拟计算的结果直接用于最小推进功率的校核。结果显示,EFD模型试验结果与模型尺度CFD计算结果误差在10%左右,计算精度满足工程要求。在规定的恶劣海况下该船型波浪增阻占总阻力的比例最高可达56.3%,螺旋桨转矩可达最大转矩的63.9%。等级2简化评估法得到的最小推进功率为等级1线评估法给出的最小功率线值的58.9%。研究表明实尺度CFD模拟计算可直接用于船舶最小推进功率的校核,此深远海养殖工船使用等级2简化评估方法进行校核更容易满足规范要求,其最小推进功率应不小于6 833 kW。     

Full scale CFD seakeeping simulations for case study ship redesigned from V-shaped bulbous bow to X-bow hull form

Increasing propulsion efficiency, safety, comfort and operability are of the great importance, especially for small ships operating on windy sites like the North Sea and the Baltic Sea. Seakeeping performance of ships and offshore structures can be analysed by different methods and the one that is becoming increasingly important is CFD RANS. The recent development of simulation techniques together with rising HPC accessibility enables performance of advanced seakeeping simulations for ships in a full scale. The paper presents CFD seakeeping analysis for a case study vessel in two variants: V-shaped bulbous bow hull form (as built) and innovative hull form (X-bow type). The study presents the influence of redesigning the ship on selected seakeeping aspects. The advanced CFD model, with the application of overset mesh technique, was described in detail. Selected numerical results were validated on the basis of experimental testing in a towing tank and showed good agreement. The approach demonstrated here of performing the CFD seakeeping simulations for the analysis of ship performance in a full scale and close to real loading conditions has direct application to the design process as well as in determination of optimal operational parameters of any ship.     

Robust sliding mode control of a mini unmanned underwater vehicle equipped with a new arrangement of water jet propulsions: Simulation and experimental study

This paper presents dynamical modeling and robust control of a Mini Unmanned Underwater Vehicle (MUUV) equipped with a new arrangement of water jet propulsion. The water jet propulsion includes some advantages comparing with a propeller one, such as, reducing the number of required motors, desired number and arrangement of the propulsions, removing adverse torque and cavitation due to propeller rotation and etc. In order to model the proposed MUUV, the gray box method is used in such a way that the dynamical equation of motion is derived analytically by Euler-Lagrangian method, and then the hydrodynamic coefficients (such as added mass and drag coefficients) are derived by performing some tests in a Computational Fluid Dynamic (CFD) software. The dynamical model is used to simulate the MUUV system and also to design the proposed controllers, which are Feedback Linearization Controller (FLC) and Sliding Mode Controller (SMC). In order to investigate and compare the performance of the MUUV and the applied controllers, three types of tests including a desired signal tracking case and two desired path tracking cases are designed. To do so, a method is presented to obtain the desired signals from a desired path under predetermined conditions. Then, an MUUV prototype is designed and constructed in order to investigate the performance of the proposed water jet propulsions and controllers for regulation and tracking desired signal purpose, experimentally. As it is expected, the simulation and experimental results show better performance of the SMC compared to FLC. Furthermore, the experimental results reveal that the water jet propulsion is implementable to practical prototypes and also can be produced in an industrial level.     

Revisiting artificial air cavity concept for high speed craft

Artificial air cavity ship concept has received some interest due to its potential on viscous resistance reduction for high speed craft. Although a small number of ships were designed and built by using this concept, further research on resistance components is required to improve the understanding of artificial air cavity forms. A method based on tank testing with wave pattern measurements to identify resistance components was adopted in the current work. Resistance tests were conducted with two forms; first of which was conventional prismatic planing hull form with a deadrise angle of 10°, and second one was an alternative form with an artificially cavity which was tested both without any air injection, and with two different air injection rates.Total resistance, running trim, sinkage, supply airflow to artificial cavity, air pressure in the cavity and wave pattern generated by the hulls were measured. Frictional resistance was calculated from wetted surface area and compared with resistance component obtained by subtracting wave pattern resistance from the total resistance. Wave pattern spectrums with air cavity configurations were compared across the speed range.     

IMO框架下智能船舶适航的法律规制研究

随人工智能技术发展,智能船舶因其无人化、智能化的特点而与传统国际法律制度产生碰撞。当前,国际海事组织将制定“海上自主水面船舶规则”工作提上日程,航行安全问题作为其中的高度优先事项,受到各国广泛关注。船舶适航作为承运人的主要义务之一,是保障航行安全的先决条件。但智能船舶是否需要符合适航标准,如果适用会产生哪些法律障碍并如何解决等诸多问题亟待研究。对此,应修订《国际海上避碰规则》并明确智能船舶适船技术标准,明确岸基操作人员的法律地位并制定其资格取得、培训、值班标准,明确安全配员标准及需船员在船承担的职责的履行方式。     

基于磁力耦合器的载人潜水器电力推进装置研究

基于磁力耦合传动技术,对载人潜水器电力推进装置进行了系统设计与传动特性研究。采用电磁场有限元方法研究了永磁式磁力耦合器的运行机理和矩角特性,分析了其稳定传动区域和失步条件;分析了螺旋桨的负载特性,采用切比雪夫多项式研究了螺旋桨的四象限全工况动态模型;建立了水下无刷直流推进电机的数学模型和传递函数,设计了推进电机的转速闭环控制系统以抑制转速波动,提高输出推力的平稳度。完成了样机的设计与制造,通过水池试验验证了该推进装置在载人潜水器上的可行性与适用性。     

Seakeeping of two ships in close proximity

Underway replenishment is an essential component of long-term naval operations. During underway replenishment, two ships travel in close proximity at moderate forward speed. This paper examines the hydrodynamic interactions that can influence seakeeping during such operations. Presented numerical predictions include the influence of interaction effects on hydrodynamic forces for two ships in waves. A scarcity of validation material for numerical predictions prompted new towing tank experiments for two ships in waves. The experiments used semi-captive models, and the numerical code was modified to include restraining forces for specified modes. The numerical predictions and experiments show that the presence of a larger ship can significantly influence the motions of a smaller ship in close proximity.     

A case study for the effect of a flow improvement device (a partial wake equalizing duct) on ship powering characteristics

A case study for the energy saving in the powering characteristics of a river going general cargo ship has been carried out. Two different hull forms were generated from the original hull form of the vessel to optimise the stern flow of the vessel. A possible energy saving concept, such as partial wake equalizing duct was investigated in this manner. Resistance, self-propulsion and flow visualization measurements were performed with the hull models to explore the effect of partial wake equalizing ducts on the powering characteristics of the hull form. Analysis of the results indicates that the partial wake equalizing duct concept with an appropriate stern design affect not only the flow characteristics at aft-end, but also the propulsion characteristics. In order to identify effect of each component (partial wake equalizing duct and stern form) a further investigation is needed.     

Propulsion of single-screw ships

On the basis of the little clause in the “Outline Specification” for a new ship: “Trial speed at a load draught of … with the engine at maximum continuous rating has to be …” some aspects regarding propulsion of single-screw ships are discussed, especially the problem of how to combine the hull form, the propeller and the machinery for propulsion in such a way that an optimal solution is obtained.In order to limit the problem, only ships provided with a single conventional propeller for propulsion are considered.A parameter study of a single-screw vessel has been done in order to get some concrete information on the interaction between ship, engine and propeller, and to investigate how the ship propeller power curve should be placed in relation to the engine operation area and to investigate changes in this relationship when the conditions change.