A numerical study of nonlinear wave interaction in regular and irregular seas: irrotational Green–Naghdi model

The irrotational Green–Naghdi model for nonlinear wave propagation in deep water is developed to simulate the irregular sea surface of a given directional wave spectrum. The model is derived from Hamilton's principle with a depthwise approximation to the flow field. The nonlinear boundary conditions are exactly satisfied on the actual free surface, and the continuity equation is satisfied exactly within the fluid domain. The ‘level’ of approximation in the depthwise direction is optimally chosen to simulate a given wave spectrum accurately with minimum computational effort. Several numerical techniques also are introduced to cut the computational cost further. Numerical results for two-dimensional nonlinear waves are presented.     

基于CFD的内河船深浅水中操纵性预报

由于岸壁效应和浅水效应,内河船舶在限制水域作操纵运动时通常受到比在开阔水域中更大的水动力.这些水动力对船舶操纵性具有不利影响,有可能导致船舶碰撞或触底等海上事故.因此,为了在船舶设计阶段预报其操纵性能,考虑浅水效应和岸壁效应以准确计算内河船舶操纵运动水动力非常重要.本文基于CFD方法,通过对粘性绕流进行数值模拟,对长江中营运的三艘内河船舶的操纵运动水动力进行计算.首先,为了验证数值方法的可靠性,对标模KVLCC2纯横荡和纯首摇试验的水动力进行计算,并将计算结果与现有的试验数据进行对比.然后,对三艘内河船舶在不同水深下的静舵试验、纯横荡和纯首摇试验进行数值模拟,计算得到水动力及相应的线性水动力导数.最后,基于计算得到的水动力导数,获得Nomoto模型中的操纵性参数,对比分析三艘内河船舶在深浅水中的操纵性能.结果表明,本文方法可以揭示不同水深下三艘内河船舶的操纵性变化趋势.该方法可为船舶设计阶段内河船舶深浅水中的操纵性预报提供一种实用的工具.     

Fatigue analysis of water intake risers: Hydrodynamic damping effect and a hybrid frequency-time domain method

The fatigue performance is key to the design of water intake risers (WIRs), which is a novel concept used to convey cooling water for liquefaction of natural gas at sea. To estimate the fatigue life, it is crucial to accurately predict the response amplitude of the WIRs, which is dominated by hydrodynamic damping. In operational conditions, the motion amplitudes of WIRs are usually smaller than their diameter, and thus leading to a flow regime of KC < 5. It is found in this flow regime; the hydrodynamic damping largely depends on the motion magnitude of the risers. To consider this coupling effect, a hybrid frequency-time domain fatigue analysis method is proposed, where a nonlinear stress transfer function is adopted. The hybrid method accounts for the coupling effect between the hydrodynamic damping and the structural motion. Significantly reducing the computational cost, this method provides results as accurate as that from a time domain analysis based on the relative velocity model with a constant drag coefficient. Furthermore, recommendations for further simplification of the fatigue analysis recognizing the coupling effect are given.     

Prediction of the forces acting on container carriers in muddy navigation areas using a fluidization parameter

To assess the safety of navigation in muddy areas, a comprehensive captive manoeuvring model test program was executed. Based on the results of this experimental program, a four-quadrant manoeuvring model was built with a separate set of coefficients for each combination of under-keel clearance and mud layer characteristics. The disadvantage of this model is that only conditions corresponding with the experimental ones can be simulated. A more consolidated mathematical model was needed. This was achieved with the introduction of a fluidization parameter that determines the corresponding hydrodynamically equivalent depth above a solid bottom. As a result, the under-keel clearance dependency of a given mathematical manoeuvring model can be reformulated in such way that the effect of any realistic muddy condition is included. In this article, the modelling of the hull forces, the propeller thrust and torque, and the forces acting on the rudder will be discussed.     

Time-domain numerical and experimental analysis of hydroelastic response of a very large floating structure edged with a pair of submerged horizontal plates

This paper is concerned with the hydroelastic problem of a pontoon-type, very large floating structure (VLFS) edged with the perforated plates, non-perforated plates or their combination anti-motion device both numerically and experimentally. A direct time domain modal expansion method, taking amount of the time domain Kelvin sources in hydrodynamic forces, in which the fluid flows across the perforated anti-motion plate by applying the Darcy's law, is applied to the fluid–structure interaction problem. A quarter of numerical model is built based on the symmetry of flow field and structure in hydrodynamic forces, and special care is paid to the rapid and accurate evaluation of time domain free-surface Green functions and its spatial derivatives in finite water depth by using interpolation–tabulation method. Using the developed numerical tools and the model tests conducted in a wave basin, the response-reduction efficiency of the perforated plates is systematically assessed for various wave and anti-motion plate parameters, such as plate width, porosity and submergence depth. As a result of the parametric study, the porosity 0.11 is selected as the optimal porosity, and the relationship between the porosity and the porous parameter is developed by using the least-squares fitting scheme. After simulation and verification, the dual anti-motion plates which are the perforated-impermeable-plate combination attached to the fore-end and back-end of the VLFS, are designed for more wave energy dissipation and added damping. Considering variation of the water depths in offshore, discussion on the effectiveness of these anti-motion devices at different water depths is highlighted.     

Influence of turbulence closure models on the vortical flow field around a submarine body undergoing steady drift

Manoeuvring underwater vehicles experience complex three-dimensional flow. Features include stagnation and boundary layer separation along a convex surface. The resulting free vortex sheet rolls up to form a pair of streamwise body vortices. The track and strength of the body vortex pair results in a nonlinear increase in lift as body incidence increases. Consequently, accurate capture of the body vortex pair is essential if the flow field around a manoeuvring submarine and the resulting hydrodynamic loading is to be correctly found. This work highlights the importance of both grid convergence and turbulence closure models (TCMs) to the strength and path of the crossflow-induced body vortices experienced by the DOR submarine model at an incidence angle of 15°. Five TCMs are considered; Spalart–Allmaras, k-ε, k-ω, shear stress transport, and the SSG Reynolds stress model. The SSG Reynolds stress model shows potential improvements in predicting both the path and strength of the body vortex over standard one- and two-equation TCMs based on an eddy viscosity approach.     

基于电子海图的船舶操纵仿真器

本文主要介绍最近研制的由微机、高分辨率显示器、图形卡、操纵控制箱等组成的基于电子海图船舶操纵仿真器的两个主要技术──船舶操纵数学模型和电子海图技术，最后还介绍了该仿真器在航海实际中的一个应用．在数学模型中，考虑到航海实际的需要，提出了一个适合常速、低速和大漂角等各种情况的水动力计算模型以及四象限舵力和浆力的算法．另外，考虑了浅水、岸壁、风、流、浪的影响及附属操纵设备──拖轮、缆绳、锚链等对船舶的作用．本仿真器的电子海图装置，不仅能实时显示船舶所在海域的海图，动态显示船舶的二维俯视图象及运动姿态、航行轨迹，还可根据需要选择性地放大、缩小海图、显示各种岸基设施，并且可以记录模拟过程中的各种数据，制作航迹图的硬拷贝以及在显示器上再现，以供分析研究．     

Comparison of CFD and EFD for the Series 60 C B= 0.6 in steady drift motion

 This paper presents comparisons of computational and experimental fluid dynamics results for boundary layers, wakes, and wave fields for the Series 60 C _B= 0.6 ship model in steady drift motion. The numerical method solves the unsteady Reynolds-averaged Navier–Stokes and continuity equations with the Baldwin–Lomax turbulence model, exact nonlinear kinematic and approximate dynamic free-surface boundary conditions, and a body/free-surface conforming grid. The experimental and computational conditions, i.e., Froude numbers of 0.16 and 0.316 for the experiments, and Froude numbers of 0 and 0.316 for the computations, allow comparisons of low and high Froude number results, respectively, which allows an evaluation of Froude number effects and validation of the computational fluid dynamics at both low and high Froude numbers. This article gives an overview of this numerical approach, and the computational conditions and uncertainty analysis are described. Results are presented for the wave and flow fields, with emphasis on the important flow features of drift- and wave-induced effects in comparison with the experiments. Finally, conclusions from the present study are given, together with recommendations for future work. Received: August 31, 2001 / Accepted: March 25, 2002     

灌河口海域泥沙悬浮和沉降试验研究

掌握灌河口海域泥沙运动规律是开展灌河口航道整治研究的基础。以现场所取泥沙为研究对象,通过大型波浪水槽试验研究灌河口海域泥沙在不同的水深、不同的波周期和波高条件下的悬浮规律。通过静水沉降试验研究灌河口海域泥沙在不同初始浓度、不同水深下的沉降特性。结果表明,在极限波高情况下,水体上部区域含沙量较小,且沿垂线分布变化较小,但水体底部附近含沙量较大,总体上底部含沙量比上部水体含沙量大0.25~0.96 kg m^3;不同水深以及不同初始含沙量情况下,泥沙沉降速度0.08~0.20 cm s,与单颗粒泥沙沉速在同一量级,灌河口海域泥沙絮凝作用较弱。     

Ship sense—striving for harmony in ship manoeuvring

Ship manoeuvring is something that many seafarers perform, although little attention has been devoted to this in research literature. The topic has generally been explained by members of the trade as gaining knowledge through experience. The purpose of this study was to identify which factors contribute to the perceived state of a ship’s physical condition during manoeuvring. Eight master mariners were interviewed. The data resulted in a division of a sea voyage into three different phases, each requiring varying levels of effort from the bridge crew. The results further describe how the shiphandler strives for harmony between his ship and the environment. This is accomplished by personal factors such as spatial awareness, knowledge and experience to handle environmental factors of context, situation and vessel specific factors of inertia and the use of navigational instruments.     

RANS simulation of a container ship using a single-phase level-set method with overset grids and the prognosis for extension to a self-propulsion simulator

Steady flow simulations for the Korean Research Institute for Ships and Ocean Engineering (KRISO) container ship (KCS) were performed for towing and self-propulsion. The main focus in the present article is on the evaluation of computational fluid dynamics (CFD) as a tool for hull form design along with application of state-of-the-art technology in the flow simulations. Two Reynolds-averaged Navier-Stokes (RANS) equation solvers were employed, namely CFDShip-Iowa version 4 and Flowpack version 2004e, for the towing and self-propulsion cases, respectively. The new features of CFDShip-Iowa version 4 include a single-phase level-set method to model the free surface and an overset gridding capability to increase resolution in the flow and wave fields. The new features of Flowpack version 2004e are related to a self-propulsion scheme in which the RANS solver is coupled with a propeller performance program based on the infinitely bladed propeller theory. The present work is based on a close interaction between IIHR-Hydroscience and Engineering of the University of Iowa and Osaka Prefecture University. In the following article, overviews are given of the present numerical methods and results are presented and discussed for the KCS in towing and self-propulsion modes, including comparison with available experimental fluid dynamics (EFD) data. Additional evaluation is provided through discussion of the recent CFD Workshop Tokyo 2005, where both methods appeared to yield very promising results.     

e-Navigation and situation-dependent manoeuvring assistance to enhance maritime emergency response

Safe ship handling in every situation and under all prevailing circumstances of ship status and the environment is a core element contributing to the safety of the maritime transportation system. Especially in case of emergencies, there is a need for quick, accurate and reliable information to manoeuvre a ship safely. This paper focusses on investigations into enhanced response to maritime emergencies by means of onboard manoeuvring support. The research and discussions are done exemplarily for person overboard (PoB) accidents. PoB is a typical situation for application of manoeuvring assistance and decision support, e.g. in order to return quickly to the position of the accident. Based on the analysis of selected accident case studies and existing solutions representing the technical state-of-the-art, shortcomings will be identified and discussed, and a potential approach for advanced manoeuvring support in the context of e-Navigation-based requirements will be introduced and discussed.     

国外大比例潜艇模型试验研究

采用大比例潜艇模型进行试验测试可有效评估、预测潜艇战技性能,从而推进潜艇研制工作.与实艇试验相比,大比例潜艇模型试验具有低成本、无人员安全风险等突出优点.本文将研究国外大比例潜艇模型试验情况,分析未来潜艇大比例模型试验发展趋势.     

Computational investigation of cavitation on a semi-spade rudder

This article examines noncavitating and cavitating flow fields around a semi-spade rudder in the ship wake and propeller slipstream based on a computational method. The article seeks to explain the erosion that can occur around the gap due to cavitation; such erosion has been reported to occur while a ship is at sea. Another area of research is the effect of the gap size and shape. The effects of erosion-evading devices such as elongated gap edges, an increased edge radius, flow control projections, and vertical and horizontal guide plates were also studied.     

Manoeuvring and hotelling external costs: enough for alternative energy sources?

Local air pollution is the most relevant externality of maritime transport, and its effects are more acute in urban areas as a result of manoeuvring, hotelling and load/unload activities at ports. This article is intended to assess ships’ local air pollution impact in generally densely populated harbour areas to decide whether alternative power supply measures are feasible. First, an optimized infrastructure investment model is developed to ease implementation and maximize the efficiency of alternative power supply projects. Once target harbours and traffic (ship types) within a national port network have been chosen, a vessel traffic analysis (ship type, tonnage, manoeuvring, and hotelling times) is carried out to quantify and evaluate annual polluting emissions (PM_2,5, SO₂, NOx, and VOCs) and their externalities. Finally, the assessment model is applied and results of the Spanish port network case study are discussed. The results obtained are significant and bring the possibility of further controlling the ship’s environmental performance at berth.     

排气角度对航行体表面等压气膜演化机制及流动特性影响研究

等压排气是一种可有效改善航行体绕流流场特性、抑制纵向偏转的流动控制技术。文章数值模拟了带等压排气的航行体水下垂直运动过程,给出了不同排气角度时的排气流量及速度、气膜长度等参数变化规律,分析了排气角度对等压气膜非定常发展过程及航行体绕流流场特性的影响,建立了排气孔附近及其下游流场、气膜尾部回射流场的拓扑结构,探讨了等压气膜的形态特征、演化规律及其降低航行体表面压力的机制,研究结果有助于深入理解等压排气技术改善航行体流体动力学特性的物理本质。     

上海港外高桥挖入式港池进口航道航行条件研究

外高桥挖入式港池规划前期论证的关键内容之一是其进口航道航行条件的评估。交通部上海船舶运输科学研究所接受委托,对规划船型的操纵运动方程进行了仔细研究。对规划船型的典型——“冰河”轮作了水动力测定;利用实船试验资料对操纵运动的数学模型进行科学率定;使用本所研制的船舶操纵模拟器对规划拟定的两个港池——外高桥嘴挖入式港池和五号沟挖入式港池的进口航道航行条件进行了比较深入的试验研究。最后,给出了两个港池安全进口的必要条件,为规划部门选定提供了科学依据。     

双桨客货轮自航船模操纵性试验研究

本文通过一组典型双桨船型,即常规船型、双尾鳍型及双尾型船的自航船模操纵性试验,探索了双桨船的操纵特点,分析研究了螺旋桨旋向及船型对操纵性的影响规律。研究表明:内旋桨使回转性及错车性能略有下降,但错车仍有正常转向,车舵并用能得到理想的效果。内旋使倒航性能大为改善,使倒航可操。单机倒航时出现有规律的反常转向,可利用作为倒航的操纵手段。双尾鳍船的回转性能优于另两种船型,倒航性能及车舵并用的转首性能亦优于常规型船,是具有良好操纵性的一种船型。双尾鳍船型配以内旋桨方案有广阔的应用前景。     

Large-eddy simulation of cross-flow around ship sections

The present work is motivated by phenomena occurring in the flow field around ship-like bodies with an incoming lateral flow (cross-flow, 90 ° drift angle). Three-dimensional unsteady flows around different ship sections are investigated by using computational fluid dynamic (CFD) tools with large-eddy simulation (LES) subgrid-scale turbulence model. The simulation results are compared to measurements at several Reynolds numbers in the 90–200,000 range. Focus in our investigation is on the characterization of the motion of vortex structures generated by the separated flow. Another target in the study is to obtain better knowledge of the hydrodynamic forces acting on the sections. Computed pressure and drag coefficients are compared with experimental measurements. The comparison between simulations and measurements shows that an LES model can predict the flow field around ship sections in detail and the hydrodynamic forces acting on the sections.