Numerical study of ice-induced loads on ship hulls

A numerical model is introduced in this paper to investigate both global and local ice loads on ship hulls. This model is partly based on empirical data, by which the observed phenomena of continuous icebreaking can be well reproduced. In the simulation of a full-scale icebreaking trial, the interdependence between the ice load and the ship’s motion is considered, and the three degree-of-freedom rigid body equations of surge, sway and yaw are solved by numerical integration. The variations in the level ice thickness and in the strength properties of ice can also be taken into account. The simulated ice loads on ship hulls are discussed through two case studies, in which the ship’s performance, the statistics of ice-induced frame loads, and the spatial distribution of ice loads around the hull are analyzed and compared with field measurements. As far as we know the present paper is the first to integrate all the features above. It is hoped that further studies on this numerical model can supplement the field and laboratory measurements in establishing a design basis for the ice-going ships especially for ships navigating in the first-year ice.     

基于规范载荷的舰船设计海况等级确定方法

针对军用规范载荷难以给出舰船设计海况等级的问题,本文通过三维时域非线性水弹性理论分析了舰船在典型航速、不同海况下的波浪载荷极值与规范载荷之间的对应关系,进而提出了一种明确舰船设计海况等级的方法。以某型舰船为例,基于该方法确定了该型舰船的设计海况等级。研究成果表明：该方法可有效明确舰船规范载荷对应下的设计海况等级,在一定程度上为舰船的安全使用提供参考。     

考虑不确定性因素的路径优化(英文)

A route optimization methodology in the frame of an onboard decision support/guidance system for the ship’s master has been developed and is presented in this paper.The method aims at the minimization of the fuel voyage cost and the risks related to the ship’s seakeeping performance expected to be within acceptable limits of voyage duration.Parts of this methodology were implemented by interfacing alternative probability assessment methods,such as Monte Carlo,first order reliability method(FORM) and second order reliability method(SORM),and a 3-D seakeeping code,including a software tool for the calculation of the added resistance in waves of NTUA-SDL.The entire system was integrated within the probabilistic analysis software PROBAN.Two of the main modules for the calculation of added resistance and the probabilistic assessment for the considered seakeeping hazards with respect to exceedance levels of predefined threshold values are herein elaborated and validation studies proved their efficiency in view of their implementation into an on-board optimization system.     

Hydroelasto-plasticity approach to predicting the post-ultimate strength behavior of a ship’s hull girder in waves

Dynamic collapse behavior of a ship’s hull girder in waves is investigated; post-ultimate strength behavior is the focus. Firstly, a simulation method is proposed. Assuming that a plastic hinge is formed during the collapse of the hull girder, the whole ship is modeled as two rigid bodies connected amidship via a nonlinear rotational spring. The post-ultimate strength behavior, such as the reduction of load carrying capacity due to buckling and yielding, is reflected in the model. Hydrodynamic loads are evaluated by using nonlinear strip theory to account for the effect of large plastic deformations on the loads. A scaled model for validation of the simulation is designed and fabricated. Then a series of tank tests is conducted using the scaled model to validate the simulation results. Post-ultimate strength behavior characteristics in waves are clarified by using the numerical and tank test results. It is shown that the hull girder collapses rapidly after reaching ultimate strength, and then the plastic deformation grows until unloading starts at the collapsed section. Finally, several parametric dependencies of the extent of the collapse behavior are discussed based on a series of the simulations.     

Plastic deformation of ship plate subjected to repeated patch loads at different locations - Elastoplastic numerical analysis and design equation

Ship structures may be subjected to repeated random patch loads at different locations. Under these circumstances, ship plates will have large accumulated permanent deformations, which will result in some serious negative effects on their work and safety performance. Therefore, the elasto-plastic response of ship structure under repeated patch loads at different locations are studied by using finite element method. The permanent deformations of plate in the whole loading and unloading process are investigated. In addition, the residual stress and plastic strain states of the panel and stiffeners are studied based on a typical wheel-on-deck interaction scenario. Moreover, according to Hughes's hypothesis, the equivalent method between repeated patch loads at different locations and full uniform pressure load is studied. Considered the influence of plate slenderness, the improved formula for equivalent load coefficient is proposed, showing a good correlation with experimental data and numerical results. The proposed equivalent method can be used for estimating the permanent deformations of ship structures under repeated patch loads at different locations in ship life.     

基于纵倾调整的集装箱船实海域航行阻力减少的研究

为应对"能效运营指标(EEOI)自愿应用导则",提出了在航行中采用调节纵倾的方法,降低营运能耗。选取了3100TEU集装箱船作为研究对象,应用Rankine源自由面势流理论计算不同纵倾下船舶兴波阻力系数以及总阻力系数,应用三维面元法计算了规则波中的波浪增阻,并针对实海域进行了増阻预报。研究表明,一定的艉倾能减小兴波阻力和总阻力。通过实海域増阻预报,服务航速下采用艉倾0.4°的纵倾航行会使波浪増阻增加4.21%,但总阻力仍能减少3.38%,较有效地降低了EEOI值。     

Short-term statistics of ice loads on ship bow frames in floe ice fields: Full-scale measurements in the Antarctic ocean

Ship operation and ice loading in floe ice fields have received considerable interest during recent years. There have been several numerical simulators developed by different institutes which can simulate ship navigation through floe ice fields and estimate ship performance and local ice loads. However, public data obtained from full-scale measurement covering comprehensively ship performance and ice loads under various ice thicknesses, concentrations and floe sizes are rare. The 2018/19 Antarctic voyage of the Polar Supply and Research Vessel (PSRV) S.A. Agulhas II gathered considerable data of the ship in floe ice fields under various thicknesses, concentrations, and floe sizes. The aim of this paper is to carry out statistical analysis to seek suitable probability distributions which adequately fit the measured ice load and therefore suitable to be used as parent distributions for long-term estimation. For this aim, three categories of probability distributions, namely standard distributions, truncated distributions and mixture distributions are tested. It is found that truncated distributions can fit the load data better than standard distributions bounded at the threshold. In addition, mixture distributions are shown to have promising features, which fit the data well and are able to separate distribution components. Subsequentially, the well-performed distributions are used as parent distributions to make long-term load estimations. The estimation results demonstrate that long-term estimations are sensitive to the selection of parent distribution, which addresses the importance of finding correct distribution to model short-term ice loads. The data of ten selected cases will be published for the use of other researchers.     

船舶变频空调风机节能技术研究

应用当量温差计算法对欧—亚航线上船舶在不同航区的空调动态负荷和风机可调送风量进行了定量描述;阐述了变频技术应用于空调风机的途径;得出了空调风机变频调速,舒适性好,节能率高达５８％以上,具有广阔发展前景的结论     

结合功率管理推力分配策略研究

由于动力定位对船舶的推进能力要求比较高,所以采用动态性能更好的电力推进方式已经成为了动力定位船舶的优先选择。对于电力推进船舶来说,推进器是其最大的负载,以起重船为研究对象,除了推进器以外,船上还有起重机和绞锚车等大功率负载。当船上其他大功率负载突然启动或者工作在风浪较大的环境时,会造成整个船舶电网功率波动较大,影响整个船舶电网的稳定性。文章提出自适应组合推力偏置结合功率管理分配方法,当船舶电网功率波动较大时,释放偏置的推力,降低整个船舶电网的功率波动,有助于增强电网的稳定性。     

穿越南沙群岛的航线设计

南沙群岛是我国南海诸岛中分布最广、范围最大、岛礁最多的一个岛屿,但长期以来,很少有船舶驶入。由于货物运输原因,我轮频繁来往于香港和东马,经认真研究分析资料,设计了四条可以穿越南沙群岛的航线,经过10多个航次的航行检验,该航线能够保证船舶安全。此文对此穿越航线作了介绍。     

深海工程船锚泊仿真系统研究

为了实现工程船定位和控位快速模拟仿真,本文以45000DWT海洋工程船为例,采用均匀设计试验方法,确定深海船舶工作不同的工况组合,基于Ansys-Aqwa软件对工程船深海锚泊动态响应进行仿真分析,对仿真结果进行回归处理,得到船舶位移和锚索张力与锚索长度、风浪流环境载荷变化的数学响应模型,再对位移数学响应模型进行求反函数处理,获取船舶控位调整锚索长度的方法,为深海锚泊软件仿真系统提供模型支撑。     

大型集装箱船能效营运指数仿真研究

为应对IMO提出的日益严格的排放法规,降低船舶EEOI值,本文分析了EEOI的数学计算公式以及简化公式,并以某8063TEU大型集装箱船为目标船,基于MATLAB/Simulink建立了船舶能效系统的仿真模型.通过仿真研究,分析了船舶航速、航期、载货量、航程对船舶EEOI的影响,同时研究分析了EEOI对航速、载货量、航程变化的敏感性.结果表明随着航期的增加船舶EEOI逐渐减小;EEOI对航速的敏感性最高,对载货量的敏感性其次,而对航程的敏感性较低;降低主机工作负荷从而降低航速,以及提高船舶载货量都能有效降低船舶EEOI值,而增加航程则对降低EEOI值效果不明显.     

Ship resistance when operating in floating ice floes: Derivation,validation, and application of an empirical equation

With the effects of global warming, the Arctic is presenting a new environment where numerous ice floes are floating on the open sea surface. Whilst this has improved Arctic shipping navigability in an unprecedented way, the interaction of such floes with ships is yet to be understood to aid the designing of ships and route planning for this region. To further explore this topic, the present work develops a procedure to derive an empirical equation that can predict the effects of such floes on ship resistance. Based on a validated computational approach, extensive data are extracted from simulations of three different ships with varying operational and environmental conditions. The ice-floe resistance is shown to strongly correlate with ship beam, ship buttock angle, ship waterline angle, ship speed, ice concentration, ice thickness and floe diameter, and the regression powers of each of the parameters on resistance are ascertained. This leads to a generic empirical equation that can swiftly predict ice-floe resistance for a given ship in a given condition. Subsequently, demonstrations are given on the incorporation of the derived equation into a set of real-time Arctic ship performance model and voyage planning tool, which can predict a ship's fuel consumption in ice-infested seas and dynamically suggest a route with the least safety concern and fuel consumption. Moreover, the equation is validated by providing ice resistance prediction for experimental and full-scale conditions from multiple sources, showing high accuracy. In conclusion, the empirical equation is shown to give valid and rapid estimates for ice-floe resistance, providing valuable insights into ship designs for the region, as well as facilitating practical applications for polar navigation.     

21000t多用途船的球首设计及尾部节能装置试验

２１０００ｔ多用途船是上海远洋公司在南美洲航线上的定期班船，根据航程、船只数量、航班期的综合分析，要求船舶在主机输出功率７２３９．７５ｋＷ，含有１５％海上功率储备时，航速达到１６．５ｋｎ。为达到船东提出的先进航速指标，进行多次球首设计及尾部前置导管舵球的优化试验。介绍其设计思想及试验结果。     

滚装重荷载应急卸载过程的浮基多体系统动力学分析

在救灾和战争等非常情况下，利用中小型近海滚装渡轮或改装后的渔轮渡海输送重荷载，具有可征用船只数量多和装卸载不依赖吊装设备等优点。缺乏港口屏蔽的海浪环境中重荷载进行滚动卸载时，必须考虑波浪对船的作用和重荷载与船的相互作用。本文通过对船在波浪中所受表观重力和表观浮力的分析，导出波浪作用力矩的计算公式。运用浮基多体系统动力学方法，建立波浪-浮基-重荷载系统的动力学方程。使用标准的龙格-库塔四阶方法进行数值积分求解。考虑海况、船型和重荷载在船上运动参数等因素，计算了各工况下的横摇运动响应。进而给出了重荷载安全快速卸载的驾驶操作要求及相关运动规律。     

风力载荷对实船参数横摇预报的影响研究

参数横摇作为一种严重危害船舶安全的现象,已被国际海事组织(IMO)列为重要的稳性失效模式开展研究。集装箱船的事故报告表明,参数横摇现象发生于相对恶劣的海况条件下,且伴随相应的气象条件。由于此时风力载荷是船舶航行过程中不可忽略的因素,因而非常有必要研究其对参数横摇运动的影响。文中基于弱非线性三自由度运动模型,通过对4艘实船参数横摇响应的计算研究,发现风力载荷对于集装箱船在规则波中的参数横摇具有重要影响,对于参数横摇起促进作用。     

深海工程船锚泊仿真系统

为实现工程船定位和控位快速模拟仿真,以45000载重吨海洋工程船为例,采用均匀设计试验方法,确定深海船舶工作的不同工况组合,基于Ansys-Aqwa软件对该船的深海锚泊动态响应进行仿真分析。对仿真结果进行回归分析处理,得到船舶位移和锚索张力与锚索长度和环境载荷(风、浪、流)之间的数学响应模型。对位移数学响应模型进行求反函数处理,获取船舶控位调整锚索长度的方法,为深海锚泊软件仿真系统提供模型支撑。     

Efficient estimation of extreme long-term stresses by considering a combination of longitudinal bending stresses

Longitudinal stresses due to combined horizontal and vertical bending moments in ships, corresponding to a return period of 20 years, are estimated by linear response analysis. In principle, the stress should be obtained by combining the stress in all sea states that can occur over a long-term period. A method to determine the desired long-term extreme stress by considering only a few short-term sea states is presented. The sea states have a certain probability of occurrence, and are each identified by a contour line in the (H _s, T _p)-plane. This approach makes it possible to estimate the extreme loads on the vessel in a practical and accurate manner. Moreover, it is shown that the long-term stress can be estimated by combining the individual long-term extreme stresses due to vertical and horizontal bending moments by using the sum-of-squares approach and accounting for the correlation between stresses. It was found that the correlation coefficient can be taken as the largest of the ones calculated along the contour line. It is shown that this correlation coefficient can even be approximated by the normalized phase angle at the wave length where the dominant response has its peak value. A comparison with the results obtained using well-known combination rules is presented. While linear analysis has been used here, it is believed that the approach can be generalized to stresses with nonlinear behavior, and hence represent a significant improvement in calculation efficiency. Received: September 18, 2001 / Accepted: December 18, 2001     

有限水深中破损船舶的运动与波浪载荷研究

由于有限水深中船舶搁浅和触礁等严重破损事故频发,为了减少事故的发生,对有限水深中船舶破损后的运动及波浪载荷的研究显得十分必要。文章基于三维势流理论,引入有限水深自由面Green函数,在频域内使用奇点分布法对一艘首部破损进水的散货船在有限水深中的运动与波浪载荷展开了计算,并根据劳氏船级社规范做了短期预报。短期预报结果表明,该散货船破损进水后,船体所受垂向和水平波浪弯矩均比破损前有明显增加,且在较浅水深中变化更为显著。     

考虑波浪影响的船速测量不确定度分析

试航时,对于在2级海况以上测得的船速数据,必须进行波浪修正.针对柏林水池(VWS)提出的波浪修正办法,以某油轮为例,采用GUM测量不确定度分析方法,对考虑波浪影响的船速测量进行了不确定度分析.