基于数值仿真与经验公式的船舶破冰阻力预报

首先选取并验证合适的冰材料模型,通过建立冰排与破冰船有限元模型,应用非线性显式动力学软件Ls-dyna对破冰船在不同冰厚、不同船速条件下的连续式破冰过程进行数值模拟,并将不同冰况下仿真结果和经验公式计算得到的冰力值做对比研究。最后对各个经验公式中的主要参数进行敏感性分析,得出各个参数对冰阻力计算的影响差异程度,对冰阻力估算和船体结构设计具有重要参考价值。     

基于流固耦合方法的船舶破冰阻力参数敏感性研究

本文基于带有塑性应变失效准则的弹性断裂失效模型建立平整冰有限元模型,采用LS-Dyna流固耦合方法对船舶在平整冰条件下航行的冰载荷开展了数值模拟,选取航速和平整冰厚度作为敏感性参数,分析了参数变化对破冰阻力的影响。研究发现:各方向上的冰载荷在时域上均存在一定的周期性,冰层在船艏撞击和浮力作用下,通常以多种破坏模式的混合方式同时出现;船舶在平整冰环境下的破冰阻力随航速和冰厚的提高基本呈线性增加的趋势,不同航速及冰厚条件下的破冰阻力数值计算结果与Lindqvist经验值的误差分别在-7.5%～13.1%和-10.8%～19.4%范围内,采用LS-Dyna流固耦合方法对船舶破冰阻力进行预报具有较高精度。     

极地船连续破冰阻力数值模拟研究

连续破冰是自破冰型极地船舶中最常用的破冰模式,连续破冰阻力精确计算是极地船舶航行性能预报和船型优化设计的基础。论文提出一种基于预设冰网格技术的连续破冰阻力数值模拟方法,预先对船体水线附近的线型进行分层离散及对冰场进行方形网格离散,通过几何计算和受力分析数值模拟连续破冰进程及产生的破冰阻力分量。进一步考虑连续破冰阻力与运动耦合效应,在时域内建立船体6自由度运动微分方程,数值求解获得连续破冰阻力时间历程结果。利用该数值模拟方法计算获得了一艘PC3级极地油船连续破冰阻力时间历程结果,并将冰阻力有义值与对应的模型试验结果进行了对比。研究表明,数值模拟获得的连续破冰阻力时历结果能够反映连续破冰进程,数值模拟获得的冰阻力有义值与模型试验结果的误差在12%以内。论文的数值模拟方法能够高效、精确地模拟连续破冰进程及冰阻力,具有一定的工程应用价值。     

船舶几种浮态下阻力的数值计算方法

商船会因装载不同而吃水大幅增减,舰艇会因战损而出现严重纵横倾,如何在浮态急剧变化时估算船舶的快速性,是一项具有普遍意义的课题.为了解决上述问题,采用计算流体力学方法对某型船模进行了大量计及自由表面的不同浮态下的阻力数值计算,在深入分析船体浮态改变时影响船舶阻力诸因素的基础上,对数值计算结果进行了研究,推导出船舶吃水、纵倾和横倾变化时的阻力估算公式.据此进行的数值计算结果与水池试验结果对比,吻合良好,从而验证了提出的计算模式的可行性,为解决船舶任意浮态下的阻力计算问题提供了新的思路.     

破冰船阻力性能估算

在预测船体冰阻力数值方法中,有许多不同的公式可以用来估算不同冰况下工作的船体冰阻力。其中模型试验仍将是最准确的预测,但其他的一些方法也可以给冰阻力的估算提供依据。对破冰船的破冰方式在破冰过程中所受的阻力进行分析,探讨其在不同冰况下的冰阻力成分,分析各种冰阻力计算公式,然后对1艘破冰船进行实际计算,最后分析各公式计算结果以及各种方法的优缺点及适用范围。     

船舶静水中拖锚淌航距离数值模拟

针对船舶拖锚淌航距离的估算问题,现有方法简单易行,但其计算过程中却忽略船体阻力和附加惯性力对淌航距离产生的影响。忽略这一影响将直接导致所估算的拖锚淌航距离与实际误差较大,不利于航海实践。为此,运用牛顿力学定律描述船舶拖锚淌航过程,以一艘万吨级船舶为对象,分析船体阻力与附加惯性力对拖锚淌航的影响。计算结果表明:万吨级船舶拖锚淌航初始阶段船体阻力大约为锚阻力的1/2;随着淌航距离增加、船速减小,船体阻力逐渐下降;而附加惯性力在整个淌航过程中变化不大,其约占单锚阻力的1/8。拖单锚淌航距离计算值与现有估算公式结果相比约小1节链长,拖双锚淌航距离计算值与现有估算公式结果相比差别不大。     

破冰船连续破冰的冰阻力预报

[目的]为了准确评估破冰船在平整冰区航行时连续破冰过程中所受的冰阻力,同时了解不同预报方法的特点,采用经验公式法、数值模拟法以及船模试验法,对破冰船在平整冰中连续航行时的冰阻力进行预报。[方法]使用非线性有限元软件DYNA,分别基于传统有限元与黏聚单元法构造冰层数值模拟模型,模拟平整冰与破冰船相互作用时发生的弯曲断裂以及相互作用的过程。同时,采用经验公式法,用3种不同的经验公式进行冰阻力计算,对影响经验公式法预报结果的参数进行敏感性分析。[结果]研究发现:冰阻力随航速、冰厚度以及弯曲强度的增大呈上升趋势,其中冰厚对冰阻力的影响最大。3种经验公式中,Lindqvist公式的预报结果与船模试验结果更为接近,而Vance和Lewis公式更为保守。传统有限元与黏聚单元法在冰厚较小的情况下,冰阻力预报结果更准确,冰厚较大时误差较大,约25%。在冰厚较小航速较高的情况下,黏聚单元法预报的冰阻力值较传统有限元方法更为准确,与船模试验结果相比精度误差在10%以内。[结论]在实际的冰阻力预报中,可结合经验公式法与数值模拟法,兼顾预报结果的准确性与高效性。     

中间渠道船舶航行阻力计算方法与试验*

中间渠道作为特殊限制性航道,船舶航行阻力是其尺度确定的关键参数。针对现有船舶航行阻力计算方法,分析其适用性,选取考虑了航道宽度和吃水比等因素的俞中奇公式作为中间渠道船舶阻力的参考计算公式,设计中间渠道船舶航行阻力试验方案,并开展3 000吨级散货船模航行试验,根据试验结果对俞中奇公式进行修正,利用Flow3D模拟船舶在不同断面系数下中间渠道中航行并提取阻力,验证修正公式的准确性。结果表明,修正后的经验公式计算结果与数模对比,最大误差不超过16.89%。该公式具有较高的计算精度,对中间渠道设计具有重要的参考价值。     

基于离散元模型的冰阻力数值研究

为了研究船舶冰阻力的预报方法,采用离散元模型对冰区航行船舶在平整冰中航行的冰阻力进行数值计算。船体结构由三角形网格离散,同时利用具有粘结-破碎特性的球体单元、三维拓展圆盘和拓展多面体单元构造海冰的离散元模型,并考虑拖曳力和浮力对海冰的影响。本文基于离散元方法,计算船模受到的总的冰阻力,研究海冰厚度、弯曲强度和航行速度对冰阻力的影响,并与Lindqvist经验模型计算的冰阻力进行了分析比较。研究结果可为冰区航行船舶冰阻力预报以及初步设计优化提供参考。     

改进的预报集装箱船波浪增阻的半经验方法

波浪增阻的精确预报对船舶实际航行的性能分析具有重要意义。论文采用理论的和半经验方法,对集装箱船进行了规则波迎浪航行波浪增阻计算,与试验结果进行了比较,分析吃水和航速影响。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,基于二阶波浪力中绕射势得到绕射增阻;经验方法采用ISO15016-2015推荐的STAWAVE2方法。通过分析两种方法波浪增阻成分占比,得出了不同方法在不同频域段的适用范围。对半经验方法计算波浪增阻的关键参数进行了讨论,结合理论计算结果的趋势,针对集装箱船船型,提出了反映船型特征的预报波浪增阻的半经验方法。     

Dilated-polyhedron-based DEM analysis of the ice resistance on ship hulls in escort operations in level ice

The ice resistance on ships in escort operations in level ice are investigated using the discrete element method (DEM). A dilated polyhedron—generated by the Minkowski sum of a sphere and a polyhedron—is employed in the DEM; this dilated polyhedron-based DEM (DPDEM) is adopted to simulate the ship–ice interaction, wherein the contact force and bond-failure criterion are considered for the collision and fracture of sea ice, respectively. A three-point bending test was simulated with DPDEM, and a field test was conducted in the Bohai Sea to validate the DEM results. Further, a parametric analysis of flexural strength was conducted to identify the parameters involved in the bond-failure criterion. The ice resistance on icebreakers and cargo ships in level ice are simulated using DPDEM. The simulated ice resistances are compared with the Lindqvist and Riska formulas and the model test, which proves the validity of the DEM simulation. The interaction between ships and level ice is simulated parametrically to investigate the ice resistance on cargo ships with and without the icebreaker escort. Influencing factors such as ship speed, ice thickness, and ship breadth were examined to investigate the ice resistance on the escorted cargo ship. Analysis and change rules of the ice resistance on cargos affected by those factors were given.     

Experimental study on the resistance of a transport ship navigating in level ice

This study investigates the resistance of a transport ship navigating in Arctic waters by conducting a series of model tests in an ice tank at Tianjin University. The laboratory-scale model ship was mounted on a rigid carriage using a one-directional load cell and then towed through an ice sheet at different speeds. We observed the ice-breaking process at different parts of the ship and motion of the ice floes and measured the resistances under different speeds to determine the relationship between the ice-breaking process and the ice resistance. The bending failure at the shoulder area was found to cause maximum resistance. Furthermore, we introduced the analytical method of Lindqvist (1989) for estimating ice resistance and then compared these calculated results with those from our model tests. The results indicate that the calculated total resistances are higher than those we determined in the model tests.     

极地平整冰区运输船航行阻力的模型试验研究（英文）

This study investigates the resistance of a transport ship navigating in level ice by conducting a series of model tests in an ice tank at Tianjin University. The laboratory-scale model ship was mounted on a rigid carriage using a one-directional load cell and then towed through an ice sheet at different speeds. We observed the ice-breaking process at different parts of the ship and motion of the ice floes and measured the resistances under different speeds to determine the relationship between the ice-breaking process and ice resistance. The bending failure at the shoulder area was found to cause maximum resistance. Furthermore, we introduced the analytical method of Lindqvist(1989) for estimating ice resistance and then compared these calculated results with those from our model tests. The results indicate that the calculated total resistances are higher than those we determined in the model tests.     

破冰型大型航标船线型开发设计及破冰阻力评估研究

结合北海航海保障中心大型航标船的破冰功能需求,为本船选取合理的推进功率,对本船具有破冰功能特点的线型设计进行分析论述,同时运用破冰阻力经验公式对本船在一定冰厚和航速下的破冰阻力进行估算,结合冰池试验结果对破冰阻力数据进行对比分析,并进行冰区航行的快速性评估。     

Numerical estimation of ship resistance in broken ice and investigation on the effect of floe geometry

In this paper, a numerical model based on the non-smooth discrete element method is presented to investigate the effect of ice floe shape on ship resistance under low-concentration broken ice condition where ice fields consist of relatively small and unbreakable floes. The accuracy of the numerical model is validated by the comparison with a series of experiments conducted by the authors with artificial ice floes made from polypropylene (PP) material. The mean ice resistance estimated by the numerical model is in fairly good agreement with both the experimental results and those from the existing semi-empirical formulas. Additionally, the floe shape effect captured in the experiment, i.e. “rectangle-like” floes results in higher resistance than “elliptic-like” floes, is also predicted by the numerical model. Then, the validated numerical model is used to further investigate the effect of floe shape on ship resistance. It has been found that the rectangle floe results in higher ice resistance than other studied floe shapes. The ratio between the maximum and minimum caliper diameters of floe shows little influence on the ice resistance of ship. Finally, the effect of ice thickness on the ice resistance is also discussed.     

Improved formula for estimating added resistance of ships in engineering applications

The authors previously introduced a semi-empirical formula that enabled fast estimation of the added resistance of ships in head waves, and in this study the formula is further refined for easy use in engineering applications. It includes an alternative ship draft correction coefficient, which better accounts for the wave pressure decay with ship’s draft. In addition, it only uses the speed and main characteristics of the ship and wave environment as input, and has been simplified to the extent that it can be readily processed using a pocket calculator. Extensive validations are conducted for different ship types at low to moderate speeds in various typical irregular sea conditions, and encouraging results are obtained. This relevant and topical research lies within the framework of the recent IMO MEPC.232(65) (2013) EEDI guidelines for estimating the minimum powering of ships in adverse weather conditions, which specify for the use of simple methods in current Level 2 assessment within engineering applications.     

一个改进的波浪增阻近似公式在船舶设计中的应用（英文）

The authors previously introduced a semi-empirical formula that enabled fast estimation of the added resistance of ships in head waves, and in this study the formula is further refined for easy use in engineering applications. It includes an alternative ship draft correction coefficient, which better accounts for the wave pressure decay with ship's draft. In addition, it only uses the speed and main characteristics of the ship and wave environment as input, and has been simplified to the extent that it can be readily processed using a pocket calculator. Extensive validations are conducted for different ship types at low to moderate speeds in various typical irregular sea conditions, and encouraging results are obtained. This relevant and topical research lies within the framework of the recent IMO MEPC.232(65)(2013) EEDI guidelines for estimating the minimum powering of ships in adverse weather conditions, which specify for the use of simple methods in current Level 2 assessment within engineering applications.     

波浪增阻计算方法对船舶航速的影响分析

失速系数（ fw）是EEDI公式的计算参数之一。文章研究了典型海况下不同的波浪增阻计算方法对船舶航速以及fw的影响。文中主要基于三种波浪增阻理论计算模型,以肥大型船为研究对象,计算分析典型海况蒲氏六级下的波浪增阻系数的分布规律以及相同收到功率下的航速和fw。结果表明：三个理论模型计算得到的fw均低于模型试验结果;Model-3高估了不规则波中的波浪增阻值;Model-1和Model-2计算得到的fw与模型试验结果较接近。     

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.