Modeling free-flow speed according to different water depths—From the viewpoint of dynamic hydraulic pressure

In this paper, we propose a method of modeling free flow speed from the viewpoint of hydroplaning. First, the lift forces for different water depths were estimated using Bernoulli’s equation. Compared with the result of the experimental test performed by the Japan Automobile Research Institute, the hydrodynamic pressure coefficient was determined to be 0.03 (tf s²/m⁴). The validation of the predicted lift force is found in another published paper. A very good match is found between the computed values by the proposed numerical model and the data in other published papers. Then, the loss of contact force is considered to evaluate the hydroplaning performance of a tire. To simulate the hydroplaning speed, a tire-sliding model was utilized to obtain the traction and friction forces between the road surface and the tire. The observation data obtained in Japan in 2009 is compared with the physically computed hydroplaning speed, yielding the conclusion that the traction force at the measured desired speed is, on average, 23.4% of the traction force at hydroplaning speed. The analytical model offers a useful tool to quantitatively show that the free flow speed changes as the water depth increase.     

复杂载荷下裂纹SIF计算的子模型技术

对船舶与海洋工程结构物进行疲劳评估,首先要通过子模型技术解决复杂应力场中裂纹应力强度因子(SIF)的计算问题。针对子模型技术实现过程繁杂且效率较低的问题,分别提出"逐周分层法","转换矩阵法"及"映射划分法"并基于VBA及APDL语言编写插件MPCarrangerV1.0,FEMcoortransferV1.0及CrackmapperV1.0,解决从Patran整体有限元模型到Ansys子模型时壳体单元间MPC创建低效、不同坐标系间节点位置转换困难及裂纹自由划分的局限性问题。基于DNV及ABS相关规范,以某B型LNG燃料舱的疲劳热点为例,对改进的子模型技术进行验证,结果表明经改进的子模型技术可成功施加合理边界条件并实现SIF的求解,可为子模型技术快速实现复杂载荷下裂纹SIF的准确计算提供参考。     

压浪板与游艇航态及阻力性能关系的研究

安装压浪板会在游艇艉部形成局部高压区,产生附加水动升力从而改变游艇的航行姿态,并影响游艇的阻力性能。采用半理论半经验方法分析安装压浪板前后游艇的姿态及阻力变化,研究压浪板对游艇产生影响的作用机理以及二者之间的匹配关系;获得压浪板最佳尺寸及安装角度的计算方法。结合方艉尖舭型游艇实例,验证压浪板在工程应用中的价值。     

复杂载荷作用下船体板格屈曲强度计算公式研究

分析复杂载荷作用下船体板格结构屈曲强度的影响因素,基于ANSYS软件APDL模块参数化建模,对这些因素进行相关性分析,排除无关参数,保留有关参数,得到屈曲强度的定性表达式。然后变更有关参数,得到不同的有限元模型,通过计算得到不同模型下的屈曲强度,分析大量数据,最终得到屈曲强度的定量表达式。该公式可以在工程上用于复杂载荷作用下船体板格结构的屈曲评估,具有重要的实用价值。     

冰激自升式钻井平台的动力响应分析

由于冰荷载研究的限制,冰区自升式钻井平台尚未形成基于动冰力响应分析的结构设计。为了合理地开展自升式平台结构的抗冰概念设计与安全评价研究,冰荷载下自升式钻井平台的动力响应分析是十分必要的。该文首先分析该类柔性结构在动冰荷载下的动力特性;其次,结合开展的自升式平台冰荷载模型实验研究,明确带齿条桩腿的自升式平台冰荷载作用形式;最后,对渤海某自升式钻井平台在典型冰况下进行冰振动力响应分析。文中的研究对冰区自升式钻井平台抗冰设计及冰振安全评估提供了合理的参考。     

考虑外环境影响的船舶操纵模拟自动舵系统

自动舵系统是建立船舶操纵离线模拟模型所要解决的关键因素之一,本文给出了一种船舶操纵模拟自动舵系统,该系统可以对船舶出入港时受到的复杂载荷,如风,浪,流,限制性航道等做出合理反应,可以应用于船舶出入港操纵运动的离线模拟中。     

小方型系数船舶的船体波浪载荷综合研究

从船级社规范对于不符合主尺度比要求的船舶船体梁波浪载荷的规定出发,采用理论预报和船模试验2种综合方式,进行了小于0.6方型系数、高航速、高海况目标船的波浪载荷研究.从规范对波浪载荷的线性理论预报值进行的非线性修正,修正后中拱和中垂波浪弯矩绝对值之和与线性理论预报极值全幅值相等出发,阐述所研究船特殊主尺度比下的模型试验结果、三维非线性水弹性理论预报结果显示出的波浪载荷非线性行为;同时综合模型试验与理论预报的共同规律,研究不同波高、航速、浪向等非常规船型船体波浪载荷的强非线性行为,从而认为规范基于的线性理论预报值进行非线性修正的统一规定太过笼统,进而建议规范对波浪载荷的非线性修正予以进一步的明确区分和规定.     

内河船舶波浪载荷研究

利用内河波浪散布图和修订波浪谱对内河系列船舶进行了波浪载荷的计算预报,首次分析了内河船舶波浪载荷的规律和特点,并与俄罗斯内河登记局(RRR)和法国-德国船级社(B-G)的内河规范载荷对应的等效模数要求进行了比较分析。结合实船测试结果表明：波浪载荷变化规律与国外同类规范一致,预报波浪载荷水平与测试结果及国外同类规范要求相当。内河船舶波浪载荷预报应考虑航速和水深的影响,载荷预报结果可以作为制定内河波浪载荷公式的基础。     

零航速减摇鳍水动力特性分析

分析零航速减摇鳍的升力模型和力矩模型,探讨正弦运动的鳍产生最大升力和最大转鳍力矩与转鳍速度的关系,经对比发现,同一鳍角幅值转鳍下任一时刻升力的大小与经过该点的角速度的平方成正比。为此,采用通用CFD软件计算方法,验证理论模型的规律,在数值仿真的基础上,拟合升力公式和力矩公式的各个系数,并将实船试验转鳍力矩与仿真结果进行对比,结果表明仿真结果能较好地反映实际转鳍力矩的变化规律。     

Variability of the Bohai Sea circulation based on model calculations

The circulation and the hydrography of the Bohai Sea are simulated with the Hamburg Shelf Ocean Model (HAMSOM). The model is three-dimensional, prognostic baroclinic and has a resolution of 5 min in latitude and longitude and 10 layers in the vertical. It is initialised and forced with the five main tidal constituents, temperature and salinity distributions taken from the Levitus database, monthly mean river run-off values and European Centre for Medium Range Weather Forecast (ECMWF) re-analysed data of air pressure, wind stress and of those parameters relevant for the calculation of heat fluxes. The simulation period covers 14 years from 1980 to 1993 due to the availability of the time-dependent ECMWF forcing.The results are analysed by means of time series and EOFs focussing on the interpretation of fluctuations with periods above the tidal cycle. Furthermore, tracer simulations are carried out and turnover times are calculated in order to evaluate the importance of these fluctuations on the renewal and transport of water masses in the Bohai Sea.One of the major outcomes of the investigation is the overall dominance of the annual cycle in all hydrographic parameters and the importance of stochastic weather fluctuations on the transport of water masses in the Bohai Sea.