Experimental study on the nonlinear pressure acting on a high-speed vessel in regular waves

It is well known that the hydrodynamic responses of a high-speed vessel traveling in regular head waves of even moderate wave height can show significant nonlinear behavior, and so linear statistical techniques become insufficient for predicting the statistics of responses in irregular waves. On the other hand, it has been shown that an approximate third-order Volterra model is applicable to handling the statistics of some nonlinear seakeeping problems, such as motions and vertical hull girder loads. In the present study, the focus is on the nonlinear behavior of the pressure responses of the hull surface, especially on the pressures acting on alternately wet and dry areas near the waterline and on the bow zone with high deadrise angles that may be subject to slight impact and water pile-up effects. To clarify the validity of applying Volterra modeling to this problem, a series of experiments in regular and irregular head waves were carried out, and approximate third-order and fifth-order Volterra models with the proposed algorithm for finding frequency response functions (FRFs) were applied as a means of validation. In the present article, the first part of the validation was performed using experimental data in regular waves. It was confirmed that the third-order Volterra model has adequate accuracy to simulate deterministically the variation of pressure responses in regular waves of different wave steepness up to a wave amplitude to wavelength ratio of 0.01 even for the highly nonlinear pressures acting on the above-mentioned areas of the hull surface.     

不规则波浪在陡坡上非线性传播变形的试验研究

通过试验研究了不规则波浪在一陡坡(1:10)上的传播过程中的非线性特征。为达到研究目的,在试验水槽中以JONSWAP谱为靶谱生成了两组随机波浪。试验结果显示,在坡前常水深区域和坡顶,两种波况下波高分布均符合瑞利分布;但是在变浅区域两种波况的波高分布却不尽相同。应用基于小波变换的二阶相位谱来分析波浪在传播过程中的非线性相位耦合特征,结果表明：随着水深的变浅,波浪的非线性逐渐增强并且参与非线性相互耦合的频率成份也越来越多。通过二阶相位谱发现：随着水深的减小,参与最强的非线性相位耦合频率向高频处移动。另外通过傅立叶频谱、二阶谱以及二阶频谱共同分析陡坡上两组波况下低频波浪的演化情况。     

Load effects on vessel-shaped fish cage steel structures,nets and connectors considering the effects of diffraction and radiation waves under irregular waves

Vessel-shaped fish cages are mainly composed of a large floating body, aquaculture nets and a number of steel frames. Due to the large scale of vessel-shaped fish cages, the velocity field induced by the diffraction waves and radiation waves cannot be ignored in the calculation of the loads on the net and steel frames. In turn, the loads can affect the wave-induced response of the floating body and hence the radiation waves as well as the sectional forces. In this paper, a novel method is proposed to consider the coupling effect. First, considering the irregular waves in short-term periods, the global response of the floating body is calculated in the time domain by the state-space method based on potential flow theory. Meanwhile, the velocity field considering the influence of the floating body is built according to the velocity transfer function. Then, the Morison formula is used to calculate the loads on the nets and the steel frames. Finally, the coupling achieved through numerical iterations is considered in the calculation of the twine tension, load effect of connector and the global cross-section under irregular waves. It is found that the diffraction and radiation waves make a significant difference in the twine tension and connector load effect.     

新概念穿梭艇自航模操控系统试验研究

自航模试验是研究船舶性能的有效手段。针对新概念穿梭艇,设计一种自航模操控系统。该系统包括岸上操控系统和船载自航控制系统2部分,利用无线局域网完成岸上操控系统与船载自航控制系统之间的通信;执行机构配备传感器获取反馈数据,驱动器采用成熟的可编程元件;使用Python语言编写下位机和上位机软件。将系统成功应用于新概念穿梭艇的自航模试验中,试验表明所设计的自航模操控系统可以减小开发工作量,操作方便,可扩展性和可移植性强,能够反映新概念穿梭艇的操纵性能。最后经与船模拖曳水池试验结果进行对比,证明所设计系统应用于自航模试验时能够有效获取可靠数据。     

Investigation on the nonlinear effects of the vertical motions and vertical bending moment for a wave-piercing tumblehome vessel based on a hydro-elastic segmented model test

Although the nonlinear effects of the ship motions, wave-induced loads and structural responses of conventional vessels have been investigated experimentally and numerically in recent years, similar studies on the wave-piercing tumblehome (WPTH) vessels are rare, in spite of the urgent necessary due to their extensive applications. This paper experimentally investigated the nonlinear effects of the vertical motions and vertical bending moment (VBM) for a WPTH vessel based on a hydro-elastic segmented model test. The model test was carried out in head regular waves for three amplitudes, in the towing tank at Harbin Engineering University. Based on the band-pass filter technique, four kinds of decomposed harmonics are defined by mean offset, linear wave-frequency response, nonlinear wave-frequency response and nonlinear high-frequency vibration. Meanwhile, based on mean offset, three kinds of combined responses are defined by considering linear wave-frequency response, nonlinear wave-frequency response and nonlinear high-frequency vibrations step by step. The transfer functions of vertical motions and VBM are presented as function of the incident wave frequency, and the measured data and VBM were compared with numerical calculations for validation. With the method proposed above, the results of VBM are analyzed by focusing on the influences of decomposed harmonics on the amplitudes and asymmetry of combined responses. Strong nonlinear effects are observed in the VBM. The nonlinearity of VBM can be identified by the significant amplitudes of decomposed harmonics, variation of amplitude with the wave amplitude and remarkable asymmetry about the zero axis. The hogging VBM of WPTH vessel can be even larger than the sagging VBM, which is in contrast to the general experiences from conventional vessels. Combined the calculated relative motion with the decomposed and combined histories of VBM, the occurrence of the transient impact and its characteristics are discussed, and these are then used to analyze the unconventional asymmetry of VBM. Furthermore, the influences of the bow shape over the vertical motions and VBM are discussed. At the end of the paper, the uncertainties in the test are provided.     

T型防波堤水平板波浪冲击压强试验研究

通过规则波与T型防波堤相互作用的试验研究,揭示了T型防波堤底部所受冲击压强产生的原因。分析波浪冲击压强历时曲线、相对板宽对冲击压强沿水平板底部分布的影响,得到T型防波堤水平板冲击压强的特性以及2大影响因素:相对超高和波陡。应用因次分析的方法,推导出T型防波堤底板最大相对冲击压强计算的经验公式。结果表明,该公式计算结果与试验值吻合较好,有一定的适用性。     

水下航行器内孤立波载荷形成机理数值模拟研究

弄清水下航行器内孤立波载荷形成机理是分析内孤立波对航行性能影响和控制研究的基础和前提。采用数值模拟方法深入分析模型位于内孤立波波面上方、穿越波面、位于波面下方3种情形下,模型受内孤立波流场水动力作用和分层密度差静力作用过程,对比不同潜深时纵向力、垂向力和俯仰力矩特性差异。研究表明,穿越波面的情况下,模型所处的流体密度变化,起了决定性作用,垂向力比纵向力大一个量级;穿越波面时,艏艉浮力不平衡,俯仰力矩有极大值和极小值出现;模型始终位于波面上方或下方时,受内孤立波流场的影响,其水动力性能也产生了明显的变化。     

薄膜型LNG液舱晃荡压力与结构响应试验

影响薄膜型LNG船大型化的一个关键问题是严重的液舱晃荡冲击压力以及由此引起的复杂和危险的结构动响应,至今模型试验是研究此类问题的最重要的方法。本文以某大型LNG船尺度较大和运动较剧烈的2号液舱为研究对象,设计了精细的三维晃荡试验模型,通过不同载液水平的系列规则和不规则运动激励的晃荡试验研究晃荡冲击压力特性;基于薄膜型液舱围护系统结构性能计算结果,设计四边简支铜板格分析液舱围护系统结构弹性效应;另外,还利用浪高仪测量液舱波面运动情况。试验结果表明不论规则运动激励,还是不规则运动激励,晃荡冲击压力幅值均表现出明显的随机性,工况可能产生远大于单自由度运动工况的晃荡冲击压力。晃荡冲击压力、应力和波面测量结果可为验证晃荡数值方法和液舱围护系统结构设计提供依据。     

内孤立波环境下半潜式平台受力研究

在2层流体基本假设下,通过实验分别研究不同波浪入射角下,作用在半潜式平台立柱群和沉箱群上的内孤立波载荷特性.实验结果表明:在任意迎流角下,作用在立柱和沉箱各部分的载荷峰值均随波幅增大而线性增大,并且波的传播方向对力的峰值有显著影响.在相同波幅、相同分层比下,当来波方向与平台中纵剖面不平行时,沉箱群水平载荷峰值在迎流角为...     

江海通航顶推船铰接装置的波浪载荷模型试验研究

在不规则波中对某5000吨级的江海通航顶推船进行了两销式铰接装置的载荷模型试验.模型试验数据的无因次分析表明,在浪向角60°情况下铰接装置受力比其它浪向角时都要大,并且铰接装置受到的水平弯曲力比垂向弯曲力、轴向力大得多.推导了服从Weibull概率分布变量的短期概率极值预报公式.针对试验数据,进行了实船12小时短期概率极值预报,结果表明,在设计波高4.2m时,超越概率1%时的最大弯曲力相当于该顶推船推轮的排水量.本次试验及其数据预报的极值可供设计同类型铰接装置的江海通航顶推船时参考使用.     

系泊Spar平台波浪中耦合运动的数值模拟及模型试验

为了研究恶劣环境载荷引起海洋结构物的非线性运动响应,文章基于三维时域格林函数理论,提出了采用时域物面非线性理论方法直接模拟系泊浮体时域耦合分析所需的水动力,建立了系泊浮体波浪中时域耦合运动的数学模型.该方法充分考虑了每时每刻浮体在瞬态波面下湿表面的变化,并计及平均水线面下瞬时空间位置的改变,系统研究了系泊Spar平台波浪中的耦合运动响应及系泊线张力.最后,将数值模拟结果与模型试验结果进行了比较,计算结果令人满意.     

不规则波作用下9桩串列群桩效应的实验研究

小尺度的群桩结构在海洋工程建筑物中应用广泛,其在波浪作用下产生的群桩效应也被国内外学者所关注,但是目前有关群桩效应的研究多限于较少桩柱。基于物理模型实验,对不规则波作用下,9桩串列群桩中各桩所受正向力、横向力进行了研究,结合对应波浪作用下孤立桩所受波浪力,分析了正向力和横向力群桩系数K_(G,1/3)、K_(GL,1/3)随相对桩距S/D和KC_(1/3)数变化的规律,并对比了群桩中各桩上群桩系数的区别。     

破损进水舰船非线性横摇运动的实验研究

通过设计破损舰船非线性横摇运动实验,对不同状态下的船模进行定频率变波高和定波高变频率的横摇激振试验,探讨舰船横摇运动的水动力特性随横摇频率和横摇幅角变化规律,分析Ⅱ类和Ⅲ类进水舱对破损舰船横摇运动的水动力特性的影响。运用混沌信号识别技术分析破损舰船进水后横摇运动的混沌特性,验证数值仿真的结果,预报破损舰船在规则波中的横摇运动的幅频响应和相频响应。     

新概念高速穿梭艇系列船型及其直航性能

  目的  为了研究船舶在波浪中约束模与自航模运动特性的差异以及船舶轴系功率特性,开展船舶波浪中自航性能数值仿真预报。  方法  首先,选取KCS船模和KP505桨模,采用URANS方法进行船舶波浪自由直航CFD模拟;然后,基于自研URANS求解器HUST-Ship与自研结构化动态重叠网格代码HUST-Overset,以及改进型体积力螺旋桨推进模型,对船舶在不同波浪条件下的运动响应进行耦合求解,包括两自由度KCS约束模运动仿真和三自由度自航模自由直航仿真,并对比这2种方法预报船舶运动特性的差异;最后,采用对数分析法得出波浪中船舶自由直航功率增加的主要成分及其具体占比。  结果  KCS船模在波浪中自航时,推进效率和波浪增阻对功率增加的贡献占比分别为23%~26%和74%~77%,即波浪增阻占比较大。  结论  因此,降低波浪中功率增加的最有效方法是减小船舶运动以降低波浪增阻。     

基于超高燃油喷射压力的喷雾特性试验研究与模型修正

为了研究超高压喷射条件下二次破碎喷雾模型对燃油雾化特性的影响,在AVL FIRE软件平台上对燃油喷雾过程进行数值模拟,搭建可视化喷雾闪光摄影试验台架。基于超高的燃油喷射压力对燃油的雾束发展形态进行了图像采集,利用试验结果对二次破碎喷雾模型进行修正,分析模型中主要参数对燃油雾化特性的影响。结果表明：KH波破碎时间常数 C2的减小有利于缩短喷雾贯穿距离,同时避免发生燃油撞壁现象;随着RT波波长常数C4的增大,二次破碎新生油滴的直径变大,雾化效果变差;由于首次破碎过程对二次破碎过程的制约作用,导致C4对喷雾计算结果的影响不像C2那样显著。     

不规则波作用下的港域波浪条件试验研究

针对数学模型很少能较好地模拟天然海浪的多向性、不规则性的特点,基于港口波浪整体物理模型试验,对不规则波作用下港域内测点的波高扰动系数的分布规律进行研究。结果表明:在绕射作用为主的掩护区域,多向波的绕射性能大于单向波,波浪扰动系数较大;波浪绕射、反射作用均十分强烈的掩护区域,多向不规则波与单向不规则波的扰动系数看不出明显的大小关系。以反射作用为主的掩护良好区域,单向不规则波的扰动系数较多向不规则波的要大,且受反射作用越大的区域,单向波的扰动系数大的越多。在以绕射作用为主的掩护区域,波浪分布对周期的敏感性较差;在以反射作用为主的掩护良好区域,波高分布对周期的敏感性较强。在绕射、反射都较强的情况下有可能单向波作用下的港内波高大于单向波,用单向不规则波来模拟反而是偏安全的。在进行港内波况整体模型试验时需要根据实际的工程条件做出综合考虑来决定波型,必要时要对单向、多向不规则波都要进行试验以确定最佳方案。     

Nonlinear effects from wave-induced maximum vertical bending moment on a flexible ultra-large containership model in severe head and oblique seas

Vertical bending moment (VBM) is of crucial importance in ensuring the survival of vessels in rough seas. With regard to conventional vessels, wave-induced maximum VBM is normally considered to be experienced in head seas. It is conservative to determine the extreme VBM based on either numerical simulations or model tests in long-crested head seas. Extensive model tests have been conducted in head seas with focus on the nonlinear vertical responses in severe seas, and the measured results were compared with numerical calculations for validation. Unexpected phenomena, however, were observed during the model tests of an ultra-large containership. The maximum sagging and hogging VBMs were encountered in oblique seas. Furthermore, the significant wave height used in oblique seas was even smaller than that used in head seas. The nonlinear vertical load effects in oblique seas require further investigations for this particular vessel. Limited experimental results in oblique seas have been reported, in which the lateral responses were always more concerned than the vertical responses. Up to now, rare systematic comparisons of the nonlinear vertical responses between head and oblique seas have been published, especially when the hydroelastic effects are also accounted for. A 13000-TEU ultra-large containership model, which was designed by Hyundai Heavy Industries (HHI), has been tested in the towing tank and the ocean basin at the Marintek center in Trondheim. The experimental results in regular waves are first compared between head and oblique seas. The statistical characteristics of the VBM amidships under nineteen irregular wave conditions are then investigated. Next, the extreme hogging and sagging VBMs are compared under different wave conditions with focus on the extreme hogging VBMs. At the end of the paper, the uncertainties in the experiments are discussed.     

混凝土铰链排护坡式海堤波压力试验研究

结合苏北滨海海域实际海堤防护工程,通过波浪断面物理模型试验,对柔性混凝土铰链排和刚性混凝土槽型块两种护坡形式分别展开各海堤断面中消浪平台及以上堤身结构在规则波及不规则波作用下的波压力研究,并比较分析两者之间的差异。试验结果表明,铰链排护坡对消减波能的效果要优于槽型块护坡,更有利于海堤的安全性和稳定性。同时根据波压力分析结果对混凝土铰链排护坡式海堤提出了相应的优化加固措施。     

不同间距下大直径圆筒防波堤波吸力试验研究

防波堤的波浪力计算对防波堤的设计和稳定具有重要意义。针对目前圆筒防波堤波吸力的设计计算方法尚未成熟,通过开展物理模型试验,进行不规则波作用下不同间距下大直径圆筒结构波吸力的分布规律、影响因素和计算方法研究。结果表明:波谷作用下,大直径圆筒结构波吸力的横向分布规律与圆筒的间距有关,纵向分布规律表现为随着水深增加先线性增大然后线性减小,且最大波吸力的位置出现在静水位一倍波高以下。圆筒的相对间距、相对水深以及波陡对不同间距大直径圆筒防波堤的波吸力影响较大。基于直立墙结构波吸力公式给出折减系数的拟合公式,用以计算圆筒周身迎浪面的波吸力。     

Experimental study of a suspended subsea module at different positions in the splash zone

During the lifting of submerged marine modules, the highest dynamic loads occur in the splash zone. These forces are highly dynamic and cannot easily be estimated with sufficient accuracy using simple calculations or high-fidelity computational fluid dynamics because of their irregular and complex geometries. We conducted an experimental study in a wave tank to investigate the dynamics of a large subsea module in the splash zone subject to irregular waves. The experiments were conducted using a 1:8 scale model of a subsea module, similar to that designed by Offshore Oil Engineering Co., Ltd., for the subsea pipeline from the Wenchang gas fields to the Yacheng pipeline. The model was examined at five different positions relative to the free surface, from completely above the surface to fully submerged. The resulting data are analyzed in the time and frequency domains. Spectral analysis and a dynamic effect parameter are used to analyze the dynamic loads on the subsea module. Several time-domain numerical analyses are performed with different peak periods, and the tension of the sub-slings is obtained. The experimental results for the relative forces and motions of the subsea module are presented, providing a reference for the design of other similar modules and their installation and validation data for computational modeling.