台风海况下半潜式钻井平台动力性能监测与分析

半潜式钻井平台在海洋油气资源开发中发挥着重要作用,目前主要采用模型试验和数值模拟方法对其动力性能进行研究,非常缺乏台风等极端海况下半潜式平台动力响应的实海域监测数据。以某半潜式钻井平台为研究对象,构建了一套比较完善的平台动力性能监测系统,并对台风“杜苏芮”过境阶段的监测数据进行了分析。根据平台艏部气隙及运动监测数据推算了平台吃水及环境波高;采用随机波浪的统计分析方法,计算得到短期海况的有效波高、谱峰周期、能量谱等信息,通过与多种典型海浪谱对比发现Jonswap谱与所测波谱吻合较好;对平台的横摇、纵摇及垂荡运动进行了时域统计分析和频域谱分析,得到了台风海况下被测平台波频运动的实际响应特征,对于指导平台抗台作业具有重要意义。     

涌浪对风浪能量影响的实验研究

在实验室风浪水槽中进行纯风浪和混合浪波面位移观测,研究波长较长的规则波对风浪能量的影响.本文用混合浪和纯风浪中的风浪显著波的零阶谱矩之比代表混合浪中的风浪与纯风浪能量之比,并以此表征涌浪对风浪能量的影响.研究了该能量比随涌浪波陡S、风区x、波龄倒数u/C、涌浪频率与纯风浪谱峰频率之比fs/fwp的变化规律.结果表明,涌浪对风浪能量的抑制作用随涌浪波陡的增加、波龄倒数的增大及涌浪频率与纯风浪谱峰频率之比的增大而增强.发现该能量比依赖于无因次量R=(1+80(πS)2)1.9(fs/fwp)0.9(u/C)0.27,并拟合得到2者的经验关系.此外,本文实验还发现,在某些情况下,涌浪的存在使风浪能量增加.     

Wave attenuation by flexible,idealized salt marsh vegetation

Wave attenuation by vegetation is a highly dynamic process and its quantification is important for understanding shore protection potential and modeling coastal hydrodynamics. Data documenting the interactions of Spartina alterniflora, represented by polyolefin tubing, and single- and double-peaked irregular waves were collected in a large-scale laboratory flume. The laboratory provided a controlled environment to evaluate wave attenuation, including the parameters of stem density, submergence, wave height, and peak period. Wave attenuation appeared to be most dependent on stem density and the ratio of stem length to water depth. Wave attention increased slightly with wave height while no clear trend with respect to wave period was seen. Treating double-peaked spectra as superimposed wave systems revealed a preferential dissipation of the higher-frequency wave system relative to the lower-frequency wave system under emergent conditions. Wave energy loss occurred at all frequencies of both spectral types, with dissipation increasing with frequency above the spectral peak. Parameterizing the spectral equilibrium range as a function of frequency showed a steepening of the spectral tail compared to the − 4 power law under emergent conditions. An empirical relationship defining the bulk drag coefficient for S. alterniflora as a function of the stem Reynolds number is found to serve as a first estimate for engineering applications.     

Model study of a shoreline wave-power system

A wave-power system which combines the concept of a breakwater and a harbor resonance chamber was developed in this study. In the caisson chamber, a multi-resonant oscillating water column (MOWC) was formed to push or suck air through the air turbine and thus continuously generated the power. The proposed wave-power system has two aims in mind: one is shore protection and the other is to extract energy from the ocean. To achieve an optimal effect of harbor resonance when excited by incident waves of various periods, a 60° opening of the cylindrical chamber with an entrance section and an arc-shaped curve board in front of the caisson was designed. In order to assess the energy-conversion efficiency and the hydraulic performance, a 1/20 model of this system was constructed and tested in the wave tank under various wave conditions. Our experimental data for the amplification factor of the MOWC agree well with previous theoretical results [Lee, J.J., 1971. Journal of Fluid Mechanics 45, 375–394]. The curve board proves to be useful: it not only broadens the resonant period but also increases the energy-extraction rate. The reflection coefficient was found to be generally low and to decrease with increasing wave height. However, due to the relatively high energy loss of the MOWC, only 28.5% of the incident-wave energy was converted into air energy, indicating that there are still areas for further improvement. In any event, the experimental results provided a clear picture of the energy-transformation process, and demonstrated the preliminary feasibility of this wave-energy device.     

Characteristics of a breaking wind-wave field in the light of the individual wind-wave concept

The relation between the intensity of breaking of individual wind-wave crests and parameters of wave size and wave form (e. g., height, period, steepness and skewness) is examined, and the process of change of these parameters is studied in a wind-wave tank (reference wind speed 15 m sec⁻¹, fetch 16 m). Distributions of the wave form parameters are different for breaking and nonbreaking waves. Fully breaking waves seem to hold the relationH ∞T ², whereH is the individual wave height andT is the period. The condition of breaking is not simply determined by the simple criterion of Stokes' limit. Wave height and steepness of a breaking wave are not always larger than those of a nonbreaking wave. This suggests the existence of an overshooting phenomenon in the breaking wave. The wave form parameters are found to change cyclically in a statistical sense during the wave propagation. The period of the cycle in the present case is estimated to be longer than four wave periods. An intermittency of wave breaking is associated with this cyclic process. Roughly speaking, two or three succeeding breaking-waves sporadically exist among a series of nonbreaking waves along the fetch.     

Laboratory study of random wave slamming on a piled wharf with different shore connecting structures

Impact pressures from random waves on the underside of a wharf deck were measured in a laboratory wave channel. Three different types of shore connecting structures were considered: open-piled, permeable slope and impermeable slope wharves. The experiments were carried out with significant wave heights ranging from 10 cm to 20 cm, spectral peak periods ranging from 1.0 s to 2.0 s, and the relative clearance of the model with respect to significant wave heights ranging from 0.1 to 0.4. The characteristics of the wave impact pressures for different shore connecting conditions are investigated, and their statistical distributions along the underside of the models are also determined. Experimental results indicate that the impact pressures depend on parameters such as the significant wave height, the spectral peak period, and the relative length and clearance of the model.     

Modeling the effect of late Quaternary interglacial sea levels on wave-cut shore platforms

A mathematical wave erosional model was used to study the effect of high sea levels during the penultimate (oxygen isotopic stage 7) and last interglacials (substage 5e), and in the late Holocene (stage 1), on the present morphology of wave-cut shore platforms. Sea level was considered to have been either the same as today or 2.25 m lower during the penultimate interglacial, and 2.25, 4.5 or 6.75 m higher than today during the last interglacial stage. The model suggested that inherited, gently sloping shore platforms in resistant rocks may be essentially protected today from erosion by high storm waves. The lowest platform gradients were in runs with mesotidal (3 m) range, and usually with low wave periods, low surf attenuation rates and weak rocks. Modern platform gradients increased with the difference in elevation between sea levels during successive interglacial stages. Shore platforms were widest in runs in which sea level was the same as today in the penultimate interglacial and 4.5 m higher than today during the last interglacial. Constant sea level, and high, last interglacial sea levels with considerable overlapping between the zones of high duration values between the mean neap high and low tidal levels in stages 7, 5e and 1, were conducive to the development of wide shore platforms, whereas sea levels lower than today's in stage 7 tended to produce narrower platforms. In general, higher sea levels during the last interglacial tended to produce higher cliff–platform junctions than constant sea level, unless the sea was lower than today during the penultimate interglacial stage. There was a lack of supratidal ledges in macrotidal (9 m) model runs with high initial gradients; this suggests that gently sloping, inherited shore platforms are essential for the subsequent development of supratidal, nonstructural ledges in high tidal environments during periods of higher sea level. Intertidal ledges developed in the upper portion of the modern intertidal zone, under a variety of tidal and sea level conditions. These ledges can develop independently of lithological or structural influences, and without any change in sea level. A single high sea level may also simultaneously produce two ledges at different supratidal elevations in mesotidal environments.     

基于ERA-Interim再分析资料的南沙海域风、浪场特征分析

基于ERA-Interim再分析资料,统计分析了南沙海域的风场、海浪场的时空特征,并进一步研究了风浪成长关系,建立了适用于南沙海域的风浪模型。月平均场分析结果表明:在季风期,南沙海域的月平均有效波高与风场的时空分布特征有良好的对应关系,位于中南半岛的东南部存在一个风速和有效波高的大值中心,冬季强于夏季,中心位置随季节转换稍向下风向移动。频率分析结果表明:南沙海域全年以4级以内风力和3级以内海浪出现的频率最高,6级以上大风和5级以上海浪主要出现在冬季风期间;全年最大风速和浪高出现在10、11月,最大风速达到8级,最大有效波高可达6级,但频率非常小;整个海域风速和浪高最小的时期是4—5月。     

The energy balance in the wind-wave spectrum

The spectral energy balance in the wind-wave spectrum is studied with taking into account the energy input from turbulent wind to waves, the energy rearrangement due to conservative nonlinear wave-wave interaction and the energy dissipation due to water turbulence. Using the Ichikawa's (1978) model on the turbulent wind field over wind-waves and assuming that the energy dissipation is times greater than that due to molecular viscosity of water, the energy input and dissipation are determined so as to satisfy the condition that the nonlinear-transfers of momentum and energy conserve the total momentum and energy of waves. The nonlinear energy-transfer is estimated from the energy balance at each frequency. It is found that the energy input and dissipation satisfying the condition on the conservative nonlinear-transfer are determined by the characteristic height of wind-wave field and the friction velocity of air, and that the spectral distribution of the nonlinear energy-transfer estimated in this paper is qualitatively similar to that estimated by the non-linear wave-wave interaction theory ofHasselmann (1962).     

Statistical characteristics of individual waves in laboratory wind waves I. Individual wave spectra and similarity structure

Statistical characteristics of individual waves in laboratory wind waves have been studied by use of a wind-wave tunnel. The individual waves are defined by actual undulations of the water surface at any instant, and are characterized by concentrated shearing stress and strong vorticity at their crests. A conspicuous self-similarity structure is found in the individual wave field. The similarity manifests itself as a simple spectral form, and as the statistical 3/2-power law between nondimensional wave height and wave period, and further as the -1/2-power relationship between nondimensional phase speed and frequency, for waves of the high frequency side. The normalized energy spectrum, specially defined for individual waves, has a form practically equivalent to the traditional spectrum for component waves in the main frequency range from 0.7 to 1.5 in the frequency normalized by the peak frequency, but does not have secondary peaks at harmonics. The phase speed of individual waves also coincides with that of component waves in the main frequency range.     

Statistical properties of microwave backscattering from laboratory wind-wave surfaces

The microwave backscattering from wind-wave surfaces is observed in a windwave tunnel under various conditions of the wind and wind waves, and its statistical features are investigated. The dependence of the backscattered power on the wind speed and the incident angle shows similar features to those predicted by models proposed previously. However, the dependence of the backscattered power on the incident angles also corresponds to the asymmetrical feature of the wind-wave surfaces with respect to the wind direction. The spectral analyses of time series of the backscattered intensity show that the propagating speed of fine structures of the wind-wave surface contributing to the backscattering at large incident angles does not coincide with the phase speed of the freely propagating Braggwaves. Atupwind incidence, the surface structures of wind waves contributing to the backscattering propagates with the dominant waves at their phase speed. This result is inconsistent with the two-scale model in which the Bragg waves are simply superimposed on longer waves, but is consistent with the results of optical observation by Ebuchiet al. (1987). At downwind incidence, the propagating speed is slower than the phase speed of the dominant waves.     

由模拟波面统计分析波高－周期联合分布

阐述以实测或拟合海浪谱为靶谱，用等能量分割法作波面数值模拟，从而利用模拟波面统计分析波高（Ｈ）－周期（Ｔ）联合分布。对波候的Ｈ－Ｔ联合分布、长时段海浪连续记录的Ｈ－Ｔ联合分布以及风浪、涌浪和混合浪的Ｈ－Ｔ联合分布进行了讨论。结果表明，只要已知特征波高和周期，就可反演出模拟波面，进而估测Ｈ－Ｔ联合分布情况，这对了解与各种特征波高对应的周期问题及在海洋工程应用上有一定的参考意义。     

一种波浪作用下软质海崖侵蚀量计算模型

基于波浪作用下软质海崖的侵蚀机理,考虑波浪水动力和海崖土质条件,建立了一种波浪作用下软质海崖侵蚀量的计算模型,利用室内水槽试验进行验证和参数回归,并使用该模型计算了平潭岛东北部软质海崖的侵蚀状况,与实测数据进行对比分析。研究发现：（1）海崖最大侵蚀量基本发生在静水位线处,随波浪持续作用,最大侵蚀量位置有所上移,当波浪持续作用一定时间时侵蚀基本停止;（2）当波高超过某一临界值时,侵蚀才会发生,而波高非常大的波浪对侵蚀的贡献相对不是很大;（3）平潭岛东北部的两处海崖,每次强台风连续作用8h时的侵蚀距离计算值为0.31m和0.25m。     

风浪和涌浪分离方法的比较

海浪通常以风浪和涌浪混合的形式存在。文中利用模型试验和实测资料,对目前提出的一种二维谱风涌浪分离方法(2D法)和3种一维谱风涌浪分离方法(PM法、WH法、JP法)进行了检验,分析发现:2D法给出的结果整体而言最为可靠,与2D法相比,PM法明显高估了风浪成分,WH法低风速时高估了风浪,高风速时跟2D法比较接近,而JP法在整体上高估了风浪成分。通过调整分割频率的比例系数,改进了PM法,改进后的PM法给出的分离结果与2D法最为一致。     

Toe Structure Stability of Sloping Breakwater

1 .IntroductionTheslopingbreakwateriswidelyusedintheprotectionofcoastalstructures ,withrubblemoundtoebermbuiltatthefootofthewave attackingslope .Thefunctionofarubblemoundtoestructureis ,inadditiontodecreasingthequantityofmainarmorstoneused ,toprovidestaticsupporttothemainarmorlayer,avoidingtherollingdownofmainarmorstonesandprotectingtheapronstonesfromero sion .TheweightoftoebermstonesisdecidedaccordingtotheCodeofBreakwaterDesignandBuildingformulatedbytheMinistryofCommunicationsofChina .When…     

基于HY-2 卫星观测分析南海风浪关系

海面有效波高(H1/3)是表征海浪的重要参数,随着卫星遥感技术的发展,雷达高度计已成为获取海面有效波高的重要手段,但也只能对卫星星下点轨迹处进行有效观测,远无法满足大范围应用的需求.本研究结合2013年10月HY-2雷达高度计观测的海面有效波高和微波散射计观测的海面风场资料,分别对高、低风速下风浪数据进行拟合,建立了适用于0~40 m/s风速范围内的南海海域风浪关系模型,经模型比对和结果验证,结果表明,基于HY-2卫星数据分析建立的南海海域风浪关系模型是可信的,特别是低风速的风浪模型与实测数据建立的风浪模型具有很好的一致性;根据建立的风浪关系模型,从卫星散射计大面观测的海面风场出发,能推算出风浪条件下海面有效波高的大面信息,数据覆盖远高于卫星高度计的星下点观测,能为分析和预报海浪、风暴潮灾害提供大范围的海面有效波高信息.     

防浪建筑物影响下珊瑚礁海岸波浪传播变形试验

通过测试一系列不规则波工况研究了防浪建筑物存在下珊瑚礁海岸附近短波、低频长波和增水的变化规律,并对比了防浪建筑物的不同位置情况。分析结果表明：波浪在沿礁传播过程中,短波波高沿礁坪持续衰减,低频长波波高沿礁坪逐渐增大,波浪增水则沿礁坪基本保持不变;海岸附近短波随着防浪建筑物与礁缘距离的变大而减小,低频长波则在防浪建筑物处于礁坪后部时达到最大,防浪建筑物位置的变化对于礁坪波浪增水的影响可以忽略。通过理论分析证明了珊瑚礁地形上低频长波是由于群波破碎造成的破碎点移动而产生的;当特定波况作用于特定位置的防浪建筑物时,低频长波在礁坪上会发生一阶共振效应导致其能量在海岸附近达到最大值。     

Application of the four models of directional spectra in the Bohai Sea

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Storm surge simulation using wind-wave-surge coupling model

Simulation of a storm surge caused by Typhoon 9918 in the Yatsushiro Sea, Kyushu, Japan was hindcasted by the synchronous coupled wind-wave-surge model composed of a Meso-scale meteorological model (MM5) for the wind and sea surface pressure, a spectral third-generation wind-wave model (Wavewatch III) for waves, and the coastal ocean model (Princeton Ocean Model). Inclusion of the whitecap wave breaking stresses (whitecap dissipation stress) in the coastal ocean model made it possible to reproduce the extreme surge height in the extremely shallow bay.     

滆湖北部人工地形重塑下风浪场变化研究

风浪是影响浅水湖泊物理生境环境重要的水动力要素之一。基于滆湖实测风浪数据, 建立了滆湖风浪模型, 验证结果表明模型可以较好模拟滆湖风浪随风场变化情况。在此基础上开展滆湖北部水域在人工地形重塑工程实施后的风浪变化情况分析。结果表明, 不同季节盛行风下, 风浪强度和湖底扰动强度均有一定程度的衰减, 这有利于水体透明度和水底光照条件的改善。风浪强度的衰减使得具有有利于水生植物生长与发育风浪条件的水域面积显著扩增。人工地形重塑的实施, 有利于滆湖北部水域水生植被物理生境环境改善, 从而为滆湖北部水域水生植被的修复提供较好的环境支撑, 也为其他浅水湖泊地形重塑工程的实施提供借鉴。