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颗粒后向散射系数是水体最重要的固有光学参量之一,也是海洋水色卫星遥感的核心参数。现场准确测量水体颗粒后向散射数据,对于水色遥感模型构建以及水色遥感产品真实性检验至关重要。本文针对常用的3种水体颗粒后向散射系数原位测量仪(HydroScat6,VSF3和BB9),通过比测实验,对三者测量结果的一致性进行了比较分析。结果表明,在清洁水体中3种仪器对颗粒后向散射系数测量具有较好的一致性;但在浑浊水体中,HydroScat6和BB9测量值会比VSF3高,三者偏差显著增大。同时,数值模拟和实验结果均表明,颗粒形状会对测量结果产生影响,3种仪器对球形颗粒的后向散射系数测量结果的一致性显著好于野外颗粒结果。 相似文献
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The problem of a two-dimensional finite-width wedge entering water near a freely floating body is considered through the velocity potential theory for the incompressible liquid with the fully nonlinear boundary conditions on the free surface. The problem is solved by using the boundary element method in the time domain. The numerical process is divided into two phases based on whether the interaction between the wedge and floating body is significant. In the first phase, when the single wedge enters water at initial stage, only a small part near its tip is in the fluid, the problem is studied in a stretched coordinate system and the presence of the floating body has no major effect. In the second phase, the disturbance by water entry of the wedge has reached the floating body, and both are considered together in the physical system. The auxiliary function method is adopted to decouple the nonlinear mutual dependence between the motions of the wedge and floating body, both in three degrees of freedom, and the fluid flow, as well as the interaction effects between them. Case studies are undertaken for a wedge entering water in forced or free fall motion, vertically or obliquely. Results are provided for the accelerations, velocities, pressure distribution and free surface deformation, and the interaction effects are discussed. 相似文献
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漂浮于自由水面的污染物的的迁移、扩散会受到天然随机海浪的影响。之前的研究（以Herterich和Hasselmann（1982）为代表）普遍认为,随机波浪作用下的斯托克司漂移速度会引起水面污染物的离散,这个离散甚至有可能跟风和海流引起的离散同一量级。本研究就随机波浪作用下的斯托克司漂移速度是否会引起水面漂移物的离散进行理论和试验探讨。从理论推导可知,随机波浪下的质量输移速度是个定常分量,因此它不会随时间变化而引起水面漂移物的离散。随后我们在实验室水槽中进行了漂移物在随机波浪（P-M谱）作用下的漂移过程的测量。试验结果也印证了随机波浪作用下的斯托克司漂移速度不会引起水面漂移物离散的结论。 相似文献
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全面地比较和总结了当前包括压力式测波、声学式测波、浮标式测波和遥测式测波在内的几种主要的海洋波浪测量方法的技术特点;对相应类型的典型代表型号的仪器主要技术指标进行了对比;对不同类型测量方法及其对应的仪器的具体适用环境给出了分析和建议。实际结合了ADCP,AWAC,Wave Duo测波浮球等几种海洋波浪测量仪器于2014年12月在江苏省南通市近海相近区域的同步实测数据,对这几种仪器的海洋波浪测量的响应和过程特征进行了对比和分析,这对相关的海洋波浪测量技术和对应的测波仪器设备特点也是一个很好的验证。 相似文献
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Many studies have been published concerning the influence of the immersed shape (in still water) of a floating body on its response and power capture from ocean waves. With a few notable exceptions, much of this analysis has assumed small amplitude motion and linear models have been employed to predict response. The form of the upper surface of such a body has received little attention. Here, we show how the shape of the upper (top) surface of a floating body can be designed to ensure that the response amplitude of the body is within a specified value. This is of considerable importance to the survivability of wave energy devices. The approach used is to achieve a large increase of both natural period and hydrodynamic damping for only a small change of float mass. These two factors impose a hydrodynamic limit on the displacement which may be exploited to avoid the ‘end-stop’ problem often encountered in wave device design. To demonstrate the change of response, experimental measurements are presented of the response of an axisymmetric float with rounded base and conical upper surface with rounded perimeter due to a range of regular, irregular and focused wave conditions. Power extraction is not considered since the mechanically undamped response represents the worst case. In contrast to a simple, straight-sided axisymmetric float, a smaller change of mass is required to satisfy a particular response amplitude limit. Although a significant reduction is not expected, hydrodynamic damping may reduce with increasing physical scale, and this remains to be quantified. 相似文献
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An optical instrument which detects the light attenuation in sediment-laden flows has been developed to measure the instantaneous and time-average suspended concentration of cohesive sediments. In a flume test with natural muds, the device showed that the instantaneous sediment concentration oscillated with the waves but that the amplitude decreased rapidly with the distance above the mud bed. Strong sediment motion was found near the benthic boundary layer. This indicates a weak vertical turbulent diffusion in the upper portion of the water column in a pure wave erosion process. It is concluded that the probe design can be easily modified and the apparatus can be deployed for both laboratory and field measurements 相似文献
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Alison Bimler 《新西兰海洋与淡水研究杂志》2013,47(4):715-720
The mud whelk Cominella glandiformis (Reeve, 1874) was observed on a tidal flat “floating” upside down beneath the water surface. Study in the laboratory showed that, when C. glandiformis is “floating”, the foot is distended with blood to approximately twice its normal surface area. In the laboratory C. glandiformis “floated” only during daylight hours, and the incidence of “floating” increased markedly as specimens became more overcrowded. Possibly “floating” is a rapid dispersal mechanism in response to overcrowding; it may also assist respiration in the event of overcrowding producing anaerobic conditions. Its occurrence only during daylight hours suggests that a reaction to light may also be involved. 相似文献
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The application of a Smoothed Particle Hydrodynamics (SPH) model to simulate the nonlinear interaction between waves and a moored floating breakwater is presented. The main aim is to predict and validate the response of the moored floating structure under the action of periodic waves. The Euler equations together with an artificial viscosity are used as the governing equations to describe the flow field. The motion of the moored floating body is described using the Newton’s second law of motion. The interactions between the waves and structures are modeled by setting a series of SPH particles on the boundary of the structure. The hydrodynamic forces acting on the floating body are evaluated by summing up the interacting forces on the boundary particles from the neighboring fluid particles. The water surface elevations, the movements of the floating body and the moored forces are all calculated and compared with the available experimental data. Good agreements are obtained for the dynamic response and hydrodynamic performance of the floating body. The numerical results of different immersion depths of the floating body are compared with that of the corresponding fixed body. The effects of the relative length and the density of the structure on the performance of the floating body are analyzed. 相似文献
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This paper deals with the evaluation of the natural frequencies in heave motion of a single floating Oscillating Water Column device along with the natural frequencies of the water column inside the oscillating chamber. Two types of OWCs are examined, a simple-type device, consisting of a partially immersed toroidal body and a novel-type device, consisting also of a partially immersed toroidal body supplemented however by a coaxial interior truncated cylinder moving in phase with the outer chamber, thus forming a floating unit. Numerical results are given concerning the three boundary value problems, namely, the diffraction, the motion- and the pressure- dependent radiation problems, obtained through an analytical solution method using matched axisymmetric eigenfunction expansion formulations. The effect of the air pressure distribution inside the oscillating chamber on the natural frequencies in heave motion of the two examined types of OWCs and on the natural frequency of the water column motion inside the chamber, is presented and discussed thoroughly. It is demonstrated that the heave natural frequencies are strongly dependent on the type of the examined OWC and the device’s inner air pressure and should be taken into consideration when designing a floating OWC device. 相似文献
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自升式连体潜标测量系统的设计与实施 总被引：1，自引：1，他引：0
针对有缆潜标系统测量质量不稳定,缆绳阻力大、浮球浮力不足,测量系统难以绷紧,导致潜标摇摆、缆绳倾斜,受海洋环境的其他外力作用,影响采集资料的质量等问题,设计了自升式连体潜标测量系统。该系统最大特点是把各种仪器设备与释放器搭载组合到同一平行面的潜标内,把仪器设备、释放器与浮体材料合成为单位体积最小的潜标测量平台。该系统还有体积小、质量轻、造价低、操作简便等特点,适用于水深1 200 m内的海区,采用座底方式进行测量。系统通过释放装置脱钩,脱钩后连体潜标可自行升浮到海面,并具有隐蔽性好不易被破坏的优点。经过近1 a的试验,已多次在南海水深400 m多的海区顺利完成了海上投放与回收试验,试验结果良好。 相似文献
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人工浮鱼礁型式多样,适应水深范围广,优化锚泊方式可规模化建设浮鱼礁群,是海洋中上层生境构建的重要手段。中上层浮鱼礁投放于近海,属于海岸工程范畴,抗浪性能是其结构设计的关键。根据有限单元法和集中质量点法,详细阐述和推导了中上层浮鱼礁各构成组件连接位置处点或单元的相互耦合受力和运动处理方法,以及浮鱼礁出水条件的判别方法和水质点速度、加速度的修正方法。建立的波浪作用下三维浮鱼礁动力响应数值模型与其在波浪水槽中的物理模型试验对比,验证了数值模型的正确性。最后建立了一种新型锚泊方式的浮鱼礁动力响应数值模型,分析了浮鱼礁摆动角度、锚绳拉力、网衣系缚点总拉力的历时变化。研究结果可为中上层浮鱼礁优化结构形状和搭配浮体、配重提供判断依据。 相似文献
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The system with one floating rectangular body on the free surface and one submerged rectangular body has been applied to a wave energy conversion device in water of finite depth. The radiation problem by this device on a plane incident wave is solved by the use of an eigenfunction expansion method, and a new analytical expression for the radiation velocity potential is obtained. The wave excitation force is calculated via the known incident wave potential and the radiation potential with a theorem of Haskind employed. To verify the correctness of this method, an example is computed respectively through the bound element method and analytical method. Results show that two numerical methods. are in good agreement, which shows that the present method is applicable. In addition, the trends of hydrodynamic coefficients and wave force are analyzed under different conditions by use of the present analytical method. 相似文献