Hydroelastic Investigation on A Pile Breakwater Integrated with A Flexible Tail for Long-Wave Attenuation

A novel concept of wave attenuator is proposed for the defense of long waves, through integrating a flexible tail to the lee-side surface of a pile breakwater. The flexible tail works as a floating blanket made up of hinged blocks, whose scale and stiffness can be easily adjusted. A two-phase-flow numerical model is established based on the open-source computational fluid dynamics (CFD) code OpenFOAM to investigate its wave attenuation performance. Incompressible Navier—Stokes equations are solved in the fluid domain, where an additional computational solid mechanics (CSM) solver is embedded to describe the elastic deformation of the floating tail. The coupling of fluid dynamics and structural mechanics is solved in a full manner to allow assess of wave variation along the deforming body. The accuracy of the numerical model is validated through comparison with experimental data. Effects of the flexible tail on performance of the pile breakwater are investigated systematically. Dynamic behaviours of the tail are examined, and characteristics of its natural frequency are identified. For safety reasons, the wave loads impacting on the main body of the pile breakwater and the stress distribution over the tail are specially examined. It is found that both the length and stiffness of the tail can affect the wave-attenuation performance of the breakwater. A proper choice of the length and stiffness of the tail can greatly improve the long-wave defending capability of the pile breakwater. The maximum stress over the flexible tail can be restrained through optimising the deformation and stiffness of the tail.

     

Field observations of waves generated by passing ships: A note

This short contribution reports the results of a field study on the nearshore characteristics of waves generated by both conventional and high speed passenger ferries. The field observations took place in the late summer of 2005, at a beach close to the port of Mytilene (Island of Lesbos, Greece), and involved the visual observation of ship waves, using digital video recordings and image processing techniques. The results showed that passage of the fast ferry was associated with a longer, more complex and energetic nearshore event; this event not only did include higher nearshore waves (up to 0.74 m) and was organised in different wave packets, but it was also an order of magnitude longer (∼ 680 s) than the conventional ferry event. Regarding the effects on beach sediment dynamics, the fast ferry waves were estimated to be very efficient in mobilising the nearshore sediments in contrast to those of the conventional ferry. The fast ferry service appears to generate daily prolonged nearshore events, which contain waves with higher energy than those expected from the normal summer wind wave regime of the area; these events also include some high and very steep waves, which can be particularly erosive. Therefore, fast ferry wakes may have considerable impacts on the seasonal beach sediment dynamics/morphodynamics and the nearshore benthic ecology, as well as they may pose significant risks to bathers, affecting the recreational use of the beaches exposed to fast ferry traffic. Finally, the study has shown that satisfactory field observations of the nearshore characteristics of ship-generated (and wind) waves can be obtained using inshore deployments of calibrated poles, digital video cameras and appropriate image processing algorithms.     

Flow-induced transverse motions of a flexible cable aligned with the flow direction

Experimental studies of the transverse motions induced in a long flexible cable by axial flows have been conducted in a large blowdown water channel. A cable with a diameter of 1.59 cm and a length of 9 m was employed. Experiments were conducted over a fluid velocity range of 4.6-9.1 m/s. Both free and fixed downstream terminations of the cable were utilized, the former simulating a towed cable and the latter a mooring cable. Measurements of the drag coefficient of the cable with the free end were also made. These results were compared with those obtained previously for a flexible cylinder with a smooth exterior surface, and the following conclusions were drawn. 1) The amplitudes of the flow-induced transverse motions in a flexible cable or cylinder with a free downstream end in general decrease with increasing distance from this end, but they exhibit weak dependence on flow velocity and surface roughness near this end. 2) The amplitudes of the flow-induced motions are in general smaller when the cable is fixed at both ends than when the downstream end is free. 3) The drag coefficient of the flexible cylinder or cable increases with increasing surface roughness.     

近海视频测量与应用

近海视频测量技术是一种基于视频传感器实时采集近海图像,再运用图像处理和信息分析,获取近海环境过程和特征参数的观测技术。文中回顾近海视频测量与应用的发展概况,介绍了测量系统的构成,讨论了测量波浪、海流和近岸过程等参数与算法的应用,建议在我国开展研究应用,促进我国海洋观测技术的发展和进步。     

刺巨藤壶精子的发生及其超微结构

采用扫描和透射电镜技术, 观察刺巨藤壶(Megabalanus volcano)精子发生和精子的超微结构特征。结果显示, 刺巨藤壶精子发生经历精原细胞、初级精母细胞、次级精母细胞、精细胞和精子等5个阶段。在精子形成期间, 圆形或椭圆形的细胞核在微管的作用下沿轴丝延长并在胞质内弯曲, 核和轴丝随着精细胞的纵向伸长而延长, 细胞核最终成为线状; 斑块状的染色质逐渐解体, 呈细小颗粒状和粗颗粒状, 最后浓缩成高密度的均质物; 高尔基体分泌的囊泡不断融合, 形成大小不一的附属小滴前体, 最后融合并延伸成一个纺锤形的附属小滴; 许多小的线粒体不断融合成一个细长的线粒体, 移至核的后端。精子为前部带有附属小滴的长线状, 全长约58.39μm, 可分为顶体、颈部、中段和尾部四部分。长锥形的顶体位于精子最前端, 其后为基体; 颈部由基体产生的“9+2”型轴丝和与之并行的线状核组成; 顶体和颈部两者长共约6.65μm。中部长约42.95μm, 纺锤形的附属小滴(长约9.33μm, 最宽处约2.13μm)紧靠核和轴丝, 其后为颗粒状糖原及一个细长的线粒体; 尾部长约8.79μm, 只有轴丝贯穿。     

基于深度学习的视频观测潮位技术研究——以厦门高崎码头为例

近岸潮位观测是海洋工程应用、海岸防灾减灾、海岸带管理以及海洋有关科研工作中最基础的工作之一。文章基于视频图像深度学习的方法,使用YOLOv5目标检测算法从安装在近岸的固定摄像机拍摄的视频帧中提取潮汐水位特征进行潮位分析。研究采用厦门高崎码头的分辨率为1920×1080的高清摄像头2023年2月的影像数据作为训练集和验证集,2023年3月的影像数据作为测试集,利用岸边验潮井逐时潮位数据进行标注,采用YOLOv5目标检测算法来训练。计算结果显示,通过视频观测潮位在训练集和测试集上的误差分别为3.9 cm和5.3 cm。视频中1个像素点代表3.8 cm,因此潮位观测的平均误差为像素级。研究表明在近岸通过高清摄像头基于图像深度学习进行潮位观测的方法是可行的,观测精度取决于图像目标物的分辨率。     

Image processing for video images of buoy motion

In this paper, image processing technique that reduces video images of buoy motion to yield time series of image coordinates of buoy objects will be investigated. The buoy motion images are noisy due to time-varying brightness as well as non-uniform background illumination. The occurrence of boats, wakes, and wind-induced white caps interferes significantly in recognition of buoy objects. Thus, semiautomated procedures consisting of object recognition and image measurement aspects will be conducted. These offer more satisfactory results than a manual process. Spectral analysis shows that the image coordinates of buoy objects represent wave motion well, indicating its usefulness in the analysis of wave characteristics.     

Side-scan sonar mapping and computer-aided interpretation in the Santa Barbara Channel,California

We have experimented with digital processing of side scan sonar data taken in a 14 sq-km area of continental shelf offshore Southern California. The data were FM tape recorded during the survey and digitized and processed later in the laboratory. The digital image processing included both image correction and image enhancement. Geometric corrections were applied to correct for image distortions due to variable ship position and speed and sonar slant range. Enhancements that were tried included contrast stretching, band-pass filtering, image restoration (inverse filtering), and various edge enhancements such as density slicing and standard deviation filters. Interpretive procedures were also attempted and included digital mosaicking, stereoscopic viewing, and falsecolor display. The most effective processing was geometric correction combined with contrast stretching. Mosaicking proved difficult due to imprecise navigation (±50 m), but was very effective in increasing the understanding of the geologic structure in the survey area.     

水下柔性鱼形机构原理及单尾鳍板水动力试验研究

柔性鱼形机构是模拟鱼类运动的一种仿生机械系统。对鱼类运动的观察与研究 ,实质上是寻求水域中最优推进形式的过程 ,是工程优化设计的途径之一。在研究及优化柔性鱼形机构时涉及到水动力学及控制模型的问题 ,因此取出鱼形机构的尾鳍部分进行敞水试验 ,既能为有关模型的建立提供依据 ,更重要的是对鱼形机构的可行性进行论证     

基于热红外视频图像监测的海面溢油识别技术研究

针对现有海面溢油检测技术难以在石油泄漏初期（尚未形成海面大规模油膜覆盖）及时发现油膜的难题,本文在前期基于热红外图像测算海面油膜面积方法研究的基础上,结合油泄漏至海面后油膜的扩散特征,提出了一种基于热红外视频图像监测油膜面积变化以及时识别海面溢油的方法。首先,基于单帧热红外图像处理算法提取海面前景区域（包含油膜区域与相似物干扰区域）并计算各区域所代表的实际物理面积。基于视频图像处理技术跟踪测算前景区域中各连通区域的实际物理面积变化情况,根据各连通区域的面积变化率识别前景区域中是否存在油膜,从而判断海面是否发生溢油。实验结果表明:所提出的方法能有效识别不同黏度的石油泄漏至海面形成的扩散油膜,在水面包含波浪与相似物干扰时也具有良好的识别精度。该方法适用于特定场景下（如码头、船舶等）的溢油事故的鉴别,能为溢油事故的及时发现和预警提供技术支持。     

Paramonohystera weihaiensis sp.nov.(Xyalidae,Nematoda) from the intertidal beach of the Yellow Sea,China

A new species of free-living marine nematode of the genus Paramonohystera was described from the intertidal beach, Weihai. Paramonohystera weihaiensis sp. nov. is characterized by cervical region with a circle of long setae;tail sexual dimorphism, male tail angled dorsally with sharp narrowed of the body at the cloaca, female tail ordinary conico-cylindrical;spicules slender, 2.5 abd long;gubernaculum plate, enlarged distal end with two teeth, without apophysis;precloacal supplements absent;Four caudal gland cells obviously extended to tail. The new species differs from the other fourteen known valid congeners by the combination of its characteristics:a circle of long cervical setae, tail sexual dimorphism, spicules slender, 2.5 abd long, gubernaculum plate with a distal pair of teeth.     

香鱼(Plecoglossus altivelis)精子的超微结构及其与鲤形目及鲑形目其他鱼类精子结构的比较研究

为了解香鱼(Plecoglossus altivelis)精子的形态结构特点,采用扫描和透射电镜技术观察了香鱼精子的超微结构,并与鲤形目及鲑形目其他鱼类精子结构进行了比较。结果表明,香鱼精子由头部、中段和尾部组成,全长约23.5μm。头部呈弹头形,由细胞核外包质膜构成,长约1.8μm、宽约0.8μm;细胞核从后端中央向前深凹至核的近前端,形成植入窝,使核呈倒U字形,核的前端无顶体;植入窝内有中心粒复合体及小段起始的鞭毛,中心粒复合体由近端中心粒和远端中心粒(基体)组成,两者之间夹角约135o。中段为"半袖套"结构,长约0.5μm,其内部为一较大的"半套筒"形线粒体。鞭毛起始于远端中心粒,由轴丝及外包轴丝的质膜组成,轴丝为典型的"9+2"微管结构;鞭毛两侧有质膜向外突起形成侧鳍。研究显示,香鱼精子与典型的鲤形目(Cypriniformes)鱼类精子卵圆形或圆球形头部及细胞核、不对称的袖套及尾部鞭毛无侧鳍等结构特征不同,也与鲑形目(Salmoniformes)鱼类精子卵圆形或椭圆形头部及马蹄形或浅U形细胞核、两中心粒相互平行或垂直、袖套结构完整等结构特征不同。香鱼精子结构具有种的特异性。     

Distribution and spatial variation of hydrothermal faunal assemblages at Lucky Strike (Mid-Atlantic Ridge) revealed by high-resolution video image analysis

Whilst the fauna inhabiting hydrothermal vent structures in the Atlantic Ocean is reasonably well known, less is understood about the spatial distributions of the fauna in relation to abiotic and biotic factors. In this study, a major active hydrothermal edifice (Eiffel Tower, at 1690 m depth) on the Lucky Strike vent field (Mid-Atlantic Ridge (MAR)) was investigated. Video transects were carried out by ROV Victor 6000 and complete image coverage was acquired. Four distinct assemblages, ranging from dense larger-sized Bathymodiolus mussel beds to smaller-sized mussel clumps and alvinocaridid shrimps, and two types of substrata were defined based on high definition photographs and video imagery. To evaluate spatial variation, faunal distribution was mapped in three dimensions. A high degree of patchiness characterizes this 11 m high sulfide structure. The differences observed in assemblage and substratum distribution were related to habitat characteristics (fluid exits, depth and structure orientation). Gradients in community structure were observed, which coincided with an increasing distance from the fluid exits. A biological zonation model for the Eiffel Tower edifice was created in which faunal composition and distribution can be visually explained by the presence/absence of fluid exits.     

A computer-aided framework for subsurface identification of white shark pigment patterns

Subsurface video footage can be used as a successful identification tool for various marine organisms; however, processing of such information has proven challenging. This study tests the use of automated software to assist with photo-identification of the great white shark Carcharodon carcharias in the region of Gansbaai, on the south coast of South Africa. A subsurface photo catalogue was created from underwater video footage. Single individuals were identified by using pigmentation patterns. From this catalogue, two images of the head for each individual were inserted into automated contour-recognition software (Interactive Individual Identification System Beta Contour 3.0). One image was used to search the database, the other served as a reference image. Identification was made by means of a contour, assigned using the software to the irregular border of grey and white on the shark's head. In total, 90 different contours were processed. The output provided ranks, where the first match would be a direct identification of the individual. The method proved to be accurate, in particular for high-quality images where 88.24% and 94.12%, respectively, were identified by two independent analysts as first match, and with all individuals identified within the top 10 matches. The inclusion of metadata improved accuracy and precision, allowing identification of even low-quality images.     

Noise Control Due to the Stator Wake Blade Interaction via Tail Articulation

The biologically inspired method of tail articulation is investigated as a means of reducing tonal noise due to wake deficit blade interaction in underwater vehicles. Experiments are carried out in a water tunnel under typical operating conditions for underwater vehicles. Tail articulation is implemented using a life scale stator model with a hinged flapping tail operating both in free-stream velocities corresponding to Reynolds number in the range 75000 < Re < 300000 and at frequencies up to 30 Hz to investigate the range of Strouhal number 0.0 < St < 0.35. Velocity measurements of the active stator wake are carried out by laser Doppler velocimetry (LDV) and particle image velocimetry (PIV) to investigate the effects of tail articulation on the stator wake. Time-averaged measurements of the stator wake by LDV show that of the tail articulation has a dominant effect on the time mean stator drag. Instantaneous phase-averaged measurements of the stator wake by PIV show a transition in the unsteady stator wake as is increased, from a deflected vortex sheet to a series of rolled up, discrete vortices. Measurements are made of the wake due to both sinusoidal and nonsinusoidal tail motion profiles, which show that significant wake alteration is achieved with tail articulation. A low-order model describing the creation and convection of vorticity by tail articulation is developed which describes wake phenomena observed in LDV and PIV measurements. Finally, a 3-D unsteady propeller simulation using both experimental wake velocity data by PIV and simulated wake velocity data generated with the reduced-order model are used to predict the effect of sinusoidal tail articulation on radiated noise. Results using simulated data indicate that a significant noise alteration is achieved in all cases, and noise reduction of 5-8 dB is achieved in some cases.     

大竹蛏精子发生和精子的超微结构

利用透射电镜观察大竹蛏(Solen grandis Dunker)精子发生和精子的超微结构,描述了从精原细胞发育到成熟精子过程中超微结构的变化。大竹蛏精子发生历经精原细胞、初级精母细胞、次级精母细胞、精细胞和成熟精子5个阶段。成熟精子属典型的原生型,全长52—57 μm,由头部、中段和尾部三部分组成。头部由顶体和细胞核组成;中段由4—5个椭圆形线粒体和2个相互垂直的中心粒组成;尾部细长,为典型的“9+2”型结构。大竹蛏与同属的长竹蛏精子发生和精子超微结构存在差异。大竹蛏精细胞前顶体囊的高电子密度物质分布在周缘呈一个带缺口的弧形而不是圆形,而长竹蛏前顶体囊周缘的高电子密度物质呈一圆形分布;大竹蛏的前顶体囊是先内凹变形,然后一边变形一边移动,而长竹蛏的前顶体囊是在到达核前端后才开始变形。大竹蛏的顶体比长竹蛏的稍长;大竹蛏精子核形似子弹头而长竹蛏精子核形为圆球状;大竹蛏有卫星体结构而长竹蛏无卫星体结构;大竹蛏精子尾部鞭毛比长竹蛏的长。结果可以为竹蛏科相似种类的鉴定及亲缘关系的探讨提供参考依据。     

Quantitative photogrammetric analysis of digital underwater videoimagery

This paper presents a photogrammetric model for digital underwater video imagery, which has been mostly applied to qualitative analysis in the marine environment. With this model, quantitative analysis of underwater images is possible, e.g., to locate positions, calculate sizes, and measure shapes of objects from image features. The underwater photogrammetric model is based on a three-dimensional optical ray tracing technique which rigorously models imaging systems with multilens configurations and multiple refractions. The calibration procedure with two independent phases has been proven to be efficient in simplifying the computation and improving the calibration accuracy. With the current imaging system configuration and photogrammetric model, an accuracy of 0.8 cm in lateral directions and 1.2 cm along the depth direction for objects located about 2-3 m from the camera system in the object space is attainable. A PC-based digital underwater photogrammetric prototype system has been developed to implement the underwater photogrammetric model     

A New Video and Digital Camera System for Studies of the Dynamics of Microtopographic Features on Tidal Flats

A newly developed video and camera system for tidal flat microtopographic studies is presented. It consists of a SONY handy cam placed in an underwater housing mounted on a frame about 70?cm above the sediment surface. A rectangular surface area of 30?×40?cm is imaged by the camera. The camera records video sequences and/or digital images at predetermined time lapses. The total number of images is about 540, and a similar number of 10-second long video sequences can be recorded. The camera is programmed with a PC before deployment, and the total deployment time depends on the time lapse between recordings. The camera is connected to an external power supply (12?volt), and a halogen projector pointing towards the sediment surface ensures that the system is operable on a 24-hours scale. The system has been tested in the Danish Wadden Sea. It has proved to be a very useful tool in studies of topographic effects of erosion and deposition sequences, and for studies of benthic organisms-sediment interactions. The test site was further equipped with sensors for water and seabed measurements, which proved to be indispensable regarding the interpretation of recorded image time-series.     

A New Video and Digital Camera System for Studies of the Dynamics of Microtopographic Features on Tidal Flats

A newly developed video and camera system for tidal flat microtopographic studies is presented. It consists of a SONY handy cam placed in an underwater housing mounted on a frame about 70 cm above the sediment surface. A rectangular surface area of 30 ×40 cm is imaged by the camera. The camera records video sequences and/or digital images at predetermined time lapses. The total number of images is about 540, and a similar number of 10-second long video sequences can be recorded. The camera is programmed with a PC before deployment, and the total deployment time depends on the time lapse between recordings. The camera is connected to an external power supply (12 volt), and a halogen projector pointing towards the sediment surface ensures that the system is operable on a 24-hours scale. The system has been tested in the Danish Wadden Sea. It has proved to be a very useful tool in studies of topographic effects of erosion and deposition sequences, and for studies of benthic organisms-sediment interactions. The test site was further equipped with sensors for water and seabed measurements, which proved to be indispensable regarding the interpretation of recorded image time-series.     

Analytical solution of mean top tension of long flexible riser in modeling vortex-induced vibrations

The vortex-induced vibration (VIV) of flexible long riser with combined in-line and cross-flow motion has been studied using a wake oscillator in this paper. The analytical solution of mean top tension of long flexible riser is evaluated and compared with experimental results, and good agreement is observed to verify its validity. Then the nonlinear coupled dynamics of the in-line and cross-flow VIV of a long tension-dominated riser were analyzed through wake oscillator model with the consideration of variation of the mean top tension. The in-line and cross-flow resonant frequencies, lift and drag coefficients, dominant mode numbers, amplitudes and instantaneous deflections are reported and compared with experimental results, and excellent agreements are observed. The comparison of mode numbers between the calculation with and without consideration of variation of mean top tension shows that the proposed analytical solution of the mean top tension can produce a better prediction of multi-mode VIV.