A three-dimensional wave field over a bidirectionally periodic ripple bottom     

Chia-Yan Cheng  Yang-Yih Chen  Guan-Yu Chen   《Ocean Engineering》2007,34(2):303-319

For gravity wave trains propagating over an arbitrary wavy bottom, a perturbation expansion is developed to the second order so that the Bragg resonance effect of the ripple bottom on the free-surface wave can be analyzed. Both the resonant and non-resonant cases are treated and the singular behavior at resonance is avoided. This theory is successfully verified by reducing to simpler situations. Then, the analytical results for the special case of a unidirectional sinusoidal bottom are compared with experimental data for validation.  相似文献   

Further evidence for non-reemergence of winter SST anomalies in the North Pacific eastern subtropical mode water area     

Shusaku Sugimoto  Kimio Hanawa 《Journal of Oceanography》2007,63(4):625-635

Following our previous study (Sugimoto and Hanawa, 2005b), we further investigate the reason why reemergence of winter sea surface temperature anomalies does not occur in the North Pacific eastern subtropical mode water (NPESTMW) area, despite its occurrence in the North Pacific subtropical mode water and North Pacific central mode water areas. We use vertical temperature and salinity profiles of the World Ocean Circulation Experiment Hydrographic Program and Argo floats with high vertical and temporal resolution, together with heat flux data through the sea surface. We point out first that one of the causes for non-occurrence of reemergence is that the thickness of NPESTMW is very thin. In addition to this basic cause, two major reasons are found: a vigorous mixing in the lower portion of NPESTMW and less heat input from the atmosphere in the warming season. Since, in the lower portion of NPESTMW and deeper, the stratification is favorable for salt-finger type convection to occur compared with the other mode water areas, vigorous mixing takes place. This is confirmed by both a large Turner Angle there and the existence of staircase structures in vertical temperature and salinity profiles. From the viewpoint of heat input, the NPESTMW area gradually gains heat in the warming season compared with other mode water areas. As a result, NPESTMW cannot be capped so quickly by the shallow summer mixed layer, and water properties of NPESTMW are to be gradually modified, even in the upper portion.  相似文献   

Geomorphological evidence for upslope canyon-forming processes on the northern KwaZulu-Natal shelf,SW Indian Ocean,South Africa     

Andrew N. Green  John A. Goff  Ron Uken 《Geo-Marine Letters》2007,27(6):399-409

A geomorphological and statistical analysis of slope canyons from the northern KwaZulu-Natal continental margin is documented and compared with submarine canyons from the Atlantic margin of the USA. The northern KwaZulu-Natal margin is characterized by increasing upslope relief, concave slope-gradient profiles and features related to upslope growth of the canyon forms. Discounting slope-gradient profile, this morphology is strikingly similar to canyon systems of the New Jersey slope. Several phases of canyon incision indicate that downslope erosion is also an important factor in the evolution of the northern KwaZulu-Natal canyon systems. Despite the strong similarities between the northern KwaZulu-Natal and New Jersey slope-canyon systems, key differences are evident: (1) the concavity of the northern KwaZulu-Natal slope, contrasting with the ∼linear New Jersey slope; (2) the relative isolation of the northern KwaZulu-Natal canyons, rather than the dense clustering of the New Jersey canyons; and (3) the absence of strongly shelf-breaching canyons along the northern KwaZulu-Natal margin. In comparison with the New Jersey margin, we surmise a more youthful stage of canyon evolution, a result of either the canyons themselves being younger or the formative processes being less active. Less complicated patterns of erosion resulting from reduced sediment availability have developed in northern KwaZulu-Natal. The reduction in slope concavity on the New Jersey margin may be the result of grading of the upper slope by intensive headward erosion, a process more subdued—or less evident—on the KwaZulu-Natal margin.  相似文献   

南海晚第四纪硅藻遗体及其地质意义Ⅵ.硅藻的2个新种和7个新记录     

程兆第  蓝东兆 《台湾海峡》1995,14(1):40-43

本文记述了南海晚第四纪沉积物中发现的两个新种[线形辐环藻（Actinocyclus lineatus Liu,Cheng et Lan sp.nov.）、星圆筛藻（Coscinodiscus aster-aeus Cheng,Liu et Lan sp.nov.）]以及在我国首次记录的圆筛藻的7个种。  相似文献   

Numerical Simulation of Wave Field near Submerged Bars by PLIC-VOF Model   总被引：2，自引：1，他引：2  

刘诚刘晓平  蒋昌波 《中国海洋工程》2005,19(3):509-518

Investigating the wave field near structures in coastal and offshore engineering is of increasing significance. In the present study, simulation is done of the wave profile and flow field for waves propagating over submerged bars, using PLIC-VOF （Pieeewise Linear Interface Construction） to trace the free surface of wave and finite difference method to solve vertical 2D Navier-Stokes （N-S） equations. A comparison of the numerical results for two kinds of submerged bars with the experimental ones shows that the PLIC-VOF model used in this study is effective and can compute the wave field precisely.  相似文献   

南澎列岛及邻近海域地质地貌与灾害地质分析   总被引：2，自引：1，他引：2  

詹文欢  张乔民  孙宗勋  唐诚  丘学林 《热带海洋学报》2002,21(1):11-17

南澎列岛及邻近海域是广东沿海灾害地质因素较集中和类型较齐全的地区之一。根据野外调查资料，简要地分析了区内地质地貌以及活动断裂、地震活动、地面沉降、滑坡、地裂和沙土液化等基本特征和分布规律，同时还对区内地质灾害进行了初步分析。  相似文献   

南沙群岛海区珊瑚礁灾害性地质分析   总被引：3，自引：0，他引：3  

詹文欢  孙宗勋  张乔民  唐诚 《热带海洋学报》2002,21(2):58-65

珊瑚礁是一种特殊的岩土介质，有独特的灾害地质类型。珊瑚礁灾害地质研究是现代工程地质学的一个新课题。通过珊瑚礁的地质记录研究了内动力灾害地质类型（包括活动断裂、地震和火山活动等）、外动力灾害地质类型（包括海底槽谷与地形突变带、崩塌、滑坡、峰礁与埋藏礁、泥丘、埋藏负地貌等），同时还分析了人类活动对珊瑚礁发育的影响。  相似文献   

Effects of scattering and resonance on energy dissipation of an internal tide in a narrow shelf     

Yuji Kawamura  Yujiro Kitade 《Journal of Oceanography》2007,63(1):15-25

The effects of scattering and resonance on the energy dissipation of an internal tide were investigated using a two-dimensional model which is a reassembled version of the theoretical generation model devised by Rattray et al. (1969) for internal tide. The basic character of the scattering process at the step bottom was first investigated with a wide shelf model. When the internal wave incited from a deep region (Region II) into the shallow shelf region (Region I), a passing wave into the shallow region, a reflected wave into the deep region, and a beam-like wave, i.e. a scattered wave (SW), emanated at the step bottom. The SW, which consists of the superposition of numerous internal modes, propagated upward/downward into both regions. The general properties of the SW were well expressed around the shelf edge, even in the present model with viscosity effect. The amplitude of the SW decreased dramatically when the depth of the velocity maximum of the incident internal wave in Region II corresponded with the depth of the shelf edge. In the narrow shelf model, where the decay distance of the internal wave in Region I is longer than the shelf width, the incident internal wave reflected at the coast to form a standing wave. When the internal wave in Region I is enhanced by the resonance, the energy of the SW in Region II is also intensified. Furthermore, the energy of the modes in Region II predominated when the velocity maximum is identical to that of the dominant mode in Region I. These results suggest that the spatial scale of shelf region is a very important factor governing the energy dissipation of the internal tide through reflection and scattering in a narrow shelf.  相似文献   

基于DSP的水下图像传输系统研究     

程恩  许茹  苏运东 《海洋技术学报》2001,20(3):44-48

本文研究了基于高性能的DSP芯片TMS320C549的水下图像传输系统，并采用Goertzel算法进行信源编码和MFSK调制方式、运用Turbo码进行信道的编、解码，来实现水下视频图像高速数据传输的目的。  相似文献   

从受训神经-模糊模型中提取知识     

冯天瑾  于树松  程军娜 《中国海洋大学学报(自然科学版)》2003,33(1):107-114

本文对用于模式分类、函数逼近、参数估计的多层感知器 (MLPs)给出 1个清晰的关于内部行为的解释。作者以单隐层的 MLP为例 ,论述了关于 MLP的内部行为的半线性分析理论。对受训的MLP,将隐层单元的输出分别定义为网络输出的正、负“内部分量”;定义内部分量的连接权重集为给定问题的“内部判别模式”;建立了 MLP和模糊集相结合的新模型 ;分析了 MLP的结构为 N- 2 - 1和N- H- 1 ,给出权重初始化的方法 ;提出了 1种从受训神经 -模糊模型 (NFMs)中提取知识的全新的具有实用价值的方法。  相似文献