Geophysical evidence of mud diapirism on the Mediterranean Ridge accretionary complex   总被引：2，自引：0，他引：2  

A. Camerlenghi  M. B. Cita  B. Della Vedova  N. Fusi  L. Mirabile  G. Pellis 《Marine Geophysical Researches》1995,17(2):115-141

Mud volcanoes, mud cones, and mud ridges have been identified on the inner portion of the crestal area, and possibly on the inner escarpment, of the Mediterranean Ridge accretionary complex. Four areas containing one or more mud diapirs have been investigated through bathymetric profiling, single channel seismic reflection profiling, heat flow measurements, and coring. A sequence of events is identified in the evolution of the mud diapirs: initially the expulsion on the seafloor of gasrich mud produces a seafloor depression outlined in the seismic record by downward dip of the host sediment reflectors towards the mud conduit; subsequent eruptions of fluid mud may create a flat topped mud volcano with step-like profile; finally, the intrusion of viscous mud produces a mud cone.The origin of the diapirs is deep within the Mediterranean Ridge. Although a minimum depth of about 400 m below the seafloor has been computed from the hydrostatic balance between the diapiric sediments and the host sediments, a maximum depth, suggested by geometric considerations, ranges between 5.3 and 7 km. The presence of thermogenic gas in the diapiric sediments suggests a better constrained origin depth of at least 2.2 km.The heat flow measured within the Olimpi mud diapir field and along a transect orthogonal to the diapiric field is low, ranging between 16 ± 5 and 41 ± 6 mW m^–2. Due to the presence of gas, the thermal conductivity of the diapiric sediments is lower than that of the host hemipelagic oozes (0.6–0.9 and 1.0–1.15 W m^–1 K^–1 respectively).We consider the distribution of mud diapirs to be controlled by the presence of tectonic features such as reverse faults or thrusts (inner escarpment) that develop where the thickness of the Late Miocene evaporites appears to be minimum. An upward migration through time of the position of the décollement within the stratigraphic column from the Upper Oligocene (diapiric sediments) to the Upper Miocene (present position) is identified.  相似文献   

Validation of a finite difference method for the simulation of vortex-induced vibrations on a circular cylinder     

J. B. V. Wanderley  C. A. Levi 《Ocean Engineering》2002,29(4):445-460

The Karman Vortex Street generated by a circular cylinder is investigated by the numerical solution of the compressible Navier–Stokes equations in the incompressible Mach number range (Mach<0.3) using the Beam and Warming implicit scheme. The agreement with the fully incompressible projection method (Chorin, 1968) is fairly good while convergence time is very much better. The investigation suggests that the compressible Navier–Stokes equations may be used as an efficient alternative to study incompressible flows as well. Mach numbers just below 0.3 are enough to simulate incompressible flow behavior and at the same time do not cause numerical ill-conditioning in the solution. In addition, some relevant features of the vortices generated and carried by the wake of the cylinder could be fairly well captured.  相似文献   

Spatial patterns and environmental risks of ringnet fishing along the Kenyan coast     

P Thoya  S Pérez-Jorge  GM Okemwa  H Mwamlavya  A Tuda  N Wambiji 《African Journal of Marine Science》2020,42(1):23-33

Ringnet fishing began in the early 20th century and is practised worldwide, mainly to target nearshore pelagic species. The method was introduced to Kenya’s coastal waters by migrant fishers from Tanzania. However, the impacts of this fishing gear remain poorly assessed. We assessed the spatial distribution of ringnet fishing effort and its possible effects on ecosystem components, such as coral reefs, marine megafauna and marine protected areas, on the south coast of Kenya. We tracked 89 ringnet fishing trips made from December 2015 to January 2016 and used spatial multicriteria analysis to determine hotspots of possible environmental risks. The results showed that habitat type and bathymetric profile influenced the spatial distribution of ringnet fishing effort. Mixed seagrass and coral habitats had the highest concentration of the effort. Most of the habitats in the study area were moderately exposed to the impacts of the ringnet fishery. The study identifies high-risk areas that require spatial measures to minimise possible environmental risks of the gear both to habitats and to endangered sea turtles.  相似文献   

Numerical Solution of Lock-Release Gravity Current with Viscous Self-Similar Regime     

张立柱李行伟  陈国谦 《中国海洋工程》2004,18(1):157-162

Lock-release gravity currents with a viscous self-similar regime are simulated by use of the renormalization group(RNG) k - ε model for Reynolds-stress closure. Besides the turbulent regime with initially a slumping phase of a conslant current front speed and later an inviseid self-similar phase of front speed decreasing as t^-1/3(where t is the time measured from release), the viseous self-similar regime is satisfactorily reproduced with front speed decreasing as t^-4/5,consistent with well known experimental observations.  相似文献   

Dynamic analysis of a vertical plate exposed to breaking wave impact     

M. Salih Kirkgoz  A. Kamil Tanrikulu  Cengiz Dündar 《Ocean Engineering》2004,31(13):2308-1635

From the experimental studies in recent years, it has become known that when a wave breaks directly on a vertical faced coastal structure, high magnitude impact pressures are produced. The theoretical and experimental studies show that the dynamic response of such structures under wave impact loading is closely dependent on the magnitude and duration of the load history. The dynamic analysis and design of a coastal structure can be succeeded provided the design load history for the wave impact is available. Since these types of data are very scarce, it is much more convenient to follow a method which is based on static analysis for the dynamic design procedure. Therefore, to facilitate the dynamic design of a vertical plate that is exposed to breaking wave impact, a multiplication factor called “dynamic magnification factor” is herein presented which is defined as the ratio of the maximum value of the dynamic response to that found by static analysis. The computational results of the present study show that the dynamic magnification factor is a useful ratio to transfer the results of static analysis to the dynamic design of a coastal plate for the maximum impact pressure conditions of p_max/γH₀≤18.  相似文献   

压力传感器的自动标定技术     

王莉娜  赵先龙  阮锐  严晓明 《海洋测绘》2007,27(4):78-80

针对压力测量设备生产和维护过程中,对关键部件压力传感器标定处于手工操作状态、效率低、操作人员不易掌控、标定结果处置复杂的现状,开发了针对压力传感器的自动标定技术。该技术将计算机控制、智能化、曲线拟合和误差分析引入到压力传感器的标定过程中,大幅度提高了标定的效率和可靠性。经此技术标定过的压力探头,在使用中具有互换性,减轻了数据后处理工作的难度。  相似文献   

海洋平台沉垫的波浪载荷试验研究   总被引：2，自引：0，他引：2  

姚美旺  张承懿  缪国平  季春群 《海洋工程》1997,(4)

本文通过对海洋平台沉垫的波浪载荷试验研究分析，着重研究了在规则波中平台沉垫总体波浪载荷和局部水动压力分布的情况，定性地考察了非线性影响、浅水影响的重要性，为今后波浪理论中粘性的引入，进而考虑粘性与波浪运动的非线性相互干扰提供实测依据  相似文献   

Prediction of impact pressure induced by breaking waves on vertical cylinders in random seas     

Michel K. Ochi  Chen-Han Tsai 《Applied Ocean Research》1984,6(3):157-165

This paper presents a method to statistically predict the magnitude of impact pressure (including extreme values) produced by deep water waves breaking on a circular cylinder representing a column of an ocean structure. Breaking waves defined here are not those whose tops are blown off by the wind but those whose breaking is associated with steepness. The probability density function of wave period associated with breaking waves is derived for a specified wave spectrum, and then converted to the probability density function of impact pressure. Impacts caused by two different breaking conditions are considered; one is the impact associated with waves breaking in close proximity to the column, the other is an impact caused by waves approaching the column after they have broken. As an example of the application of the present method, numerical computations are carried out for a wave spectrum obtained from measured data in the North Atlantic.  相似文献   

Fluid flow equations governing primary oil migration as a separate phase     

Ismail Ozkaya 《Marine and Petroleum Geology》1989,6(4)

A mathematical model of primary oil migration as a separate phase out of compacting shales is presented. During burial and oil generation, source rock porosity decreases and oil saturation increases until residual oil saturation is reached. At this stage oil is expelled out by capillary and excess fluid pressure gradients. The model is a system of differential equations which relate changes in oil and water saturation in time to water and oil flow out of the source rock during burial. An additional set of equations for periods of erosion of overburden are also provided. The equations can be numerically solved by finite difference method. If oil and water flow is to be simulated during oil generation, then at each time step, changes by oil generation in oil and water saturations and porosity must be calculated. The solution procedure is briefly outlined.  相似文献   

中国海岸湿地退化压力因素的综合分析   总被引：39，自引：1，他引：39       下载免费PDF全文

谷东起  赵晓涛  夏东兴 《海洋学报》2003,25(1):78-85

对我国海岸湿地类型、特点和分布进行了论述.通过分析指出围垦、城市与港口开发、污染、海岸侵蚀、油气资源开发、生物资源过度利用和海平面上升等环境压力因素是造成湿地退化的主要原因.综合矩阵因子分析表明,不同的海岸湿地类型所承受的环境压力和所遭受的环境退化程度是不同的,其中三角洲、海岸潟湖、砂质海岸、珊瑚礁、淤泥质海岸、滨岸沼泽和红树林等湿地类型遭受的环境压力最大,环境退化也最严重;指出了人为因素是造成海岸湿地环境退化的主要原因.  相似文献