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1.
Abstract

The high-frequency acoustic properties of seafloor sediments are very significant in seafloor study and underwater acoustic study field. In order to measure the sound speed and the attenuation for the small-scale sediment cores more accurately, this study developed a water coupled acoustic laboratory measurement system based on Richardson-Briggs technique. This method used the correlation comparison of waveforms received in sediment core and in identical reference tubes filled with water to measure sound speed and attenuation. The sound speed and attenuation of a clayey silt sediment sample were measured using the water coupled acoustic laboratory measurement system. This frequency dependence of the sound speed and attenuation showed that the clayey silt sediment has a weak positive sound speed dispersion, while the attenuation increases with a strong positive gradient within the measurement frequency range. This study also noted that the measured sound speed ratio match well with the empirical equations from literature. The measured attenuation factor data can fall in the Hamilton’s empirical prediction range.  相似文献   

2.
Abstract

The mechanical characteristics of calcareous silt interlayers play an important role in the stability of island-reef foundations. Direct shear and consolidation tests were performed to study the relationship between the mechanical properties and the physical parameters of calcareous silt. Based on the consolidation test results and analysis of the settling examples, different calculation methods for soil settling were compared. The results show the following. (1) The relationship between the cohesion and water content of calcareous silt can be represented by an M-shaped curve. The water contents corresponding to the two peaks of the M-type curve increase with increasing dry density. (2) When the dry density is less than 1.33?g/cm3, increasing the density significantly improves the internal friction angle of calcareous silts. When the dry density of the calcareous silt is greater than 1.33?g/cm3, the internal friction angle is affected by both the dry density and the water content. (3) The shear strength decreases when the water content exceeds the optimum level. (4) The compressive modulus of calcareous silt is larger than that of terrigenous silt. Specifically, it decreases with decreasing dry density and increasing water content. (5) The stepwise loading method should be used to estimate the soil settling before fill engineering construction.  相似文献   

3.
Abstract

Blast response of submerged pipelines has been a research focus in recent years. In this article, a three-dimensional numerical model is established to investigate dynamic response of pipelines due to underwater explosion. The u–p approximation is integrated into finite element method (FEM) to simulate pore water effect in the seabed. Numerical continuity between hydraulic pressure in the flow field and pore pressure in the marine sediment is guaranteed to realize the blast response of submerged pipelines in ocean environment. Both fluid–structure interaction (FSI) and pipeline–seabed interaction (PSI) have been considered in the proposed model simultaneously. A comprehensive parametric study is carried out after validation of the present model with test data from underground explosion and underwater explosion, respectively. The effect of embedment depth, TNT equivalent, stand-off distance, pipeline diameter, and pipeline thickness to blast response of the submerged pipelines is investigated based on numerical results. Variation of deformation patterns and stress distribution of the pipeline with various installation and structure parameters has been illustrated and discussed to facilitate engineering practice.  相似文献   

4.
Abstract

On the basis of the Atterberg indexes of various sediments collected in the Mediterranean Sea, we select two major parameters indicative of the mechanical behavior of marine soils: the sedimentary facies (i.e., mechanism of deposition expressed by silt content) and the clay mineral association characterized by smectite content in the fraction finer than 2 μm. Activity and real thixotropic ability appear to be particularly important parameters in marine engineering; better values are obtained by a double test operation in distilled and marine water.  相似文献   

5.
Abstract

This article deals with the effect of salinity variation on underwater wireless optical communication (UWOC). Effect of different concentration of salt on underwater optical communication has been carried out experimentally in terms of received power at different link lengths. Based on the analysis of experimental data, a mathematical model has been proposed to describe the saline water channel. A simulation study is performed for different data rates and link lengths. It is seen that with increased salinity the attenuation is higher and the UWOC system performance degrades with higher data rate and increased link length.  相似文献   

6.
为深入研究井喷和管道破损等海底事故后溢油在水下环境中的输移扩散过程，文章利用自制的组合式环形水槽（周长9.7 m、宽0.45 m、深1 m），以阿曼原油与消油剂混合物和淡水（含示踪剂）为模拟污染物，初步开展静水和动水环境中海底溢油浮射流的物理模拟实验，并应用基于拉格朗日积分方法的水下溢油浮射流模型进行数值模拟比较分析。研究结果表明:静水环境中，水下溢油浮射流主要沿喷口的垂直中心线向水面输移扩散；非均匀流动水环境中，横流速度越大，浮射流输移轨迹的弯曲程度越明显；数值模拟的浮射流轨迹总体上与实验观测结果符合较好；研究结果可为今后相关物理实验和数值模型的改进研究提供有益参考。  相似文献   

7.
珠江口伶仃洋滩槽发育演变影响因素的分析   总被引：4，自引：1，他引：4  
珠江口伶仃洋汇集了虎门、蕉门、洪奇沥、横门的来水来沙,这些水、沙进入伶仃洋后,在各种因素的综合作用下,不断地运移,造成今天的伶仃洋三滩两槽复杂的水下地形。  相似文献   

8.
为探究东海带鱼(Trichiurus lepturus)在低压核磁共振(LF-NMR)技术下的品质变化及水分迁移特性,以挥发性盐基氮(TVB-N)含量、pH、水分含量为指标,并分析NMR横向弛豫时间T2反演谱图和MRI成像,研究不同电场强度(DY1~DY4分别为0,2,2.5,3kV/m)对带鱼内部水分迁移及品质的影响。分析TVB-N数据发现,DY3(E=2.5kV/m)、DY4(E=3kV/m)在贮藏后期表现出更佳的保鲜优势。在0~40d贮藏期内,不同电场强度条件下的带鱼pH值均呈先降后升趋势。电场的添加能降低自由水的流动性,抑制微生物生长,减少带鱼体内水分流失。分析NMR横向弛豫时间T2反演谱图发现,T21、T22、T23峰面积均有不同程度减小,其中T22信号幅度变化最大,表明电场的添加能改变带鱼体内水分迁移路径,维持较高的水分含量,增加带鱼持水性和保水性。MRI成像图表明在贮藏期间,电场处理后带鱼水分保有率得到了提升,保鲜效果优于未施加电场带鱼,且电场强度越大,体外迁移水分越少。实验表明低压核磁共振(LF-NMR)技术对东海带鱼具有良好的保鲜效果,对低压核磁共振(LF-NMR)技术的保鲜应用提供一定的理论指导作用。<  相似文献   

9.
Intermittently closed and open lakes and lagoons (ICOLLs) are shallow barrier lakes which are intermittently connected to the sea and experience saline intrusions. Many ICOLLs are mechanically opened to prevent flooding of surrounding agricultural and urban land and to flush water of poor quality. In this study, the effects of modified opening regimes (frequency and duration of barrier openings and closures) on water quality and phytoplankton in two New Zealand ICOLLs were investigated over a number of opening/closure cycles. Water quality in Lake Ellesmere (Te Waihora) responded weakly to both opening and closing events, indicating that sea–ICOLL exchange did not markedly improve water quality. Conversely, water quality in Waituna Lagoon responded rapidly to barrier openings; water level decreased to near sea level within days of opening and subsequent seawater exchange resulted in rapid decreases in nitrate and chlorophyll a concentrations. The closure of Waituna Lagoon resulted in rapid rise in water level and a pulse of nitrate and phosphorus in the water column and phytoplankton chlorophyll a concentrations increased with increasing closed-period duration. Based on data on the underwater light climate and nutrient dynamics, phytoplankton in Lake Ellesmere was probably light-limited, whereas phytoplankton in Waituna Lagoon was rarely light-limited, and appeared to be predominately P-limited. The marked differences in responses of Lake Ellesmere and Waituna Lagoon to barrier openings and closures reflected differences in ICOLL water levels and morphological characteristics, which dictated the degree of tidal flushing when the barriers were open. The inter-ICOLL differences observed in this study indicate that unless the effects of ICOLL openings/closures on phytoplankton and nutrient dynamics are understood, changes to ICOLL opening regimes may have unintended consequences for the water quality and ecology of these systems.  相似文献   

10.
围填海工程施工过程导致海域悬浮物迅速增加,影响周围海洋生态系统,研究围填海工程悬浮泥沙的输移扩散规律对于区域生态环境质量及工程建设的综合生态影响评价具有重要的参考意义．针对湄洲湾峰尾围垦工程施工期悬浮泥沙可能造成的生态影响,对爆破挤淤（5．17t／s）和抛石挤淤（1．39kg／s）的悬沙源强进行了分析计算．在工程海区平面二维潮流场数学模型的基础上,采用二维对流扩散数学模型对施工范围内的模型网格点（40m×40m）进行了逐点计算,数值模拟结果表明,悬浮泥沙扩散范围和形态主要受潮流控制,工程施工联合影响下悬沙质量浓度大于10mg／dm3的全潮最大影响包络面积为5．848km2,施工9h后悬沙影响基本消失,为工程施工期环境管理提供了参考依据．施工悬浮泥沙的扩散整体表现为总悬沙质量浓度在离工程区较近的范围内较大,而距离越远质量浓度越接近自然状态的本底含沙量．施工悬浮泥沙对浮游生物、游泳生物和底栖生物等均会产生一定的影响,但随着施工结束而消失,不会对海洋生态产生长期的不利影响．  相似文献   

11.
Abstract

Due to the strong disintegration and water erosion of completely weathered granite, water and mud inrush disasters are apt to take place in this zone during underwater tunnel construction. The pore, compactness, seepage path length, fracture geometries and their interconnections for water and mud transfer are strongly influenced by confining pressure and waterproof-resistant slab safety thickness. In order to inspect the influence, a series of experiments based on a self-designed testing system and non-Darcy testing method were performed. The results indicated that the water and mud inrush evolution increased with the increase of confining pressure and decreased with the increase of safety thickness. In particular, the confining pressure mainly influences the initial evolution stage, and a critical safety thickness to prevent water and mud inrush is obtained. Besides, the non-Darcy testing method results shows that the water and mud inrush evolution affects the influence of non-Darcy flow. For example, while the safety thickness was smaller than the critical value, the evolution was large and unstable and its behavior transferred into nonlinear. In this case, the flow changed to non-Darcy flow.  相似文献   

12.
ABSTRACT

Phosphorus (P) stores in gravel-bed rivers are released for uptake by periphyton when pH levels exceed 8.5. The Tukituki River has low alkalinity water and frequently experiences periphyton blooms, and daytime pH?>?9 during summer low-flows. We measured dissolved reactive P (DRP) and EPC0, the water concentration of DRP at which no net release or sorption from the river bed occurs, in sediment samples from the Tukituki River subject to controlled pH levels before (2014) and after (2017) changes to two wastewater discharges that reduced P release to the river by 95%. DRP released from 2014 sediments at pH 8.5–10 were 30?±?10?mg/m3 above background (pH 8) whereas those released from 2017 sediments were 5?±?3?mg/m3 above background. EPC0 levels in 2014 and 2017 were 11?±?6 and 7?±?2?mg/m3, respectively. Field estimates of released DRP calculated from continuous pH and the Redfield equation suggested that most of the readily available DRP released from sediments at elevated pH is derived from material attached to recently deposited sediment. Subsequently, a reduction in wastewater inputs or agricultural runoff should reduce sediment DRP stores, and hence sediment fluxes, within a few years and mitigate periphyton blooms in addition to directly lowering water column concentrations.  相似文献   

13.
ABSTRACT

Reliable power supply, precise position determination and effective communication are the key requirements for strategic autonomous underwater vehicles (AUV) involved in long duration scientific missions, search operations and when operated as a swarm. The paper presents the challenging range of AUV developed for deep water, Polar and intervention applications; demanding technical requirements for strategic AUV; reliability modeling done on the lithium-ion batteries to identify the redundancy requirements for achieving near-zero failures; navigation model to estimate the achievable level of position accuracies using the state-of-the-art navigation system; limitations in underwater communication; and their importance in realizing vehicle autonomy and swarm intelligence. It is identified that a strategic grade Doppler velocity- aided inertial navigation system could provide position accuracies of about 0.5% of the distance travelled when navigated using sea bottom or ice reference, and a 38?kWh lithium-ion battery pack requires about 7% redundant battery capacity to achieve a failure probability of <?1% in a period of 1 year.  相似文献   

14.
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15.
A laboratory-based microcosm experiment was carried out to examine both the behavioral and antioxidant response of the clam Gomphina veneriformis under the conditions of 3 types of burial material(sand,silt,silt-sand mixture) with 3 burial depths(5 cm,15 cm,30 cm).The concentration of dissolved oxygen decreased significantly after 3 d of burial in all experimental groups.In silt and sand-silt mixture groups,the interstitial water quality became worsened with lower pH,and higher NH_4~+-N concentration,where clam mortality occurred simultaneously.However,clam samples in all sand groups and 5 cm,15 cm sand-silt mixture groups survived well for 8 d.Obviously fewer individuals left in the bottom sand in the 15 cm,30 cm silt groups and 30 cm sand-silt mixture groups than in the 5 cm groups.Therefore,it suggests that adding silt and increasing burial depth could stimulate the vertical movement of organisms and cause lethal effects.It was found that the burial depth was the key factor that influenced the activities of antioxidant enzymes,such as superoxide dismutase(SOD) and catalase(CAT).The SOD and CAT activities in the gills and hepatopancreases of organisms both showed significant upregulation in 30 cm burial depth after buried for 8 d.Higher enzyme activities were found in gills than in hepatopancreases,which indicated that the gills of the bivalve G.veneriformis were more susceptible to burial effects than hepatopancreases.Overall,this study shows that sediment burial could cause effects on the biological behavior and antioxidant enzyme activities.  相似文献   

16.
ABSTRACT

The use of suction caissons can reduce the development costs of offshore wind energy and has broad application prospects. However scour around marine foundations is inevitable, it gravely affects the stability of marine engineering. Therefore, there is an urgent need to study the weakening effects of scour on suction caisson. In this study, the variation trends of remaining soil parameters (the effective unit weight and the peak effective friction angle) after scour are examined with consideration of the dilatancy and stress history of sandy silt. It is found that the parameters of shallow soil change considerably after scour, and the larger the scour depth, the greater is the change in the parameters. However, the deep soil is less affected. On the basis of these findings, scour effects on the ultimate moment capacity of suction caisson are studied. The ultimate moment capacity is found to greatly reduce under scour, and its calculated value is larger than the actual value when the effects of dilatancy and stress history are ignored. To simplify calculation, it is feasible to replace the ultimate moment capacity when both dilatancy and stress history are considered with that when only dilatancy is considered.  相似文献   

17.
海底管道敷设过程中产生的悬浮泥沙会对工程海域的水质和海洋生物造成影响.建立了2D悬浮泥沙输移模型,结合水动力模型,对舟山市临城至虾峙岛、六横岛输配水工程中海底管线敷设引起的悬浮泥沙的输移规律进行模拟研究,预测悬浮泥沙的影响程度和范围,为海洋环境影响评价提供依据.计算结果表明:1号工段管道敷设对海水水质影响最大,2号工段...  相似文献   

18.
文章基于自制的组合式环形水槽（周长9.7 m、宽0.45 m、深1.0 m）,分别以阿曼原油及其消油剂混合物和淡水（含示踪剂）为模拟污染物,开展水下溢油的物理模拟实验,以浮射流输移轨迹、污染物扩散范围和油滴粒径分布为考察指标,研究横流环境和消油剂的使用对水下溢油输移扩散的影响。实验结果表明:在横流环境中,浮射流输移轨迹开始弯曲的高度随着流速的增加而降低;与淡水浮射流主要在水中输移扩散的情况不同,当污染物为原油时,大粒径油滴脱离浮射流主体并上浮至水面,导致扩散范围更大;消油剂的添加会使原油浮射流内部油滴的体积中值粒径变小,油滴粒径分布曲线向小尺寸方向偏移。实验结果可为后续的物理模拟实验和数值模拟研究提供参考。  相似文献   

19.
Abstract

Fault fracture zones have always been a key problem in the construction of submarine tunnels. To efficiently summarize the safety impact of different construction schemes on a submarine tunnel crossing a fault fracture, a theoretical model using numerical simulation has been established via the benching tunnelling construction method, three-step method, Center Diaphragm method (CD method), both sides heading method, Cross Diaphragm method (CRD method) and two kinds of supporting methods: pre-grouting and shotcreting. Numerical simulation studies on the excavation and support of submarine tunnels crossing fault fracture zones have been carried out. The research indicates: the fracture zone is the main area where sedimentation instability occurs; the CRD method has the lowest horizontal convergence under the support of the diaphragm; increasing the grouting strength is more effective in controlling the deformation of the surrounding rock than increasing the range of the pre-grouting and the thickness of the shotcrete in the initial support is increased, and its resulting effect is obvious. To optimize the construction scheme, we compared the settlement, horizontal convergence and surrounding rock stress of the tunnel according to the simulation results of different excavation support methods, which could provide theoretical guidance for better on-site construction techniques.  相似文献   

20.
城市淡水系统的富营养化风险是世界范围内普遍关注的问题。多种物理、生物和化学技术手段被应用到富营养化湖库的治理当中，以期抑制水体的富营养化程度和藻类生物量。经证实，在未有效降低营养盐来源的情况下，这些手段的效果有限。而在发展中国家，控制营养盐来源可能需要花费数十年的时间。本研究旨在分析某一高营养盐负荷的沿海水库的富营养化和藻类水华风险，以期确认通过水利调度来抑制水库富营养化状态的可行性。该案例水库为位于长江口的青草沙水库。该水库2009至2012年期间的库内五个点位的水质数据被用于进行案例分析。水质指标包括水温、透明度、溶解氧、总氮、总磷和浮游植物叶绿素a。该水库的建设期为2009年4月至2010年10月，期间水库未曾与长江口发生水体交换。该水库的试运营期为2010年10月至2011年1月，正式运营期为2011年1月至今。在运营期间，库内与长江口的水体交换逐步上升。综合营养状态指数（TLI）被用于评估该水库的营养状态变化情况，该指数是通过数个代表性水质指标计算得到。库区的TLI指数峰值在2009年夏季可达51，在2011年夏季可达55，超过TLI指数的富营养化阈值50。TLI的谷值32出现在2010年的夏季。水质观测期的其他时段的TLI指数均可保持在50以下。以上分析结果表明：水库在2009年和2011年夏季由于过量的营养盐负荷和藻类水华迅速恶化到富营养化状态。水库在2010年和2012年均未出现富营养化状态和藻类水华，这是由于2010年期间水库缺少营养盐输入，2012年期间水库调度充分地置换了库区水体。库区水质指标的时空变化均通过文中的观测资料和数据分析进行展示。经分析表明，通过潮汐涨落来充分置换库区水体的水库调度手段是一个极为经济有效的抑制高营养盐水体富营养化和藻类水华的工程手段。  相似文献   

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