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1.
Ben Belgacem  I.  Cheikh  L.  Barhoumi  E. M.  Khan  W.  Ben Salem  W. 《中国海洋工程》2019,33(1):114-126
In this paper, we present a numerical simulation of a water jet impacting a new aeronautical material Ti555-03 plate.The Computational Fluid Dynamics(CFD) behavior of the jet is investigated using a FV(Finite Volume) method.The Fluid–Structure Interaction(FSI) is studied using a coupled SPH(Smoothed Particle Hydrodynamics)-FE(Finite Element) method. The jets hit the metal sheet with an initial velocity 500 m/s. Two configurations which differ from each other by the position(angle of inclination) of the plate relatively to the axis of revolution of the jet inlet are investigated in this study. The objective of this study is to predict the impact of the fluid produced at high pressure and high speed especially at the first moment of impact. Numerical simulations are carried out under ABAQUS. We have shown in this study that the inclination of the titanium alloy plate by 45° stimulates the phenomenon of recirculation of water. This affects the velocity profile, turbulence and boundary layers in the impact zone. The stagnation zone and the phenomenon of water recirculation are strongly influenced by the slope of the plate which gives a pressure gradient and displacement very important between the two configurations. Fluctuations of physical variables(displacement and pressure) prove the need for a noise and vibratory study. These predictions will subsequently be used for the modeling of the problem of an orthogonal cut in a high-speed machining process assisted by high-pressure water jet.  相似文献   

2.
The development of embryos and larvae of Babyloniaformosae habei living along the southeast coast of China is observed under laboratory conditions. The egg masses are laid by females on hard substrate at night and each capsule contains 100-500 eggs. Each egg is 250-280 mm in diameter. The fast two cleavages of the embryo are meridional and equal, and a polar lobe is produced. Larval kidney, which only consists of a single cell, appears during the gastrula stage on each side of the embryo. The right tentacle develops prior to the left one. At 25-27 ℃, an intracapsulate veliger stage is reached about 4.5 d after deposition. The larvae hatch on the fifth day as swimming veligers with a shell length of 360 -500 mm. The newly hatched larva can ingest suspended algal cells from the water column and remains in the pelagic stage for 8-10 d. The newly settled juveniles are 900-1 200 mm in shell length.  相似文献   

3.
On cruises 25 (2007) and 28 (2011) of the R/V Akademik Nikolai Strakhov in the northern part of the Barents Sea, the Geological Institute, Russian Academy of Sciences, conducted comprehensive research on the bottom relief and upper part of the sedimentary cover profile under the auspices of the International Polar Year program. One of the instrument components was the SeaBat 8111 shallow-water multibeam echo sounder, which can map the acoustic field similarly to a side scan sonar, which records the response both from the bottom and from the water column. In the operations area, intense sound scattering objects produced by the discharge of deep fluid flows are detected in the water column. The sound scattering objects and pockmarks in the bottom relief are related to anomalies in hydrocarbon gas concentrations in bottom sediments. The sound scattering objects are localized over Triassic sequences outcropping from the bottom. The most intense degassing processes manifest themselves near the contact of the Triassic sequences and Jurassic clay deposits, as well as over deep depressions in a field of Bouguer anomalies related to the basement of the Jurassic–Cretaceous rift system  相似文献   

4.
Line integral convolution(LIC)is a useful visualization technique for a vector field.However,the output image produced by LIC has many problems in a marine vector field.We focus on the visual quality improvement when LIC is applied in the ocean steady and unsteady flow field in the following aspects.When a white noise is used as the input in a steady flow field,interpolation is used to turn the discrete white noise into continuous white noise to solve the problem of discontinuity.The"cross"high-pass filtering is used to enhance the textures of streamlines to be more concentrated and continuity strengthened for each streamline.When a sparse noise is used as the input in a steady flow field,we change the directions of background sparse noise according to the directions of vector field to make the streamlines clearer and brighter.In addition,we provide a random initial phase for every streamline to avoid the pulsation effect during animation.The velocities of vector field are encoded in the speed of the same length streamlines so that the running speed of streamlines can express flow rate.Meanwhile,to solve the problem of obvious boundaries when stitching image,we change the streamline tracking constraints.When a white noise is used as an input in an unsteady flow field,double value scattering is used to enhance the contrast of streamlines;moreover,the"cross"high-pass filtering is also adopt instead of two-dimensional high-pass filtering.Finally,we apply the above methods to a case of the surface wave field in typhoon condition.Our experimental results show that applying the methods can generate high-quality wave images and animations.Therefore,it is helpful to understand and study waves in typhoon condition to avoid the potential harm of the waves to people's lives and property.  相似文献   

5.
We investigated the spatial distribution of glycerol dialkyl glycerol tetraethers (GDGTs), alkenones, and polyunsaturated fatty acids in particulate organic matter collected at four sites along a depth transect from the continental shelf to the Okinawa Trough in the East China Sea during the spring bloom in 2008. The maximum alkenone concentration appeared in the top 25?m at all sites and the $ U_{37}^{{{\text{K}}'}} $ values were consistent with in situ water temperatures in the depth interval, suggesting that the alkenones were produced mainly in surface water. At the slope and shelf sites, GDGTs in the water column showed a concentration maximum at 74?C99?m depth, and the $ {\text{TEX}}_{86}^{\text{H}} $ agreed with in situ water temperatures, suggesting the in situ production of GDGTs in the depth interval. The low-salinity surface water above 20?m depth was characterized by low GDGT concentrations and low $ {\text{TEX}}_{86}^{\text{L}} $ -based temperatures, suggesting either the production of GDGTs in winter season or the lateral advection of GDGTs by an eastward current. At the slope and Okinawa Trough sites, TEX86-based temperatures were nearly constant in the water column deeper than 300?m and corresponded to temperatures at the surface and near-surface waters rather than in situ temperatures. This observation is consistent with a hypothesis that Thaumarchaeota cells produced in surface waters are delivered to deeper water and also indicates that the residence time of suspended GDGTs in the deep-water column is large enough to mix the GDGTs produced in different seasons.  相似文献   

6.
Sources of very low frequency (0.01 to 1.0 Hz) ambient seismic noise in the shallow (<100 m) water continental margin sediments are investigated using Ocean Bottom Seismometers (OBS). The predominant seismic motions are found to be due to surface gravity (water) waves and water-sediment interface waves. Actual experimental measurements of seabed acceleration and hydrodynamic pressure are given, including side by side comparisons between buried and plate-mounted OBS units. OBS-sediment resonant effects are found to be negligible at the low frequencies under investigation. Wherever there exists relative motion between the seabed and the water, however, an exposed OBS is subject to added mass forces that cause it to move with the water rather than the sediments. Calculations based on measured seabed motions show that a neutral density, buried seismometer has superior sediment coupling charactersitics to any exposed OBS design.  相似文献   

7.
Disequilibrium between 234Th and 238U in water column profiles has been used to estimate the settling flux of Th (and, by proxy, of particulate organic carbon); yet potentially major non-steady-state influences on 234Th profiles are often not able to be considered in estimations of flux. We have compared temporal series of 234Th distributions in the upper water column at both coastal and deep-water sites in the northwestern Mediterranean Sea to coeval sediment trap records at the same sites. We have used sediment trap records of 234Th fluxes to predict temporal changes in water column 234Th deficits and have compared the predicted deficits to those measured to determine whether the time-evolution of the two coincide. At the coastal site (327 m water depth), trends in the two estimates of water column 234Th deficits are in fairly close agreement over the 1-month deployment during the spring bloom in 1999. In contrast, the pattern of water column 234Th deficits is poorly predicted by sediment trap records at the deep-water site (DYFAMED, 2300 m water depth) in both 2003 and 2005. In particular, the transition from a mesotrophic to an oligotrophic system, clearly seen in trap fluxes, is not evident in water column 234Th profiles, which show high-frequency variability. Allowing trapping efficiencies to vary from 100% does not reconcile the differences between trap and water column deficit observations; we conclude that substantial lateral and vertical advective influences must be invoked to account for the differences.Advective influences are potentially greater on 234Th fluxes derived from water column deficits relative to those obtained from traps because the calculation of deficits in open-ocean settings is dominated by the magnitude of the “dissolved” 234Th fraction. For observed current velocities of 5–20 cm s−1, in one radioactive mean-life of 234Th, the water column at the DYFAMED site can reflect 234Th scavenging produced tens to hundreds of kilometers away. In contrast, most of the 234Th flux collected in shallow sediment traps at the DFYFAMED site was in the fraction settling >200 m d−1; in effect the sediment trap can integrate the 234Th flux over distances 40-fold less than water column 234Th distributions. In some sense, sediment trap and water column sampling for 234Th provide complementary pictures of 234Th export. However, because the two methods can be dominated by different processes and are subject to different biases, their comparison must be treated with caution.  相似文献   

8.
台湾海峡中、北部海域春、夏季水团分析   总被引：13，自引：2，他引：13  
本文依据1983,1984,1987,1988几年的有关资料,利用“对应分析法”对台湾海峡中、北部海域春、夏季(5—8月)的水团及有关问题进行了分析。结果表明:(1)5—8月间该海域存在两种水团分布类型,其中5月属冬季型,全海域存在浙闽沿岸水和海峡暖流水两个水团;6—8月属夏季型,全海域均为海峡暖流水盘踞,按温度不同,它又分为上层水和深层水两部分。(2)浙闽沿岸水具低温、低盐、高溶解氧特征,均一性较差,年际变异较大;海峡暖流水以高盐为主要特征,温、盐度和溶解氧分布较均匀,且诸特征相对稳定。(3)海峡东、西两侧均存在上升流现象,西侧的上升流出现于6—8月,中心在海潭岛附近;东侧的上升流7月见于澎湖群岛北方海区。(4)6—8月间,海峡暖流深层水(核心)主要沿海峡偏西一侧北上,而不是紧靠东侧径直向北。  相似文献   

9.
The Wadden Sea (North Sea, Europe) is a shallow coastal sea with high benthic and pelagic primary production rates. To date, no studies have been carried out in the Wadden Sea that were specifically designed to study the relation between pelagic respiration and production by comparable methods. Because previous studies have suggested that the import of primary-produced pelagic organic matter is important for benthic Wadden Sea carbon budgets, we hypothesised that on an annual average the northern Wadden Sea water column is autotrophic. To test this hypothesis, we studied annual dynamics of primary production and respiration at a pelagic station in a shallow tidal basin (List Tidal Basin, northern Wadden Sea). Since water depth strongly influences production estimates, we calculated primary production rates per unit area in two ways: on the basis of the mean water depth (2.7 m) and on the basis of 1 m depth intervals and their respective spatial extent in the List Tidal Basin. The latter more precise estimate yielded an annual primary production of 146 g C m− 2 y− 1. Estimates based on the mean water depth resulted in a 40% higher annual rate of 204 g C m− 2 y− 1. The total annual pelagic respiration was 50 g C m− 2 y− 1. The P/R ratio varied between seasons: from February to October the water column was autotrophic, with the highest P/R ratio of 4–5 during the diatom spring bloom in April/May. In autumn and winter the water column was heterotrophic. On an annual average, the water column of the List Tidal Basin was autotrophic (P/R 3). We suggest that a large fraction of the pelagic produced organic matter was respired locally in the sediment.  相似文献   

10.
深水半潜式平台系泊锚链的倾角变化是评价平台系泊状态与锚链受力的重要指标,是半潜式平台重要的监测内容。目前,深水锚链的测量主要是采用自容式的传感器,针对其水下长时间测量的应用特点,要求它的设计必须具有低功耗、高可靠性、大存储量、体积小、防水耐压等指标。根据我国南海流花平台的锚链监测需要,设计与制作了专用的水下自容式倾角传感器,并在实际应用中进行了检验。  相似文献   

11.
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   

12.
An inversion method using a towed system consisting of a source and two receivers is presented. High-frequency chirp signals that have been emitted from the source are received after multiple penetrations and reflections from the shallow water sub-bottom structure and are processed for geoacoustical parameter estimation. The data are processed such that a good resolution and robustness is achieved via matched filtering, which requires information about the source signal. The inversion is formulated as an optimization problem, which maximizes the cost function defined as a normalized correlation between the measured and modeled signals directly in the time domain. The very fast simulated reannealing optimization method is applied to the global search problem. The modeled time signal is obtained using a ray approach. An experiment was carried out in the Mediterranean Sea using a towed source and receiver system. The inversion method is applied to the experimental data and results are found to be consistent with previous frequency-domain analyses using measurements from a towed horizontal array of receivers and measurements on a vertical array.  相似文献   

13.
Passive sonar systems that localize broadband sources of acoustic energy estimate the difference in arrival times (or time delays) of an acoustic wavefront at spatially separated hydrophones, The output amplitudes from a given pair of hydrophones are cross-correlated, and an estimate of the time delay is given by the time lag that maximizes the cross correlation function. Often the time-delay estimates are corrupted by the presence of noise. By replacing each of the omnidirectional hydrophones with an array of hydrophones, and then cross-correlating the beamformed outputs of the arrays, the author shows that the effect of noise on the time-delay estimation process is reduced greatly. Both conventional and adaptive beamforming methods are implemented in the frequency domain and the advantages of array beamforming (prior to cross-correlation) are highlighted using both simulated and real noise-field data. Further improvement in the performance of the broadband cross-correlation processor occurs when various prefiltering algorithms are invoked  相似文献   

14.
Microbial community composition varies based on seasonal dynamics (summer: strongly stratified water column; autumn: weakly stratified water column; winter: vertically homogeneous water column) and vertical distributions (surface, middle, and bottom depths) in the Gadeok Channel, which is the primary passage to exchange waters and materials between the Jinhae-Masan Bay and the South Sea waters. The microbial community composition was analyzed from June to December 2016 using 16S rRNA gene sequencing. The community was dominated by the phyla Proteobacteria (45%), Bacteroidetes (18%), Cyanobacteria (15%), Verrucomicrobia (6%), and Actinobacteria (6%). Alphaproteobacteria (29%) was the most abundant microbial class, followed by Flavobacteria (15%) and Gammaproteobacteria (15%) in all samples. The composition of the microbial communities was found to vary vertically and seasonally. The orders Flavobacteriales and Stramenopiles showed opposing seasonal patterns; Flavobacteriales was more abundant in August and December while Stramenopiles showed high abundance in June and October at all depths. The genus Synechococcus reached extremely high abundance (14%) in the June surface water column, but was much less abundant in December water columns. Clustering analysis showed that there was a difference in the microbial community composition pattern between the strongly stratified season and well-mixed season. These results indicate that the seasonal dynamics of physicochemical and hydrologic conditions throughout the water column are important parameters in shaping the microbial community composition in the Gadeok Channel.  相似文献   

15.
The multistreamer Side-Looking Seismic system presented in this paper makes a sonograph of uncovered or buried crustal topography, thus revealing the structural fabric of the oceanic basement, even when this is covered with a sedimentary layer. Major elements of the system are an airgun as a sound source, five single-channel parallel streamers and two minicomputers for signal capture and processing.The system is used simultaneously for enhanced single-channel seismic profiling and for side-looking seismics. A vertical section with an improved signal-to-noise ratio and a suppression of side-echoes is produced on a digital seismic recorder. Primary side-looking seismic output in the form of 5 profiles with different angles of incidence is obtained within 10 seconds. This part of the processing can be done in real time.In sediment-covered areas the low frequencies used cause the slanted profiles (the side beams in the primary output) to be side-looking sonar images of buried topography. The projection process yielding final side-looking output corrects for slant range deformation caused by the water column and, if necessary, for deformation caused by refraction within the sedimentary column. The result approaches a conformal map of the structure of the traversed basement. Swath width is mainly determined by water depth and refraction effects in the sediment. In Madeira abyssal plain a swath width of 8000 m was attained in a water depth of 5000 m.Within the swath, oceanic basement structures are recognized in the form of elongate more or less parallel reflectors. They are interpreted as buried spreading topography. The lack of side-echoes within fracture zones combined with typical wall signatures can be used to trace fracture zones. These features are demonstrated for an area in Madeira abyssal plain.  相似文献   

16.
Wave direction has for the first time been consistently, accurately and unambiguously evaluated from array measurements using the phase/time/path difference (PTPD) methods of Esteva in case of polygonal arrays and Borgman in case of linear arrays. We have used time series measurements of water surface elevation at a 15-gauge polygonal array, in 8 m water depth, operational at the CERC's Field Research Facility at Duck, North Carolina, USA. Two modifications have been made in the methodology. One modification is that we use the true phase instead of the apparent phase, the other modification being that estimates of wave direction are registered only if the relevant gauges in the array are coherent at 0.01 significance level. PTPD methods assume that in a spectral frequency band the waves approach from a single direction, and are simple, expedient and provide redundant estimates of wave direction. Using Esteva's method with the above modifications, we found that at Duck: (i) the directions of swell and surf beat, when energetic swell is present, conform to the schematic diagram of surf beat generation given by Herbers et al., (ii) surf beat of remote origin occurs when the significant wave height, Hmo, falls below 0.41 m, (iii) the surf beat of remote origin is not normally incident at the shore contrary to Herbers et al. In fact we found that the surf beat of remote origin is incident at angles in excess of 45° with respect to the shore normal, and (iv) the surf beat of remote origin is largely trans-oceanic in origin.  相似文献   

17.
Characteristics of stationary Rossby-waves are investigated by use of equations expressing conservation of potential vorticity for a quasi-geostrophic two-layer flow of an incompressible inviscid fluid on a beta-plane. A two-dimensional problem is discussed; the basic flow is directing eastward without horizontal shear, and the stationary Rossby-waves are produced by a two-dimensional bump extending in the north-south direction which is located on a sloping bottom with a constant north-south gradient.When the slope is steep, stream-lines are scarcely displaced being influenced by the bump. When the bottom has no north-south inclination, however, there is a case where group velocity of Rossby-waves produced by the bump directs westward and the stream-lines meander sinusoidally at the west of the bump. This phenomenon is called upstream influence. These two special cases have a possibility to explain two different mean paths for the Kuroshio namely, the path along the continental slope and the path with a stationary meander at the west of the Izu-Ogasawara Ridge.  相似文献   

18.
A method has been developed to measure water column integrated primary production (PPint) in the water column using photosynthesis-irradiance relations for surface phytoplankton, the vertical profile of chlorophyll a concentration, and the underwater light intensity. Good correlation has been found for the results calculated with this method and light dependences in situ. The advantages of this method are the independence of PPint calculation from CTD profiling and water sampling, and thus optimization (reduction) of the station working time.  相似文献   

19.
Phosphorus dynamics in Tokyo Bay waters were investigated along with other oceanographic variables. Seasonal variations of dissolved inorganic phosphorus (DIP) and particulate phosphorus (PP) are inversely correlated with each other, and reflect variation in biological activity. A high concentration of PP in summer surface waters is caused by high primary production. The PP settled in the deeper layer is decomposed, and orthophosphate is regenerated within the water column and in sediments. Even during summer stratification period, the regenerated orthophosphate is occasionally advected upward by wind-induced water mixing and contributes to phytoplankton growth in the upper layer. Some dissolved organic phosphorus is producedin situ from PP, but it may be rapidly decomposed in the water column. The ratios of Cchlorophylla and CN in particulate matter suggest that phytoplankton in the summer surface waters of Tokyo Bay are limited neither by nitrogen nor by phosphorus. The PN ratio in particulate matter varies substantially but it is positively correlated with the ambient concentration of DIP. Phytoplankton take up and store phosphorus within their cells when ambient DIP exceeds their demand. An abundance of total phosphorus in the summer water column can be attributed to increased discharge of river waters, although enhanced release of orthophosphate from anoxic sediments cannot be discounted.  相似文献   

20.
Field sampling of the dissolved and particulate material field downstream of a large volume bucket dredge operating in the lower Thames River estuary near New London, Connecticut, was conducted in order to examine the magnitude and character of the dredge-induced resuspension. These data indicate that large amounts of dissolved phosphate, ammonia, silica, manganese, copper and particulate materials are released into the water column, whereas cadmium concentrations were unaffected. Concentrations in the vicinity of the dredge exceed background levels by two to nine times for the dissolved materials and by two orders of magnitude for particulates. During the ebb cycle, downstream material concentrations decrease rapidly to background within approximately 180 m for dissolved materials and 700 m for particulates.Two mechanisms were found to control the distribution of materials downstream of the dredge: (a) physical transport, including advection, turbulent mixing and diffusion, and (b) geochemical processes (i.e. adsorption, desorption, precipitation, dissolution, etc.). The concentration of dissolved materials downstream of the dredge decrease at a first order exponential rate. The downstream distribution of the dissolved ammonia and silica was found to be consistent with the reactivity experiments (Figure 8) which predicted that PO4 would undergo a decay in concentration in the presence of suspended sediments. Absorption of phosphate onto suspended sediments and gravitational settling of the suspended particulates were the processes. Manganese and copper underwent a dual transformation which involved an initial dissolution, followed by flocculation and possible coprecipitation as MnO2. Cadmium concentrations in the water column were unaffected by the dredging process due to low pore water concentrations.The observed spatial distribution indicates that dredge-induced injection of dissolved and particulate materials is primarily a near field phenomenon producing relatively minor variations as compared to those caused by naturally occurring storm events. These latter systems have been shown (Tramontano, 1978; Bohlen et al., 1979) to produce estuary-wide variations in suspended materials, PO4 and NH4 concentrations increasing the mass of materials in suspension by at least a factor of two. This increase in total suspended load, PO4 and NH4, is nearly an order of magnitude larger than that produced by the dredge.  相似文献   

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