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1.
Sound velocity in each type of seafloor sediment from the South China Sea varies with the development of strain in the controlled stress-strain course. Experiments show that there may exist three cases for the maximum sound velocity: (1) it appears at the stress peak; (2) it appears in the phase of no load; and (3) it appears at the end of the strain course. These results are related to physical-mechanical properties and structure of sediments. 相似文献
2.
在轴向应力-应变下海底沉积物声速及其变化 总被引：2，自引：0，他引：2
对南海南部海域海底浅表层沉积物短柱状样进行轴向应力-应变/声学测量,结果表明沉积物纵波声速有三种不同的变化结果:(1)声速从应变过程开始随应力-应变曲线变化,在最大应力时声速同时也是最大值,结束时可能高于或低于开始时的声速;(2)声速从应变过程开始逐渐减小,结束时是最小值;(3)声速从应变过程开始逐渐增大,最大值出现在结束时.这些结果与海底浅表层沉积物的物理力学性质、颗粒接触状态、颗粒的微结构等特征有关.研究结果可为深入认识南海南部各种海底沉积物作为承载界面的可靠性、声遥测遥感海底沉积物的工程力学性质等科学目的提供理论依据. 相似文献
3.
4.
本文阐述了对海底沉积物样品在应力-应变过程中进行同步声学测量的实验工具和方法,分析了采自南海45个站位的海底沉积物样品的实验数据资料,结果表明,沉积物颗粒越粗、孔隙越小、无侧限抗压强度越大,声速越高。沉积物样品在受力应变过程中,声速具有明显的随应力而变化的特征。进一步探讨了不同应变阶段沉积物的声学特征以及应力所导致沉积物微结构变化对其声速的影响过程,这一研究将在石油地质测井和海底工程基底稳定性评价等方面具有重要的应用意义。 相似文献
5.
对南海某海域深度100～400 m的海底浅层（约2 m埋深范围）沉积物柱状样在接近海底水压力下进行三轴应变-声学同步测量,结果表明沉积物纵波声速有两个特征:（1）从应变过程开始到结束,沉积物纵波声速不断变化;（2）平均声速随着平均静弹性模量的增加,由大变小又由小变大,存在声速最小值。这些结果与海底浅表层沉积物的物理力学性质、围压、颗粒的结合状态改变有关。此外,沉积物动弹性模量和孔隙度呈良好的负相关性,这与孔隙度增大含水量增大有关;动弹性模量是静弹性模量的10～100倍,这主要与三轴应变试验的应变数量级与声波振动产生的应变数量级的差异大有关。采用本论文实验测量的数据分别建立了双复合参数-声速和孔隙度-声速经验公式,分析结果表明双复合参数-声速公式声速预报误差约是孔隙度-声速公式的1/4,表明双复合参数-声速公式更加有效。 相似文献
6.
Michael L. Peterson Joan Fabres Stuart G. Wakeham Cindy Lee Ivn J. Alonso Juan Carlos Miquel 《Deep Sea Research Part II: Topical Studies in Oceanography》2009,56(18):1547-1557
Further development of the large, surface-tethered sediment trap (NetTrap) employed as part of the MedFlux program is described whereby the large collection capacity of the NetTrap is combined with an Indented Rotating Sphere/Sample Carousel (IRSC) sediment trap (IRSC–NT). This trap is capable of collecting particle flux either in a time series or settling velocity mode; settling velocity mode allows the collection of particles that fall within discrete settling velocity intervals. During short field deployments in the Mediterranean Sea the IRSC–NT configured in the settling velocity mode successfully collected unpoisoned samples for chemical and microbiological experiments. In addition to the development of the IRSC–NT, particle-settling behavior above and below the swimmer-excluding IRS valve was tested during on-deck experiments using a specially constructed water-tight trap. Chemical analyses of settling materials (published elsewhere) suggested that separation of particles by settling velocity was achieved. However, due to the motion of the ship, it was not possible to directly measure particle-settling velocities within the trap. Particle release from the IRS did not bias the apparent settling velocity spectrum. Rotation of the IRS did not engender turbulence at the surface of the sphere or within the skewed funnel below. Tests of different ball designs over the course of the MedFlux program showed that a “ridge and saddle” pattern was optimal for efficiently transferring particles under the IRS seal while still reducing swimmer entrance to the collection funnel. The large size of the IRSC–NT did not prevent it from drifting effectively with the current. Several modifications of the present design are proposed that should improve the accuracy of the settling velocity measurements. 相似文献
7.
Gravity installed anchors (GIAs) are released from a height of 30–150 m above the seabed, achieving velocities up to 19–35 m/s at the seabed, and embed to depths of 1.0–2.4 times the anchor length. Challenges associated with GIAs include the prediction of anchor initial embedment depth, which determines the holding capacity of the anchor. Based on the coupled Eulerian–Lagrangian approach, a numerical framework is proposed in this paper to predict the embedment depth of GIAs, considering the effects of soil strain rate, soil strain-softening and hydrodynamic drag (modeled using a concentrated force), with the anchor-soil friction described appropriately. GIAs are influenced by the hydrodynamic drag before penetrating into the soil completely, hence the anchor accelerates less than the previous investigations in shallow penetration, even decelerates directly at the terminal impact velocity. The hydrodynamic drag has more influence on OMNI-Max anchors (with an error of ∼4.5%) than torpedo anchors, and the effect becomes more significant with increasing impact velocity. An extensive parametric study is carried out by varying the impact velocity, strain rate and strain-softening parameters, frictional coefficient, and soil undrained shear strength. It is concluded that the dominant factor affecting the penetration is the soil undrained shear strength, then are the impact velocity, strain rate dependency and frictional coefficient, and the minimal is the strain-softening of soil. In addition, although the strain rate dependency is partly compensated by the softening, the anchor embedment depth accounting for the effects of strain rate and strain-softening is lower than that for ideal Tresca soil. Strain rate dependency dominates the combined effects of strain rate and strain-softening in the dynamic installation of GIAs, on which should pay more attention, especially for the calibration of the related parameters and the measured solutions. In the end, the theoretical model based on the bearing resistance method is extended by accounting for the hydrodynamic drag effect. 相似文献
8.
悬跨海底电缆作为细长柔性结构,在静力平衡状态下具有一定的垂度,在水流作用下的涡激振动特性与海底管线和海洋立管等结构也有很大的不同,其振动模态受垂跨比影响很大。通过物理模型试验开展了不同垂跨比下悬跨海缆的涡激振动和疲劳损伤特性研究。试验模型按照水弹性相似准则设计,试验中测量了不同流速下海缆模型产生涡激振动时的应变历时数据,采用模态分析法获得了模型涡激振动时的振动模态和振幅。分析了不同流速下海缆模型的振动模态、应变和疲劳损伤的变化和分布特征。试验结果表明：垂跨比显著影响了海缆的涡激振动模态和应变幅值大小。在本试验流速范围内,对一定长度的悬跨海缆模型,当垂跨比较大时,随着流速的增大,模型涡激振动的主响应振动依次出现反对称1阶和对称1阶模态;当垂跨比较小时,模型涡激振动的主响应模态依次出现反对称1阶和对称2阶模态。当涡激振动主响应模态为反对称1阶时,疲劳损伤最大值达到0. 1~0.7。 相似文献
9.
This paper presents a predictive model for undrained penetration of cylinders into soft seafloor soils. The penetration depth will depend on the velocity of the cylinder as it touches down at the seafloor, and the net deceleration of the cylinder as it is acted on by forces of self-weight, soil buoyancy, and soil-shearing resistance. The soil-shearing resistance force increases as a function of penetration depth and, due to the dependence of undrained shear strength on strain rate, penetration velocity. This paper presents finite element (FE) simulations that quantify both effects and form the basis of a simplified soil-resisting force model. Strain-rate effects are modeled within a framework of rate-dependent plasticity, with shearing resistance increasing semilogarithmically with increasing strain rate above a certain threshold strain rate. With all forces acting on the cylinder, estimated penetration depths are predicted from simple equations of motion for a single particle. Comparisons to laboratory tests involving penetration of cylinders into soft reconstituted marine clay show reasonable agreement between model predictions and measurements. 相似文献
10.
A P - vector method is optimized using the variational data assimilation technique(VDAT). The absolute geostrophic velocity fields in the vicinity of the Luzon Strait (LS) are calculated, the spatial structures and seasonal variations of the absolute geostrophic velocity field are investigated. Our results show that the Kuroshio enters the South China Sea (SCS) in the south and middle of the Luzon Strait and flows out in the north, so the Kuroshio makes a slight clockwise curve in the Luzon Strait, and the curve is strong in winter and weak in summer. During the winter, a westward current appears in the surface, and locates at the west of the Luzon Strait. It is the north part of a cyclonic gyre which exits in the northeast of the SCS; an anti-cyclonic gyre occurs on the intermediate level, and it exits in the northeast of the SCS, and an eastward current exits in the southeast of the anti-cyclonic gyre. 相似文献
11.
Vertical Variations of Core Sound Velocity: Evidence of Paleooceanographic History Since the Pleistocene Epoch 总被引：1，自引：0，他引：1
The vertical variations in the borehole core sound velocity (Cp) of the submarine sediments are related to the events of marine transgression and regression in the geologic history. This article establishes the vertical variation of Cp curve for the borehole sound velocity in the northern South China Sea continental shelf and the East China Sea continental shelf, thus providing evidence for revealing at least (3) sedimentary cycle events of marine transgression and regression occurring in the west Pacific marginal sea since the Pleistocene Epoch. The sound velocity of marine sediments brought in the course of marine transgression is lower (1450-1510 m/s) while that of continental sediments formed in the course of marine regression is higher (1650-1720 m/s). 相似文献
12.
Stokes' expansion is applied to the internal waves of finite amplitude, which propagate on the interface between two layers of infinite thickness. Stream function, wave profile, phase velocity and mass transport velocity are given in the fifth order approximation. It is shown that (a) phase velocity increases with increase of wave steepness, (b) mass transport appears in the direction of the wave propagation in both layers as in the case of the surface waves, and (c) when the density difference is very small, the wave profile is flattened not only at the troughs but also at the crests. 相似文献
13.
Yukio Oonishi 《Journal of Oceanography》1978,34(4):140-159
Characteristics of the tidal residual flow, the steady current induced in the tidal current system, are studied by a numerical method. The model basin has the same topography as that studied byYanagi (1976) and byOonishi (1977) where only the horizontal motion of the residual flow is concerned. In this study, the effect of the vertical motion is investigated as it is associated with the tidal residual flow. To this end, the bottom friction omitted in the previous study (Oonishi, 1977) is included and a two-leveled model is adopted.The first two experiments exclude the earth's rotation and the buoyancy effect on the flow. The results are as follows. The horizontal flow pattern is essentially the same as that obtained in the previous Oonishi study. The bottom friction results in the reduction of the velocity of the residual flow especially in the bottom level. An important result is that vertical velocity is as strong as the horizontal velocity multiplied by the scale ratio and that it remains even in the time-average. Upwelling appears at the center of the residual circulation. This upwelling explains Yanagi's observation in the hydraulic model that the sediment is swept by the flow and accumulates horizontally in the area at the bottom below the center of the residual circulation. The distribution of a tracer, which is simultaneously calculated in these cases, indicates the important role of vertical motion in the material dispersion in the model.The last experiment includes the earth's rotation and the buoyancy effect presuming a more actual sea. It shows another effect of the vertical motion. The Coriolis term, which operates only under the condition that a horizontal divergence of the flow is present, skews the horizontal residual flow pattern. 相似文献
14.
《Coastal Engineering》1987,11(2):115-129
The continuity equation for mean longshore current velocity, V = gmT sin 2θb, agrees with selected field and laboratory data covering a wide range of conditions. Agreement between continuity equation and data is improved by eliminating those laboratory data which imply deep-water wave crests at angles near or greater than 90 degrees to the shoreline. Agreement between continuity equation and data is further improved by adjusting breaker angles to account for convection of the breaker point by the longshore current. Breaker point convection increases breaker angle by an amount predictable from the analysis developed here. This increase in angle is significant in those laboratory experiments with breaking wave crests at high angles to the shoreline.In the continuity equation, m is bottom slope, T is wave period, and θb is breaker angle, but breaker height does not appear. According to radiation stress theory, mean velocity does depend on breaker height, but only weakly. Consistency between the two approaches would require a dimensionless velocity, Cb/gT, to be relatively constant, which it is. (The same dimensionless velocity appears in the analyses of breaker point convection.) The continuity equation is functionally independent of friction and mixing, in keeping with its derivation from simple conservation of mass considerations. The equation has no adjustable coefficients. The degress of agreement with data and the internal consistency of the analysis suggests that it is a good predictor of mean velocity in ordinary longshore currents. 相似文献
15.
一株菲降解细菌的筛选及其
降解条件的优化 总被引：1，自引：0，他引：1
Use subimate-pethod,a PAHs-degrading bacteria was isolated from the surface seawater of Botan oil port im Xiamen,and was denominated as strain H.The strain H was classified to Sphingomonas genus according to its 16Sr DNA sequence.The HPLC result showed that the stain H had degraded 81.9% of phenanthrene(final conc.400mg/L)within five days and the velocity is 5.95mg/(L.h).Using uciform design experimentation to optimize the degradation conditions,the degradation velocity of phenanthrene(498.46726mg/L)was the largest after 47.09892 hours,the density of cells was 0.5(OP600). 相似文献
16.
《Oceanologica Acta》2002,25(2):87-99
During previous field experiments in the North Sea it was often assumed that the water column in such shallow coastal tidal waters is vertically well mixed and stratification was neglected when discussing the Normalized Radar Cross Section modulation caused by the sea floor. In this paper the influence of quasi resonant internal waves with the sea bed on the radar imaging mechanism of submarine sand waves itself is investigated. In situ data of the tidal current velocity and several water quality parameters such as sea surface temperature, fluorescence, and beam transmittance were measured in the Southern Bight of the North Sea in April 1991. Simulations of the total NRCS modulation caused by sand waves and internal waves as a function of the current gradient or strain rate induced by the internal wave current field at the sea surface have been carried out using the quasi-steady approximation and linear internal wave theory. As a first approximation the strain rate depending on stratification was calculated using the two-layer model. These simulations demonstrate that at least a density difference between the two layers of the order of Δρ ≈ 1 kg m–3 is necessary for a sinusoidal thermocline to effect the total NRCS modulation considerably. The NRCS modulation as a function of wind friction velocity has been calculated independently and is discussed with regard to the strain rate of the surface current field caused by the superimposed imaging mechanisms of sand waves and internal waves. It turned out that the existence of a surface roughness-wind stress feedback mechanism cannot be excluded. 相似文献
17.
The tidal current in Kagoshima Bay is simulated by the two-dimensional subdomain finite-element method. At the open boundary, the sea level is forced to be oscillatory with a linear combination of the four harmonic constituents (M2, S2, K1, O1) of the tide. A calculation having only M2 sea level at the open boundary is also performed and the harmonic constants of M2 are compared with those calculated by the four components.In the calculated velocity vector, a large difference between the two maxima or the two minima in one day appears when the vector is directed to the open sea. On the other hand, when it is directed into the bay, the two extreme velocities are almost equal. In tide-killer residual flow, the flow pattern is almost independent of the tidal age; however, the absolute value of the current velocity depends on the tidal age. The pattern is nearly the same as that calculated by giving only M2 sea level at the open boundary.In relation to the nonlinear interaction, the kinetic energy ratio KER is defined by the ratio of kinetic energy of the induced harmonic components to that of harmonic constituents given at the open boundary. KER is large where the tidal current is disturbed by obstacles,e.g. along the west coast at the mouth of the bay and in the southern sea of Mt. Sakurajima. The distribution of KER seems to be independent of the number of harmonic constituents (one or four) given at the open boundary. The difference of kinetic energy of the M2 tidal constituent between the two calculations.i.e. with the open boundary conditions of four components (M2, S2, K1, O1) and of a single component (M2), is found to be large where the current velocity is large. 相似文献
18.
Arata Kaneko Noriaki Gohda Wataru Koterayama Masahiko Nakamura Shinjiro Mizuno Hirohito Furukawa 《Journal of Oceanography》1993,49(4):383-395
An intelligent ADCP (Acoustic Doppler Current Profiler) fish, called DRAKE (Depth and Roll Adjustable Kite for Energy flux measurements) was developed with the controllable wings which can adjust the submerging depth of the fish and stabilize its roll motion. The Kuroshio west of Okinawa was measured in a roundtrip course on the same traverse line by the ADCP fish. The forward survey obtained the maximum submerging depth of 208 m at a fish operation speed of 2.9 ms–1. The maximum fish speed of 5.4 ms–1 was achieved at a submerging depth of 48 m in the return survey. The data in the overlapped area of data acquisition between depths 212 and 276 m were used to examine the accuracy of velocity measurement for the towed ADCP system. The summation of both survey data made it possible to estimate a sectional velocity structure and transport of the upper 600 m corresponding roughly to the whole section of the Kuroshio in this region. 相似文献
19.
Semigeostrophic gravity waves associated with a coastal boundary current, which has finite and uniform potential vorticity
and is bounded away from the coastline by a density front on the ocean surface, are investigated. It is shown that the semigeostrophic
coastal current has two waves which are named here the Semigeostrophic Coastal Wave (SCW) and the Semigeostrophic Frontal
Wave (SFW). The SCW becomes an elementary Kelvin wave at some limit while the SFW is caused by the existence of the surface
density front. The SCW appears mainly as variations in the upper layer depth at the coast and as alongshore velocity at the
density front. On the other hand, the SFW appears mainly as variations in the width of the current. When the weak nonlinearity
and ageostrophic effect are included, these semigeostrophic gravity waves satisfy the Kortweg- de Vries equation, which suggests
that the local changes in the width and/or velocity of the semigeostrophic coastal current propagate as wave-like disturbances. 相似文献
20.
An instrument which measures the velocity and direction of benthic water currents at depths of up to 80 m is described. Characteristics of this meter include: (i) readings are not affected by water flow during sinking or retrieval; (ii) it is portable; (iii) it operates unattended; (iv) it is inexpensive; and (v) it requires only simple maintenance. A timing circuit which operates two time periods in succession is used to activate and de-activate a revolution counter and a fluidfilled compass which are mounted on a special frame and vane system. In the field, the instrument accurately measured average current velocities of up to 6 m s−1. Data are presented which illustrate the usefulness of this instrument in describing the velocity and direction of benthic currents along the east coast of Australia and demonstrate a positive correlation between benthic current velocity and catch rates of the commercially-exploited spanner crab Ranina ranina. 相似文献