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1.
A three-dimensional multi-level hydrodynamic model has recently been developed and applied to tidal motion in Singapore’s coastal waters. This paper describes a series of numerical experiments to evaluate the sensitivity of the tidal currents and elevations to model parameters. The results show that the predicted tidal elevations are insensitive to three model parameters: horizontal eddy viscosity coefficient (Smagorinsky constant, ch), bottom friction coefficient (cb) and internal friction coefficient (cv), whereas the effects of these parameters are quite different for tidal current velocities. The velocities are slightly reduced with an increase in ch and cb. The bottom friction effects on velocity profiles increase with water depth. The effect of cv might be significant for the tidal velocities at all levels. The velocities at upper layers of the water column decrease with the increase in cv, whereas the velocities at the bottom layer show the reverse trend. The effects of three model parameters on the magnitude and phase of the simulated currents are in the order (from strong to weak) of cv, cb and ch.  相似文献   

2.
Although extensive research has been performed on the mechanical properties of cement-stabilized clays, quite a few attempts have been made on the compression behavior of remolded cement-admixed clays. The results from oedometer tests have been discussed to investigate the compressibility of remolded cement-admixed clays, taking into consideration cement amount and curing time. The findings show that the difference in shape and position of compression curves is attributed to cement amount and curing time. Most compression index (Cc) values of remolded cement-admixed clays are greater than those of untreated clay due to the presence of remolded yield stress σ′yr that is closely related to initial water content and clay fabric. Based on the obtained test data, the relationships of Cc vs. e0, Cc vs. w0, Cc vs. e1, Cc vs. eyr, and σ′yr vs. eyr are preliminarily discussed and quantitatively established. Especially, an important divergence of void index Iv at effective stress σ′v less than remolded yield stress σ′yr can be observed at different cement amounts and curing durations. Being independent on cement amount, curing time, and initial state of soil, an excellent convergence occurs at stress σ′v greater than yield stress σ′yr. The normalized compression curves of Iv vs. σ′v at σ′v?>?σ′y can be expressed by a unique line that agrees well with intrinsic compression line (ICL) and extended ICL.  相似文献   

3.
The increased off shore activity in arctic waters has occasioned investigations with the purpose of reducing the ice forces acting on structures. Korzhavin (Novosibirsk, U.S.S.R.) has shown that the ice forces will be appreciably reduced if wedges or cones are introduced instead of vertical faces. A theory is presented in the following, by which it is possible to calculate the forces based on the physical and geometrical parameters of the system. The theory has been verified by model tests with both artificial and natural ice.For an inclined wedge or cone the force will F = CFFmax where CF is a reduction factor and Fmax = rced is the maximum force acting on a vertical faced structure, rc being the compression strength, e the thickness of the ice and d the width of the structure. The value of CF will normally vary from 0·1 to 0·4.  相似文献   

4.
An analysis is presented of snapshot data (eastward and northward velocity components: u and v; tracer such as potential temperature: τ) from an eddy-resolving (Rgrid: 1/12°) ocean model experiment, in order to explore a method for improving eddy-permitting model performance. Horizontal 3 × 3 R-grid averages give the eddy-permitting grid (P-grid: 1/4°) variables: 〈u〉, 〈v〉, and 〈τ〉, where 〈〉 denotes the spatial P-grid scale average. The difference between the horizontal tracer flux across the boundary face of a P-grid and that across the corresponding faces of R-grids is estimated as F2E. It is found that the correlations among the gradients of u, v, and τ give a good approximation F2C to the estimated flux F2E. The approximated flux is a function of these gradients and the grid size. A method is presented for implementing the F2C for density to an eddying ocean model as an additional advection. Practical experiments were conducted with a realistic configuration. It is shown that the zonal mean isotherms in the Kuroshio extension region are more flattened in the run using the proposed method than in another run using the conventional horizontal biharmonic operator, suggesting that the additional flux correction leads to an enhancement of sub-basin scale mixing.  相似文献   

5.
Abstract. Cell‐specific fluorescence characteristics were used to characterize the light tolerance of the toxic benthic dinoflagellate Gambierdiscus toxicus. The fluorescence parameter Fv : Fm was measured using pulse amplitude modulation (PAM) fluorometry on individual cells collected from foliose red algae growing in the sub‐tidal margin of South Water Cay, Belize. Samples were collected over several days during sunny and cloudy conditions and compared to samples incubated in situ. The data from individual cells were used to generate both Fv : Fm frequency histograms and averages. Maximum individual cell values of Fv : Fm reached 0.81 in pre‐dawn samples, a value near the theoretical maximum for PAM fluorometry. In field samples from macroalgal hosts, average Fv : Fm values declined only slightly during the day, but cells incubated in bottles under 47 % incident sunlight showed a significant mid‐day depression. In freshly collected samples, near‐maximum Fv : Fm values could be found in individual cells during the entire day; however, the frequency histograms indicated a greater range in Fv : Fm values during the afternoon than in the morning. In contrast, cultures of G. toxicus showed a tight distribution around a mean. Field samples showed a rapid recovery to near‐maximum Fv : Fm within 2 min when assayed using a standardized actinic light series. Similar results were obtained in laboratory cultures of G. toxicus grown at 73 µmol photons · m‐2 · s‐1, but not at 383 µmol photons · m‐2 · s‐1. These data provide empirical support for suggestions that G. toxicus exploits the three‐dimensional structure of the algal host thallus to minimize light exposure. This strategy permits G. toxicus, a high‐light intolerant species in culture, to thrive in shallow, well‐lit tropical seas. It may also partially explain the observed preference of G. toxicus for complex, foliose macroalgae as hosts.  相似文献   

6.
We studied the effects of nitrogen and phosphorus supply on Fv/Fm (maximal quantum yield of photosystem II) in the diatom Chaetoceros debilis and dinoflagellate Scrippsiella trochoidea in nitrogen (N) and phosphorus (P) depleted cultures to determine whether this parameter could be used to monitor N or P limitation. In the nutrient depleted experiments, no obvious decrease of cell density and chlorophyll concentration was observed except in N-depleted incubation of S. trochoidea. For C. debilis, Fv/Fm decreased quickly in periods of N- and P-depletion and re-supply of N and P induced a quick recovery of Fv/Fm. However, in S. trochoidea culture, Fv/Fm remained unchanged in N- and P-depleted conditions and addition of sufficient N and P to N- and P-depleted cultures did not affect Fv/Fm. Therefore, Fv/Fm is insensitive to N and/or P limitation in growth of S. trochoidea. The results suggested that Fv/Fm was not a robust diagnostic for nutrient limitation in dinoflagellates. The differences in the sensitivity of Fv/Fm to nutrient limitation may result from different nutrient storage abilities among algal species.  相似文献   

7.
Abdul Hayir   《Ocean Engineering》2006,33(5-6):654-664
The aim of this study is to present the solutions for the near-field tsunami amplitudes caused by submarine landslumps and slides spreading in two orthogonal directions. A linearized shallow water wave theory is derived. The transform techniques (Fourier and Laplace transform) are used for the solution of Laplace equation. The results show that if the ratio of the velocties is v1/v2=0.1, the numerical results are almost the same as the values obtained for one dimensional movement of the slumps and slides. But, when the ratio of the velocties is v1/v2=1, obtained normalized peak amplitudes, ηmax/ζ0 are smaller than the numerical values for one dimensional solution. It is concluded that normalized peak amplitudes for the models are small because of the interaction of the velocities. Numerical examples are presented for various parameters.  相似文献   

8.
Cement and lime are widely employed in soil and sediment treatment for an improvement of geotechnical properties, such as an increase in mechanical strength which enables beneficial use in various geotechnical applications. In this study, fine organic-rich dredged harbour sediments of 120% relative water content were treated with dry cement at contents varying between 2% and 10% of bulk sediment wet weight. Tests based on assessments of one-dimensional compression and Atterberg limits were performed on untreated and cement-treated sediments for various curing periods, as well as grain-size, SEM and X-ray diffraction analyses. The results confirm that increasing the cement content improves the geotechnical properties of these harbour sediments. Already in the early phase of curing (first 3 days of curing), particle size increases while sediment plasticity decreases. Changes in the compressibility behaviour include an increase in apparent preconsolidation pressure, in the compression index C c and in the primary consolidation coefficient C v, and a decrease in the secondary compression index . This means that the new materials are characterized by a behaviour intermediate between that of fine and that of coarser soils.  相似文献   

9.
采用植物激素的微量LC-MS检测等方法,研究了24-表油菜素内酯(EBR)对宁波浒苔(Ulva prolifera)内源植物激素含量及其叶绿素荧光参数、可溶性蛋白和糖含量、抗氧化酶活性等的影响。结果表明,浒苔体内含有吲哚乙酸、赤霉素、玉米素、反式玉米素核苷、异戊烯腺嘌呤核苷、茉莉酸等多种促生长性内源植物激素,但不含有异戊烯腺嘌呤。内源植物激素对24-表油菜素内酯的响应程度不同,大多数植物激素在处理第1天含量变化最快。低浓度24-表油菜素内酯处理时,各种内源植物激素的含量增高,均呈现先升高后降低的趋势。0.2 mg/L 24-表油菜素内酯处理组的效果最明显。在该浓度下,24-表油菜素内酯对生长相关激素含量、最大光能转化效率(Fv/Fm)和相对电子传递速率(ETR)、可溶性蛋白和可溶性糖含量、POD活性等均有较大的促进作用;在0.1 mg/L 24-表油菜素内酯处理组中,浒苔的体外抗氧化能力最强。  相似文献   

10.
-In this paper, an improvement and revision of the theory of Miiller (1974, 1976), has been made under two conditions: (1) the horizontal component of the Coriolis force has been taken into account in the equations of motion for the internal wave field; and (2) the role of internal waves with frequencies close to the inertial frequency has been considered. The values of the viscosity coefficients and the diffusivity coefficients obtained in this paper are: Theappearance of the cross-diffusion (vc) of momentum is a natural result from the effect of the horizontal Coriolis force. Therefore the role of the horizontal shear of the mean flow cannot be absolutely separated from that of the vertical shear. So far in testing Muller's theory, the approximation of effective wave stress obtained by Ruddick and Joyce (1979) was extensively used, but it has to be revised under the conditions of this paper. The revised approximation shows that the internal waves with low frequencies close to the inertial frequency pl  相似文献   

11.
The Sea of Okhotsk is one of the most productive marine basins in the world ocean and plays an important role in transport of organic carbon and iron to the western subarctic Pacific. We report the first measurements of phytoplankton growth and microzooplankton grazing rates in the Sea of Okhotsk, in late summer of 2006. The study area can be divided into two areas: nutrient-sufficient waters on the continental shelf along the east coast of Sakhalin Island and in the vicinity of Bussol Strait, and surface nutrient-depleted waters beyond the shelf break and in the vicinity of Sakhalin Bay. Phytoplankton growth rate in the studied area was strongly affected by nutrient availability, with high phytoplankton growth rate (0.55±0.14 d?1) in the nutrient-replete region and severely depressed growth (0.03±0.05 d?1) in the nutrient-depleted region. On the other hand, microzooplankton grazing rates in both the nutrient-replete and nutrient-depleted regions were approximately the same (0.26±0.20 d?1 vs. 0.27±0.24 d?1). Consequently, microzooplankton grazing consumed <50% of the phytoplankton growth in nutrient-rich waters but >3 times the phytoplankton growth in nutrient-depleted waters. Phytoplankton physiological condition as measured by the maximum photochemical quantum efficiency (Fv/Fm) of algal photosystem II (PS II) showed a general trend in agreement with the in situ growth rate of phytoplankton. In contrast to the phytoplankton community, picophytoplankton, especially the cyanobacteria Synechococcus, showed no nutrient effect on their growth, and the growth and mortality rates were well balanced, suggesting that they have a low nutrient requirement and their biomass was controlled principally by microzooplankton grazing.  相似文献   

12.
Abstract

Vacuum preloading with plastic vertical drains has been applied widely to accelerating consolidation of dredger fills. As a result of nonlinear variations in permeability and compression during the process of dredger fill consolidation, an axisymmetric consolidation method for dredger fill treatment using PVD with vacuum is proposed with varied Ru. The effects of Cc/Ck and the loading ratio on the proposed method are discussed. It is found that the difference between the traditional method and proposed method is obvious in the case of large loading ratio (such as dredger fill treated with vacuum preloading). The degree of consolidation in the early phase of consolidation obtained using the proposed method was less than that obtained using the traditional method and the degree of consolidation in the later phase of consolidation obtained using the modified expression was larger than that obtained using the traditional method, as Cc/Ck?<?1. However, opposite trends were observed when Cc/Ck?>?1, the proposed method was closer to the actual situation. The applicability of the proposed method was verified by laboratory and field tests. For the consolidation of dredger fill with high water content, we recommend the adoption of the proposed method for calculating the degree of consolidation.  相似文献   

13.
为了助力海洋牧场减流防护工程, 研究Savonius型转轮阵列减流性能。作者建立Savonius型转轮三角阵列尾流场数值模型, 并通过水池实验验证准确性, 基于可靠数值模型探究转轮阵列尾涡减流机理, 研究三角阵列结构参数LX、LY, 以及动力参数TSR、初始流速、旋向对整体减流性能的影响规律。结果表明,下游转轮产生的涡流呈现非对称分布, 并且产生更多涡流的转轮拥有更好的减流效果。另外, LX为3D和LY为2D时减流性能最佳。最后对比发现, 在叶尖速比为0.9~1.1减流效果更好; 初始流速大小不影响减流效果; 下游转子对称分布时, 随着上游转子改变旋转方向, 减流效果出现明显差异。  相似文献   

14.
Size-fractionated seawater samples were collected from the Gulf of Maine to determine the fraction (fc/d) of total dissolved (< 1 μm) Cd, Cu, Ni and 234Th in the colloidal size range (1,000 nominal molecular weight, NMW, to 1 μm) using cross-flow filtration. Colloidal Cd, Cu and Ni represents < 1–7% of the total dissolved concentration in these shelf waters and increases with an increase in particle concentration. By comparison, results obtained for particle-reactive 234Th indicate that < 1–47% of total dissolved is associated with the colloidal size fraction. A revised relationship between the concentration of colloids (Cc) and suspended particles (Cp) is reported (log Cc = 0.66 log Cp −2.01 kg L−1) and used to examine the dependence of fc/d for these metals on the concentration of suspended particles for Cp = 0.01–100 mg L−1. Results indicate that a significant fraction (˜ 10–30%) of Cd, Cu, Ni and 234Th in the traditionally defined ‘dissolved’ fraction may exist in the colloidal size range in regions characterized by high particle concentrations (Cp > 1–10 mg L−1), such as in near-shore and estuarine waters.  相似文献   

15.
This study compares the composition, species richness and biomass of macrofaunal and algal assemblages on intertidal boulder shores as compared with those on adjacent rock-platforms, at six sites along the southwest coast of South Africa. Of 214 species identified, 175 were recorded on boulder shores and 124 on rock-platform shores; of these, 99 species were common to both habitat types, 92 were exclusive to boulders, and 23 were exclusive to rock-platforms. Significant differences in community structure (F(1,95) = 13.02, p < 0.01) (PERMANOVA test), species richness (F(1,95) = 14.28, p < 0.01), biomass (F(1,95) = 9.45, p < 0.01) and diversity (F(1,95) = 578.83, p < 0.01) (two-way ANOVA) were detected between the two habitat types. Average dissimilarity of community structure between rock-platform and boulder shores was 87.96% (SIMPER analysis). The increased species richness and biomass on boulder shores extended across all tidal levels, but was most marked in the highshore. These results confirm that boulder shores along the southwestern Cape support a distinct biota, richer and very different from that on adjacent rock-platforms, and rich in boulder-dependent species. We propose that boulder shores merit separate management and conservation targets as compared to rock-platforms, though the ecology of boulder shores in the region remains very poorly known and requires further study.  相似文献   

16.
Enzymic mixtures were prepared from digestive organs of the three species of sea Snails. All the three mixtures can break down the cell-walls of seaweeds.The present paper reports only three of the enzymic components in these mixtures, two cellulates (Cx,C1) and one pectinase.The level of activity of the cellulose Cx is in the order: Lunclla cornata coreensis > Monodonta labio > Purpura clavigera,and of the cellulate C1 is in the order: L.. cornata coreensis >> M. labio= P clavigera. These two cellulases play an important role in decomposing cell walls of seaweeds.The level of activity of the pectinase is in the order of M,. Iahio > L. cornata coreensis > P. clavigera.  相似文献   

17.
The results of one-dimensional compression tests conducted on undisturbed specimens of Jiangsu soft marine clay is presented. Because of its high in situ void ratios and natural water content, Jiangsu soft marine clay displays high values of both the virgin compression index, Cc, and the secondary compression coefficient, Cα. The laboratory data indicates that the value of the ratio Cα/Cc for Jiangsu soft marine clay is constant. However, neither Cα nor Cc are constant: they both depend upon the natural water content (or void ratio) and thus are also dependent on the deformation (or compression) of Jiangsu soft marine clay. Settlement analyses show that the secondary settlement of Jiangsu soft marine clay is a significant component of the field settlement. The concept of a constant value for Cα/Cc is used to predict the secondary settlement of a surcharged embankment founded upon Jiangsu soft marine clay. The predictions are in agreement with the limited post-construction field measurements of the embankment settlement.  相似文献   

18.
尽管单一逆境条件对浮游植物产生的影响已被广泛重视,然而对于多重逆境条件对藻细胞生长生理的研究仍有空白。本研究通过测定强壮前沟藻(Amphidinium carterae Hulbert)光密度(OD750)、叶绿素a含量(chl a)、光合作用效率(F_v/F_m)、碳氮比(C/N)等多个生理指标,分析其在9种环境下(常温光照、低温和低温黑暗三种物理环境,结合全营养、缺氮、缺磷三种营养状态)对多重逆境的生长和生理响应。研究结果表明,在多重逆境条件下,单一物理逆境因素(低温或黑暗)较氮限制或磷限制对藻细胞生长和生理的不利影响更为显著。营养限制并同低温环境双重作用对生物量和碳氮比产生显著性影响(P0.01)。此外,低温和黑暗条件耦合作用下,SYTOX Green染色强度处于较低水平,chl a稳定、F_v/F_m有所升高,强壮前沟藻在逆境环境下作为群体的衰亡得以缓解。  相似文献   

19.
《Journal of Oceanography》2007,63(6):983-994
A mesoscale iron-enrichment study (SEEDS II) was carried out in the western subarctic Pacific in the summer of 2004. The iron patch was traced for 26 days, which included observations of the development and the decline of the bloom by mapping with sulfur hexafluoride. The experiment was conducted at almost the same location and the same season as SEEDS (previous iron-enrichment experiment). However, the results were very different between SEEDS and SEEDS II. A high accumulation of phytoplankton biomass (∼18 mg chl m−3) was characteristic of SEEDS. In contrast, in SEEDS II, the surface chlorophyll-a accumulation was lower, 0.8 to 2.48 mg m−3, with no prominent diatom bloom. Photosynthetic competence in terms of F v/F m for the total phytoplankton community in the surface waters increased after the iron enrichments and returned to the ambient level by day 20. These results suggest that the photosynthetic physiology of the phytoplankton assemblage was improved by the iron enrichments and returned to an iron-stressed condition during the declining phase of the bloom. Pico-phytoplankton (<2 μm) became dominant in the chlorophyll-a size distribution after the bloom. We observed a nitrate drawdown of 3.8 μM in the patch (day 21), but there was no difference in silicic acid concentration between inside and outside the patch. Mesozooplankton (copepod) biomass was three to five times higher during the bloom-development phase in SEEDS II than in SEEDS. The copepod biomass increased exponentially. The grazing rate estimation indicates that the copepod grazing prevented the formation of an extensive diatom bloom, which was observed in SEEDS, and led to the change to a pico-phytoplankton dominated community towards the end of the experiment.  相似文献   

20.
Preference tests were performed over a two-week period in September 2001 in which isopods (Idotea baltica) and amphipods (Gammarus oceanicus) were offered choices of three common species of algae from the Baltic Sea: Enteromorpha intestinalis, Cladophora spp., and Fucus vesiculosus. After a 48-hour starvation period, 20 individuals of each grazer species were placed in aquaria containing approximately 1.0 g of each algal species. Fifteen trials for each grazer species were run for 20 hours. We found that G. oceanicus ate significantly more Cladophora spp. and E. intestinalis than F. vesiculosus (p<0.001), with a preference order of: Cladophora spp.>E. intestinalis>F. vesiculosus. Similarly, I. baltica ate significantly more of both the filamentous green algae than F. vesiculosus (p<0.001), with a preference order of: E. intestinalis>Cladophora spp.>F. vesiculosus. Given the preference of isopods and amphipods for filamentous green algae, we might expect these algae to be maintained at low biomass levels. However, this is clearly not the case in the Baltic Sea. Nutrient enrichment (bottom-up effects) is the accepted dominant reason for the non-controlling impact of algal grazers, but other reasons may include cascading trophic effects resulting from the removal of large piscivorous fish (top-down effects).  相似文献   

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