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1.
Gross sedimentation rates (GSR) have been measured using sediment traps placed at nine different levels above the bed (0·3, 0·5, 0·8, 1·0, 2·0, 4·0, 6·0, 8·0 and 10·0 m). The sediment traps were deployed for 1·25 years and recovered 28 times during the study period. Low average GSR values of 5·5 g m-2 day-1 were obtained at 10·0 m, and high average GSR values of 114·8 g m-2 day-1 were obtained at 0·3 m. An expression for the eddy diffusion coefficient of suspended particulate matter (Ks), based on the measured GSR is given. The expression has been used for modelling of Ks at the different trap levels above the bed. High values (≈42 cm2 s-1) of Ks were obtained at the upper traps, whereas low values (≈2 cm2 s-1) were obtained near the bed. Comparison between level of turbulent energy in terms of shear stress at the boundaries of the water column, i.e. from the wind and the bed flow, showed that wind energy exceeded that of the bed flow by a factor 16. At 5·0 m Ks was positively correlated (r=0·66) to the eddy diffusion coefficient of momentum (Km) derived from the wind energy transfer to the water, giving an average β of 0·5 for Ks =βKm. The density difference between surface and bottom waters has been designated a parameter of stratification, and is discussed in relation to variations of Ks and Km .  相似文献   

2.
In this paper, it is held that the universal relationships of wave growth in fetch-limited conditions , i. e.,(f|~) p=A(x|~)-Band (m|~)0= C(x|~) Dshould satisfy the Toba 3/2 power law and the wave energy balance equation. In the ideal generation situation, theoretically it can be derived that the ideal fetch-limited wave growth relationship should have D=3B and D B =1, (i.e., B = 0.25, D = 0.75 ) and A3C=2. 1×l(T4C~(1/2)_d , where Cd is the drag coefficient. The 3/2 power law, the wave energy balance equation and the decrease of wave steepness with increasing fetch have became three requirements which should be satisfied by fetch-limited wave growth algorithms. A semi-empirical and semi-theoretical model for fetch-limited wave growth is presented. In the application to the slanting wind situation an un(?)ersal relationship of dimensionless wave energy vs dimensionless peak frequency is presented and the comparisons show that the model is in good agreement with observations.  相似文献   

3.
A series of measurements of winds and wind-waves were carried out in wind-wave flumes. A data analysis based on the hypothesis of local equilibrium yielded a new empirical formula on the controversial quantity of roughness heightz 0 over the water surface: , where the nondimensional roughness height is defined bygz 0/u * 2 and the wave-wind parameterũ byω p u */g, g being the gravitational acceleration,u * the friction velocity of air,ω p the peak frequency of wind-wave spectra. The obtained formula is compared with Charnock's (1955) and Toba's (1979) proposals; is constant in the former and inversely proportional toũ in the latter. As in Toba's, this formula immediately leads to a practically important conclusion that the drag coefficientC d depends not merely on the usual variableU 10 (wind velocity at 10m height over the water surface), but also on the surface state represented by wind-waves. An explicit expression is provided for the drag coefficient incorporating the wave-wind parameter; it covers the range ofC d calculated from most of the previous drag formulas, by varying the wave-wind parameter.  相似文献   

4.
Midsummer (1 August) population estimates of about 2 million O-group plaice (Pleuronectes platessa L.) were derived for sandy bays around the Firth of Forth in 1979–1980. This is an order of magnitude less than similar estimates made for the Clyde Sea Area in 1973–1974. Autumn population estimates of 0·4–1·0 million fish were comparable to estimates by the Ministry of Agriculture, Fisheries and Food for the area between the Scottish border and Flamborough Head (2·3 million for 1970 and 1973) which represented 4·8% (1973) to 5·3% (1970) of the total number of O-group fish on the English east coast.Largo Bay was the most important nursery area holding 25% of the total population. It is particularly well situated to receive newly metamorphosed plaice carried in water currents along the north side of the Forth from the spawning ground off Fife Ness. Plaice in the Forth are mainly distributed on fine to medium sandy beaches (186–480 μm), the mean number per haul in midsummer (D) being correlated with the median diameter (m.d. in μm) of the low water sediments by the equation: D=−45·7666+0·2327 m.d. (n=11,r=0·68,P<0·02 but>0·01).The shallow inshore water in sandy bays in the outer Firth was well mixed and more marine than estuarine (27·7–35·0‰). The correlation coefficient between fish density and water temperature was low, while that with salinity (S‰) was: D=6·1618+0·2238S (n=23,r=0·62,P<0·005).Regression analysis demonstrated that the relationship between the instantaneous mortality rate (Z) and the initial population density (Dp) was: Z×100=0·7480+0·0546dp (n=12,r=0·87,P<0·001).The mean mortality rate for the O-group plaice in the Forth nursery areas was 53% month−1.  相似文献   

5.
The air-ice drag coefficient under neutral stratification C DN was measured with the eddy correlation method in the southern Sea of Okhotsk. The disturbance of the wind field caused by the ship’s structure was evaluated by computational fluid dynamics (CFD), and two types of correction methods were applied to estimate the error span of C DN : one is based on the results of CFD, and the other is based on the parameterization of C DN over open water suggested by Taylor and Yelland (2001). The C DN × 103 values finally obtained ranged from 1.9 to 5.4 with a mean value of 2.7 by the CFD correction and from 1.5 to 5.0 with a mean value of 3.1 by the other method. This is somewhat larger than the value of 2.5 suggested by Shirasawa (1981), and in the same range as 2.2–4.0 over rough ice and 3.1–5.0 over very rough ice, values which were complied by Guest and Davidson (1991) for first year ice. Most of the ice conditions were characterized by broken floes with a diameter less than 100 m and raised rims, which made the surface rougher than flat, level ice. The relation between C DN and ice concentration was not clear, mainly because the contribution of the form drag caused at the freeboard was undetectable due to the great variation of ice surface condition. The roughness length z M was also evaluated using the model developed for snow covered ice in a previous study.  相似文献   

6.
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   

7.
A coupled model of air-wave-sea interaction is modified based on a new roughness formulation and the latest data. The model parameters for aerodynamic roughness from below (ARB) and wave-dependent roughness from above (ARA, z 0a ) are assumed equal. The combined roughness is assumed to be a function of friction velocity, gravity, air and seawater densities, and wave age (c w ). The model is used in a study of wave-enhanced turbulence under breaking waves to predict turbulent dissipation (), ARA, and drag coefficient (C d ). Both waves and shear production are considered as sources of ocean turbulent energy. The atmospheric part of the model is used only to specify a correct condition at the interface. Numerical experiments are performed to study the -distribution, z 0a and C d , and to compare with data. The major achievement is model verification using all available data. The first full application of this model is in conjunction with an ocean circulation model in a coupled circulation-wave system. Simulations show that the -distribution is strongly dependent on local wind-forced wave heights. For each wind and wave state there is a particular wave-dependent depth that is verified by data. The comparison shows that the model predicted agrees well with the observed of the z –4 law distribution of Gargett (1989). Simulations also show that waves have an important role in causing to differ from the classical wall-layer theory and z 0a , with a value of 0.30 for the empirical constant a a . The model-predicted , z 0a , C d and C gd agree well with data.  相似文献   

8.
We present a numerical study on the hydrodynamic performance of undulation NACA0012 foil in the near wake of D-section cylinder. Computations are conducted using unsteady incompressible Navier-Stokes equations with a moving adaptive mesh based on laminar flow. Investigations are focused on the effect of distance ratio between foil tip and centre of cylinder (L/D≤2.0) on the thrust/drag performance of foil and cylinder at various foil undulation frequency (St). We found that, foil thrust coefficient (Ct) increases considerably with the appearance of cylinder and an optimal distance exists at which Ct reaches maxima. The maximum increment is about eleven times that of its counterpart of single foil, which is obtained at St=0.23 and L/D=0.5. Our results for the cylinder drag coefficient (Cd) observed the existence of optimal parametric map, combined with various gap ratios and foil frequencies. With these parameters, insertion of an undulation foil can significantly lead to the drag reduction indicating that undulating foil could work efficiently as a passive vortex control device for cylinder drag reduction.  相似文献   

9.
The skin friction of a two-dimensional planing flat plate is made up of two opposing components; a drag force from the flow aft of the stagnation line and an opposing thrust force from the jet flow. This paper is concerned only with the drag term and the wake velocity defect which it causes in the water behind the transom.It is concluded that the skin friction is less than would be expected from a flat plate at ambient static pressure (Dfo say) and is approximately equal to Dfo (1 − CR), where CR is the normal force coefficient based on wetted area. The wake velocity decrement due to this drag is found to be significant, particularly for surface piercing propellers.  相似文献   

10.
Dependence of sea surface drag coefficient on wind-wave parameters   总被引：3，自引：2，他引：1  
The relationships between sea surface roughness z 0 and wind-wave parameters are analyzed,and spurious self-correlations are found in all of the parameterization schemes.Sea surface drag coefficient C D is fitted by four wind-wave parameters that are wave age,wave steepness,windsea Reynolds number R B and R H ,and the analyzed data are divided into laboratory,field and combined data sets respectively.Comparison and analysis of dependence of C D on wind-wave parameters show that R B can fit the C D most appropriately.Wave age and wave steepness are not suitable to fit C D with a narrow range data set.When the value of wave age has a board range,R H is not suitable to fit C D either.Three relationships between C D and R B are integrated into the bulk algorithm COARE to calculate the observational friction velocity,and the results show that the relationship between C D and R B which is fitted with field data set can describe the momentum transfer in the open ocean,under low-moderate wind speed condition,most appropriately.  相似文献   

11.
进一步研究强风条件下海-气湍流动量交换以及海浪特征,有助于提高数值天气模式对台风强度演变、移动路径以及恶劣海况的预报能力。依照前人的方法将台风分为风向与浪向(1)相同,(2)相反,和(3)交叉3个扇形区,并结合台风路径数据,得到了浮标数据相对于台风的方位。分别对3种类型的浮标数据进行分析,进而发现了波浪高度和相速度随风速增加而变化的规律。并利用GWW参数化方案计算出摩擦速度(u*)、拖曳系数(CDN)和粗糙长度(z0)。将这些结果与前人代表性的研究论文中所用观测数据和所得研究结论进行比较,结果表明二者有较强的一致性。该研究证明GWW参数化方案在强风条件下依然有很好的适用性。  相似文献   

12.
Crangon crangon (L.) (Crustacea: Decapoda) were subjected to three metals (Cd, Cu and Zn) at respective concentrations (0·35, 1·6 and 14·4mg/litre) that would induce 50% mortality in 5–6 days. Significantly different (P < 0·05) rates of mortality occurred in the three groups, although their ET50's were almost identical. No moultstage-dependent mortality was observed for Cd, but in Cu and Zn the post-moult stages (A and B) were more susceptible than either the intermoult (Ca and Cb) or premoult (D0–D4) stages.No significant (P> 0·05) sex- or size-dependent mortality was evident at the tested concentrations of these metals.Feeding and ecdysis were inhibited in all metals after day 3 and development from one moult-stage to the next was greatly reduced in Cd.Possible modes of toxicity have been discussed in terms of the physiological condition inferred from the moult-stage at the time of death.  相似文献   

13.
Relationships between the surface concentrations of phytoplankton pigments (C ph), total suspended matter (C sm), particulate organic carbon (C poc), and total suspended phosphorus (C sp), on the one hand, and the relative water transparency determined through the Secchi disc depth (z d), on the other, are analysed using the data compiled in the Guinean coastal waters (Tabunsu and Tonkima river estuaries) during November–December 1990. The functions ofC ph,C sm=f(z d) are matched up with the experimentally derived data, as well as with the model bio-optical state of seawater. The general regression equation has been calculated using the data characteristic of various types of water.Translated by Vladimir A. Puchkin.  相似文献   

14.
A nonlinear theory for the generation of the Ulleung Warm Eddy (UWE) is proposed. Using the nonlinear reduced gravity (shallow water) equations, it is shown analytically that the eddy is established in order to balance the northward momentum flux (i.e., the flow force) exerted by the separating western boundary current (WBC). In this scenario, the presence of β produces a southward (eddy) force balancing the northward momentum flux imparted by the separating East Korean Warm Current (EKWC).It is found that, for a high Rossby number EKWC (i.e., highly nonlinear current), the eddy radius is roughly 2Rd/ε1/6 (here ε≡βRd/f0, where Rd is the Rossby radius), implying that the UWE has a scale larger than that of most eddies (Rd). This solution suggests that, in contrast to the familiar idea attributing the formation of eddies to instabilities (i.e., the breakdown of a known steady solution), the UWE is an integral part of the steady stable solution. The solution also suggests that a weak WBC does not produce an eddy (due to the absence of nonlinearity).A reduced gravity numerical model is used to further analyze the relationship between β, nonlinearity and the eddy formation. First, we show that a high Rossby number WBC which is forced to separate from the wall on an f plane does not produce an eddy near the separation. To balance the northward momentum force imparted by the nonlinear boundary current, the f plane system moves constantly offshore, producing a southward Coriolis force. We then show that, as β is introduced to the problem, an anticyclonic eddy is formed. The numerical balance of forces shows that, as suggested by the analytical reasoning, the southward force produced by the eddy balances the northward flow force imparted by the boundary current. We also found that the observed eddy scale in the Japan/East Sea agrees with the analytical estimate for a nonlinear current.  相似文献   

15.
Use of the quadratic shear-stress law for estimating boundary drag requires specific knowledge of the magnitude of a drag coefficient, CD, and sectional mean velocity, u?. In previous attempts to adapt the relationship for use in studies of marine-sediment transport, the flow measurement has been standardized at a level 100 cm above the bed. The particularized value of the drag coefficient has been designated as C100.In the entrance area to Chesapeake Bay, Virginia, C100 has been found to range through unacceptably wide limits. Two-thirds of the values obtained are between 3.5 · 10?3 and 5.4 · 10?2. Mean C100 for the area is 1.3 · 10?2 as compared to 3 · 10?3 for tidal channels within Puget Sound, Washington.Present data suggest that, given a moveable bed, a size hierarchy of mobile bed forms, time-varying flow, and a lack of equilibrium between flow and bed, C100 changes continuously with boundary shear stress.Accurate evaluation of boundary shear stress in tidal entrances with high flow rates and mobile beds presently requires measurement of velocity profiles.  相似文献   

16.
Rates of transformation, recycling and burial of nitrogen and their temporal and spatial variability were investigated in deep-sea sediments of the Porcupine Abyssal Plain (PAP), NE Atlantic during eight cruises from 1996 to 2000. Benthic fluxes of ammonium (NH4) and nitrate (NO3) were measured in situ using a benthic lander. Fluxes of dissolved organic nitrogen (DON) and denitrification rates were calculated from pore water profiles of DON and NO3, respectively. Burial of nitrogen was calculated from down core profiles of nitrogen in the solid phase together with 14C-based sediment accumulation rates and dry bulk density. Average NH4 and NO3-effluxes were 7.4 ± 19 μmol m−2 d−1 (n = 7) and 52 ± 30 μmol m−2 d−1 (n = 14), respectively, during the period 1996–2000. During the same period, the DON-flux was 11 ± 5.6 μmol m−2 d−1 (n = 5) and the denitrification rate was 5.1 ± 3.0 μmol m−2 d−1 (n = 22). Temporal and spatial variations were only found in the benthic NO3 fluxes. The average burial rate was 4.6 ± 0.9 μmol m−2 d−1. On average over the sampling period, the recycling efficiency of the PON input to the sediment was 94% and the burial efficiency hence 6%. The DON flux constituted 14% of the nitrogen recycled, and it was of similar magnitude as the sum of burial and denitrification. By assuming the PAP is representative of all deep-sea areas, rates of denitrification, burial and DON efflux were extrapolated to the total area of the deep-sea floor (>2000 m) and integrated values of denitrification and burial of 8 ± 5 and 7 ± 1 Tg N year−1, respectively, were obtained. This value of total deep-sea sediment denitrification corresponds to 3–12% of the global ocean benthic denitrification. Burial in deep-sea sediments makes up at least 25% of the global ocean nitrogen burial. The integrated DON flux from the deep-sea floor is comparable in magnitude to a reported global riverine input of DON suggesting that deep-sea sediments constitute an important source of DON to the world ocean.  相似文献   

17.
An experimental study, conducted in the large wave flume of CIEM in Barcelona, is presented to evaluate the effects of Posidonia oceanica meadows on the wave height damping and on the wave induced velocities. The experiments were performed for irregular waves from intermediate to shallow waters with the dispersion parameter h/λ ranging from 0.09 to 0.29. Various configurations of the artificial P. oceanica meadow were tested for two stem density patterns (360 and 180 stems/m2) and for plant's height ranging from 1/3 to 1/2 of the water depth.The results for wave height attenuation are in good agreement with the analytical expressions found in literature, based on the assumption that the energy loss over the vegetated field is due to the drag forces. Based on this hypothesis, an empirical relationship for the drag coefficient related to the Reynolds number, Re, is proposed. The Reynolds number, calculated using the artificial P. oceanica leaf width as the length scale and the maximum orbital velocity over the meadow edge as the characteristic velocity scale, ranges from 1000 to 3500 and the drag coefficient Cd ranges from 0.75 to 2.0.The calculated wave heights, using the analytical expression from literature and the proposed relationship for the estimation of Cd, are in satisfactory agreement with those measured. Wave orbital velocities are shown to be significantly attenuated inside the meadow and just above the flume bed as indicated by the calculation of an attenuation parameter. Near the meadow edge, energy transfer is found in spectral wave velocities from the longer to the shorter wave period components. From the analysis it is shown that the submerged vegetation attenuates mostly longer waves.  相似文献   

18.
A salient feature of sea level records from the Adriatic Sea is the frequent occurrence of energetic seiches of period about 21 h. Once excited by a sudden wind event, such seiches often persist for days. They lose energy either to friction within the Adriatic, or by radiation through Otranto Strait into the Mediterranean.The free decay time of the dominant (lowest mode) seiche was determined from envelopes of handpassed sea level residuals from three locations (Bakar, Split and Dubrovnik) along the Croatian coast during twelve seiche episodes between 1963 and 1986 by taking into consideration only time intervals when the envelopes decreased exponentially in time, when the modelled effects of along-basin winds were smaller than the error of estimation of decay time from the envelopes and when across-basin winds were small. The free decay time thus obtained was 3.2±0.5 d. This value is consonant with the observed width of the spectral peak.The decay caused by both bottom friction and radiation was included in a one dimensional variable cross section shallow water model of the Adriatic. Bottom friction is parameterized by the coefficient k appearing in the linearized bottom stress term ρ0u (where u is the along-basin velocity and ρ0 the fluid density). The coefficient k is constrained by values obtained from linearization of the quadratic bottom stress law using estimates of near bottom currents associated with the seiche, with wind driven currents, with tides and with wind waves. Radiation is parameterized by the coefficient f appearing in the open strait boundary condition ζ =auh/c (where ζ is sea level, h is depth and c is phase speed). This parameterization of radiation provides results comparable to allowing the Adriatic to radiate into an unbounded half plane ocean. Repeated runs of the model delineate the dependence of model free seiche decay time on k and a, and these plus the estimates of k allow estimation of a.The principle conclusions of this work are as follows.
1. (1) Exponential decay of seiche amplitude with time does not necessarily guarantee that the observed decay is free of wind influence.
2. (2) Winds blowing across the Adriatic may be of comparable importance to winds blowing along the Adriatic in influencing apparent decay of seiches; across-basin winds are probably coupled to the longitudinal seiche on account of the strong along-basin variability of across-basin winds forced by Croatian coastal orography.
3. (3) The free decay time of the 21.2 h Adriatic seiche is 3.2±0.5 d.
4. (4) A one dimensional shallow water model of the seiche damped by bottom stress represented by Godin's (1988) approximation to the quadratic bottom friction law ρ0CDu|u| using the commonly accepted drag coefficient CD = 0.0015 and quantitative estimates of bottom currents associated with wind driven currents, tides and wind waves, as well as with the seiche itself with no radiation gives a damping time of 9.46 d; radiation sufficient to give the observed damping time must then account for 66% of the energy loss per period. But independent estimates of bottom friction for Adriatic wind driven currents and inertial oscillations, as well as comparisons between quadratic law bottom stress and directly measured bottom stress, all suggest that the quadratic law with CD=0.0015 substantially underestimates the bottom stress. Based on these studies, a more appropriate value of the drag coefficient is at least CD=0. In this case, bottom friction with no radiation leads to a damping time of 4.73 d, radiation sufficient to give the observed damping time then accounts for 32% of the energy loss per period.
  相似文献   

19.
Simple prediction methods are proposed to estimate the wave induced pressures on smooth impermeable seawalls. Based on the physics of the wave structure interaction, the sloped seawall is divided into a total of five zones (zones 1, 2 and 3 during run-up (corresponding pressures are called as positive pressures) and zones 4 and 5 during run-down (corresponding pressures are called negative pressures)) (Fig. 1). Zone 1 (0<z<d−Hi/2), where the wave pressure is governed by the partial reflection and phase shift; Zone 2 (d−Hi/2<z<d), where the effect of wave breaking and turbulence is significant; Zone 3 (d<z<Run-up height), where the pressure is induced by the run-up water; Zone 4 (Run-down<z<d), where the wave pressure is caused by the run-down effect and Zone 5 (0<z<d-Run down), where the negative wave pressures are due to partial reflection and phase shift effects. Here d is the water depth at the toe of the seawall, Hi is the incident wave height and z is the vertical elevation with toe of the seawall as origin and z is positive upward. For wave pressure prediction in zones 1 and 5, the empirical formula proposed by Ahrens et al. (1993) to estimate the wave reflection and Sutherland and Donoghue's recommendations (1998) for the estimation of phase shift of the waves caused by the sloped structures are used. Multiple regression analysis is carried out on the measured pressure data and empirical formulas are proposed for zones 2, 3 and 4. The recommendations of Van der Meer and Breteler (1990) and Schüttrumpf et al. (1994) for the prediction of wave run-down are used for pressure prediction at zone 4. Comparison of the proposed prediction formulas with the experimental results reveal that the prediction methods are good enough for practical purposes. The present study also shows a strong relation between wave reflection, wave run-up, wave run-down and phase shift of waves on wave pressures on the seawalls.  相似文献   

20.
The acute toxicity of bromochlorinated estuarine water (ca. 20%) was determined for several estuarine organisms. The most sensitive species were oysters (Crassostrea virginica, larvae and juveniles) and copepods (Acartia tonsa) with 48-h LC50's of 0·10 to 0·21 mg BrCl/litre. Palaemonetes pugio was most tolerant with a 96-h LC50 of 0·70 mg BrCl/litre. The fish species tested (Menidia menidia, Brevoortia tyrannus and Leiostomus xanthurus) all had a 96-h LC50 of 0·21–0·23 mg BrCl/litre.The BrCl toxicity data are compared with Cl2 toxicity data for the same species. When the LC50's are expressed as equivalents per litre, BrCl is found to be two to four times less toxic than Cl2. The ranking of species in terms of sensitivity is the same for both disinfectants.Some data are provided concerning the decay rates of BrCl and Cl2 in estuarine water. BrCl was found to decay more rapidly than Cl2 at higher ammonia levels (0·25 mg NH4-N/litre). The question of chemical speciation is discussed with particular reference to the differential toxicities.  相似文献   

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