Experimental Study on Crescent Waves Diffracted by A Circular Cylinder     

Kai Yan  Liang-duo Shen  Jin-wei Shang  Liang Ma  Zhi-li Zou 《中国海洋工程》2018,32(5):624-632

Crescent waves often observed on the sea surface are unusual wave pattern induced by the instability of Stokes wave. The paper presents the experimental results of the wave field around a circular cylinder generated by the diffraction of crescent wave in order to examine the difference of diffracted crescent waves from the commonly-used diffracted Stokes waves. The results show that with the existence of the cylinder, the crescent wave pattern can still get fully developed, and with the presence of this type of wave pattern, the symmetry breaking of the wave amplitude distribution occurs and there are extra wave components at the frequencies of 0.5ω₀, 1.5ω₀ and 2.5ω₀ (ω₀ is the frequency of Stokes waves) appearing in the wave amplitude spectrum.  相似文献   

Anomalously low alkenone temperatures caused by lateral particle and sediment transport in the Malvinas Current region, western Argentine Basin     

Albert Benthien  Peter J. Müller 《Deep Sea Research Part I: Oceanographic Research Papers》2000,47(12):373

We analysed the alkenone unsaturation ratio (U^K′₃₇) in 87 surface sediment samples from the western South Atlantic (5°N–50°S) in order to evaluate its applicability as a paleotemperature tool for this part of the ocean. The measured U^K′₃₇ ratios were converted into temperature using the global core-top calibration of Müller et al. (1998) and compared with annual mean atlas sea-surface temperatures (SSTs) of overlying surface waters. The results reveal a close correspondence (<1.5°C) between atlas and alkenone temperatures for the Western Tropical Atlantic and the Brazil Current region north of 32°S, but deviating low alkenone temperatures by −2° to −6°C are found in the regions of the Brazil–Malvinas Confluence (35–39°S) and the Malvinas Current (41–48°S). From the oceanographic evidence these low U^K′₃₇ values cannot be explained by preferential alkenone production below the mixed layer or during the cold season. Higher nutrient availability and algal growth rates are also unlikely causes. Instead, our results imply that lateral displacement of suspended particles and sediments, caused by strong surface and bottom currents, benthic storms, and downslope processes is responsible for the deviating U^K′₃₇ temperatures. In this way, particles and sediments carrying a cold water U^K′₃₇ signal of coastal or southern origin are transported northward and offshore into areas with warmer surface waters. In the northern Argentine Basin the depth between displaced and unaffected sediments appears to coincide with the boundary between the northward flowing Lower Circumpolar Deep Water (LCDW) and the southward flowing North Atlantic Deep Water (NADW) at about 4000 m.  相似文献   

A review of the analyses of ocean wave groups     

J.R. Medina  R.T. Hudspeth 《Coastal Engineering》1990,14(6)

The most common parameters and functions used to characterize wave groups in linear seas are reviewed and interrelated in a unified manner. A three-axes representation of run lengths is used to characterize wave groups using exponential and Markov chain approximations. A relationship between four parameters (Q_p, Q_e, κ², and ρ²) and the correlation coefficient between consecutive wave heights [r_HH(1)] is demonstrated. The wave-height function method is reviewed in some detail in order to relate the run length theory with envelope theories. The theoretical estimates used to demonstrate the relationships between the various parameters must be considered as only first-order trends to parameter estimates computed from real wave data due to the statistical variability in these estimates when computed from real wave data.  相似文献   

Improving estuarine net flux estimates for dissolved cadmium export at the annual timescale: Application to the Gironde Estuary     

Aymeric Dabrin  Jrg Schfer  Grard Blanc  Emilie Strady  Matthieu Masson  Ccile Bossy  Sabine Castelle  Naïg Girardot  Alexandra Coynel 《Estuarine, Coastal and Shelf Science》2009,84(4):429-439

Dissolved Cd (Cd_D) concentrations along the salinity gradient were measured in surface water of the Gironde Estuary during 15 cruises (2001–2007), covering a wide range of contrasting situations in terms of hydrology, turbidity and season. During all situations dissolved Cd concentrations displayed maximum values in the mid-salinity range, reflecting Cd addition by chloride-induced desorption and complexation. The daily net Cd_D fluxes from the Gironde Estuary to the coastal ocean were estimated using Boyle's method. Extrapolating Cd_D concentrations in the high salinity range to the freshwater end member using a theoretical dilution line produced 15 theoretical Cd concentrations (Cd_D⁰), each representative of one distinct situation. The obtained Cd_D⁰ concentrations were relatively similar (201 ± 28 ng L⁻¹) when freshwater discharge Q was >500 m³ s⁻¹ (508 ≤ Q ≤ 2600 m³ s⁻¹), but were highly variable (340 ± 80 ng L⁻¹; 247–490 ng L⁻¹) for low discharge situations (169 ≤ Q ≤ 368 m³ s⁻¹). The respective daily Cd_D net fluxes were 5–39 kg day⁻¹, mainly depending on freshwater discharge. As this observation invalidates the existing method of estimating annual Cd_D net fluxes, we proposed an empirical model, using representative Cd_D⁰ values and daily freshwater discharges for the 2001–2007 period. Subsequent integration produced reliable Cd_D net flux estimates for the Gironde Estuary at the annual timescale that ranged between 3.8–5.0 t a⁻¹ in 2005 and 6.0–7.2 t a⁻¹ in 2004, depending on freshwater discharge. Comparing Cd_D net fluxes with the incoming Cd_D fluxes suggested that the annual net Cd_D addition in the Gironde Estuary ranged from 3.5 to 6.7 t a⁻¹, without any clear temporal trend during the past seven years. The annual Cd_D net fluxes did not show a clearly decreasing trend in spite of an overall decrease by a factor 6 in Cd gross fluxes during the past decade. Furthermore, in six years out of seven (except 2003), the annual Cd_D net fluxes even exceeded river borne total (dissolved + particulate) gross Cd fluxes into the estuary. These observations were attributed to progressive Cd desorption from both suspended particles and bottom sediment during various sedimentation–resuspension cycles induced by tidal currents and/or continuous dredging (navigation channel) and diverse intra-estuarine sources (wet deposition, urban sources, and agriculture). Provided that gross fluxes remain stable over time, dissolved Cd exportation from the Gironde Estuary to the coastal ocean may remain at the present level for the coming decade and the estuarine sedimentary Cd stock is forecast to decrease slowly.  相似文献   

Steepness and spectrum of nonlinear deformed shallow water wave     

Narcisse Zahibo  Irina Didenkulova  Andrey Kurkin  Efim Pelinovsky   《Ocean Engineering》2008,35(1):47-52

  相似文献   

Seasonal variations of alkenones and U₃₇ in the Chesapeake Bay water column     

Jennifer L. Mercer  Meixun Zhao  Steven M. Colman   《Estuarine, Coastal and Shelf Science》2005,63(4):675-682

Alkenone unsaturation indices (U^K₃₇ and U^K′₃₇) have long been used as proxies for surface water temperature in the open ocean. Recent studies have suggested that in other marine environments, variables other than temperature may affect both the production of alkenones and the values of the indices. Here, we present the results of a reconnaissance field study in which alkenones were extracted from particulate matter filtered from the water column in Chesapeake Bay during 2000 and 2001. A multivariate analysis shows a strong positive correlation between U^K₃₇ (and U^K′₃₇) values and temperature, and a significant negative correlation between U^K₃₇ (and U^K′₃₇) values and nitrate concentrations. However, temperature and nitrate concentrations also co-vary significantly. The temperature vs. U^K₃₇ relationships (U^K₃₇=0.018 (T)−0.162, R²=0.84, U^K′₃₇=0.013 (T)−0.04, R²=0.80) have lower slopes than the open-ocean equations of Prahl et al. [1988. Further evaluation of long-chain alkenones as indicators of paleoceanographic conditions. Geochimica et Cosmochimica Acta 52, 2303–2310] and Müller et al. [1998. Calibration of the alkenone paleotemperature index U^K′₃₇ based on core-tops from the eastern South Atlantic and the global ocean (60°N–60°S). Geochimica et Cosmochimica Acta 62, 1757–1772], but are similar to the relationships found in controlled studies with elevated nutrient levels and higher nitrate:phosphate (N:P) ratios. This implies that high nutrient levels in Chesapeake Bay have either lowered the U^K₃₇ vs. temperature slope, or nutrient levels are the main controller of the U^K₃₇ index. In addition, particularly high abundances (>5% of total C₃₇ alkenones) of the tetra-unsaturated ketone, C_37:4, were found when water temperatures reached 25 °C or higher, thus posing further questions about the controls on alkenone production as well as the biochemical roles of alkenones.  相似文献   

Effects of bed perturbation and velocity asymmetry on ripple initiation: wave-flume experiments     

Tomohiro Sekiguchi  Tsuguo Sunamura 《Coastal Engineering》2004,50(4):231

Laboratory experiments using a wave flume were designed to examine the threshold condition for ripple formation under asymmetrical oscillatory flows on an artificially roughened bed. Three types of sand beds were prepared in the experiments: they were flat, notched, and notch-mounded beds with bed roughness increasing in this order. The beds were constructed with three kinds of well-sorted sand with similar density, but different diameters. Data analyses were made using the two dimensionless parameters: the mobility number, M, a simplified form of the Shields number, and the Ursell number, U, a surrogate for asymmetry of flow field. The result confirmed that the threshold for ripple initiation is decreased with increasing bed perturbation and that as the bed perturbation increases, the dependency of this threshold on the flow asymmetry becomes less and finally null for the notch-mounded bed. This relationship is quantified by the following equations: M=17−14.5e^−0.03U on the flat bed, M=5.0−2.5e^−0.1U for the notched bed, and M=2.5 for the notch-mounded bed. A comparison between the previous field data and the present laboratory findings indicates that the threshold in the notch-mounded bed experiment, M=2.5, seems to provide a critical condition for rippling in the natural environment.  相似文献   

On the planing of a flat plate at high Froude numbers in a two-dimensional case     

Y.K. Chung  H.H. Chun   《Ocean Engineering》2008,35(7):646-652

We seek the solution of the planing of a flat plate at high Froude numbers by a perturbation procedure. The angle of attack of the plate is assumed to vary with the speed of the plate in the present study. A harmonic function K is introduced for the solution of the first-order disturbance potential which becomes the Green function in the limiting case when the Froude number tends to infinity. We get the solution of the first-order potential from Green's theorem applied to K and the first-order potential. Then we obtain the asymptotic solutions of the angle of attack α, lift L and drag D as follows: where α1. Here W, L_W, and U are the weight of the plate per unit width, wetted length, and speed of the plate, respectively.  相似文献   

Ship hull characteristics from surface wake synthetic aperture radar (SAR) imagery     

Owen M. Griffin  Henry T. Wang  Guy A. Meadows 《Ocean Engineering》1996,23(5):363-383

Improved data collection and processing technologies along with the use of high resolution spectral techniques soon will make it possible to obtain estimates of the Kelvin wave amplitude function A(θ), ship speed U, and ship heading α from synthetic aperture radar images of ship wakes. This paper presents a series of methods for deriving additional hull characteristics such as the length L, volume V, and offsets ζ(x,z) from this spectral and surface wave information. The first method estimates the ship length by taking the Fourier transform of the slope amplitude function |kA|. The remaining estimates make use of the hull inversion code developed at the University of Michigan by Wu in 1991. The accuracy of the hull offsets predicted by the code is first determined for various options for solving the linear inversion problem. In this case, both the magnitude and phase of A(θ) are known in addition to the hull draft H. Since the draft is not often known a priori, the accuracy of the code is determined next by predicting the volume of the ship for an approximate though plausible input value of H. Finally, the accuracy of the non-linear inversion problem of obtaining offsets along the entire hull is investigated when only the magnitude but not the phase of A(θ) is known.  相似文献   

Determination of gas bubble fractionation rates in the deep ocean by laser Raman spectroscopy     

S.N. White  P.G. Brewer  E.T. Peltzer 《Marine Chemistry》2006,99(1-4):12

A new deep-sea laser Raman spectrometer (DORISS—Deep Ocean Raman In Situ Spectrometer) is used to observe the preferential dissolution of CO₂ into seawater from a 50%–50% CO₂–N₂ gas mixture in a set of experiments that test a proposed method of CO₂ sequestration in the deep ocean. In a first set of experiments performed at 300 m depth, an open-bottomed 1000 cm³ cube was used to contain the gas mixture; and in a second set of experiments a 2.5 cm³ funnel was used to hold a bubble of the gas mixture in front of the sampling optic. By observing the changing ratios of the CO₂ and N₂ Raman bands we were able to determine the gas flux and the mass transfer coefficient at 300 m depth and compare them to theoretical calculations for air–sea gas exchange. Although each experiment had a different configuration, comparable results were obtained. As expected, the ratio of CO₂ to N₂ drops off at an exponential rate as CO₂ is preferentially dissolved in seawater. In fitting the data with theoretical gas flux calculations, the boundary layer thickness was determined to be  42 μm for the gas cube, and  165 μm for the gas funnel reflecting different boundary layer turbulence. The mass transfer coefficients for CO₂ are k_L = 2.82 × 10^− 5 m/s for the gas cube experiment, and k_L = 7.98 × 10^− 6 m/s for the gas funnel experiment.  相似文献   

A 3-D model based on Navier–Stokes equations for regular and irregular water wave propagation     

Bin Li   《Ocean Engineering》2008,35(17-18):1842-1853

A spatial fixed σ-coordinate is used to transform the Navier–Stokes equations from the sea bed to the still water level. In the fixed σ-coordinate system only a very small number of vertical grid points are required for the numerical model. The time step for using the spatial fixed σ-coordinate is efficiently larger than that of using a time dependent σ-coordinate, as there is substantial truncation error involved in the time dependent σ-coordinate transformation. There is no need to carry out the σ-coordinate transformation at each time step, which can reduce computational times. It is important that wave breaking can be potentially modeled in the fixed σ-coordinate system, but in a time-dependent σ-coordinate system the wave breaking cannot be modeled. A projection method is used to separate advection and diffusion terms from the pressure terms in Navier–Stokes equations. The pressure variable is further separated into hydrostatic and hydrodynamic pressures so that the computer rounding errors can be largely avoided. In order to reduce computational time of solving the hydrodynamic pressure equation, at every time step the initial pressure is extrapolated in time domain using computed pressures from previous time steps, and then corrected in spatial domain using a multigrid method. For each time step, only a few of iterations (typically six iterations) are required for solving the pressure equation. The model is tested against available experimental data for regular and irregular waves and good agreement between calculation results and the measured data has been achieved.  相似文献   

An approach for eliminating re-reflected waves     

Sheng-Wen Twu  Jyh-Jong Duann 《Ocean Engineering》1995,22(5)

Theoretical and experimental studies were conducted to eliminate the re-reflected waves in a wave channel by installing a wavefilter in front of the wavemaker. A thin porous mesh is installed in front of the wavemaker.to serve as a wavefilter. A porous-effect parameter [Chwang, A. T. and Li, W. (1983), A piston-type porous wavemaker theory. J. Engng Math. 17, 301–313], G₀ = bω/μL₀, is employed to characterize the transmissability of the wavefilter. Theoretical relationships are established between the amplitude of progressive wave and G₀, and the distances between the wavefilter, the wavemaker and the test structure. The proper location for the wavefilter to eliminate re-reflected waves can be determined. Several experimental tests were conducted to verify the theory.Both theoretical and experimental studies show that re-reflected waves can be effectively eliminated by placing a wavefilter at a proper position between the wavemaker and the test structure, provided G₀ ≤ 1. For G₀ > 1 however, the wavefilter would fail.  相似文献