Theoretical wind wave frequency spectra in shallow water     

Wen Shengchang 《海洋学报(英文版)》1988,7(3):325-343

The method developed by Wen et al. (1988 a) for deriving theoretical wind wave frequency spectrum in deep water is extended to the case of water of finite depth, in which a parameter η=H/d is introduced, where H and d represent the average wave height and water depth respectively. The derived spectra reduce to those in deep water when η=0. The case of η=1/2 corresponds to waves impending to break because of the effect of the bottom. Simplified forms of spectra are given. The theoretical results agree with the observed spectra well.  相似文献   

Trace metals in selected organisms from the Adriatic sea     

D. Martin i&#x;  Z&#x;. Kwokal  M. Branica  M. Stoeppler 《Marine Chemistry》1987,22(2-4)

Extensive surveys were made to establish the concentrations of several metals (Zn, Cd, Pb, Cu and Hg) in various marine organisms from different parts of the Adriatic Sea in the period from 1979 to 1985. The results obtained are based on analyses which were performed in conjunction with carefully tested procedures. Proper sampling, sample storage, treatment of samples and final analytical determination has excluded artefacts which would influence the accuracy, or cause contamination and/or trace metal losses.The metal concentrations in shellfish from the coastal areas of the Adriatic Sea are in the range of the lowest values obtained for similar organisms from other localities throughout the Mediterranean Sea. Special attention has been paid to the anthropogenic influence on trace metal concentrations in organisms living in the vicinity of domestic sewage and/or industrial waste-water outflows.  相似文献   

Phytoplankton productivity in relation to light intensity: A simple equation     

D. H. Peterson  M. J. Perry  K. E. Bencala  M. C. Talbot 《Estuarine, Coastal and Shelf Science》1987,24(6)

A simple exponential equation is used to describe photosynthetic rate as a function of light intensity for a variety of unicellular algae and higher plants where photosynthesis is proportional to (1-e^−β1). The parameter β ( ) is derived by a simultaneous curve-fitting method, where I is incident quantum-flux density. The exponential equation is tested against a wide range of data and is found to adequately describe P vs. I curves. The errors associated with photosynthetic parameters are calculated. A simplified statistical model (Poisson) of photon capture provides a biophysical basis for the equation and for its ability to fit a range of light intensities. The exponential equation provides a non-subjective simultaneous curve fitting estimate for photosynthetic efficiency (a) which is less ambiguous than subjective methods: subjective methods assume that a linear region of the P vs. I curve is readily identifiable. Photosynthetic parameters β and a are used widely in aquatic studies to define photosynthesis at low quantum flux. These parameters are particularly important in estuarine environments where high suspended-material concentrations and high diffuse-light extinction coefficients are commonly encountered.  相似文献   

Effects of taxonomic uncertainty on species diversity indices     

R.S.S. Wu 《Marine environmental research》1982,6(3):215-225

As a result of taxonomic uncertainty, generic and higher taxonomic ranks (family, order, class or phylum) are often treated as units in calculating diversity indices, instead of species. In this paper, the errors introduced by such practices are examined for various diversity indices (Shannon - Wiener Index, Maximum Information Index, Evenness, Margalef's Species Richness Index and Hurlbert's Probability of Interspecific Encounter). The use of higher taxonomic ranks may invalidate comparison of diversity indices. In a single study, substantial error and erroneous conclusion may arise, even if consistent practices are adopted.  相似文献   

Geotechnical aspects of fine-grained mass flow deposits: California Continental Borderland     

F. J. Hein  D. S. Gorsline 《Geo-Marine Letters》1981,1(1):1-5

Seismic reflection profiling demonstrates the importance of mass movement in the north-central California Borderland. Bulk properties of surficial hemipelagic sediments in the Santa Barbara, Santa Cruz, and San Nicolas basins show that different types of mass-transported sediments have different properties, although their general sedimentologic characteristics are very similar. Slump deposits have moderate water contents (48% wet weight basis), high plasticity indices (46%), and moderate activities (1.6). For debris flows these values are low: 28%, 5%, and 0.3, respectively, and for other types (liquefied flow, mudflows, and turbidities) the values are high: 54 to 63%, 49 to 58%, and 1.2 to 1.5, respectively.  相似文献   

Sea-structure interaction for tripod-type steel gravity platform     

M. Berta  A. Blandino  D. Marcon  A. Paruzzolo 《Applied Ocean Research》1981,3(3):113-118

The paper deals with a numerical integrated procedure to calculate the effects of the interaction between sea waves and a tripod-type steel gravity platform. The main aspects to be taken into account for a reliable wave loading analysis of such a new type of platform are emphasized. Among them, the field perturbation effect due to the large bodies presence is analysed. Finally, some principal results in terms of structure global loads obtained by the numerical integrated procedure are presented.  相似文献   

Waveform Shaping of Sonar Transducers for Improving the Vertical Resolution in Sub-bottom Sediments Profiling     

P. Cobo  C. Ranz  A. Fernández  M. Cuesta  D.K. Anthony  M. Siguero 《Marine Geophysical Researches》2005,26(2-4):87-95

Vertical resolution is of fundamental importance in sonar exploration and is directly related to the duration of the acoustic pulse generated by the transducer. The shorter the radiated pulse, the higher the vertical resolution. Many sub-bottom profiling sonar systems use piezoelectric transducers because they are reversible and well understood. Piezoelectric projectors are normally resonant transducers, which are intrinsically narrowband. A piezoelectric transducer is usually driven by a tone-burst. However, it is possible to use Fourier techniques to find a pre-compensated electrical driving function so that the transducer radiates a prescribed wider band acoustic waveform. This technique can be applied to synthesize zero-phase cosine-magnitude, Gaussian, and bionic pulses, with a conventional sandwich transducer. Zero-phase cosine-magnitude waveforms provide minimum length pulses (and therefore maximum resolution) within a prescribed frequency band.The aim of this paper is to illustrate the synthesis of wideband acoustic pulses using an underwater piezoelectric projector. The conventional acoustic waveform radiated when a Tonpiltz transducer is transiently excited using a “click” and allows its frequency response function to be measured. This function is used to design the electrical signal which then drives the transducer so that it radiates the shortest pulse compatible with its mechanical response. The significant resolution enhancement of the waveform shaping process is illustrated by its application to a sediment wedge model.  相似文献   

Using ocean ambient noise for array self-localization and self-synchronization   总被引：2，自引：0，他引：2  

Sabra  K.G. Roux  P. Thode  A.M. D'Spain  G.L. Hodgkiss  W.S. Kuperman  W.A. 《Oceanic Engineering, IEEE Journal of》2005,30(2):338-347

Estimates of the travel times between the elements of a bottom hydrophone array can be extracted from the time-averaged ambient noise cross-correlation function (NCF). This is confirmed using 11-min-long data blocks of ambient noise recordings that were collected in May 1995 near the southern California coast at an average depth of 21 m in the 150-700 Hz frequency range. Coherent horizontal wavefronts emerging from the time derivative of the NCF are obtained across the array's aperture and are related to the direct arrival time of the time-domain Green's function (TDGF). These coherent wavefronts are used for array element self-localization (AESL) and array element self-synchronization (AESS). The estimated array element locations are used to beamform on a towed source.  相似文献   

Numerical prediction of performance of submerged breakwaters   总被引：1，自引：0，他引：1  

A. Chiranjeevi Rambabu  J.S. Mani 《Ocean Engineering》2005,32(10):88-1246

The results of a numerical model study on the transmission characteristics of a submerged breakwater are presented. Study aimed to determine the effect of depth of submergence, crest width, initial wave conditions and material properties on the transmission characteristics of the submerged breakwater. The results highlight the optimum crest width of the breakwater and optimum clear spacing between two breakwaters. A submerged permeable breakwater with d_s/d=0.5, p=0.3 and f=1.0, reduces the transmission coefficient by about 10% than the impermeable breakwater. The results indicates an optimum width ratio of B/d=0.75 for achieving minimum transmission. By restricting the effective width ratio of the series of breakwaters to 0.75, studies were conducted to determine the effect of clear spacing between breakwaters on transmission coefficient, suggesting an optimum clear spacing of w/b=2.00 to obtain K_t below 0.6.  相似文献   

Degradation in Cemented Marine Clay Subjected to Cyclic Compressive Loading   总被引：1，自引：0，他引：1  

G. Gerald Moses  S. Narasimha Rao 《Marine Georesources & Geotechnology》2003,21(1):37-62

The influence of cyclic loading on the strength and deformation behavior of cemented marine clay has been studied. This marine clay is of recent Pleistocene origin and deposited in a shallow water marine environment. Open pits were dug in sheeted enclosures and from these pits, undisturbed samples were taken for strength testing. A series of standard triaxial shear tests and stress controlled one-way cyclic load tests were conducted at consolidation stress ranges below and above the preconsolidation pressure. For the stress levels below the preconsolidation pressure, the cyclic loading has brought about the collapse of the cementation bond through an increase in strains, and at higher pressure ranges, the soil behaves like typical soft clay. This experiment studied the rate of development of strain and pore water pressure and shows that rate is a function of number of cycles, applied stress, and stress history. In addition, soil degradation during cyclic loading is studied in terms of Degradation Index. Attempt has been made to predict stain, pore water pressure, and degradation index through an empirical model.  相似文献