Measurements of the dissipation coefficient at the wavemaker in the process of generation of the resonant standing waves in a tank     

L. Shemer  M. Chamesse  E. Kit 《Mineralium Deposita》1993,28(4):506-512

The complex dissipation at the wavemaker used for direct excitation of nonlinear standing waves in the vicinity of the cut-off frequency, is measured experimentally. The results indicate that the absolute value of this dissipation coefficient exceeds significantly the estimate based on purely viscous dissipation. This is attributed to the turbulent effects resulting from the vortex shedding at the discontinuities of the wavemaker surface. It is shown that incorporation of this dissipation in the boundary condition at the wavemaker as a nonlinear term in a form generally used to describe dissipation in a turbulent boundary layer, is more appropriate allowing to remove hysteresis in the value of the wavemaker dissipation coefficient. Such hysteresis is observed when a linear dissipation model is applied.  相似文献   

Diver-operated piston corer for nearshore use     

Francis J. Sansone  James T. Hollibaugh  Sue M. Vink  Randoph M. Chambers  Samantha B. Joye  Brian N. Popp 《Estuaries and Coasts》1994,17(3):716-720

A diver-operated piston corer suitable for collecting cores of >3 m length from fine-grained nearshore sediment has been developed. The corer uses a platform that rests on the sediment surface supporting both the operators and a derrick that maintains the piston at the sediment-water interface. The core is insected into and recovered from the sediment manually. The technique offers several advantages; low cost, minimal disruption of the sediment-water interface, little compaction of the sediment, the ability to collect longer length cores than is possible with gravity corers, and the ability to be deployed from relatively small boats. Dissolved ammonium and inorganic carbon data are presented from a 3.3-m core collected by this technique from Tomales Bay, California.  相似文献   

Human influence upon sedimentation in Llangorse Lake,Wales     

R Jones  K. Benson-Evans  F. M. Chambers 《地球表面变化过程与地形》1985,10(3):227-235

Palaeolimnological studies at Llangorse Lake, Wales, constitute part of the British contribution to IGCP Project 158 (The Palaeohydrology of the Temperate Zone in the Last 15000 Years). The lake has been adopted as the Reference Site for the South Wales region under Subproject 158B (Lake and Mire Environments) and is located in the Reference Area for Britain: the Severn Basin. Results of biological, physical, and multielement chemical analyses on a 12.35 m Livingstone core are presented and compared with previous analyses on short Mackereth cores taken from two troughs in the lake basin. Human impact upon post-glacial sedimentation is assessed with reference to sediment chemistry, physical properties, and sedimentation rates, based on relative pollen, ¹⁴C, and ²¹⁰Pb dating. Vegetational history of the catchment is inferred from a pollen diagram for a section of the core from c. 8 to 6.75 m depth in which evidence for human impact is first apparent. Water content, loss on ignition, and carbonate content are presented for the whole core; density, water content, loss on ignition, carbonates, and elemental analyses of P, Ca, Mg, K, Ti, Al, Fe, and Mn for the interval 6 75 and 8.25 m depth. Sedimentation rates were low during Boreal and Atlantic times (c. 9000- 5000 BP), rose significantly from the time of the elm decline (estimated at 5000 BP) and increased further at c. 1800 BP when nekron muds were succeeded by deposition of silty clay. Inferred rates of erosion of soils from the catchment are discussed and related to sediment chemistry.  相似文献   

Third- and fourth-order mixed moments of turbulent velocity and temperature fluctuations in the atmospheric surface layer     

R. A. Antonia  A. J. Chambers  E. F. Bradley 《Boundary-Layer Meteorology》1982,22(4):421-430

Fourth-order mixed moments of velocity and temperature fluctuations, measured within the atmospheric surface layer, are compared with results obtained by assuming the quasi-Gaussian approximation. Standard deviations of the products uw, u and w(u and w are the longitudinal and vertical velocity fluctuations; is the temperature fluctuation) are in good agreement with those obtained using the quasi-Gaussian assumption. Good agreement is also obtained between measured and Gaussian estimates of fourth-order moments including all three fluctuations u, w, Schwarz inequalities, commonly used in the clipping approximation in turbulence modelling, are found to provide bounds for third-order moments of w, that are too conservative. More reasonable, tighter, bounds for these moments are given by inequalities obtained by Lumley.  相似文献   

Sulfur isotope study of a modern intertidal environment,and the interpretation of ancient sulfides     

L.A. Chambers 《Geochimica et cosmochimica acta》1982,46(5):721-728

Extensive sulfur isotope distribution data for sulfides precipitated in an intertidal environment show no distinctive features when compared with isotope values for other marine, sedimentary sulfides. The fractionation ranges from α = 1.030 to α = 1.048. The pattern is characteristic for a system essentially open to sulfate, and isotope analyses of interstitial sulfates are corroborative. A population of sulfate-reducing bacteria of the order of 10⁹ organisms per cc of interstitial water is indicated. Seasonal variation of the isotope distribution reflects a transient sulfide composition and a bacterial population in which the fractionation effect is indirectly controlled by temperature. The data presented for this modern shallow water environment are at variance with an earlier assessment of isotopic distributions in ancient sulfides which linked shallow water environments with limited fractionation (α ? 1.025) in a closed system.  相似文献   

A rod-less piston corer for lake sediments; an improved, rope-operated percussion corer   总被引：2，自引：0，他引：2  

J.W. Chambers  N.G. Cameron 《Journal of Paleolimnology》2001,25(1):117-122

A lightweight, percussion corer, suitable for use in remote lakes of moderate depth, is described. The operation of the corer and suggestions for securing and transporting long sediment cores are presented. In particular, the design and use of a recovery pot, which allows the retrieval of undisturbed cores from sediments of unknown depth, is detailed.  相似文献   

Tracer Test Evaluation of a Drainage Ditch Capture Zone   总被引：1，自引：0，他引：1  

Lucy W. Chambers  Jean M. Bahr 《Ground water》1992,30(5):667-675

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Taylor's hypothesis and spectra of velocity and temperature derivatives in a turbulent shear flow     

R. A. Antonia  A. J. Chambers  N. Phan-Thien 《Boundary-Layer Meteorology》1980,19(1):19-29

Spectral densities of temporal velocity and temperature derivatives, measured in the atmospheric turbulent boundary layer and on the axis of a turbulent plane jet, are compared with the spectral densities of the ratios of these derivatives and of the local longitudinal instantaneous velocity. The comparison between the spectral densities, when both are normalized such that the areas under the spectra are equal, shows that the corrected spectrum is lower than the measured spectrum at frequencies larger than about one-seventh of the Kolmogorov frequency while the opposite trend is observed at low frequencies. A qualitatively similar result has been obtained when the measured velocity derivative spectrum is compared with that corrected using Lumley's method. While the unnormalized spectral densities and moments of the derivatives, as corrected by Lumley's method are smaller than the corresponding measured quantities, the opposite trend is found when the correction is made by dividing the temporal derivative by the longitudinal instantaneous velocity.  相似文献   

Note on the viscous heating term in the temperature variance equation     

R. A. Antonia  A. J. Chambers  C. A. Friehe 《Boundary-Layer Meteorology》1980,19(3):269-272

Experimental results in the atmospheric surface layer indicate that the viscous heating term in the equation for the mean-square value of the turbulent temperature fluctuation is small, but the correlation between temperature and turbulent energy dissipation fluctuations is significant.  相似文献   

Spectra of temperature derivatives in the atmospheric surface layer     

Antonia  R. A.  Chambers  A. J. 《Boundary-Layer Meteorology》1978,15(3):341-345

Measured spectra ofθ _x,θ _y,θ _z, the derivatives of temperature in streamwise, lateral and vertical directions, respectively, indicate that the spectral densities ofθ _z andθ _y are nearly similar but significantly different from the spectral density ofθ _x. The high-frequency parts of the three spectra satisfy, in a qualitative sense, local isotropy requirements. In the high-frequency end of the inertial subrange, the relative behaviour of spectra ofθ _x,θ _y andθ _z is also consistent with local isotropy.  相似文献