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Vengatesan Venugopal Kamlesh S. Varyani Nigel D.P. Barltrop 《Ocean Engineering》2006,33(11-12):1669-1704
The results of wave force measurements carried out on a section of horizontally submerged rectangular cylinders, which are used as pontoons in many offshore structures, are reported in this paper. Two rectangular cylinders with aspect (depth–breadth) ratios equal to and and a square section (aspect ratio=1.0) cylinder are chosen for this study. Experiments are carried out in a wave tank at a water depth of 2.2 m at low Keulegan–Carpenter (KC) numbers to measure the horizontal and vertical wave forces acting on a 100 mm section, located at mid-length of the cylinders. For each cylinder, tests are carried out for two relative depths of submergence of 2.68 and 4.68. Measured wave forces in regular and irregular waves are then used to derive drag (CD) and inertia coefficients (CM). The analysis show that at very low KC numbers the inertia coefficients for all cylinders approached the potential flow values for both horizontal and vertical forces. The drag coefficients at low KC numbers exhibited large values and they decreased sharply with increase in KC number. For the square cylinder, where relatively a large KC number is obtained compared to other cylinders, inertia coefficients reached minimum values in the range of KC of about 3–4 and increased thereafter. In this range, CM values are about 50% or so, smaller than the same at KC close to zero. The results of the experiments reveal that aspect ratio has large influence on hydrodynamic coefficients. 相似文献
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Estimation of sediment sources using selected chemical tracers in the Perry lake basin,Kansas,USA 总被引：1，自引：0，他引：1
The ability to achieve meaningful decreases in sediment loads to reservoirs requires a determination of the relative importance of sediment sources within the contributing basins. In an investigation of sources of fine-grained sediment （clay and silt） within the Perry Lake Basin in northeast Kansas, representative samples of channel-bank sources, surface-soil sources （cropland and grassland）, and reservoir bottom sediment were collected, chemically analyzed, and compared. The samples were sieved to isolate the 〈63μt m fraction and analyzed for selected nutrients （total nitrogen and total phosphorus）, organic and total carbon, 25 trace elements, and the radionuclide cesium-137 （^137Cs）. On the basis of substantial and consistent compositional differences among the source types, total nitrogen （TN）, total phosphorus （TP）, total organic carbon （TOC）, and ^137Cs were selected for use in the estimation of sediment sources. To further account for differences in particle-size composition between the sources and the reservoir bottom sediment, constituent ratio and clay-normalization techniques were used. Computed ratios included TOC to TN, TOC to TP, and TN to TP. Constituent concentrations （TN, TP, TOC） and activities （^137Cs） were normalized by dividing by the percentage of clay. Thus, the sediment-source estimations involved the use of seven sediment-source indicators. Within the Perry Lake Basin, the consensus of the seven indicators was that both channel-bank and surface-soil sources were important in the Atchison County Lake and Banner Creek Reservoir subbasins, whereas channel-bank sources were dominant in the Mission Lake subbasin. On the sole basis of ^137Cs activity, surface-soil sources contributed the most free-grained sediment to Atchison County Lake, and channel-bank sources contributed the most fine-grained sediment to Banner Creek Reservoir and Mission Lake. Both the seven-indicator consensus and ^137Cs indicated that channelbank sources were dominant for Perry Lake and that channel-bank sources increased in importance with distance downstream in the basin. 相似文献