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31.
Stephen R. Turnock Alexander B. Phillips Joe Banks Rachel Nicholls-Lee 《Ocean Engineering》2011,38(11-12):1300-1307
An improved method is developed to couple an inner domain solution of the blade element momentum theory with an outer domain solution of the Reynolds averaged Navier Stokes equations for evaluating performance of tidal current turbines. A mesh sensitivity study shows that a mesh of at least 6 M cells with at least 40% of these within the turbine wake is required to ensure satisfactory convergence of the velocity deficit. In addition to the usually applied axial momentum source terms, angular momentum and turbulence intensity source terms are shown to be required to model the near wake evolution. Three different lateral turbine spacing of 2, 4 and 6 turbine diameters are used to demonstrate the influence of the effective channel blockage on the velocity distribution in the turbine bypass region, the rate of spread of the wake and the recovery of velocity distribution. A final study shows that for a fixed number of turbines minimising the lateral spacing within each row, with a small number of staggered rows spaced as longitudinally as far apart as practical, is the most effective strategy for energy capture. 相似文献
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Enhanced meteorological observations were made during the 2015 Pan and Parapan American Games in Toronto in order to measure the vertical and horizontal structure of lake-breeze events. Two scanning Doppler lidars (one fixed and one mobile), a C-band radar, and a network including 53 surface meteorological stations (mesonet) provided pressure, temperature, humidity, and wind speed and direction measurements over Lake Ontario and urban areas. These observations captured the full evolution (prior, during, and after) of 27 lake-breeze events (73% of observation days) in order to characterize the convective and dynamic processes driving lake breezes at the local scale and mesoscale. The dominant signal of a passing lake-breeze front (LBF) was an increase in dew-point temperature of \(2.3 \pm 0.3 \,^{\circ }\hbox {C}\), coinciding with a \(180^{\circ }\) shift in wind direction and a decrease in air temperature of \(2.1 \pm 0.2 \,^{\circ }\hbox {C}\). Doppler lidar observations over the lake detected lake breezes 1 hour (on average) before detection by radar and mesonet. On days with the synoptic flow in the offshore direction, the lidars observed wedge-shaped LBFs with shallow depths, which inhibited the radar’s ability to detect the lake breeze. The LBF’s ground speed and inland penetration distance were found to be well-correlated (\(r = 0.78\)), with larger inland penetration distances occurring on days with non-opposing (non-offshore) synoptic flow. The observed enhanced vertical motion \(({>} 1\hbox { m s}^{-1})\) at the LBF, observed by the lidar on 54% of lake-breeze days, was greater (at times \({>} 2.5\hbox { m s}^{-1}\)) than that observed in previous studies and longer-lasting over the lake than over land. The weaker and less pronounced lake-breeze structure over land is illustrated in two case studies highlighting the lifetime of the lake-breeze circulation and the impact of propagation distance on lake-breeze intensity. 相似文献
37.
Absolute Calibration of an Ashtech Z12-T GPS Receiver 总被引:3,自引:0,他引:3
Dual-frequency carrier phase and code measurements from geodetic type receivers are a promising tool for frequency and time
transfer. In order to use them for clock comparisons, all instrumental delays should be calibrated. We have carried out the
calibration of one such receiver, an Ashtech Z12-T type, by two different methods: first, by absolute calibration using a
GPS simulator; second, by differential calibration with respect to a time transfer receiver that had previously been calibrated.
We present the experimental set-ups and the results of the two experiments and estimate the uncertainty budget. An ultimate
uncertainty of order 1 ns in the absolute calibration seems to be attainable. ? 2001 John Wiley & Sons, Inc. 相似文献
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North Sea cod recovery? 总被引:3,自引:3,他引:3
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Winter appearance of a northeastward warm current off the southern coast of China against gale force winds is well documented but lacks a plausible explanation. Relaxation of northeasterly winds is envisaged here as a possible cause of the South China Sea Warm Current in winter. A three-dimensional circulation model for the South China Sea is first driven to equilibrium by climatological forcings. Thereafter, wind forcing is relaxed from the 15th day of each month for 9 days. In winterlike months from December to April, the wind relaxation invariably triggers a northeastward current of which the location and alongshore span are comparable to that of the observed warm current. This current is driven by the pressure gradient along the northwestern boundary of the South China Sea, sea level being high to the southwest and low to the northeast. The sea level gradient is built up by the monsoon-driven southwestward coastal current along the northwestern boundary and, after wind relaxes, triggers a return current and a sea level drop that expand southwestward from the southern coast of China to the east coast of Vietnam. The current is initially barotropic, becoming increasingly baroclinic in time as warm waters from the south are advected northeastward. The model also suggests that the sea level gradient is present in most of the months of the year, but is not as dramatic as in winter to trigger fundamental changes in the circulation of the South China Sea. 相似文献