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251.
Considerations on the squat of unevenly trimmed ships 总被引:1,自引:0,他引:1
In existing publications about empirical studies of ship squat trim is only dealt with implicitly by focussing the concern on the maximum squat. This restriction is only sufficient if a non-zero static trim is always increased dynamically, which, however, turns out to be wrong. Instead of maximum squat, we suggest a more suitable definition of the quantity relevant for under-keel clearance. In an example, it is shown that a non-zero static trim can actually be reduced dynamically, indicating a possible optimisation of trim. For a correct estimation of the squat effect on under-keel clearance, trim must be treated as an explicit parameter. Our arguments are based on full-scale experiments as well as results from numerical simulations. 相似文献
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By employing the CCM1(R15L12)long-range spectral model, study is undertaken of the effects of
sea surface temperature anomaly(SSTA) for tropical Indian ocean on circulation transformation in the early
summer in East Asia in 1991. The results indicate that warmer SSTA contributes to the increasing of the
temperature over the Plateau in early summer, resulting in the intensification of tropical easterly jet on 100 hPa
and northward shift of Northern Hemisphere subtropical westerly jet in May. It is obviously favorable for the
subtropical high enhancement over western Pacific Ocean in May and subtropical westerly jet maintaining at
35~40 °N in June, making the Mei-Yu come earlier and stay over the Changjiang basin in 1991. Furthermore,
warmer SSTA is also advantageous to averaged temperature rise in East Asia land region and Nanhai monsoon
development. These roles are helpful in accelerating the seasonal transition for East Asia in early summer. 相似文献
254.
This paper describes a geostatistical technique based on conditional simulations to assess confidence intervals of local
estimates of lake pH values on the Canadian Shield. This geostatistical approach has been developed to deal with the estimation
of phenomena with a spatial autocorrelation structure among observations. It uses the autocorrelation structure to derive
minimum-variance unbiased estimates for points that have not been measured, or to estimate average values for new surfaces.
A survey for lake water chemistry has been conducted by the Ministère de l'Environnement du Québec between 1986 and 1990, to assess surface water quality and delineate the areas affected by acid precipitation on the southern
Canadian Shield in Québec. The spatial structure of lake pH was modeled using two nested spherical variogram models, with
ranges of 20 km and 250 km, accounting respectively for 20% and 55% of the spatial variation, plus a random component accounting
for 25%. The pH data have been used to construct a number of geostatistical simulations that produce plausible realizations
of a given random function model, while 'honoring' the experimental values (i.e., the real data points are among the simulated
data), and that correspond to the same underlying variogram model. Post-processing of a large number of these simulations,
that are equally likely to occur, enables the estimation of mean pH values, the proportion of affected lakes (lakes with pH≤5.5),
and the potential error of these parameters within small regions (100 km×100 km). The method provides a procedure to establish
whether acid rain control programs will succeed in reducing acidity in surface waters, allowing one to consider small areas
with particular physiographic features rather than large drainage basins with several sources of heterogeneity. This judgment
on the reduction of surface water acidity will be possible only if the amount of uncertainty in the estimation of mean pH
is properly quantified.
Received: 3 March 1997 · Accepted: 16 November 1998 相似文献
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Smoothed particle hydrodynamics with radiation transfer 总被引:1,自引:0,他引:1
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