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41.
本文从动力学的角度研究了台风流场与台风运动的关系,在实际预报中考虑地形摩擦改变的流场对台风移动的影响取得了明显的效果。 相似文献
42.
Waterfront retaining walls supporting dry backfill are subjected to hydrostatic pressure on upstream face and earth pressure on the downstream face. Under seismic conditions, if such a wall retains a submerged backfill, additional hydrodynamic pressures are generated. This paper pertains to a study in which the effect of earthquakes along with the hydrodynamic pressure including inertial forces on such a retaining wall is observed. The hydrodynamic pressure is calculated using Westergaard's approach, while the earth pressure is calculated using Mononobe-Okabe's pseudo-static analysis. It is observed that when the horizontal seismic acceleration coefficient is increased from 0 to 0.2, there is a 57% decrease in the factor of safety of the retaining wall in sliding mode. For investigating the effect of different parameters, a parametric study is also done. It is observed that if φ is increased from 30° to 35°, there is an increase in the factor of safety in the sliding mode by 20.4%. Similar observations were made for other parameters as well. Comparison of results obtained from the present approach with [Ebeling, R.M., Morrison Jr, E.E., 1992. The seismic design of waterfront retaining structures. US Army Technical Report ITL-92-11. Washington DC] reveal that the factor of safety for static condition (kh=0), calculated by both the approaches, is 1.60 while for an earthquake with kh=0.2, they differ by 22.5% due to the consideration of wall inertia in the present study. 相似文献
43.
To the first order in a Stokes expansion, the pressure force exerted by a sea state on a large horizontal cylinder represents a stationary random Gaussian process. A relationship is obtained between the spectrum of this process and the wave spectrum. As a consequence, the basic statistical properties of the height and period of the individual waves of the force-process are also obtained. It is proven that these statistical properties agree very well with the data from a small scale field experiment. 相似文献
44.
The effects of free-surface waves on the floating structures are of great importance in the offshore industry. Among the six degrees of motions of a surface ship the absence of restoring forces in surge, sway and yaw led to critical situations for moored ships in the recent times. The order of forces in horizontal plane and their exciting frequencies are matters of interest. The resonance with the presence of moored chains led to many accidents in the recent past. The lines in dry conditions may not give good damping and in wet condition they may trigger the system to chaotic motions and jumps. Two different loading conditions of a container ship model are tested with waves in laboratory conditions in two different drafts. The mooring lines are chosen as per scale law and the energy under the response spectrum is determined from the plots. The results give new insights into the movement of a berthed ships subjected to waves. Response of the moored ship to different loading conditions in different water depths are discussed in this paper. The paper gives the order of energy due to first-order and slowly varying movement of a berthed container model in a towing tank. 相似文献
45.
The stochastic properties of the drag force maxima on a circular cylinder subjected to nonlinear random waves are investigated. Unseparated laminar high Reynolds number flow is considered. A simplified approach based on second order Stokes waves is presented, including the sum-frequency effect only. It is demonstrated how a drag force formula valid for regular linear waves can be used to find the cumulative distribution function of individual drag force maxima for nonlinear irregular waves. Here the [Wang, 1968] drag force coefficient is used. 相似文献
46.
The atomic force microscopy (AFM) is a recently developed, bench-top instrument that can image the surface structures of biological
specimens at high resolution with simultaneous measurement of their size. This paper describes the application of AFM to marine
bacteria. Both natural and cultured bacteria were retained on a filter or placed on glass, washed, air-dried and observed
by AFM. The instrumental condition, the choice of suitable filter, effect of fixation and filtration, comparison with epifluorescent
microscopic (EFM) count, and the size and shape of bacterial cells were investigated. An Isopore filter was best for concentration
and subsequent observation because of its surface flatness. Cross section images showed that both rod and coccoid cells were
flattened, the former usually having a two-humped shape. Bacterial cells were differentiated from non-living particles based
on their cross section shape and size. Bacterial counts by AFM and EFM showed good agreement. Although size measurement is
easily done by the instrument, AFM tends to overestimate the size of microspheres. More work is thus needed on the size measurement
of living organisms. Because AFM easily provides images of natural bacterial cells at high magnification, it can be used as
a new tool to study the fine structures of marine bacteria.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
47.
Experimental studies on the friction coefficient between concrete and the top surface of a rubble mound foundation in China are reviewed. Through comparison of different test results, the development of this research is comprehensively analyzed. An experiment is carried out in the condition similar to prototype. The process curve of friction coefficient with the test block sliding is analyzed and a standard for determination of the friction coetfficient is defined. The variation features of the friction coefficient are analyzed on the basis of the present experimental results and other studies in China. It is shown that the friction coettfficient between concrete and the top surface of a rubble mound foundation decreases with the increase of the foundation pressure, and the friction coettqcient for a very fine leveling bed is smaller than that for a fine leveling bed. 相似文献
48.
研究具有窄谱和Weibull波高分布的波群对非线性桩柱系统作用力的统计性质。求得了桩桩的波浪峰力的各种特征值及其比值。指出这些数值不仅是阻力一惯性力参数bH的函数,也随着波群因子而变化。本文模式更具广泛性。文中给出了一系列计算图表,可从理论计算波群作用于桩柱的波浪峰力。 相似文献
49.
The effects of Coriolis force on long waves have been discussed based on gravity waves propagating in an unbounded ocean, channel and basin. In case of ocean, results show that the Coriolis effect will be significant and negligible, when the wave period is comparable to 2π/f and much shorter, respectively. Results also show in a channel, the wave amplitude and water particle velocity decrease exponentially in the positive y direction in the northern hemisphere (where f is positive). Moreover, in a basin, the Cotidal lines have been found as curves and rotate counterclockwise around the origin. 相似文献
50.
根据浅水波浪的底摩擦效应,对鲁南灵山湾和臼-岚山镇近岸区进行了波浪的海底摩擦力计算。波浪的海底摩擦力等值图与已知滨海锆石砂矿资料对比表明,底摩擦力大于0.18N/m^2的动力分选区有利于重矿物砂富集。据此,进一步预测了鲁南近岸带的砂矿富集区。 相似文献