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跃移砂粒起跳的受力机制 总被引:4,自引:1,他引:3
根据作者拍摄的高速电影摄影实验发现, 沙粒起跳后垂直加速度均为负值, 亦即沙粒跳离地面后再无大于重力的、向上的外力作用于其上, 从而排除了八种起跳学说中的五种有关非接触力的起动学说, 即: 升力起动说、压差起动说、湍流起动说, 负压起动说和涡旋起动说。在余下的三种有关接触力的起动学说中, 作者估算后认为: 跃移起跳是斜面飞升与冲击碰撞相结合作用的结果。在凸凹不平的地面上滚动的沙粒只需很小的速度(厘米/秒量级)就可离地而去, 并从风中获取更多的能量。在地面上滚动或在空中飞行的沙粒, 以不同的角度冲击其它颗粒, 能以锐角和钝角反弹飞开。运动沙粒的动能只需有1/10转换为转动动能, 就可使沙粒获得数百以至上千转/秒的转速。 相似文献
174.
Efficient Simulation of Freak Waves in Random Oceanic Sea States 总被引:1,自引:0,他引:1
Numerical simulations of freak wave generation are studied in random oceanic sea states described by JONSWAP spectrum.The evolution of initial random wave trains is numerically carried out within the framework of the modified fourorder nonlinear Schruedinger equation (mNLSE),and some involved influence factors are also discussed.Results show that if the sideband instability is satisfied,a random wave train may evolve into a freak wave train,and simultaneously the setting of the Phillips parameter and enhancement coefficient of JONSWAP spectrum and initial random phases is very important for the formation of freak waves.The way to increase the generation efficiency of freak waves thsough changing the involved parameters is also presented. 相似文献
175.
2-D Numerical Simulation of Natural Gas Hydrate Decomposition Through Depressurization by Fully Implicit Method 总被引:1,自引:0,他引:1
Natural gas hydrate, as a potential energy resource, deposits in permafrost and marine sediment with large quantities. The current exploitation methods include depressurization, thermal stimulation, and inhibitor injection. However, many issues have to be resolved before the commercial production. In the present study, a 2-D axisymmetric simulator for gas production from hydrate reservoirs is developed. The simulator includes equations of conductive and convective heat transfer, kinetic of hydrate decomposi... 相似文献
176.
The experimental studies of the wave breaking effects on freak wave generation are presented within a finite-depth random wave train in a laboratory wave tank. The main attention is paid to the abnormal index,AI=Hmax/Hs,being used to characterize the freak waves,and the changes of the coefficient due to wave breaking. The results show that the occurrence probability of freak wave events in non-breaking waves is much larger than that in breaking waves and such occurrence in deep water is larger than that in ... 相似文献
177.
Dynamic Load Identification in Time Domain 总被引:1,自引:0,他引:1
Chu Liangcheng Qu Natsi Wu Ruifeng Lu Min Yang Guojin Assistant M. S. Dalian University of Technology Dalian
Associate Professor Dalian University of Technology Dalian
Professor Dalian University of Technology Dalian
Engineer Bohai Oil Company
Senior Engineer Bohai Oil Company 《中国海洋工程》1991,(3)
- In the time domain method the dynamic load is successfully identified when the accelerations, velocities and displacements or velocities and displacements of the structure are known. But in engineering practice or experiments usually only the acceleration response is recorded. In this paper an improved time domain method is proposed for dynamic load identification. In this method by using of Duhamel integral, only the acceleration response is required for load identification. As an application of the present method, the dynamic ice load on a Bohai offshore platform is identified based on some measured acceleration. The identified values of ice load are in good agreement with the measured ones. 相似文献
178.
He Guangne Yang Bin
Professor Dalian University of Technology Dalian Engineer Design Research Institute of Shanghai Harbour Engineering Shanghai 《中国海洋工程》1995,(4)
The current safety factor method for evaluating earth embankment stability is not very rational since the assessment of slope stability is really an uncertainty problem. In order to consider the random property of this problem, the probabilistic analysis is introduced herein. Finally, the stability of a real beach earth embankment is analysed by means of the suggested probabilitic approach. It may be seen that the results of analysis can represent the numerical assessment of the degree of seismic stability. 相似文献
179.
XiaoXiwu Wang Haiqi Lecturer Huazhong University of Science Technology Wuhan Hubei Province Professor Huazhong University of Science Technology Wuhan Hubei Province 《中国海洋工程》1994,(2)
- Studied in this paper is free vibration of a long span pipeline with nonlinearities taken into account. The pipeline sags under gravity and takes the shape of a plane curve. Vibration in the plane and out of the plane is regarded as small motions about the large static deflection. Manifestations of nonlinearities such as amplitude-dependent frequencies and internal resonance are investigated. 相似文献
180.
Li Dejun Shen Guoguang Wang Rixin Cheng Hong Professor Dept. of Ocean Architecture Engineering Tianjin University Tianjin Lecturer Dept. of Ocean Architecture Engineering Tianjin University Tianjin Engineer Naval Research Centre P. L. A. of China Beijing 《中国海洋工程》1995,(4)
Using the axial symmetry results of marker and cell (MAC) method as initial value in this paper, two numerical calculating methods are presented for the late wavemaking response induced by explosion in harbour. One of the methods is the superposition method of the vibration mode based on fluid slosh in container. Another one is the joining method of the MAC results with the shallow wave theory calculation in time domain. As a practical example, it is conducted to the numerical calculation about 1000 ton TNT equivalent explosion within touch of water surface. The results show that it can be rationally described with the methods to the wavemaking progress and character. The numerical results are identical with the observed scene on the spot experiment. The methods are simple and applicable in the engineering design. 相似文献