共查询到20条相似文献，搜索用时 15 毫秒
1.
Impulsive force of debris flow on a curved dam 总被引：8，自引：0，他引：8
Although Sabo dams are an efficient method for river and basin management, traditional Sabo dams have a great impact on ecology and landscape. Moreover, such dams are hit and often damaged by great impulsive force when they block the debris flow. Therefore, alternative shapes for Sabo dam deserve thorough investigation. In this investigation, a curved dam was designed by changing the upstream-dam-surface geometric shape to reduce the impulsive force of the debris flow, with enhanced stability and reduced concrete mass being the anticipated outcomes. In this study, the flume and laboratory facilities simulated the impulsive force of the debris flow to the Sabo dams. Three geometric forms, including vertical, slanted and curved Sabo dams, were used to determine the impulsive force. Impulsive force theories of the debris flow were derived from the momentum equation and the Bernoulli equation. In these, the impulsive force was balanced by the friction force of the Sabo dam and the opposite force of the load cell behind the dam as it was hit by the debris flow. Positive correlations were found when comparing the experimental data with the theoretical results. These findings suggest that our impulsive force theory has predictive validity with regard to the experimental data. The results from both theory and experimental data clearly show that curved darns were sustained less force than the other darns under the same debris flow. This comparison demonstrates the importance of curved geometry for a well-designed Sabo dam. 相似文献
2.
Sushil Chandra Das Gupta 《Pure and Applied Geophysics》1954,27(1):1-6
Summary Displacements and stresses produced by impulsive radial pressure and by impulsive twists have been determined. In the former case total flow of energy across a spherical boundary has been obtained. 相似文献
3.
《Journal of Atmospheric and Solar》2007,69(14):1680-1689
The analysis of simultaneous observations of 128 cases of high-latitude magnetic impulse events (MIEs), as well as geomagnetic pulsations in the Pc1–2 band observed in the area of the dayside cusp, was carried out. We investigated magnetograms from the Mirny Observatory, Antarctica. As a result of the examination, three groups of impulses were identified: (1) impulses accompanied by impulsive bursts of intervals of pulsations with rising periods (IPRPs)-type geomagnetic pulsations—16% of all events, (2) impulses accompanied by impulsive bursts of the Pi1B type (bursts of irregular magnetic pulsations)—48% of all events, and (3) impulses which were not accompanied by geomagnetic pulsations within a high-frequency band—36% of all events.It was found that the maximum frequency of occurrence of the impulses accompanied by impulsive bursts of the IPRP and Pi1B types was observed between 1200 and 1300 MLT. The events of the first two groups were observed predominantly when Bz>0. It was shown that the filling frequency of impulsive bursts that accompany the occurrence of impulses depends on the amplitude of the bursts. The maximum frequency of the occurrence of impulses which were not accompanied by impulsive bursts is between 1000 and 1100 MLT. The events of the third group were observed predominantly when Bz<0. In most cases, the occurrence of impulsive bursts coincided with the leading edge of the MIE.It is supposed that the MIE generation is stimulated by intensification of the plasma turbulence level at the dayside magnetopause in consequence of modulation instability development or reconnection processes. 相似文献
4.
Sakti Kanta Chakraborty 《Pure and Applied Geophysics》1961,48(1):23-26
Summary The disturbances produced in a visco-elastic medium by impulsive forces on the surface of a spherical cavity inside the medium have been studied. 相似文献
5.
Arabinda Mukhopadhyay 《Pure and Applied Geophysics》1966,65(1):29-36
Summary The disturbances produced by time-dependent torsional body forces in a layer of elastic material lying on a rigid foundation have been discussed in this paper. Solutions have been obtained first for a general type of body force, and the solutions for an impulsive cylindrical source and an impulsive torsional line source of finite length have been deduced. It has been found that for any point in the layer, there is no disturbance up to a certain instant, after which there is a sudden displacement, which gradually falls off and tends to zero as the timet increases. 相似文献
6.
Shyamal Kumar Chatterjee 《Pure and Applied Geophysics》1969,76(1):107-109
Summary In the present note the author has considered the problem of torsional vibration of a semi-infinite non-homogeneous elastic medium by an exponentially decreasing impulsive twist applied on the plane surface. 相似文献
7.
D. Fischer 《地震工程与结构动力学》1979,7(6):587-601
The velocity potential of a compressible fluid is found by Galerkin's method. Free surface displacements and a flexible tank wall are assumed. Explicit expressions for the impulsive mass, the impulsive moment and the overturning moment are derived for wave number m = 1. In the case of m ≥ 1 the dynamic effect of the fluid is represented by a fictitious apparent mass in explicit form. 相似文献
8.
9.
Midwater signatures of eight common types of marine seismic sources have been recorded and characteristics of importance for high-resolution reflection profiling have been analyzed. Analyzed characteristics include wavelet shape, peak frequency, bandwidth, repeatability and directivity. Digitization rates required to describe the signatures before any processing and after whitening deconvolution were determined.It was intended that most of the broad range of available source types be represented. Toward that end, both resonant and impulsive types were studied; the impulsive types being both electric-discharge and pneumatic. They included a conventional sonar transducer, a chirped sonar transducer, a boomer, a plasmagun, a multi tip sparker, a watergun, an airgun and three sizes of sleevegun.It was observed that the peak frequency of each conventional sonar is similar to its nominal value and that of the chirped sonar is about the midpoint of its nominal sweep bandwidth. The dominant frequencies of the electric-discharge impulsive sources are about an order of magnitude higher than those of the pneumatic impulsive sources. Among impulsive sources, the boomer has the highest peak frequency and the watergun has the broadest bandwidth. The sleevegun and airgun were found to be comparable, both having low frequencies, poor repeatability and weak directivity. The conventional sonar and the boomer are the most repeatable sources. The boomer shows the strongest directivity with the chip sonar and the watergun being the most nondirectional.Sample rates required to describe the unprocessed signatures vary from 2 to 88 times the peak frequency and from 1 to 4 times the bandwidth 40dB below peak power. The required rate depends largely on source type but can also be affected by energy level. Bandwidth seems to be a more stable indicator than peak frequency. Rates required to describe the results of applying whitening deconvolution to signatures were about 1.5–3 times higher than rates calculated for the unprocessed signatures. This leads to the conclusion that the digitization rate required in a specific situation can depend as much on the intended processing scheme as it does on source type. 相似文献
10.
We present a compelling similarity of impulsive nitrate enhancements observed in polar ice from the northern and southern hemispheres. This analysis concentrates on the period 1940–1950, during which time the first four recorded solar cosmic ray ground-level enhancements (GLEs) occurred. GLEs are strong solar proton events. We show that large and sudden enhancements in the nitrate records from both hemispheres were observed within weeks following the recorded solar cosmic ray ground-level event. The observation of impulsive nitrate enhancements simultaneously in both hemispheres shortly after a large fluence solar proton event is strong evidence in support of a causal connection and argues strongly for rapid transport of atmospheric nitrates generated through the polar atmosphere by energetic solar proton events. 相似文献
11.
The orientations of ground motions are paramount when the pulse‐like motions and their unfavorable seismic responses are considered. This paper addresses the stochastic modeling and synthesizing of near‐fault impulsive ground motions with forward directivity effect taking the orientation of the strongest pulses into account. First, a statistical parametric analysis of velocity time histories in the orientation of the strongest pulse with a specified magnitude and various fault distances is performed. A new stochastic model is established consisting of a velocity pulse model with random parameters and a stochastic approach to synthesize high‐frequency velocity time history. The high‐frequency velocity history is achieved by integrating a stochastic high‐frequency accelerogram, which is generated via the modified K‐T spectrum of residual acceleration histories and then modulated by the specific envelope function. Next, the associated parameters of pulse model, envelope function, and power spectral density are estimated by the least‐square fitting. Some chosen parameters in the stochastic model of near‐fault motions based on correlation analysis are regarded as random variables, which are validated to follow the normal or lognormal distribution. Moreover, the number theoretical method is suggested to select efficiently representative points, for generating artificial near‐fault impulsive ground motions with the feature of the strongest pulse, which can be used to the seismic response and reliability analysis of critical structures conveniently. Finally, the simulated ground motions demonstrate that the synthetic ground motions generated by the proposed stochastic model can represent the impulsive characteristic of near‐fault ground motions. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
12.
13.
Subhas Dutta 《Pure and Applied Geophysics》1961,49(1):36-42
Summary In this paper, the propagation of disturbance due to a twisting impulsive force on the surface of a spherical cavity, in a non-homogeneous isotropic medium, in which the rigidity and density vary inversely as the distance from the centre is investigated. Numerical solution is done by the method suggested byKromm. 相似文献
14.
Shree Surendralal Ghosh 《Pure and Applied Geophysics》1969,75(1):88-92
Summary In this paper disturbances due to impulsive as well as transient load in a thin elastic finite circular plate resting on viscoelastic foundation of Pasternak type have been considered separately. 相似文献
15.
Mr. Ghasi Ram Verma M. A. 《Pure and Applied Geophysics》1957,37(1):16-20
Summary In this note displacements and stresses produced in an infinite elastic solid by impulsive radial and twisting displacements applied to the inner surface of a spherical cavity have been determined. 相似文献
16.
基于时变窄带滤波技术提取可控震源扫频信号方法研究 总被引：1，自引：0，他引：1
精密主动地震监测为我们主动探测地下介质结构, 并监视其动态变化提供了一条可能的技术途径。 由于精密控制震源释放的能量强度小, 随着传播距离的增加, 信号的快速衰减, 在离震源较远处有用的震源信号被掩盖在很强的噪声中, 这对于震相的识别与走时的拾取精度有着很大的影响。 本文设计了一种时变窄带滤波器进行更为精细的滤波, 期望进一步提高观测数据信噪比, 再结合匹配滤波方法实现主动震源信号的检测与波形变换。 另外, 由于不同震相有一定的到时差, 使用时变窄带滤波器提取一个震相波形信息时, 将压制其他震相的波形信号, 从而实现了震相分离的技术。 仿真计算与实际资料处理显示了该方法在提高观测资料质量、 震相识别分辨率及震相分离方面具有一定的有效性与优越性。 通过对广东省新丰江库区精密可控震源试验数据进行时变窄带滤波方法的处理, 在震中距为200 km左右处的台站记录中检测到主动源信号, 体现了对远台弱信号的提取能力。 相似文献
17.
Bani Pramanik 《Pure and Applied Geophysics》1972,93(1):60-67
Summary In this note displacement of a thin perfectly conducting viscoelastic plate of Reiss type in contact with vacuum on both sides and in a uniform magnetic field has been discussed. The plate has been assumed to be acted on by an impulsive load. Solutions have been obtained for small and large values of time. Results have also been discussed for some particular cases. 相似文献
18.
This paper focuses on the interstory drift ratio (IDR) demands of building structures subjected to near-fault ground motions having different impulsive characteristics based on generalized interstory drift spectral analysis. The near-fault ground motions considered include the idealized simple pulses and three groups of near-fault ground motions with forward directivity pulses, fling-step pulses and without velocity pulse. Meanwhile, the building systems are equivalently taken as shear-flexural beams with representative lateral stiffness ratios. The IDR distribution of continuous beams subjected to three groups of near-fault ground motions is acquired. It is illustrated that the maximum IDR shifts from the upper half to the lower half of buildings with an increase in lateral stiffness ratio. For long-period systems, the average IDR under impulsive ground motions is significantly greater than that under non-pulse motions. Finally, for moment-resisting frame buildings the forward directivity pulses amplify the drift response of higher modes, while the fling-step pulses excite primarily their contribution in the first mode and generate large deformation in the lower stories. The essential reason for this phenomenon is revealed according to the distinct property of near-fault impulsive ground motions and generalized drift spectral analysis. 相似文献
19.
为了探索研究各种地震前兆现象,我国地震工作者已开始对地下水化学成分在地震发生前的变化进行观测。利用爆破作实验,是企图发现地下水化学成份在冲击力的作用下的变化,为识别地震前兆提供一定的依据。 本文着重研究江西永平铜矿前后三次爆破所取得的大量水化学观测资料,探讨爆破时水化学效应的特征,并确认爆破膨胀冲击力是使氡及水化学组分发生变化的主导因素,而各观测井孔所处的地质、水文地质条件及地球化学环境的不同,又起了加强或削弱的控制作用。为合理地选择水化学观测井孔(泉),以及研究在力的作用下水化学组分的变化特征,提供了实验依据。 相似文献
20.
N. Bhanja 《Pure and Applied Geophysics》1971,85(1):182-188
Summary Stress and displacement components in a solid circular cylinder of transversely isotropic material under the torsional vibration set up by an impulsive twist applied at one and while the other end remains fixed, have been obtained by the application of Laplace transformation. 相似文献