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91.
Grain size is a fundamental property of sediments and is commonly used to describe sedimentary facies and classify sedimentary environments. Among the various conventional techniques utilized to determine grain‐size frequency distributions, sieving is the most widely applied procedure. The accuracy of such analyses is, among other factors, strongly dependent on the sieving time. However, despite a substantial amount of research in this field, optimal sieving times for different types of sediments have, to date, not been established. In this article, the influence of sieving time on grain‐size analyses of medium‐grained microtidal and mesotidal beach and dune sands has been determined. To assess the precision of important textural parameters, such as median grain size, sorting, skewness and kurtosis, an error analysis was carried out for different sieving times (2, 5, 10, 15 and 20 minutes). After calibrating the analytical and sampling methodologies, significant deviations were registered when sieving time was less than 10 minutes. However, such deviations were very small and grain‐size distributions remained almost identical for sieving times of 10 minutes and longer, relative errors being as low as 0% in some cases. 相似文献
92.
在GPS/INS组合导航中,传统UKF(Unscented Kalman Filter)计算量大,无法满足实时性要求。而且当动力学模型受到异常扰动误差影响时,其精度与稳定性易受到影响。针对以上问题,利用最小偏度单形采样策略降低UKF计算量以提高精度;通过自适应调整过程噪声以降低动态异常扰动误差对UKF精度与稳定性的影响。由此提出了一种改进UKF算法,用于GPS/INS组合导航。仿真实验结果表明,改进UKF算法用于GPS/INS组合导航的精度要优于UKF算法。 相似文献
93.
A method for detecting site liquefaction by seismic records 总被引:1,自引:0,他引:1
A simple semi-theoretical method for straightforward identification of the liquefied site by using surface acceleration records is presented by taking the natural frequency decreasing ratio of the site (NFDRS) as a fundamental benchmark and taking the time–frequency decreasing ratio of the surface acceleration (TFDRSA) as a basic index. The TFDRSA of an accelerogram is calculated and the critical point of the TFDRSA is taken as a divisive point which distinguishes liquefied sites from non-liquefied sites. The critical point value of TFDRSA is assumed to be equal to the lower limit of NFDRS caused by liquefaction and the lower limit of NFDRS is attained approximately by a two-degree-of-freedom system which is employed to simulate site liquefaction. Based on the analysis for actual earthquake records, it is proved that the theoretical model and the basic assumption here are reasonable. The reliability of the method in the paper is verified by the actual earthquake records and the comparison results indicate that the method can detect the liquefied site and non-liquefied sites including the soft sites correctly. 相似文献
94.
A series of 1 g shaking table tests, followed by the numerical simulations, is performed to investigate the effect of a circular subway tunnel on the ground motion amplification pattern. Effects of various parameters, including shear wave velocity of soil, frequency content of input motion, flexibility ratio and tunnel depth on the amplification pattern is investigated. Experimental study revealed that the tunnel did not affect free field response at dimensionless period greater than 10. Subsequent parametric study demonstrated that the amount of amplifications were mainly controlled by dimensionless period, dimensionless depth and flexibility ratio. Tunnel effect on the amplification pattern is more prominent for dimensionless period between 3 to 10, flexibility ratio greater than 1 and dimensionless depth less than 3. The study revealed that subway tunnel influences the seismic response of low period buildings, constructed above the tunnel. 相似文献
95.
96.
文中以某一实际工程为例,讨论工程场地地震安全性评价中加速度反应谱规准化对工程场地地震位移时程所带来的影响。数值结果表明,根据规准化加速度反应谱得出的位移时程存在很大的误差。建议在工程场地地震安全性评价工作中,不宜进行加速度反应谱的标定工作。 相似文献
97.
本文根据时域实时方法,对辽宁省共同台基的数字宽频带加速度记录和地震仪速度型记录进行相互仿真,并做了对比分析。结果表明,可以由加速度记录仿真得到真实的速度与位移时程;同样,地震仪速度型记录通过仿真也能得到加速度时程。由此可见,强震观测和地震观测在一定范围内是可以相互替代的。 相似文献
98.
摘要:岩质高边坡整体稳定性主要受软弱结构面及其组合控制,在组合有利的情况下,边坡主要发生浅表层块体失稳,开挖时的爆破振动作用是影响浅表层块体稳定的重要因素。本文以大渡河中游某岩质块状结构高边坡为例研究浅表层块体的稳定性,在总结浅表层块体失稳特征的基础上,实测爆破振动曲线,进行块体稳定性评价。研究结果表明,开挖后已失稳浅表层块体大多小于10m3,80%受软弱结构面控制,70%集中在马道下缘;实测的浅表层块体爆破振动加速度曲线显示,与邻近围岩相比,浅表层块体振动持续时间长,频率低,峰值小;等效静力法评价结果较爆破参数推算法更适用于临界失稳浅表层块体的稳定性评价。 相似文献
99.
APPROXIMATE REPRESENTATION OF THE p-NORM DISTRIBUTION 总被引:1,自引:0,他引:1
SUN Haiyan 《地球空间信息科学学报》2001,4(3)
1 IntroductionInsurveyingdataprocessing ,itisoftensupposedthatobservationalerrorsdistributenormally .Ifob servationscomefromthenormaldistributionalclass ,themethodofleastsquarescangivethemini_ProjectsupportedbytheSustentationPlanforOutstandingTeachersofA… 相似文献
100.
G. Siemieniec-Ozi
b
o 《Astroparticle Physics》2002,16(4):425-428
In the previous paper [Astropart. Phys. 10 (1999) 121] we showed that the opposite helicity circularly polarized Alfvén waves of finite amplitudes provide conditions to forward–backward asymmetry of particle scattering. In this letter we present an analytic solution of kinematic equation proving the enhancement of stochastic acceleration efficiency due to regular (asymmetry) term. The process is controlled by the ratio of the regular and the ordinary diffusion term. 相似文献