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641.
The study of localized failure under controlled conditions can be accomplished within a laboratory setting with the University of Minnesota plane-strain compression apparatus. The device provides an opportunity to observe shear faulting and to compare displacements from acoustic emission (AE) sources with global measurements. A biaxial compression test on a sandstone specimen was performed with monitoring of AE. The plane-strain test showed that the shear fault was not formed until after peak load. Compaction of the shear fault was observed from the axial and lateral measurements of displacement and the orientation of the failure plane. The AE events were modeled as displacement discontinuities. The complicated deconvolution process for the transducer transfer function was eliminated by using a simplified calibration procedure. The sources of the postpeak events were characterized as being caused predominantly by slip in the direction of the global failure plane, although components of displacement associated with closing were identified. To provide an order of magnitude estimate of the slip, the field observation of a 10−4 strain drop over the seismic area was assumed. The tangential displacement from 110 AE events was estimated to be 0.01 mm. During the same period of time, the displacement along the shear fault from global measurements was 0.03 mm. 相似文献
642.
AnewapproachtonumericalsimulationofsourcedevelopmentofearthquakeCHUN-ANTANG(唐春安)YU-FANGFU(傅宇方)WENZHAO(赵文)CenterforRockbursts... 相似文献
643.
P.S. Skjærbæk S.R.K. Nielsen A.?. Çakmak 《Soil Dynamics and Earthquake Engineering》1996,15(6):347-358
A method for the localization of structural damage in seismically excited reinforced concrete (RC) structures using a measured acceleration response time series is presented. From the measured response of some or all storeys, the two lowest smoothed eigenfrequencies and mode shape coordinates are estimated. These estimated values are used as an input to a developed substructure iteration method where local storey damages are estimated in such a way that these smoothed values are reproduced. The local damage indicator of a substructure is defined as the average reduction of the stiffness matrix of the initial undamaged substructure. The method is applied to simulated data of a six-storey, two-bay test frame (scale 1:5) that is to be tested at the Structural Laboratory of Aalborg University, Denmark. The simulations are performed using the non-linear finite element program SARCOF. Special emphasis is put on the investigation of the optimal location of measurement sensors, i.e. at which locations along the structure is the most information about the damage distribution gained. In all cases it is assumed that measurements are performed at top storey and ground surface, and the investigations are concentrated on putting one or two more measurement points in between. The two cases where the structure is excited in the first and second mode are investigated, and it is found that in general the sensors should be placed in the lower part of the structure. Furthermore, it is found that the method provides good results even when only the measurements at top storey and ground surface are used. 相似文献
644.
645.
Hartmut Spetzler Guennadi Sobolev Anatoli Koltsov Arno Zang Ivan C. Getting 《Pure and Applied Geophysics》1991,137(1-2):95-112
In this paper we report results obtained from various friction experiments under direct and oblique shear loading conditions. We used four rock types of varying brittleness (quartzite, anhydrite, limestone, pyrophyllite) with different surface roughness. The observations concentrate on the time span several milliseconds before dynamic failure occurs. During this period a premonitory, unstable phase of slip (slip 2) occurs. This differs importantly from a premonitory, stable process (slip 1) with durations of hundreds of seconds. On smooth surfaces slip 2 is usually observed with ductile rocks and less reliably with brittle rocks. Slip 2 is mostly accompanied by acoustic emissions, which increase in rate of occurrence and in magnitude until the stick-slip event. Foreshocks are observed during approximately 50% of the slip 2 events on rough surfaces. Foreshocks far exceed the acoustic noise level, which is also prevalent before stick-slip events on rough surfaces. In the direct shear experiment, where two faults are being loaded simultaneously, in about 20% of the cases precursory slip 2 was observed on the opposite side on which the final stick-slip event occurred. 相似文献
646.
According to analysis on field data obtained by ADCP(Acoustic Doppler Current Profiler),the flow regime of the Yangtze River Estuary is studied by use of a 3-D numerical model.The flow field characteristics,under the influence of Coriolis force,saltwater intrusion and freshwater inflow and tidal current interaction,are depicted in details.The main driving forces and some important effective factors of lateral,longitudinal and horizontal circulation are also analyzed. 相似文献
647.
LADCP数据处理方法的探讨及其对应软件包的使用 总被引:2,自引:0,他引:2
针对国内当前在LADCP数据处理过程中出现的问题,引入了国际海洋界目前普遍使用的两种方法,即剪切方法和逆方法,着重阐述了它们的主要思想,并详细介绍了基于这两个方法而编写的软件包,包括它们的构成、各部分的功能、具体使用步骤及注意事项。利用2005年9月至12月‘863规范化外海试验’的数据进行了大量验证,结果表明利用这两种方法获得的绝对流速与AANDERRA海流计和150 kH z船载ADCP的流速结果符合良好,平均误差为±3 cm.-s 1,可以作为一个有力的工具广泛应用于以后的海洋调查中。 相似文献
648.
声波在松散沉积物上的反射 总被引:3,自引:0,他引:3
将海底沉积物的为一种松散的湿颗粒介质,并假设海水与沉积物的界面是平的,由位移,动量密度及压强在界面处在连续性,导出平面声波在其上的反射系数,建立反射系数与沉积物的具体参数的联系。所得结果可化为前人用唯象理论所获得的形式。将理论与实验比较的结果表明,两者的一致性是好的。 相似文献
649.
水声信道高速率数据传输技术 总被引:2,自引:0,他引:2
本文介绍近年来水声信道高速率数所传输技术的一些研究进展,并结合本所研究的水声数据遥测,数字语音通讯和视频图像传输实验样机,讨论了具有抗多途干扰的声传输系统在调制信号设计及信号处理上所采用的关键技术。 相似文献
650.
Enrico De Marinis Paola Picco Alessandro Crise Otello Gasparini Stefano Salon 《Marine Ecology》2002,23(S1):122-137
Abstract. This paper describes a new Ocean Acoustic Tomography (OAT) methodology - a passive tomography - presently in an advanced development phase. This technique has been developed for long-term, extensive, remote monitoring of the seawater temperature spatial distribution, which is estimated from the received noise emitted from ships of opportunity. To test the passive tomographic processor under controlled conditions, the components of the naval noise from different kinds of vessels was analysed and realistic naval noise was simulated. The feasibility of the proposed methodology was confirmed by test-runs on semi-synthetic data; its capability to resolve temperature profiles will be better assessed with the use of real acoustic and environmental data collected during the INTIMATE00 experiment performed in October 2000 in the Atlantic Ocean off the Portuguese coast. An analysis of the space and time variability of the Empirical Orthogonal Function (EOF) decomposition of the sound speed (SSP) in the Mediterranean Sea has been carried out to identify areas where acoustic tomography can be successfully applied. Results from simulations in the South Adriatic Sea, which was identified as a region with a high sound speed variability associated with the seasonal cycle and with the main oceanographic processes, are reported. 相似文献