A novel coupled FDM-DEM modelling method for flexible membrane boundary in laboratory tests     

Hua-Xiang Zhu  Zhen-Yu Yin  Qiang Zhang 《国际地质力学数值与分析法杂志》2020,44(3):389-404

Difficulties are involved in discrete element method (DEM) modelling of the flexible boundary, that is, the membranes covering the soil sample, which can be commonly found in contemporary laboratory soil tests. In this paper, a novel method is proposed wherein the finite difference method (FDM) and DEM are coupled to simulate the rubber membrane and soil body, respectively. Numerical plane strain and triaxial tests, served by the flexible membrane, are implemented and analysed later. The effect of the membrane modulus on the measurement accuracy is considered, with analytical formulae derived to judge the significance of this effect. Based on an analysis of stress-strain responses and the grain rotation field, the mechanical performances produced by the flexible and rigid lateral boundaries are compared for the plane strain test. The results show that (1) the effect of the membrane on the test result becomes more significant at larger strain level because the membrane applies additional lateral confining pressure to the soil body; (2) the tested models reproduce typical stress and volumetric paths for specimens with shear bands; (3) for the plane strain test, the rigid lateral boundary derives a much higher peak strength and larger bulk dilatation, but a similar residual strength, compared with the flexible boundary. The latter produces a more uniform (or ‘diffuse') rotation field and more mobilised local kinematics than does the former. All simulations show that the proposed FDM-DEM coupling method is able to simulate laboratory tests with a flexible boundary membrane.  相似文献   

Chaos and elliptical galaxies     

D. Merritt 《Celestial Mechanics and Dynamical Astronomy》1996,64(1-2):55-67

Recent results on chaos in triaxial galaxy models are reviewed. Central mass concentrations like those observed in early-type galaxies - either stellar cusps, or massive black holes — render most of the box orbits in a triaxial potential stochastic. Typical Liapunov times are 3–5 crossing times, and ensembles of stochastic orbits undergo mixing on timescales that are roughly an order of magnitude longer. The replacement of the regular orbits by stochastic orbits reduces the freedom to construct self-consistent equilibria, and strong triaxiality can be ruled out for galaxies with sufficiently high central mass concentrations.  相似文献   

Interference of Multiple Strip Footings on Sand Using Small Scale Model Tests   总被引：2，自引：1，他引：1  

Jyant Kumar  Manas Kumar Bhoi 《Geotechnical and Geological Engineering》2008,26(4):469-477

By using small scale model tests, the interference effect on the vertical load-deformation behavior of a number of equally spaced strip footings, placed on the surface of dry sand, was investigated. At any stage, all the footings were assumed to (i) carry exactly equal magnitude of load, and (ii) settle to the same extent. No tilt of the footing was permitted. The effect of clear spacing (s) among footings on the results was explored. A new experimental setup was proposed in which only one footing needs to be employed rather than a number of footings. The bearing capacity increases continuously with decrease in spacing among the footings. The interference effect becomes further prominent with increase in soil friction angle. In contrast to an increase in the bearing capacity, with decrease in spacing of footings, an increase in the footing settlement associated with the ultimate state of shear failure was observed. The present experimental observations were similar to those predicted by the available theory, based on the method of characteristics. As compared to the theory, the present experimental data, however, indicates much greater effect of interference especially for larger spacing among footings.  相似文献   

饱和软黏土动力学特性循环扭剪试验研究   总被引：2，自引：0，他引：2  

李驰  王建华 《岩土力学》2008,29(2):460-464

以饱和软黏土的循环扭剪试验研究为基础,阐明不固结不排水条件下饱和软黏土的动力学特性。在循环扭剪和循环三轴两种不同试验应力状态下,通过研究不同围压和不同静、动应力组合下饱和软黏土的应力等效破坏关系和应变等效破坏关系,提出在循环荷载作用下饱和软黏土的循环破坏同样遵循Mises屈服准则,且在Mises屈服准则下,饱和软黏土的循环强度趋于不变量。循环破坏的过程可以等效为一种拟静力弹塑性循环蠕变,建立了饱和软黏土循环累积变形随静荷载、循环荷载以及循环破坏振次之间的关系式。上述结论分别从应力和变形两个方面阐述饱和软黏土的动力学特性,与试验应力状态和围压无关,可以推广到一般应力状态下。  相似文献   

岩石破坏前后曲线分类及脆-延转换围压研究——蚀变岩常规三轴压缩试验Ⅰ   总被引：2，自引：0，他引：2  

杨根兰  黄润秋  蔡国军  付小敏  林锋  徐德敏 《岩土力学》2008,29(10):2759-2763

蚀变岩是工程中少见的软弱岩类,在西南某重大水电工程中,蚀变岩处于工程的重要部位,为保证工程的长期稳定性,对蚀变岩力学特性进行了深入全面的试验研究.通过对孔隙度不同的饱水蚀变岩进行系统的常规三轴压缩试验和总结分析,提出了蚀变岩三轴压缩下破坏前应力.应变曲线可分为3大类,破坏后应力-应变曲线亦可分为3大类的形态模式.并得出结论:蚀变岩的破坏类型受围压与孔隙度的共同影响,在给定的12 MPa围压下蚀变岩以脆性破坏为主,只有孔隙度大于16%且围压大于4 MPa时才有可能进入脆-延转换状态,且脆-延转换围压随孔隙度增加而降低,临界状态应力比随孔隙度增大而增加.  相似文献   

Effect of Cyclic Loading Frequency on Undrained Behaviors of Undisturbed Marine Clay   总被引：2，自引：0，他引：2  

陈云敏  姬美秀黄博 《中国海洋工程》2004,18(4):643-651

Based on a series of cyclic triaxial tests, the effect of cyclic frequency on the undrained behaviors of undisturbed marine clay is investigated. For a given dynamic stress ratio, the accumulated pore water pressure and dynamic strain increase with the number of cycles. There exists a threshold value for beth the accumulated pore water pressure and dynamic strain, below which the effect of cyclic frequency is very small, but above which the accumulated pore water pressure and dynamic strain increase intensely with the decrease of cyclic frequency for a given number of cycles. The dynamic strength increases with the increase of cyclic frequency, whereas the effect of cyclic frequency on it gradually diminishes to zero when the number of cycles is large enough, and the dynamic strengths at different frequencies tend to the same limiting minimum dynamic strength. The test results demonstrate that the reasons for the frequency effect on the undrained soil behaviors are beth the creep effect induced by the loading rate and the decrease of sample effective confining pressure caused by the accumulated pore water pressure.  相似文献   

Low-frequency damping of a moored semisubmersible obtained from simulated extinction tests and mean wave drift forces     

T.E. Schellin  A. Kirsch 《Applied Ocean Research》1989,11(4):202-211

Low-frequency damping of a moored semisubmersible drilling platform was obtained from numerical extinction tests simulated in still water and in regular waves and from mean wave drift forces calculated at zero forward speed. The influence of drag forces was represented by the modified Morison equation. The platform as used for the 18th ITTC Comparative Mooring Study was analyzed in irregular beam waves. The computed time series of sway as well as the corresponding sway response spectrum compared favourably with model test measurements, demonstrating that this procedure to determine low-frequency damping can be effective.  相似文献   

装载GPCTD传感器的海翼水下滑翔机观测数据实时质量控制     

刘增宏  许建平  俞建成 《海洋学报(英文版)》2020,39(3):130-140

Profiles observed by Sea-Wing underwater gliders are widely applied in scientific research. However, the quality control(QC) of these data has received little attention. The mismatch between the temperature probe and conductivity cell response times generates erroneous salinities, especially across a strong thermocline. A sensor drift may occur owing to biofouling and biocide leakage into the conductivity cell when a glider has operated for several months. It is therefore critical to design a mature real-time QC procedure and develop a toolbox for the QC of Sea-Wing glider data. On the basis of temperature and salinity profiles observed by several Sea-Wing gliders each installed with a Sea-Bird Glider Payload CTD sensor, a real-time QC method including a thermal lag correction, Argo-equivalent real-time QC tests, and a simple post-processing procedure is proposed. The method can also be adopted for Petrel gliders.  相似文献   

环胶州湾公路海上段汽车尾气的环境影响     

杨三才  徐静琦  竺维丽  洪光  吴玉坤 《中国海洋大学学报(自然科学版)》1993,(1)

对类比路段进行连续模拟试验,进行现场调查,给出汽车尾气主要污染物的排污强度,预测了汽车尾气中CO、C_nH_m和NO_x的扩散范围。  相似文献   

Comparison of Strain-rate Dependent Stress-Strain Behavior from Ko-consolidated Compression and Extension Tests on Natural Hong Kong Marine Deposits     

Jian-Hua Yin  Chun-Man Cheng 《Marine Georesources & Geotechnology》2006,24(2):119-147

This article presents results from a series of K_o-consolidated compression and extension triaxial tests on specimens from undisturbed samples of Hong Kong Marine Deposits (HKMD). To investigate the strain-rate effects, a total of seven K_o-consolidated triaxial tests were conducted including four compression tests and three extension tests. After K_o-consolidation, the triaxial test specimens were sheared at step-changed axial strain rates under three different confining pressures of 50 kPa, 150 kPa, and 400 kPa, respectively. The step-changed strain rates were applied in the following order: +2%/h, +0.2%/h, +20%/h, -2%/h (unloading) and +2%/h (reloading) for the four compression tests and -2%/h, -0.2%/h, -20%/h, +2%/h (unloading) and -2%/h (reloading) for the three extension tests. The results are reported and analyzed in the paper. The results show that the strain rate effects, the stress-strain characteristics, and the effective stress paths of the specimens for tests in a compression state are different from those for tests in an extension stage. One order of magnitude increase in axial strain rate causes an average 8.6% increase in undrained shear strength for compression tests and a 12.1% increase for extension tests. It is also found that the failure mode of the specimens in compression is different from that in extension. The stress-strain behavior of specimens shows strain-softening and a clear shear band in compression tests, but strain-hardening without any clear shear band in extension tests for the same absolute value of axial strain.  相似文献