超导/磁阻式复合磁传感器高灵敏及三轴化研究

超导/磁阻式复合磁传感器利用超导磁放大器上千倍的磁场放大能力,可大幅提升磁阻式传感器灵敏度,有望实现fT级的磁场分辨力,满足水下目标探测、生物磁场检测等新型弱磁探测需求。经过几十年的研究,超导/磁阻式复合磁传感器相关工作取得了重要进展和系列成果。首先从复合磁传感器工作原理、高灵敏和三轴化研究现状等方面进行了系统的回顾和总结,其中超导磁放大器的放大倍数在实验上已经超过1 000,低温下(4.2 K)的热噪声仅为2 fT/√Hz,然后针对目前存在的问题对下一步研究工作进行了简要展望。论文相关工作对于提升超导/磁阻式复合传感器性能、促进其推广应用具有重要的借鉴和指导意义。

堆石料三轴湿化变形特性试验研究

通过对2种不同堆石料的高压三轴湿化试验,分析了引起湿化变形的因素,并对湿化应力与湿化变形进行了初步的分析,发现湿化应力与湿化变形之间存在有双曲线关系,其规律类似三轴压缩的应力应变关系;但湿化应力–应变的初始切线模量与周围压力之间的关系并不完全符合Janbu公式,同时对湿化轴向应变与湿化体应变进行分析,发现不同于三轴压缩,其关系并非双曲线。

压实黄土三轴湿化变形特性试验研究

采用常规三轴试验研究压实黄土浸水湿化变形特性,分析了不同初始含水率、压实度、围压、主应力差及湿化水头条件下黄土浸水湿化变形特点及原因。结果表明:土样固结稳定后进行浸水湿化再次达稳定状态所需时间随主应力差和初始含水率的增大而增大,随压实度、所加围压及湿化水头的增大而减小;土样湿化轴向应变随主应力差、湿化水头的增大而增大,随围压、初始含水率、压实度的增大而减小;而体变则随湿化水头增大而增大,随主应力差、围压、初始含水率、压实度的增大而减小。

张峰水库粗粒料三轴湿化试验研究

通过对张峰水库两组粗粒料试样进行高压三轴湿化试验,分析了湿化后的剪切强度特征,以及湿化体积应变、湿化轴向应变与围压和应力水平的关系。结果表明:不同应力水平对湿化后强度特征的影响较小;在应力水平较低时,湿化体积应变基本不随围压和应力水平的变化而变化;无论是在较低应力水平下还是在较高应力水平下,湿化体积应变随着围压的增大会有所波动,但总体趋势呈随围压的增大而增大;湿化轴向应变在低应力水平下随围压变化产生的变化量很小;同种试样在同样的试验条件下,在水的润滑作用下,固结排气剪试验得到的抗剪强度较大,固结排水剪试验得到的抗剪强度较小,三轴湿化试验得到的抗剪强度居中。

基于数字图像技术的砂土液化可视化动三轴试验研究

常规动三轴试验不能实现试样细观结构的观测,对原有CKC型振动三轴仪实施可视化改进,开发用于试验过程试样细观结构观测的试验系统。在砂土振动液化试验中,利用显微数码摄录技术全程动态摄录整个试验过程砂土细观结构的变化,从摄录录像中提取特征时刻的数字图像照片,导入自主开发的数字图像细观结构分析软件DeoDIP,对比分析液化前后砂土细观结构(颗粒定向性、接触法向、接触数)的演化规律,追踪标志砂颗粒的运动轨迹。结果表明:液化时,颗粒长轴没有明显的优选方向,制样引起的初始各向异性被消除;接触法向呈现各向异性特征,其主方向在整个试验过程中一直偏于竖直方向;平均接触数发生了损失,液化排水后得到恢复,说明试样振动密实。液化前,各标志颗粒具有基本相同的运动轨迹,颗粒运动以平动为主,旋转作用很小,颗粒运动与试样变形保持较好的整体性;颗粒之间相对运动加剧,颗粒之间不断接触分离,部分颗粒出现悬浮现象,且颗粒旋转明显。可视化三轴试验结果不仅有助于研究砂土液化的细观力学机理,并能为液化细观数值模拟提供试验基础。

真三轴煤层钻孔承载破坏层理效应试验研究

为探究层理对真三轴环境下煤层钻孔动态破坏特征影响,采用煤岩体单面可视真三轴试验仪器开展含层理煤层钻孔承载破坏试验,并结合数字图像相关和声发射分析方法进行研究。研究结果表明:试样破坏经历3个阶段,阶段Ⅰ,分析区域边缘剪切应变集中,孔壁破裂伴随煤颗粒弹射,声发射累计事件数和能量活跃性较低;阶段Ⅱ,孔周剪切应变场呈蝴蝶形状分布特征,孔壁两侧煤碎片弹射、煤块剥落,呈“V”形破坏,声发射累计事件数和能量活跃性较高;阶段Ⅲ,试样层理处剪切应变集中,出现宏观剪切裂纹,呈拱形分布特征,声发射累计事件数和能量活跃性强烈。研究结果对钻孔卸压机制研究具有参考意义。

三维二值掩模零化法结合体素绘制法切割及渲染CT与MRI体积数据

目的 观察三维二值掩模零化法联合体素绘制法对于切割及渲染CT与MRI体积数据的作用。方法 利用Matlab软件将DICOM形式头颈部CT、腹部平扫CT、正常头部MR T1WI及脑胶质瘤T1WI转化为体积数据,以半自动或手动方法获得相应掩模图像;基于原始掩模以零化法在x、y、z轴方向对体积数据进行正向与反向切割,结合三维体素绘制法对切割后的模型进行渲染。结果 所获目标结构原始掩模可在体素绘制后突出显示CT及MRI数据中的相应解剖结构。基于体素绘制法实现了以三维二值掩模零化法与原体数据点积后切割模型,结合手动输入不同阈值进行切割可显示脑胶质瘤及其毗邻结构。结论 三维二值掩模零化法联合体素绘制法可结合不同层面CT与MRI体积数据显示其内部结构。

土石坝蓄水饱和湿化变形探讨

土石坝在蓄水期产生的过量变形会导致坝体结构应力重分布,进而使得某些部位损坏。对此,大量学者在筑坝料室内湿化特性及土石坝初期蓄水阶段应力变形的有限元模拟方面,开展了一系列研究。为进一步提高土石坝蓄水阶段变形控制水平,对现有研究成果进行了归纳分析,结果表明:坝料室内湿化试验技术的核心在于湿化变形测量、含水量测量及应力控制方法,在这些方面仍待进一步优化;关于湿化机理,目前仍缺乏有力的验证;按不同的湿化变形分解模式,会得到各异的湿化变形经验模型;“初应变法”数值模拟需假定湿化应变分解法则,“初应力法”得到的湿化变形较小。结合分析结果,提出以湿化孔隙比取代湿化变形,研究浸水饱和全过程中的孔隙比—饱和度关系的新研究思路。

大数据时代的智慧城市管理

随着经济的不断发展,城市发展步伐越来越快,政府部门和社会逐渐开始重视城市的管理问题。而大数据作为一种全新的现代化技术,就为城市管理的创新带来的新的技术与途径。所以,本文基于大数据作为背景,对于智慧城市管理(以下简称智慧城管)进行探讨,希望可以推动城市管理的进一步发展。

Experimental investigation on deformation characteristics and permeability evolution of rock under confining pressure unloading conditions

Deformation behavior and hydraulic properties of rock are the two main factors that influence safety of excavation and use of rock engineering due to in situ stress release.The primary objective of this study is to explore deformation characteristics and permeability properties and provide some parameters to character the rock under unloading conditions.A series of triaxial tests with permeability and acoustic emission signal measurement were conducted under the path of confining pressure unloading prior to the peak stress.Deformation behavior and permeability evolution in the whole stress–strain process based on these experimental results were analyzed in detail.Results demonstrate that,under the confining pressure unloading conditions,a good correspondence relationship among the stress–axial strain curve,permeability–axial strain curve and acoustic emission activity pattern was obtained.After the confining pressure was unloaded,the radial strain grew much faster than the axial strain,which induced the volumetric strain growing rapidly.All failures under confining pressure unloading conditions featured brittle shear failure with a single macro shear rupture surface.With the decrease in deformation modulus during the confining pressure unloading process,the damage variable gradually increases,indicating that confining pressure unloading was a process of damage accumulation and strength degradation.From the entire loading and unloading process,there was a certain positive correlation between the permeability and volumetric strain.

Macro-mechanical properties of columnar jointed basaltic rock masses

From the geological structure of the columnar jointed rock mass, a visual model was established in software AUTOCAD by programming based on the algorithm of the Voronoi diagram. Furthermore, a program to convert the AUTOCAD model into 3DEC (3-dimensional distinct element code) model was developed, and a numerical model was established in 3DEC. Moreover, the results of triaxial compression tests of columnar jointed rock masses were simulated numerically. The REV (representative element volume) scale was studied, and the result shows that the REV size is 3 m × 3 m. The proposed approach, the established model and the numerical simulation were applied to study the macro-mechanical properties and the equivalent strength parameters of the columnar jointed rock mass. The numerical simulation results are in good accordance with the in-situ test results.

A triaxial creep model for coal containing gas and its stability analysis

Triaxial creep tests on CCG specimens were systematically performed using aself-made creep seepage experimental apparatus for determining the creep law of CCG.An improved triaxial creep model of CCG was established on the basis of a Nishiharamodel and another visco-elasto-plastic model,parameters of which were fitted on test data.Furthermore,the creep model is validated according to the result of triaxial creep experiments,and the outcome shows that the proposed triaxial creep model can properly characterizethe properties of various creep deformation phases of CCG,especially the acceleratingcreep phase.At the same time,the instability conditions of CCG were presentedbased on the discussion of the improved model's stability in terms of stability theories ofdifferential equation solution.

Mechanical and damage evolution properties of sandstone under triaxial compression

To study the mechanical and damage evolution properties of sandstone under triaxial compression, we analyzed the stress strain curve characteristics, deformation and strength properties, and failure process and characteristics of sandstone samples under different stress states. The experimental results reveal that peak strength, residual strength, elasticity modulus and deformation modulus increase linearly with confining pressure, and failure models transform from fragile failure under low confining pressure to ductility failure under high confining pressure. Macroscopic failure forms of samples under uniaxial compression were split failure parallel to the axis of samples, while macroscopic failure forms under uniaxial compression were shear failure, the shear failure angle of which decreased linearly with confin- ing pressure. There were significant volume dilatation properties in the loading process of sandstone under different confining pressures, and we analyzed the damage evolution properties of samples based on acoustic emission damage and volumetric dilatation damage, and established damage constitutive model, realizing the real-time Quantitative evaluation of samnles damage state in loading process.

Grain crushing and its effects on rheological behavior of weathered granular soil

To disclose the grain crushing effects on the weathered granular soil rheological behavior,a series of rheological tests (odometer compression and triaxial shearing) were carried out.At the same time,the sieving analysis tests of these specimens were also executed before and after tests,and the grain crushing degree,Br and n5,were collectively adopted to estimate the grain crushing.The grain crushing degree depends on the stress path,stress level,and load time,especially,the longer load time and more intensive gradient shearing path will increase the grain crushing quantity.The Hardin crushing degrees Br are 0.191,0.118 and 0.085 in the ordinary compression,rheological compression and triaxial rheological shearing,respectively;The grain crushing degrees n5 are 1.9,1.4 and 1.32,respectively.The strain softening phase indicates the grain crushing and diffusive collapse,and the strain hardening phase indicates the rearrangement of these crushed grains and formation of new bearing soil skeleton.The rheological deformation of granular soil can be attributed to the coarse grain crushing and the filling external porosity with crushed fragments.

Softening response under undrained compression following anisotropic consolidation

Experimental evidence has indicated that clay exhibits strain-softening response under undrained compression following anisotropic consolidation.The purpose of this work was to propose a modeling method under critical state theory of soil mechanics.Based on experimental data on different types of clay,a simple double-surface model was developed considering explicitly the location of critical state by incorporating the density state into constitutive equations.The model was then used to simulate undrained triaxial compression tests performed on isotropically and anisotropically consolidated samples with different stress ratios.The predictions were compared with experimental results.All simulations demonstrate that the proposed approach is capable of describing the drained and undrained compression behaviors following isotropic and anisotropic consolidations.

THE REAL IN TIME CT MONITORING OF THE MESO-DAMAGE EVOLUTION LAW OF SANDSTONE UNDER TRIAXIAL COMPRESSION

The real in time computerized tomography (CT) testing of the meso damage propagation law of the whole sandstone failure process under triaxial compression has been completed using the newest specified triaxial loading equipment corresponding to the CT machine. Through the CT scanning, the clear CT images which include from the microcracks compressed stage to growth stage, bifurcation stage, development stage, crack fracture stage,the rock sample failure until to unloading stage in the different stress states were obtained. The CT values, CT images and the other data have been analyzed. Based on the results of the CT testing of meso damage evolution law of rock,the stress threshold value of meso damage of rock is given, and the stress strain complete process curve of rock is divided into some sections. The initial rock damage propagation law is given in this paper.

True triaxial behavior of sandy soils under both drained and undrained conditions:A discrete element perspective

An advanced discrete element servomechanism that can simultaneously and independently control the evolution equations of six stress and strain components without introducing severe stress concentration is implemented.Such a comprehensive series of discrete element method simulations of both drained and undrained behavior of transversely isotropic sandy soils are successfully conducted in the true triaxial setting.During the simulation process,the evolution patterns of the load-bearing structure of the granular specimen are tracked using a contact-normal-based fabric tensor.The simulation results show that sandy soils exhibit more significant non-coaxiality between the loading direction and the major principal direction of the fabric tensor under extension than under compression.Therefore,the fabric of the sandy soils under extension has a stronger tendency to evolve toward the loading direction than that under compression,causing a more significant disturbance to the load-bearing structure.Consequently,compared with the extension loading condition,the transversely isotropic specimen under compression exhibits a higher shear strength and stronger dilatancy under drained conditions and a stronger liquefaction resistance under undrained conditions.

Evolution laws of strength parameters of soft rock at the post-peak considering stiffness degradation

To evaluate the strength attenuation law of soft rock in the western mining area of China, we established an evolution model for the strength parameters of soft mudstone at the post-peak stage by employing a tri-linear strain softening model. In the model, a stiffness degradation coefficient co and a softening modulus coefficient a were introduced to take into account the stiff- ness degradation, and the subsequent yield surfaces at post-peak stage were all assumed to meet the Molar-Coulomb yield criterion. Furthermore, attenuation laws of stiffness and strength parameters of soft mudstone were analyzed according to an engineering case. Finally, the model＇s accuracy was verified by comparison of results from numerical calculation and tri-axial compression tests. Results showed that the attenuation of the friction angle was dominated mainly by the instantaneous stress states and damage features, while the attenuation law of cohesion was also related to the plastic behavior. The degradation rates of strength param- eters decreased with increasing confining pressure and the friction angle tended towards its initial value. Residual strengths were also enhanced with increasing confming pressure. The results indicate that the evolution model can accurately describe the strain softening behavior of soft rock.

Subsurface crack propagation under rolling contact fatigue in bearing ring

The influences of subsurface cracks,distributing along the axial direction,on the rolling contact fatigue(RCF)faliure in a bearing ring are investigated.A realistic three-dimensional model of the bearing ring containing three subsurface cracks is used to evaluate the fatigue crack propagation based on stress intensity factor(SIF)calculations.Moreover,the distributions of the subsurface cracks along the axial direction are varied to study their effects on RCF.The results provide valuable guidelines for enhanced understanding of RCF in bearings.