Support design method for deep soft-rock tunnels in non-hydrostatic high in-situ stress field

Due to the long-term plate tectonic movements in southwestern China,the in-situ stress field in deep formations is complex.When passing through deep soft-rock mass under non-hydrostatic high in-situ stress field,tunnels will suffer serious asymmetric deformation.There is no available support design method for tunnels under such a situation in existing studies to clarify the support time and support stiffness.This study first analyzed the mechanical behavior of tunnels in non-hydrostatic in-situ stress field and derived the theoretical equations of the ground squeezing curve(GSC)and ground loosening curve(GLC).Then,based on the convergence confinement theory,the support design method of deep soft-rock tunnels under non-hydrostatic high in-situ stress field was established considering both squeezing and loosening pressures.In addition,this method can provide the clear support time and support stiffness of the second layer of initial support.The proposed design method was applied to the Wanhe tunnel of the China-Laos railway in China.Monitoring data indicated that the optimal support scheme had a good effect on controlling the tunnel deformation in non-hydrostatic high in-situ stress field.Field applications showed that the secondary lining could be constructed properly.

Influences of lithology on in-situ stress field in low permeability reservoirs in Bonan Oilfield, Bohai Bay Basin, China

The differences of rock mechanical properties were analyzed based on triaxial compression test in low permeability reservoirs of the Bonan Oilfield. Through the analysis of reservoir mechanics, the influence mechanisms of different mechanical properties of rocks on reservoir in-situ stress were studied. By means of stress ellipse and finite element simulation, the influence rules of different mechanical properties of rocks on in-situ stress field were discussed. For the low permeability reservoirs of the Bonan Oilfield, the coarser rock has a larger Young’s modulus value and a lower Poisson’s ratio. The rock mechanical parameters and stress-strain relationship of sandstone facies and mudstone facies are different. Different rocks have different mechanical properties, which cause extra stress at the lithological contact interface, and the existence of extra stress affects the reservoir in-situ stress. Without considering the influence of structural features on the in-situ stress field, the reservoir in-situ stress is controlled by the magnitude of extra stress and the angle between lithological contact surface and boundary stress.

A workfow to Predict the Present-day in-situ Stress Field in Tectonically Stable Regions

Knowledge of the present-day in-situ stress distribution is greatly import-ant for better understanding of conventional and unconventional hydro-carbon reservoirs in many aspects,e.g,reservoir management,wellbore stability asssment,etc.In tectonically stable regions,the present-day in-situ stress field in terms of stress distribution is 1argely controlled by lithological changes,which can be predicted through|a numerical simulation method incorporating specific mechanical properties of the subsurface reservoir.In this study,a workflow was presented to predict the present-day in-situ stress field based on the finite element method(FEM).Sequentially,it consists of:i)building a three-dimensional(3D)geometric framework,i)creating a 3D petrophysical parameter field,11)integrating the geometric framework with petrophysical parameters,iv)setting up a 3D heterogeneous geomechanical model,and finally,v)calculating the present-day in-situ stress distribution and calibrating the prediction with measured stress data,e.g.,results from the extended leak-off tests(XLOTs).The approach was sucessfully applied to the Block W in Ordos Basin of central China.The results indicated that the workflow and models presented in this study could be used as an effective tool to provide insights into stress perturbations in subsurface reservoirs and geological references for subsequent analysis.

Reversibility of visual field defects through induction of brain plasticity: vision restoration, recovery and rehabilitation using alternating current stimulation

For decades visual field defects were considered irreversible because it was thought that in the visual system the regeneration potential of the neuronal tissues is low.Nevertheless,there is always some potential for partial recovery of the visual field defect that can be achieved through induction of neuroplasticity.Neuroplasticity refers to the ability of the brain to change its own functional architecture by modulating synaptic efficacy.It is maintained throughout life and just as neurological rehabilitation can improve motor coordination,visual field defects in glaucoma,diabetic retinopathy or optic neuropathy can be improved by inducing neuroplasticity.In ophthalmology many new treatment paradigms have been tested that can induce neuroplastic changes,including non-invasive alternating current stimulation.Treatment with alternating current stimulation(e.g.,30 minutes,daily for 10 days using transorbital electrodes and^10 Hz)activates the entire retina and parts of the brain.Electroencephalography and functional magnetic resonance imaging studies revealed local activation of the visual cortex,global reorganization of functional brain networks,and enhanced blood flow,which together activate neurons and their networks.The future of low vision is optimistic because vision loss is indeed,partially reversible.

Piezomagnetic In-situ Stress Monitoring and its Application in the Longmenshan Fault Zone

The relative change of in-situ stress is an inevitable outcome of differential movement among the crust plates. Conversely, changes of in-situ stress can also lead to deformation and instability of crustal rock mass, trigger activity of faults, and induce earthquakes. Hence, monitoring real-time change of in-situ stress is of great significance. Piezomagnetic in-situ stress monitoring has good and longtime applications in large engineering constructions and geoscience study fields in China. In this paper, the new piezomagnetic in-situ stress monitoring system is introduced and it not only has overall improvements in measuring cell＇s structure and property, stressing and orienting way, but also enhances integration and intelligence of control and data transmission system, in general, which greatly promotes installing efficiency of measuring probe and quality of monitoring data. This paper also discusses the responses of new piezomagnetic system in large earthquake events of in-situ stress monitoring station at Qiaoqi of Baoxing and Wenxian of Gansu. The monitoring data reflect adjustments and changes of tectonic stress field at the southwestern segment of and the northern area near the Longmenshan fault zone, which shows that the new system has a good performance and application prospect in the geoscience field. Data of the Qiaoqi stress-monitoring station manifest that the Lushan Earthquake did not release stress of the southwestern segment of the Longmenshan fault zone adequately and there still probably exists seismic risk in this region in the future. Combined with absolute in-situ stress measurement, carrying out long-term in-situ stress monitoring in typical tectonic position of important regions is of great importance for researchers to assess and study regional crust stability.

THERMAL STRESS FIELD WHEN CRACK ARREST IN AN AXIAL SYMMETRY METAL DIE USING ELECTROMAGNETIC HEATING

In order to solve the thermal stress field around crack tip in metal die when crack prevention using electromagnetic heating, a metal die with a half-embedded round crack was selected as the study object. The complex function method was used as a basis for the theoretical model of the space crack prevention in metal dies using electromagnetic heating. The crack arrest was accomplished by a pulse current discharge through the inner and outer. The theoretical analysis results show that the temperature around the crack tip rises instantly above the melting point of the metal. Small welded joints are formed at a small sphere near the crack tip inside the metal die by metal melting as a result of the heat concentration effect when the current pulse discharged. The thermal compressive stress field appears around the crack tip at the moment. The research results show that the crack prevention using electromagnetic heating can decrease the stress concentration and forms a compressive stress area around the crack tip, and also prevents the main crack from propagating further, and the goal of crack preventing can be reached.

Recent tectonic stress field research in Shanxi graben system

By comprehension of earthquake focal mechanism solutions and the data of in-situ stress measurements, the tectonic stress field in Shanxi region has been summarized, which indicate that the stress state in this region is different from that of its eastern surrounding regions. The next, by fitting the measured data, the boundary forces that influenced the distribution of the stress field in this region has been studied using inversion method. The inversion results showed the following messages: the effect of the boundary force between the blocks is the main determinative factor for the recent tectonic stress field in Shanxi and the regional material and its property is a secondary factor; the horizontal main stress of tectonic stress field in Shanxi region is consistent with the stretch of fault basins.

脉冲电流下对AL6061合金进行熔孔止裂与愈合的仿真研究

Al6061铝合金常应用于航空航天领域蒙皮制造,因其中等硬度与低强度的弱点,在承受复杂载荷时容易出现微裂纹,进而影响服役安全可靠性。脉冲电流是一种极速、非平衡的金属材料微小裂纹修复工艺,可以克服该材料不易焊接修复的短板。在既有的实验基础上建立单边预制裂纹缺口模型,采用有限元仿真手段,进行了热-电-力三场耦合数值模拟,计算不同参数下裂纹区域的电场、温度场和应力场分布。使用“生死单元”法模拟止裂熔孔的产生,并获得了不同几何、物理参数下止裂熔孔尺寸变化的规律。结果表明:焦耳热形成的止裂熔孔降低裂尖的集中应力,抑制裂纹扩展,裂纹区域高温区与基体常温区形成温度梯度相互约束产生巨大的热压应力促使裂纹宽度减小,进而直至愈合;初始熔孔尺寸与裂纹长度成正比、与板厚成反比,最佳尺寸直径为0.1 mm以内;电流值和电流加载时间均能控制熔孔生长,电流值一定时,当时间达到0.12 s形成的熔孔尺寸超出最佳止裂尺寸范围。研究成果为特定金属材料的裂纹止裂与愈合提供了机理参考和仿真方法。

考虑温度影响的电磁轨道发射装置温度场与热应力分析

为探究温度对电磁轨道发射装置电枢电流密度和温度场的影响,分析了发射装置的热载荷来源,建立了电枢温度场理论计算模型,并对其进行求解。用脉冲成形网络对发射装置供电,采用有限元法,求出接触电阻随时间的变化曲线,在考虑电磁场-温度场-应力场等的情况下建立三维有限元计算模型,对比分析理想接触状态下、仅考虑接触电阻、既考虑接触电阻又考虑温度影响的3种状态下的电流密度、温度场及热应力。结果表明:3种状态下电枢最大电流密度的变化趋势相同,均为先急剧增大再急剧减小再缓慢减小,电枢最高温度和最大应力的变化趋势也相同,均为先缓慢上升再迅速上升最后缓慢减小趋于稳定,但考虑接触电阻与温度影响下的电枢最高温度和最大应力的峰值时间推迟,峰值增大;在发射过程中,电枢尾部首先开始熔化,随后热量向头部传播,在间隔0.3 ms后整个接触区域温度均超过熔点,电枢尾翼熔化厚度约为0.25 mm,接触电阻产生的热量发生在电枢臂尾翼纵向0.7 mm区域内。

Effectof Neutral Traps on Tunneling Current and SILC in Ultrathin Oxide Layer

The effect of neutral trap on tunneling currentin ultrathin MOSFETs is investigated by num erical analy- sis.The barrier variation arisen by neutral trap in oxide layer is described as a rectangular potential well in the con- duction band of Si O2 .The different barrier variation of an ultrathin metal- oxide- sem iconductor(MOS) structure with oxide thickness of4nm is numerically calculated.It is shown that the effect of neutral trap on tunneling cur- rent can not be neglected.The tunneling current is increased when the neutral trap exists in the oxide layer.This simple m odel can be used to understand the occurring mechanism of stress induced leakage current.

Screening-current-induced magnetic fields and strains in a compact REBCO coil in self field and background field

REBa_(2)Cu_(3)O_(7−x)(REBCO)coated conductors,owing to its high tensile strength and current‐carrying ability in a background field,are widely regarded a promising candidate in high‐field applications.Despite the great potentials,recent studies have highlighted the challenges posed by screening currents,which are featured by a highly nonuniform current distribution in the superconducting layer.In this paper,we report a comprehensive study on the behaviors of screening currents in a compact REBCO coil,specifically the screeningcurrent‐induced magnetic fields and strains.Experiments were carried out in the self‐generated magnetic field and a background field,respectively.In the self‐field condition,the full hysteresis of the magnetic field was obtained by applying current sweeps with repeatedly reversed polarity,as the nominal center field reached 9.17 T with a maximum peak current of 350 A.In a background field of 23.15 T,the insert coil generated a center field of 4.17 T with an applied current of 170 A.Ultimately,a total center field of 32.58 T was achieved before quench.Both the sequential model and the coupled model considering the perpendicular field modification due to conductor deformation are applied.The comparative study shows that,for this coil,the electromagnetic–mechanical coupling plays a trivial role in self‐field conditions up to 9 T.In contrast,with a high axial field dominated by the background field,the coupling effect has a stronger influence on the predicted current and strain distributions.Further discussions regarding the role of background field on the strains in the insert suggest potential design strategies to maximize the total center field.

基于阵列涡流及交流电磁场检测技术的压力容器应力腐蚀裂纹检测

采用阵列涡流和交流电磁场两项无损检测技术对压力容器内壁表面及近表面裂纹缺陷实施不打磨情况下的快速检测,提供了一种高效可靠的压力容器应力腐蚀裂纹无损检测方法,并采用该方法对一台杀菌锅进行了检测。在实验室工艺研究的基础之上,制定了阵列涡流和交流电磁场两项技术的专用检测工艺,并开展检测验证。检测结果表明,该检测工艺可实现对杀菌锅表面及近表面裂纹缺陷的快速检测,对压力容器的定期检验有重要的意义。

镍铁矿热炉内温度与应力场分析

本文建立了三维矿热炉电-磁-热-应力多物理场耦合模型,利用数值模拟手段计算了熔池的电流密度和温度场,在同一位置选用了两种不同的炉衬材料,即高铝砖和碳化硅砖,计算了矿热炉炉体的温度场与热应力分布。结果表明:电流密度集中于电弧两侧,且满足交流电的趋肤效应和邻近效应原则。在炉膛底部,最高温度出现在熔池内的高温坩埚区正下方,达到2156 K。外炉壳的最大应力和变形位于Z=3.15 m高度处。使用高铝砖的矿热炉炉膛内保温性能和炉衬的使用寿命均优于碳化硅砖。

不同宽长比的柔性LTPS TFT的电应力可靠性

为了研究不同宽长比的柔性低温多晶硅薄膜晶体管(LTPS TFT)的电应力可靠性,测试了器件的I-V特性,以表征器件在强电场直流应力下由于自热效应和热载流子效应带来的电学性能退化。通过瞬态电流法表征了器件在强电场直流应力下的时间常数谱,并对其产生的新陷阱进行定位,分析了产生陷阱的内在机理。结果表明,在相同的强电场直流应力下宽长比为3/2.5的器件,其电学参数变化最大,自热效应以及热载流子效应带来的影响也最大。自热效应导致器件性能退化的主要原因是较大的栅源电压导致Si/SiO2界面处和栅氧化层中的陷阱增多,而热载流子效应导致器件性能退化的主要原因则是由于较大的漏源电压使得漏极晶界陷阱态密度急剧升高。

Study on Mechanism of Concrete Failure Induced by Steel Corrosion under Externally Applied Direct Current

With the combination of electrochemical corrosion due to stray current in running tunnels of metro, the formula to determine the corrosion products of rebars in reinforced concrete subjected to externally applied direct current is proposed, and the influence of corrosion on stress in concrete is also discussed. Meanwhile, the concept of corrosion stress field and its mathematical formula are presented in the paper. Finally the failure mode of concrete and its shortest breaking time are also analyzed.

激光流速仪测量离心泵叶轮内流场特性研究

考虑到传统方法在测量离心泵叶轮内流场特性时受到实验硬件设施的影响,存在忽视测量区域的问题,提出了激光流速仪测量离心泵叶轮内流场特性研究。利用激光流速仪数值模拟了离心泵叶轮内流场特性的测量,弥补了流场特性测量在硬件设施上的不足,深入研究了离心泵叶轮内流场地分布、结构演变以及动静干涉,实现离心泵叶轮内流场特性的测量。实验结果表明,利用激光流速仪测量离心泵叶轮内流场特性时,叶轮内干涉区、隔舌附近以及离心泵叶轮后缘位置处的流场分布比较紊乱,存在复杂的流动现象,在测量离心泵叶轮内流场特性时应该加以重视。

带有裂纹的金属薄板构件裂尖处电热应力的数值分析

讨论了带有裂纹的金属构件通入脉冲电流瞬间，裂纹尖端附近电流、温度和热应力的耦合关系。分析采用了有限元法，通过热－电耦合（焦耳热问题）和热－机械耦合两个过程来实现。通过数值解析模型，模拟了脉冲放电瞬间的电流－温度－热应力的演变过程，求解了脉冲放电瞬间裂纹前缘的热压应力场。温度场、应力场数值计算结果同理论分析有很好的吻合。

真空泵屏蔽电动机温度场与屏蔽套应力场分析

针对真空泵屏蔽电动机屏蔽套出现变形、开裂和泄漏导致光伏产业生产线真空度下降的工程问题,采用有限元分析法,对使用三种不锈钢材质屏蔽套的屏蔽电动机稳态温度场和热应力场进行分析.结果表明:屏蔽套采用Hastelloy-C材质时屏蔽套涡流损耗小,屏蔽电机各部件温度均低于采用Sus316L材质时的温度;屏蔽套采用Sus430导磁材质时屏蔽电动机损耗最小,在降低温升方面效果明显.采用Hastelloy-C和Sus430材质时,屏蔽套最大形变量比采用Sus316L时分别下降17%和19%,最大热应力分别降低12%和16%.因Sus430不锈钢价格低廉,且有很好的防腐性能,所以Sus430不锈钢比较适合真空泵屏蔽电动机.

带有半埋藏空间裂纹的Cr12构件电磁热止裂分析

对带有半埋藏环形裂纹的Cr12标准拉伸试件进行了电磁热止裂研究.通过ZL-2型放电装置实现了半埋藏空间裂纹的止裂实验,采用微机控制电子万能试验机完成了止裂前后试件拉伸性能测试,同时计算了电磁热止裂前后应力强度因子的变化;建立了超强脉冲电流放电瞬间,环形裂纹尖端附近电流绕流、温度场和热应力场的数值分析模型,通过热-电耦合和热-机械耦合两个过程得到了脉冲放电瞬间拉伸试件中的电流矢量场、温度场和热应力场.研究表明:脉冲电流放电瞬间,围绕裂纹尖端金属熔化,钝化了裂尖,并围绕裂尖形成了热压应力场,得到了超细化的金属组织,止裂后抗拉强度得到了提高,达到了止裂的目的.

克深气田储层地质力学特征及其对开发的影响

克拉苏构造带深层裂缝型致密砂岩气藏经历强挤压构造变形,复杂的现今地应力场和天然裂缝系统导致储层非均质性和各向异性较强,不同构造之间和同一构造不同位置的气井产能差异明显。为明确影响该区天然气开发中的地质主控因素,在井筒一维地质力学参数评价和构造格架搭建的基础上开展了克深气田储层地质力学建模,深入分析克深气田多个构造带储层岩石力学性质、现今地应力场及天然裂缝的发育特征,归纳总结不同构造带、同一构造带不同部位及不同层位的储层地质力学特征,并结合克深气田典型井的开发现状,建立地质力学特征与产能的关联,最后,针对不同类型的气藏分别提出与之匹配的布井原则。研究表明:(1)不同构造类型气藏地应力场分布特征差异较大,应力方位与天然裂缝产状之间的关系也有明显不同;(2)气藏内储层地质力学属性呈现自分层特征,其直接影响储层孔隙度和渗透率分布;(3)气藏内部处于应力低值、裂缝走向与水平主应力方位之间夹角小的位置,储层渗透性能较好,单井产能更高。研究不仅为储层评价和气藏描述提供了有力的补充,同时也为井位优化提供有利的依据。