井内偏心声源激发的三维声场的数值研究

为了研究环形声波测井仪和扇区水泥胶结测井仪的工作原理,本文利用实轴积分 法计算了井内靠近井壁的偏心声源激发的声场,得到了在井壁不同位置的接收波形,分析了 直达波、井壁反射波、纵波、横波和面波在这些波形中的反映．偏心声源激发的三维声场没有 轴对称性,比井轴上的居中声源的情况复杂．     

球形氢键模型预测电解质溶液中的离子水合数

建立了以球形氢键模型为基础的离子-水键长和配位水分子数之间的关系式,并利用该式对20种金属离子的水合数进行了预测,预测结果令人满意。     

延脆性变化对隧道掘进机刀具破岩过程及其破坏模式影响的颗粒元模拟分析

在全断面岩石掘进机（TBM）刀具破岩的颗粒元模拟中颗粒参数的选取至关重要,其中颗粒间平行黏结切向、法向强度是关键控制性参数之一,它们之间的比值关系直接决定所模拟试样的延脆性质,影响刀具破岩过程及其破岩效果。为探讨延脆性对刀具破岩模式的影响,（1）建立9种采用不同平行黏结强度比值的数值模型,分别进行单轴压缩及巴西劈裂模拟,研究不同延脆性试样的力学行为及破坏模式的变化。（2）对9种模型进行双刀破岩,并监控其裂缝的发展情况及刀具的受力状况。（3）为减小随机性对模拟结果的影响,通过改变随机数,每种模型重复模拟5次,综合分析5次的计算结果。模拟分析发现,随着切向和法向黏结强度比值( )的增大,试样的脆性增加,破坏模式逐渐从剪切破坏转变为脆性张拉破坏,刀具破岩压碎区范围减小,张拉裂缝更容易在刀具间贯通延伸从而切割出块体更大的岩渣;随着试样脆性的增加,归一化比能减小,刀具破岩的效率增加;平行黏结强度比值相同的条件下采用不同随机数种子生成的模型中,试样的具体破坏情况有一定的差别,但总体破坏模式相似。     

硅碳双键稳定性的CNDO/2法研究

本文用CNDO/2法研究了硅碳双键Si=C不稳定的原因。通过分析SiH_2CH_2的烷基和苯基取代物的计算结果,对有大基因连接硅碳双键的化合物之所以能稳定存在做了合理的说明。     

The complex band structure for armchair graphene nanoribbons

Using a tight binding transfer matrix method, we calculate the complex band structure of armchair graphene nanoribbons. The real part of the complex band structure calculated by the transfer matrix method fits well with the bulk band structure calculated by a Hermitian matrix. The complex band structure gives extra information on carrier's decay behaviour. The imaginary loop connects the conduction and valence band, and can profoundly affect the characteristics of nanoscale electronic device made with graphene nanoribbons. In this work, the complex band structure calculation includes not only the first nearest neighbour interaction, but also the effects of edge bond relaxation and the third nearest neighbour interaction. The band gap is classified into three classes. Due to the edge bond relaxation and the third nearest neighbour interaction term, it opens a band gap for N=3M-1. The band gap is almost unchanged for N=3M+1, but decreased for N=3M. The maximum imaginary wave vector length provides additional information about the electrical characteristics of graphene nanoribbons, and is also classified into three classes.     

Numerical study of inter‐particle bond failure by 3D discrete element method

The cohesive‐frictional nature of cementitious geomaterials raises great interest in the discrete element method (DEM) simulation of their mechanical behavior, where a proper bond failure criterion is usually required. In this paper, the failure of bond material between two spheres was investigated numerically using DEM that can easily reproduce the failure process of brittle material. In the DEM simulations, a bonded‐grain system (composed of two particles and bond material in between) was discretized as a cylindrical assembly of very fine particles connecting two large end spheres. Then, the bonded‐grain system was subjected to compression/tension, shear, rolling and torsion loadings and their combinations until overall failure (peak state) was reached. Bonded‐grain systems with various sizes were employed to investigate bond geometry effects. The numerical results show that the compression strength is highly affected by bond geometry, with the tensile strength being dependent to a lesser degree. The shear, rolling and torsion strengths are all normal force dependent; i.e., with an increase in the normal force, these strengths first increase at a declining rate and then start to decrease upon the normal force exceeding a critical value. The combined actions of shear force, rolling moment and torque lead to a spherical failure envelope in a normalized loading space. The fitted bond geometry factors and bond failure envelopes obtained numerically in this three‐dimensional study are qualitatively consistent with those in previous two‐dimensional experiments. The obtained bond failure criterion can be incorporated into a future bond contact model. Copyright © 2015 John Wiley & Sons, Ltd.     

Laboratory Tests on Shotcrete-Rock Joints in Direct Shear, Tension and Compression

Summary. A series of laboratory tests was performed on cemented shotcrete-rock joints to investigate the strength and stiffness of the interfaces, while simulating field conditions as close as possible. The direct shear test formed the core of the experimental work, while the tension and compression tests were complementary. To simulate loading conditions experienced in practical cases the direct shear tests were performed under fairly low normal stresses. In most practical cases when shotcrete is used with rock bolts, the normal load on shotcrete lining seldom exceeds 0.2 to 0.5 MPa. The direct shear test results show that, for such normal load range the shear strength is determined by the bond strength for genuinely bonded shotcrete-rock interfaces. For higher normal stresses (σ_n > 1.0 MPa), which rarely exist at the shotcrete-rock interface, the shear strength is largely influenced by friction resulting in the cohesive strength being less significant. Assessment of the shear surface revealed that the steel fibres in the shotcrete appeared to contribute significantly to the frictional component. The shear and normal stiffnesses of the interface were also determined, which were in principal the stiffnesses of the bond. An interesting observation was the complex interaction at the interface and the mechanisms that controlled the peak shear strength which depended on the surface roughness, the existence of natural flaws and the normal load.     

形状记忆合金绞线与混凝土的粘结滑移性能及影响因素研究

采用拉拔试验对SMA绞线与混凝土之间的粘结滑移性能进行研究,分析了拉拔试件的破坏模式和受力过程,阐述了SMA绞线与混凝土之间粘结滑移的相互作用机理,讨论了拉拔试件粘结滑移性能随混凝土强度、混凝土保护层厚度、SMA绞线锚固长度以及加载速度的变化规律,建立了SMA绞线锚固长度的计算公式。结果表明:拉拔试件的破坏模式以典型破坏为主,其受力过程分为5个阶段:弹性阶段、转动脱胶阶段、内部拥塞阶段、衰减阶段和残余阶段。同时,随着混凝土强度的增大,试件的极限粘结强度也增大;当保护层厚度达到一定数值后,增加保护层厚度对试件的极限粘结强度几乎没有影响;SMA绞线的锚固长度越大,试件的极限粘结强度越小;试件的极限粘结强度会随着加载速度的增大而小幅增大,若加载速度过快,SMA绞线则会发生散捆断裂。此外,所建立的SMA绞线锚固长度计算公式可以考虑多种影响因素,对SMA绞线用于土木工程结构中需要考虑的锚固、搭接和细部构造等结构设计问题具有一定的理论意义及实用价值。     

浅谈井用人工动态观测设施的改良与创新

通过对天津地区地热井现有人工观测设施中“固定焊接式水位测管”、“悬挂插拔式水位测管”利弊全面客观的分析,指出规范的、标准的、专用的井用人工观测（水位）系统是保证地热井水位动态数据有效采集率的关键。由多眼更换了新型水位测管的地热井实测结果来看,“具有悬挂插拔式水位测管的专用潜水泵管”有利于提高水位数据采集的连续性和完整性,具有广泛的市场推广前景。     

平行黏结模型宏细观力学参数相关性研究

采用变量控制法较全面地分析了各细观参数与宏观参数的定量关系,表明：弹性模量E随颗粒模量Ec、黏结模量 、平行黏结半径乘子 呈线性增长,随颗粒刚度比kn /ks、黏结刚度比 呈对数减小;泊松比则主要受kn /ks和 的影响,两者之间呈对数关系;颗粒键的黏结强度决定了材料的强度,室内材料黏聚力c和抗拉强度 主要受法向平行黏结强度 、平行黏结强度比 的影响,随 线性增长,随 对数减小;摩擦角 主要受颗粒摩擦系数u影响,两者呈对数关系。分析裂隙扩展特征,表明材料法向黏结强度 和切向黏结强度 的相对大小决定裂纹分布规律,随 增大,岩样的拉破坏区域减少,而压剪破坏区域增加,破坏面由剪切破坏向共轭破坏发展;材料的强度离散性越小,岩样破坏趋于集中,破坏面明显,强度均值标准差比值 >3.5为宜; 增加,宏观破坏形式向共轭破坏发展。细观参数的选取除了匹配强度参数,同时还需要考虑破坏形式的一致,考虑多参数相互影响,建立了宏细观参数之间的经验公式,对细观参数进行优化选择,并做了实例验证。室内试验和数值模拟获得的峰值荷载、变形参数、剪切强度等数值接近,应力-应变演化规律相同,破坏形态一致,表明细观参数结果是可靠的。