爆炸冲击波的动态破岩特性研究

运用爆炸冲击波理论，讨论了炮孔柱状装药爆破时的岩石粉碎区及其形成时间、爆腔半径及其扩胀规律。通过分析表明:影响粉碎区半径和爆腔半径的主要因素是冲击波的强度、岩石的性质和炮孔尺寸等。     

泄爆面积对甲烷-空气预混泄爆容器结构响应影响的实验研究

利用自主搭建的泄爆容器结构响应测试系统,开展了不同泄爆面积条件下甲烷-空气预混气体泄爆实验,结合振动加速度、内部超压、火焰演化和信号频率-时间分布等探究了泄爆面积对容器结构响应的影响特征及机制。研究发现:（1）容器振动加速度曲线和内部超压曲线具有相似的变化趋势,两者均存在双峰现象,且两者一一对应,但加速度峰值出现略迟;随着无量纲泄爆系数增大,第1个内部超压和加速度峰值主体为增大趋势,而第2个内部超压和加速度峰值的变化趋势为先减小后增大再减小;（2）火焰未到达泄爆口之前,上部的火焰平均速度随着无量纲泄爆系数增大而减小,无量纲泄爆系数较小时火焰较早从泄爆口喷出;（3）在当前实验条件下,当无量纲泄爆系数为25.00时,热声耦合现象最剧烈,表现为最大幅值的振动响应和最大能量的高频振荡,而随着无量纲泄爆系数进一步增大或者减小,热声耦合现象逐渐衰减。     

夯扩异形桩施工振动效应分析

建筑垃圾夯扩异形桩是-种新型地基加固处理技术, 但是由于夯击能量较大, 施工过程中产生-定的振动效应。此种振动效应能否对环境、特别是临近建筑物产生有害影响, 是制约本施工工艺普遍应用的关键问题之-。本文通过对两侧建筑垃圾夯扩异桩施工振的监测, 对夯扩异形桩施工振动效应进行了分析, 研究了不同施工状态对地面振动参数的影响, 指出夯扩异形施工振动随距离呈负幂函数的形式进行衰减, 不同的施工状态对地面振动参数的影响只局限于距离夯击点非常有限的范围内。     

水平光面爆破激发地震波的成分及衰减特征

借助极化偏振分析方法,针对一组现场爆破实验,分析了水平光面爆破激发地震波的成分构成及特性,比较了不同波的衰减特征及各自对爆破振动的影响,并探讨了水平光面爆破的内在力学机理。结果表明,爆破振动中不同波的相对量值及主导波的类型均会随测点位置的改变而变化,爆源特性和沿传播路径的不同衰减共同决定波的成分构成及演化,各测点的优势振动方向也与波的成分构成密切相关。对于水平光面爆破,在光爆孔平面上,P波的影响可忽略,S波主要在竖直向振动,R波对水平及竖直向的振动均有贡献,其中水平向的振动主要由R波引起,而S波的竖直向振速在近区远高于R波,但归因于S和R波的不同衰减,R波在距离爆源22.5 m/kg^1/2(58~67 m)处开始主导竖直向的振动;在光爆孔平面外,P波的影响不可忽略,且在特定位置会成为优势波型。     

台阶地形爆破振动放大与衰减效应研究

基于台阶地形爆破振动数值模拟与边坡振动监测实验，研究台阶地形爆破振动速度在传播过程中高程放大效应的产生及变化规律。结果表明，单个台阶坡顶质点的振动速度放大效应是在距爆源一定距离、达到一定高差的条件下产生的；坡顶质点振动速度放大倍数并不随台阶高度的增加而单调增加，在台阶高度超过某一临界值后，放大倍数随台阶高度的增加而减小。台阶高程对爆破振动速度既有放大作用，同时也随高度的增加产生衰减作用。根据模拟计算及现场观测数据分析结果，给出了台阶地形爆破振动速度预测模型，该模型为类似边坡工程的爆破地震波传播规律研究提供一定的参考。     

基于小波包能量谱爆炸参量对爆破振动信号能量分布的影响

基于现场实测爆破振动数据,根据爆破振动信号具有短时非平稳的特点,采用小波包分析技术对不同爆炸参量(爆心距、最大段药量和微差雷管段数)下产生的爆破振动信号进行小波包能量谱分析,获得了爆破振动信号不同频带的能量分布,研究了不同爆炸参量下的爆破振动信号能量分布特征,从爆破振动信号能量角度探讨了不同爆炸参量下爆破地震波的衰减规律,为研究爆破地震效应提供了一种新的分析技术。     

不同炸药性能对爆破振动效应的影响

从岩石内炸药爆轰能量释放形式的角度,结合现场实时爆破振动监测数据,对比分析2种不同炸药性能的炸药产生的爆破振动特性,并对质点振动速度峰值的衰减规律及爆破振动持续时间进行回归分析.结果表明:除单响炸药量和爆心距,炸药自身性能对爆破振动效应的衰减规律和振动持续时间也有很大影响.     

基于双折线抗力模型的空爆荷载梁式构件振动位移研究

为研究双折线抗力模型对空爆荷载梁式构件振动位移的影响,提出了柔性、刚性两类梁式构件正向弹塑性振动及回弹阶段弹塑性振动的分析法。应用等效单自由度法建立了各阶段振动方程并依据不同的初始条件推导出了各阶段的理论解。采用此理论解和代表性塑性强化系数,开展了双折线抗力模型中不同塑性强化程度对两类梁式构件正向弹塑性振动及回弹阶段弹塑性振动位移的典型工况验证。研究结果表明:基于双折线抗力模型位移理论解的适用范围更广;随着双折线抗力模型塑性强化系数的增大,两类梁式构件的最大弹塑性位移、残余变形均逐渐减小,且残余变形降低程度高于最大弹塑性位移;塑性强化系数增大到一定程度,梁式构件回弹阶段将出现塑性振动位移,进一步降低残余变形,无塑性回弹位移的理想弹塑性抗力模型会高估空爆荷载下梁式构件的残余变形。     

微差爆破震动叠加起始位置数值模拟

采用ANSYS/LS-DYNA3D程序对岩体中双孔微差爆破近源场爆破振动进行了模拟。结果表明,随着离爆源距离的增加,质点振动波形的持续时间变长,同时二炮孔爆破振动波形中质点处于静止状态的间隔变小并产生叠加。因此通过数值模拟可确定微差爆破近区振动叠加起始位置。     

地应力水平对深埋隧洞爆破振动频谱结构的影响

爆破振动的频谱特性对隧洞安全施工具有重要意义。采用动力有限元方法,分析了不同地应力水平条件下围岩爆破振动频率特征,通过对实测爆破振动信号的时域和频域联合分析,研究了不同频带上的振动能量分布。结果表明,爆破振动的主频及各个振动能量优势频带都有随地应力水平升高而降低的趋势,伴随爆破破岩过程而发生的地应力瞬态卸载动力效应是产生这一现象的主要原因。地应力水平越高,爆破振动信号中20～100 Hz的低频振动能量比重越大。当爆区的地应力为20 MPa时,20～100 Hz频带内的振动能量可达到总振动能量的35%左右;当爆区的地应力为30～50 MPa时,20～100 Hz频带内的振动能量可达到总振动能量的50%以上。除地应力水平外,应力卸载速率及岩体的力学特性也对爆破振动主频具有显著影响,卸载速率越高,低频振动能量比重越大。卸载速率取决于掏槽爆破方式,直孔掏槽导致岩体应变能释放速率最高。岩体弹性模量越大,爆破振动的主频越高。     

On formulas for the Rayleigh wave velocity in pre-stressed compressible solids

In this paper, formulas for the velocity of Rayleigh waves in compressible isotropic solids subject to uniform initial deformations are derived using the theory of cubic equation. They are explicit, have simple algebraic forms, and hold for a general strain energy function. Unlike the previous investigations where the derived formulas for Rayleigh wave velocity are approximate and valid for only small enough values of pre-strains, this paper establishes exact formulas for Rayleigh wave velocity being valid for any range of pre-strains. When the prestresses are absent, the obtained formulas recover the Rayleigh wave velocity formula for compressible elastic solids. Since obtained formulas are explicit, exact and hold for any range of pre-strains, they are good tools for evaluating nondestructively prestresses of structures.     

Convective heat transfer from two rotating circular cylinders in tandem arrangement by using lattice Boltzmann method

The numerical investigation of the two-dimensional laminar flow past two ro- tating circular cylinders in the tandem arrangement is conducted by the lattice Boltzmann method. The numerical strategy is used for dealing with curved and moving boundaries of the second-order accuracy for velocity and temperature fields. The effects of various rotational speed ratios and gap spacing are studied with the Reynolds number of 100 and the Prandtl number of 0.71. A varied range of rotational speed ratios are investigated for four different gap spacing, i.e., 3.0, 1.5, 0.7, and 0.2. The results show that, for the first cylinder, the lift and drag coefficients for large gap spacing are similar to those for a single cylinder; for the second cylinder, the lift coefficient descends with the increase in the angular velocity for all gap spacing, while the drag coefficient ascends except for the gap spacing of 3.0. The results of the averaged periodic Nusselt number on the surface of the cylinders show that, for small distances between the cylinders and low angular velocities, conduction is a dominant mechanism of heat transfer, but for large distances and high angular velocities, convection is the main mechanism of heat transfer.     

Boundary element simulations of spheres settling in circular,square and triangular conduits

Numerical simulations of a spherical particle sedimenting in circular, triangular and square conduits containing a viscous, inertialess, Newtonian fluid were investigated using the Boundary Element Method (BEM). Settling velocities and pressure drops for spheres falling along the centre-lines of the conduits were computed for a definitive range of sphere sizes. The numerical simulations for the settling velocities showed good agreement with existing experimental data. The most accurate analytic solution for a sphere settling along the axis of a circular conduit produced results which were almost indistinguishable from the present BEM calculations. For a sphere falling along the centre-line of a square conduit, the BEM calculations for small spheres agreed well with analytic results. No analytic results for a sphere falling along the axis of a triangular conduit were available for comparison. Extrapolation of the BEM predictions for the pressure drops, to infinitely small spheres, showed remarkable agreement with analytic results. For the circular conduit, the sphere's settling velocity and angular velocity were computed as a function of drop position for small, medium and large spheres. Excellent agreement with a reflection solution was achieved for the small sphere. In addition, end effects were investigated for centre-line drops and compared where possible with available experimental data and analytic results.Los Alamos National Laboratory, Los Alamos, New Mexico, USA.     

软弱破碎围岩变形特性

本文在连续十余年原位监测试验资料的基础上,描述了全断面开挖的软弱围岩变形u-t全过程曲线;阐明了不同变形阶段的变形速率、变形量以及这些变形的时空效应;探讨了岩体工程地质特性、埋深、洞径、开挖方式和支护及时性等主要因素对围岩变形特性的影响;并针对具体工程提出了围岩稳定性状态划分及其判别标准、失稳险情预报原则、变形控制标准与初期支护抗力的确定原则、后期支护最佳施作时期的选择以及合理开挖方式。     

The re-examination of the weakly nonlinear theory of hydrodynamic stability

The weakly nonlinear theory has been widely applied in the problem of hydrodynamicstability and also in other fields.However,although its application has been successful forsome problems,yet,for other problems,the results obtained are not satisfactory,especiallyfor problems like transition or the evolution of the vortex in the free shear flow,for whichthe goal of the theoretical investigation is not seeking for a steady state,but predicting anevolutional process.In this paper,we shall examine the reason for the unsuccessfulness andsuggest ways for its amendment.     

Measurement of coatings' elastic properties by mechanical methods: Part 1. Consideration on experimental errors

A critical analysis of some mechanical methods employed for measuring the elastic properties of coatings is presented. A rational basis for properly choosing test methods, transducers and layer thicknesses is provided. The analyzed methods, usually applied to relatively thick coatings, include four-point bending tests and the resonance technique. General relationships for the evaluation of coatings' elastic properties, derived from the multilayer beam and plate theories, are discussed. On the basis of the error propagation theory, for different combinations of materials and layer thicknesses, the influence of typical experimental errors, test setup parameters and material properties is analyzed, and sensitivity coefficients for relative errors are discussed. The critical experimental variables and their effect on measurement accuracy are highlighted, suggesting suitable conditions for selecting specimen geometry and testing conditions. A procedure for measurement at high temperature is outlined.     

Hypoplasticity theory for granular materials—II: Three-dimensional axially symmetric exact solutions

In part I of this paper, we consider the governing equations of hypoplasticity theory for two-dimensional steady quasi-static plane strain compressible gravity flow and determine some exact analytical solutions applying for certain special cases. Similarly, for the three-dimensional situation considered here in part II, we undertake a similar mathematical investigation to determine some simple solutions of the governing equations for three-dimensional steady quasi-static axially symmetric compressible gravity flow for hypoplastic granular materials. We again find that for certain special cases, we are able to determine some exact solutions for the stress and velocity profiles. We comment that hypoplasticity theory generally gives rise to complicated systems of coupled non-linear differential equations, for which the determination of any analytical solutions is not a trivial matter, and that the solutions determined here might be exploited as benchmarks for full numerical schemes.     

Renormalization Group Model of Large-Scale Turbulence in Porous Media

Renormalization group methods are used to develop a macroscopic (large-scale) turbulence model for incompressible flow in porous media. The model accounts for the large-distance and large-time behavior of velocity correlations generated by the momentum equation for a randomly stirred, incompressible flow. Utilizing the renormalization procedure, the transport equations for the large-scale modes and expressions for effective transport coefficients are obtained. Expressions for renormalized turbulent viscosity, which accounts for the ultraviolet subrange of the turbulent kinetic energy spectrum, are also obtained.