电爆炸丝的电气特性

根据金属导体电阻与比作用量的关系和A.Hobson提出的金属丝阻抗随时间的变化规律分别建立了2种仿真模型研究电爆炸丝断路开关的电气特性;测量了电爆炸过程中金属丝两端的电压,结果表明:A.Hobson模型只有在电爆炸丝汽化前有效;电阻率-比作用量模型适用于整个电爆炸过程的宏观描述.因此,对含电爆炸丝元件的电路仿真模拟采用...     

水中电爆炸的实验研究

利用冲击大电流通过水中的一段金属丝进行水中电爆炸实验 ,通过对水中电爆炸的放电电压、电流波形测量以及高速阴影摄影和扫描摄影 ,记录了冲击波的传播、汽泡增长和等离子体半径的时间特性 ;由不同充电参数的实验 ,得到了一些基本规律。比较了水中电爆炸和空中电爆炸的异同 ,揭示了水中电爆炸存在的放电模式。     

10m3爆炸罐中甲烷燃烧爆炸发展过程

在大型多相混合物爆炸实验系统(10m3爆炸罐)中对甲烷/空气混合物在40J电火花点火条件下爆炸发展过程进行了实验和数值模拟研究.采用中心电火花点火,并在距点火点不同距离处设置4个压力传感器.得到下列实验结果:甲烷爆炸上、下限分别为13.9%、4.75%;甲烷浓度为9.5%的爆炸特性参数随距离变化规律;不同甲烷浓度对超压...     

高电压点火有效能量的测量及相关问题

建立了测量高电压点火产生的爆炸波参数装置,利用PCB压力传感器测定了在空气中高压电火花产生的爆炸波压力及其到达时间。改变点火能量和测试距离,得到了爆炸波的变化趋势和传播规律,并探讨了爆炸波各参数的标度尺寸。结果表明,电火花产生的爆炸波符合Hopkinson-Sachs爆炸相似律。把1/4周期放电能量与数值模拟结果进行比较,得知初始1/4周期放电能量(点火能量)与爆炸波能量基本吻合;因此,1/4周期放电能量可被视为作用于直接起爆引起爆轰的有效能量。进一步探讨了高电压点火各能量的分布;结果表明,储存于电容的总能量1/2CU2中约91%消耗于能量损失和欧姆损耗,初始1/4周期放电能量仅约占2%,其余的点火能量只起到加热混合物的作用。     

爆炸式电磁感应脉冲发生器

为了探索脉冲发生器新的技术方法,在传统脉冲发生器的基础上,提出了一种依靠爆炸驱动的电磁感应脉冲发生器。介绍了发生器的工作过程,对发生器中炸药的爆炸和冲击过程进行了计算和数值模拟,建立了带有初始电压和初始静磁场的发生器的工作电路模型,得出了感应电压的计算方法。设计了一种通过永磁体提供初始静磁场的脉冲发生器,并分别对装有两种不同炸药的发生器进行了实验。实验表明:爆速较高的炸药驱动发生器可产生峰值更高的电压脉冲。实验结果偏低于计算结果,原因是理论计算中简化了磁芯磁场和冲击波速度。     

氢气定容燃烧的实验研究

利用定容燃烧弹和高速数据采集系统对氢气定容燃烧进行实验研究,得出氢气定容燃烧压力变化过程、燃烧爆压及爆炸常数的变化规律。研究结果表明:中心点火定容燃烧的压力变化过程为:从开始的火花跳火干扰到平稳的等压燃烧,再到压力的慢速和快速增加,在燃烧的中后期会出现压力振荡;在非燃烧极限工况下,随着燃空当量比的增加燃烧爆压先增加后减小,随着初始压力的升高燃烧爆压几乎线性增加,随着温度的增加燃烧爆压和最大燃烧爆压都减小;随着燃空当量比的增加爆炸常数先增加后减小,在燃空当量比小于4.0的工况,燃烧爆炸常数随初始压力的升高而增加,而燃空当量比大于4.0的工况随着初始压力的升高而下降;在燃空当量比小于2.5时,燃烧爆炸常数随温度升高而减小,在燃空当量比大于2.5时,则正好相反。     

爆炸荷载作用下围岩与地下结构的动力相互作用

利用ANSYS/LS-DYNA非线性显式动力有限元程序和流固耦合计算方法,对炸药在地下拱形结构上方岩石中垂直爆炸过程进行数值模拟,借助波动理论p-u Hugoniot线对爆炸冲击波在围岩与结构之间的传播和加卸载过程进行理论分析;得到了不同跨度拱形结构与围岩之间的最大相互作用力及相互作用力分布图。研究结果表明:冲击波由高阻抗围岩向低阻抗混凝土传播时,围岩卸载,应力减小;反向传播时,岩石加载,应力增大;爆距为5 m时爆炸冲击波对40 m跨度拱形结构整体产生拉压震荡,引起的震动效应显著。     

含节理岩体爆生裂纹扩展的动焦散模型实验研究

应用动态焦散线测试系统,模拟含节理岩体断裂爆破过程,进行了PMMA模型透射式动态焦散线实验,着重研究了爆炸初始裂纹与节理面不同夹角的情况下,裂纹尖端动态应力强度因子的变化规律,裂纹穿过节理面的扩展规律,以及裂纹扩展速度的变化规律。实验结果分析表明,爆生裂纹穿过节理面时,裂纹尖端的动态应力强度因子和裂纹扩展速度显著下降,穿过节理面后,应力强度因子又有所增强;裂纹穿过节理面时,裂纹会沿节理面偏离一段距离后沿初始裂纹方向继续扩展。研究结果可以为节理岩体的断裂爆破提供理论依据。     

电爆炸丝断路开关性能实验研究

详细研究了初始能量、电爆炸丝截面积和丝长度等参数对含电爆炸丝断路开关的电感储能脉冲功率调节系统输出电流、电压的影响,并将实验结果与数值模拟结果进行了比较,给出了相关的结果。实验结果表明初始能量爆炸丝参数对丝电流、丝电压的影响有一定的规律。     

巷道壁面与瓦斯爆炸相互作用的数值模拟

通过物理机制分析,建立合理的巷道物理模型,并对燃烧爆炸反应模型中阻力系数C_D和湍流特征尺度L_t进行修正,模拟实际巷道内壁粗糙情况对瓦斯爆炸传播过程的影响,为模型计算提供修正参数。研究结果表明,巷道壁面条件对瓦斯爆炸过程有很大影响;C_D和L_t越大,爆炸峰值超压越大;当C_D＝3、L_t＝0.008时,模拟结果与实验值的偏差最小。     

Ultrasound influence on the erosive capacity at the electrodischarge processing with ultrasonic activated wire electrode in a single point

Paper presents results of experimental research for the electricaldischarge processing machines efficiency improvement, machines which are using as electrode a wire, abbreviated W-EDM. These machines were equipped with special devices for the ultrasonic activation of the wire electrode. It was noticed that the introduced ultrasound influenced the erosive capacity of the machining process. The paper presents in graphical and tabular forms, the variation of erosive capacity due to the way how the ultrasonical activation of the wire electrode is produced: into the fixed or mobile arm (two subassemblies of the W-EDM machine), after a direction parallel or perpendicular to the direction of the working advance.     

Thermodynamics of Shape Memory Alloy Wire: Modeling, Experiments, and Application

A thermomechanical model for a shape memory alloy (SMA) wire under uniaxial loading is implemented in a finite element framework, and simulation results are compared with mechanical and infrared experimental data. The constitutive model is a one–dimensional strain-gradient continuum model of an SMA wire element, including two internal field variables, possible unstable mechanical behavior, and the relevant thermomechanical couplings resulting from latent heat effects. The model is calibrated to recent and new experiments of typical commercially available polycrystalline NiTi wire. The shape memory effect and pseudoelastic behaviors are demonstrated numerically as a function of applied displacement rate and environmental parameters, and the results compare favorably to experimental data. The model is then used to simulate a simple SMA actuator device, and its performance is assessed for different thermal boundary conditions.     

Vibration of two beams connected by nonlinear isolators: analytical and experimental study

To study the coupling vibration of nonlinear isolators and flexible bodies, test rigs of two flexible beams connected by wire mesh isolators are constructed and investigated both experimentally and analytically. A five-parameter polynomial model of wire mesh isolators is derived by identifying parameters in the frequency domain with the sine-sweep test. For obtaining the parameters that are valid in a wide range of frequency, a numerically assisted identification method is developed. With this model, the vibration of two flexible beams connected by wire mesh isolators is studied. The frequency response is obtained analytically by employing the Green’s function method and harmonic balance method. Sine-sweep test results with three test rigs show good coherence with the corresponding numerical results. With obtained experimental results and numerical results, effect of connection parameters is studied in detail. It is found that traditional design rules for isolators are no longer effective and the coupling vibration must be investigated in the design phase. Another phenomenon is that the damping has a function of weakening the effect of nonlinear stiffness. Nonlinear stiffness and nonlinear damping can decrease the transmissibility along with the increase of the excitation level.     

钢丝软轴抗扭刚度的计算及测量

根据钢丝软轴基本参数的变化,确定其受载后其它几何尺寸的变化量,由此导出软轴两端相对扭转角进而得到钢丝软轴抗扭刚度的计算公式,此外,笔还在扭转试验机上对钢丝软轴的抗扭刚度进行实验测量,结果证实本理论计算值吻合于实际测量值。     

Experimental‐theoretical analysis of nonstationary interaction of deformable impactors with soil

An experimental method for determining the force of resistance to penetration of a deformable impactor into soft soil was developed in the inverted formulation: the impactor and the target exchange roles and the necessary parameters of contact interaction are recorded in an immovable measuring rod (impactor). To verify the basic principles of this experimental technique, wave processes were analyzed numerically using a modified Godunov's scheme. The applicability of various models of soil deformation was studied, and the calculation results obtained were compared with experimental data.     

Formation and basic parameters of vortex rings

This paper describes an experimental study of the properties of vortex rings with variation of parameters of the air jet expelled from a round nozzle by a special device. Characteristics of the vortex rings were determined by hotwire anemometer measurements of the velocity field at a certain distance from the nozzle exit where vortex formation is presumably completed. A mathematical model for the formation of a vortex ring based on conservation laws is proposed, and a comparison of theoretical results with experimental data is given.     

Computational fluid dynamics simulations of respiratory airflow in human nasal cavity and its characteristic dimension study

To study the airflow distribution in human nasal cavity during respiration and the characteristic parameters of nasal structure, three-dimensional, anatomically accurate representations of 30 adult nasal cavity models were recons- tructed based on processed tomography images collected from normal people. The airflow fields in nasal cavities were simulated by fluid dynamics with finite element software ANSYS. The results showed that the difference of human nasal cavity structure led to different airflow distribution in the nasal cavities and variation of the main airstream passing through the common nasal meatus. The nasal resistance in the regions of nasal valve and nasal vestibule accounted for more than half of the overall resistance. The characteristic model of nasal cavity was extracted on the basis of characteristic points and dimensions deduced from the original models. It showed that either the geometric structure or the airflow field of the two kinds of models was similar. The characteristic dimensions were the characteristic parameters of nasal cavity that could properly represent the original model in model studies on nasal cavity.     

New Correlative Models to Improve Prediction of Fracture Permeability and Inertial Resistance Coefficient

Presence of fracture roughness and occurrence of nonlinear flow complicate fluid flow through rock fractures. This paper presents a qualitative and quantitative study on the effects of fracture wall surface roughness on flow behavior using direct flow simulation on artificial fractures. Previous studies have highlighted the importance of roughness on linear and nonlinear flow through rock fractures. Therefore, considering fracture roughness to propose models for the linear and nonlinear flow parameters seems to be necessary. In the current report, lattice Boltzmann method is used to numerically simulate fluid flow through different fracture realizations. Flow simulations are conducted over a wide range of pressure gradients through each fracture. It is observed that creeping flow at lower pressure gradients can be described using Darcy’s law, while transition to inertial flow occurs at higher pressure gradients. By detecting the onset of inertial flow and regression analysis on the simulation results with Forchheimer equation, inertial resistance coefficients are determined for each fracture. Fracture permeability values are also determined from Darcy flow as well. According to simulation results through different fractures, two parametric expressions are proposed for permeability and inertial resistance coefficient. The proposed models are validated using 3D numerical simulations and experimental results. The results obtained from these two proposed models are further compared with those obtained from the conventional models. The calculated average absolute relative errors and correlation coefficients indicate that the proposed models, despite their simplicity, present acceptable outcomes; the models are also more accurate compared to the available methods in the literature.     

金属圆管在炸药滑移爆轰作用下的运动姿态

采用二维Ｌａｇｒａｎｇｅ数值摸拟方法，计算在管内装填岩石硝铰炸药滑移爆轰作用下，２０＃无缝钢管的运动过程，计算结果与用斜电阻丝法测量得到的结果基本相符。