基于SPH 法的爆炸螺栓冲击特性研究

由于爆炸螺栓解锁过程具有瞬时性、变形大等特点,同时接触爆炸过程中交界面处介质阻抗相差 较大,因此基于计及材料强度的SPH 方法,在控制方程的粒子近似过程中将其转化为粒子密度及质量对物理 量近似过程影响较小的形式,建立了爆炸螺栓三维SPH 数值模型,分析了爆炸螺栓解锁过程中的冲击特性。 同时,通过与LS-DYNA软件的计算结果进行对比,验证了本文所建立数值模型的准确性和可靠性。     

影响无网格方法求解精度的因素分析

基于移动最小二乘法的无网格方法的计算精度除受到节点的分布密度和基底函数的阶次影响外，还受到其它因素的影响，其中权函数的选取、权函数影响域的大小及位移边界条件的引入对计算精度影响较大。本文分析了几种常用权函数在数值计算时的特点，包括计算精度、收敛情况、计算效率等，同时分析了影响域大小及边界条件的引入对计算精度的影响。通过分析给出了确定权函数及其影响域大小的方法。当受约束的自由度较多时，通过配点法引入位移边界条件会引起计算结果的振荡，通过施加稳定项可以消除振荡现象，通过对带孔方板的受力分析证明了其可行性。应用以上结论对J23—10曲柄压力机机身进行了受力分析，应力集中部位的计算结果得到了较高的精度。     

影响流体力学仿真精度的数值积分因素

为了获得精确的流体力学仿真效果,本文对其中的影响因素之一－数值积分因素进行了研究,得到了满意结果时应用的数值积分方法的精度和步长。     

球形爆炸容器法兰联接螺栓的应变增长现象

本文在球形爆炸容器法兰连接螺栓的动态响应实验研究中,发现了法兰螺栓的应变增长现象。以实验数据为基础,通过数值模拟对螺栓发生应变增长的原因进行分析。研究结果表明:受到开口结构的影响,端盖螺栓受到的压力载荷强度较容器内壁大幅增强。螺栓的应变增长是被增强压力载荷的前2个周期与结构响应形成共振时引发的,通过改变端盖质量、预紧力大小可以避免螺栓发生应变增长。     

Mechanism of track random irregularity affecting dynamic characteristics of rack vehicle

Nonlinear Dynamics - The track random irregularity not only worsens the running stability and smoothness of the rack vehicle, but increases the vibration and impact of the gear-rack system. To...     

大长径比、高密实火药床点火管点传火特性的影响因素

利用计算程序对影响大长径比、高密实火药床点火管点火性能的主要因素进行了对比模拟,讨论了不同结构尺寸和装填条件下的点传火性能,通过对计算结果的分析,总结了结构参数和装填条件对大长径比、高密实火药床点火管点传火性能的影响规律：小孔直径、首孔高度、单位长度小孔面积及装填密度显著影响点火压力及点传火性能;小孔直径、首孔高度及单位长度小孔面积是影响破膜后泄压速度的主要因素,而装填密度会影响药床的透气性及火焰传播的通畅性,均对点火安全性、瞬时性及一致性产生重要影响作用。

     

Factors affecting the stability of viscous axial flow in annuli with a rotating inner cylinder

Hot-wire measurements are presented of the onset of instability in developed axial flow and in both developing and developed tangential flow caused by inner cylinder rotation in concentric annuli of radius ratio N of 0.909, 0.809 and 0.565 for axial-flow Reynolds numbers (Re) between 86 and 2000. Within assessed uncertainty intervals, the consistency of marginal stability measurements, at four azimuthal locations 90° apart, indicates insensitivity to small variations in gap width; the measurements also confirm the destabilisation of nearly-developed and developed tangential flow identified by Takeuchi and Jankowski¹ with the occurrence at increasing Re of three-dimensional initial disturbances of spiral-vortex form. Comparison with earlier measurements suggests that in particular annuli, destabilisation may be delayed to higher Re by high values of certain geometrical factors, including radius ratio and the resultant end-effects parameter. Stability may also be restored or improved at high Re by reversion to developing tangential flow in which the initial instability is not of spiral-vortex form and where, for given N, the critical Taylor number appears uniquely related to the dimensionless axial co-ordinate. Stability is then generally greatest at low N.     

Factors affecting temperature measurement using phase measurement interferometry in small scale devices

This paper presents full-field temperature measurements of buoyancy opposing mixed convection flow within a miniscale fluidic geometry. The technique used is phase measurement interferometry and a Mach–Zehnder layout is employed. The popular two-dimensional microfluidic geometry of three streams merging at a junction is chosen for this analysis. The apparatus set-up is described and measures taken to limit experimental errors discussed. Also presented, are corresponding flow visualization images for comparison with the interferometric results. The results are compared for similar boundary conditions over the range of Richardson numbers of 0.5–1.7. The results of the interferometric study are presented in the form of full-field temperature maps depicting the type of thermal plume structure present through isotherms and are seen to compare well with the results of the flow visualization study. Some factors affecting the measurement technique at this scale are then discussed. These include the effect of using different transparent materials for sealing the fluidic device and temporal vibrations caused by either varying boundary conditions or by slight pulsations in the flow supplied. Also, due to discrepancies that exist in the literature for the temperature coefficient of the refractive index of the working fluid, thermocouples are embedded in the flow field and used to convert the measured phase change to a corresponding temperature change. The corresponding values of refractive index change with temperature are discussed and compared to published values. Overall, PMI is demonstrated to provide excellent full-field temperature plots that can be used to measure local heat transfer rates from this non-intrusive measurement technique.     

注浆锚杆中扭转导波的传播特性

理论研究了扭转导波在注浆锚杆中的传播特性。首先建立了注浆锚杆两层复合结构中的扭转导波的频散方程,之后数值计算得到了扭转导波的能量速度、衰减频散曲线及导波在注浆锚杆中的位移分布情况。结果表明,(1)500kHz范围内,注浆锚杆中具有三种扭转导波模态T(0,1)~T(0,3),三种模态均具有频散性。随着频率逐渐增大,导波的能量速度逐渐增大,而衰减值逐渐减小。(2)50kHz和200kHz的T(0,1)模态扭转导波在锚杆体内的周向位移值较大,所以对锚杆体表面的轴向缺陷敏感,而导波在锚杆与注浆体接触面上的周向位移较大,从锚杆泄漏至注浆体中的能量较大,导波衰减较严重。(3)频率高于100kHz,锚杆直径的变化对T(0,1)模态的能量速度几乎无影响,而频率低于100kHz,注浆体弹性模量越大,T(0,1)模态的能量速度越小。     

A method to simplify the strength design of bolted joints—Case of connecting-rod bolts

This study shows the development of the strength-design system for general bolted joints. Specifically, a simplified method of the strength design for the connectingrod bolts is proposed. The connecting-rod joint is transformed into a single-bolted-joint model by using the ring model. The axial stress on the bolt and separation behavior at the contact plane are discussed. The strength design of the connecting-rod joint can be performed by applying the unified procedure to the single-bolted-joint model. The local deformation of the connecting-rod joint and the stress on the bolt were measured and the analytical results are compared with the experimental results. Both results show fairly good agreement.     

复合受力下焊接栓钉SRC柱抗扭承载力计算

为研究压、弯、剪、扭复合受力下焊接栓钉型钢混凝土(SRC)柱的抗扭承载力计算方法,基于滞回性能试验结果,分析了试验过程和破坏形态,利用了空间桁架理论与叠加原理,提出了复合受力下焊接栓钉SRC柱抗扭计算模型和强度统一方程.结果表明:所提出的强度统一方程和抗扭承载力计算方法的计算结果与试验结果均值误差均在3％内,吻合较好.     

三维加锚弹塑性损务模型在溪洛渡地下厂房工程中的应用

本文根据断续裂隙岩体的损伤机制,建立了三维弹塑性损伤本构模型反映裂隙岩体的损伤变形特性。考虑断续裂隙岩体的岩锚支护效应,建立了空间损伤锚柱单元模型模拟锚杆的支护效果。最后将建立的模型应用于溪洛渡水电站地下厂房,进行了洞室群开挖弹塑性损伤及岩锚支护三维非线性有限元计算,获得了一些有益的工程结论。     

输电铁塔四地脚螺栓塔脚板抗拉承载力试验与计算方法研究

针对架空输电线路铁塔中常用的四地脚螺栓塔脚板进行了抗拉承载力试验和理论计算方法研究。首先,选取8个试件进行塔脚板抗拉承载力试验研究,分析塔脚底板板厚及有无加劲板对塔脚板抗拉承载力的影响;其次,通过有限元模拟塔脚板的应力分布情况,并结合“塑性分析,弹性设计”的思想,提出了一种基于屈服线理论的四地脚螺栓塔脚板抗拉承载力计算公式;最后,与试验结果、有限元仿真结果、已有技术规定中的计算结果进行了对比。结果表明:建议公式与试验结果和仿真结果较为吻合,相关技术规定中的计算结果偏于保守,验证了本文建议公式的精确性;底板厚度和加劲板的作用对塔脚板承载力影响较大。研究结果可为输电铁塔四地脚螺栓塔脚板结构设计提供参考。     

Linear interactions affecting the propogation of waves in a linear elastic fluid

Small linear interactions affecting the propogation of waves in a linear elastic fluid are investigated. These linear interactions may occur as a result of impurities on the surface of a linear elastic fluid. These interactions are imposed on the linear wave equations which were investigated in Momoniat (Propogation of waves in a linear elastic fluid, submitted for publication) using the non-classical contact symmetry method. The occurrence of a small parameter in the wave equations under consideration in this paper makes the problem ideal for analysis using an approximate non-classical contact symmetry method. Approximate contact symmetries and approximate solutions are determined and discussed for the problems under consideration. Comparisons are made with the case of no interaction.     

Study of the phenomena affecting the accuracy of a video- based particle tracking velocimetry technique

 The development of a video-based Particle Tracking Velocimetry (PTV) technique has focused on the problem of the accuracy of this method. The PTV-method can be decomposed into three parts: the recording of the experiment, the image processing and the evaluation of the velocities. The accuracy of each stage has been studied. Inaccuracies due to resolution, length scale, light intensity and distortion of the x and y direction are analysed. One of the main factors influencing the accuracy is the selection of the time difference between frames. During the evaluation of velocities, incorrect identifications of particles may occur. The relation between the time-step of the frames and the percentage of incorrect identifications has been shown. The percentage of false identifications increases with the size of the time-step. The resolution accuracy is however improved when the time-step is increased. An adequate selection of the time-step has to be made to obtain a high resolution accuracy and a limited number of incorrect identifications. Received: 22 April 1996 / Accepted: 17 November 1996     

A study of system parameters affecting self-excited torsional oscillations

Self-excited oscillations are of considerable importance in mechanical systems, and are capable of completely defeating the purpose for which a device is intended, including the possibility of self-destruction. The results of a theoretical and experimental investigation of this phenomenon are presented, with particular reference to the effect of variations in the system parameters upon the critical threshold velocity at which such oscillations commence. Good correspondence between theory and experiment is observed. Results are presented in terms of dimensionless parameters β (dependent upon system stiffness and solid friction) and ζ (internal damping ratio). It is concluded that for β<0.0001 (very stiff system) there is little danger of self-excited oscillations, and also that the critical threshold velocity is extremely sensitive to small changes in ζ when ζ is small (on the order of ζ=0.01).     

On the characteristics of Applied Mathematics

In this paper,four aspects of particular characteristics of Applied Mathematicsdifferent from those of Pure Mathematics are summarized by comparison.     

Mathematical characteristics of the pom-pom model

 Recently, in order to describe the complex rheological behavior of polymer melts with long side branches like low density polyethylene, new constitutive equations called the pom-pom equations have been derived in the integral/differential form and also in the simplified differential type by McLeish and Larson on the basis of the reptation dynamics with simplified branch structure taken into account. In this study, mathematical stability analysis under short and high frequency wave disturbances has been performed for these constitutive equations. It is proved that the differential model is globally Hadamard stable, as long as the orientation tensor remains positive definite or the smooth strain history in the flow is previously given. However both versions of the model are Hadamard unstable if we neglect the arm withdrawal in the case of maximum backbone stretch. It is also dissipatively unstable, since the steady shear flow curves exhibit non-monotonic dependence on shear rate. Additionally, in the flow regime of creep shear flow where the applied constant shear stress exceeds the maximum achievable value in the steady flow curves, the constitutive equations exhibit severe instability that the solution possesses strong discontinuity at the moment of change of chain dynamics mechanisms. Received: 14 August 2001 Accepted: 18 October 2001