EXPERIMENTAL STUDY OF MECHANICAL PROPERTIES OF WATER-COOLED GRANITE UNDER HIGH TEMPERATURE1)

通过对高温加热-遇水快速冷却后的花岗岩试样进行单轴和三轴实验,研究了800°C内高温花岗岩遇水快速冷却后的力学性质随温度和围压的变化规律。实验结果表明：(1)400°C为高温加热-遇水快速冷却对花岗岩力学性质影响的阈值;(2)同一温度条件下,峰值偏应力、峰值应变随围压的增大而增大;弹性模量随围压的增大先增大后减小;(3)单轴实验中,温度低于400°C时,岩样表现为复合破坏,随着温度的升高破坏形式转变为拉破坏;三轴实验中,岩样整体上表现为剪切破坏。     

INFLUENCE OF SEDIMENTARY DIRECTION ON SHEAR STRENGTH OF SATURATED DENSE SAND IN CONSOLIDATED DRAINED TRIAXIAL TEST1)

基于砂土颗粒的毛细效应制备具有不同沉积方向的密砂试样,通过三轴固结排水剪切试验研究沉积方向对试样强度和体变特性的影响,建立沉积方向和峰值强度的拟合公式。研究结论表明,在0°~90°范围内,沉积方向对峰值强度和变形的影响比较显著,对残余强度的影响较弱。当沉积方向与破坏面方向(45°+ϕ/2)接近时,试样更容易达到破坏状态,所对应的峰值强度更低。拟合公式能够反映沉积方向和峰值强度的关系,围压对该关系有显著的影响,同时,公式能够预测最不利沉积方向的大小。     

Natural convection in an inclined quadrantal cavity heated and cooled on adjacent walls

Natural convective flow and heat transfer in an inclined quadrantal cavity is studied experimentally and numerically. The particle tracing method is used to visualize the fluid motion in the enclosure. Numerical solutions are obtained via a commercial CFD package, Fluent. The working fluid is distilled water. The effects of the inclination angle, ? and the Rayleigh number, Ra on fluid flow and heat transfer are investigated for the range of angle of inclination between 0° ? ? ? 360°, and Ra from 10⁵ to 10⁷. It is disclosed that heat transfer changes dramatically according to the inclination angle which affects convection currents inside, i.e. flow physics inside. A fairly good agreement is observed between the experimental and numerical results.     

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为降低用来确定疲劳极限的升降法试验的工作量，以热力学为基础，引入损伤驱动力，构建 损伤演化方程. 积分此方程得到疲劳寿命与应力或应变的理论关系. 对光滑试件，根据成组 法疲劳试验结果利用最小二乘法拟合包括疲劳极限在内的材质参数. 利用损伤力学方法求得 高应力区的疲劳寿命曲线，由此递推得到低应力区寿命值和疲劳极限. 所得理论疲劳极限值 与升降法疲劳试验结果十分吻合. 节约了疲劳试验的机时、费用与人力.     

The motion of explosion products behind the front of a detonation wave

The velocity of the explosion products behind the detonation wavefront in a 50/50 TNT-hexogen explosive was measured by an electromagnetic method.The experimental data on the mass velocity profile behind the wavefront in charges of different lengths, and the results of measurements of the motion of the backward rarefaction waves can be well described if in the mass velocity-time curves one isolates a stationary zone of 0.1 sec and regards the rest of the motion as self-similar.The experimentally observed sharp drop of mass velocity behind the wavefront indicates that the isentropic exponent of the explosion products increases upon expansion.The observed data on the distribution of mass velocities were used to calculate the isentrope of the explosion products in the pressure range 100–250 000 atm.     

A comparison between a collocation and weak implementation of the rigid‐body motion constraint on a particle surface

In this work, we implemented and compared two different methods to impose the rigid‐body motion constraint on a solid particle moving inside a fluid. We consider a fictitious domain method to easily manage the particle motion. As the solid as well as the fluid inertia are neglected, the particle can be discretized through its boundary only. The rigid‐body motion is imposed via Lagrange multipliers on the boundary. In the first method, such constraints are imposed in discrete points on the boundary (collocation), whereas in the second the constraint is imposed in a weak way on elements dividing the particle surface. Two test problems, that is, a spherical and an ellipsoidal particle in a sheared Newtonian fluid, are chosen to compare the methods. In both cases, the analysis is carried out in 2D as well as in 3D. The results show that for the collocation method an optimal number of collocation points exist leading to the smallest error. However, small variations in the optimal value can generate large deviations. In the weak implementation, the error is only mildly affected by the number of elements used to discretize the particle boundary and by the Lagrange multiplier's interpolation space. A further analysis is carried out to study the effect of an approximated integration of weak constraints. A comparison between the two methods showed that the same accuracy can be achieved by using less constraints if the weak discretization is used. Finally, the rigid‐body motion imposed via weak constraints leads to better conditioned linear systems. Copyright © 2009 John Wiley & Sons, Ltd.     

计算域可变的CEL方法

为了更好地兼顾拉氏方法和欧拉方法各自的特长,提出一种可将拉氏介质映射到欧拉计算域的耦合欧拉-拉格朗日(CEL)方法。通过这种映射,将欧拉-拉格朗日重叠区域的接触面协调问题转换为欧拉区域内的多介质计算问题,简化了CEL方法的构造过程。通过与侵彻实验和结构对爆炸冲击波响应实验的比较,验证了新算法,计算结果与实验数据符合较好。     

成层半空间出平面自由波场的一维化时域算法

提出了一种计算出平面SH波斜入射时弹性水平成层半空间中自由波场时域计算的一维化有 限元方法. 在进行有限元网格划分时，竖向单元取满足有限元模拟精度的任意尺寸，水平向 网格尺寸由时间离散步长和水平视波速确定，并自动进行虚拟网格划分. 基底设置人工边界， 并将波动输入转化为等效荷载施加在边界节点上. 然后将集中质量有限元法和中心差分法相 结合建立节点运动方程，并将水平方向相邻节点的运动用该节点相邻时刻的运动表示，从而 将求解节点运动的二维方程组转化为一维方程组. 求解此方程组，即得到自由场中竖向一列 节点的运动. 最后根据行波传播的特点，可方便地确定全部自由波场. 理论分析和数值算例 表明，该方法具有较高的精度和良好的稳定性.     

阶梯型加速段对旋流喷嘴雾化特性的影响

旋流内芯是压力旋流式喷嘴最主要的旋流发生构件, 其几何特征直接影响压力旋流式喷嘴的喷雾特性.目前采用平滑型加速段的旋流内芯导流效率较低.为减小高流量条件下的能量损失, 使喷嘴旋流内芯加速段对喷雾介质产生预旋效应, 增强旋流强度, 本文设计喷嘴旋流内芯加速段为阶梯型, 其下段阶梯相对上段阶梯旋转15°, 旋向与喷嘴旋流槽方向相同.利用粒子动态分析仪(particle dynamics analysis system, PDA) 和高速摄影(charge coupled device, CCD)系统实验研究了加速段结构改进前后喷嘴的喷雾流量、雾场索特尔平均直径(Sauter mean diameter, SMD)、雾滴速度以及喷雾锥角, 并分析了SMD、 雾滴速度的轴向和径向分布特性. 结果表明, 背压差0.08\mathrm{~} 0.46 MPa 范围内, 阶梯型加速段对喷雾介质具有较好的预旋效果.喷嘴的流量提高了48.0% ~ 51.8%; 喷雾的轴向速度提升了31.4% ~ 32.8%, 径向速度提升了1.6% ~ 16.8%; 喷雾锥角减小了4.21°~6.57°; 较高背压差下喷雾下游的SMD减小了9.8%.与平滑型加速段相比, 阶梯型加速段的设计有效地提高了喷嘴的雾化质量.      

Correlations predicting frictional pressure drop and liquid holdup during horizontal gas-liquid pipe flow with a small liquid holdup

Experimental data and correlations available in the literature for the liquid holdup ε_L and the pressure gradient ΔP_TP/L for gas-liquid pipe flow, generally, do not cover the domain 0 < ε_L < 0.06. Reliable pressure-drop correlations for this holdup range are important for calculating flow rates of natural gas, containing traces of condensate. In the present paper attention is focused on reliable measurements of ε_L and ΔP_TPIL values and on the development of a phenomenological model for the liquid-holdup range 0 < ε_L < 0.06. This model is called the “apparent rough surface” model and is referred to as the ARS model. The experimental results presented in this paper refer to air-water and air-water + ethyleneglycol systems with varying transport properties in horizontal straight smooth glass tubes under steady-state conditions. The holdup and pressure gradient values predicted with the ARS model agree satisfactorily with both our experimental results and data obtained from the literature referring to small liquid-holdup values 0 < ε_L < 0.06. Further, it has been shown that in the domain 38 < < 72 mPa m the interfacial tension of the gas-liquid system has no significant effect on the liquid holdup. The pressure gradient, however, increases slightly with decreasing surface tension values.     

Level-set simulations of buoyancy-driven motion of single and multiple bubbles

This paper presents a numerical study of buoyancy-driven motion of single and multiple bubbles by means of the conservative level-set method. First, an extensive study of the hydrodynamics of single bubbles rising in a quiescent liquid is performed, including its shape, terminal velocity, drag coefficients and wake patterns. These results are validated against experimental and numerical data well established in the scientific literature. Then, a further study on the interaction of two spherical and ellipsoidal bubbles is performed for different orientation angles. Finally, the interaction of multiple bubbles is explored in a periodic vertical channel. The results show that the conservative level-set approach can be used for accurate modelling of bubble dynamics. Moreover, it is demonstrated that the present method is numerically stable for a wide range of Morton and Reynolds numbers.     

Two-phase flow measurements with sharp-edged orifices

This paper contains the results of a set of two-phase flow measurements of 4 different ratios of vapor to liquid density (up to 0.328) across a sharp-edged circular orifice. Test fluid was R-113. Tests were carried out upon 3 orifices whose diameter ratios were 0.312, 0.439 and 0.625. The test quality ranged from 0–100%, while the mass velocity from 917–1477 kg/m².s. On the basis of a modified separated flow model, a relationship is developed for the flow rate and quality and is compared with experimental data and 5 proposed correlations. Comparison shows this method can be used to calculate the flow rate or the quality of vapor liquid (or steam water) mixture in the range 0.00455 to 0.328 of the density ratio, and in pipe size ranging from 8 to 75 mm (β = 0.25–0.75).

The RMS error of this method is about 12% when the quality, x, ranges from 2% to 100%.     

双材料界面应力分析的局部杂交法

本文用云纹干涉法测取双材料高梁受集中载荷时沿ｘ，ｙ轴的位移场ｕ，ｖ．以其作为界面局部微区的边界条件，用有限元计算此微区内界面上的应力分量．与光弹性及全梁有限元法比较，发现局部杂交法的精度最高．     

内埋武器高速风洞弹射投放模型试验关键技术研究

针对新一代战斗机超声速内埋武器弹射投放分离安全性问题,采用高速风洞投放实验技术研究内埋武器从开式武器舱弹射投放分离动态运动过程,风洞投放模型试验过程中采用除垂直加速度不足外,其余全部运动严格相似的轻模型相似设计方法,并针对轻模型法垂直加速度不足所导致的投放垂直位移偏离实物位移问题,采用一种简单易行的公式修正法进行补偿,试验给出了不同初始弹射投放分离条件下,内埋武器从载机投放分离后运动轨迹与姿态角随分离时间的变化规律,试验马赫数$Ma = 1.5$.研究结果表明:初始投放分离角速度对内埋武器投放分离后的运动轨迹及姿态角有较大的影响,当初始投放分离角速度$\omega _{z0}^s = 0^\circ/{\rm s}$时,内埋导弹出舱后先向下运动远离载机的流场干扰区,之后逐渐向载机方向抬升靠近并最终碰撞载机,高速风洞投放试验结果是不安全的,但经过公式修正后投放试验结果比较乐观,垂直方向运动仍然一直下降远离载机,这说明采用高速风洞投放试验得出的导弹不安全投放分离对真实载机来说不一定会出现,高速风洞投放试验结果比较保守. 当初始投放分离角速度$\omega _{z0}^s= 15^\circ/{\rm s}$和$\omega _{z0}^s = 30^\circ/{\rm s}$时,内埋导弹投放分离后运动趋势几乎一致, 均没出现向载机靠近的现象,内埋导弹具有一定的初始投放分离角速度有利于内埋武器的安全分离.      

高超声速飞行器气动热关联换算方法研究

气动热风洞实验是地面研究和预测飞行器气动热环境的重要手段之一, 但由于风洞实验模拟能力的限制, 风洞实验的流场参数和模型的几何尺度都会与实际飞行情况存在一定的差别, 导致地面风洞实验中得到的模型表面气动加热率数据无法直接用于飞行条件下的热环境预测和热防护设计. 以往通过针对具体飞行器的试验结果进行数据拟合后外插的气动热关联换算方法指向性较强, 没有考虑到气动热的具体影响参数, 存在一定局限性, 难以外推应用于其他外形的飞行器. 为解决通过气动热风洞实验数据外推预测飞行条件下气动热的技术难题, 基于无量纲NS方程和边界层理论分析研究了影响气动热的主要参数, 并通过推导化简边界层近似解热流公式, 针对层流流态建立了气动热关联换算方法, 可以考虑当地边界层外缘参数的影响, 具有一定通用性. 在此基础上, 利用建立的方法将Reentry-F飞行器缩比模型的风洞实验数据换算到该飞行器飞行条件下的典型工况, 并与飞行测量结果进行了比较, 外推预测结果与飞行测量结果符合较好, 表明建立的关联方法可以用于气动热风洞实验数据的外推换算.      

Computational and experimental studies of convective fluid motion and heat transfer in inclined non-rectangular enclosures

Computational and experimental studies of the fluid motion and heat transfer characteristics of an incompressible fluid contained in a non-rectangular inclined enclosure are described in this paper. The enclosure has two 45° inclined side walls one of which was heated and the other cooled. The remaining two sides of the enclosure are parallel and insulated. The enclosure was rotated about the long axis in steps of 30° through 360°. Experiments were performed to study the effects of Rayleigh number, aspect ratios and orientation of the enclosure. The computational method uses a mesh transformation technique coupled with the introduction of ‘false transient’ parameters for the steady state solution of the problem. The experimental method uses smoke for flow visualization studies. With aspect ratios of 3 and 6, the results indicate that the heat transfer and fluid motion within the enclosure is a strong function of both the Rayleigh number and the cavity orientation angle. A minimum and a maximum mean Nusselt number occurred as the angle of inclination was increased from 0 to 360°. A transition in the mode of circulation occurred at the angle corresponding to the minimum or maximum rate of heat transfer. Stream lines and isotherms are presented for the most representative cases     

深海多立柱浮式平台涡激运动特性研究

基于不可压缩纳维-斯托克斯(Navier-Stokes)方程和改进的延迟脱体涡模拟方法(improved delayed detached edd ysimulation method,IDDES),数值研究了深海多立柱浮式平台在海流作用下的涡激运动响应特性.以张力腿平台为对象,计算了该平台在0°,22.5°和45°流向角下的横向和艏摇涡激运动响应,分析了涡激运动响应幅度、频率比随约化速度的变化规律,研究了涡激运动响应能量的分布趋势.数值预报结果与模型实验数据吻合良好,证实了数值模型的有效性;研究发现,当约化速度介于7.0和14.0之间时,横向运动发生锁频,运动幅值稳定在0.2D~0.4D(D为立柱宽)之间,而艏摇涡激运动和约化速度呈线性递增关系;在横向运动锁频区间内,由于艏摇激振力矩主要受升力主导,艏摇频率与横向运动频率相同;相对于0°来流,22.5°和45°流向下的涡激运动频率更高,但艏摇运动能量仅为0°流向角下的10%.基于计算结果,进一步分析了多立柱平台涡激运动中的三维流场结构.      

卸载柔度法测定JR阻力曲线的微机自动化系统

本文依据我国有关试验规范,在国内广泛引进的日本岛津(Shimadzu)DSS—25T 型电子万能试验机上,研制配备了用微型计算机实现的单试样卸载柔度法的加、卸载控制与数据采集、处理的自动化系统。全部实验结果由打印机直接输出,可以大幅度地提高测试效率,试验精度也得到改善。     

On the radiation properties of an asymmetric cylinder

The radiation properties of an asymmetric cylinder, formed by slicing a circular cylinder with a plane making an angle π/2 − Λ with the cylinder axis, are investigated as a model problem of relevance to noise emission by novel aeroengine intakes. We consider the scattering of incident duct modes and use asymptotic analysis in the limit Λ 1; the unsteady flow then comprises an inner incompressible region around the cylinder rim and an outer region comprising the rest of space, and the radiation in the outer region is determined using the method of matched asymptotic expansions. From this we are able to conclude that the correction to the radiation directivity is O(Λ), whilst the correction to the total integrated sound power reaching infinity is much weaker, and is in fact only O(Λ²).     

自由下落猫姿态最优控制的混合优化策略

研究猫自由下落时的转体运动对探索宇航员在太空失重状态下的空间运动规律具有重要的参考价值.针对猫自由下落时四肢先着地现象的姿态最优控制问题,提出一种由Gauss伪谱法求解可行解与直接打靶法求解最优精确解相结合的混合优化策略.首先,根据猫在自由下落过程中的角动量守恒原理,推导出简化后的两对称刚体系统的非完整姿态运动方程;然后基于Gauss伪谱法将此无漂移系统的姿态非完整运动规划问题离散为非线性规划问题,并在不考虑实际性能指标函数的条件下利用序列二次规划算法求解此非线性规划问题在较少节点时对应的控制变量可行解,再通过三次样条插值获取较多节点时的控制变量值;最后基于直接打靶法将插值得到的控制值作为序列二次规划算法的初始猜测值,从而求解得到最优的控制输入,再代入系统姿态运动方程,通过数值积分得到落体猫的转体姿态运动曲线.通过数值仿真,求解得到的姿态运动曲线是光滑的,能以较高的精度到达预定的目标姿态;最优控制输入也能满足预先设计的零边界控制要求以及最大控制要求;结果表明了此混合优化策略具有较强的鲁棒性和有效性.