火场条件下相邻汽油罐油蒸汽泄漏及爆炸规律

油库发生火灾时,临近的油罐内汽油受热形成油蒸汽从呼吸阀泄出,泄漏的油蒸汽与空气混合易点燃,易引起燃烧爆炸事故。本文中以容积为5 000 m^3(22 m×13 m)的汽油罐泄漏油蒸汽为研究对象,以数值模拟为研究方法,研究了汽油蒸汽泄漏及爆炸规律。研究发现:在距地面高1 m的平面上,当无风且呼吸阀泄漏油蒸汽速率为0.25 m/s时,距该罐中心50 m以外就可视作安全区域;当呼吸阀泄漏的油蒸汽速率为0.25 m/s时,风速达到5.0 m/s及以上,不易积聚成爆炸油蒸汽;当无风时,呼吸阀泄漏油蒸汽的速率增大1个量级,油蒸汽积聚达到爆炸下限1/2所需时间缩短2个量级;当风速为3.0 m/s、呼吸阀泄漏油蒸汽速率为0.25 m/s、泄漏时间为200 s、着火点距罐壁1 m时,距点火源距离增大1个量级,超压峰值下降1~2个量级。     

“Inviscid Finger” Instability in Regular Models of a Porous Medium

Displacement of a fluid from a porous medium is considered. The flow is assumed to be fast enough, i.e., the Reynolds number based on the characteristic pore size is large. If he driving fluid is less dense (for example, a gas), the interface is unstable. This instability is similar to the well–known viscous finger instability but the governing parameter is density instead of viscosity. The instability is demonstrated experimentally using two–dimensional models. In square lattices of perpendicular channels, noticeable branching of fingers is not observed, which is attributed to the anisotropy of such an artificial porous medium. A more ordinary pattern with finger branching is obtained in a two–dimensional layer of spheres, which appears to be more isotropic. A simple model describing flow in a square lattice is proposed. The initial stage of growth is considered, and the instability increment is estimated. A qualitative analysis of the nonlinear stage is performed.     

Orientational effect of the extensional flow field on solutions of rigid rodlike macromolecules-disappearance of the isotropic to nematic phase transition

The effect of steady state uniaxial extensional flow on a solution of rigid rodlike macromolecules is theoretically studied. The mean field theory of Maier and Saupe is extended to cover situations in which the macromolocular solution is subjected to an extensional flow field. It is found that for a given solution a critical flow gradient exists beyond which the first order nematic-isotropic phase transition, which is typical of such solutions in the absence of flow, disappears. A similar result is obtained when the theory of Onsager is applied to the problem. Order parameter as a function of flow gradient is calculated and it is shown that the contribution of flow to the ordering of macromolecules is most significant when the stationary solution is isotropic but close to the transition point.     

Stable Nucleation for the Ginzburg-Landau System with an Applied Magnetic Field

We consider the Ginzburg‐Landau system with an applied magnetic field and analyze the behavior of solutions when the domain is a cylinder (of radius ) and the applied field is parallel to the axis. It is shown that there is an upper critical value such that if the modulus of the applied field is greater than , the normal (nonsuperconducting) state (in which the order parameter is identically zero) is stable and if the modulus of the applied field is slightly below , the normal state is unstable. In addition, it is shown that there is a positive lower critical value such that the normal state is unstable if the modulus of the applied field is less than and stable if the modulus is slightly above . In the case of type‐II materials for whic h the Ginzburg‐Landau constant κ is large, it is shown that there is a discrete set of radii ℬ(κ) such that if and is sufficiently large, then for each applied field of modulus slightly less than (or slightly more than ) there is precisely one small superconducting solution (up to a gauge transformation) which is stable. Moreover for this solution, the complex‐valued order parameter ψ is zero only on the axis of the cylinder, and its winding number is proportional to the product of κ² and the cross‐sectional area of the cylinder. In addition, the solution exhibits “surface superconductivity” as predicted by the physicists de Gennes and St. James. (Accepted July 15, 1996)     

Augmented perpetual manifolds and perpetual mechanical systems-part II: theorem for dissipative mechanical systems behaving as perpetual machines of third kind

Perpetual points in mathematics defined recently, and their significance in nonlinear dynamics and their application in mechanical systems is currently ongoing research. The perpetual points significance relevant to mechanics so far is that they form the perpetual manifolds of rigid body motions of unforced mechanical systems, which lead to the definition of perpetual mechanical systems. The perpetual mechanical systems admit as perpetual points rigid body motions which are forming the perpetual manifolds. The concept of perpetual manifolds extended to the definition of augmented perpetual manifolds that an externally excited multi-degree of freedom mechanical system is moving as a rigid body, and may exhibit particle-wave motion. This article is complementary to the work done so far applied to natural perpetual dissipative mechanical systems with motion defined by the exact augmented perpetual manifolds, whereas the internal forces, and individual energies are examined, to understand further the mechanics of these systems while their motion is in the exact augmented perpetual manifolds. A theorem is proved stating that under conditions when the motion of a perpetual natural dissipative mechanical system is in the exact augmented perpetual manifolds, all the internal forces are zero, which is rather significant in the mechanics of these systems since the operation on augmented perpetual manifolds leads to zero internal degradation. Moreover, the theorem is stating that the potential energy is constant, and there is no dissipation of energy, therefore the process is internally isentropic, and there is no energy loss within the perpetual mechanical system. Also in this theorem is proved that the external work done is equal to the changes of the kinetic energy, therefore the motion in the exact augmented perpetual manifolds is driven only by the changes of the kinetic energy. This is also a significant outcome to understand the mechanics of perpetual mechanical systems while it is in particle-wave motion which is guided by kinetic energy changes. In the final statement of the theorem is stated and proved that the perpetual dissipative mechanical system can behave as a perpetual machine of third kind which is rather significant in mechanical engineering. Noting that the perpetual mechanical system apart of the augmented perpetual manifolds solutions is having other solutions too, e.g., in higher normal modes and in these solutions the theorem is not valid. The developed theory is applied in the only two possible configurations that a mechanical system can have. The first configuration is a perpetual mechanical system without any connection through structural elements with the environment. In the second configuration, the perpetual mechanical system is a subsystem, connected with structural elements with the environment. In both examples, the motion in the exact augmented perpetual manifolds is examined with the view of mechanics defined by the theorem, resulting in excellent agreement between theory and numerical simulations. The outcome of this article is significant in physics to understand the mechanics of the motion of perpetual mechanical systems in the exact augmented perpetual manifolds, which is described through the kinetic energy changes and this gives further insight into the mechanics of particle-wave motions. Also, in mechanical engineering the outcome of this article is significant, because it is shown that the motion of the perpetual mechanical systems in the exact augmented perpetual manifolds is the ultimate, in the sense that there are no internal forces which lead to degradation of the internal structural elements, and there is no energy loss due to dissipation.

     

Chebyshev polynomial curve-fitting technique for strain-gage applications

A curve-fitting technique is presented which is especially suited to strain-gage measurements. The location of the strain gages is inherently specified by the method, and the number of gages to be used is also prescribed. The method of Chebyshev polynomial curve fitting assures a best fit in the least-squares sense. The procedure of using the method of strain-gage measurement and subsequent curve fitting is explained. The method is suitable for hand calculation but is more easily done on a digital computer. An example problem is given to illustrate the procedure, and a discussion of errors and error techniques is included.     

Stagnation-point flow of a viscoelastic fluid towards a stretching surface

An analysis is made of the steady two-dimensional stagnation-point flow of an incompressible viscoelastic fluid over a flat deformable surface when the surface is stretched in its own plane with a velocity proportional to the distance from the stagnation-point. It is shown that for a viscoelastic fluid of short memory (obeying Walters’ B′ model), a boundary layer is formed when the stretching velocity of the surface is less than the inviscid free-stream velocity and velocity at a point increases with increase in the elasticity of the fluid. On the other hand, an inverted boundary layer is formed when the surface stretching velocity exceeds the velocity of the free stream and the velocity decreases with increase in the elasticity of the fluid. A novel result of the analysis is that the flow near the stretching surface is that corresponding to an inviscid stagnation-point flow when the surface stretching velocity is equal to the velocity of the free stream. Temperature distribution in the boundary layer is found when the surface is held at constant temperature and surface heat flux is determined. It is found that temperature at a point decreases with increase in the elasticity of the fluid.     

基于CFD-DEM的高炉风口回旋区形状和传热特性数值模拟研究

采用计算流体力学-离散单元法(CFD-DEM)耦合方法,对高炉风口回旋区进行了数值模拟研究。首先通过与实验结果对比,验证了CFD-DEM模型的正确性;然后考察了不同气速对风口回旋区形状和传热特性及颗粒接触的影响。数值模拟结果表明:风口回旋区的大小和形状均受气速影响较大,在较大进气速度下,颗粒受到的曳力大于颗粒间的摩擦阻力并破坏颗粒间的桥力,形成较大尺寸的回旋区;且颗粒之间接触力较小,形成较大的空隙结构,更有利于热气体向周围扩散以强化传热。目前考察的三种气速结果表明:当气速为11m/s时,热量向下方传递速度最快;当气速为13m/s时,热量向上方传递速度最快;而当气速为15m/s时,热量向右方传递速度最快;此外,气速越大流态化越明显,颗粒间接触越少,接触力也越小。     

两斜交圆柱壳应力分析的边界元法

本文研究了两斜交圆柱壳的边界元法。提出了用板的基本解叠加级数形式的修正项构成圆柱壳的基本解,提高了计算精度,缩短了计算时间。对区域积分进行特殊处理,从而避免了内部网格的划分,大大减少了数据准备工作量和占机内存。并编制了FORTRAN计算程序,进行了数值计算。     

A VIEWPOINT OF THE TENSORAL PROPERTY OF COORDINATE TRANSFORMATION COEFFICIENT AND ANALYSISON THE CONCEPT OF HYBRID TENSOR1)

本文致力于澄清一个十分基本的问题：坐标变换系数是否为张量?传统观念认为,坐标变换系数不是张量。为了揭示坐标变换系数的本质,本文采用“从一般到特殊”的研究策略,重塑了张量的内涵和外延,引入了杂交张量概念,进而颠覆了坐标变换系数不是张量的传统观念,确切地讲,它就是度量张量的杂交分量。这一结果扩张了张量概念的集合,提升了张量分析学内在的统一性、对称性和不变性,减少了连续介质力学的运算量。     

小波分析用于陀螺仪漂移测试信号分析的研究

为建立陀螺仪漂移特性模型，需对其进行测试。由测试得到的数据是含有噪声的，且一般是非平稳的，用小波分析测试数据是一种很有效的方法。在简述小波分析中的多分辨分析理论的基础上，用其对某型陀螺仪的实测数据进行了分析－预处理，其结果证实了所研究方法的有效性。     

The double mode model of the chaotic motion for a large deflection plate

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Low-dimensional chaotic response of axially accelerating continuum in the supercritical regime

Summary Nonlinear dynamics of one-mode approximation of an axially moving continuum such as a moving magnetic tape is studied. The system is modeled as a beam moving with varying speed, and the transverse vibration of the beam is considered. The cubic stiffness term, arising out of finite stretching of the neutral axis during vibration, is included in the analysis while deriving the equations of motion by Hamilton's principle. One-mode approximation of the governing equation is obtained by the Galerkin's method, as the objective in this work is to examine the low-dimensional chaotic response. The velocity of the beam is assumed to have sinusoidal fluctuations superposed on a mean value. This approximation leads to a parametrically excited Duffing's oscillator. It exhibits a symmetric pitchfork bifurcation as the axial velocity of the beam is varied beyond a critical value. In the supercritical regime, the system is described by a parametrically excited double-well potential oscillator. It is shown by numerical simulation that the oscillator has both period-doubling and intermittent routes to chaos. Melnikov's criterion is employed to find out the parameter regime in which chaos occurs. Further, it is shown that in the linear case, when the operating speed is supercritical, the oscillator considered is isomorphic to the case of an inverted pendulum with an oscillating support. It is also shown that supercritical motion can be stabilised by imposing a suitable velocity variation. Received 13 February 1997; accepted for publication 29 July 1997     

自适应卡尔曼滤波在惯性测量组合误差补偿中的应用

惯性元件误差是捷联惯导系统的主要误差源，必须在导航过程中加以补偿。根据机动目标跟踪理论和惯性测量组合动态模型，分别建立状态方程和观测方程，利用机动频率自适应的算法进行卡尔曼滤波，以此达到惯性测量组合动态误差和随机误差补偿的目的。仿真结果说明该方法可行有效，优于传统的误差补偿算法，能较好地提高系统导航精度。     

Formation of condensed oxide particles by combustion of metal droplets

The formation of condensed oxide particles in combustion of metal droplets is discussed; it is assumed that the characteristic diffusion time is much less than the characteristic time for the heterogeneous reaction at the condensate particle surfaces, and the structure of the reaction zone is discussed; the size spectrum is derived for the condensed oxide particles. It is found that condensation in the gas has little effect on the droplet combustion rate. Heat needed to evaporate the metal is produced directly at the surface of the drop and the rate-limiting step in the combustion is the diffusion of oxidant to the surface.     

Rayleigh-Taylor instability of an interface in a nonwettable porous medium

The diffusion of vapor through the roof of an underground structure located beneath an aquifer is considered. In the process of evaporation, an interface between the upper water-saturated layer and the lower layer containing an air-vapor mixture is formed. A mathematical model of the evaporation process is proposed and a solution of the steady-state problem is found. It is shown that in the presence of capillary forces in the case of a nonwettable medium the solution is not unique. Using the normal mode method, it is shown that Rayleigh-Taylor instability of the interface can develop in the nonwettable porous medium. It is found that there are two scenarios of loss of stability corresponding to the occurrence of the most unstable wavenumber at zero and at infinity, respectively. It is shown that for zero wavenumber the stability limit is reached at the same time as the solution of the steady-state problem disappears.     

椭圆颗粒在剪切流中旋转特性的数值研究

研究颗粒在流体剪切作用下的运动特性是理解和预测颗粒悬浮流流动行为的关键.当流体的惯性不能忽略时,颗粒的运动往往变得非常复杂.本文采用格子Boltzmann方法对中等雷诺数下椭圆颗粒在剪切流中的旋转运动进行了模拟.首先,研究了雷诺数(0Re 170)的影响,结果表明当雷诺数低于临界值时,颗粒以周期性的方式旋转,角速度最小时对应的长轴方向随着雷诺数的增大而逐渐远离水平方向,而且这一倾角与雷诺数呈分段线性关系;当雷诺数大于临界值时,椭圆形颗粒最终保持静止状态,且静止时的转角与雷诺数呈幂函数关系,雷诺数越大,转角越小,椭圆的长轴越远离水平位置.其次,研究了椭圆颗粒的长短轴之比α(1α10)的影响,结果表明颗粒旋转的周期与α呈幂函数关系,α越大,颗粒旋转周期越小.此外,当α超过临界值时,颗粒也在水平位置附近保持静止状态,此时的转角与α也呈幂函数关系,α越大,转角越小.研究还发现,当雷诺数较大时椭圆颗粒在旋转过程中会产生过冲现象.     

数字全息计量技术及其在微小位移测量中的应用

数字全息是用数字的方式记录和处理全息图像，避免了传统全息照相的化学处理，既简化了处理过程，更便于用数字图像处理的方式来改进图像质量和提取信息。数字全息干涉计量技术是一种全场、非接触的光学测量方法，该方法测量精度高，光路简单，对防振要求低，实验条件容易满足，特别适合微小物体的微小位移或变形的精确测量。本文运用数字全息干涉计量法测定了两端固支梁的微小离面位移；经实验验证数字全息计量术能精确测量物体0．01微米量级位移或变形；而且该方法可靠性好、成本低；是非接触的无损测量。数字全息计量技术的这些特点使得该技术在小物体的微小变形测量上具有特别的优越性，因而在MEMS结构及MEMS材料参数(如弹性模量、泊松比、热变形系数等)的测定中有广阔的应用前景。