Generalized shock hugoniot of condensed substances

It is shown that in order to predict the shock Hugoniot of any substance up to a compression ratio equal to two it is sufficient to know the initial density and the initial compressibility. The possibility of finding a priori the equations of state of nonporous mixtures of two substances, porous samples, and solutions is discussed.     

Impossibility of steady mach shock wave reflection for media with a special hugoniot

The conditions under which steady Mach shock wave reflection in a porous material is impossible for any incident wave angles, if the approach-stream parameters are fixed, are found.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 2, pp. 181–184, March–April, 1991.     

钢筋混凝土柱二阶配筋的不同计算方法对比

计算钢筋混凝土柱的配筋,需要迭代求解材料非线性和几何非线性问题,不便实际应用。基于混凝土和钢筋的本构关系,根据截面应变求解精确的截面内力-曲率关系,简化杆件变形曲线为二次抛物线来计算外部作用。根据精确的截面内力-曲率曲线和外部作用曲线的特点,分别按照我国《混凝土结构设计规范》(GB 50010-2010)和欧洲规范(Eurocode 2),对截面的极限曲率进行了简化,最后绘制了计算杆件二阶总弯矩和配筋的总诺模图。通过具体算例对比分析,结果显示欧洲规范的简化与精确值更相符,且更经济。     

Analysis of the possibilities of the methods for calculating turbulent jet noise

Two methods for calculating the noise of turbulent exhaust jets of civil aircraft nozzles are considered. The first method is chiefly intended for engineering mass-volume calculations and is based on the solution of the averaged Navier-Stokes equations closed by a two-equation turbulence model. The second method uses direct numerical simulation of large eddies in a turbulent jet and the Kirchhoff surface for calculating noise spectra and radiation patterns in the far field. The possibilities and certain important restrictions of these methods are analyzed. The results obtained using these methods are compared with experimental data.     

Experimental verification of methods for calculating partial dam-break waves

This paper presents results of an experimental study of waves generated by partial break of two model dams. The previously proposed calculation methods are extended and compared with the experimental data obtained. It is shown that the wave propagation speed in the tailwater is significantly influenced by the energy losses due to flow through the breach. __________ Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 49, No. 5, pp. 61–69, September–October, 2008     

用VLW 状态方程计算水的冲击Hugoniot曲线

采用L-J(Lennard-Jones12-6)势函数,结合VLW 状态方程,计算了水的冲击压缩Hugoniot曲线。 将理论计算结果与实验结果进行了比较,当势函数参数/K=120、b0=30.42时,计算值与实验符合较好。与 采用BKW 状态方程计算结果相比,VLW 状态方程能够更准确地描述水的冲击Hugoniot曲线。     

A comparison of quasi-static uniaxial-strain and hugoniot tests for quartz-phenolic composite

The purpose of this paper is to show that, within experimental uncertainty, the change in volume with stress obtained by quasi-static uniaxial-strain tests matches that obtained by hugoniot experiments over the same pressure range for quartz phenolic. The result of these tests shows that comparing the data by both techniques is meaningful. In addition, the use of the relatively simple and inexpensive quasi-static uniaxial-strain test (strain rates of 10^?4/sec) may provide designers and materials engineers a method for rapid surveying of materials for their hugoniot properties.     

On the structure of shock waves in liquid-bubble mixtures

Asbtract The structure of shock waves in liquids containing gas bubbles is investigated theoretically. The mechanisms taken into account are the steepening of compression waves in the mixture by convection and the effects due to the motion of the bubbles with respect to the surrounding fluid. This relative motion, radial and translational, gives rise to dissipation and to dispersion caused by the inertia of the radial flow associated with an expanding or compressed bubble. For not too thick shocks the dissipation by radial motion around the bubbles dominates over the dissipation by relative translational motion, in mixtures with low gas content. The overall thickness of the shock appears to be determined by the dispersion effect. Dissipation, however, is necessary to permit a steady shock wave. It is shown that, analogous to undular bores, a stationary wave train may exist behind the shock wave.     

锥形长药柱水下爆炸冲击波参数计算方法

为了计算锥形长药柱水下爆炸冲击波压力,以及研究长脉宽冲击波的传输特性,基于叠加原理建立了冲击波压力-时间曲线的计算方法,通过实验验证了该方法的有效性,在此基础上分析了锥形长药柱不同方位冲击波压力的分布规律。研究结果表明:锥形长药柱产生的冲击波压力具有各向异性,在起爆端一侧形成的是具有厚波头特征的低幅值长脉宽冲击波,在装药径向形成的是接近指数衰减的高幅值冲击波,而在远离起爆端的冲击波压力幅值和脉宽则介于前两者之间。锥形长药柱与球形装药冲击波分布的差异是由于装药形状和起爆方式的改变所导致的,由于装药不同部位起爆的时间差,导致水下爆炸冲击波在不同位置的叠加效果存在明显差异,药柱周围流场中形成的冲击波压力具有方向性。利用提出的计算方法得到的计算结果与实验结果和数值模拟结果吻合较好,研究结果可为锥形长药柱水下爆炸冲击波威力场和毁伤评估提供参考和依据。     

Methods of calculating thermal conductivity of binary mixtures involving polyatomic gases

Summary The experimental binary thermal conductivity data of nineteen different gas pairs have been discussed and the competence of the rigorous, approximate and empirical procedures to represent them is investigated and discussed. In addition a new semi-theoretical method is suggested and tested. The suggested semi-theoretical procedure works very satisfactorily and is of good accuracy. It also compares favourably with the other methods. We also suggest a procedure for estimating thermal conductivity values at high temperature. This is an interesting and useful suggestion in view of the great practical need and their meagre availability.     

Numerical investigations of shock waves in gas-particle mixtures

The propagation of shock waves in gas-particle mixtures in one- and two-dimensional geometries is numerically investigated. Two schemes for approximating conservation laws for particles, which are collectively treated as a continuum medium, are compared and discussed. Different models of the drag coefficient and Nusselt number, directly affecting the interaction between the gas and particle phases, are used for obtaining shock profiles, and the results are compared. The oblique shock reflections at a solid wedge in a gas-particle mixture are simulated. The results demonstrate that the reflection pattern changes as the shock propagates along the wedge, revealing strong non-selfsimilarity of the phenomenon.Received: 22 May 2003, Accepted: 28 August 2003, Published online: 12 November 2003 Correspondence to:T. Saito     

轴对称热冲击SIF过渡过程分析的热权函数法

热权函数法利用温度与热权函数的乘积的积分来直接计算热冲击过程中裂纹尖端的应力强度因子过渡过程。热权函数与时间τ无关,由于免除了对每一时刻τ所需作的有限元或边界元分析,计算过程大大简化,计算效率得到极大提高,本文将热权函数与有限元法直接耦合,给出了基于刚度阵导数法的轴对称问题的热权函数计算格式,实例计算表明,本文给出的热权函数计算格式具有满意的计算精度。     

冲击载荷下瞬态温度的实时测量方法

将红外瞬态测温装置引入SHPB冲击实验,确定了不同材料试件的温度标定曲线,并实时测量了冲击下Al合金和伪弹性TiNi合金试样的表面温度。结果表明,2种试样温度变化都经历了加载过程的温度升高,主要不同在于卸载过程,Al合金卸载过程中温度保持最大加载温度不变,而TiNi合金试样卸载过程中温度降低,这反映了2种材料不同的物理变形过程和温度变化机制。直接红外测温的实验结果与根据能量守恒理论计算的温度较好吻合,说明采用的红外测温方法实时测量冲击瞬态温度是可行的。

     

High-order strand grid methods for shock turbulence interaction

ABSTRACT

In this work, we examine the flux correction method for three-dimensional transonic turbulent flows on strand grids. Building upon previous work, we treat flux derivatives along strands with high-order summation-by-parts operators and penalty-based boundary conditions. A finite-volume like limiting strategy is implemented in the flux correction algorithm in order to sharply capture shocks. To achieve turbulence closure in the Reynolds-Averaged Navier–Stokes equations, a robust version of the Spalart–Allmaras turbulence model is employed that accommodates negative values of the turbulence working variable. Validation studies are considered which demonstrate the flux correction method achieves a high degree of accuracy for turbulent shock interaction flows.     

Some methods of calculating the steady motion of a rarefied gas

Vacuum molecular pumps have been long known and have several advantages [1–3].Several studies have been devoted to the design of vacuum molecular pumps [7–10]. The methods developed in these studies have been based either on the formulas for gas diffusion in long pipes or on the integral equations of material balance. However, these theories do not permit obtaining design data for real designs of molecular pumps which are close to the experimental data, and, moreover, do not permit solving the practically important problem of optimizing the parameters and geometry of the molecular and turbomolecular pumps with respect to output and compression ratio. The calculations made in [8–10] are valid only for rotor speeds which are much less than the average velocities of the gas molecules. However, the studies in the second direction cannot be continued to a final result in view of the extreme complexity of the solution of the resulting system of integral equations.In the following we describe the calculation of vacuum molecular pumps, based on the Monte-Carlo method (the Monte-Carlo method has been used to calculate the conductance of the elements of vacuum lines in the free molecular regime in [4, 5, 6] and to calculate using the method of sequential approximations the flow of a rarefied gas with account for the collisions between molecules in [11]).We shall apply this method not only to systems with a high vacuum, when the collisions between molecules may be neglected, but also to systems in which in addition to the molecule collisions with the wall it is necessary to consider the possibility of a small number of mutual collisions.     

Revisit of dilation-based shock capturing for discontinuous Galerkin methods

The idea of using velocity dilation for shock capturing is revisited in this paper, combined with the discontinuous Galerkin method. The value of artificial viscosity is determined using direct dilation instead of its higher order derivatives to reduce cost and degree of difficulty in computing derivatives. Alternative methods for estimating the element size of large aspect ratio and smooth artificial viscosity are proposed to further improve robustness and accuracy of the model. Several benchmark tests are conducted, ranging from subsonic to hypersonic flows involving strong shocks. Instead of adjusting empirical parameters to achieve optimum results for each case, all tests use a constant parameter for the model with reasonable success, indicating excellent robustness of the method. The model is only limited to third-order accuracy for smooth flows. This limitation may be relaxed by using a switch or a wall function. Overall, the model is a good candidate for compressible flows with potentials of further improvement.