稠密流体中双原子分子振动弛豫的非谐性及质量效应

利用分子动力学计算机模拟方法研究了稠密流体中双原子分子的振动弛豫问题，证实了双原产分子的振动弛豫速率随着其非谐性的增大而加快，同时，其速率也随其质量因子的变大而加速。     

凝聚态物质振动-平动能量弛豫过程的分子动力学模拟

本文利用分子动力学计算机模拟方法,研究了稠密态双原子分子振动-平动弛豫速率与分子离解能、密度和温度的关系。发现振动弛豫速率随着分子离解能的增高而下降。这一现象与由光谱数据得到的结果是一致的。它可以用振动频率的下降来解释;分子振动弛豫速率随密度增大而加快,在我们所作的范围内,似乎看不到弛豫速率与温度有关。     

凝聚态物质振动-平动能量弛豫过程的分子动力学模拟

本文利用分子动力学计算机模拟方法,研究了稠密态双原子分子振动-平动弛豫速率与分子离解能、密度和温度的关系。发现振动弛豫速率随着分子离解能的增高而下降。这一现象与由光谱数据得到的结果是一致的。它可以用振动频率的下降来解释;分子振动弛豫速率随密度增大而加快,在我们所作的范围内,似乎看不到弛豫速率与温度有关。     

双原子分子晶体振动弛豫过程的分子动力学研究

用分子动力学方法研究瞬时加热振动自由度后的能量弛豫过程.晶元包含128个双原子分子,采用周期性边界条件和体心立方结构,对于分子内和分子间原子相互作用采用双莫尔斯势.发现平衡时间的对数与因子,f_21之间存在线性关系,而f_21正比于分子内振动与格波振动的频率比.     

高温非平衡流动中的氧分子振动态精细分析

高超声速流动在头激波压缩后常处于高 温条件下的热化学非平衡状态. 本文采用态-态方法和双温度模型计算分析了一维正激波后和高超声速钝体绕流驻点线上的氧气热化学非平衡流动. 态-态方法将氧气的每个振动能级当成独立的组分,通过耦合 Euler 方程或驻点线上的降维 Navier-Stokes 方程,数值求解得 到了高温流动中的精细热化学非平衡状态. 而双温度模型假设氧气的振动能级服从 Boltzmann 分布,通过求解振动能方程得到振动温度. 一维正激波后热化学松弛过程的计算结果表明,态-态计算预测的温度分布和氧原子浓度分布较好地吻合了文 献中的实验结果,而经典的双温度模型的预测结果误差较大,且不同双温度模型的计算结果比较发散. 态-态方法详细地给出了所有振动能级的变化过程. 无论是正激波还是脱体激波后的流场,都是高振动能级首先得到激发;但是数密度大的低振动能级先达到热平衡,而高能级 分子要经过很长距离后才能达到热平衡. 在驻点附近,复合反应生成的氧气分子处于高振动能级,导致高振动能级分子数密度显著高于平衡分布. 计算还发现,经典双温度模型的离解反应速率明显偏离态-态计算结果,无法准确体现振动离解耦合效应对离解反应 速率的影响,但是 Park 双温度模型将离解失去的振动能取为 0.3$\sim 高超声速流动在头激波压缩后常处于高 温条件下的热化学非平衡状态. 本文采用态-态方法和双温度模型计算分析了一维正激波后和高超声速钝体绕流驻点线上的氧气热化学非平衡流动. 态-态方法将氧气的每个振动能级当成独立的组分,通过耦合 Euler 方程或驻点线上的降维 Navier-Stokes 方程,数值求解得 到了高温流动中的精细热化学非平衡状态. 而双温度模型假设氧气的振动能级服从 Boltzmann 分布,通过求解振动能方程得到振动温度. 一维正激波后热化学松弛过程的计算结果表明,态-态计算预测的温度分布和氧原子浓度分布较好地吻合了文 献中的实验结果,而经典的双温度模型的预测结果误差较大,且不同双温度模型的计算结果比较发散. 态-态方法详细地给出了所有振动能级的变化过程. 无论是正激波还是脱体激波后的流场,都是高振动能级首先得到激发;但是数密度大的低振动能级先达到热平衡,而高能级 分子要经过很长距离后才能达到热平衡. 在驻点附近,复合反应生成的氧气分子处于高振动能级,导致高振动能级分子数密度显著高于平衡分布. 计算还发现,经典双温度模型的离解反应速率明显偏离态-态计算结果,无法准确体现振动离解耦合效应对离解反应 速率的影响,但是 Park 双温度模型将离解失去的振动能取为 0.3$\sim $0.5 倍分子离解能是比较合理的.     

高温非平衡流动中的氧分子振动态精细分析

高超声速流动在头激波压缩后常处于高温条件下的热化学非平衡状态.本文采用态-态方法和双温度模型计算分析了一维正激波后和高超声速钝体绕流驻点线上的氧气热化学非平衡流动.态-态方法将氧气的每个振动能级当成独立的组分,通过耦合Euler方程或驻点线上的降维Navier-Stokes方程,数值求解得到了高温流动中的精细热化学非平衡状态.而双温度模型假设氧气的振动能级服从B oltzmann分布,通过求解振动能方程得到振动温度.一维正激波后热化学松弛过程的计算结果表明,态-态计算预测的温度分布和氧原子浓度分布较好地吻合了文献中的实验结果,而经典的双温度模型的预测结果误差较大,且不同双温度模型的计算结果比较发散.态-态方法详细地给出了所有振动能级的变化过程.无论是正激波还是脱体激波后的流场,都是高振动能级首先得到激发;但是数密度大的低振动能级先达到热平衡,而高能级分子要经过很长距离后才能达到热平衡.在驻点附近,复合反应生成的氧气分子处于高振动能级,导致高振动能级分子数密度显著高于平衡分布.计算还发现,经典双温度模型的离解反应速率明显偏离态-态计算结果,无法准确体现振动离解耦合效应对离解反应速率的影响,但是Park双温度模型将离解失去的振动能取为0.3～0.5倍分子离解能是比较合理的.     

由衰减常数确定振动弛豫速率

分子的振动弛豫过程,在高速气体动力学、化学动力学及超声的许多过程中,特别是在分子激光器中,起着重要的作用。已积累了丰富的弛豫实验数据。但是,弛豫实验中只能测得某宏观物理量的变化,如在激波管或激光荧光实验中,观察特定波长的光辐射随时间的变化,可监视相应振型的弛豫过程。这种变化除开始的短暂时期外,呈Ⅰ—     

非晶材料弛豫过程加杨氏模量的唯象研究

从晶态材料弛豫过程中模量的唯象描述的基本思想出发，同时考虑到近年来对非晶材料弛豫规律的种种研究，将传统的构造力学参数模型作为弛豫单元的作法与现在流行的双能级模型统一起来，对非晶材料弛豫过程中的杨氏模量进行了唯象处理，得到了与以往不同的弛豫规律。     

气动激光器的非平衡流计算

本文对CO_2-N_2-H_2O激光体系提出了三振型四温度的振动弛豫模型,并给出了较严格的弛豫方程组.对准一维非平衡流计算中有关的一系列问题作了分析,并用自己整理的弛豫速率数据进行了大量的数值计算.我们的计算结果消除了其他作者的计算与实验不能很好相符的现象.加大膨胀面积比,可有效地改进器件性能,适当地减小喉道高度,对性能也有所改进.对于燃烧型气动激光器,滞止温度有一个最佳值,在1400—1600°K范围内.与Anderson的论证相异,我们的计算结果表明,在高滞止温度、大面积比的喷管流中,水的最佳含量仍在1％附近,器件性能随水含量的增加而迅速变坏.研究了各段喷管型线对器件性能的影响.初步讨论了弛豫模型、方程和数据对计算的影响,表明它们对结果影响颇大.     

地应力水平对深埋隧洞爆破振动频谱结构的影响

爆破振动的频谱特性对隧洞安全施工具有重要意义。采用动力有限元方法，分析了不同地应力水平条件下围岩爆破振动频率特征，通过对实测爆破振动信号的时域和频域联合分析，研究了不同频带上的振动能量分布。结果表明，爆破振动的主频及各个振动能量优势频带都有随地应力水平升高而降低的趋势，伴随爆破破岩过程而发生的地应力瞬态卸载动力效应是产生这一现象的主要原因。地应力水平越高，爆破振动信号中20～100 Hz的低频振动能量比重越大。当爆区的地应力为20 MPa时，20～100 Hz频带内的振动能量可达到总振动能量的35%左右；当爆区的地应力为30～50 MPa时，20～100 Hz频带内的振动能量可达到总振动能量的50%以上。除地应力水平外，应力卸载速率及岩体的力学特性也对爆破振动主频具有显著影响，卸载速率越高，低频振动能量比重越大。卸载速率取决于掏槽爆破方式，直孔掏槽导致岩体应变能释放速率最高。岩体弹性模量越大，爆破振动的主频越高。     

Nonequilibrium vibration-dissociation phenomena behind a propagating shock wave: Vibrational population calculation

An analysis of nonequilibrium phenomena behind a plane shock is presented concerning the vibrational relaxation and the dissociation of a pure diatomic gas. In the first part, the temperature range is 600 K–2500 K and the dissociation processes are neglected. The population of each vibrational level is computed by solving relaxation and conservation equations. The relaxation process is described by the master equations of each vibrational level. The vibrational transition probabilities appearing in the relaxation equations are calculated analytically and take into account the anharmonicity of molecular vibration and the potential angular dependence. The populations obtained are compared to those calculated using a Treanor model and to those calculated with a nonequilibrium Boltzmann distribution. For moderately high levels significant differences may be observed. The importance of the V-V process is found to be weak for the transitions involving the lowest levels. In the second part, the temperature range is 2500 K–5500K and the dissociation process is taken into account as well as the gas dynamic behavior which did not appear in several recent works. The kinetic equations are transformed to obtain a first order differential system and the resolution of such a system coupled with the conservation equations leads to the population of each vibrational level. The vibrational transition probabilities associated with the atom-molecule interaction are deduced from the cross section calculation used in the first part. The bound-free transition probabilities are obtained, following Marrone and Treanor, assuming that dissociation must occur preferentially from the higher vibrational states: the Marrone and Treanor probability model is extended and employed with an anharmonic oscillator. In the present investigation, behind the shock wave, the evolution of the population distribution expressed as a function of the distance is not monotonous: a lag time appears as shown experimentally in previous works for the macroscopic parameters. For moderately high levels the influence of the anharmonicity and those of the V-V processes appear significant and strongly related. In a general way, in both temperature ranges investigated, the V-V processes reduce the effects of the T-V transfer. Finally the influence of thecharacteristic probability temperature U of Marrone and Treanor is analyzed and a method of determination of local varying U is proposed.     

Quasiequilibrium model of the kinetics of coupled modes of CO2 molecules

The correct allowance for the influence of anharmonicity in the vibrational spectrum of CO₂ on the level distribution of molecules under nonequilibrium conditions, when the vibrational temperature departs significantly from the gas temperature, has become especially urgent in connection with obtaining generation on a number of long-wavelength transitions of CO₂ molecules [1, 2]. The shifts in the levels of coupled modes (symmetric and deformation) are due mainly to Fermi resonance and can reach a considerable value, comparable with the gas temperature even for low levels. In [3] the main features of the quasisteady level distribution of coupled modes were clarified within the framework of the Treanor model of vibrational kinetics. The influence of the ascending flux of quanta, excited by VV exchange under nonequilibrium conditions, on the vibrational distribution was considered in [4–6]. In the present paper we propose a quasiequilibrium model of CO₂ kinetics, obtained without presuming quasisteadiness of the ascending flux of quanta, and making it possible, in contrast to [3–6] to describe the dynamics of the variation of the distribution of molecules among multiplets as a result of processes of VV exchange and VT relaxation between multiplets, with allowance for possible processes of pumping by outside sources. With a Boltzmann population distribution within the multiplets, having the translational temperature of the gas, the problem of studying relaxation in coupled modes is reduced to the equations for an effective anharmonic oscillator with levels corresponding to the multiplets of CO₂ molecules. In this case the levels of the effective oscillator are degenerate with a multiplicity equal to the number of levels in the corresponding multiplet, and they have an anharmonicity constant dependent on the gas temperature. The population distribution of the effective oscillator can be studied by methods developed for the investigation cf a one-mode anharmonic oscillator. The proposed quasiequilibrium model was used for a numerical calculations of the temporal evolution of the distribution function of CO₂ molecules over the levels of coupled modes under the conditions of an extremely maintained discharge.Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, No. 3, pp. 16–22, May–June, 1986.     

Effect of vibrational relaxation of molecules on dissociating air characteristics behind a strong shock front

Molecular vibrational relaxation has a considerable effect on the dissociation rate in a gas consisting of molecules of a single type [1]. In gas mixtures such as air, vibrational relaxation also affects the other reaction rates, which may be important in solving several problems of hypersonic aerodynamics. This is due to the fact that in air at temperatures above 5000° the vibrational excitation of nitrogen molecules and the dissociation of oxygen molecules proceed almost simultaneously. We study the effect of vibrational relaxation on the conditions behind a strong shock front.     

Kinetic equations for vibrational relaxation in a mixture of polyatomic gases

Kinetic equations are derived for the relaxation of the vibrational energy in a mixture of polyatomic gases, which are ones with molecules simulated by harmonic oscillators. The most general case is envisaged, where the energy relaxation occurs not only via vibrational-translational transitions but also via multiquantum vibrational exchange involving an arbitrary number of vibrational modes. The analysis also incorporates the possible degeneracy of each mode when the molecules colliding are the same. An expression is derived that extends previous results [1–6] and that relates the vibrational temperatures in the case of quasiequilibrium. Equations are derived for the vibrational relaxation for the CO₂-N₂ case.Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, No. 6, pp. 29–37, November–December, 1972.We are indebted to L. A. Shelepin for valuable discussions on the results.     

Equation for the number of quanta and the dissociation rate in a diatomic gas

We examine vibrational relaxation in a one-component diatomic gas, the molecules of which are described by a Morse potential. An expression is obtained for the mean number of quanta of a molecule assuming there exists a sharp boundary which separates vibrational levels into two groups. In each group there dominates either vibrational-quantum exchange processes or energy-exchange processes between the vibrational and translational degrees of freedom. By solving numerically the system of equations for the number of quanta and for the dissociation rate for times larger than the vibrational relaxation time, the dependence of the dissociation constant on the number of quanta is obtained.     

Comparison of different approaches to the calculation of chemically nonequilibrium flow with allowance for vibrational relaxation

Chemically nonequilibrium flows with allowance for vibrational relaxation are investigated numerically within the framework of the hypersonic viscous shock layer equations with reference to the example of the flow in the neighborhood of the critical line of the “Buran” orbital vehicle in its motion along a re-entry trajectory. It is found that the vibrational temperatures of the molecular components differ markedly. The distinctive feature of the model in question, as compared with a model with one average vibrational temperature, is the stronger effect on the flow characteristics over the thermally stressed part of the trajectory. The models proposed in the literature for dissociation from an effective vibrational level are compared with the model for dissociation with a certain probability from all the vibrational levels. It is shown that the use of an approximation of the total dissociation constant as a function of translational temperature only may lead to a considerable variation from the results of calculations with allowance for vibrational relaxation on the basis of the equilibrium dissociation rate constant. Moscow. Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No. 2, pp. 138–146, March–April, 1994.