二次涡与卡门涡形成过程

本文用离散涡位流理论与边界层理论相结合的方法,同时考虑到边界层及后剪切层分离的离散涡模型,研究并计算了圆柱非定常运动过程中二次涡的发生、发展与影响。研究了对称主涡发生运动不稳定性的直接原因和条件,分析卡门涡的形成过程。本文提出,在二次涡的影响下对称主涡从有涡量补充的非自由涡变为没有涡量补充的自由涡,这是对称主涡发生运动不稳定性的条件,在小扰动影响下可诱发成卡门涡。 本文考虑不可压、大雷诺数、层流情况。所得结果与流场显示结果十分相似

圆柱高雷诺数层流非定常运动初期流动

本文用离散涡位流理论与边界层理论相结合的方法,研究高雷诺数、不可压、层流情况下圆柱非定常运动的初期流动(圆柱由静止突然起动而后保持匀速运动),给出了柱后旋涡发展的详细过程;流场分布、边界层分离点及阻力等随时间的变化规律。本文耦合计算结果包含了流动过程中边界层、外流与近尾迹三者的相互作用。计算所得的旋涡发展与实验显示的图象十分相似,物面压力与速度分布合理,阻力计算与实验结果相符很好。在分离点耦合计算中将stratford方法应用到准定常边界层情况,计算方法简单结果也较满意。对于准定常变化前分离产生的离散涡,其脱落时间和初始位置,本文根据非定常M. R. S. 分离准则确定。文中还讨论了这些离散涡对柱后旋涡发展及流动的影响

利用固体点阵模型进行加卸载响应比的统计研究——兼论潮汐诱发与地震预测

为了验证Mora等人利用固体点阵模型研究加卸载响应比结果的统计稳定性,本文进行了统计实验。每种情况使用24组试件,每一个试件具有相同的宏观参数(潮汐扰动应力的振幅A、周期T、构造应力加载率k),但是粒子的排列方式不同。单轴压缩实验的结果表明:在灾变破坏发生以前的一定时间内,整体平均的加卸载响应比值明显升高,与大地震发生前观察到的加卸载响应比值异常升高是一致的。在剪切实验中,我们发现有两个参数控制着地震与潮汐应力的相关性。一个参数是A/(kT),该参数控制着最大地震率与扰动应力最大振幅的相角差。当该参数增加时,该相角差降低。另一个参数是AT/k,该参数控制着模型地震概率密度函数的高度。当这个参数增加时,概率密度函数变得又尖又狭窄,表明潮汐应力有很强的诱发作用。剪切实验中加卸载响应比的统计研究结果也表明,除了在潮汐诱发作用很强的情况下,卸载周期中数据缺乏导致加卸载响应比不能计算外,较大事件更容易出现在加卸载响应比的较高阶段,该结论更进一步支持加卸载响应比理论

OH Produced from o-nitrophenol photolysis: A combined experimental and theoretical investigation

As an important class of nitroaromatic compounds, nitrophenols are of particular interest since their presence in the environment has been acknowledged. Much work on the occurrence of nitrophenols in the environment, both in the gas and in the condensed phase, has been done, and nitrophenols have been discovered in different atmospheric compartments, such as ambient air, clouds, fog, and snow. Moreover, previous spectroscopic studies revealed that the strong absorption band of nitrophenols is in the atmospherically relevant UV region (300-400 nm), implying the photochemistry of nitrophenols might be important for the atmosphere. In the present work, photodissociation dynamics of o-nitrophenol (HOC6H4NO2) in the gas phase at different photolysis wavelengths (361-390 nm) is investigated, and the nascent OH radical is observed by the single-photon laser-induced fluorescence (LIF) technique. At all photolysis wavelengths, the OH radicals are formed in vibrationally cold state (υ″ = 0), and have similar rotational state distributions. The average rotational temperature for all photolysis wavelengths is approximately 970 ± 120 K, corresponding to a rotational energy of 1.9 ± 0.2 kcal mol-1. The spin-orbit and Λ-doublet states of the OH fragments formed in the dissociation are measured to be nonstatistical distributions. To get an insight into the dissociative mechanism leading to OH formation in the photolysis of o-nitrophenol, the potential energy surfaces of the OH-forming channels are mapped by ab initio theoretical calculations. According to both experimental and theoretical results, a possible mechanism for OH formation is proposed. It is suggested that electronically excited o-nitrophenol mostly relaxes to the lowest excited triplet state (T1) via intersystem crossing followed by intramolecular H transfer to form an aci-nitro isomer, from which OH elimination takes place by N-OH bond cleavage most likely. The transition state for the N-OH bond rupture channel is located on the T1 state and characterization of the dissociative state to be T1 state strongly supports much of our experimental findings