• International Journal of Aeronautical and Space Sciences
• /
• v.18 no.1
• /
• pp.28-37
• /
• 2017

Recent modeling of thermal nonequilibrium processes in simple molecules like hydrogen and nitrogen has indicated that rotational nonequilibrium becomes as important as vibrational nonequilibrium at high temperatures. In the present work, in order to analyze rovibrational nonequilibrium, the rotational mode is separated from the translational-rotational mode that is usually considered as an equilibrium mode in two- and multi-temperature models. Then, the translational, rotational, and electron-electronic-vibrational modes are considered separately in describing the thermochemical nonequilibrium of nitrogen behind a strong normal shock wave. The energy transfer for each energy mode is described by recently evaluated relaxation time parameters including the rotational-to-vibrational energy transfer. One-dimensional post-normal shock flow equations are constructed with these thermochemical models, and post-normal shock flow calculations are performed for the conditions of existing shock-tube experiments. In comparisons with the experimental measurements, it is shown that the present thermochemical model is able to describe the rotational and electron-electronic-vibrational relaxation processes of nitrogen behind a strong shock wave.

• Bulletin of the Korean Chemical Society
• /
• v.25 no.9
• /
• pp.1397-1402
• /
• 2004

The vibrational predissociation of triatomic, i.e., atom-diatom, van der Waals complexes in transient electronic excited state has been widely investigated. The predissociation rates or lifetimes are major concerns of the previous studies. Experimentally rotational state distributions of diatomic product are hardly investigated and few theoretical stuides on rotational state distributions have appeared in literature. In this work, choosing the frequently studied $I_2(B)-Ne$ complex as an example, we investigate the change of rotational state distributions of $I_2(B)-Ne$ produced from predissociation of the various initial states of $I_2(B)-Ne$. The present study on the rotational distributions indicates that rotational state distributions depend significantly on the predissociation energy and the van der Waals vibrational modes of $I_2(B)-Ne$. That is, the initial state dependency of rotational state distributions is extensively discussed.

• Bulletin of the Korean Chemical Society
• /
• v.16 no.4
• /
• pp.341-344
• /
• 1995

Laser-induced fluorescence (LIF) excitation spectra were measured for fluorene (FR) cooled in pulsed supersonic expansions of He in the range 283.7-296.7 nm. Ab initio studies of FR have also been carried out for determining the electronic and vibrational structures by using the standard 3-21G basis sets. In the LIF excitation spectra of FR, highly resolved vibronic bands are observed having the band origin of 33,791 cm-1. The vibrational bands above the electronic origin were assigned on the basis of the well-characterized electronic vibrational bands reported previously and of normal modes of vibrations derived by our HF/3-21G calculations.

• Bulletin of the Korean Chemical Society
• /
• v.25 no.8
• /
• pp.1217-1224
• /
• 2004

We have calculated the probability of HBr formation and energy disposal of the reaction exothermicity in HBr produced from the reaction of gas-phase bromine with highly covered chemisorbed hydrogen atoms on a Si (001)-(2 ${\times}$1) surface. The reaction probability is about 0.20 at gas temperature 1500 K and surface temperature 300 K. Raising the initial vibrational state of the adsorbate(H)-surface(Si) bond from the ground to v = 1, 2 and 3 states causes the vibrational, translational and rotational energies of the product HBr to increase equally. However, the vibrational and translational motions of product HBr share most of the reaction energy. Vibrational population of the HBr molecules produced from the ground state adsorbate-surface bond ($v_{HSi}$ =0) follows the Boltzmann distribution, but it deviates seriously from the Boltzmann distribution when the initial vibrational energy of the adsorbate-surface bond increases. When the vibration of the adsorbate-surface bond is in the ground state, the amount of energy dissipated into the surface is negative, while it becomes positive as vHSi increases. The energy distributions among the various modes weakly depends on surface temperature in the range of 0-600 K, regardless of the initial vibrational state of H(ad)-Si(s) bond.

• Journal of KSNVE
• /
• v.8 no.1
• /
• pp.99-111
• /
• 1998

An analytical method using the substructure synthesis and assumed modes method is developed to investigate the effect of flexibility of bladed disk assembly on vibrational modes of flexible rotor system. In modeling the system, Coriolis forces, gyroscopic moments, and centrifugal stiffening effects are taken into account. Then the coupled vibrations between the shaft and bladed disk are extensively investigated using simplistic models, as the shaft rotational speed and the pretwist and stagger angles of blade are varied.

• The Journal of the Acoustical Society of Korea
• /
• v.18 no.7
• /
• pp.39-44
• /
• 1999

An analysis of the frequency parameters and vibrational modes is described for a rectangular plate. Double Fourier sine series is used as a modal displacement functions of a rectangular plate and applied to the free vibration analysis of a rectangular plate under various boundary conditions. The frequency parameters obtained by the double Fourier sine series method are compared with those obtained by the theory of finite element method and Ritz method. Frequency parameters are presented for the various aspect ratios for plate. The first four modal shapes for the rectangular plate under various boundary conditions are accurately described.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2004.05a
• /
• pp.273-277
• /
• 2004

This paper deals with the dynamic stability and vibration of a non-uniform cantilevered pipe conveying fluid. The present model consists of two segments with different cross-sections. Governing equations of motion are derived by extended Hamilton's principle, and the numerical scheme using finite element method is applied to obtain the discretized equations. The critical flow velocities and stability maps of the pipe are obtained by changing step ratios, mass ratios and internal damping parameters of the pipe. Finally, the vibrational modes associated with flutter are shown graphically.

• Bulletin of the Korean Chemical Society
• /
• v.35 no.2
• /
• pp.531-538
• /
• 2014

The quantum mechanical properties of a series of oligo-para-phenylenes (2-11) were characterized using DFT B3LYP/6-311G(d,p) calculations. The global minimum among the various torsional conformers of an oligo-p-phenylene is calculated to be a twist conformation. A less stable planar conformation, in which all the dihedral angles in oligo-p-phenylene are restricted to be planar, has also been calculated. The total electronic energies, normal vibrational modes, Gibbs free energies, and HOMOs and LUMOs of the two different conformations (twisted and planar) of the oligo-p-phenylenes were analyzed. The energy differences between the HOMOs and LUMOs of the substrates are in accord with the maximum absorption peaks of the experimental UV spectra of 2-6. The calculated normal vibrational modes of 2-6 were comparable with their experimental IR spectra.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2004.05a
• /
• pp.267-272
• /
• 2004

Vertical pump are widely used owing to the fact that they occupy small floor space. In this type of pumps, however, the vibrational problems are very important, since, in many cases, they have less stiffness in comparison with later pumps. This study presents a simple solution method for calculating the natural frequencies and modes of vertical pumps. In this study, a model of a vertical pump was developed and the nondimensional parameters for the vibrational characteristics of it were determined. Added mass was calculated for the effects of water and the transfer matrix method was used.

• Journal of KSNVE
• /
• v.9 no.5
• /
• pp.928-935
• /
• 1999

Vertical pumps are widely used owing to the fact that they occupy small floor space. In this type of pumps, however, the vibrational problems are very important, since, in many cases, they have less stiffness in comparison with lateral pumps. This study presents a simple solution method for calculating the natural frequencies and modes of vertical pumps. In this study, a mode of a vertical pump was developed and the nondimensional parameters for the vibrational characteristics of it were determined. Added mass was calculated for the effects of water and the transfer matrix method was used.