Ab Initio Calculations on Nitramide and Its Methyl Derivatives( Ⅱ )——The Harmonic Force Fields and Vibrational Spectra of Nitramide and Its Isotopic Derivatives

The harmonic force field and the vibrational spectrum of nitramide were calculated by using the ab initio gradient program TEXAS at the Hartree-Fock level with a 4-21G basis set. The directly computed theoretical harmonic force field was scaled by using empirical scale factors which are transferred from other molecules and provided an a priori prediction of fundamental frequencies and intensities. The average deviations between predicted vibrational frequencies of nitramide and experimental IR spectrum in an argon matrix are 63 cm-1 for symmetric vibrations and 41 cm-1 for antisymmetric modes. A new set of scale factors was optimized in this paper. These scale factors reduced the average deviations to 2. 3 cm-1 for symmetric modes and 0. 8 cm-1 for antisymmetric ones. The vibrational spectra of three isotopic derivatives of nitramide were predicted by using the force field resulted from the optimized set of scale factors, which are in good agreement with their experimental data in an argon matrix.

Studies on nitramide and its methyl derivatives with ab initio calculations——Ⅳ.The harmonic force field and vibrational spectra of dimethylnitramine and its isotopic derivatives

The complete harmonic vibrational force field of dimethylnitramine has been calculated at the Hartree-Fock level using 4-21G basis set.The harmonic force field was then scaled with scale factors previously derived from N-methylnitramine,and the vibrational spectrum of dimethylnitramine was computed.This apriori prediction,made with no reference to observations on dimethylnitramine, agrees with the experimental IR spectrum in gas phase with a mean deviation of 8.4 cm^(-1).Some of the scale factors were reoptimized by fitting of the computed force field to experimental data.The new set of scale factors reduced the mean deviation to 4.5 cm^(-1),and was used to predict the vibrational spectrum of deuterated form of dimethylnitramine(-6D).Dipole moment derivatives were also cal- culated and used to predict infrared intensities which are comparable with experimental values.

Quantization of the 1-D Forced Harmonic Oscillator in the Space (<i>x</i>, <i>v</i>)

The quantization of the forced harmonic oscillator is studied with the quantum variable (x, v∧), with the commutation relation , and using a Schrödinger’s like equation on these variable, and associating a linear operator to a constant of motion K (x, v, t) of the classical system, The comparison with the quantization in the space (x, p) is done with the usual Schrödinger’s equation for the Hamiltonian H(x, p, t), and with the commutation relation . It is found that for the non-resonant case, both forms of quantization bring about the same result. However, for the resonant case, both forms of quantization are different, and the probability for the system to be in the exited state for the (x, v∧) quantization has fewer oscillations than the (x, p∧) quantization, the average energy of the system is higher in (x, p∧) quantization than on the (x, v∧) quantization, and the Boltzmann-Shannon entropy on the (x, p∧) quantization is higher than on the (x, v∧) quantization.

Vibration Control for Two Air Compressor Units Used in Tandem

The paper presents the vibration control for two air compressors used in tandem to an oxygen generating station. The compressors are identical in terms of constructive and functional properties, and are both located on similar foundations. Each compressor is supported on a foundation made from one massive block of concrete, provided with some elastic and damping parts. This anti vibrating structure insulates the machines compared to other station equipment. During operation, were observed dangerous levels of vibration at one of the machines, which forced some unwanted stoppages for the station. Two hypotheses have been promoted. One of them referred to a pronounced wear of one compressor, although this was relatively new. The second hypothesis has taken in consideration the appearance of some cracks in the foundation massive concrete block. Experimental research conducted on the spot led to the identification of some errors done at foundation fabrication. The experimental results and some theoretical investigations are presented in this paper.

Isola in a linear one-degree-of-freedom feedback system with actuator rate saturation

This short communication uses numerical continuation to highlight the existence of an isola in a simple one-degree-of-freedom harmonically forced feedback system with actuator rate limiting as its only nonlinear element.It was found that the isola(1)contains only rate-limited responses,(2)merges with the main branch when the forcing amplitude is sufficiently large,and(3)includes stable solutions that create a second attractor in regions where rate limiting is not expected.Furthermore,the isola is composed of two solutions for a given forcing frequency.These solutions have the same amplitudes in the state(pitch rate)projection;however,they have distinct phases,and their amplitudes are also distinct when projected onto the integrator state in the controller.The rich dynamics observed in such a simple example underlines the impact of rate limiting on feedback systems.Specifically,the combination of feedback and rate limiting can create detrimental dynamics that is hard to predict and requires careful analysis.

Circular cylinder wakes and their control under the influence of oscillatory flows: A numerical study

Understanding and control of wake vortices past a circular cylinder is a cardinal problem of interest to ocean engineering.The wake formation and vortex shedding behind a variety of ocean structures such as spars,are subjected to fatigue failure limiting their life span.The additional influences due to ocean waves and currents further exacerbate these effects.In the present study,flow past an isolated circu-lar cylindrical structure subjected to an oscillatory upstream are numerically investigated.These studies involve high resolution simulations over the low Reynolds number range(100-200).Although the prac-tical range of interest is in high Reynolds number range of 103-105,the flow physics and a number of qualitative and quantitative aspects are similar to the low Reynolds number flows.In the high Reynolds number range,statistical averaging tools in conjunction with suitable closure models would be neces-sary.The control of wake vortices is achieved with the aid of two small rotors located in the aft of the main cylinder.A control algorithm was coupled to determine the quantum of actuation to the rotating elements.Although control of wake vortices was observed for harmonic in-let forcing,residual vortical structures were found to persist at higher amplitudes of oscillation.To study the efficacy of this control,numerical simulations were further extended,when the circular cylinder was flexibly mounted.The con-trol of flow induced vibrations was observed to be reasonably effective in controlling the wake generated behind the main cylinder due to oscillatory upstream.