Influence of wall vibrations on the sound of brass wind instruments

The results of an experimental and theoretical investigation of the influence of wall vibrations on the sound of brass wind instruments are presented. Measurements of the transmission function and input impedance of a trumpet, with the bell both heavily damped and freely vibrating, are shown to be consistent with a theory that assumes that the internal pressure causes an oscillation of the diameter of the pipe enclosing the air column. These effects are shown to be most significant in sections where there are flaring walls, which explains why damping these vibrations in cylindrical pipes normally produces no measurable effects.     

Prestress effects on the eigenfrequencies of the soundboards: experimental results on a simplified string instrument

This paper presents an experimental study of the effects of prestresses on the vibration behavior of string instruments. These prestresses are created by gluing ribs (crowning) and tensioning string (downbearing). The effects of these prestresses were previously studied numerically for a piano soundboard by Mamou-Mani et al. [J. Acoust. Soc. Am. 123, 2401-2406 (2008)] and analytically for simplified models by Mamou-Mani et al. [Acta Acust. Unit. Acust. 95, 915-926 (2009)]. In the present study, a specified test bench is designed, including a simplified soundboard (a rectangular plate), a bridge, and a single string. The plate is subjected to in-plane and transverse loads. Vibrational eigenmodes are identified using nearfield acoustical holography (NAH) measurement. The evolution of eigenfrequencies with these specific prestresses is studied. The results show the effectiveness of NAH for this purpose and a very good qualitative concordance with previous numerical and analytical calculus.     

多倍频简谐振动合成实验仪

研制了能够直观演示多倍频简谐振动合成的仪器.利用单片机控制直接数字合成芯片,精确产生任意频率和相位的4路正弦信号,通过模拟加法电路实现信号的合成.通过与计算机仿真结果的比较,实验仪能够很好地演示多倍频简谐振动的合成.     

Influence of Coulomb-excited vibrations on a nuclear Josephson effect

The transfer of nucleonic Cooper pairs during the scattering of two superfluid nuclei just below the Coulomb barrier is discussed microscopically. Break-up of pairs, especially by Coulomb excitation of vibrational states, and competition from other channels reduce the transfer probability.     

Aerodynamic vibrations of a maglev vehicle running on flexible guideways under oncoming wind actions

This paper intends to present a computational framework of aerodynamic analysis for a maglev (magnetically levitated) vehicle traveling over flexible guideways under oncoming wind loads. The guideway unit is simulated as a series of simple beams with identical span and the maglev vehicle as a rigid car body supported by levitation forces. To carry out the interaction dynamics of maglev vehicle/guideway system, this study adopts an onboard PID (proportional-integral-derivative) controller based on Ziegler-Nicholas (Z-N) method to control the levitation forces. Interaction of wind with high-speed train is a complicated situation arising from unsteady airflow around the train. In this study, the oncoming wind loads acting on the running maglev vehicle are generated in temporal/spatial domain using digital simulation techniques that can account for the moving effect of vehicle's speed and the spatial correlation of stochastic airflow velocity field. Considering the motion-dependent nature of levitation forces and the non-conservative characteristics of turbulent airflows, an iterative approach is used to compute the interaction response of the maglev vehicle/guideway coupling system under wind actions. For the purpose of numerical simulation, this paper employs Galerkin's method to convert the governing equations containing a maglev vehicle into a set of differential equations in generalized systems, and then solve the two sets of differential equations using an iterative approach with the Newmark method. From the present investigation, the aerodynamic forces may result in a significant amplification on acceleration amplitude of the running maglev vehicle at higher speeds. For this problem, a PID+LQR (linear quadratic regulator) controller is proposed to reduce the vehicle's acceleration response for the ride comfort of passengers.     

Effects of bending portions of the air column on the acoustical resonances of a wind instrument

The need to keep long wind musical instruments compact imposes the bending of portions of the air column. Although manufacturers and players mention its effects as being significant, the curvature is generally not included in physical models and only a few studies, in only simplified cases, attempted to evaluate its influence. The aim of the study is to quantify the influence of the curvature both theoretically and experimentally. A multimodal formulation of the wave propagation in bent ducts is used to calculate the resonances frequencies and input impedance of a duct segment with a bent portion. From these quantities an effective length is defined. Its dependence on frequency is such that, compared to an equivalent straight tube, the shift in resonance frequencies in a tube with bent sections is not always positive, as generally stated. The curvature does not always increase the resonances frequencies, but may decrease them, resulting in a complex inharmonicity. An experimental measurement of the effect of the curvature is also shown, with good agreement with theoretical predictions.     

Influence of a sea structure on the surrounding wind field

Summary We have experimentally studied the kinematic influence of an oceanographic tower on the surrounding wind field. The tower is located in the open sea in the northern Adriatic. The paper describes the tests carried out in a wind tunnel and their results.

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Riassunto Abbiamo studiato sperimentalmente l'influenza cinematica di una struttura sul campo di vento circostante. La struttura è una piattaforma oceanografica situata nel nord Adriatico. La nota descrive i test eseguiti in galleria del vento ed i risultati ottenuti.

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Резюме Мы экспериментально исследуем кинематическое влияние океанографической платформы на окружающее поле ветров. Платформа расположена в открытом море в северной части Адриатики. В статье описывается проверка, проведенная в ветряном туннеле, и приводятся полученные результаты.

     

Influence of molecular vibrations on substitution coordinates

The consistency of the substitution method has been checked by examining the change of the planar moment of inertia upon substitution in those cases where this change should be zero by symmetry. From 438 literature data it was concluded that Costain's estimate for the reliability of substitution coordinates is adequate except for the HD substitution where it is too optimistic by at least a factor of 2. A special case is formed by the substitution CH₃CH₂D, where absurdly large differences in the planar moments of inertia occur. It is shown that these differences can be largely eliminated when the effects of the torsion on parent and substituted molecules are properly accounted for. Approximate formulas for this purpose are derived and tested. It appears that neglect of these corrections is not justified when the geometry of a methyl group is to be determined accurately.     

Glass-specific behavior in the damping of acousticlike vibrations

High frequency sound is observed in lithium diborate glass, Li2O-2B2O3, using Brillouin scattering of light and x rays. The sound attenuation exhibits a nontrivial dependence on the wave vector, with a remarkably rapid increase towards a Ioffe-Regel crossover as the frequency approaches the boson peak from below. An analysis of literature results reveals that the boson-peak frequency is closely related with a Ioffe-Regel limit for sound in many glasses. We conjecture that this relation, specific to glassy materials, might be rather common among them.     

基于虚拟仪器的风力发电机组噪声分析系统*

该文基于LabVIEW虚拟技术设计了一款界面友好、操作便捷、实用性强的噪声测试分析系统。重点阐述了频率计权算法设计,依据IEC 61672-1:2002标准中频率计权规范,对比分析了快速傅里叶变换法和数字滤波器法在实现频率计权结果中的差异。在此基础上,根据IEC 61400-11-2012《风力发电机组噪声测试方法》标准,结合LabVIEW中的声音与振动工具包以及高级信号处理等函数,实现后续功能,使系统具有比较完备噪声测试分析功能。最后,以内蒙古风电场采集到的风力发电机组噪声数据为例,进行风力发电噪声分析系统的仿真验证,并对分析结果做了归纳总结。     

A simplified Time Reversal method used to localize vibrations sources in a complex structure

The main issue while dealing with problems due to structural vibrations is the identification of the sources that create annoyance. One of the experimental processes that permit to tackle this reverse problem uses Time Reversal method to localize the origin of the vibration detected on the surface of a structure.The Time Reversal experiment is based on a principle of time symmetry of waves propagation in a media. Using transceivers located on the structure, one can record its state of vibration. If all the signals recorded by the transceivers are reversed in time and reemitted from the position where they have been recorded, the resulting vibration will converge back to the point where it was originally emitted. In the standard approach, localization is observed both in time and space. We propose here a simplified localization process based on space localization only. We will apply this method on a complex industrial structure, stimulated with bursts. We shall show in the article the influence of certain parameters such as the number of transceivers or the structure complexity. Finally, all the tests presented hereby will allow us showing that the Time Reversal method is a very efficient and very easy to use method.     

Effect of wall temperature on the thermal behavior of a packed bed

The present work is concerned with numerically studying the thermal behaviour of a packed bed storage system under various wall temperatures. The packed bed is mathematically described using a two-phase model, in which the air and solid phases are governed by two coupled partial differential equations representing the energy conservation in each phase separately. The axial and radial conduction in the solid are taken into account while the thermal conductivity of air is ignored. The modeling equations are numerically solved at various fixed wall temperatures, ranging from 5°C to 55°C. The temporal, axial and radial distributions of air and solid temperatures obtained during thermal charging of the bed are studied, and used to compute and investigate the behaviour of energy stored inside the bed as well as the heat loss to the surroundings under such a wide range of wall temperatures.     

Influence of interactions of excited vibrations on the molecular parameters

The interaction of vibrations is studied by the algebraic method of perturbation theory. Formulas are derived that take into account the influence of interactions on the anharmonic spectroscopic parameters of excited vibrations with compound frequencies. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 27–32, March, 2008.     

Measurement of wall pressure fluctuations in the presence of vibrations induced by a turbulent flow

A systematic study of the methods of measuring wall pressure fluctuations against a background of intense vibrations is carried out. The method of separating the turbulent signal from noise on the basis of monitoring the level of vibration interference is considered. Active methods of vibration control are developed for a miniature receiver of turbulent pressure fluctuations. It is shown that the methods based on the spatial filtering of the noise field offer the greatest promise. The filtering properties of vibration-proof receivers and measuring systems are investigated.     

Influence of chemisorbed oxygen on nickel surface vibrations

We calculate the lattice vibration spectra near free and oxygen covered nickel surfaces. The phonon frequencies are deduced from the surface band structure using a simple band scheme for the nickel d and oxygen p states. Comparison is made with recent measurements obtained by electron loss spectroscopy.     

Influence of ultrasonic vibrations on the growth of semiconductor single crystals

The influence of ultrasonic vibrations on striations in InSb, GaAs and Bi-Sb alloy single crystals grown by a modified Czochralski method was investigated. Ultrasonic vibrations at frequencies of 0.15, 0.25, 0.6, 1.2, 2.5, 5 or 10 MHz were introduced into the melt parallel to the pulling axis. The introduction of ultrasonic vibrations at a frequency up to 5 MHz eliminates the striations in GaAs and Bi-Sb alloy single crystals growing with constant diameter. It was found that for Bi-Sb alloy single crystals of constant diameter growth, after ‘processing’ of the melt with ultrasonic vibrations, the striations do not reappear until after 2 h. The effectiveness of the influence of the ultrasonic vibrations on the decrease of growth striations in InSb, GaAs and Bi-Sb alloy growing crystals was estimated with the help of the calculation of the sound absorption coefficient.     

Influence of the ferromagnetic structure on the speed of propagation of magnetoelastic vibrations

The effect of thermomagnetic treatment temperature on the speed of magnetoelastic vibrations propagating in aFe _81.5 B _13.5 Si ₃ C ₂ metal alloy is investigated. A minimum is found in the plot of the dependence of the speed of magnetoelastic vibrations on the thermomagnetic treatment temperature. No minimum is observed in this dependence for amorphous metal alloys treated without magnetic field. It is found that the dependences of the speed of magnetoelastic vibrations on the external magnetic field differ for samples treated differently. The results obtained are explained based on concepts of reorganization of the domain structure of the samples under study. Irkutsk State University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 46–49, September, 1999.