Audible Noise Spectrum Research Articles

Research on the correlation between corona current spectrum and audible noise spectrum of HVDC transmission line

Audible noise is closely related to corona current on a high voltage direct current (HVDC) transmission line. In this paper, we measured a large amount of audible noise and corona current waveforms simultaneously based on the largest outdoor HVDC corona cage all over the world. By analyzing the experimental data, the related statistical regularities between a corona current spectrum and an audible noise spectrum were obtained. Furthermore, the generation mechanism of audible noise was analyzed theoretically, and the related mathematical expression between the audible noise spectrum and the corona current spectrum, which is suitable for all of these measuring points in the space, has been established based on the electro-acoustic conversion theory. Finally, combined with the obtained mathematical relation, the internal reasons for these statistical regularities appearing in measured corona current and audible noise data were explained. The results of this paper not only present the statistical association regularities between the corona current spectrum and the audible noise spectrum on a HVDC transmission line, but also reveal the inherent reasons of these associated rules.

The Effect of Non-Circular Bearing Shapes in Hydrodynamic Journal Bearings on the Vibration Behavior of Turbocharger Structures

Increasing quality demands of combustion engines require, amongst others, improvements of the engine’s acoustics and all (sub)components mounted to the latter. A significant impact to the audible tonal noise spectrum results from the vibratory motions of fast-rotating turbocharger rotor systems in multiple hydrodynamic bearings such as floating bearing rings. Particularly, the study of self-excited non-linear vibrations of the rotor-bearing systems is crucial for the understanding, prevention or reduction of the noise and, consequently, for a sustainable engine acoustics development. This work presents an efficient modeling approach for the investigation, optimization, and design improvement of complex turbocharger rotors in hydrodynamic journal bearings, including floating bearing rings with circular and non-circular bearing geometries. The capability of tonal non-synchronous vibration prevention using non-circular bearing shapes is demonstrated with dynamic run-up simulations of the presented model. These findings and the performance of our model are compared and validated with results of a classical Laval/Jeffcott rotor-bearing model and a specific turbocharger model found in the literature. It is shown that the presented simulation method yields fast and accurate results and furthermore, that non-circular bearing shapes are an effective measure to reduce or even prevent self-excited tonal noise.

Conductor Surface Conditions Effects on Audible Noise Spectrum Characteristics of Positive Corona Discharge

Conductor surface conditions of high voltage overhead transmission lines have a large influence on corona characteristics. Both audible noise and corona current is highly depended on the corona discharge characteristics. However, relatively few investigations have previously been made on conductor surface conditions effects on audible noise spectrum characteristics. In the present work, the artificial pollution experiments were carried out to simulate the various surface conditions. At the same time, the audible noise spectra and the corona current of the polluted conductor are recorded. From the analysis of the experiment results, it was found that the audible noise spectra level (>1 kHz) and corona current increased obviously as the relative permittivity grew and the amount of pollution increased. Furthermore, from the results of the long-term statistical measurement about A-weighted equivalent continuous sound level (LAeq) of the polluted conductor, the close correlation between the surface potential gradient and the audible noise spectra were obtained.

Studying on the Application of Using Audible Sound to Detect Cavitation Phenomenon in a Centrifugal Pump

Cavitation within a centrifugal pump can cause more undesirable effects, damage of the pump by pitting and erosion and structure vibration and resulting noise, therefore it must be prevented. To prevent the onset of the cavitation, we have to detect the beginning of the cavitation process, the emitted noise can also be used, among other possibilities. Experiments have shown that there is a discrete frequency tone within the audible noise spectra, which is strongly dependent on the cavitation process and its development. Therefore, the discrete frequency tone was separated from the noise spectra of cavitating pumps and then used to detect the incipient of cavitation and its development.

Detection of cavitation in situ operation of kinetic pumps: Effect of cavitation on the characteristic discrete frequency component

Cavitation within a pump causes structural vibration with noise, among other by-products. Experiments have shown that there is a discrete frequency or broadband peak within the audible noise spectra, which is in strong correlation with the development of the cavitation process in the pump. Furthermore, the peak of the discrete frequency, or broadband peak, coincides with the net positive suction head (NPSH) critical value, which corresponds to a 3% drop in the total delivery head. Therefore, the discrete frequency tone can be used to detect the incipience of cavitation and its development as well as to determine the NPSH required or critical value with in situ operation of a pump. In this study, we wanted to clarify the mechanism of noise generation, which is responsible for the discrete frequency component and on which cavitation has an important effect. For this purpose, three different measurement methods were used: the first is based on measurement of the sound pressure level (SPL) in the surrounding air, the second is based on measurement of the underwater acoustics and the third is based on measurement of the structural vibration. Experiments have shown that the characteristic discrete frequency tone, which is in close correlation with the cavitation process, is a result of structural vibrations (modes) or resonances caused by implosion of bubbles and bombardment of the inner surfaces of the pump.

Detection of cavitation in operation of kinetic pumps. Use of discrete frequency tone in audible spectra

Safe operation of kinetic pumps, as liquid movers, can be threatened by cavitation phenomenon in, amongst others. Cavitation is the Achilles’ heel of kinetic pumps. It can cause deterioration of the hydraulic performance, damage of the pump by pitting and material erosion, and structure vibration and noise. Cavitation can appear within the entire range of operating conditions, therefore it must by all means be prevented. To prevent cavitation in a pump we have to know the beginning and development of the cavitation in the pump. For this purpose, the emitted noise in the audible range can be used, amongst other possibilities. Experiments have shown that there is a discrete frequency tone within the audible noise spectra, which is in strong correlation with development of the cavitation process in the pump. Therefore, the discrete frequency tone can be separated from the noise spectra of a cavitating pump and used to detect the incipient of cavitation and its development as well as to prevent the onset of the cavitation process in the pump, by means of initiating an alarm, shutdown, or control signal via an electrical control system.

Use of audible sound for safe operation of kinetic pumps

Safe operation of kinetic pumps, as liquid movers, can be threatened by cavitation phenomenon, among others. Cavitation is the Achilles heel of kinetic pumps. It can deteriorate hydraulic performance, damage the pump by pitting and material erosion, and structure vibration and resulting noise. Cavitation can appear within the entire range of operating conditions; therefore it must, by all means, be prevented. To prevent cavitation in a pump, we have to know the beginning and development of cavitation in the pump. For this purpose, the emitted noise in the audible range can be used, among other possibilities. Experiments have shown that there is a discrete frequency tone within the audible noise spectra, which is in strong correlation with the development of the cavitation process in the pump, and so with the net positive suction head ( NPSH) critical value, which corresponds to the 3% drop in the total delivery head. The discrete frequency tone can thus be used to detect the incipient of cavitation and its development as well as to prevent the onset of the cavitation process in the pump and also in situ operation. Two different measurement methods were used to clarify the noise-generating mechanism, which is responsible for the discrete frequency component: by using a microphone and an accelerometer. Experiments have shown that the characteristic discrete frequency tone, which is in close correlation with the cavitation process, is a result of structural vibrations (modes) or resonances caused by implosion of bubbles and bombardment of the inner surfaces of the pump.

DETECTION OF CAVITATION PHENOMENON IN A CENTRIFUGAL PUMP USING AUDIBLE SOUND

One of the sources of instability in a centrifugal pump is cavitation phenomenon. Cavitation within a centrifugal pump can cause more undesirable effects, such as deterioration of the hydraulic performance (drop in head-capacity and efficiency curves), damage of the pump by pitting and erosion and structure vibration and resulting noise. Cavitation can appear within the entire range of operating conditions; therefore it must, by all means, be prevented. To prevent the onset of the cavitation, we have to know the beginning of cavitation phenomenon in the pump. To detect the beginning of the cavitation process, the emitted noise can also be used, among other possibilities. Experiments have shown that there is a discrete frequency tone within the audible noise spectra, at 147 Hz or BPF/2, which is strongly dependent on the cavitation process and its development. Therefore, the discrete frequency tone at 147 Hz was separated from the noise spectra of cavitating pumps and then used to detect the incipient of cavitation and its development. It was also used to determine the net positive suction head required or the critical value, as well as to prevent cavitation in the pump by means of initiating an alarm, shutdown or control signal via an electrical control system.

Speech enhancement based on audible noise spectrum and short-time spectral amplitude estimator

Subtractive-type algorithms are effective in reducing background noise, but always produce musical noise. An algorithm based on an audible noise spectrum is proposed and tested using various noise types and levels. The performance evaluation shows that the residual noise is significantly removed and it renders better quality than those without masking.

Speech enhancement based on audible noise suppression

A novel speech enhancement technique is presented based on the definition of the psychoacoustically derived quantity of audible noise spectrum and its subsequent suppression using optimal nonlinear filtering of the short-time spectral amplitude (STSA) envelope. The filter operates with sparse spectral estimates obtained from the STSA, and, when these parameters are accurately known, significant intelligibility gains, up to 40%, result in the processed speech signal. These parameters can be also estimated from noisy data, resulting into smaller but significant intelligibility gains.

Audible noise of transmission lines caused by the corona effect: Analysis, modelling, prediction

The paper presents the results of investigations of audible noise of high voltage transmission lines of alternating current (a.c. UHV) caused by the corona effect. The investigation results concern the 400 kV lines in two basic layouts existing in Poland: single horizontal and double vertical. Environmental investigations in real conditions were executed in a whole year cycle with the short-term method. Apart from the results of the environmental investigations the paper contains also the laboratory investigation results. The influence of constructional design and environmental parameters on the sound level distribution along a span was analysed. The influence of the conductor surface state and weather conditions on the level and shape of the emitted audible noise spectrum was particularly taken into account. The evaluation of the influence of the line audible noise on the acoustic climate of the environment was carried out. The analysis of possibilities of the application of well known computational procedures to the prediction of the line audible noise caused by the corona effect in Polish conditions was executed and an original form of a line acoustic model with the audible noise prediction possibility as a function of rainfall was presented.

Audible noise in speed‐controlled inverter‐fed medium‐sized induction motors

AbstractThe audible noise produced by three‐phase, squirrel‐cage induction motors, is caused by the space harmonics of the flux‐density distribution in the air gap of the machine. When the motor is supplied by a frequency inverter in order to control the speed, time harmonics in both current and voltage are present, yielding new components in the audible noise spectrum. In the paper, a number of motor‐inverter combinations are compared for medium‐sized induction motors (90 kW). As a reference case, the motors are supplied with a generator, delivering a variable frequency without harmonics. Theoretical explanations for the increase of the audible noise level and the additional frequency components are given.

Modification of Transmission Line Audible Noise Spectra to Reduce Environmental Impact

The aversiveness of audible noise from EHV electric transmission lines was evaluated for spectral modifications of 5 different tape-recorded samples. The relative contributions of low-frequency humming and buzzing and of high-frequency hissing and crackling components of the noise were determined. The high-frequency components of the hoise proved more aversive for all five samples to a group of 25 listeners. Therefore, for outdoor or open window listening, engineering efforts should be directed at reducing the high-frequency portion of the audible noise spectrum.

Modification of Transmission Line Audible Noise Spectra to Reduce Environmental Impact

Modification of Transmission Line Audible Noise Spectra to Reduce Environmental Impact