Introduction of innovative technologies in friction units of heavy-duty tribosystems and monitoring of their condition

The article describes studies of heavy-duty metal-polymer tribosystems: wheel-brake pad and pyatnik-podpyatnik of rolling stock, as well as spline couplings of the MI-26 helicopter tail rotor transmission. Tests of the wheel - brake pad system were carried out on an inertial stand with two-way braking at loads and speeds close to real operating conditions. Methods for modifying polymers, fillers, and nanoscale additives have been developed for the Pyatnik - podpyatnik tribosystem of rolling stock. To increase the wear resistance of work surfaces two-layer carbon fibers were applied to the spline couplings. DLC- coatings. Bench tests of these coatings showed a 4.5-fold reduction in wear when testing full-scale slots with a load of 30,000 kg. H and the number of completed cycles in 1,000,000. Methods for monitoring spline couplings based on the analysis of the frequency spectrum of the acoustic-emission (AE) vibration signal generated during the operation of the friction unit are considered. The results of studying the working state of spline couplings obtained by vibration diagnostics in the acoustic frequency range are presented. The state estimation is based on both the characteristics of the time signal and the transformation of the signal in the frequency domain using modal decomposition of the signal using Hilbert-Huang transformations. It is shown that for the effective for monitoring heavy-duty tribosystems, it is advisable to use neural networks.

Investigation on collision-coalescence of droplets under the synergistic effect of charge and sound waves: orthogonal design optimization

As an efficient approach to improve the visibility, defogging technology is essential for the operation of ports and airports. This paper proposes a new and hybrid defogging technology, i.e. electric–acoustic defogging method. Specifically, the droplets are charged by corona discharge, which is beneficial to overcome the hydrodynamic interaction force to improve the droplet collision efficiency. Meanwhile, sound waves (especially acoustic turbulence) promote the relative movement of droplets to increase the collision probability. In this study, the effects of acoustic frequency ( f ), sound pressure level (SPL), and voltage (V) on the droplet growth ratio were studied by orthogonal design analysis. The results of difference analysis and multi-factor variance analysis show that frequency and sound pressure level are the dominant factors that affect the collision of droplets, and the effect of voltage is relatively weak. And f = 400 Hz, SPL = 132 dB, and V = -7.2 kV are the optimal parameters in our experiment. In addition, we further studied the impact of single factor on droplet growth ratio. The results show that there is an optimal frequency of 400 Hz. That is, the impact of frequency is non-linear. The droplet growth ratio increases with sound pressure level and voltage level. The new technology proposed in this paper can provide a new approach for defogging in open space.

Acoustic frequency-dependent physical mechanism of sub-MHz ultrasound neurostimulation

Ultrasound is an innovative physical modality allowing non-invasive and reversible modulation of neural circuit activity in the brain with high spatial resolution. Despite growing interest in clinical applications, the safe and effective use of ultrasound neuromodulation has been limited by a lack of understanding of the physical mechanisms underlying its effects. Here, we demonstrate acoustic frequency-dependent physical effects that underlie ultrasound neuromodulation, where cavitation and radiation forces are the dominant sources of low- and high-frequency stimulation, respectively. We used 39.5 kHz and 500 kHz acoustic frequencies to stimulate cultured neural and glial cells, excised from rat cortex, to study acoustic frequency-dependent neural responses. We demonstrate increased evoked responses due to increased cavitation activity at the 39.5 kHz acoustic frequency. In contrast, notable cavitation activity was not detected at 500 kHz despite detection of evoked responses. Our work highlights the dependence of ultrasound neuromodulation on acoustic frequencies, with different physical effects underlying cell responses to low and high sub-MHz acoustic frequency ranges.

Compatibility in acoustic telemetry

Acoustic telemetry is widely used to investigate aquatic animal movement. Pulse position modulation (PPM) is an acoustic telemetry method that allows multiple unique identification codes to be transmitted at a single acoustic frequency, typically in the 69 kHz range. However, because the potential number of unique identification codes (i.e. tags) is ultimately limited by the number of pulses in the PPM signal, this poses a practical limitation. In addition, different manufacturers have developed different approaches to encoding the transmitted data, hampering compatibility across brands. A lack of broad compatibility across telemetry systems restricts users to a single manufacturer and operating system, reduces market competition and limits innovation. As the aquatic animal tracking research community organises towards networks of devices and data, incompatibility becomes more problematic and jeopardizes the unique scientific benefits offered by the networking approach. Here, we make a plea for collaboration among the manufacturers globally and propose a set of open protocols to ensure equipment interoperability as a medium-term solution.

Interaction between Strong Sound Waves and Cloud Droplets: Theoretical Analysis

Recently strong sound wave was proposed to enhance precipitation. The theoretical basis of this proposal has not been effectively studied either experimentally or theoretically. Based on the microscopic parameters of atmospheric cloud physics, this paper solved the complex nonlinear differential equation to show the movement characteristics of cloud droplets under the action of sound waves. The motion process of individual cloud droplet in a cloud layer in the acoustic field is discussed as well as the relative motion between two cloud droplets. The effects of different particle sizes and sound field characteristics on particle motion and collision are studied to analyze the dynamic effects of thunder-level sound waves on cloud droplets. The amplitude of velocity variation has positive correlation with Sound Pressure Level (SPL) and negative correlation with the frequency of the surrounding sound field. Under the action of low-frequency sound waves with sufficient intensity, individual cloud droplets could be forced to oscillate significantly. The droplet smaller than 40μm can be easily driven by sound waves of 50 Hz and 123.4 dB. The calculation of the collision process of two droplets reveals that the disorder of motion for polydisperse droplets is intensified, resulting in the broadening of the collision time range and spatial range. When the acoustic frequency is less than 100Hz (@ 123.4dB) or the Sound Pressure Level (SPL) is greater than 117.4dB (@ 50Hz), the sound wave can affect the collision of cloud droplets significantly. This study provides theoretical perspective of acoustic effect to the microphysics of atmospheric clouds.

A Study of Standardizing Frequencies Using Channel Raster for Underwater Wireless Acoustic Sensor Networks

In this paper, we propose the method to standardize acoustic frequencies for underwater wireless acoustic sensor networks (UWASNs) by applying the channel raster used in the terrestrial mobile communications. The standardization process includes: (1) Setting the available acoustic frequency band where a channel raster is employed via the frequency specification analysis of the state-of-the art underwater acoustic communication modems. (2) Defining the center frequencies and the channel numbers as a function of channel raster, and the upper limit of the value of channel raster. (3) Determining the value of the channel raster suitable for the available acoustic frequency band via simulations. To set the value, three performance metrics are considered: the collision rate, the idle spectrum rate, and the receiver computational complexity. The simulation results show that the collision rate and the idle spectrum rate according to the value of channel raster have a trade-off relationship, but the influence of channel raster on the two performance metrics is insignificant. However, the receiver computational complexity is enhanced remarkably as the value of channel raster increases. Therefore, setting the value of channel raster close to its upper limit is the most adequate in respect of mitigating the occurrence of a collision and enhancing the reception performance. The standardized frequencies based on channel raster can guarantee the frequency compatibility required for the emerging technologies like the Internet of Underwater Things (IoUT) or the underwater cognitive radio, but also improves the network performance by avoiding the arbitrary use of frequencies.