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This article introduces the main mechanisms of friction noise generated by submarine rubber-based propeller bearings and analyzes their respective scope of application and limitations. Then, the research on suppressing friction noise through the optimization of the structure and improvement of materials of rubber-based propeller bearings is discussed. Finally, the article summarizes a promising research direction aimed at eliminating friction noise in submarine rubber-based propeller bearings. By improving the structure and materials, the friction noise of propeller bearings can be effectively suppressed, thereby improving the deterrence and stealth performance of submarines.

Underwater noise classification is of great significance for identifying ships as well as other vehicles. Moreover, it is helpful in ensuring a marine habitat-friendly, noise-free ocean environment. But a challenge we are facing is the small-sized underwater noise samples. Because noise is influenced by multiple sources, it is often difficult to determine and label which source or which two sources are dominant. At present, research to solve the problem is focused on noise image processing or advanced computer technology without starting with the noise generation mechanism and modeling. Here, a typical underwater noise generation model (UNGM) is established to augment noise samples. It is established by generating noise with certain kurtosis according to the spectral and statistical characteristics of the actual noise and filter design. In addition, an underwater noise classification model is developed based on UNGM and convolutional neural networks (CNN). Then the UNGM-CNN-based model is used to classify nine types of typical underwater noise, with either the 1/3 octave noise spectrum level (NSL) or power spectral density (PSD) as the input features. The results show that it is effective in improving classification accuracy. Specifically, it increases the classification accuracy by 1.59%, from 98.27% to 99.86%, and by 2.44%, from 97.45% to 99.89%, when the NSL and PSD are used as the input features, respectively. Additionally, the UNGM-CNN-based method appreciably improves macro-precision and macro-recall by approximately 0.87% and 0.83%, respectively, compared to the CNN-based method. These results demonstrate the effectiveness of the UNGM established in noise classification with small-sized samples.

Flapping-foil thrusters are systems that operate at a substantially lower frequency compared with marine propellers and are characterized by a much smaller power concentration. These biomimetic devices are able to operate very efficiently, offering desirable levels of thrust required for the propulsion of small vessels or autonomous underwater vehicles (AUVs), and can be used for the standalone propulsion of small vessels or for augmenting ship propulsion in waves, alleviating the generation of noise and its adverse effects on sea life, particularly on marine mammals. In this work, we consider the generation of noise by flapping foils arranged in the neighborhood of the above vessels including the scattering effects by the hull, which, in addition to free-surface and seabed effects, significantly contribute to the modification of the characteristics of the acoustic field. A Boundary Element Method (BEM) is developed to treat the 3D scattering problem in the frequency domain forced by monopole and dipole source terms associated with the Ffowcs Williams and Hawkings (FW-H) equation. Numerical results are presented in selected cases illustrating that the hull geometry and acoustic properties, as well as the sea surface and seabed effects, are important for the determination of the directionality of the generated noise and significantly affect the propagation in the underwater ocean environment.

Power noise generation for masking power traces is a powerful countermeasure against Simple Power Analysis (SPA), and it has also been used against Differential Power Analysis (DPA) or Correlation Power Analysis (CPA) in the case of cryptographic circuits. This technique makes use of power consumption generators as basic modules, which are usually based on ring oscillators when implemented on FPGAs. These modules can be used to generate power noise and to also extract digital signatures through the power side channel for Intellectual Property (IP) protection purposes. In this paper, a new power consumption generator, named Xored High Consuming Module (XHCM), is proposed. XHCM improves, when compared to others proposals in the literature, the amount of current consumption per LUT when implemented on FPGAs. Experimental results show that these modules can achieve current increments in the range from 2.4 mA (with only 16 LUTs on Artix-7 devices with a power consumption density of 0.75 mW/LUT when using a single HCM) to 11.1 mA (with 67 LUTs when using 8 XHCMs, with a power consumption density of 0.83 mW/LUT). Moreover, a version controlled by Pulse-Width Modulation (PWM) has been developed, named PWM-XHCM, which is, as XHCM, suitable for power watermarking. In order to build countermeasures against SPA attacks, a multi-level XHCM (ML-XHCM) is also presented, which is capable of generating different power consumption levels with minimal area overhead (27 six-input LUTS for generating 16 different amplitude levels on Artix-7 devices). Finally, a randomized version, named RML-XHCM, has also been developed using two True Random Number Generators (TRNGs) to generate current consumption peaks with random amplitudes at random times. RML-XHCM requires less than 150 LUTs on Artix-7 devices. Taking into account these characteristics, two main contributions have been carried out in this article: first, XHCM and PWM-XHCM provide an efficient power consumption generator for extracting digital signatures through the power side channel, and on the other hand, ML-XHCM and RML-XHCM are powerful tools for the protection of processing units against SPA attacks in IoT devices implemented on FPGAs.

The development of large-format detector arrays with background-limited performance is of particular interest at the terahertz (THz) band, which is a unique band in search of our cosmic origins. With high sensitivity and being more promising in the pixel number and multiplexing technology, superconducting kinetic inductance detectors (KID) are emerging as a major choice of detectors of this type. Here we fabricate three-THz-band (0.35/0.85/1.4 THz) KIDs on a single chip from a 120-nm-thick aluminum (Al) superconducting film and measure photon-noise-limited performance and intrinsic generation-recombination noise at high (>1 pW) and low (<1 fW) optical radiation power, respectively. Their responses to blackbody (optical) radiation are proven to be purely from photons compared with the responses of two dark KIDs intentionally arranged on the same detector chip. The lowest optical noise equivalent power (NEP) reaches 6×10 −18 W/Hz 0.5 and the optical coupling efficiency is in the range of 49%–56% for the three KIDs, which are in good agreement with the simulation results.

In this paper, we study the effect of corrosion inhibitors in compositions of friction composites on corrosion processes and noise generation in friction units. Model composites containing complex corrosion inhibitors as target additives were prepared. Tribological tests of the friction composite were performed using the “plane-to-plane” scheme. Transfer films on the surface of a steel counterbody are shown to be formed predominantly by laminar wear particles of the composite with sizes up to 50 μm. X-ray photoelectron spectroscopy data confirmed the presence in the transfer films of all elements related to the main components of the friction material, including corrosion inhibitors. Climatic tests were carried out. In a friction pair with a composite containing no corrosion inhibitor, continuous corrosion of the metal counterbody is shown to be predominant while pitting actively develops over time. The degree of corrosion damage to the surface reaches 90–95% of the nominal contact area. The introduction of a complex corrosion inhibitor into the composition of friction composites in an amount of 1.5–3.0 wt % was established to reduce the degree of corrosion damage to the nominal friction area of the metal counterbody by 20–35%. Outside the nominal friction area, the effect of reducing the degree of corrosion damage to the surface area of the metal counterbody by 50–60% was found. Triboacoustic tests were carried out on metal counterbodies subject to corrosion during climatic tests. Levels of sound pressure produced by the friction pair in the frequency range of 50 Hz–20 kHz are determined. The use of corrosion inhibitors was found to lead to a decrease in noise levels while the most significant decrease of 7–30 dB occurs in the high-frequency region of 6–20 kHz.

The noise behavior of a proposed Ge-source counter-doped pocket-based double-gate tunnel FET (GS-PNPN-TFET) in the presence and absence of interfacial trap charge conditions is presented. The noise behavior was studied in terms of drain current noise power spectral density ( S id , unit A 2 /Hz) and gate voltage electron noise power spectral density ( S vg ee, unit V 2 /Hz) against variation of various device parameters, viz., body thickness ( T si ), pocket length ( L p ), gate-oxide thickness ( T ox ), gate-oxide material, mole fraction, and doping density using Sentaurus TCAD software. Oxide–semiconductor interfacial trap charge of Gaussian distribution was used at two frequencies − 1 MHz and 10 GHz. Our analysis also includes the impact of temperature variation on noise. As per our findings, the noise spectrums are comparable for the presence and absence of interfacial trap charges in the proposed TFET. This is because the noise spectrum depends on on-current ( I ON ) and the I ON is negligibly influenced by the interfacial trap charges in the proposed TFET. However, off-current ( I OFF ) degrades when trap charges are present at the interface. In comparison with other FET devices, the proposed device offers improved S id and S vg ee values of roughly 1.82 × 10 –29  A 2 /Hz and 5.5 × 10 –20  V 2 /Hz, respectively, at 10 GHz frequency. Furthermore, the diffusion noise predominates at higher frequencies, while the generation–recombination noise is found to be dominant at low frequencies, as expected. Flicker noise is most noticeable at low and medium frequencies but fades away at higher frequencies.

The present paper contains the results of the numerical analysis of the interaction between a Newtonian incompressible turbulent flow and a linear elastic slender body, together with the influence of the fluid–structure interaction (FSI) on the noise generation and propagation. The purpose is to evaluate the differences in term of acoustic pressure between the case where the solid body is rigid (infinite stiffness) and the case where it is elastic (finite stiffness). A partitioned and implicit algorithm with the arbitrary Lagrangian–Eulerian method (ALE) is used for the interaction between the fluid and solid. For the evaluation of the turbulent fluid motion, we use a large eddy simulation (LES) with the Smagorinsky subgrid scale model. The equation for the solid is solved through the Lagrangian description of the momentum equation and the second Piola–Kirchoff stress tensor. In addition, the acoustic analogy of Lighthill is used to characterize the acoustic source (the slender body) by directly using the fluid dynamic fields. In particular, we use the Ffowcs Williams and Hawkings (FW-H) equation for the evaluation of the acoustic pressure in the fluid medium. As a first numerical experiment, we analyze a square cylinder immersed in a turbulent flow characterized by two different values of stiffness: one infinite (rigid case) and one finite (elastic case). In the latter case, the body stiffness and mean flow velocity are such that they induce the lock-in phenomenon. Finally, we evaluate the differences in terms of acoustic pressure between the two different cases.

This paper describes the problem of rising temperature of the friction elements during braking. Negative influence of brake pads heating on the vehicle efficiency and traffic safety is well known. Methods of temperature stabilization in the contact of tribological elements during braking are proposed. Variants of brake pad application with additional elements consisting of phase transition material are considered. Their effectiveness is estimated. The effect of the contact characteristics on noise generation is analysed. The method of noise reduction is considered. The target function for the tribological processes management in the contact of the brake elements has been developed. The application of this target function allows using the braking reserve with the achievement of maximum braking effect with minimal wear and noise.

In the present paper, noise generation due to supersonic hot jet impingement (M=1.4 and Tt=950 K) to an inclined flat plate is experimentally investigated. In general, four types of acoustic waves are defined for jet impingement: acoustic waves generated by the shear layer of the main jet (type-A), by the impingement region (type-B), by the shear layer of the wall/jet downstream of the impinging region (type-C), and tonal acoustic waves observed in normal impingement. An attempt is made to understand the sources of the noise of the impinging jet by comparing acoustic scalograms of the impinging and free jets at the far-field. It is determined that the type-C acoustic wave images are similar to the far-field scalogram images of the free jet at the same polar angles. Further, the type-B acoustic waves in oblique jet impingement have similar acoustic signature with tonal noise due to normal jet impingement.