Small Speed Research Articles

Modal structure of the sound field in a shallow-water waveguide with a gassy sediment layer: Experiment and theory

Motivated by a series of experiments in the Lake Kinneret (Israel), the paper investigates low-frequency sound propagation in the three-layer model of the shallow water waveguide, where a thin layer of gas-saturated sediment is situated between a homogeneous fluid sub-bottom and a continuously stratified water column. Typical values of the thickness and sound speed in the gassy layer are 1 m and 250 m/s. The layer is thin compared to typical water depth of about 40 m. Normal mode structure of the acoustic field is analyzed. It is shown that with increasing frequency each normal mode transforms into a mode trapped in the gassy layer. These modes have unusually small phase and group speeds that are significantly less than the sound speed in water. Theoretically predicted normal mode dispersion curves are compared to the dispersion curves retrieved from observations of shipping noise. Phase speeds of normal modes are measured by cross-correlatingthe noise recorded on two sparse vertical arrays. A technique is proposed for solving the inverse problem of determining the parameters of a gas-saturated layer by matching the measured and modeled frequency dependencies of the normal mode phase speed.

Surface Currents Along the Coast of the Chinese Mainland Observed by Coastal Drifters During April‐May 2019

Abstract We have analyzed the surface current characteristics along the coast of the Chinese mainland in autumn and winter by the trajectories of coastal drifters in a previous study (Yang et al., 2021). This paper is a follow-up study focusing on the surface current characteristics in spring. By the trajectories of coastal drifters in April‐May 2019, we continue to analyze the characteristics of surface currents. It is indicated that: (1) the surface currents were generally southwestward along the coasts of Zhejiang and Fujian, while they flowed northeastward in the offshore area in April 2019. (2) In May 2019, the surface current in the sea area north of 28°N had a small speed without a fixed direction nearshore, but had larger speed offshore. (3) The surface currents along the Zhejiang coast were variable in April‐May 2019, mainly corresponding to the change of wind field. (4) The coastal drifter is a useful instrument to observe circulation systems more precisely in nearshore but not deep ocean.

Direct shear behavior of dredged soil under dynamic normal load conditions

Dredged soil is commonly encountered in estuarine and coastal engineering constructions; however, its dynamic frictional behavior is still unclear. In this research, DJZ-500 shear apparatus was utilized for conducting direct shear test on the dredged soil. The periodic normal stress was employed in the vertical direction of soil sample, and simultaneously, shear stress was applied in the horizontal direction to supply a constant speed. The influences of different shear rates, dynamic normal stress frequencies, and dynamic normal stress amplitudes on the shear properties of the dredged soil under dynamic normal stress conditions were explored. It was found that shear stress periodically varied with the periodic normal stress, characterizing a phase lag with the peak shear stress. The dynamic normal stress manifested an enhancement effect and also a weakening effect on the shear strength. Generally, a small dynamic normal stress frequency, a high shear speed, and an appropriate dynamic normal stress amplitude induced frictional strengthening, whereas a small shear speed, a large dynamic normal stress frequency, and a very large or small dynamic normal stress amplitude caused frictional weakening. Therefore, the dynamic frictional behavior of the dredged soil depended on shear velocity and the frequency and amplitude of dynamic normal stress. The results of this paper provide technical support to improve the resistance of coastal constructions to dynamic disturbances, such as earth tides, ocean waves, earthquakes, typhoons, and traffic loads.

Optimization of rock cutting process parameters with disc cutter for wear and cutting energy reduction based on the discrete element method

The significance of the study is that the analysis of cutting performance and parameter optimization of the disc cutter can effectively improve the service life of the tool and reduce the cutting energy consumption. The method of the study is as follows: The numerical model based on the discrete element method was developed for rock cutting. The validation experiment was carried out to prove the reliability of the numerical model. The effect of swing arm speed, spindle speed and cutting depth on the wear, cutting specific energy and broken rock volume of the disc cutter was analyzed. The prediction models of cutting wear and cutting specific energy were established based on the response surface method, and the parameters were optimized. The validation experiment was carried out with the obtained optimal parameters as experimental conditions. The experiment verifies the reliability of the disc cutter wear and energy consumption optimization models. The conclusion is as follows: The cutting depth has the greatest effect on the wear of the disc cutter, followed by the spindle speed, while the swing arm speed has the least effect on the wear of the disc cutter. With the increase of the swing arm speed and cutting depth, the wear of the disc cutter increases. The maximum cutting wear can reach 4.75 mm and 5.03 mm. The average cutting wear can reach 2.57 mm and 2.29 mm. With the decrease of the spindle speed, the wear of the disc cutter increases, and the maximum wear and average wear can reach 4.71 mm and 2.30 mm. The increase of swing arm speed and cutting depth can improve cutting efficiency, but excessive swing arm speed and cutting depth will increase the wear and reduce the tool life. The swing arm speed has the greatest influence on the cutting specific energy, followed by the spindle speed, while the cutting depth has the least influence on the cutting specific energy. As the swing arm speed increases, the energy consumption of cutting becomes larger. The increase of the swing arm speed can improve the cutting efficiency, but the excessive swing arm speed will increase the energy consumption. With the increase of spindle speed, the rock cutting efficiency of the disc cutter becomes larger, and the energy consumption first decreases and then increases. Too small spindle speed will aggravate the energy consumption. The maximum cutting specific energy can reach 29.85 MJ/m3. When the swing arm speed v = 5 mm/s, the spindle speed n = 99 r/min and the cutting depth h = 14 mm, the wear and energy consumption of the disc cutter are minimal at the same time, which shows that the cutting performance of the disc cutter is better. The average wear and cutting specific energy of the disc cutter after parameter optimization are 1.64 mm and 17.59 MJ/m3, respectively. The conclusion of the study is that the experiments have verified the reliability of the discrete element disc cutter rock cutting analysis model, which can simulate the disc cutter cutting process more accurately. The optimization model is reliable, and the wear and energy consumption of the disc cutter are minimal at the same time after the optimization analysis, which provides a theoretical reference for improving the service life of the disc cutter and reducing the cutting energy consumption.

Numerical studies on detonation propagation in inhomogeneous mixtures with periodic reactant concentration gradient

In detonation engines and accidental explosions, a detonation may propagate in an inhomogeneous mixture with non-uniform reactant concentration. In this study, one- and two-dimensional simulations are conducted for detonation propagation in hydrogen/oxygen/nitrogen mixtures with periodic sinusoidal or square wave distribution of the reactant concentration. The objective is to assess the properties of detonation propagation in such inhomogeneous mixtures. Specifically, detonation quenching and reinitiation, cellular structure, cell size and detonation speed deficit are investigated. It is found that there exists a critical amplitude of the periodic mixture composition distribution, above which the detonation quenches. When the amplitude is below the critical value, detonation quenching and reinitiation occur alternately. A double cellular structure consisting of substructures and a large-scale structure is found for a two-dimensional detonation propagating in inhomogeneous mixtures with a periodic reactant concentration gradient. The detonation reinitiation process and the formation of the double cellular structure are interpreted. To quantify the properties of detonation propagation in different inhomogeneous mixtures, the large cell size, critical amplitude, transition distance and detonation speed deficit are compared for hydrogen/air without and with nitrogen dilution and for periodic sine wave and square wave distributions of the reactant concentration. The large-scale cell size is found to be linearly proportional to the wavelength, and both the critical amplitude and the transition distance decrease with the wavelength. The small detonation speed deficit is shown to be due to the incomplete combustion of the reactant. This work provides helpful understanding of the features of detonation propagation in inhomogeneous mixtures.

MobileNet-SVM: A Lightweight Deep Transfer Learning Model to Diagnose BCH Scans for IoMT-Based Imaging Sensors.

Many individuals worldwide pass away as a result of inadequate procedures for prompt illness identification and subsequent treatment. A valuable life can be saved or at least extended with the early identification of serious illnesses, such as various cancers and other life-threatening conditions. The development of the Internet of Medical Things (IoMT) has made it possible for healthcare technology to offer the general public efficient medical services and make a significant contribution to patients' recoveries. By using IoMT to diagnose and examine BreakHis v1 400× breast cancer histology (BCH) scans, disorders may be quickly identified and appropriate treatment can be given to a patient. Imaging equipment having the capability of auto-analyzing acquired pictures can be used to achieve this. However, the majority of deep learning (DL)-based image classification approaches are of a large number of parameters and unsuitable for application in IoMT-centered imaging sensors. The goal of this study is to create a lightweight deep transfer learning (DTL) model suited for BCH scan examination and has a good level of accuracy. In this study, a lightweight DTL-based model "MobileNet-SVM", which is the hybridization of MobileNet and Support Vector Machine (SVM), for auto-classifying BreakHis v1 400× BCH images is presented. When tested against a real dataset of BreakHis v1 400× BCH images, the suggested technique achieved a training accuracy of 100% on the training dataset. It also obtained an accuracy of 91% and an F1-score of 91.35 on the test dataset. Considering how complicated BCH scans are, the findings are encouraging. The MobileNet-SVM model is ideal for IoMT imaging equipment in addition to having a high degree of precision. According to the simulation findings, the suggested model requires a small computation speed and time.

SSR Stable Wind Speed Range Quantification for DFIG-Based Wind Power Conversion System Considering Frequency Coupling

The subsynchronous resonance (SSR) characteristics of doubly-fed induction generation-based wind power conversion system (DFIG-WPCS) varies with the wind speed. Obtaining the small signal SSR stable wind speed range is urgently important for wind farm dispatch planning. However, there are few methods to quantify the small signal SSR stable wind speed range of DFIG-WPCS. Moreover, the inherent frequency coupling when DFIG-WPCS is integrated to modular multilevel converter-high voltage direct current (MMC-HVDC) may lead to inaccurate stability assessment results. In this article, the frequency coupling mechanism between WPCS and MMC is revealed by analyzing the law of harmonic interaction in the interconnected system. The wind speed-frequency two-variable equivalent admittance model of DFIG-WPCS is established by taking the frequency coupling account. Relying on the two-variable open-loop transfer function, the multiple phase margin contours plot approach is proposed to quantify the small signal SSR stable wind speed range and damping properties. The effectiveness of two-variable admittance and analysis method are validated against electromagnetic transient (EMT) testbed with MATLAB /SimPowerSystems. The analysis results can provide a reference for the early planning and stable operation of DFIG-WPCS.

Novel Error-Tolerant Voltage-Divider-Based Through-Silicon-Via Test Architecture

A voltage-divider-based through-silicon-via (TSV) test architecture tests the TSV by using the voltage value differently divided according to TSV defects. This architecture is widely used for TSV testing owing to its small hardware overhead and high test speed. However, the existing voltage-divider-based TSV test architectures are vulnerable to process–voltage–temperature (PVT) variations and noise. In addition, they cannot effectively detect pinhole defects. This study proposes a novel error-tolerant voltage-divider-based TSV test architecture to address these problems. The proposed architecture reduces the test errors by appropriately adjusting the on-resistance value of each MOSFET and adding a compensator circuit. In addition, it effectively detects the pinhole defects by modifying the voltage divider structure and changing the MOSFET control method. Experimental results reveal that the proposed architecture promptly tests various TSV defects and significantly reduces the test errors.

Coercivity for travelling waves in the Gross-Pitaevskii equation in $\mathbb{R}^2$ for small speed

In the previous paper, we constructed a smooth branch of travelling waves for the 2 dimensional Gross-Pitaevskii equation. Here, we continue the study of this branch. We show some coercivity results, and we deduce from them the kernel of the linearized operator, a spectral stability result, as well as a uniqueness result in the energy space. In particular, our result proves the non degeneracy of these travelling waves, which is a key step in the classification of these waves and for the construction of multi-travelling waves.

A quantum study of argon induced line mixing in ammonia doublets

We present a theoretical study of pressure broadening and coupling coefficients for selected doublets of the ν 4 band of ammomia in argon bath. Generalized spectroscopic kinetic energy dependent cross sections are determined quantum mechanically making use of available NH3-Ar potential energy surfaces. Thermally averaged values at various temperatures are also provided. Results are in overall good agreement with data available in the literature. A further study focusses on the speed dependence of the corresponding line shape parameters. The pressure broadening coefficients are found to have a well marked speed dependence while the intradoublet coupling terms show a small speed dependence at room temperature.

Study on a generator and turbine designed for an efficient wind power plant in low speed wind currents

This article presents the advantages of improving and developing new types of turbines and generators designed for the production of electricity from low-speed wind and free-flowing water, at a time when the environment is deteriorating and there is a shortage of electricity. It has been analyzed that low-speed micro-hydroelectric power plants and wind power plants bring great benefits to the environment and economy through their mass use in meeting the needs of the population and businessmen for electricity. For this purpose, the effective structure of low-speed generators, micro-hydroelectric power plants and wind power plants were considered, and the issues of improving them so that they work efficiently at low speeds were considered. Mathematical equations of a low-speed generator designed to obtain electricity from low-speed wind and free-flowing water are presented. At the same time, scientific research was conducted to study, improve, and develop new types of micro-hydroelectric and wind power plants suitable for low-speed generators. As a result of scientific research, an improved wind power device designed for small speed was developed and the results of research were analyzed.

Call rate as an index of nest count in wading bird colonies

Traditional monitoring methods for colonial waterbirds, such as nest counts, can be expensive, time‐intensive, disruptive to nesting birds and limited by colony accessibility. Our study tested the use of acoustic sampling as a colony monitoring technique for three species of colonially nesting herons (Ardeidae) by quantifying the relationship between chick call rate and nest count in colonies. Because acoustic detection can be influenced by soundscape variables, we measured day since colony initiation, body condition index of small heron chicks, nest height, vegetation density and wind speed and evaluated their effects on call rate detection. Generalized linear mixed‐effects models showed that call rate detection increased with daily nest count for all species. Snowy Egret Egretta thula and Tricoloured Heron Egretta tricolour detected call rate was also dependent on environmental, temporal and physiological variables, whereas Great Egret Ardea alba call detection was affected by vegetation density around nests and wind speed. Our study showed that wading bird nest counts can be estimated using acoustic sampling, reducing the need for manual colony surveys, and facilitating long‐term monitoring of wading bird nesting trends, which are important measures of wetland restoration worldwide.

An AEFA-Based Optimum Design of Fuzzy PID Controller for Attitude Control Flywheel with BLDC Motor

A new method for optimizing the fuzzy PID controller, based on an artificial electric field algorithm (AEFA), is proposed in this paper, aiming at improving the stability indicator of the Brushless DC (BLDC) motor for the small satellite attitude control flywheel. The BLDC motor is the basic part of the small satellite attitude control flywheel. In order to accurately control the attitude of the small satellite, a good motor control system is very important. Firstly, the mathematical model of the BLDC motor is established and the BLDC motor speed control system using traditional PID control is designed. Secondly, considering that the small satellite speed control system is a nonlinear system, a fuzzy PID control is designed to solve the shortcomings of the fixed parameters of the traditional PID control. Finally, we find that the control accuracy of the fuzzy PID control will change with the range of the input. Therefore, we introduce the AEFA to optimize fuzzy PID to achieve high-precision attitude control of small satellites. By simulating the BLDC motor system, the proposed fuzzy PID controller based on AEFA is compared with the traditional PID controller and the fuzzy PID controller. Results from different controllers show that the proposed control method could effectively reduce steady state error. In addition, the proposed fuzzy PID–AEFA controller has the better anti-jamming capability.

Study on Process Parameters of Low-power Semiconductor Laser Stripping PTFE Insulating Layer of Aviation Wire

Faced with the increasingly high-quality requirements for the insulation layer stripping at the end of aviation wires, laser wire stripping technology is becoming more and more popular due to its good processing quality and production efficiency. Traditional laser wire strippers generally have problems of bulky size and high control cost and are not suitable for the decentralized processing of large wire harness products. This work explores the feasibility of using a low-power semiconductor laser to strip the PTFE insulating layer of aviation wires. The influence of the parameter changes of each processing factor on the cut morphology of the insulating layer was studied separately. It was found that higher laser power removed more insulating layers per unit of time, but reduced the cutting quality. High laser scanning speed can obtain good insulation cutting quality, but too large or too small scanning speed will reduce the stripping efficiency. Simultaneous improvements in insulation cutting quality and efficiency depend on the right mix of power and scanning speed.

On the global stability of solutions to the compressible Navier–Stokes equation around the Taylor–Couette flow

In this paper, we are concerned with the global stability of solutions to the compressible Navier–Stokes equation in a bounded annular domain. The result confirms the Taylor–Couette flow remains stable with small perturbations in physical literatures when the outer and inner cylinders are in a certain small speed.

On-chip distribution of quantum information using traveling phonons.

Distributing quantum entanglement on a chip is a crucial step toward realizing scalable quantum processors. Using traveling phonons-quantized guided mechanical wave packets-as a medium to transmit quantum states is now gaining substantial attention due to their small size and low propagation speed compared to other carriers, such as electrons or photons. Moreover, phonons are highly promising candidates to connect heterogeneous quantum systems on a chip, such as microwave and optical photons for long-distance transmission of quantum states via optical fibers. Here, we experimentally demonstrate the feasibility of distributing quantum information using phonons by realizing quantum entanglement between two traveling phonons and creating a time-bin-encoded traveling phononic qubit. The mechanical quantum state is generated in an optomechanical cavity and then launched into a phononic waveguide in which it propagates for around 200 micrometers. We further show how the phononic, together with a photonic qubit, can be used to violate a Bell-type inequality.

Rigid wheel/roller on infinite beam or plate attached to Winkler, Pasternak, or elastomeric foundation

If a rigid wheel or roller acts on an infinitely-long beam or a narrow (1-D) plate that is attached to a deformable foundation, point contact or a region of circular contact may occur. The following problems are analyzed: (1) an Euler-Bernoulli beam or an elastica attached to a Winkler foundation; (2) an Euler-Bernoulli beam or an elastica attached to a Pasternak foundation; (3) an Euler-Bernoulli beam attached to a foundation with two different stiffnesses; (4) point contact of a moving wheel with constant speed on an Euler-Bernoulli beam or an elastica attached to a Winkler or Pasternak foundation; (5) point contact of a 1-D plate on an elastomeric foundation; and (6) point contact of a 1-D plate attached to a combined foundation (including Winkler and elastomeric actions). The Euler-Bernoulli beam model tends to predict larger maximum deflections than the elastica model. For small speeds, the maximum deflection increases as the speed increases.

A Simple Method to Calculate the Torque of Magnet-Rotating-Type Axial Magnetic Coupler Using a New Magnetic Equivalent Circuit Model

A magnet-rotating-type axial magnetic coupler (MAMC), namely, a novel axial magnetic coupler with rotatable monopole permanent magnets (PMs), is proposed. The speed of the MAMC can be adjusted by rotating the rotatable PMs mounted on the PM disk, or changing the axial air gap length between the PM disk and the conductor sheet (CS), or combining these methods. In order to analyze the torque performance, the magnetic circuit model of MAMC is established when the rotatable PMs are not parallel to the CS. Specifically, the influence of the induced eddy current is introduced into a new magnetic equivalent circuit (MEC) model. Combined with Kirchhoff’s law, the calculation formula of torque is derived. Moreover, according to Ampere’s law, the formula for calculating the induced eddy current is derived when the rotatable PMs after rotating are not parallel to the CS. Finally, the effectiveness of the proposed model is verified by the finite element method (FEM). The results obtained by the new MEC model proposed are consistent with those obtained by the FEM, and the formula derived is effective in the case of small rotational speed differences, small air gap lengths, and small thicknesses of the CS.

Asymmetric integral barrier Lyapunov function-based dynamic surface control of a state-constrained morphing waverider with anti-saturation compensator

To satisfy wide-speed and long-range mission requirements, morphing aircraft can maintain optimal flight performance by changing their configuration during flight. As an advanced morphing aircraft, a cross-domain morphing waverider can change its wing geometry to maintain a high lift-to-drag ratio across the subsonic, transonic, and supersonic to hypersonic speed ranges. During the highly dynamic morphing process, the trajectory tracking problem of the morphing waverider is characterized by strong coupling, time-varying characteristics, parameter uncertainties, input saturation, and asymmetric state constraints. To address these problems, this paper proposes an asymmetric integral barrier Lyapunov function (AIBLF) based dynamic surface controller consisting of two loops, based on the six-degrees-of-freedom partial decoupled control-oriented model of a symmetric-sweep-wing morphing waverider. Specifically, a virtual control signal of three-axis angular rates is provided by the AIBLF-based flight controller to satisfy the predefined asymmetric constraints of the angle of attack, sideslip angle, and bank angle, combined with a disturbance observer to approximate the disturbances of multiple parameter uncertainties. Subsequently, the desired virtual control signal consisting of three-axis angular rates is derived by passing the above virtual control signal through a nonlinear adaptive filter to avoid the problem of complexity explosion. The control command is generated by the dynamic surface controller and a finite-time anti-saturation compensator to overcome input saturation. Additionally, a nonlinear disturbance observer is applied to estimate the lumped disturbance to realize feedforward compensation. According to the stability analysis, all signals in the closed-loop system are uniformly ultimately bounded while the states remain in the constraint sets. Finally, the performance of the proposed controller is evaluated through extensive and comparative numerical simulations under multiple disturbances. The proposed controller has a small tracking error and high convergence speed and can prevent states from exceeding the given bounds.

Effect of the Sliding Element Surface Topography on the Oil Film Thickness in EHD Lubrication in Non-Conformal Contact.

Under hard operating conditions such as high load, low speed and a lack of a sufficient quantity of lubricant, the sliding pairs could suffer serious damage. One of the methods that improves the tribological performance of sliding elements in hard operating conditions is the appropriate surface creation that keeps lubricating substance in cavities. This article presents the results obtained in experimental investigations of the oil film thickness in lubricated non-conformal contact with a different surface topography of the sliding element. The tests were conducted on a ball-on-disc instrument equipped with colorimetric interferometry. Balls of diameter equaled to 19.05 mm were produced from 100 Cr6 steel. To provide hard operating conditions, the glass disc rotated at small speeds in the range of 0.1-0.2 m/s. The tests were carried out at loads of 20 N and 30 N. As a result, in most cases, the highest minimum and average oil film thickness values were obtained when the surface of steel balls was characterized by high negative asymmetry with mainly shallow cavities and some valleys of great depth compared to the height of the peaks. The modified sliding surface that had better performance comprised a comparatively small number of peaks and the curvature of the peaks were large.