High Speed Ratio Research Articles

Chip breakage in silk microfibre production using elliptical vibration turning

To overcome the precision limitation and environmental impact of current chemical-based production methods for manufacturing silk microfibres used for targeted drug delivery, this paper presents a high-precision, scalable, eco-friendly mechanical machining approach to produce such microfibres in the form of discontinuous chips obtained through elliptical vibration turning of silk fibroin film using a diamond tool. The length and waist width of fabricated microfibres can be precisely controlled. As each vibration cycle will produce one silk microfibre, complete and deterministic chip breakage becomes an essential and challenging task in this approach due to its unique two-phase structure. Thus, the hybrid FE-SPH numerical simulations and machining experiments were conducted to gain a pioneering and in-depth exploration of the chip-breaking mechanism in this process. It was found that applying a low depth ratio (ratio of the nominal depth of cut to the tool path vertical amplitude) and a high horizontal speed ratio (the nominal cutting speed versus the critical workpiece velocity) could effectively reduce the average tool velocity angle (the angle from the deepest cut to the tool exit point along the cutting direction). A smaller angle would enhance the diamond tool's shearing action and led to the reduction of hydrostatic pressure in the cutting zone and a consequent decrease in the ductility of silk fibroin due to its unique structure dominated by beta-sheet crystallites. The above adjustments collectively facilitated chip breakage. This paper, therefore, established a governing rule for the controlled and repeatable formation of microfibres based on the average tool velocity angle for the first time and revealed that the cutting chips would undergo complete and deterministic breakages once the angle approached below 22.6°. On this basis, the high-precision and scalable manufacturing of silk microfibres with precisely controllable length and waist width was ultimately achieved.

Investigation of transmission characteristic for harmonic magnetic gears considering dynamic eccentricity using magnetic equivalent circuit

AbstractHarmonic magnetic gears (HMGs) have the advantage of lubrication‐free, high speed ratio and high torque density, which make it an attractive solution for safety critical applications. Due to eccentricity caused by machining and assembly, HMG suffers from dynamic eccentricity (DE) in operation, however, its effect on HMG performance is still unknown. Transmission characteristic of HMG under DE is studied. First, a magnetic equivalent circuit (MEC) model of HMG is proposed to build the magnetic coupling torque analytically, and the geometry of air gap is analysed parametrically to derive its equivalent reluctances. Flux density and coupling torque can be acquired by solving MEC equations. The accuracy of the MEC model is verified by finite element method. To study the transmission characteristic, an electromechanical coupling simulation framework for HMG is constructed, motion trajectories of rotors are investigated in case of DE, the output torque in locked‐rotor condition and speed response in continuous operation can be derived by simulation. It is found that torque ripples that have the same frequency with input rotor are induced by DE; the results are then verified in the experiment. This paper provides a theoretical guidance for the design and condition monitoring of HMG.

A multi-layer network security system to enhance autonomous mobile carrier in smart manufacturing system

Nowadays, wireless communication technology is widely used and accepted by industry to improve the flexibility and efficiency of smart factories. The Wi-Fi 6 high-speed communication technology is integrated into the autonomous mobile carrier (AMC) in this research to make it possible for interacting with many other machines at the same time with high transmission speed, high reliability, and low packet loss ratio. The indoor positioning accuracy of autonomous mobile carrier is enhanced by Ultra-wideband (UWB) technology, so that it can then move and complete multi-station automation processing tasks more smoothly. Finally, a multi-layer network system with security function to protect all the equipment in the manufacturing environment is proposed and developed in this research. The threats that may come with the use of wireless network technology can then be avoided. In this research, an overall system framework with multi-layer network security mechanism is developed and introduced into the autonomous mobile carrier, and the enhanced autonomous mobile carrier is applied into a manufacturing field for performance test. The results show that the enhanced autonomous mobile carrier can maintain positioning accuracy within ±100 mm, wireless network packet transmission latency rate less than 5 ms, and wireless network packet transmission loss rate less than 1%. It shows that this autonomous mobile carrier system benefits from UWB and Wi-fi 6 communication technology and has a very high potential for realizing smart manufacturing applications.

Lower extremity isokinetic strength characteristics of amateur boxers.

Aim: Sufficient strength and dynamic stability of the lower limbs are essential for improving punching force and preventing injury in amateur boxers. However, there are still no comprehensive reports on the isokinetic knee strength of boxers with different performance levels. The current study aimed to profile the isokinetic muscle strength of flexion and extension of the knee in boxers, as well as bilateral, unilateral, and functional ratios, and investigate the variation in these muscle strength characteristics associated with different performance levels. Methods: Boxers were divided in two performance groups, elite (five males and four females) and non-elite groups (five males and four females). Muscle strength of the knee was determined via an IsoMed2000 device. Parameters examined included peak torque of the hamstring (H) and quadriceps (Q) during concentric (con) and eccentric (ecc) contractions at low (60°/S), medium (180°/S), and high (240°/S) speed and bilateral ratios (BLs), unilateral ratios (ULs), and functional ratios of dominant (D) and non-dominant limbs. Results: In all angular velocities, the peak torque of H and Q was stronger in the elite group than in the non-elite group. ULs were lower in the elite group than in the non-elite group in Hcon/Qcon at 180D (p < 0.01) and 180ND (p < 0.05) and in Hecc/Qecc at 60D, 180D (p < 0.05) and 240D (p < 0.01). The elite group had higher BLs than the non-elite group in Hcon at 60°/S (p < 0.05) and Qcon at 180°/S (p < 0.05). The non-elite group had a higher functional ratio than elite boxers in Hecc/Qcon at 180D and 240D (p < 0.01). Conclusion: Elite boxers had stronger knee strength in con and ecc contractions. All boxers had normal Hecc/Qecc and Hcon/Qecc. Hcon/Qcon and Hecc/Qcon were abnormal at lower angular velocity. Elite boxers had higher BLs and lower ULs, indicating that they are at a higher risk of injury.

Design and Backdrivability Modeling of a Portable High Torque Robotic Knee Prosthesis With Intrinsic Compliance For Agile Activities.

High-performance prostheses are crucial to enable versatile activities like walking, squatting, and running for lower extremity amputees. State-of-the-art prostheses are either not powerful enough to support demanding activities or have low compliance (low backdrivability) due to the use of high speed ratio transmission. Besides speed ratio, gearbox design is also crucial to the compliance of wearable robots, but its role is typically ignored in the design process. This paper proposed an analytical backdrive torque model that accurately estimate the backdrive torque from both motor and transmission to inform the robot design. Following this model, this paper also proposed methods for gear transmission design to improve compliance by reducing inertia of the knee prosthesis. We developed a knee prosthesis using a high torque actuator (built-in 9:1 planetary gear) with a customized 4:1 low-inertia planetary gearbox. Benchtop experiments show the backdrive torque model is accurate and proposed prosthesis can produce 200 Nm high peak torque (shield temperature <60°C), high compliance (2.6 Nm backdrive torque), and high control accuracy (2.7/8.1/1.7 Nm RMS tracking errors for 1.25 m/s walking, 2 m/s running, and 0.25 Hz squatting, that are 5.4%/4.1%/1.4% of desired peak torques). Three able-bodied subject experiments showed our prosthesis could support agile and high-demanding activities.

Pemodelan Numerik Aliran Angin di Sekitar Gedung Tinggi Menggunakan Metode RANS Standard K-ε dengan Program OpenFOAM

Amplified wind loads around buildings could induce structural failure, thus making it important to understand the behavior of fluid flow between buildings. In this study, the analysis is performed using RANS, a computational fluid dynamics (CFD) simulation with faster computation time compared to other methods. OpenFOAM, an open-source software, is used to run the simulations. This study used a structured mesh with standard RANS k − ε turbulence model. Four symmetrical buildings with a scale of 1: 420 are used as the model of this study. Numerical modelling of different computational domain size and different degrees of fineness of the meshing is simulated to determine margin of errors. The result indicates that changes in computational domain has a significant effect on CFD analysis in lowering the error value in area with high flow speed ratio (U/U0&gt; 1) to reach the acceptable error limit. Contrastingly, changes in the degree of fineness of the meshing do not give a significant change in error value. A relatively coarse meshing with fast computation time could give a similar result as A fine meshing model with longer computation time.

Contact stress analysis of a spur gear using Lewis and Hertz theory

The rapid development of the automobile and aircraft industries has made applying gear technology necessary. Gears offer the benefits of efficiency, reliability, simplicity and a higher speed ratio with power transmission. However, they cannot transmit power over a long period, are more expensive when compared to belts and chain drives and requires continuous lubrication. They are used for transmitting high load in gear tools. The gear teeth fail when subjected to a high load beyond a certain limit. A deciding factor in gear design is the amount of stress developed on the contact surface of the mating gears. This paper deals with contact stress analysis of spur gear. The theoretical analysis presented in this paper aims to analyse rolling bearing contacts based on the principles of the Hertz and Lewis equations. A 3D domain-based finite element method was used to calculate the stresses between the contact surfaces of the structure. Contact analysis was performed using ANSYS Workbench software to figure out the deformation and optimum stress developed on the teeth of the gear. The simulation results indicated that the stress distribution on the gear contact surface has a maximum value of 144.82 MPa, while the deformation is at a maximum value of 0.01676 mm. The safety factor indicates the maximum level of 15, indicating the safety of the design.

Research Progress of p-Type Oxide Thin-Film Transistors.

The development of transparent electronics has advanced metal–oxide–semiconductor Thin-Film transistor (TFT) technology. In the field of flat-panel displays, as basic units, TFTs play an important role in achieving high speed, brightness, and screen contrast ratio to display information by controlling liquid crystal pixel dots. Oxide TFTs have gradually replaced silicon-based TFTs owing to their field-effect mobility, stability, and responsiveness. In the market, n-type oxide TFTs have been widely used, and their preparation methods have been gradually refined; however, p-Type oxide TFTs with the same properties are difficult to obtain. Fabricating p-Type oxide TFTs with the same performance as n-type oxide TFTs can ensure more energy-efficient complementary electronics and better transparent display applications. This paper summarizes the basic understanding of the structure and performance of the p-Type oxide TFTs, expounding the research progress and challenges of oxide transistors. The microstructures of the three types of p-Type oxides and significant efforts to improve the performance of oxide TFTs are highlighted. Finally, the latest progress and prospects of oxide TFTs based on p-Type oxide semiconductors and other p-Type semiconductor electronic devices are discussed.

Effect of roll speed ratio on the texture and microstructural evolution of an FCC high-entropy alloy during differential speed rolling

A very coarse-grained (335 μm) Fe 41 Mn 25 Ni 24 Co 8 Cr 2 high-entropy alloy with a single FCC phase was cold rolling to a 80% reduction in thickness using the differential speed rolling technique with various speed ratios (SRs) ranging between 1 and 4. As the SR was increased, the volume fraction of the region of high-density micro-shear bands increased to accommodate the higher shear strain. At SR = 4, the entire thickness of the sheet was covered with micro-shear bands, and ultrafine (sub)grains with a size of 1.4 μm were uniformly formed along the shear bands. A continuous dynamic recrystallization (CDRX) mechanism occurred during rolling, and a higher SR accelerated the CDRX process. During conventional rolling (at SR=1), a brass { 110 } 〈 112 〉 orientation texture with minor components of S { 123 } 〈 634 〉 and Cu { 112 } 〈 111 〉 orientations developed. At higher SRs, shear texture developed as the main type, while the development of rolling texture was suppressed. The microstructure at SR=4 obtained after annealing at 973 K showed a fully recrystallized microstructure composed of a five times smaller grain size (4 μm) with a higher intensity of γ fiber texture compared with that prepared by conventional rolling. The samples processed with high SRs exhibited better tensile properties compared with the conventionally rolled sample in terms of strength and ductility after annealing. The current results demonstrate that by using differential speed rolling with a high SR, one can achieve a significantly finer and more homogeneous microstructure, stronger shear texture, and superior tensile mechanical properties for an FCC high-entropy alloy compared to that obtained by conventional rolling. The strength of the as-rolled and annealed samples was quantitatively explained by considering the contribution of grain size and dislocation density to strengthening.

Collisionless jet expanding into vacuum from a circular aperture

Collisionless flows expanding into a vacuum from a circular slit are investigated using the gaskinetic theory. Both accurate and approximate expressions to the plume fields along a centerline and a constant radius are obtained, including the density, velocity components, and translational temperature. Special non-dimensional parameters such as the exit semi-opening angle, gas speed ratio at the exit, and positions are included in these expressions. Particle simulations with the direct simulation Monte Carlo method are performed to validate the above results. These expressions are complex and may need computers for evaluations; however, the cost is minor when compared to particle simulations. With the assumptions of a high or low exit speed ratio and small exit angle, simple explicit expressions for properties along the centerline and a constant radius are obtained. The investigations also find out that the cosine law relations can provide fast and crude estimations, but it is not recommended to use the cosine law relation to compute collisionless plume flowfields with a large exit speed.

Influence of active flow modulation on conjugate mixed convection inside a vented cavity

The current work is an attempt to examine the performance of mixed convection heat transfer within a vented square cavity with dynamic flow modulation via a rotating heat conducting circular cylinder. External cold air is forcibly imposed through an inlet opening located at the bottom of the left wall of the cavity, while an exit port is placed at the top of the right wall. Isoflux heating is applied on the right wall, while the remaining solid wall boundaries are assumed insulated. A solid circular cylinder serving as dynamic flow modulator and rotating in counter-clockwise direction is placed near the bottom portion of the right heated wall. The governing mass, momentum, and energy equations representing the mathematical model of the present problem are solved in non-dimensional form using Galerkin finite element method. Parametric simulation is performed for wide range of governing parameters (Reynolds, Grashof, and Richardson numbers) within mixed convection regime under different dynamic conditions of the rotating cylinder characterized by the ratio of cylinder peripheral speed to mean inflow air velocity. Effects of the above governing parameters are analyzed through the visualization of streamline and isotherm plots, and the distribution of average and normalized Nusselt numbers of the heated wall, average fluid temperature in the cavity and the variation of pumping work required. Findings of the present study reveal that maximum heat transfer can be obtained by simultaneous increase of Reynolds and Grashof numbers, while careful selection of speed ratio of the rotating cylinder is necessary to obtain the optimum results within mixed convection regime. About 5.3% higher heat transfer enhancement is observed at highest speed ratio and higher Reynolds and Grashof numbers compared to the same for having stationary cylinder.

The Effect of Rotating Speeds on the Cavitation Characteristics in Hydraulic Torque Converter

Hydraulic torque converter is a kind of high speed rotating machine using viscosity hydraulic oil as working medium, and its internal flow field is very complex. Thereby cavitation can occur easily in the working process, resulting in severe degradation of torque converter performance, noise, vibration and even failure. In order to reveal the effect of rotating speeds on the cavitation characteristics, a full flow passage geometry and a computational fluid dynamics (CFD) model with cavitation were developed to analyze the flow behavior in the torque converter. The results show that cavitation occurs when the speed difference between pump and turbine exceeds 1400 rpm for the basic model torque converter, which could be used as a useful indicator for the occurrence and degree of severity of flow cavitation. The increase of pump rotating speed or the decrease of speed ratio will intensify cavitation, which reduces the hydraulic transmission capacity and efficiency by over 20%, and seriously alters the shape, size, vapor volume fraction and region of cavitation bubbles. In extreme cases, more than 80% of the area on the suction side of the stator blade could be covered by cavitation bubbles. Moreover, the increase of pump rotating speed also changes the critical cavitation number and extends the cavitation range towards high speed ratio conditions not previously affected. These findings can provide guidance on how to choose the operating conditions of the hydraulic torque converter and how to improve its hydrodynamic performance and stability.

Mechanisms of an innovative hybrid arc welding process in enhancing joint penetration and weld property control through resistive and induction heat

Low costs (material, energy and time), high joint properties are the eternal pursuit of modern welding. In this paper, mechanisms of an innovative high frequency electric cooperated arc welding (HFAW) in enhancing welding productivity (joint penetration) and weld property control were comprehensively investigated. The process properties and weld mechanisms of this method were systematically compared with that of the traditional GMAW welding under typical process parameters. The results showed that 4.8 mm joint with an large aspect ratio of 4 was achieved by single pass HFAW at a high welding speed (15 mm/s) and a low welding heat input (reduced 1/3 than the traditional GMAW). The research on weld property control shows that the microstructure of weld zone and heat affected zone (HAZ) in the HFAW joint was much smaller than that in the GMAW joint under optimal parameters. The width of each zone in the HAZ, thermal cycle parameters such as elevated temperature holding time and cooling rate can be regulated independently by the high frequency electric heat input ratio. Such regulation is of great significance for high strength steel welding, which needs to control the welding thermal cycle process accurately. Combined with three-dimensional solid reconstruction of liquid filler metal, the mechanism of the HFAW in enhancing joint penetration was demonstrated. An interesting “self-tracking heating” of the high frequency current was found. The cutting-edge of the liquid metal was violently heated and more than half of the weld in thickness direction was achieved by a novel ultra-speed “interfacial tension driving penetrating” weld forming mechanism, which promises the HFAW high welding speed and large aspect ratio on the premise of satisfactory welding quality.

Stress analysis of marine gears considering 3D mixed lubrication-contact state

Marine transmission gears usually have large size, and often experience severe working conditions, such as heavy load, large transmission power and high speed ratio, together with the effect of surface asperities, which cause coexisting lubrication-contact state and seriously stress concentration, and further may lead to micro-pitting and fatigue failure. In this paper, the subsurface stress prediction model of the timing transmission spur gears of marine engine is developed, together with considering real 3D machined surface roughness and mixed lubrication-contact state. Results show, when the contact bodies with perfect elastic behavior,the maximum von Mises stress appears on the surface and no longer shows regular distributions along the line of action because of the 3D roughness.The transverse turned surface can reduce the subsurface stress greatly, the shaved and ground surfaces cause large subsurface stress and high-pressure area on the surface. The influence of surface roughness on the stress state is increased under the special conditions of low velocity and high power density, and the contact state is greatly improved by optimizing the parameters of tooth width. Effects of different materials indicate nylon-nylon contact surfaces has the smallest maximum stress compared with that in other four pairs. However, nylon-nylon contact surfaces have the highest friction coefficients, which can easily lead to severe wear or scuffing failures.

Static and dynamic characteristics and stability analysis of high-speed water-lubricated hydrodynamic journal bearings

The purpose of this paper is to analyze the influence of turbulent, inertia, and misaligned effects on the static and dynamic characteristics and stability of high-speed water-lubricated hydrodynamic journal bearings. Based on the Navier–Stokes equation, the mixing-length theory, and the essential assumption that the velocity profile is not strongly affected by inertia force, the fluid lubrication model with turbulent, inertia, and misaligned effects is established, and then the stability analysis of bearings is carried out based on the equation of motion with four degrees of freedom. The model is solved by the finite difference method and the numerical results are compared under different operating conditions. The results show that the turbulent effect greatly increases the load capacity, power consumption, stiffness and damping coefficients, and stability of bearings, and the inertia effect significantly increases the volume flow rate of bearings, and the misaligned effect increases the load capacity, stiffness and damping coefficients, and stability of bearings. In high rotary speed and moderate eccentricity ratios, the influence of the inertia effect on the load capacity, stiffness coefficients, and stability cannot be neglected.

Analysis of Turbulent Flow on Tidal Stream Turbine by RANS and BEM

Nowadays, concerns arise because of the depletion of fossil fuel resources that forced scientists to develop new energy extraction methods. One of these renewable resources is tidal energy, where Iran has this potential significantly. There are many ways to obtain the kinetic energy of the fluid flow caused by the moon’s gravitational effect on seas. Using horizontal axis tidal turbines is one of the ways to achieve the kinetic energy of the fluid. Since this type of turbine has similar technology to horizontal axis wind turbines, they may be an appropriate choice for constructing a tidal power plant in Iran. This paper presents the numerical simulation and momentum method of a three-bladed horizontal axis tidal turbine. To validate the thrust and power coefficients for a fixed pitch angle at the blade tip speed ratio of 4 to 10 are compared with experimental results. In this modelling, the rotating geometry simulation has been used. Results show that using a numerical method and blade element momentum, we can predict the horizontal axis tidal turbine’s thrust with an error of less than 10%. The numerical method has better accuracy in higher speed ratios, and it is appropriate to predict the behaviour of fluid in collision with turbines and its wake effects.

Microstructure, Texture and Mechanical Properties of Mg-6Sn Alloy Processed by Differential Speed Rolling.

The effect of shear deformation introduced by differential speed rolling (DSR) on the microstructure, texture and mechanical properties of Mg-6Sn alloy was investigated. Mg-6Sn sheets were obtained by DSR at speed ratio between upper and lower rolls of R = 1, 1.25, 2 and 3 (R = 1 refers to symmetric rolling). The microstructural and textural changes were investigated by electron backscattered diffraction (EBSD) and XRD, while the mechanical performance was evaluated based on tensile tests and calculated Lankford parameters. DSR resulted in the pronounced grain refinement of Mg-6Sn sheets and spreading of basal texture as compared to conventionally rolled one. The average grain size and basal texture intensity gradually decreased with increasing speed ratio. The basal poles splitting to transverse direction (TD) or rolling direction (RD) was observed for all Mg-6Sn sheets. For the as-rolled sheets, YS and UTS increased with increasing speed ratio, but a significant anisotropy of strength and ductility between RD and TD has been observed. After annealing at 300 °C, Mg-6Sn sheets became more homogeneous, and the elongation to failure was increased with higher speed ratios. Moreover, the annealed Mg-6Sn sheets were characterized by a very low normal anisotropy (0.91–1.16), which is normally not achieved for the most common Mg-Al-Zn alloys.

Research on Performance Test System of Space Harmonic Reducer in High Vacuum and Low Temperature Environment

The harmonic reducer, with its advantages of high precision, low noise, light weight, and high speed ratio, has been widely used in aerospace solar wing deployment mechanisms, antenna pointing mechanisms, robot joints, and other precision transmission fields. Accurately predicting the performance of the harmonic reducer under various application conditions is of great significance to the high reliability and long life of the harmonic reducer. In this paper, a set of automatic harmonic reducer performance test systems is designed. By using the CANOpen bus interface to control the servo motor as the drive motor, through accurately controlling the motor speed and rotation angle, collecting the angle, torque, and current in real time, the life cycle test of space harmonic reducer was carried out in high vacuum and low temperature environment on the ground. Then, the collected data were automatically analyzed and calculated. The test data of the transmission accuracy, backlash, and transmission efficiency of the space harmonic reducer were obtained. It is proven by experiments that the performance data of the harmonic reducer in space work can be more accurately obtained by using the test system mentioned in this paper, which is convenient for further research on related lubricating materials.

All-optical computing circuits half-subtractor and comparator based on soliton interactions

The speed limitations of electronic processors have created a demand for a high bandwidth and ultra-fast computing circuits. By replacing the electric logic gates with photonic ones, a high bandwidth and fast photonic microprocessor will be achieved which will overcome the speed limitations of electronic circuits. Digital photonic logic circuits are key elements in the next generation optical computers. In this paper, all-optical logical half-subtractor and digital comparator are designed based on spatial optical solitons. These computational gates are designed simply with repulsive and attractive interactions of three inphase and out of phase spatial optical solitons in a bulky nonlinear Kerr medium. With tuning the phase input solitons and exploiting inphase and out of phase soliton interactions a high functional circuit with broad operational bandwidth, high switching speed and high contrast ratio between ON/OFF states is achieved by a simple structure.

Development of China Light-Duty Vehicle Test Cycle

Driving cycles provide a basis for vehicle development and calibration and also serves as the foundation for energy consumption and emissions certification of vehicles. This paper presents the China Light-Duty Vehicle Test Cycle (CLTC) developed by the China Automotive Technology & Research Center (CATARC). First, the important steps and technical routes toward the CLTC development process are summarized. Second, the specific CLTC development process is presented in detail, including the data acquisition and data analysis procedures, weighting factor development and driving cycle construction. Then, the main driving characteristics of the New European Driving Cycle (NEDC), the Worldwide Harmonized Light-Duty Vehicles Test Cycle (WLTC), the Federal Test Procedure (FTP-75), the CLTC and the actual collected data are compared. The CLTC has low average speed, a high idle speed ratio and more frequent acceleration and deceleration characteristics. Finally, 70 vehicles are tested based on the NEDC, WLTC, and CLTC according to their legislative procedures in the vehicle emission laboratories of the CATARC and the manufacturers. The results show that the CLTC’s fuel consumption is much higher than that of the NEDC and WLTC, and CLTC can effectively reflect the actual fuel consumption of users.