Large Speed Ratio Research Articles

Analysis of Mechanical Parameters of Asymmetrical Rolling Dealing with Three Region Percentages in Deformation Zones.

A series of mathematical models were proposed to calculate the roll force, torque and power for cold strip asymmetrical rolling by means of the slab method, taking the percentages of the forward-slip, backward-slip and cross-shear zones into account. The friction power, plastic work and total energy consumption can be obtained by the models. The effects of variable rolling parameters—such as the speed ratio, entry thickness, friction coefficient and front and back tension—on the process of asymmetrical rolling are analyzed. In all cases, an increase in speed ratio leads to an increase in friction work and its proportions. The increase in entry thickness and deformation resistance causes both friction work and plastic deformation work to increase. The proportion of friction work decreases with increasing deformation resistance, entry thickness, front tension and back tension. In the circumstances of a thin strip being rolled with a large speed ratio, the proportion of friction work could exceed that of plastic deformation work. The concept of a threshold point of friction work was proposed to explain this phenomenon. As an example, threshold points T1, T2, T3 with the effect of the entry thickness and S1, S2, S3 with the effect of the friction coefficient have been obtained by computation. Finally, the experiment of the strip asymmetrical rolling was conducted, and a maximum error of 9.7% and an RMS error of 5.9% were found in the comparison of roll forces between experimental measurement values and calculated ones.

Analysis of Aerodynamic Characteristics of Vertical Axis Wind Turbine (VAWT) Based on Modified Double Multiple Stream Tube Model

To further improvement of the aerodynamic performance simulation model accuracy of Vertical Axis Wind Turbine (VAWT), based on the traditional double multi-flow tube theoretical model, the aerodynamic parameters of the airfoil before and after stall are modified by the Lanchester method. Prand model is used to modify the aspect ratio of the airfoil under the condition of the small angle of attack before stall. Viterna Corrigan model is used to modify the aspect ratio, lift and drag coefficients of the airfoil under the stall. And a relaxation factor is introduced to correct the induction factor, also to improve the iterative non-convergence of the simulation under the condition of large tip speed ratio. The simulation results match the experimental data very well. Based on this new aerodynamic performance analysis method, the influence of blade tip speed ratio, blade number, blade chord length, rotor radius, and incoming wind speed on power coefficient and tangential force coefficient is studied, which can provide a reference for the design of aerodynamic performance parameters of the wind turbine.

Asymmetric loading multi-roller planetary traction drive: Modeling and performance analysis

The development of high-speed motors has stimulated the demand for high-speed reducers. Aiming at the lack of high-speed reducer and the NVH problem of high-speed gear transmission, an asymmetric loading multi-roller planetary traction drive (AL-MPTD) scheme is proposed to fill the gap of traction drive with large speed ratio, zero spin and self-adaptively loading. By comprehensively considering the effects of axis tilt, elastic deformation, rough surface contact and elastohydrodynamic lubrication (EHL), this paper establishes a more refined theoretical analysis model and provides the analysis method under the condition of the non-smooth surface and non-ideal contact. This paper also studies the transmission performance of AL-MPTD from the aspects of traction ability, transmission efficiency and so on. The results obtained by theoretical calculations show that AL-MPTD can be considered to achieve zero-spin transmission in the entire operation range. In addition, the loading mechanism achieves a good self-adaptively loading effect, effectively reducing the sliding of the AL-MPTD and improving its efficiency, with the peak of the global sliding coefficient being only 0.402% and the maximum transmission efficiency of 98.5%.

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.

Analysis of Dynamic Characteristics of the Multistage Planetary Gear Transmission System with Friction Force

Multistage planetary gear transmission system has been widely utilized in engineering practice due to the salient characteristics, such as high bearing load and large speed ratio. This paper addresses a two-stage planetary gearbox and establishes a system coupling torsional dynamical model which considers the time-varying mesh stiffness, friction forces, and interstage coupling factors. Meanwhile, the friction and lubrication states are classified to comprehensively analyze the calculation of friction coefficients under different conditions. Considering the time-varying influence of friction on the tooth surface under the condition of fluid lubrication, the vibration response under parametric excitation is solved by a numerical method. A multistage planetary transmission test bench is built in the back-to-back form so as to test the vibration of the two-stage planetary gearbox. It shows that the simulation results of the dynamical model are consistent with the test data. Consideration of the calculation of friction on the tooth surface and the friction coefficients is helpful for the establishment of the more accurate dynamical model and lays the foundation for the structural design, fault diagnosis, and dynamic optimization of the multistage planetary gear transmission system.

Forces and stress for a two-stage planar sine-wave movable tooth drive

Planar movable tooth drives are compact in structure and simple in processing technology. However, the speed ratio of the single-stage drive is small, whereas the size of the double-stage drive is large. To obtain a planar movable tooth drive with small size and large speed ratio, a two-stage planar movable tooth drive with integrated structure is proposed. For it, the quasi-static force analysis is completed, and the equations of the force distribution and output torque for the drive are derived. According to Hertz’s theory of point contact, the equation for the contact stress in the drive is given. Using these equations, the distribution of forces and output torque in the drive is studied. Changes of forces and torque distribution with main parameters are revealed. The contact stress of the drive is calculated under a given load. The finite element analysis software is used to simulate the contact stress of the drive, and the theoretical calculation is verified.

Novel Design of Speed-increasing Compound Coupled Hydromechanical Transmission on Tidal Current Turbine for Power Generation

A key topic discussed in the energy industry has long been how to steadily convert tidal energy into mechanical energy and then electrical power. Gear transmissions are widely used in mechanical systems for electrical power production, converting low-speed input rotation into high-speed output rotation to drive a generator rotor. However, to achieve a large speed ratio and stepless speed change, gear transmissions must be accompanied by complex structures and high-precision manufacturing technology. The application of gear transmissions in tidal energy power generation must therefore come at a high cost. A large speed ratio and stepless speed-changing capability are precisely the two essential elements of the mechanical system for tidal energy power generation. In this paper, a new type of speed-increasing CCHMT has been proposed that is capable of achieving large transmission ratio speed change between the blade rotor input and the generator rotor output. It is also capable of changing the input speed steplessly into a stable output speed suitable for power generation and for high-quality electric power production. To verify the feasibility of using a speed-increasing CCHMT in tidal energy, a simulation model has been established for the wave power at the input end. With the assistance of a volumetric speed-control system and hydraulic accumulator, the speed-increasing CCHMT can stably transmit disordered input speed. Simulation results show that the output rotational speed gained a stable amplification ratio within 20 and 30. The mean square error of the rotational speed was controlled to within 29 and the output speed is limited within 85% to 115% of the average output speed, thus ensuring the quality of power generation.

Effect of Wind Tunnel Blockage on the Performance of a Horizontal Axis Wind Turbine with Different Blade Number

Blockage corrections for the experimental results obtained for a small-scale wind turbine in a wind tunnel are required in order to estimate how the same turbine would perform in real conditions. The tunnel blockage is defined as the ratio of the wind turbine swept area to the wind tunnel cross-section area. Experimental measurements of the power coefficient were performed on a horizontal-axis wind turbine with two rotors of diameter equal to 2 m and different numbers of blades, namely three and five. Measurements were carried out for different tip speed ratios in the closed circuit open test section wind tunnel of the University of Perugia (Italy). The obtained experimental results were compared with the numerical ones carried out in free conditions by using a CFD approach based on the steady-RANS method with the SST k-ω turbulence model, adopting the multiple reference frame (MRF) strategy to reduce the computational effort. The comparison showed that the maximum value of blockage, which is reached in the asymptotic limit at very large tip speed ratio (TSR) values, does not depend appreciably on the number of blades. A higher number of blades, however, makes the occurrence of the maximum blockage come earlier at lower TSRs.

Elastic hydrodynamic lubrication analysis for a sine movable tooth drive

The sine movable tooth drive has small radial dimension such that the heat, caused by friction, becomes an important factor in deciding its load-carrying ability. It is important to determine the amount of tooth lubrication in order to reduce the heat caused by the friction. This study provides equations for the meshing performance and provides the forces for the sine movable tooth drive. Using these equations, the minimum oil film thickness for the drive system is investigated. Results show that the minimum film thickness between the movable tooth and input shaft or shell changes periodically along the input shaft rotation angle. A large movable tooth radius and a movable tooth rotation radius could increase the film thickness between the movable tooth and the input shaft or the shell. In addition, a large speed ratio could increase the film thickness between the movable tooth and the input shaft, but this would also decrease the film thickness between the movable tooth and the shell. A large sine amplitude could increase the film thickness between the movable tooth and the input shaft, but this does not change the film thickness between the movable tooth and the shell. Under normal operation speeds, the hydrodynamic lubrication condition occurs between the movable tooth and the input shaft, and the partial membrane hydrodynamic state occurs between the movable tooth and the shell.

Investigations of the static and dynamic characteristics of water-lubricated hydrodynamic journal bearing considering turbulent, thermohydrodynamic and misaligned effects

Abstract A misaligned thermohydrodynamic (THD) model considering turbulent-flow is presented to predict the performance of water-lubricated hydrodynamic journal bearing (WHJB). The load capacity, frictional power loss, flow rate, mid-plane pressure distribution, translational, tilting and coupled translational-tilting dynamic coefficients versus the rotary speed, eccentricity ratio and tilting angle are analyzed; quantitative comparisons between models considering and without considering turbulent, THD and misaligned effects are given. Results show that the turbulence improves the load capacity while the THD effect decreases it; the THD effect reduces the frictional power loss significantly while the turbulent effect is weak; at large rotary speed and eccentricity ratio, the THD and turbulent effects on the dynamic coefficients should be fully considered at both of aligned and misaligned conditions.

Consensus formation in opinion dynamics with online and offline interactions at complex networks

Nowadays, with the development of information communication technology and Internet, more and more people receive information and exchange their opinions with others via online environments (e.g. Twitter, Facebook, Weibo, and WeChat). According to eMarketer Report [Worldwide Internet and Mobile Users: eMarketer’s Updated Estimates and Forecast for 2015–2020 (eMarketer Report). Published October 11, 2016, https://www.emarketer.com/Report/Worldwide-Internet-Mobile-Users-eMarketers-Updated-Estimates-Forecast-20152020/2001897 ).], by the end of 2016, more than 3.2 billion individuals worldwide will use the Internet regularly, accounting for nearly 45% of the world population. By contrast, the other half of the global population still obtain information and regularly exchange their opinions in a more traditional way (e.g. face to face). Generally, the speed at which information spreads and opinions are exchanged and updated in an online environment is much faster than in an offline environment. This paper focuses on jointly investigating the challenge of consensus formation in opinion dynamics with online and offline interactions. Without loss of generality, we assume the speed at which information spreads and opinions are exchanged and updated in an online environment is [Formula: see text] times as fast as in an offline environment. We demonstrate that the update speed ratio in mixed online and offline environments (i.e. [Formula: see text]) strongly impacts the consensus formation at complex networks: a large update speed ratio of online and offline environments (i.e. [Formula: see text]) makes it difficult for all agents to reach consensus in opinion dynamics. Furthermore, these effects are often further intensified as the number of online participating agents increases.

Quasi-static analysis of forces and stress for a novel two-step movable tooth drive

ABSTRACTFor sine movable tooth drive, the movable tooth number must be increased to obtain large speed ratio of the drive which increases largely radial size of the drive. Here, a novel two-step movable tooth drive is proposed. The drive can realize small size and large speed ratio simultaneously. For the two-step movable tooth drive, 3D design was done; the forces and the contact stress in the drive system were investigated; results show that the maximum force on the second step drive depends on radius of the movable teeth, size parameters of the second step drive, and radius of the sine ball track in the first step drive; the contact stresses between the meshing elements change periodically, the contact stress between the movable teeth and cap end is the maximum which can be taken as design factor for the load-carrying ability of the drive system.

Two-step sine movable tooth drive

For sine movable tooth drive, the movable tooth number must be increased to obtain large speed ratio of the drive which increases largely radial size of the drive. Here, a two-step sine movable too...

Development of an Analytical Unsteady Model for Wind Turbine Aerodynamic Response to Linear Pitch Changes

A simple unsteady blade element analysis is used to account for the effect of the trailing wake on the induced velocity of a wind turbine rotor undergoing fast changes in pitch angle. At sufficiently high tip speed ratio, the equation describing the thrust of the element reduces to a first order, nonlinear Riccti's equation which is solved in a closed form for a ramp change in pitch followed by a constant pitch. Finite tip speed ratio results in a first order, nonlinear Abel's equation. The unsteady aerodynamic forces on the NREL VI wind turbine are analyzed at different pitch rates and tip speed ratio, and it is found that the overshoot in the forces increases as the tip speed ratio and/or the pitch angle increase. The analytical solution of the Riccati's equation and numerical solution of Abel's equation gave very similar results at high tip speed ratio but the solutions differ as the tip speed ratio reduces, partly because the Abel's equation was found to magnify the error of assuming linear lift at low tip speed ratio. The unsteady tangential induction factor is expressed in the form of first order differential equation with the time constant estimated using Jowkowsky's vortex model and it was found that it is negligible for large tip speed ratio operation.

Torque for an electromagnetic harmonic movable tooth drive system

The output torque of the mechanical harmonic drive is large but the teeth should be produced on the flexible ring which is a difficult task. To overcome the difficulty, the authors proposed an electromagnetic harmonic movable tooth drive system in which a large output torque can be obtained meanwhile the teeth are removed from the flexible ring. Here, the operating principle of the electromagnetic harmonic movable tooth drive system is illustrated. The forces on the flexible ring and the movable teeth are analyzed. The equation of the output torque for the drive system is developed. Using the equation, the output torque of the drive system and its changes along with the system parameters are investigated. The results show that large coil current, large speed ratio, large flexible ring radius and small flexible ring length, small gas gap should be selected to obtain a large output torque. The results are useful for the further study and application of the drive system.

Developing the full-field wind electric generator

A conventional wind electric generator generally works with a fixed normal rated power (NRP). Moreover, a gearbox for providing such generator the quasi-constant rotational speed to reach its maximum working efficiency is required. It is well known, an electric generator with large NRP also receives relatively small working efficiency while the input power is too small due to it needs gearbox with relatively larger speed ratio to reach the required rotational speed. In general, the larger the speed ratio of gearbox, the larger the transmission loss. In other words, if the mechanical resistance is considered, the conventional wind electric generator actually loses a lot of energy in the slow wind speed field. To avoid the use of gearbox with large speed ratio in the slow wind speed field, a special generator with changeable NRP should be used. This work presents a special wind electric generator using the multi-layer magnetic cutting electric generator, which effectively works in full wind field with the help of the changeable NRP and is already patented by our CCT laboratory. The developed multi-layer magnetic cutting electric generator is the so-called disk or axial flux permanent magnet electric generator with multi-layer structure, which is mainly composed of the rotational axis, the rotational magnet frameworks, and the fixed electric coil frameworks. In process, the numbers of the active fixed electric coil frameworks are changeable due to the different numbers of the active fixed electric coil frameworks has the different NRP. In other words, the developed multi-layer magnetic cutting electric generator can automatically adjust its NRP to match various wind speeds and always reach the maximum working efficiency in the full wind field. The results show that the total working efficiency of the developed full-field wind electric generator has increased ca. 3%.

Effect of rolling parameters on plate curvature during snake rolling

In order to predict the plate curvature during snake rolling, FE model was constructed based on plane strain assumption. The accuracy of the FE model was verified by the comparison between the plate curvature conducted by FE model and experiment respectively. By using FE model, the effect of offset distance, speed ratio, reduction, roll radius and initial plate thickness on the plate curvature during snake rolling was investigated. The experimental results show that, a proper offsetting distance can efficiently decrease plate curvature, however an excessive offsetting distance will increase plate curvature. A larger speed ratio, reduction will cause a large plate curvature, however a larger roll radius has effect to reduce plate curvature. Plate which undergoes a larger reduction and plate with a larger initial thickness always need a larger offset distance to keep the plate the minimum plate curvature, but for a larger roll radius a smaller offset distance is needed.

Friction and Diapycnal Mixing at a Slope: Boundary Control of Potential Vorticity

Abstract Although atmospheric forcing by wind stress or buoyancy flux is known to change the ocean’s potential vorticity (PV) at the surface, less is understood about PV modification in the bottom boundary layer. The adjustment of a geostrophic current over a sloped bottom in a stratified ocean generates PV sources and sinks through friction and diapycnal mixing. The time-dependent problem is solved analytically for a no-slip boundary condition, and scalings are identified for the change in PV that arises during the adjustment to steady state. Numerical experiments are run to test the scalings with different turbulent closure schemes. The key parameters that control whether PV is injected into or extracted from the fluid are the direction of the geostrophic current and the ratio of its initial speed to its steady-state speed. When the current is in the direction of Kelvin wave propagation, downslope Ekman flow advects lighter water under denser water, driving diabatic mixing and extracting PV. For a current in the opposite direction, Ekman advection tends to restratify the bottom boundary layer and increase the PV. Mixing near the bottom counteracts this restratification, however, and an increase in PV will only occur for current speeds exceeding a critical value. Consequently, the change in PV is asymmetric for currents of the opposite sign but the same speed, with a bias toward PV removal. In the limit of a large speed ratio, the change in PV is independent of diapycnal mixing.

Research on Automatic Mechanical Transmission Shift Schedule

In order to solve some problems existing in the process of shift for automatic mechanical transmission vehicles such as great shift impact, engine noise and low shift success ratio between gears which have large speed ratio differences, a new method used to determine shift schedule was put forward in this paper. In this method, shift schedule and shift quality were synthetically considered, the downshift schedule was obtained based on the same optimization target with upshift schedule and proper downshift delay with shift impact and shift time controlled in a predetermined range. An optimal power shift schedule was developed with this method, and the performance of the automatic mechanical transmission vehicle controlled by this method was compared with that of controlled by skilled driver. The results indicate that the former obviously improved the performance of the vehicle with the shift quality controlled in a predetermined range.

Transmissionless Selectively Aligned Surface-Permanent-Magnet BLDC Motor in Hybrid Electric Vehicles

An axial-flux permanent-magnet brushless motor is designed with variable stator alignment of independent stators, thus allowing field weakening via a controllable and variable generated-voltage constant. This feature is particularly valuable in vehicle traction motors with large constant-power speed ratio, where there is also a strong desire to eliminate the need for gear changes and keep the overall size of the motor drive as small as possible. The advantage of high pole count as applied to this technique is discussed, and the simulation impact on motor drive kilovoltampere, efficiency, gradability, acceleration, and maximum speed over typical driving cycles is shown.