Coefficient of friction of a starved lubricated spur gear pair

Hua iju Liu,Caichao Zhu,Zhangdong Sun,Yuanyuan Zhang,Chaosheng Song 대한기계학회 2016 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.30 No.5

The frictional power loss issue of gear pairs becomes an important concern in both industry and academia due to the requirement of the energy saving and the improvement of power density of gear drives. A thermal starved elastohydrodynamic lubrication model is developed to study the tribological performance of a spur gear pair under starved lubrication conditions. The contact pressure, the film thickness, the temperature rise, the frictional power loss, as well as the coefficient of friction are evaluated by considering the variation of the curvature radius, the sliding/rolling motion, and the load distribution of gear tooth within the meshing period. Effects of lubrication starvation condition, load and speed on the coefficient of friction are studied.

Parametric studies of lubrication performance of a helical gear pair with non-Newtonian fluids

Mingyong Liu,Caichao Zhu,Hua iju Liu,Chenhui Wu 대한기계학회 2016 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.30 No.1

In this paper, Thermal elastohydrodynamic lubrication (TEHL) model of a helical gear pair is proposed to study contact performanceduring the whole meshing period. Effects of working conditions and design parameters on lubrication performance, i.e. film thickness,pressure, temperature, friction coefficient, etc. are investigated. Influence of thermal effect and non-Newtonian effect are evaluatedthrough a detailed study on three characteristic meshing positions. Results show that, the thermal effects and non-Newtonian fluid bothhave significant effects on the lubrication performance of the helical gear pair, especially in high speed, heavy load cases. The effects ofnormal pressure angle, helix angle and module on lubrication performance along the line of action are discussed.

Shakedown analysis of a wind turbine gear considering strain-hardening and the initial residual stress

Haifeng He,Hua iju Liu,Caichao Zhu,Longhua Yuan 대한기계학회 2018 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.32 No.11

Under some heavy-duty conditions, the shakedown state may occur on gears such as those used in a megawatt wind turbine gearbox. The plastic deformation and the residual stress formed within the shakedown process further influence the contact behavior and the service life of the gear. The initial residual stress caused by the heat treatment of the case-hardening gear, together with the strain-hardening constitutive behavior of the material, have a combined effect on the shakedown state. A two-dimensional elastic-plastic contact numerical model was developed for a case-hardened wind turbine gear to study effects of the initial residual stress and the strain-hardening properties. Plastic strain and residual stress are calculated at each loading cycle without the consideration of the tooth friction. The initial yield limit and the hardening modulus of the material were obtained through a tension test on a universal tensile test machine. The initial residual stress distribution was measured with the X ray diffraction method and then embedded in the finite element model. The results show that strain-hardening behavior can significantly improve the shakedown performance, and the larger the hardening modulus is, the less the maximum plastic strain is at the final shakedown state. Initial residual compressive stress is helpful to improve the shakedown performance, while initial residual tensile stress has negative influence on the shakedown performance. As the normal load increases, the influence of the initial residual stress on the shakedown state becomes weakened.

Oil film stiffness and damping in an elastohydrodynamic lubrication line contact-vibration

Yuanyuan Zhang,Hua iju Liu,Caichao Zhu,Mingyong Liu,Chaosheng Song 대한기계학회 2016 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.30 No.7

An elastohydrodynamic lubrication line contact-vibration model is proposed to study the stiffness and damping of the oil film existed in the EHL contact region. An initial mutual approach between interacting surfaces, which deviates from the steady-state balanced position, is assumed under the free contact-vibration to predict the response of the mutual approach. An inertia term, which represents the acceleration of the gap motion, is added to the classical force balance equation to form the equation of motion of the mutual approach. Response of the mutual approach is solved based upon the solving of the contact-dynamic model. The oil stiffness is calculated according to the natural frequency of the response under damped and non-damped conditions, the latter of which represents dry contact conditions. The oil film damping is calculated in terms of the principle of the energy conservation which utilizes the whole history of response compared with the log decrement method. Effect of the normal load, the rolling speed and the amplitude of the regular sinusoidal surface waviness on the oil film stiffness, the contact stiffness and the oil film damping are studied. The study provides an insight on the oil film dynamic characteristics of lubricated contact-vibration problems which appear in gears, bearings, etc. The results show that the oil film damping factor decreases with the increasing normal load as well as the increasing rolling speed. The oil film stiffness increases with the normal load and decreases with the rolling speed. Also, compared to the contact stiffness, the oil film stiffness makes less contribution to the total stiffness. The surface waviness amplitude has little effect on the oil film stiffness and the oil film damping.

Dynamic analysis of the drive train of a wind turbine based upon the measured load spectrum

Caichao Zhu,Shuang Chen,Hua iju Liu,Huaqing Huang,Guangfu Li,Fei Ma 대한기계학회 2014 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.28 No.6

A dynamic model of the drive train of a megawatt wind turbine is proposed in which the blades, the hub, the main shaft, and the speedupgearbox are assumed as flexibilities. The external excitation due to the measured load spectrum and the internal excitations due to thetime-varying mesh stiffness, the transmission errors, and the meshing impacts within the gearbox are considered to predict the dynamicresponse of the system. Results show that the most vibration energy occurs at the speed-up gearbox, followed by the generator, and thenthe main shaft. An experimental remote real-time system is developed to monitor vibration performance of the drive train, with which theaccelerations of components are detected. The experimental results are in accordance with the theoretical results.

Dynamic characteristics and experimental study on a wind turbine gearbox

Liang Xu,Caichao Zhu,Hua iju Liu,Guo Chen,Wei Long 대한기계학회 2019 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.33 No.1

A gearbox is part of the transmission chain of wind turbine, which can increase rotational speed and reduce torque. Dynamic characteristics of the gearbox directly influence the vibration and the service life of the wind turbine system. In this paper, dynamic behaviors of a megawatt level wind turbine gearbox are studied theoretically and experimentally by dividing the gearbox into a transmission sub-system and a body sub-system. The transmission sub-system, i.e., the gear-shaft-bearing sub-system, is coupled with the gearbox body using bearings which are simulated as mass-less springs. The theoretical study applies a finite element model for the gearbox, where the internal excitations are caused by time-varying stiffness, transmission errors and mesh impacts. The time-varying wind load is considered as the external excitation, collected by a remote real-time online test and transformed into load spectrums through the rain-flow counting method. With boundary conditions and working conditions being defined in the finite element model, the natural characteristic analysis and the dynamic response analysis are conducted. Results show that the operating frequencies of the gearbox are far away from the main natural frequencies of the system, thus avoiding resonances. The main vibration components of the gearbox are with meshing frequencies of the second and third gear stage and their multiplication counterparts. Moreover, the greatest vibration occurs at the bearing housing of the high-speed shaft with the root-mean-square value of its vibration speed less than 3.5 mm/s. A test rig is developed and the experimental vibration conditions are monitored by acceleration sensors. The experimental results are in accordance well with the theoretical results. In this way, the theoretical model is validated. The methodology reported in this paper can provide valuable guidance for practical industrial engineers.

Dynamic modeling and analysis for transmission system of high-power wind turbine gearbox

Hongfei Zhai,Caichao Zhu,Chaosheng Song,Hua iju Liu,Guangfu Li,Fei Ma 대한기계학회 2015 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.29 No.10

As a key component to adjust the speed and torque, double-fed speed up gearbox plays a vital role in reliability and stability for thewind turbine system. Considering the base helix angle, normal pressure angle, position angle, rotation of carrier and the mesh of the ringgear and planet gear, a coupled dynamic model for high-power wind turbine gearbox transmission system, which consists of two helicalplanetary stages and one helical gear stage was established using the lumped parameter method in this paper. Numerical integration applyingthe explicit 4/5th order Runge-Kutta algorithm was used to solve the proposed model and the dynamic responses of transmissionsystem were investigated. Results show that the modal frequencies for the system are not coincided with the gear mesh frequencies of thestages. Then, the dynamic mesh forces of the 1st stage in different models are compared and analyzed in frequency domain.

Dynamic analysis of a megawatt wind turbine drive train

Caichao Zhu,Shuang Chen,Chaosheng Song,Hua iju Liu,Houyi Bai,Fei Ma 대한기계학회 2015 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.29 No.5

The dynamic performance of a wind turbine drive train significantly influences the operation of an entire machine. In this work, amegawatt wind turbine drive train is subject to theoretical and experimental dynamic analysis. The method of rigid-flexible couplingmultibody dynamics was applied to develop a dynamic model of the entire drive train. This model was then used to study the naturalcharacteristics of the system. The blades, hub, main shaft, and speed-up gearbox in the dynamic model were modeled as flexible bodies. The potential resonances of the system were detected through Campbell and modal energy distribution analyses. Theoretical results showthat the first-order natural frequency of the system is approximately 1.72 Hz. This frequency represents a torsional vibration mode,Moreover, resonances are not observed within the normal operating speed range of the drive train. An experimental remote real-timesystem was developed to monitor the torsional vibration of the drive train. This vibration was used to measure the torsional vibration ofthe system overall. The experimental results are consistent with the theoretical results.

Multi-objective optimization of a co-rotating twin-screw gear transmission system based on heuristic search

Mingzhu Hu,Haixia Wang,Peitang Wei,Genshen Liu,Lei Zhang,Zhiqiang He,Hua iju Liu 대한기계학회 2023 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.37 No.11

The positive characteristics observed in terms of compact structural sizes and high torque-transmitting capacities have allowed co-rotating twin-screw (CRTS) gear transmissions to be extensively applied to instances requiring small central distances and large power densities. In this study, a multi-objective optimization model for the quick determination of structural parameters of the CRTS gear transmission system is proposed based on the heuristic search and non-dominant sorting genetic algorithm. Results reveal that the optimized scheme with 17 design variables and 18 constrained parameters can be achieved with this model. The system reduces mass by 7.74 % from the original mass of 199.06 kg, while the safety factor variance of the transmission system decreases by 29.3 %. This method applies to other transmission systems with different structures and thus provides general theoretical support for modern gear transmission optimizations.