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Fly ash-based paste-filling mining can not only effectively control land subsidence and increase the coal recovery rate, but it also solves the problem of fly ash accumulation in coal-fired power plants. The release of ammonia from fly ash-based filling paste contaminates the air environment of the coal mine filling face, necessitating immediate remediation. This study proposes a new method of using ultrasound to promote the release of paste ammonia. Through the ultrasonic treatment of fly ash slurry, the ultrasonic time (A), ultrasonic power (B) and solid-liquid ratio (C) are used as investigation factors. The results show that the ammonia release rate increases first and then decreases with the increase of ultrasonic time, ultrasonic power and solid-liquid ratio, and reaches the maximum when the ultrasonic time, ultrasonic power and solid-liquid ratio are 30 min, 80 W and 1∶10, respectively. The response surface experiment is conducted on the basis of single factor test to establish a regression model. The optimal experimental parameters are determined by response surface optimization. The results show that the order of influencing factors is: A > B > C, AB > AC > BC. The optimum experimental parameters for ammonia removal are as follows: ultrasonic time is 32 min, ultrasonic power is 80 W, and solid-liquid ratio is 1∶7.7. Through verification, it is found that there is only a relative error of −1.6% between the measured value and the predicted value. The optimized experimental parameters are used to treat the fly ash to prepare the filling paste to determine the ammonia release amount. It is found that the ammonia release amount of the paste is reduced by 95.94%. The ammonia release rate increases by 84.02%, and the uniaxial compressive strength of the paste at 3 d and 28 d increases by 185.00% and 86.50%, respectively. The slump, bleeding rate and setting time are decreased, and the number of harmful pores in the paste is reduced, so that the porosity is decreased from 33.58% to 28.13%. It provides a new method for the ammonia release treatment of the fly ash-based filling paste.

At present， the traditional Archard wear model is mostly used to study the influence of wear on the dynamic characteristics of gears， without considering the lubrication characteristics of gears, and the main research objects are mostly straight gears. In order to make up for the shortage of research on helical gear， the wear process under mixed elastohydrodynamic lubrication is numerically simulated. An eight-degree of freedom dynamics model of helical gear is established to investigate the influence of tooth surface wear on gear dynamic characteristic. The gear fatigue test is carried out on a helical gearbox test rig to validate the numerical results. The results show that the wear mainly occurs on the region close to the tooth root and tooth tip， and the maximum wear occurs at the tooth root due to the relative high sliding-to-roll ratio. The variation of the amplitudes of the gear meshing frequency and its harmonics demonstrates that the wear causes an increase in gear vibrations. The experimental results show a good agreement with the numerical results， which implies the study can provide a reliable theoretical basis for the prediction and fault diagnosis of helical gear wear.

Tooth surface wear and bearing clearance are important factors affecting gear system dynamics, in order to reveal the influence of tooth wears and bearing clearance on the dynamics of gear system, a six-degree-of-freedom bending-torsion coupled model is established, which takes into account the tooth surface wear, bearing clearance, friction and backlash. The dynamic differential equations are solved by Runge-Kutta method and the dynamic response of the system is obtained. The results show that when the gear changes in unworn phase to mild wear phase, the amplitude of dynamic transfer error decreases and the vibration is weakened. With the increment of tooth surface wear, the amplitude of dynamic transmission error increases and the vibration is strengthened when the gear reaches severe wear phase. With the increase of bearing clearance, the peak-to-peak value of dynamic transfer error will increase and resonance phenomenon will appear, the stability of system will decrease.