Research on nonlinear dynamic characteristics of high-speed gear in two-speed transmission system.

The working performance and service life of the two-speed transmission system directly affects the performance and service life of helicopters and other equipment. One of the main tasks of the two-speed transmission system research is to improve its dynamic characteristics. For the two-speed transmission system in high-speed gear, a purely torsional nonlinear dynamic differential equation set considering the number of planetary gears, backlash, and clutch dynamic load is established by using the lumped parameter method, and the equations are dimensionless. Then the dimensionless differential equation set is solved by using the variable step-size fourth-order Runge-Kutta method, and the phase diagram and Poincare diagram of high-speed gear are obtained. By changing the dynamic friction coefficient of the friction clutch and the backlash of the gear pair, the influence of parameter change on the nonlinear dynamic characteristics of the system is analyzed. The results show that, with the increase of excitation frequency, the system has experienced single cycle, quasi-cycle, chaos, and double cycle, then changed from double cycle to chaotic motion, and then changed from chaotic motion to double cycle and single cycle motion in turn, and found the path to chaos. In the low-frequency band, reducing the friction coefficient of the friction clutch can reduce vibration amplitude; In the middle-frequency band, reducing the friction coefficient will make the system tend to unstable vibration. In the high-frequency band, it is a single-cycle movement, which is not affected by friction coefficient.

Simultaneous methanogenesis and denitrification coupled with nitrifying biofilm for high-strength wastewater treatment: Performance and microbial mechanisms.

A combined system consisting of an upflow blanket filter (UBF) and a moving-bed biofilm reactor (MBBR) was developed for the simultaneous removal of organic matters and ammonia from high-strength wastewater. With a constant COD of approximately 2000 mg/L and ammonium nitrogen in a series of concentrations (e.g., 50, 200 and 400 mg/L in stages I to III) of the influent wastewater, the removal efficiencies of COD, ammonium nitrogen and total nitrogen reached 96.10%-98.19%, 100%, and 79.12%-82.15%, respectively. With the increase of influent ammonia nitrogen concentration, the specific methanogenic activity of the UBF granules decreased significantly, while the specific denitrification rates of the UBF granules and specific nitrification rates of the MBBR biofilms increased significantly. Microbial community analysis showed that Methanobacterium and Methanosaeta were the dominant methanogens in the UBF granules, while Candidatus Competibacter, Thauera and Acinetobacter were identified as dominant denitrifiers. In addition, nitrifiers were enriched in MBBR biofilms at 11.33% and 13.87% of the average abundance of Nitrosomonas and Nitrospira, respectively, at stage III (influent ammonium at 400 mg/L, COD/NH4+-N =  5). The ecological network analysis, including full-networks and sub-networks, indicated that the interactions between methanogens and denitrifiers in the UBF granules were strong when the influent ammonium concentration reached 400 mg/L. No intensive interactions were observed among the functional bacteria in the MBBR biofilms over the entire operation. Overall, this study provides a new strategy for the application and construction of efficient biological processes to achieve simultaneous removal of organic matter and nitrogen for high-strength wastewater treatment.

Achieving simultaneous nitrification, denitrification, and phosphorus removal in pilot-scale flow-through biofilm reactor with low dissolved oxygen concentrations: Performance and mechanisms.

In this pilot-scale study, a flow-through biofilm reactor (FTBR) was investigated for municipal wastewater treatment. The removal efficiencies for ammonium, total nitrogen, total phosphorus, and chemical oxygen demand were 87.2 ± 17.9%, 61.1 ± 13.9%, 83.5 ± 11.9%, and 92.6 ± 1.7%, respectively, at low dissolved oxygen concentrations (averaged at 0.59 mg/L), indicating the feasibility and robustness of the FTBR for a simultaneous nitrification, denitrification, and phosphorous removal (SNDPR) process. The co-occurrence network of bacteria in the dynamic biofilm was complex, with equivalent bacterial cooperation and competition. Nevertheless, the bacterial interactions in the suspended sludge were mainly cooperative. The presence of dynamic biofilms increased bacterial diversity by creating niche differentiation, which enriched keystone species closely related to nutrient removal. Overall, this study provides a novel FTBR-based SNDPR process and reveals the ecological mechanisms responsible for nutrient removal.