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In conjunction with global warming, the frequency and intensity of typhoons in the Pearl River Estuary region are increasing annually, and coastal cities are becoming more vulnerable to compound disasters triggered by upstream flooding, typhoons, and astronomical tide surges, seriously threatening the lives and properties of people in the delta region. Quantitative analysis of the degree of variability of each factor associated with a compound flood event and accurate assessment of the magnitude of the compound flood event strongly impact the efficacy of coastal city responses aimed at disaster prevention and damage mitigation. In this study, focused on the Pearl River Estuary area, the tide levels at Sanzao station, wind speeds at Macao station, and daily maximum the maximum daily flow at Sanshui and Makou stations spanning 30 years from 1988 to 2017 were used to characterize the flood magnitude, typhoon magnitude, and astronomical tide magnitude of compound flood events in the Pearl River Estuary area. Data were screened using the annual maximum method. Based on the generalized additive model (GAMLSS) and the time-varying copula function, the encounter combinations of composite flood events of different levels and their main controlling factors were investigated. The results show that: 1) the main factors influencing initiation and magnitude of composite flood events in the Pearl River estuary area are non-consistent sequences that display interdependence. The time-varying copula model constructed in this study is more suitable for studies of composite floods than the traditional constant parameter copula model. Copula models are most applicable to studies of the encountered characteristics of multiple elements contributing to compound flood events and are most in line with actual situations. 2) Compared with the joint return period of traditional constant copula parameters, the period of occurrence of typical compound flood events in the Pearl River Estuary from 1988 to 2017 continuously shortens with time, the probability of occurrence increases, and the probability of future occurrence of extreme compound flood events is strengthening. The trend in which the return period of compound flood events is shortening with higher grades is accelerating. 3) Compound flood events throughout the Pearl River estuary area are more affected by typhoons and astronomical tides and less affected by water flow. When the return period of the three factors is one in 5 years, water flow causes the smallest increase in the co-occurrence return period; i.e., the influence of astronomical tide and typhoon on the scale of upstream flooding, composite flood events of typhoon, and astronomical tide is proportionately larger. Thus, composite flood events in the Pearl River estuary area are mainly impacted by typhoons with higher wind speeds. When the return period of the three factors is one in 10, 20, and 50 years, the increase in the co-occurrence return period caused by flow changes the most; and when the return period of the three factors is one in 10, 20, and 50 years, the acceleration of the co-occurrence return period caused by flow is the largest. When the three factors have a larger return period, astronomical tide exerts proportionately greater influence on the scale of the composite flood event of upstream flood, typhoon, and astronomical tide.

To avoid the circularly shift range on multi-range hydro-mechanical continuously variable transmission（HMCVT）,taking the multi-range hydro-mechanical CVT of the wheel tractor of YTO-400 as example,the transmission characteristic of multi-range hydro-mechanical CVT is analyzed.The causes of the circularly shift range are researched,and eliminating mechanism is presented.The effectiveness of principle of averting the circularly shift range is simulated by using the theory of Finite State Machine,which employs the actual and theoretical displacement ratio,output speeds of multi-range hydro-mechanical CVT as the control parameter.The research results indicate that,the volumetric efficiency of the pump-motor system is the important reason for the factor of efficiency difference of the circularly shift range.By controlling the increase of the theory displacement ratio of the multi-range hydro-mechanical CVT,the actual displacement ratio is maintained at the same time,which effectively avoids the cycle change of the multi-range hydro-mechanical CVT.A theoretical foundation for the development of multi-range hydro-mechanical CVT control system is provided.

The cutting principle of epicycloid bevel gears is analyzed,the operation mode and characteristics of five-axis with four-linkage epicycloid tooth bevel gear CNC machine are introduced,the feasibility of cutting epicycloid bevel gears based on the four-axis linkage is proposed and analyzed. The equivalent transformation for the processing mode of CNC machine and traditional mechanical machine is completed by analyzing the distinctions of mathematical models between the two kinds of machine. The tooth surface equation of the gear processed of the CNC machine is obtained. The relations among motion axes real-time motion coordinates are analyzed,and real-time coordinates of each motion axis of CNC machine are calculated. The ideal contact region is obtained by the gear cutting processing and rolling-inspection test. The correctness of the theory of cutting cycloid bevel gears based on four-axis linkage is verified and a theoretical support for the domestic independent research and development of spiral bevel gear processing equipment is provided.

In the current severe situation of continuous shortage of energy resources, the global energy structure is undergoing profound changes. New energy is the main direction of the energy transformation, and the iterative innovation of new energy technology is an important means to promote the transformation of the global energy industry. From the perspective of new energy technology, this paper mainly introduces wind power generation technology and photovoltaic power generation technology. Firstly, the basic principles of wind power and photovoltaic power generation technology are described; Secondly, it counts the current status of the global wind power and photovoltaic market in 2019 and the change trend of installed capacity during 2001-2019, further analyze the development status of these two new energy technologies; finally, it summarizes the development status of new energy technology and makes a prospect for its future development.

In order to explore the risk assessment method of the multi-unit nuclear power plant site, this paper selects the dual-unit plant nuclear site to analyze lose off-site power accident. By combining and improving the single-unit ET/FT model, to establish the dual-unit ET/FT model. From the analysis of the accident sequence, it can be concluded that the common cause failure of equipment is the main challenge faced by the dual-units. Especially the RPC sub-channel in the reactor protection system and the failure of emergency diesel engine circuit breaker. As can be seen from the high proportion of core CD occurring simultaneously in both uints, it has a great significance to study the risk of mult-units sites.

When working at light load operation（ such as sowing,weeding,transplanting,harvesting,etc.）,the traditional tractor has the problem of low power utilization ratio and high fuel consumption. Through analyzing the best economy index and its influence factors of tractor,a kind of economical shift rule is put forward,which based on the minimum fuel consumption rate of tractor. It requires not only the operating point of the engine located at the lowest fuel consumption zone,also need the tractor traction efficiency to be higher. For this reason,the slip rate of driving wheel is introduced to constitute economical shift rule and its control strategy,which takes the speed,drive wheel speed,engine speed,throttle opening and transmission gear ratio of tractor as control parameters. The fuzzy control is used to identify the driving intention,and the driver intervention on the shifting process is introduced to the transmission control,which can reflect the actual working environment of the tractor. Taking the YTO LA2004 wheeled tractor which equipped with automatic power shift transmission as investigative subject,the simulation analysis of light load working condition is carried out. The results show that the gear and throttle opening change with traction load,which ensure that the working point of the engine is in a low fuel consumption zone. The fuel consumption rate of tractor is reduced and the stability of the actual speed of the tractor is achieved. A theoretical basis for the development of automatic transmission control system of tractor is provided by the research.

In order to realize the control for multi- range hydro- mechanical continuously variable transmission（ HMCVT） in tractor,the fuzzy adaptive PID control for multi- range HMCVT in tractor is studied.The transmission system dynamics model of tractor and fuzzy adaptive PID control model are established based on Matlab / Simulink platform. According to the actual deviation of the actual vehicle speed and the target vehicle,the fuzzy control method is adopted to automatically adjust the PID control parameters,so as to achieve the purpose of control. The fuzzy adaptive PID control simulation on the tractor dynamics model and comparison with the PID control simulation. The results show that the stronger adaptive ability and robustness of fuzzy adaptive PID control of tractor.