فهرست مطالب h. cheng

The current issue of global warming is prominent, and there are many factors that affect global temperature changes. Therefore, how to correctly judge the relationship between each influencing factor and global temperature changes and accurately find out the main reasons of global temperature rise which are the problems that must be considered and solved to alleviate global warming at present. According to previous official data, this paper proposed a correlation analysis method based on principal components to comprehensively analyze the relationship between natural disaster factors, human factors, and global temperature changes, and find out the main reasons that affect global temperature rise. Compared with traditional research methods, the new method provided in this paper can still remain scientific and accurate calculation results while reducing computational dimensions. The experimental results showed that in the relationship between natural disasters and global temperature changes, the average correlation coefficient of the principal component represented by biological disasters and geological disasters was the highest at 0.6097 and a test value of p<0.05, indicating a significant positive correlation between them and global temperature. However, the correlation coefficient of the principal component represented by floods and storms was negative, indicating a negative correlation between them and global temperature. In exploring the main factors affecting global temperature rise, both the total global population and the total global CO2 emissions had a significant positive correlation with global temperature. Among them, the average correlation coefficient of the total global population was the highest at 0.9972, and its weight also was the highest at 26.42%. Therefore, this indicates that the total global population is the most important factor affecting global temperature rise. This study can provide reference for countries to make decisions in response to global warming.

The impact of varying the tip clearance of each rotor on the performance of a counter-rotating axial compressor has been investigated based on numerical simulations. The main purpose was to investigate the sensitivity to the tip clearance of each of the two individual rotors and the corresponding aerodynamic mechanisms associated with the performance variation in this compressor. The results indicated that both the total pressure ratio and the efficiency decreased as the tip clearance was increased, and the sensitivity curve for peak efficiency for both rotors was found to be an approximately linear negative relationship with increasing tip clearance. The variations of peak efficiency and stability margin of Rotor 2 were more sensitive to changing tip clearance than Rotor 1. An optimum combination of tip gaps existed for this compressor, i.e. 0.5τ for Rotor 1 and 0.25τ for Rotor 2 (where τ represents the nominal tip clearance value). At this optimum configuration, the peak efficiency and stability margin were improved by 0.63% and 29.4%, respectively. The location of the onset of the tip leakage vortex was found to be shifted downstream when the tip clearance increased. The nature of the tip leakage flow for each rotor was found to be influenced by the variation of tip clearance in the other rotor. Rotor 2 showed a more significant impact on Rotor 1. Additionally, varying the combination of tip clearances changed which of the two rotors was the first to stall.