A coupling thermo-mechanical model of wheel/rail in rolling-sliding contact is put forward using finite element method. The normal contact pressure is idealized as the Hertzian distribution, and the tangential force p...A coupling thermo-mechanical model of wheel/rail in rolling-sliding contact is put forward using finite element method. The normal contact pressure is idealized as the Hertzian distribution, and the tangential force presented by Carter is used. In order to obtain thermal-elastic stress, the ther-mal-elastic plane stress problem is transformed to an elastic plane stress problem with equivalent fictitious thermal body force and fictitious boundary distributed force. The temperature rise and ther-mal-elastic stress of wheel and rail in rolling-sliding are analyzed. The non-steady state heat transfer between the contact surfaces of wheel and rail, heat-convection and radiation between the wheel/rail and the ambient are taken into consideration. The influences of the wheel rolling speed and wear rate on friction temperature and thermal-elastic stress are investigated. The results show the following： ① For rolling-sliding case, the thermal stress in the thin layer near the contact patch due to the friction temperature rise is severe. The higher rolling speed leads to the lower friction temperature rise and thermal stress in the wheel; ② For sliding case, the friction temperature and thermal stress of the wheel rise quickly in the initial sliding stage, and then get into a steady state gradually. The expansion of the contact patch, due to material wear, can affect the friction temperature rise and the thermal stress during wear process. The higher wear rate generates lower stress. The results can help under-stand the influence of friction temperature and thermal-elastic stress on wheel and rail damage.展开更多
Based on the theoretical and empirical research of economists in the past decade,this article intends to address the following issues about the effects of China’s economy on the global economy:What impact does China...Based on the theoretical and empirical research of economists in the past decade,this article intends to address the following issues about the effects of China’s economy on the global economy:What impact does China’s fast-growing economy have on the global trade flow and trade pattern?Does China’s sustained export growth pose a significant competitive threat to some countries and regions(particularly the developing countries in East Asia,Latin America and Africa)?In the midst of fast economic growth driven by its reform and opening,China has become the largest FDI recipient among all developing countries and regions.Does the FDI received by China have"transfer effects"on other countries(especially in terms of FDI inflows into neighboring countries)?展开更多
In the design of cool-supply system, the temperature rise of cooling water pipeline is usually determined by experience, but not calculated. In gcnacral, the temperature rise is 1℃ for cooling water supply pipes and ...In the design of cool-supply system, the temperature rise of cooling water pipeline is usually determined by experience, but not calculated. In gcnacral, the temperature rise is 1℃ for cooling water supply pipes and 0.5℃ for return pipes. The calculated results of TR according to classical approaches of thermodynamics are smaller than the tested data. This paper has analysed the causes that affect the temperature rise in detail. The heat transfer of pipe wall and the pressure drop in pipeline are two main factors. Besides, the paper gives another five factors as follows: 1. The heat radiation from the sun to pipelines; 2. The increased heat transfer due to the water condensation around the outer wall of pipelines; 3. For the underground pipelines, the existing unstable heat transfer; 4. The effects of insulation material as well as the installed quality of insulation layer; 5.The additional cool loss produced by the accessories, such as valves, brace etc. According to the above analysis, the paper展开更多
基金This project is supported by National Natural Science Foundation of China (No. 50375129)Foundation for Author of National Excellent Doctoral Dis-sertation of China (FANEDD) (No. 200248)Program for Changjiang Scholars and Innovative Research Team in University, China (No. IRT0452).
文摘A coupling thermo-mechanical model of wheel/rail in rolling-sliding contact is put forward using finite element method. The normal contact pressure is idealized as the Hertzian distribution, and the tangential force presented by Carter is used. In order to obtain thermal-elastic stress, the ther-mal-elastic plane stress problem is transformed to an elastic plane stress problem with equivalent fictitious thermal body force and fictitious boundary distributed force. The temperature rise and ther-mal-elastic stress of wheel and rail in rolling-sliding are analyzed. The non-steady state heat transfer between the contact surfaces of wheel and rail, heat-convection and radiation between the wheel/rail and the ambient are taken into consideration. The influences of the wheel rolling speed and wear rate on friction temperature and thermal-elastic stress are investigated. The results show the following： ① For rolling-sliding case, the thermal stress in the thin layer near the contact patch due to the friction temperature rise is severe. The higher rolling speed leads to the lower friction temperature rise and thermal stress in the wheel; ② For sliding case, the friction temperature and thermal stress of the wheel rise quickly in the initial sliding stage, and then get into a steady state gradually. The expansion of the contact patch, due to material wear, can affect the friction temperature rise and the thermal stress during wear process. The higher wear rate generates lower stress. The results can help under-stand the influence of friction temperature and thermal-elastic stress on wheel and rail damage.
文摘Based on the theoretical and empirical research of economists in the past decade,this article intends to address the following issues about the effects of China’s economy on the global economy:What impact does China’s fast-growing economy have on the global trade flow and trade pattern?Does China’s sustained export growth pose a significant competitive threat to some countries and regions(particularly the developing countries in East Asia,Latin America and Africa)?In the midst of fast economic growth driven by its reform and opening,China has become the largest FDI recipient among all developing countries and regions.Does the FDI received by China have"transfer effects"on other countries(especially in terms of FDI inflows into neighboring countries)?
文摘In the design of cool-supply system, the temperature rise of cooling water pipeline is usually determined by experience, but not calculated. In gcnacral, the temperature rise is 1℃ for cooling water supply pipes and 0.5℃ for return pipes. The calculated results of TR according to classical approaches of thermodynamics are smaller than the tested data. This paper has analysed the causes that affect the temperature rise in detail. The heat transfer of pipe wall and the pressure drop in pipeline are two main factors. Besides, the paper gives another five factors as follows: 1. The heat radiation from the sun to pipelines; 2. The increased heat transfer due to the water condensation around the outer wall of pipelines; 3. For the underground pipelines, the existing unstable heat transfer; 4. The effects of insulation material as well as the installed quality of insulation layer; 5.The additional cool loss produced by the accessories, such as valves, brace etc. According to the above analysis, the paper
