Greenhouse is an important place for crop growth, and it is necessary to control the temperature of growing environment in winter. In addition, the root temperature underground also plays a decisive role for plants gr...Greenhouse is an important place for crop growth, and it is necessary to control the temperature of growing environment in winter. In addition, the root temperature underground also plays a decisive role for plants growth. Adopting underground heating to increase the temperature can effectively improve the yield of crops. The objective of our study was to model the heat transfer of greenhouse underfloor heating which is analyzed and simplified based on the FLUENT software by changing the several important factors that affect the temperature distribution: pipe diameter, pipe spacing, laying depth, supplied water temperature and flow rate, as boundary conditions to simulate the changes of the soil temperature field around the winter night environment. Researching the temperature distribution of the greenhouse, the soil surface and the plant root layer under the different parameters and the basic rules of the heating system are summarized. The results show that the water supply temperature, pipe spacing and diameter of the pipe has a greater impact on the ground and room temperature, and the laying depth has greater impact on the temperature uniformity of the ground, the velocity of water in pipe has little impact on the uniformity of ground temperature.展开更多
提出多载荷时间历程的外推方法,给出车下设备承载结构疲劳试验载荷谱编制方法。基于载荷时间历程的雨流计数矩阵,利用二维核密度估计方法(Kernel density estimation,KDE),提出在多载荷时间历程输入条件下的外推方法;应用平均应力修正...提出多载荷时间历程的外推方法,给出车下设备承载结构疲劳试验载荷谱编制方法。基于载荷时间历程的雨流计数矩阵,利用二维核密度估计方法(Kernel density estimation,KDE),提出在多载荷时间历程输入条件下的外推方法;应用平均应力修正公式、累积损伤理论和等效损伤准则,根据外推载荷数据,给出疲劳试验程序谱的编制方法;结合动车组车下设备线路测试数据对外推方法进行验证,编制了车下设备承载结构疲劳试验程序谱,并分别使用疲劳试验程序谱和振动测试数据对承载结构进行疲劳强度计算。数据外推结果表明:多载荷时间历程外推方法计算的损伤与实际载荷损伤误差为3.6%,大的扩展倍数下KDE可以给出低周、大幅值载荷;疲劳强度计算结果表明:由于KDE外推产生了大幅值载荷,疲劳试验程序谱计算的损伤比振动测试数据计算的损伤增加了43.8%,所以,在进行疲劳试验载荷谱编制时,需要计算可能出现的大幅值载荷。此研究为其他结构程序载荷谱的编制提供借鉴案例。展开更多
文摘Greenhouse is an important place for crop growth, and it is necessary to control the temperature of growing environment in winter. In addition, the root temperature underground also plays a decisive role for plants growth. Adopting underground heating to increase the temperature can effectively improve the yield of crops. The objective of our study was to model the heat transfer of greenhouse underfloor heating which is analyzed and simplified based on the FLUENT software by changing the several important factors that affect the temperature distribution: pipe diameter, pipe spacing, laying depth, supplied water temperature and flow rate, as boundary conditions to simulate the changes of the soil temperature field around the winter night environment. Researching the temperature distribution of the greenhouse, the soil surface and the plant root layer under the different parameters and the basic rules of the heating system are summarized. The results show that the water supply temperature, pipe spacing and diameter of the pipe has a greater impact on the ground and room temperature, and the laying depth has greater impact on the temperature uniformity of the ground, the velocity of water in pipe has little impact on the uniformity of ground temperature.
文摘提出多载荷时间历程的外推方法,给出车下设备承载结构疲劳试验载荷谱编制方法。基于载荷时间历程的雨流计数矩阵,利用二维核密度估计方法(Kernel density estimation,KDE),提出在多载荷时间历程输入条件下的外推方法;应用平均应力修正公式、累积损伤理论和等效损伤准则,根据外推载荷数据,给出疲劳试验程序谱的编制方法;结合动车组车下设备线路测试数据对外推方法进行验证,编制了车下设备承载结构疲劳试验程序谱,并分别使用疲劳试验程序谱和振动测试数据对承载结构进行疲劳强度计算。数据外推结果表明:多载荷时间历程外推方法计算的损伤与实际载荷损伤误差为3.6%,大的扩展倍数下KDE可以给出低周、大幅值载荷;疲劳强度计算结果表明:由于KDE外推产生了大幅值载荷,疲劳试验程序谱计算的损伤比振动测试数据计算的损伤增加了43.8%,所以,在进行疲劳试验载荷谱编制时,需要计算可能出现的大幅值载荷。此研究为其他结构程序载荷谱的编制提供借鉴案例。
