Numerical Analysis on Residual-Stress in Direct Welded Joint of Long Span Transmission Steel Tower

Abstract The direct welding K-joint of steel tubular members is a kind of usual joint of Steel Tube Tower for Large Crossing of Transmission Lines. However, the dynamic stress-strain and the subsequent formation of residual stress produce in welding process,which are the main factors affecting the load carrying capacity, so it is necessary to research and analyze.Based on thermoelastic-plastic theory, the use of ANSYS Software thermal - structural coupling function and the indirect method, combined with element birth and death technology. The temperature field and stress field calculations have been residual stress and deformation distribution. Providing a reference for direct welding joint of steel tubular members of temperature field, stress and deformation are analizes

Evaluation of algorithms to estimate daily evapotranspiration from instantaneous measurements under all-sky conditions

Instantaneous EvapoTranspiration (ET) can be estimated using a single set of instantaneous observations by polar orbiting satellites during the day. Daily, weekly or monthly total ET is required for hydrological studies and water resources assessment. This requires daily total ET regardless of cloud cover. The daily total ET is usually determined assuming that the evaporative fraction (EF) remains constant during at least the central hours of the day and that the product of EF times the daily total net radiation gives a satisfactory estimate of daily total ET. The impact of cloud cover is rarely discussed. In this paper, we used data collected at two experimental sites in the Heihe River basin in northwestern China: Arou with grassland in an alpine region and Yingke with agricultural crops in a semi-arid region. Two methods were evaluated to determine daily total ET with instantaneous observations: a) self-conservation of evaporative fraction (EF-const); b) assuming the diurnal course of ET is the same sinusoidal function of the time of the instantaneous observation as the solar irradiance (Rs) (ET-Rs). Daily ET calculated with the two methods were evaluated against observed daily values. The results showed that these assumptions did not hold and the accuracy of ET estimates obtained with either method was reduced by: a) diurnal variation of ET and b) the time lag between ET and net radiation under clear skies. Larger errors occurred when applying both methods under cloudy conditions during the growing season, while in the remaining part of the year the impact of cloud cover was lower.</p