Effects Of Solar Radiation On Thermal Analysis Of Arch Dams And Engineering Application

A major reason for downstream cracks of high arch dams is excess thermal loads from recent research, but the research of thermal loads require more efforts. As a series of high arch dams have been built or are under construction in China, so how to compute the accurate thermal loads of arch dams at the operation stage and to evaluate the safety degree against cracking are very important for safty operation of high arch dams. Based on 3D finite element model of high arch dams, the present dissertation develops a method to compute the accurate 3D solar radiation distribution on the dam. Inverse and prediction thermal analysis are performed incorporating with large number of prototype monitoring data of Ertan arch dam. The phenomenon of downstream cracks of Ertan arch dam is analyzed in the dissertation. Laxiwa arch dam is taken as an example for 3D solar radiation computation method. Thermal and stress analyses for Laxiwa are carried out at the operation stage. The influence of surrounding terrain and dam orientation to temperatures and stresses are studied. This study includes:1. Based on 3D finite element model of arch dams, a computation procedure of dam surface solar radiation is presented considering shade of surrounding terrain and structure itself. ASHRAE clear sky model and ray-tracing algorithm are employed in the procedure. The advantages are requiring only a few monitoring data, high accuracy, good efficiency and wide scope of application.2. The thermal boundary conditions of arch dam are analyzed. An inverse thermal analysis procedure using conjugate gradient method to compute solar radiation adjusting coefficient is presented based on the prototype monitoring temperatures. Comparisons of computation results and measured temperature data demonstrate that the presented method taking solar radiation effects into account has fair good accuracy and good convergence. 3. A linear static stress analysis of Ertan arch dam is performed considering self weight, hydro pressure and thermal loads. The computation results of deformation due to thermal load and variance of reservoir level agree well with the instrumentation records at Ertan Arch Dam. It can be concluded from the stress analysis that thermal loads play the dominant role in downstream face cracking of Ertan Arch Dam. Alteration rock under the right bank is also an important factor for cracks.4. The distribution regularity of solar radiation for Laxiwa arch dam is analyzed considering surrounding terrain based on 3D finite element model. Thermal and stress analyses are also performed. Large difference of downstream temperatures exists, which is influenced by high mountains of left bank for Laxiwa arch dam. Results of stress analysis show that large tensile stress exists probably at the region adjacent to the river surface and dam abutments.5. The results considering 3D variation of solar radiation are compared with the results based on converting the solar radiation to air temperature increase. The comparison shows the method presented in the dissertation can improve the simulation accuracy of thermal loads. Influence of terrain and orientation of arch dam are discussed. The conclusion is the two factors are important especially to downstream face of arch dams and have to be considered in the numerical simulation of high arch dams.