Papers by Keyword: Thermal Stress

Abstract: Setting in the youshui Bridge Project and referring to the stipulation on the temperature gradient in current code, this aims to investigate the effects on the stress condition of concrete box-girder bridges caused by the overall heating, cooling or standard temperature changes. The process was carried out by virtue of the general finite element analysis software—MIDAS/CIVIL. The result showed that temperature would greatly affect the structural behavior of a bridge, in particular that the stress condition of the top plate is sensitive to temperature changes. It was therefore suggested that climate conditions should be taken into consideration when determining the temperature gradient values in the code.

Abstract: Two sets of 4H-SiC signal-lateral JFETs were thermally aged at 400°C and 500°C in furnaces open to air for 1000 hours. I"-" V and low frequency noise measurements were performed on these devices and the results were compared against the as-fabricated sample. The data from I"-" V characterisation demonstrates that the linear and saturated drain-source current decreases monotonically with stress temperature. In addition, the linear characteristics of the JFETs have shifted approximately 1.5V along the drain-source voltage axis. Whilst the devices thermally aged at 400°C show no degradation in magnitude and behaviour in Noise Power Spectral Density (NPSD), the NPSD of 500°C stressed devices has increase approximately 30dB and it shows a full frequency spectrum of 1/ƒ dependency up to 100 kHz. A further investigation of the noise origin reveals that the Normalised Noise Power Spectral Density (NNPSD) of the aged sample is directly proportional to R_DS which is similar to the as-fabricated sample. Thus we hypothesize that the existing noise sources have intensified possibly due to the evolution of defects.

Abstract: Thermal stress, as one of the most important stress of the arch dam during construction period, strongly influences the sliding stability of the arch dam. To analyze this kind of impact on arch dam sliding stability, numerical modeling of a typical slope dam section from 300-meter-high levels arch dam during construction period was conducted. Based on the rigid body limit equilibrium method, results of the case considering thermal stress as well as those without thermal stress were presented. Detailed comparison with the results of multiple monoliths was also made. In addition, the relevant sliding stability coefficient with the consideration of thermal stress was suggested.

Abstract: Cyclic changes of temperature in space may cause thermal deformation and thermal stresses at the silver welding spots on solar cells, which result in the solar array work abnormally. According to the temperature conditions in the thermal vacuum, the thermal stress and deformation at silver welding spot that between solar cell and inter-link chip were analyzed. The result shows that thermal cycling can make the sliver welding spot separated or contacted, which cause the solar array work wrong. The phenomenon of thermal vacuum reliability test was corresponding with these results. This paper could offer some references for the design and manufacture of solar array in the future.

Abstract: With the development of the power grid, the proportion of large capacity unit is increasing rapidly. It requires a more in-depth study on the reliability of the unit, especially for the unit adjusting the peak. This paper concerned on the research of the surface heat transfer coefficient, which is the key factor affect the precision in thermal stress analysis. The surface heat transfer coefficient is obtained via the numerical calculation for the steam’s flow state and the transient heat transfer between rotor. This paper mainly describes the steam’s flow state and the transient heat transfer with the steam seal, and the results show that the direct numerical calculation is resultful in this subject.

Abstract: The simulation system on the thermal stress of the rotor during startup & shutdown for a domestic 300MW steam turbo unit, by the simulation, the surface of the shaft was suffered a crushing stress, but it was a pulling stress when a unit shutdown. The max thermal stress & the max combined stress produced on the rotor of a medium pressure cylinder was about 16% bigger than those on the rotor of the high pressure cylinder when they had the same increase rate of temperature. When thought from economics & safety, the optimal temperature-increase-rate of the rotor was 1.6°C/min when the unit startup at cold state, but it was 1. 8°C/min when started up and shut down the unit at hot state, it’s optimal for slipping-parameter and the optimal temperature-decease-rate of the rotor was 0.85°C/min.

Abstract: In order to alleviate thermal stress of piston head, the causes of thermal stress are studied. The original piston is modified from the perspective of easing strain concentration. The thermal stress and strain fields of the original and modified pistons are analyzed with FEM. Comparison of the analysis results shows that analyzing strain concentration is an efficient way to find out the fundamental causes of high thermal stress of piston head. Thus viable approaches are proposed to solve the problem.

Abstract: This paper focuses on the influence of the conjugative heat transfer in a regenerative cooling structure. With proper numerical modelling by both finite element method and computational fluid dynamic method, the distribution of the temperature in the solid and coolant, the interfacial heat flux, and the stress state and the deformation of this cooling structure are obtained. These results show that the thermal equilibrium of the cooling structure can be achieved in a given flow condition. The present numerical method has significant benefits to solve the heat transfer between engine coolant and solid components.

Abstract: Several cracks were found on some actual floating roofs of a crude oil tank in the oil refinery located in southern Japan. We assumed that one of reasons would be due to thermal stress caused by temperature changes during the day. In order to consider whether the thermal stress could the cause damages on the floating roof, strain and temperature were measured on the actual floating roof by using optical fiber gauges. Furthermore, fracture possibility due to thermal stress was calculated to discuss whether thermal stress could cause fracture or not. As a result, the probability showed that thermal stresswasnot enough to cause fracture. Anotherexternal factor such as Typhoon could be related.

Abstract: During oil and gas development, high pressure, high temperature and non-uniform earth stress increase the complexity of stresses in well bore which is composed of casing, cement sheath and formation. In order to obtain well bore stresses in hostile conditions, a new model is established with cement sheath and formation are treated as different materials. To predict well bore stresses rapidly, stress conversion coefficients are obtained that may change loads into stresses at key points conveniently.