Bai Feng Ji

Comparative Analysis of Davenport Wind Spectrum and Kaman Wind Spectrum in the Towering Structural Design

To the Yangtze River a long-span transmission tower as an example, this paper makes a comparative analysis on the davenport wind spectrum and kaman wind spectrum, using two different wind spectrum calculation of wind-induced response of the structure. Obtained the conclusions that kaman wind spectrum of considering vertical correlation get greater wind-induced response in a large span transmission tower engineering.

Study on Downburst Wind Load under Characteristic Topography

Gemorphological type is the important factor influencing the downburst wind profile. In this thesis, firstly we determine four categories of landform types under the criteria of roughness. The CFD pre-processing software GAMBIT was used to build considering the landscape types downburst CFD computational model. Then, the established CFD computational model was imported to the calculated hydrodynamics software FLUENT to take the numerical simulation of the downburst under different landforms. Finally, in allusion to the numerical simulation result, make the research of the wind characteristics.

Welding Residual Stress Numerical Simulation of Guyed Mast Earplate Welded Joint

Fatigue damage of guyed mast earplate welded joint is one of the main failure forms of guyed mast under wind load, and the welding residual stress is a important influence on fatigue performance of the welded joints, therefore, accurate welding residual stresses assessment of earplate welded joint is of great significance to the research on fatigue performance of guyed mast earplate welded joint under wind load. In this paper, welding temperature field of earplate welded joint was simulated by using thermal finite element method and the gauss heat source was used as thermal input. Then, welding residual stress of earplate welded joint was simulated by using thermal elastic-plastic finite element method and the temperature field results were used as the load. The welding temperature field simulation results better reflect the locality of heating, mobility of heat source and instantaneity of heating and cooling process during the welding process. The welding residual stress simulation results show that the residual stress peak of earplate welded joint reaches the yield strength of material, and appears at the dangerous point of earplate welded joint under structural external load. This point under influence of the welding residual stress and structure load is likely to be fatigue crack initiation location.

Study on the Downburst Field Characteristics under the Influence of Two-Dimensional Continuous Mountains at Different Distance

Downburst is an outburst strong wind on or near the ground, and its wind field characteristics are significantly different from boundary layer winds. Continuous mountains at different distance are one of the main factors for the influence of downburst wind field characteristic. In this thesis, the changes of the wind field characteristics under the influence of continuous mountains at different distance after the downburst happened are studied by CFD numerical simulation. The impact of downburst is analysed and summarized through the charts.

Study on Downburst Wind Field Characteristics under Mountainous Terrain

Downburst is a strong downdraft thunderstorm in the ground formed after the violent impact and spread along the ground very sudden and destructive winds near the ground short. From an engineering point of view for the structure of wind-resistant design, researching downburst wind field characteristics and ultimately determining a reasonable downburst wind profile is one of the core objectives of the study. Terrain conditions are the major factors of downburst wind field characteristics based on the typical mountain terrain on the wind storm flow condition, this paper established typical 2D slope mountain terrain model, using the method of computational fluid dynamics to calculate the velocity contours and pressure cloud in different locations of the mountain. Finally we get the two-dimensional slope typical mountain terrain wind field distribution.

Simulation for Wind Pressure of Pedestrian Bridge Induced by Main Line Train

Wind pressure of pedestrian bridge induced by main line train has been investigated using numerical simulation. Based on time-filtered Reynolds Averaged Navier-Stokes equations, meanwhile, the RNG k-ε turbulent model is selected to close the equations, the three-dimensional incompressible unsteady flow computational fluid dynamics model have been established by commercial software FLUENT. The distribution of wind pressure and the time histories of wind pressure on surface of the bottom of bridge are obtained, moreover, the characteristics of variation process are summarized.

Trend Study on Economic Loss Induced by Typhoon Disaster in Chinas Southeast Coast

Chinas southeast coast is one of the regions with most severely influenced by typhoons in the world, which suffers significant casualties and huge economic losses every year. In this paper, the trends of economic loss educed by typhoon disaster in coastal areas of southeastern china were studied using regression analysis methods. Firstly, the data sources were introduced and the typhoon landing areas are all over the east coast of China were analyzed.Then, development trends of the affected area , deaths, houses collapsed and the direct economic losses were studied in detail. The results indicate that the affected area and deaths induced by typhoon disaster fluctuate greatly and the number of deaths has been showing a declining trend. The linear regression, exponential regression and logistic regression analysis results all indicate that the number of houses collapsed due to Typhoon present a downward trend year by year while the direct economic losses induced by typhoon disaster present an upward trend year by year.

Fatigue Life Numerical Prediction of Butt Welded Plate under Cyclic Loading

Fatigue failure of welded structure has been highly concerned in structural engineering field. At present, the numerical simulation method has been actively applied on fatigue life prediction of welded structures. In this paper, welding residual stress of a butt welded plate was simulated by thermal elastic-plastic finite element method, and welding residual stress relaxation behavior under overload was analyzed. Then, the fatigue life of the welding plate under cyclic loading was numerically predicted with considering the welding residual stress and welding residual stress relaxation, and the result was compared with that calculated according to current steel structures design code of China. The results show that, considering fatigue reliability, the fatigue life calculated based on design formulas of the steel design code is more conservative, and numerical method for fatigue life prediction of welded structures, considering the welding residual stress and welding residual stress relaxation, is a feasible method.

Wind Speed Profiles of an Actual Downburst Based on CFD Numerical Simulation

Downbursts have led to large number of transmission tower failures in the world, so more and more wind engineers are very interested in such strong wind load. Currently the main numerical simulation method of downburst wind load for structural analysis is based on the horizontal divergent wind speed profile of downburst. There have been several available types of empirical wind speed profiles in which some parameters still need to be artificially determined. So, this is a semi-empirical-analytical method which can not be linked with actual downbursts. Some academics have also used CFD numerical method to simulate downburst wind speed profile of high precision grid. But the initial conditions of these CFD simulations were all assumed ideally. In this paper, the wind speed profiles of an actual downburst are simulated by CFD method based on the initial speed of downdraft entrance provided by cloud model. The simulated wind speed profile decays more slowly than an empirical wind speed profile. This conclusion could be of significance for structural engineers to consider downburst wind load reasonably in the structural wind resistant design.

Transient Simulation of a Three-Dimensional Moving Downburst

Thunderstorm microbursts, which are sources of extreme wind loadings in nature, have caused numerous structural failures, especially collapses of transmission tower around the world. Numerical simulation using computational fluid dynamics (CFD) has recently made significant progress in simulating downbursts. In this paper, transient simulation of a three-dimensional moving downburst was studied using computational fluid dynamics simulation method. Transient simulation of a three-dimensional moving downburst was conducted using time-filtered Reynolds Averaged Navier-Stokes (RANS) numerical simulation method. The three-dimensional transient wind field characteristics in a moving downburst were studied in detail. The results indicate that transient wind field characteristics in a moving downburst present quite different characteristics compared with stationary downburst at different heights and radial positions.