Papers by Author: He Len Wu

Abstract: The breathing mechanism of a transverse crack in an elastic shaft has been extensively researched. Although many different crack models have been presented, little published research has explored experimentally how the shaft crack breathing mechanism interacts with the change of stiffness during each revolution. This study addressed static analysis of the stiffness of elastic shafts with experimentally-induced fatigue, welding or wire cut transverse cracks. Bending stiffness was measured from different angles under a three point bending fixture, to efficiently define the correct periodical stiffness variation for different crack types. The opening and closing of each crack (breathing effect) were investigated for their association with shaft stiffness. It was found that width of the crack opening gap is a crucial factor which influences the crack breathing behaviour. Experimental results are expected to assist with crack diagnosis.

Abstract: Fluctuating wind speed spectrum, which is closer to the actual working conditions, was simulated by davenport wind speed model, and displacement and stress distribution of blade under fluctuating wind speed were calculated by finite element analysis software. The numerical results indicate that the growth trend of vibration amplitude for whole blade at flapping direction is nonlinear along the wingspan. The max von-mises stress appears when the vibration amplitude of tip reaches the maximum, and it is mainly concentrated in the central part of the blade. The stress at trailing edge and tip is smaller than the central part. Above results provide a reference for the strength safety design of wind turbine blade.,Fluctuating wind speed spectrum, which is closer to the actual working conditions, was simulated by davenport wind speed model, and displacement and stress distribution of blade under fluctuating wind speed were calculated by finite element analysis software. The numerical results indicate that the growth trend of vibration amplitude for whole blade at flapping direction is nonlinear along the wingspan. The max von-mises stress appears when the vibration amplitude of tip reaches the maximum, and it is mainly concentrated in the central part of the blade. The stress at trailing edge and tip is smaller than the central part. Above results provide a reference for the strength safety design of wind turbine blade.

Abstract: Shaft fatigue crack is one of the most common defects in rotating equipment, due to its extensive operation with continuous heavy loads. Finding an efficient way to evaluate the true stiffness variation due to the crack rotation is the key step to develop both on-line and off-line crack diagnostic techniques. This study analyzed time-variant bending stiffness of elastic shafts with experimentally-induced fatigue, welding and wire cut transverse cracks. It was found that crack gap has a significant effect on the opening and closing behaviour of the transverse crack. As in the case of a cut crack, large crack gap could completely prevent the crack from closing during rotation. A fatigue crack without a clear gap shows a typical opening and closing behavior. Further, it remains fully closed within a small angular range and most of time it is partially closed. It was also observed that both switch and harmonic models cannot describe periodic stiffness variation well enough to represent the actual breathing function of the fatigue crack.

Abstract: The paper proposes an aseismic hybrid control system to control the response of structures subjected to large ground motions caused by large magnitude earthquakes. The proposed hybrid control system consists of a base isolation system (laminated rubber bearings) connected to an active control system (a tuned mass damper and an actuator). The base isolation system is used to decouple the horizontal ground motions from the structure, whereas the active control system is used to protect the safety and integrity of the base isolation system. A 5-story benchmark building model is developed to study the effectiveness of the hybrid control system against different ground motions. It was found from the numerical results that rubber bearing system alone shows good performance and resists ground motion due to Hachinohe 1968, Kobe 1995, and Northridge 1994 earthquakes, but is somewhat unable to protect the model against El-Centro 1940 earthquake. After the installation of an active control system onto the rubber-isolated model, further improvements to earthquake resistance against these four earthquakes were observed, especially against the El-Centro earthquake. The merit of the hybrid control system lies in its capability to protect against different ground motions, with varying intensity and frequency content.