Abstract: Wind-induced static torsional angle has significant influence on the results of sectional model test. To accomplish accurate flutter analysis, wind-induced static torsional angle should be adjusted in sectional model test. An attack angle control facility was used to eliminate static wind induced additional attack angle. A comparison of test results before and after the attack angle adjustment based on the Xiang Shan Gang Bridge shows that static wind induced additional attack angle has influence on aerodynamic tortional damping ratio, aerodynamic derivatives related to torsional movement and critical wind speed. Before the adjustment, the wind induced additional attack angle on the sectional modal under critical wind speed was 0.32°at 3°initial attack angle. After the adjustment, the critical wind speed increased by 7%.
Abstract: Structural damage identification based on an improved sensitivity technique of structural flexibility is studied in this paper. The drawback of the existing sensitivity methods is discussed firstly and then an improved technique is presented. The most significant contribution of this work is in the development of a simple accelerated formula used in the iteration process. With the introduction of the accelerated formula, the proposed method is able to quantify large damages without any high-order analysis on the flexibility or multi-iterations. The effectiveness of the proposed method is illustrated using simulated data with measurement noise on two numerical examples. The results show that the proposed procedure is economical in computation and is simple to implement. Regardless of whether the damage is small or large, the proposed method can identify both locations and extents of structural damages accurately only using the first iteration. It has been shown that the presented scheme may be useful for structural damage identification.
Abstract:In order to obtain a more accurate boundary condition of structure in dynamic analysis and optimization design, the parameter identification of joint as one of the key technologs. In combination with engineering practice, proposed the method of frequency response function (FRF) to identify the characteristic parameters of the joint. Whether it can obtain complete FRF is studied and propose the corresponding solution strategy in this paper. This method avoids the matrix inversion directly, and transforms contradictory equation to definite solution of equation with least-square principle, which ensures the stability of numerical calculation. Considering the damping information is inferior to stiffness information in identification process, in order to identify the damping more accurately, using the second identification method to identify damping parametres. This method has a certain practical value and the identification process is simple. Example analysis confirmed that this method has high identification accuracy.
Abstract:Ground vibrations induced by urban rail traffic are a major environmental concern in urban areas. In order to study the vertical vibration characteristics and its propagation behavior, an in situ test was carried out near the Line 13 of the Beijing Urban Railway between the Huilongguan Station and the Huoying Station. The responses of the free field ground were analyzed from three aspects as acceleration time histories, power spectra and vibration levels. Results show that the PGA of ground surface displays a pronounced attenuation with the increase of distance from track, while the vibration duration is somewhat prolonged. The dominant frequency ranges from 10Hz to 80Hz, whose lower band is primary for the points near track and upper band is primary for the ones further from track. The weighing VLz monotonic decay with distance, whereas at some frequency points close to natural frequencies of ground, the banded VLzs are amplified notably at certain distances. There is no significant change in the weighing VLz whether coaches are full or not. Comparing with InterCity railways, the urban rail traffic produces a more moderate ground vibration.
Abstract: Based on the theory of random vibration and system identification, the ambient vibration tests of the three wind turbine towers in wind-power station of the Inner Mongolia Wulanyiligeng were carried out. The method of coupling overall modeling of blade, hub, nacelle and tower was put forward, and the numerical stimulation and tests results show that the wind turbine towers can effectively avoid resonance, and meet the standard design requirements of Germanischer Lloyd. The vibrational forms of wind turbine tower mainly are lateral bending vibration, forth-and-back bending vibration and torsional vibration; the translational damping ratio in the first phrase is about 1.75%, and the torsional damping ratio in the first phrase about 0.6%. The overall modeling shows excellent consistency with the tests results, which can benefit the wind-induced dynamic response analysis and the vibration control research on the wind turbine tower system.
Abstract:The types of shock impulse of ship shaft system are introduced. A shock dynamic model of ship shaft system is built up with the finite element method, and a software (SHAFTFE) for the ship shaft system dynamics and shock response simulation is developed on MATLAB. Dynamic characteristics of a ship power shaft system including propulsion shaft, propulsion electric motor and vibration isolator of electric motor, are analyzed by the SHAFTFE in the condition of different shock forces and parameters, and effects of the structure design parameters of the ship shaft system on the shock response are dealt with. It shows that the ship power shaft system will have a large motion on the action of base shock, so we must pay more attention on the shock character of the ship power shaft system during the design in order to increase the reliability and survival performance of whole ship.
Abstract:The dynamic model of the metal plate spring vibration isolator system was built up. The friction curve was calculated using finite element method. Through the analysis of dynamic equation, the responses of the system under different harmonic exciting forces, as well as the impact of acceleration response were studied .The results indicate: When electronic cabinet loaded on the isolator, the system maximum acceleration reduces by 72%. The metal plate spring vibration isolator has good vibration damping and impact resistance performance. This study will provide a theoretical basis of optimal designing for the dry friction absorber.