Papers by Keyword: Vibration Test

Abstract: Experimental studies magnetorheological elastomer specimens dynamic properties under the magnetic fields action on the vibrostend are carried out. Amplitude-frequency characteristics have been obtained. The magnetic field effect on the silicone magnetoreactive elastomers deformation properties and damping coefficients experimentally is established.

Abstract: Reinforced Concrete (RC) Beam undamaged and damaged were investigated by free vibration to obtain a variation of frequency values at different degree of damage. Experimental tests were carried out on RC beams in scale and in real scale. The damage of RC beams in real scale was obtained by cracking under static bending tests, while in the case of beam in scale is obtained by notches on the concrete cover with different width. In general, the effects on the dynamic response of diffused damages and of concentrated damages on a section of beam have been experimentally analyzed. The envelope of frequency response functions (FRFs) obtained by dynamic experimental tests was elaborated and the changes of natural frequency values were then correlated to the damage degree of RC beams. The experimental data have been discussed and analyzed by comparison with theoretical results.

Abstract: Vapour compression heat pump will have good prospects in future large-scale spacecraft thermal control technology. Its environmental reliability and safety needs to be tested on the ground before being carried with the spacecraft launch. Vibration test is used to assess the anti-vibration capability in its transport and use. It is essential to build a performance test system of vapour compression heat pump to explore its operating characteristics at a given random vibration conditions. The results shows that the vapour compression heat pump is normal operation after the vibration and the cooling performance (COP) of 3.09 is achieved. Vibration test is equipped to provide a guarantee for future success carrying. The performance of vapour compression heat pump at high and low temperature and vacuum environment will be carried out.

Abstract: Dynamic characteristics of numerical control (NC) machine tools, such as natural frequency and vibration property, directly affect machining efficiency and finished surface quality. In general, low-order natural frequencies of critical components have significant influences on machine tool’s performances. The headstock is the most important component of the machine tool. The reliability, cutting stability, and machining accuracy of a machining center largely depend on the structure and dynamic characteristics of the headstock. First, in order to obtain the natural frequencies and vibration characteristics of the headstock of a vertical machining center, modal test and vibration test in free running and cutting conditions were carried out by means of the dynamic signal collection and analysis system. According to the modal test, the first six natural frequencies of the headstock were obtained, which can not only guide the working speed, but also act as the reference of structural optimization aiming at frequency-shift. Secondly, by means of the vibration test, the vibration characteristics of the headstock were obtained and the main vibration sources were found out. Finally the corresponding vibration reduction plans were proposed in this paper. That provides the reference for improving the performance of the overall unit.

Abstract: The test was simulated for the thin-walled cylinder structure of aeroengine stator casing. Based on the software of LMS-TEST, the experiment of the structure with bolted flange joints was successfully completed for the vibration test analysis and the paper completed the testing under different pre-tightening force. Through the analysis of the measured data, the corresponding spectrum and difference value curve were obtained, the research results showed that the nonlinear characteristics of the bolted flange joint was significant influence on the dynamic responses of the structure, the various nonlinear vibration phenomenon and the signal asymmetry were obvious under different pre-tightening force, which was closely related to the state of the bolted pre-tightening force. By the information of the spectrum and acceleration difference curve, the extent of the bolt tightness can be determined, which can provide relevant reference information for the diagnosis of bolted joint status in the aeroengine stator casing.

Abstract: In order to control the degree of comfort in vibration caused by human in a steel aerobridge of Shenzhen T3 terminal building, the theory of structural vibration control and TMD (Tuned Mass Damper) was used to control the vibration caused by human and conduct comfort design. At first, 3D analysis model of the structure was developed through general finite element analysis software MIDAS / GEN. And time-history analysis was carried out in different working conditions of human walking or jumping to analyze the dynamic response before and after the TMD was installed. Then, vibration test was conducted in-situ to determine its dynamic property and record its peak acceleration before and after the TMD were installed. Test data was then compared with data from the analysis model of the structure based on analysis software. The results show that the installing of TMD and making adjustment of the stiffness of the TMD based on the actual test make the structure meet requirements of degree of comfort in vibration caused by human. The effect of the vibration control is good.

Abstract: This paper reviewed techniques of vibration sensors, studied structure and working principle of phase modulated optical fiber vibration sensor, and designed a new structure of non-contact optical vibration sensor. Use this structure, expect accuracy of 0.1um can be obtained in the range of 1mm. At the same time, this system is simple, anti-interference ability, high reliability and ease of practical.

Abstract: The aim of this work was to determine by vibration tests the longitudinal elastic modulus and shear modulus of welded joints by flux cored arc welding. These two material properties are characteristic elastic constants of tensile stress respectively torsion stress and can be determined by several non-destructive methods. One of the latest non-destructive experimental techniques in this field is based on the analysis of the vibratory signal response from the welded sample. An algorithm based on Pronys series method is used for processing the acquired signal due to sample response of free vibrations. By the means of Finite Element Method (FEM), the natural frequencies and modes shapes of the same specimen of carbon steel were determined. These results help to interpret experimental measurements and the vibration modes identification, and Youngs modulus and shear modulus determination.

Abstract: In welded structures subjected to dynamic cyclic loads may appear and propagate fatigue cracks due to local structural damage. These cracks may initiate due to technological damages induced by welding process, or by environmental operating conditions. In the present work, it is determined, by the means of Finite Element Method (FEM), the natural frequencies and mode shapes of more steel specimens that are welded together. The analysis is carried out in undamaged condition as well as in damaged one, after the damage has been artificially induced. The experimental measurement of the vibration response is carried out by using a condenser semi-professional microphone Samson C01U, which is suitable for high-fidelity acoustic measurements in the frequency range of 40 18.000 Hz. A first post-processing of the vibration responses of the welded specimens, in free-free conditions, is carried out using an algorithm based on Prony series. A second post-processing is carried out by means of signal processing using DWT together with Shannon entropy. The results are compared to modal parameters estimated using FE Analysis.

Abstract: The separation between the filled-concrete and the steel tube would reduce tremendously the bearing capacity of the concrete-filled steel tubular (CFST) arch bridge. However, there is no efficient method to monitor and detect the separation so far, which is a great engineering problem we have to solve. Therefore, this paper firstly proposes a vibration test method aiming at the local modal of the steel tube. Distributed accelerometer array deployed along the tube is used to acquire the vibration signal induced by quantitative excitation via telecontrol. Changes in frequency and amplitude of the steel tube are selected as parameters for the separation detection based on the theory of surface wave transmission. This method can satisfy the demand of the real-time monitoring of interface separation of the CFST arch bridge.