| Air-cooling system has obvious environmental benefits, which widely used in our coal-rich water of the northern region. Safety of air cooling structure directly affecting the normal operation of thermal power plants, previous studies have focused on the overall structure suffered wind loads, earthquake, etc., the studies about fan operation vibration problems seem inadequate. Since air cooling bridge and the fan is coupling system, fan running would inevitably lead to vibration of the bridge. Especially in air cooling structure long-term status, disturbing force from fan operation will cause the bridge structure fatigue damage. Based on the field measurement results of bridge vibration, we establish load model of fan disturbance force in this paper, then take random vibration response analysis of air cooling structure at disturbing force loads, Finally, make quantitative evaluation of the reliability of the bridge structure during period of service under the influence of fan disturbance force.(1) This paper we describe an inevitable trend about development of air cooling structure in China, systematically summarize current research status about air cooling structure, introduce load identification methods from the perspective of the frequency and time domain. Around site measurement vibration of the fan bridge showing random characteristics, we discuss the basic concepts of stochastic processes, statistical properties of narrowband random process and calculation of random vibration analysis methods.(2) Based on field measured vibration velocity responses of direct air cooling system fan bridge at different rotation speed, the vibration responses of the fan bridge are analyzed in both time and frequency domains. The vibration responses under traditional harmonic oscillation force can’t reflect the narrowband random characteristics of the actual results whose amplitude and phase slowly varying. In this paper, we establish the random oscillation force model of the fan according to the carrier theory based on the measured vibration response and combined with the fan bridge vibration time and frequency domains analysis, identify oscillation force model parameters as the power spectrum of vibration responses for the target. The results show that the proposed oscillation force model can well reflect randomness of bridge vibration.(3) According to the theory of random vibration mode superposition method and the center differential principle, we derive the inverse calculation method of random loads to the structure, Based on the measured output structural vibration responses of bridge to each conditions and combined with modal analysis results of finite element model, We use inversion methods to identify the fan disturbance force and compare the inverse analysis results to validate reliability in the frequency and time domains. The results show that disturbing force equivalent load model obtained by inversion of this article and can reflect the impact of fan running to the support bridge under actual different operating conditions. The disturbing force could be as the basis for the reliability analysis of direct air cooling system structure fan vibration in the future.(4) We establish the actual air-cooled structural finite element model, use harmonic superposition method to generate disturbance force sample according to power spectrum target, calculate and analysis random vibration response of air cooling structure under disturbance force. Then extract multiple sets of random vibration stress results of the bridge, use rain flow counting program to statistic stress amplitude, calculate accumulated fatigue damage of bridge danger points in different service period, give the reliability that structural fatigue failure does not occur. |
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