Here,in order to correctly predict effects of portable pneumatic extinguisher vibration on operator arm and reduce operator arm model’s complex level, according to theactual operation condition of portable pneumatic extinguisher, a biodynamic model with 5-DOF for operator arm’s hand-transmitted vibration was built considering his elbow in a posture of a curved arm of 90°. According to biodynamic characteristics of the arm system and its dynamic balance state in operation process, mechanical analysis was conducted to establish the mechanical equivalent model of the arm system, and then the standard vibration test platform was designed to identify parameters of the arm model and compare the model’s predicted vibration data with the actual measured values of portable pneumatic extinguishers.The results showed that under conditions of operator elbow in a posture of 90°, gripping force of 30 N and thrust one of 50 N, vibration response of the model isbetter consistent to the average measured value, the model can correctly fit the response feature curve of arm’s

hand-transmitted vibration; the model can be used to better predict operator’s arm vibration responses brought by operation of portable pneumatic extinguishers, and provide a quantitative theoretical prediction model for vibration risk evaluation.

In order to study self-excited vibration mechanism of the main inlet valve of a pumped storage power station, its waterflowing system’sprecision numerical simulation model was established based on the transient flow theory to obtain the variation curve of water level of the upstream pressure measuring pipe with time by calculation.The empirical wavelet transform (EWT)method was used to do feature extraction and spectral analysisfor self-excited vibration signals and simulatedonesof the main inlet valve,and verify the correctness of the numerical model.The modified Morris method was introduced to find pipeline length, pipelinewater hammer wave velocity and valve clearance of main inlet valve being sensitive parameters invarious performance ones.Finally, aiming at sensitive parameters,3 schemes were set to do numerical simulation, respectively and study their specific effects on self-excited vibration process. The results showedthat main inlet valve clearance has a large influence on self-excited vibration amplitude and its growth rate, but has little effect on system’s period; pipeline water hammer wave velocity and pipeline length have great influence on self-excited vibration amplitude, its growth rate and system’s period.

 

To clarify vertical interaction between a static human body and a light and flexible structure, a simply supported footbridge model with the vertical fundamental natural frequency of 3.67 Hz and a span of 11.80 m was designed and manufactured as a test platform to measure effect laws of a standing occupant, a squatting one, a sitting one and corresponding equal weight mass blocks on vertical dynamic characteristics of a human-structure interaction system. The test results were compared with those published in literature. Test results showed that a standing occupant or a sitting one can reduce the first order vertical natural frequency of the system, while a squatting occupant can increase this frequency, and occupant sitting posture has the largest effect on this frequency; three occupant postures all can increase the first order modal damping ratio of the system, occupant sitting posture has the most significant increase effect; corresponding equal weight mass blocks are used to simulate human bodies with three postures, they have almost the same effects on the first order vertical natural frequency of the system, however, they can’t effectively simulate changes of the system’s modal damping ratio. Based on test results here and data published in literature, it was shown that there are two main factors to cause the discreteness of different results in which the most important factor is the ratio of human mass to structure one, and the second one is the ratio of human natural frequency to structure one.

Based on the transfer matrix method, a new method was proposed to solve natural frequencies of a variable cross-section beam with multi-crack. Aiming at a kind of variable cross-section beams with their vibration modal shape functions being able to be deduced, some bending springs without mass were used to be equivalent transverse cracks, the transfer matrix for a typical segment of a beam with variable cross-section parameters and crack geometric parameters was derived. Then, according to boundary conditions of simply supported beam, the characteristic transfer matrix of the whole variable cross-section simply supported beam with multi-crack was derived to study effects of variable cross-section parameters, crack number and crack geometric parameters on natural frequencies of the beam. Results indicated that effects of cracks on vibration modes of the variable cross-section beam are very large, they can significantly reduce each order natural frequency of the variable cross-section simply supported beam.

Through monitoring a certain offshore wind power field’s two multi-pile-concrete 5 MW wind turbines’ towers vibration, its characteristics were obtained. From the analysis results of three years，monitoring data, multi-pile-concrete wind turbine towers revealed vibration characteristics that when wind turbines are in working states, cabin yaws to the wind cause towers’ frequent strong vibrations, these strong vibrations last for tens of seconds, their acceleration peaks can reach 10 m/s2, these strong vibrations appear for hundreds times per month; when wind turbines are in shutdown state, under action of small wind, tower vibration is steady and its acceleration peak is below 0.1 m/s2, under action of typhoon, tower vibration fluctuates largely and its acceleration peak can reach 10 m/s2, but the wind excites the second and third orders modal shapes of tower, the maximum acceleration of tower appears in its middle; within 3-year long monitoring period, the first 3 natural frequencies and damping ratios of tower unchanged. The monitoring results showed that towers of multi-pile-concrete wind turbines cause strong vibrations during typhoon and cabin yaws to the wind; so, besides typhoon, cabin yaws to the wind causing tower strong vibrations too often is also one of important factors to lead to fatigue damage of wind turbines’ towers. The study results provided a reference for design, safe monitoring in operation and damage diagnosis of this type wind turbines.

Dynamic characteristics of a dry gas seal device directly affect its seal reliability. Here, operational modes of a dry gas seal device with complex structure were studied. Based on the poly-reference least-squares complex frequency domain (PolyLSCFD) method, the operational modal analysis and identification of this system was performed using the cross power spectrum(CPS) andthe half-cross power spectral density (Half-CPSD). The modal analysis results were verified using mathematical indexes including the modal assurance criterion (MAC), the mode phase deviation (MPD), the mode phase collineation (MPC), the mode complexity (MOV) and themode indication function (MIF). The results showed that the modal analysis results with Half-CPSD are better than those with CPS, Half-CPSD is more suitable for the operational modal analysis of this type system; effects of rotating speed on the system’s modes are larger than those of medium pressure. At the same time, a model for time-varying modal parametric identification was established based on the response surface method. Taking operating conditions including medium pressure, rotating speed, rotating speed direction and modal order as response surface variables, appropriate variable sample points were selected using Box-Behnken test design. The complete quadratic polynomial operational modal response surface model for the system’s modal parameters was built and its effectiveness was verified. The results provided a new method and technical support for time-varying modal identification.