Papers by Author: He Li

Abstract: The random factor method (RFM), an effective numerical simulation method, is employed to analyze the probabilistic characteristics and reliability sensitivity of uncertain structure system. The natural frequencies of the system can be expressed as the function of the random factors. By using the random variable’s algebra synthesis method, the expressions for the mean value and standard deviation of natural frequencies are derived from Rayleigh quotient. The reliability mode and the safety probability of random systems are defined, and then the frequency reliability sensitivity analysis method is presented. The formulas of failure probability sensitivity are derived when random variables are normally distributed. The reliability index is evaluated, and its sensitivity to mean values and variances are mathematically expressed, then the efficiency and accuracy of the proposed method are demonstrated by a numerical example.

Abstract: This paper proposes an analytical approach to study self-synchronous motion and stabilizing conditions of a novel vibrating mechanism excited by two unbalanced rotors. This approach begins with utilizing Lagrange equation to establish differential motion equations of the system, and then obtains the dimensionless coupled equation of the unbalanced rotors with a modified average small parameter method. The zero solutions of dimensionless coupled equations are used to achieve the condition to implement self-synchronization of the vibrating system, and finally the Routh-Hurwitz criterion is used to derive the conditions of self-synchronous motion stability.

Abstract: In this paper, the noise of the rotor system is classified at first, and then the sound intensity experiment of the rotor system is conducted based on “two-microphone” method. Then the sound intensity contour maps were obtained from the measurement results. An investigation towards the relationship between the characteristics of contour maps and distributions of the rotor system on space was taken; the main noise sources of the engine were identified. The result provides guidelines for taking measures to reduce noise.

Abstract: To make the structure of the car more rational, we established a modal test system of car's body-in-white in this paper. In experiments, we use the method of single-point excitation and multi-point collecting vibration, PULSE 12.5 modal test consultant and Mescope modal analysis software. Meanwhile, the excitation point is in the front of the load beam of better rigid. Through the system, different order modal frequencies and modal characteristics of body in white are computed. The modal analysis results and frequency characteristics of the car’s excitation are compared and analyzed, and they can supply the reference standard for dynamic design and revision．

Abstract: A dynamic model of the single vertical centrifugal pump was established to avoid seismic disadvantageous direction towards the direction of continually occurring earthquake during the designing and the installing. Finite element method was used to analyse the single vertical centrifugal pump and educe the first 20 natural frequencies and vibration shapes. Response spectrum method was adopted to do earthquake analysis. Response spectrum was inputted from different directions for getting different displacements and loads. According to the results, model’s direction of 45°~75° should be located at the direction of continually occurring earthquake to avoid the maximum vibration.

Abstract: In this paper, we analysed the level of radiation noise and distribution of noise sources of car’s engine and front panels by using sound intensity method. To get the nephogram of sound intensity and sound power spectrum, we used the sound intensity probe and Multi-channel Data Acquisition Regulation System B&K 3560-D and Pulse Data Processing Analysis Software. By analysing experimental results, we can conclude the location of noise sources of these parts. The measurement results will serve as a reference for the car noise reduction.

Abstract: To reduce noise and make the structure of the car more rational, we established modal test system of car's body-in-white in this paper. Car body-in-white was mounted on rigid platform with four coil springs. The car was excited by an electromagnetic exciter. The method of single-point excitation and multi-point collecting vibration was used in this test. Excitation point was chosen in the bearing beam. Signals picked up by the acceleration sensors were processed in the software of Mescope. With this system, different modal frequencies and modal characteristics of the car are acquired. The results show that modal parameters are effective and reliable and those parameters can be basis for the designer to improve the structure of the car.

Abstract: In the experiment, a new non-destructive method for discriminating three vigour of soybean seeds was developed by near infrared spectroscopy (NIRS) combined with principal component and Mahalanobis distance model. The result show that NORMALIZE was the best pretreatment method of NORMALIZE, MSC, First Derivative and Second Derivative, the ideal spectral acquisition range of Soybean seed was 4000cm^-1～6900cm^-1, the cumulative contribution rate of the front four principal components reached 99.82%, it established the best model. The model could successfully complete the calibration samples and identify the prediction sample. This study proved that the use of near infrared spectroscopy combined with pattern recognition methods to rapid and nondestructive determination of seed vigor was indeed feasible. This study will offer a new method of testing soybean seed vigour with quick, non-destructive characters.

Abstract: In this paper, the effect of laser radiation on the germination percentage and growth of soybean seed is introduced. The experimental result demonstrate that soybean seed various measurement value is optimum when the soybean seed was irradiated on the seed hilum for 10 minute, using He-Ne laser of 5mw. And the experimental results is also most significant when the soybean seed was irradiated on the seed hilum for 90 second, using He-Ne laser of 40mw. It is founded the experimental data is not significant if the dose of He-Ne laser is less and soybean growth is restrained if the dose of He-Ne laser is more. This shows proper dose of He-Ne laser of soybean seed conducted radiation, promoted soybean seed enzyme activity enhanced, its germination process, the nutrient supply full, thereby improving the soybean seed germination rate, soybean seedlings plant height and chlorophyll content. The results offer us a reference for laser radioactive breed and Laser Biology.

Abstract: Transient Statistic Energy Analysis (T. S. E. A.) for transient response of a vibration system is investigated in this paper. Mathematical expressions of the rise time and the peak energy were derived. Numerical modeling of the system was also made. It showed that the peak energy decrease as the internal loss factor and the coupling stiffness decrease, the rise time decease as the internal loss factor and the coupling loss factor increase. It was found that the results of TSEA and the traditional methods are identical.