Papers by Author: Min Li

Abstract: High-speed aircraft is in service condition of high temperature, high pressure and strong noise during flight. Strong noise will damage structures and equipments of an aircraft, and the existence of high temperature and high pressure will greatly increase the damage degree. Therefore, research on aircraft structure characteristic and surface acoustic characteristic is very significant. The hybrid method of CFD and acoustic solver combination method can accurately obtain aerodynamic noise load on the aircraft structure surface in a high velocity environment. The hybrid method can make acoustic and vibration analysis for aircraft structure, and get influence of noise load on it. The simulated results show that the presence of high temperature and high pressure can make the natural frequency of typical components and whole machine model reduction, and the acoustic load on the aircraft structure model surface is larger at low frequency, smaller at high frequency.

Abstract: The problem of off-tracking in looper area of a cold rolling strip production line is usually unavoidable especially when the looper carriage is located far away from the strip deviation detection device. The looper carriage itself is the best place for installing the detecting sensor. However, the wired monitoring system is not suitable because the carriage is moving and the power of common wireless monitoring system has to be recharged manually and frequently due to a high power consumption of the detecting sensor. A novel method of strip off-tracking online monitoring method via wireless sensor network with self-powered nodes is proposed, which is helpful to overcome the difficulties of the conventional methods. The energy of the wireless monitoring node was supplied by an electromagnetic induction generator driven by a devised transmission mechanism. An intelligent power-recharging control module including a single-ended primary-inductor converter was designed to charge the lead acid battery using a floating charging strategy. A selective space diversity scheme for receiving node in the wireless sensor network was put forward to resist path loss and fading in industrial environment. Theoretical analysis and experiment results have proved the feasibility of the proposed method.

Abstract: The characteristic of cyclical impact is reflected on the signal of rolling bearing in fault condition. The carrier frequency is modulated by times of the failure frequencies. When the traditional cyclical spectrum density (CSD) method is used to analyze the signal, all the modulation frequencies will be demodulated in the cyclic frequency spectrum. In this case, it is difficult to recognize the fault type of the bearing. Therefore, a new cyclical spectrum density method based on the kurtosis energy (CSDK) is proposed. The kurtosis of every cyclic frequency’s slice is used as the weight coefficient of the cyclic frequency’s energy accumulation to extract fault feature effectively. The proposed method has greatly reduced times of the harmonic frequencies’ effect in traditional CSD method. The analysis of the signal gathered from the outer rolling bearing of blast furnace belt cylinder shows that the fault feature extracted by the new method is more clear and accurate than CSD method.

Abstract: At present, the flight velocity and flight performance of an aircraft are higher, so that aerodynamic noise caused by an engine jet in the take-off and flight processes can reach 160 dB. The high strength of the jet aerodynamic noise is very harmful to vehicle drivers, vehicle structures and airborne equipments. Two numerical calculation methods to aerodynamic noise, the FW-H acoustic analogy method and the FW-H acoustic analogy and boundary element combining method, were introduced. These two methods were used to predict the aerodynamic noise, and the numerical calculation results were compared with the physical experimental results. Results show that the FW-H acoustic analogy method can predict aerodynamic noise. However, it cannot predict the sound field distribution. The FW-H acoustic analogy and boundary element combining method is able to predict the sound field distribution with sound reflection.

Abstract: In order to solve the time delay problem between the process parameters and the quality indicators in the modeling processes, a method of time delay estimation on COREX parameters is proposed based on Dynamic Time Warping (DTW) algorithm. The method solves the problem existing in the conventional methods which demand the number of calculating sample to be same. Taking the real field data from Baosteel COREX-3000 as the research object, the DTW distances between the process parameters and the quality indicators are calculated, and then the delay time is estimated. The real field data are used for verification, the results show that the proposed method can estimate the time daley effectively, and the prediction accuracy of model which used time delay estimation becomes higher. It provides an effective measure for model preprocessing.

Abstract: The application of the temper mill is mainly to improve the mechanical property of strip and to rectify the shape of strip. The working roll of a temper mill is often running with alternating load that prone to lead to faults such as wear, crack and spalling, which cause severe quality problems in the production of strip steel. In order to gain the information of crack's location and depth, the proposed method employs two circles of AE sensors along the direction of the roll body and use static pressure as external loads together with time-of-arrival localization method to detect the exact location of the roll cracks. The positioning results confirmed the validity of the proposed method with the post-repair grinding data. The advantage of this detection method is not requiring the full roll body scan point by point. With only one layout of the sensors, the method can detect the crack location with high efficiency and good real-time property.

Abstract: Aimed at the problem of low resolution and cross term interference of the traditional time-frequency analysis methods, a new time-frequency filtering method based on generalized S transform is proposed. The method is extended under the premise of the linearity, lossless invertibility, high time-frequency resolution of S transform. On the basis, a coefficient which is direct to the signal energy distribution is introduced. In this way, the resolution of the S transform can be adjust adaptively. Eventually, this method is applied to the time-frequency filtering. The results of simulation and faulty bearing show that the proposed methodology can achieve good effect of noise reduction, and be more suitable for the non-stationary characteristics of vibration signals.

Abstract: Selecting feature in slow-speed and heavy-load equipments has always been a difficult problem. A new feature selection method based on Laplacian Score is used to Acoustic Emission signal. The more capable of describing the sample clustering property, the more important the selected feature is. The method is a ‘filter’ and unsupervised feature selection method which is just dependent on the space distribution of the sample instead of classifier. Therefore, the method enjoys a simple algorithm and low complexity. The effectiveness of the method is verified by the AE datasets from the bearings of a blast furnace’s belt conveyor.

Abstract: In COREX processes, the cold gas is produced in melter gasifier, after being cooled and dust controlled, blown into the blast furnace and used in the reduction reaction. The cold gas content plays a key role in the reaction of lump ore and pellets reduction. A prediction model of COREX cold gas content of carbon dioxide is proposed based on modified orthogonal signal correction partial least squares algorithm (MOSC-PLS). Firstly, the input and output variables of the model are selected according to the COREX processes principle. Secondly, MOSC algorithm is used to preprocess the data, in order to remove the irrelevant information between the input and output variables of the model. Finally, prediction model is built based on PLS. The real field data of cold gas content of carbon dioxide from Baosteel COREX are used for verification. The results show that MOSC-PLS has an advantage over the orthogonal signal correction partial least squares (OSC-PLS) in prediction accuracy. Thus the necessary decision supports and analysis tools for the cold gas content control are provided.

Abstract: A method for setting up flexible and web based remote laboratory for mechatronics system experiment course is proposed. Unlike most current remote laboratories, in which the experiment procedures are always fixed, the new remote laboratory provides more flexibility to students in designing and testing programs and watching experiment results remotely via network. The proposed remote laboratory is implemented through windows remote desktop and web service technology, and also includes a course web site which is established for experiment selection and management. The whole new remote laboratory platform is easy to develop and maintain, and has been used during teaching practice of mechatronics system experiment course in University of Science and Technology Beijing, covering experiments of PLC-based stepper motor control and DAQ card based condition monitoring.