Jianqiang Guo

The detection of wheel-flats based on fiber optic Bragg grating array

During the long-time working circle, the wheels will be damaged to a certain degree caused by the wearing, the impact, the loads, the climate and so on. In order to evaluate the health of the wheels and reduce the potential losses, many effective methods are used in railway health monitoring, such as laser method or ultrasonic method. But few of them can reach the demand of the real-time online detection, and integrate more comprehensive inspection function at the same time. A composite detection scheme for wheel-tread defects based on FBG sensing technique has been investigated in this paper. By collecting and analyzing the data from the sensors which are distributed on tracks and rails, we can precisely evaluate the Wheel-flats and also measure some other parameters used in rail health monitoring scheme such as speed, loads and axle counting measurement.

Method of ultrasonic phased array imaging based on segment amplitude apodization

Single amplitude apodization technology applied in ultrasound imaging system can obtain better imaging resolution only within a certain distance, outside of this range the resolution is significantly lower, while using segment dynamic apodization technique can make up for this shortfall. Therefore, we make an analysis and research on the basis of the beams about the 3 dB equivalent distribution with a variety of single amplitude apodization functions, and observe to come to the best imaging resolution range for each function, then calculate the dynamic weighting value by establishing a linear phased array sound field simulation model, thus find a way to achieve segment dynamic amplitude apodization, and draw the 3 dB contour and the distribution of sound field to prove the feasibility of this technique.

Influence of the concentration measurement of carbon monoxide with temperature

In order to figure out the concentration of carbon monoxide, by measuring the second and third harmonics of the absorption spectrum line, this paper obtained results which indicate that this method can be applied to industry field. Tunable semiconductor laser of 1.58um can be used, and its wavelength is a nice window of communication in long wavelength band of fiber. The measurement optical paths can well be integrated with fiber and passive component in fiber system and it is already applied to industry field. Moreover, the 1.58um spectrum line is an absorption peak of carbon monoxide and around the spectrum line, there is a good transmission window in the background gas of atmosphere. It is very well to measure carbon monoxide concentration. Through measuring peaks of the first and second harmonic or the second and fourth harmonic of absorption spectrum lines of carbon monoxide with tunable diode laser absorption spectroscopy (TDLAS) technique, the carbon monoxide concentration can accurately be calculated by composition algebra. This paper focuses on the study that the absorption coefficient changes with temperature. As the absorption coefficient of different temperature changes, the parameters of concentration measurement will change. This is a very complicated process.

Implementation of total focusing method for phased array ultrasonic imaging on FPGA

This paper describes a multi-FPGA imaging system dedicated for the real-time imaging using the Total Focusing Method (TFM) and Full Matrix Capture (FMC). The system was entirely described using Verilog HDL language and implemented on Altera Stratix IV GX FPGA development board. The whole algorithm process is to: establish a coordinate system of image and divide it into grids; calculate the complete acoustic distance of array element between transmitting array element and receiving array element, and transform it into index value; then index the sound pressure values from ROM and superimpose sound pressure values to get pixel value of one focus point; and calculate the pixel values of all focus points to get the final imaging. The imaging result shows that this algorithm has high SNR of defect imaging. And FPGA with parallel processing capability can provide high speed performance, so this system can provide the imaging interface, with complete function and good performance.

Detection of wheel rim by immersion scan of phased array ultrasonic flaw testing

In order to achieve the in-service detection to high speed train wheel rims, this article analyzed the effects of the number of array elements to image focusing and image quality using water immersion ultrasonic phased array technology. Also, the effects of the depth of water to detecting technique had been researched. According to the results of the experiments, the number of optimal array elements, the corresponding thickness of immersion layer, and the optimal range of water’s depth had been obtained. Thus, appropriate references had been provided to water immersion ultrasonic phased array testing.

Ultrasonic TOFD image registration algorithm of sub-pixel accuracy based on DFT

This article is based on the correlation of FFT(Fast Fourier Transform) to study the ultrasonic TOFD(Time Of Flight Diffraction) image registration algorithm and according to the principle of template matching algorithm, the process is simple and the registration locations are accurate, so that the detected images are clear and defected features are obvious. The subsequent sub-pixel image registration algorithm of TOFD will improve registration accuracy to sub-pixel level, to further perfect the TOFD image registration algorithms, more conducive to subsequent image processing.

Defect detection study on total focus method of sound field imaging based on parallel processing

In order to process real-time phased array ultrasound imaging, to improve imaging resolution, and achieve on-line defect detection, total focusing method (TFM) imaging algorithm is used for the complete data, thrust reversers the focus and algorithm in different positions, the computational problems of large data can be solved by the FPGA parallel algorithms. After that, the total focusing method imaging algorithm can be realized in the real-time detection.

Wheel rim stress detecting using ultrasonic testing technology

Train wheels should undergo heat treatment, thus producing circumferential compressive force on the tread to void crack propagation, and this way eventually increases the train wheel service life, excluding situations like wheel burst due to crack. Hem shoes braking will lead to calorification and cooling of wheel rim,in this case stress state of wheel rim will would change under the influence of caloric and mechanical load, and compressive stress will turn to circumferential tensile force. For wheels in service, small flaws appear in the shallow layer of wheel tread, and will expand into depth. Consequently, detecting of wheel rim stress state should be attached more importance. Ultrasonic testing technology is an extremely important method for convenient, fast and non-destructive detecting in routine application of wheel sets. Verification of ultrasonic detecting method in detecting stress of wheel rim is given in this paper. On experimentation platform established with wheel rim stress detecting equipment and tensile stress mechanism, ultrasonic wheel rim stress detecting method is verified to be reliable and stable in the light of contrast between theoretical and experimental results. Basing on wheel rim stress measurement method using transverse straight probe, results are obtained by measuring test block and wheel rim stress, and ultrasonic wheel rim stress detecting method is approved to be feasible in application.

Study on LDPC Application in Wireless Communication System

Low-density-parity-check (LDPC) is linear group code with sparse check-up matrix. It not only has the good performance of approaching the Shannon limit, but also lowers decoding complexity and the structure is more flexible. This paper mainly focuses on LDPC whose length is 672 bit and rate is 2/3 in the IEEE802.16e standard, and completes LDPC simulation in wireless communication system using Matlab and Simulink. The conclusion shows that LDPC has good performance in a simulation atmosphere noise condition.

Study of instrument measurement of carbon monoxide concentration by absorption spectrum

This paper presents the measurement of the carbon monoxide concentration in industry field by scanning absorption spectrum. In the measurement, the frequency of DFB laser is stabilized in the central frequency point of absorption peak in 1.57μm absorption band of carbon monoxide by a control system with a standard CO gas chamber, fiber loop, TEC controlled by MCU and its temperature stability is 0.01°C at long time to stabilize the central frequency. In the process of measurement, at first, the CO absorption spectrum will be determined by a standard gas camber to choose a maximum CO absorption peak in its frequency band and its frequency point will be stabilized. The parameters of the operation frequency and environment will be stored in the NV memory in MCU as next operation condition. The concentration can be calculated in a composite algebra operation by first and second harmonic intensity passed through test gas chamber. It has very high measurement precision and real time. The experiment result is consistent with actual gas concentration. It shows that the measurement scheme is valuable for fast, real-time and efficiency measurement.