Shijiu Jin

Study on the distributed optical fiber sensing technology for pipeline leakage protection

A new distributed optical fiber sensing technology to detect pipeline leakage in real time is introduced in this paper, which is based on Mach-Zehnder optical fiber interferometer. The principle of this technology is analyzed, and the phase change of light wave caused by the leakage acoustic wave is discussed as well. The results of the theory analysis and the experiments show that the measuring sensitivity of detecting leakage is greatly improved. Using this technology, the gas leakage of 0.4m3/min can be detected and the measured distance is about 50km under the condition that the pressure of the gas pipe is less than 0.2Mpa.

Detection of the abnormal events along the oil and gas pipeline and multi-scale chaotic character analysis of the detected signals

This paper studies the monitoring principle of abnormal events along oil and gas pipelines, which is conducted by a Mach?Zehnder optical fiber interferometer based distributed optical fiber pipeline pre-warning system. The detected signals of three typical abnormal events are analyzed by a multi-scale chaotic character analysis method based on orthogonal wavelet packet decomposition. In this pre-warning system, an optical cable is laid parallel to the pipeline in the same ditch and three single mode optical fibers in the optical cable make up the distributed micro-vibration measuring sensor. Using this system, leakage and other abnormal events can be detected by the sensor in real time and located with good precision. By orthogonal wavelet packet decomposition, the detected signals are analyzed by a multi-scale chaotic character analysis method, which calculates the correlation dimension under different frequency scales, resulting in more distinguishable differences among the three kinds of signals. The method proves more effective in recognizing the typical abnormal events by signals obtained from the experiment field.

Crucial technologies of oil-transporting pipe leak detection and location based on wavelet and chaos

By detecting pressure and flux simultaneously, the leak of an oil-transporting pipe can be found and diagnosed synthetically. The flux of pipes is measured by an ultrasonic flow meter; considering the precision of the flux measured, a method based on the character of intermittent chaos of the Duffing system to detect weak signals under strong noise is introduced. The ultrasonic signals with a certain frequency could be extracted accurately from the complicated strong noise. So the flux of pipes can be computed precisely by an accurate ultrasonic signal. The location of a leak position is mainly determined by the time difference between the negative pressure waves measured by the pressure sensors located at both ends of the oil-transporting pipe. A singular point of a negative pressure wave can be judged accurately by a coefficient feature of the local extreme values of the wavelet transform. So, the precise location of the leak position of the oil-transporting pipe can be found. It can be shown by results of experiments that the precision of the leak location has been improved effectively, which can be about 1%.

Two-beam phase-sensitive optical time domain reflectometer based on Jones matrix modeling

Abstract. A two-beam phase-sensitive optical time domain reflectometer (OTDR) is proposed and experimentally demonstrated. Optical pulses are launched into two distributed fibers. With the interference effect of two channel Rayleigh scattering signals and the positioning principle of the traditional OTDR, detection and location of vibration events along sensing fibers can be achieved using a new signal processing scheme. What is more, to investigate the sensitivity fading problem that often occurred when polarization controller (PC) is not utilized, the optical polarization model based on the equivalent Jones matrices of sensing fibers is established. Simulation results show that due to the polarization characteristic discrepancy of the sensing fibers, the signal amplitude varies a lot for different polarization states of the incident light. Experimental result shows that with the PC, the signal signal to noise ratio can be stabilized as 9.5 dB, which verifies the effectiveness of the sensor.

Development of Magnetostriction Sensor for on-line Liquid Level and Density Measurement

A new magnetostriction sensor and an on-line liquid level and density measuring equipment were developed. The operating principle of the measuring equipment with magnetostrictive sensor was described and a multi-floater relative displacement algorithm based on Wiedemann and Viuary effect was brought forward. The effect of density change on liquid level was investigated by considering of five liquids which density varies from 0.69 to 0.89 g/cm3 . Density correction algorithm was given to increase measuring precision of liquid density. With these correction algorithms, the measuring resolution of the magnetostrictive liquidometer may reach 0.1mm and the precision of magnetostrictive densimeter reaches 0.0001g/cm3. Good agreement has been obtained between the experiments and predictions for liquid level and density measurement. The equipment was installed on four tanks of a gas station in Jiangsu Province, China; one year site service showed that the equipment works very well

A New Method of Using Sensor Arrays for Gas Leakage Location Based on Correlation of the Time-Space Domain of Continuous Ultrasound

This paper proposes a time-space domain correlation-based method for gas leakage detection and location. It acquires the propagated signal on the skin of the plate by using a piezoelectric acoustic emission (AE) sensor array. The signal generated from the gas leakage hole (which diameter is less than 2 mm) is time continuous. By collecting and analyzing signals from different sensors’ positions in the array, the correlation among those signals in the time-space domain can be achieved. Then, the directional relationship between the sensor array and the leakage source can be calculated. The method successfully solves the real-time orientation problem of continuous ultrasonic signals generated from leakage sources (the orientation time is about 15 s once), and acquires high accuracy location information of leakage sources by the combination of multiple sets of orientation results. According to the experimental results, the mean value of the location absolute error is 5.83 mm on a one square meter plate, and the maximum location error is generally within a ±10 mm interval. Meanwhile, the error variance is less than 20.17.

Defect Characteristic Prediction of Pipeline by Means of Wavelet Neural Network Based on the Hierarchical Clustering Algorithm

It is very difficult to generalize the relationship between MFL signal and the defect geometric parameters of the pipeline because the relationship is nonlinear. Many applications of wavelet neural network on this field show that the defect geometric parameters can be obtained with this method to some extent. However, the initial centers have great influence on performance of the network. Hierarchical clustering algorithm is proposed in this paper and applied to classification of defect samples, centers selection and calculation of basis function width. With this algorithm, clusters similarity is computed to create tree structure and the perfect clustering is obtained. The sample set created from finite element defect simulation are used to train and validate the efficiency and reliability of the network based on hierarchical clustering algorithm. The experiment shows that the training speed and the prediction precision of the network can be improved simulataneously.Copyright

A Location Method Using Sensor Arrays for Continuous Gas Leakage in Integrally Stiffened Plates Based on the Acoustic Characteristics of the Stiffener.

This paper proposes a continuous leakage location method based on the ultrasonic array sensor, which is specific to continuous gas leakage in a pressure container with an integral stiffener. This method collects the ultrasonic signals generated from the leakage hole through the piezoelectric ultrasonic sensor array, and analyzes the space-time correlation of every collected signal in the array. Meanwhile, it combines with the method of frequency compensation and superposition in time domain (SITD), based on the acoustic characteristics of the stiffener, to obtain a high-accuracy location result on the stiffener wall. According to the experimental results, the method successfully solves the orientation problem concerning continuous ultrasonic signals generated from leakage sources, and acquires high accuracy location information on the leakage source using a combination of multiple sets of orienting results. The mean value of location absolute error is 13.51 mm on the one-square-meter plate with an integral stiffener (4 mm width; 20 mm height; 197 mm spacing), and the maximum location absolute error is generally within a ±25 mm interval.

Pull-In Analysis of the Flat Circular CMUT Cell Featuring Sealed Cavity

Capacitive micromachined ultrasonic transducers (CMUTs) are one of the appealing MEMS devices. Most studies treat CMUTs as rigid plates vibrating in open air, ignoring the mechanical boundary conditions for simplification and resulting in cumulative errors in coupled fields. This paper presents a new analytical model for the pull-in characteristics of the flat circular CMUT cell featuring sealed cavity. Utilizing the plate theory coupled with Boyle’s law, the paper establishes a strong relation between the pressures inside the sealed cavity and the pull-in characteristics for the first time. Not only did we point out that the existence of the pressure inside the sealed cavity cannot be omitted, but we also quantified the direct effect of the pressure ratios on the pull-in phenomenon. The pull-in voltages increase while the pull-in ratios decrease with the pressure ratios of the pressure inside the sealed cavity to the ambient pressure. The proposed calculation process delivers a good approximation of the pull-in voltages and displacements, which are consistent with COMSOL simulation results. Particularly, the percentage error of our calculation process is 6.986% for the worst case. Therefore, our proposed analytical model accurately and efficiently predicts the pull-in characteristics and this paper offers new perspectives and reference value in designing and modeling the CMUTs.

Multicarrier Spread Spectrum Communication Scheme for Cruising Sensor Network in Confined Underwater Space

A cruising sensor network works as an online monitoring system for industrial liquid environments such as oil tanks and nuclear storage ponds. The cruising sensor network consists of a few submerged nodes which can actuate themselves to execute tasks like “cruising.” This paper presents a multicarrier spread spectrum scheme, which is designed for communications between the nodes and the control station. Although underwater acoustic communication has been widely researched due to the growing demands from ocean development and marine research, communication in confined underwater space is an unexplored domain as most research focuses on communication in spacious water areas. The occasions that the cruising sensor network works in are confined. The main distinction in confined underwater spaces is the existence of strong multipath arrivals reflected by the boundaries, which can cause more severe intersymbol interference (ISI). We propose a communication scheme which applies spread spectrum in orthogonal frequency-division multiplexing (OFDM) to address severe frequency selective fading channels. This scheme can be robust in confined underwater channels when coupled with turbo code. The simulation and experimental results prove the feasibility and reliability of this scheme. It is demonstrated that significantly better performance is achieved than that of the conventional OFDM method.