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Accurate determination of gas content in deep coal mine is the premise for the prevention and control of gas disaster, as well as the efficient development and utilization of coalbed methane. Traditional coring technology of coal seam is generally open-ended and requires to obtain the amount of gas loss during the coring process by using estimation methods, making it difficult to ensure the accuracy and validity of the in-situ parameters of coalbed methane. Based on the academic idea of “in-site condition-maintaining coring”, the in-situ pressure- and gas-maintaining coring technology for deep coal seam was proposed, and the in-situ pressure- and gas-maintaining corer for deep coal seam was developed. The strength verification for corer outer tube, pressure-maintaining chamber and key weak parts were conducted based on three-dimensional numerical simulation. Meanwhile, the pressure-maintaining capacity of controller was measured and analysed relied on the self-developed pressure-maintaining coring laboratory simulation test platform, and the reliability of corer was verified through field tests in coal mine. The results shown that, the self-developed corer had the advantages of strong pressure-maintaining capacity, long pressure-maintaining time and stable anti-disturbance performance. The equivalent stress of the corer under internal fluid pressure of 20 MPa and torque of 1000 N·m was 121.1 MPa, which was much smaller than the yield strength of the material and met the strength design requirements. The equivalent stress of corer under the pressure of 20 MPa was 63.9 MPa, which met the strength design requirements. The corer can operate continuously and stably at the pressure of 19.4 MPa, which met the demand for gas testing in most of deep coal mines. The field test shown that, the pressure-maintaining controller of the pressure- and gas-maintaining corer closed well, with 100% of coring rate in the field. The research provides a theoretical, technical and equipment foundation for the accurate determination of gas content in deep coal seams, which is of great significance for the prevention and control of coal mine gas disasters and the exploration and development of coalbed methane.

ObjectiveIn order to solve the remotely operated vehicle (ROV) motion control being easily influenced by the environment and model uncertainty factors, as it is difficult to achieve the desired control effect, a sliding mode control method of ROV based on a parameter disturbance model is proposed. MethodsOn the base of standard ROV model, taking the external environmental disturbance, and the uncertainty parameter of the model as the model disturbance parameters, the ROV model with parameter disturbance is established, and the depth direction control model is obtained by decoupling the model. Under the new model, the sliding mode controller is designed for the depth determination motion of ROV. The sliding mode controller is designed based on the new model.ResultsThe simulation results show that the sliding mode controller based on the ROV model can control the ROV depth stabily, effectively and efficiently, and the control method can improve the influence of external disturbance and model parameter uncertainty.ConclusionThe design method of the controller can provide a solution to the problem of disturbance and model uncertainty in the ROV control process.

An anti-fading diversity receiving approach to body-area communications was proposed.A pair of opposite-sense called planar endfire circularly polarized antennas (PECPA) was employed to implement the receiving approach.The wide beamwidth CP characteristic of the PECPA was used to mitigate the height-dependent fadings.Antenna designs and body-area propagation measurements were performed at 5.8 GHz-band.An off-body channel model was established,and a channel simulator was accordingly developed.All results were compared to the cases using linearly polarized (LP) antennas diversity on equal conditions.The results show that the equal-gain-combination (EGC) signal levels for CP diversity reception are 2.1 dB greater than the LP one (with polarization mismatching loss removed).The rootmean-square delay spread (RDS) and number of multi-path component (MPC) can be significantly reduced.In addition,the simulated bit error rate (BER) of the body-area communication system using CP diversity can be improved by one order of magnitude compared the LP diversity one.The correctness and effectiveness of the proposed approach has been evidently validated by the experimental and simulated results.