Search

In order to accurately divide the risk range of coal spontaneous combustion in multiple goafs of shallow buried deep coal seam group and take effective prevention and control measures, based on the porous medium seepage equation and oxygen volume fraction equilibrium equation, the mathematical model is established by using particle flow discrete element software PFC, and the development law of fracture channel under the influence of repeated mining is studied. The results show that 78 % of the floor cracks are distributed in the range of 20 m of the boundary of mined-out area. The porosity distribution in the upper part of the mining space continues to expand with the advance of the working face, and maintains a slender shape. The areas with large porosity are still distributed above, behind and near the working face. According to the calculation results and the mining process, the danger range of the goaf area of the 1203 working surface is divided into serious air leakage danger area, general air leakage danger area, weak air leakage danger area and difficult air leakage danger area.

The new lattice floating wind turbine integrated system (also known as Dot Matrix Floating wind turbine, and hereinafter referred to as DMF) is proposed as a new concept. It is a design scheme that combines multiple wind turbines into a polygonal floating foundation in the form of a lattice arrangement, which can meet the research and development requirements of higher power generation equipment in the future. More far-reaching, it has obvious advantages over the traditional floating wind turbine scheme in terms of structural cost and motion stability, which provides a new idea for the development of offshore wind power energy. Firstly, the structural parameters and mechanical model of DMF are analyzed to determine the feasibility and superiority of the overall scheme of the new lattice foundation. Combined with the traditional OC4 semi-submersible wind turbine system, the hydrodynamic simulation under wind, wave, and current load is carried out, and the hydrodynamic response law of DMF under the different environmental factors is summarized and analyzed. It is concluded that the stability of DMF in pitching motion is 70% higher than that of traditional OC4 system. In order to further verify the feasibility of the DMF system and the accuracy of the theoretical model, based on the similarity theory, this study carried out the small-scale prototype processing of DMF and the simulation experiment of wind wave flume. The test results are in good agreement with the simulation data. Finally, aiming at the problem of the large amplitude of swaying motion response of DMF in the simulation results, a mooring optimization scheme suitable for the new DMF is proposed, which provides 47% stability compared with the traditional catenary mooring through comparative analysis. This study provides a reference and theoretical basis for the research and development of offshore multi-wind turbine combined equipment and hydrodynamic stability optimization. It has certain theoretical guiding significance and economic development value.

Due to low stiffness of compliant series robot body, the influence of joint flexible deformation caused by the gravity load of the end-effector on the absolute positioning accuracy cannot be ignored. In order to improve the flexible positioning accuracy of the robot end-effector, a calibration method for predicting and compensating the flexible positioning error of the 7-DOF series compliant robot due to the gravity load of the end-effector is proposed. The method identifies and predicts the pose configuration with similar flexible positioning error through the semi-parametric error model based on joint stiffness identification and of BP neural network. The feedforward method is used to compensate the positioning error. In this study, a 7-DOF series compliant robot is selected as the research object. Based on the principle of error similarity, the measurement points and the corresponding pose configurations are selected as the training data for the parameter identification of the semi-parametric error model, and the flexible positioning errors on the continuous trajectory of the end-effector are compensated according to the predicted values of the model. When the mass of the end-effector is 5 kg, by this method, the maximum value, mean value and mean square error of flexible positioning error on multiple straight-line trajectories on the plane are increased from 8.4779, 5.6039, and 1.8496 mm to 0.9720, 0.3079, and 0.2303 mm, respectively. It means the positioning accuracy are increased by 88.53%, 94.50%, and 87.55%, respectively, by which could observe that the precision of this robot's end-effector was significantly improved. [ABSTRACT FROM AUTHOR]

The fracture analysis of girth‐welded pipes is a vital link in the integrity assessment of oil and gas pipelines. However, the effect of welding residual stresses (WRS) on the load‐carrying capacity of the girth‐welded pipe with the crack remains unclear. In this study, based on the WRS simulation results verified by the full‐scale pipe welding experiment, a dynamic fracture finite element model could describe the fracture process of the pipe with the crack in the inner surface of the girth weld considering WRS was developed by the Gurson–Tvergaard–Needleman (GTN) damage model. Based on this fracture model, the fracture behavior of the pipe under tensile load in the presence of WRS was clarified, and the effect of WRS on the load‐carrying capacity was studied. The results indicated that the critical displacement and strain capacity of the pipeline decreased by 12.42% and 13.04% due to the negative action of the WRS. Highlights: A dynamic fracture model of the girth‐welded pipe considering WRS was developed.The differences in material properties of the girth weld were considered in the model.The effect of WRS on the load‐carrying capacity of the pipeline was studied. [ABSTRACT FROM AUTHOR]

In order to improve the accuracy and stability of rolling bearing performance prediction,a prediction method combining soft predictive ART-RBF integrated forecasting model and confidence CV value is proposed. The soft ART is introduced into the RBF neural network to establish the soft ART-RBF neural network prediction model. Combining with weighted average technology,the establishment of integrated soft ART-RBF neural network prediction model is carried out. And the confidence degree（CV） value with rich fault information is obtained through the self-organizing map（SOM） network as a comprehensive index to characterize the degradation of rolling bearing performance. Finally,the above method is verified by the acceleration signal obtained by the accelerated fatigue test of the rolling bearing. The results show that the method can effectively improve the accuracy and stability of the prediction of the degradation trend of rolling bearings.

Accurate prediction of tensile strain capacity (TSC) is the key to the strain-based design and assessment (SBDA) of buried pipelines. Various TSC prediction models proposed by research institutions such as the Pipeline Research Council International (PRCI) and the Center for Reliable Energy Systems (CRES) are not applicable to pipelines with corrosion defects. In view of this, this study proposed a new TSC prediction model for corroded pipes based on extensive parametric finite-element analysis (FEA) validated by full-size pipe (FSP) tensile tests. In the proposed model, the corrosion defects were assumed to be a curved boxed shape. Based on the dependence of the TSC on the input parameters, the model considered the combined effect of material properties and internal pressure on TSC and employed a defect geometry factor function based on the corrosion defect depth, width, and length. The accuracy and reliability of the proposed method were validated by extensive parametric FEA and error analysis. The results showed that the method can be applied to the practical safety assessment of corroded pipelines in strain-based design guidelines. Assessing the safety of pipelines by axial strain can solve the problem that it is difficult to monitor the complex strain state of the pipe body under ground movements. Tensile strain capacity is an element to assess the tensile resistance of buried pipes to fracture. This study developed a tensile strain capacity prediction model for corroded pipes, which is faster to calculate compared to existing evaluation methods. When corrosion anomalies are discovered in areas with ground movement hazards, the proposed model can be used to quickly estimate the tensile strain capacity of the pipeline to make contingency measures. When the evaluated corroded pipe still has sufficient serviceability, the strain monitoring equipment can be used to monitor the remote strain of the pipeline in real time, which needs to be guaranteed to be less than the tensile strain capacity to fully utilize the pipeline performance. The work in this study can provide a reference for strain-based assessment and design of corroded pipes. [ABSTRACT FROM AUTHOR]