Effects of sub-/super-critical CO_(2)on the fracture-related mechanical characteristics of bituminous coal

Injecting carbon dioxide CO_(2)into a coal seam is an important way to improve coalbed methane recovery and to store geological carbon.The fracture mechanical characteristics of bituminous coal determine the propagation and evolution of cracks,which directly affect CO_(2)storage in coal seams and the efficiency of resource recovery.This study applied CO_(2)adsorption and three-point bending fracture experiments using bituminous coal samples in a gaseous state(4 MPa),subcritical state(6 MPa),and supercritical state(8 and 12 MPa)to investigate the influence of CO_(2)state and anisotropy on the fracture-related mechanical response of bituminous coal.The results show that the change in mechanical properties caused by CO_(2)adsorption is CO_(2)state-dependent.The supercritical CO_(2)adsorption at 8 MPa causes the largest decrease in the mode-I fracture toughness(KIC),which is 63.6%lower than the toughness before CO_(2)adsorption.The instability characteristics of bituminous coal show the transformation trend of“sudden-gradual-sudden fracture”.With or without CO_(2)adsorption,the order of the KIC associated with three types of bituminous coal specimens is crack-divider type>crack-arrester type>crack-short transverse type.Phenomenologically,the fracture toughness of bituminous coal is positively correlated with its specific surface area and total pore volume;the toughness is negatively correlated with its average pore size.

Beam-pointing error compensation method of phased array radar seeker with phantom-bit technology

A phased array radar seeker（PARS） must be able to effectively decouple body motion and accurately extract the line-of-sight（LOS） rate for target missile tracking.In this study,the realtime two-channel beam pointing error（BPE） compensation method of PARS for LOS rate extraction is designed.The PARS discrete beam motion principium is analyzed,and the mathematical model of beam scanning control is finished.According to the principle of the antenna element shift phase,both the antenna element shift phase law and the causes of beam-pointing error under phantom-bit conditions are analyzed,and the effect of BPE caused by phantom-bit technology（PBT） on the extraction accuracy of the LOS rate is examined.A compensation method is given,which includes coordinate transforms,beam angle margin compensation,and detector dislocation angle calculation.When the method is used,the beam angle margin in the pitch and yaw directions is calculated to reduce the effect of the missile body disturbance and to improve LOS rate extraction precision by compensating for the detector dislocation angle.The simulation results validate the proposed method.