In this study,a novel testing method is proposed to characterize the dynamic shear property and failure mechanism of rocks by introducing the short beam compression(SBC)specimen into the split Hopkinson pressure bar(S...In this study,a novel testing method is proposed to characterize the dynamic shear property and failure mechanism of rocks by introducing the short beam compression(SBC)specimen into the split Hopkinson pressure bar(SHPB)system.Firstly,the stress distribution of SBC specimen is comprehensively analyzed by finite element method(FEM),and the results show that the optimal notch separation ratio of SBC specimen is C/H?0.2 to achieve successful dynamic simple-shear tests.Then,dynamic shear tests are conducted on sandstone using the SBC-SHPB method.Via careful pulse shaping technique,the dynamic force balance is guaranteed for SBC specimens,and the testing results show that the dynamic shear strength of sandstone is significantly rate-dependent.Combining the results of dynamic compression and tension tests,the failure envelopes of sandstone under different loading rates are obtained in the principle stress plane.It is found that the failure envelope of sandstone constantly expands outwards with increasing loading rate.Moreover,the energy partition of SBC specimen is quantified by virtue of high-speed digital image correlation(DIC)technique.The results show that the kinetic energy portion is non-negligible,and the shear fracture energy increases with increasing loading rate.In addition,the microscopic shear cracking mechanism of SBC specimen is analyzed by the thin section observation:the intra-granular(TG)fracture of minerals dominates the dynamic shear failure of sandstone,and the portion of TG fracture increases with increasing loading rate.This study provides a convenient and reliable method to investigate the dynamic shear property and failure mechanism of rocks.展开更多
A wood-based X-type lattice sandwich structure was manufactured by insertion-glue method.The birch was used as core,and Oriented Strand Board was used as panel of the sandwich structure.The short beam shear properties...A wood-based X-type lattice sandwich structure was manufactured by insertion-glue method.The birch was used as core,and Oriented Strand Board was used as panel of the sandwich structure.The short beam shear properties and the failure modes of the wood-based X-type lattice sandwich structure with different core direction(vertical and parallel),unit specification(120 mm×60 mm and 60 mm×60 mm),core size(50 mm and 60 mm),and drilling depth(9 mm and 12 mm)were investigated by a short beam shear test and the establishment of a theoretical model to study the equivalent shear modulus and deflection response of the X-type lattice sandwich structure.Results from the short beam shear test and the theoretical model showed that the failure modes of the wood-based X-type lattice sandwich structure were mainly the wrinkling and crushing of the panels under three-point bending load.The experimental values of deflection response of various type specimens were higher than the theoretical values of them.For the core direction of parallel,the smaller the unit specification is,the shorter the core size is,and the deeper the drilling depth is,the greater the short beam shear properties of the wood-based X-type lattice sandwich structure is.展开更多
With the help of the extended Huygens-Fresnel principle and the short-term mutual coherence function, the analytical formula of short-term average intensity for multi-Gaussian beam （MGB） in the turbulent a^mosphere ...With the help of the extended Huygens-Fresnel principle and the short-term mutual coherence function, the analytical formula of short-term average intensity for multi-Gaussian beam （MGB） in the turbulent a^mosphere has been derived. The intensity in the absence of turbulence and the long-term average intensity in turbulence can both also be expressed in this formula. As special cases, comparisons among short-term average intensity, long-term average intensity, and the intensity in the absence of turbulence for flat topped beam and annular beam are carried out. The effects of the order of MGB, propagation distance and aperture radius on beam spreading are analysed and discussed in detail.展开更多
毫米波频段拥有非常丰富的频谱资源,支持更高速的数据传输,因此成为通信领域近年来的研究热点。基于大规模输入输出(Massive Multiple Input Multiple Output,mMIMO)的波束成形技术可以有效补偿毫米波的高路损,是5G毫米波通信中的一项...毫米波频段拥有非常丰富的频谱资源,支持更高速的数据传输,因此成为通信领域近年来的研究热点。基于大规模输入输出(Massive Multiple Input Multiple Output,mMIMO)的波束成形技术可以有效补偿毫米波的高路损,是5G毫米波通信中的一项关键技术。但是在高速移动场景下,信道变化加速,必须进行频繁的波束切换才能保证良好的通信质量,故而大大增加了信令开销与资源消耗。如何在高动态场景下降低波束切换开销、提升波束切换速度与效率成为关键问题。针对直射径(Light of Sight,LOS)被遮挡情况下的复杂信道环境,文中提出了一种基于长短期记忆(Long Short Term Memory,LSTM)网络的多站点协作波束切换算法,根据过去一段时间的波束信息,学习信道环境与服务波束序号的内在联系,并预测当前时刻切换的最佳波束。仿真结果表明,与基于当前信道环境信息的遍历搜索算法相比,所提波束切换算法在上行发射功率较高时性能接近,在上行发送功率较低时,性能更优,体现了所提算法的优势。展开更多
基金The authors thank the financial support from the National Natural Science Foundation of China(Grant.Nos.52039007 and 52225904)the Youth Science and Technology Innovation Research Team Fund of Sichuan Province(Grant.No.2020JDTD0001).
文摘In this study,a novel testing method is proposed to characterize the dynamic shear property and failure mechanism of rocks by introducing the short beam compression(SBC)specimen into the split Hopkinson pressure bar(SHPB)system.Firstly,the stress distribution of SBC specimen is comprehensively analyzed by finite element method(FEM),and the results show that the optimal notch separation ratio of SBC specimen is C/H?0.2 to achieve successful dynamic simple-shear tests.Then,dynamic shear tests are conducted on sandstone using the SBC-SHPB method.Via careful pulse shaping technique,the dynamic force balance is guaranteed for SBC specimens,and the testing results show that the dynamic shear strength of sandstone is significantly rate-dependent.Combining the results of dynamic compression and tension tests,the failure envelopes of sandstone under different loading rates are obtained in the principle stress plane.It is found that the failure envelope of sandstone constantly expands outwards with increasing loading rate.Moreover,the energy partition of SBC specimen is quantified by virtue of high-speed digital image correlation(DIC)technique.The results show that the kinetic energy portion is non-negligible,and the shear fracture energy increases with increasing loading rate.In addition,the microscopic shear cracking mechanism of SBC specimen is analyzed by the thin section observation:the intra-granular(TG)fracture of minerals dominates the dynamic shear failure of sandstone,and the portion of TG fracture increases with increasing loading rate.This study provides a convenient and reliable method to investigate the dynamic shear property and failure mechanism of rocks.
基金supported by National Natural Science Foundation of China(31470581)Fundamental Research Funds for the Central Universities(2572016EBJ1).
文摘A wood-based X-type lattice sandwich structure was manufactured by insertion-glue method.The birch was used as core,and Oriented Strand Board was used as panel of the sandwich structure.The short beam shear properties and the failure modes of the wood-based X-type lattice sandwich structure with different core direction(vertical and parallel),unit specification(120 mm×60 mm and 60 mm×60 mm),core size(50 mm and 60 mm),and drilling depth(9 mm and 12 mm)were investigated by a short beam shear test and the establishment of a theoretical model to study the equivalent shear modulus and deflection response of the X-type lattice sandwich structure.Results from the short beam shear test and the theoretical model showed that the failure modes of the wood-based X-type lattice sandwich structure were mainly the wrinkling and crushing of the panels under three-point bending load.The experimental values of deflection response of various type specimens were higher than the theoretical values of them.For the core direction of parallel,the smaller the unit specification is,the shorter the core size is,and the deeper the drilling depth is,the greater the short beam shear properties of the wood-based X-type lattice sandwich structure is.
文摘With the help of the extended Huygens-Fresnel principle and the short-term mutual coherence function, the analytical formula of short-term average intensity for multi-Gaussian beam （MGB） in the turbulent a^mosphere has been derived. The intensity in the absence of turbulence and the long-term average intensity in turbulence can both also be expressed in this formula. As special cases, comparisons among short-term average intensity, long-term average intensity, and the intensity in the absence of turbulence for flat topped beam and annular beam are carried out. The effects of the order of MGB, propagation distance and aperture radius on beam spreading are analysed and discussed in detail.
文摘毫米波频段拥有非常丰富的频谱资源,支持更高速的数据传输,因此成为通信领域近年来的研究热点。基于大规模输入输出(Massive Multiple Input Multiple Output,mMIMO)的波束成形技术可以有效补偿毫米波的高路损,是5G毫米波通信中的一项关键技术。但是在高速移动场景下,信道变化加速,必须进行频繁的波束切换才能保证良好的通信质量,故而大大增加了信令开销与资源消耗。如何在高动态场景下降低波束切换开销、提升波束切换速度与效率成为关键问题。针对直射径(Light of Sight,LOS)被遮挡情况下的复杂信道环境,文中提出了一种基于长短期记忆(Long Short Term Memory,LSTM)网络的多站点协作波束切换算法,根据过去一段时间的波束信息,学习信道环境与服务波束序号的内在联系,并预测当前时刻切换的最佳波束。仿真结果表明,与基于当前信道环境信息的遍历搜索算法相比,所提波束切换算法在上行发射功率较高时性能接近,在上行发送功率较低时,性能更优,体现了所提算法的优势。
