The mechanical properties of residual coal pillars under the influence of upward mining disturbances significantly affect the safety of residual mining activities on working faces.This study conducted low-frequency di...The mechanical properties of residual coal pillars under the influence of upward mining disturbances significantly affect the safety of residual mining activities on working faces.This study conducted low-frequency disturbance dynamic uniaxial compression tests on coal specimens using a self-developed dynamic-static load coupling electro-hydraulic servo system,and studied the strength evolutions,surface deformations,acoustic emission(AE)characteristic parameters,and the failure modes of coal specimens with different static preloading levels were studied.The disturbance damage is positively correlated with the coal specimen static preload level.Specifically,the cumulative AE count rates of the initial accelerated damage stage for the coal specimens with static preloading level of 60%and 70%of the uniaxial compressive strength(UCS)were 2.66 and 3.19 times that of the 50%UCS specimens,respectively.Macroscopically,this behaviour manifested as a decrease in the compressive strength,and the mean strengths of the disturbance-damaged coal specimens with 60%and 70%of UCS static preloading decreased by 8.53%and 9.32%,respectively,compared to those of the specimens under pure static loading.The crack sources,such as the primary fissures,strongly control the dynamic response of the coal specimen.The difference between the dynamic responses of the coal specimens and that of dense rocks is significant.展开更多
In order to suppress the low-frequency ultrasound vibration in the broadband range of 20 k Hz—100 k Hz,this paper proposes and discusses an acoustic metamaterial with low-frequency ultrasound vibration attenuation pr...In order to suppress the low-frequency ultrasound vibration in the broadband range of 20 k Hz—100 k Hz,this paper proposes and discusses an acoustic metamaterial with low-frequency ultrasound vibration attenuation properties,which is configured by hybrid arc and sharp-angle convergent star-shaped lattices.The effect of the dispersion relation and the bandgap characteristic for the scatterers in star-shaped are simulated and analyzed.The target bandgap width is extended by optimizing the geometry parameters of arc and sharp-angle convergent lattices.The proposed metamaterial configured by optimized hybrid lattices exhibits remarkable broad bandgap characteristics by bandgap complementarity,and the simulation results verify a 99%vibration attenuation amplitude can be obtained in the frequency of20 k Hz—100 k Hz.After the fabrication of the proposed hybrid configurational star-shaped metamaterial by 3D printing technique,the transmission loss experiments are performed,and the experimental results indicate that the fabricated metamaterial has the characteristics of broadband vibration attenuation and an amplitude greater than 85%attenuation for the target frequency.These results demonstrate that the hybrid configurational star-shaped metamaterials can effectively widen the bandgap and realize high efficiency attenuation,which has capability for the vibration attenuation in the application of highprecise equipment.展开更多
In this paper,a control scheme based on current optimization is proposed for dual three-phase permanent-magnet synchronous motor(DTP-PMSM)drive to reduce the low-frequency temperature swing.The reduction of temperatur...In this paper,a control scheme based on current optimization is proposed for dual three-phase permanent-magnet synchronous motor(DTP-PMSM)drive to reduce the low-frequency temperature swing.The reduction of temperature swing can be equivalent to reducing maximum instantaneous phase copper loss in this paper.First,a two-level optimization aiming at minimizing maximum instantaneous phase copper loss at each electrical angle is proposed.Then,the optimization is transformed to a singlelevel optimization by introducing the auxiliary variable for easy solving.Considering that singleobjective optimization trades a great total copper loss for a small reduction of maximum phase copper loss,the optimization considering both instantaneous total copper loss and maximum phase copper loss is proposed,which has the same performance of temperature swing reduction but with lower total loss.In this way,the proposed control scheme can reduce maximum junction temperature by 11%.Both simulation and experimental results are presented to prove the effectiveness and superiority of the proposed control scheme for low-frequency temperature swing reduction.展开更多
In order to analyze the possibility of detecting defects in bend pipe using low-frequency ultrasonic guided wave, the propagation of T(0,1) mode and L(0,2) mode through straight-curved-straight pipe sections was studi...In order to analyze the possibility of detecting defects in bend pipe using low-frequency ultrasonic guided wave, the propagation of T(0,1) mode and L(0,2) mode through straight-curved-straight pipe sections was studied. FE(finite element) models of bend pipe without defects and those with defects were introduced to analyze energy distribution, mode transition and defect detection of ultrasonic guided wave. FE simulation results were validated by experiments of four different bend pipes with circumferential defects in different positions. It is shown that most energy of T(0,1) mode or L(0,2) mode focuses on extrados of bend but little passes through intrados of bend, and T(0,1) mode or L(0,2) mode is converted to other possible non-axisymmetric modes when propagating through the bend and the defect after bend respectively. Furthermore, L(0,2) mode is more sensitive to circumferential notch than T(0,1) mode. The results of this work are beneficial for practical testing of pipes.展开更多
Shiology,abbreviated from the study of shiance,stands as a"disciplinary category"level knowledge system.Within the Chinese educational system's subject catalog,it is an extension of agricultural science(...Shiology,abbreviated from the study of shiance,stands as a"disciplinary category"level knowledge system.Within the Chinese educational system's subject catalog,it is an extension of agricultural science(09),and it is a knowledge system that integrates the eater needs,food acquisition and shiance order.Cognition of previously unrecognized objects requires new concepts,and the construction of a new knowledge system cannot be separated from the support of new concepts.Shiance knowledge system is a huge collection of shiance concepts,and this research limits its discussion to the connotations and extensions of four core groups of concepts:shiance,food,eaters,and eating.These core concepts of shiance knowledge also serve as the foundational terms for constructing the shiology framework.Establishing the foundational terms and definitions of shiology is a fundamental research endeavor.If one were to liken the shiology framework to a building,then its foundational terms are akin to the"bricks";defining these terms is comparable to setting standards for these"bricks",facilitating the construction of a more robust structure.The basic words discussed in this research include 34 in the category of"shiance",31 in the category of"food",seven in the category of"eaters"and 16 in the category of"eating".These basic words play a fundamental and leading role in the process of constructing the system of shiology system,and they are used in the names of 40 subjects in the 53 basic shiology systems.The absence and narrowing of cognitive concepts are at the root of the lack of systematic governance of human shiance issues.展开更多
短时交通流预测在智能交通系统中扮演重要的角色。针对交通流复杂多变的时空特征、非平稳性及外部因素引发的数据异常,提出考虑异常因素的混合深度神经网络预测模型(hybrid deep neural network forecasting model considering anomalou...短时交通流预测在智能交通系统中扮演重要的角色。针对交通流复杂多变的时空特征、非平稳性及外部因素引发的数据异常,提出考虑异常因素的混合深度神经网络预测模型(hybrid deep neural network forecasting model considering anomalous factors,HDNNF-CAF)。该模型将邻接矩阵、交通流量矩阵及交通流其他参数矩阵结合异常数据处理理论,进行数据预处理和异常数据识别。建立异常数据时空特征提取理论,捕获异常数据时空信息;利用变分模态分解(VMD)降低交通流数据非平稳性,并提出图卷积网络(GCN)优化Informer理论分别对各个子序列进行特征提取,以组合生成交通流时空信息。最终结合异常数据与交通流数据的时空信息生成预测结果。在真实数据集PeMS04上进行验证,实验结果表明,HDNNF-CAF能够有效识别交通流异常数据,提高预测精度,优于一些现有方法。展开更多
基金Projects(51925402,52334005,52304094)supported by the National Natural Science Foundation of ChinaProject(20201102004)supported by the Shanxi Science and Technology Major Project,China。
文摘The mechanical properties of residual coal pillars under the influence of upward mining disturbances significantly affect the safety of residual mining activities on working faces.This study conducted low-frequency disturbance dynamic uniaxial compression tests on coal specimens using a self-developed dynamic-static load coupling electro-hydraulic servo system,and studied the strength evolutions,surface deformations,acoustic emission(AE)characteristic parameters,and the failure modes of coal specimens with different static preloading levels were studied.The disturbance damage is positively correlated with the coal specimen static preload level.Specifically,the cumulative AE count rates of the initial accelerated damage stage for the coal specimens with static preloading level of 60%and 70%of the uniaxial compressive strength(UCS)were 2.66 and 3.19 times that of the 50%UCS specimens,respectively.Macroscopically,this behaviour manifested as a decrease in the compressive strength,and the mean strengths of the disturbance-damaged coal specimens with 60%and 70%of UCS static preloading decreased by 8.53%and 9.32%,respectively,compared to those of the specimens under pure static loading.The crack sources,such as the primary fissures,strongly control the dynamic response of the coal specimen.The difference between the dynamic responses of the coal specimens and that of dense rocks is significant.
基金National Natural Science Foundation of China(Grant Nos.51821003,52175524,61704158)the Natural Science Foundation of Shanxi Province(Grant No.202103021224206)Shanxi"1331 Project"Key Subjects Construction to provide fund for conducting experiments。
文摘In order to suppress the low-frequency ultrasound vibration in the broadband range of 20 k Hz—100 k Hz,this paper proposes and discusses an acoustic metamaterial with low-frequency ultrasound vibration attenuation properties,which is configured by hybrid arc and sharp-angle convergent star-shaped lattices.The effect of the dispersion relation and the bandgap characteristic for the scatterers in star-shaped are simulated and analyzed.The target bandgap width is extended by optimizing the geometry parameters of arc and sharp-angle convergent lattices.The proposed metamaterial configured by optimized hybrid lattices exhibits remarkable broad bandgap characteristics by bandgap complementarity,and the simulation results verify a 99%vibration attenuation amplitude can be obtained in the frequency of20 k Hz—100 k Hz.After the fabrication of the proposed hybrid configurational star-shaped metamaterial by 3D printing technique,the transmission loss experiments are performed,and the experimental results indicate that the fabricated metamaterial has the characteristics of broadband vibration attenuation and an amplitude greater than 85%attenuation for the target frequency.These results demonstrate that the hybrid configurational star-shaped metamaterials can effectively widen the bandgap and realize high efficiency attenuation,which has capability for the vibration attenuation in the application of highprecise equipment.
基金supported by the National Natural Science Foundation of China(No.62271109)。
文摘In this paper,a control scheme based on current optimization is proposed for dual three-phase permanent-magnet synchronous motor(DTP-PMSM)drive to reduce the low-frequency temperature swing.The reduction of temperature swing can be equivalent to reducing maximum instantaneous phase copper loss in this paper.First,a two-level optimization aiming at minimizing maximum instantaneous phase copper loss at each electrical angle is proposed.Then,the optimization is transformed to a singlelevel optimization by introducing the auxiliary variable for easy solving.Considering that singleobjective optimization trades a great total copper loss for a small reduction of maximum phase copper loss,the optimization considering both instantaneous total copper loss and maximum phase copper loss is proposed,which has the same performance of temperature swing reduction but with lower total loss.In this way,the proposed control scheme can reduce maximum junction temperature by 11%.Both simulation and experimental results are presented to prove the effectiveness and superiority of the proposed control scheme for low-frequency temperature swing reduction.
基金Project(51265044)supported by the National Natural Science Foundation of ChinaProject(2013TT2028)supported by the Science and Technology Project of Hunan Province of ChinaProject(2012QK162)supported by the Science and Technology Project of General Administration of Quality Supervision,Inspection and Quarantine of China
文摘In order to analyze the possibility of detecting defects in bend pipe using low-frequency ultrasonic guided wave, the propagation of T(0,1) mode and L(0,2) mode through straight-curved-straight pipe sections was studied. FE(finite element) models of bend pipe without defects and those with defects were introduced to analyze energy distribution, mode transition and defect detection of ultrasonic guided wave. FE simulation results were validated by experiments of four different bend pipes with circumferential defects in different positions. It is shown that most energy of T(0,1) mode or L(0,2) mode focuses on extrados of bend but little passes through intrados of bend, and T(0,1) mode or L(0,2) mode is converted to other possible non-axisymmetric modes when propagating through the bend and the defect after bend respectively. Furthermore, L(0,2) mode is more sensitive to circumferential notch than T(0,1) mode. The results of this work are beneficial for practical testing of pipes.
文摘Shiology,abbreviated from the study of shiance,stands as a"disciplinary category"level knowledge system.Within the Chinese educational system's subject catalog,it is an extension of agricultural science(09),and it is a knowledge system that integrates the eater needs,food acquisition and shiance order.Cognition of previously unrecognized objects requires new concepts,and the construction of a new knowledge system cannot be separated from the support of new concepts.Shiance knowledge system is a huge collection of shiance concepts,and this research limits its discussion to the connotations and extensions of four core groups of concepts:shiance,food,eaters,and eating.These core concepts of shiance knowledge also serve as the foundational terms for constructing the shiology framework.Establishing the foundational terms and definitions of shiology is a fundamental research endeavor.If one were to liken the shiology framework to a building,then its foundational terms are akin to the"bricks";defining these terms is comparable to setting standards for these"bricks",facilitating the construction of a more robust structure.The basic words discussed in this research include 34 in the category of"shiance",31 in the category of"food",seven in the category of"eaters"and 16 in the category of"eating".These basic words play a fundamental and leading role in the process of constructing the system of shiology system,and they are used in the names of 40 subjects in the 53 basic shiology systems.The absence and narrowing of cognitive concepts are at the root of the lack of systematic governance of human shiance issues.
文摘短时交通流预测在智能交通系统中扮演重要的角色。针对交通流复杂多变的时空特征、非平稳性及外部因素引发的数据异常,提出考虑异常因素的混合深度神经网络预测模型(hybrid deep neural network forecasting model considering anomalous factors,HDNNF-CAF)。该模型将邻接矩阵、交通流量矩阵及交通流其他参数矩阵结合异常数据处理理论,进行数据预处理和异常数据识别。建立异常数据时空特征提取理论,捕获异常数据时空信息;利用变分模态分解(VMD)降低交通流数据非平稳性,并提出图卷积网络(GCN)优化Informer理论分别对各个子序列进行特征提取,以组合生成交通流时空信息。最终结合异常数据与交通流数据的时空信息生成预测结果。在真实数据集PeMS04上进行验证,实验结果表明,HDNNF-CAF能够有效识别交通流异常数据,提高预测精度,优于一些现有方法。
