This paper presents a non-smooth multibody dynamic formulation and error analysis of an antenna pointing mechanism including frictional spatial revolute joints(FSRJs)with small clearance in the framework of the specia...This paper presents a non-smooth multibody dynamic formulation and error analysis of an antenna pointing mechanism including frictional spatial revolute joints(FSRJs)with small clearance in the framework of the special Euclidian group SE(3).The formulation leads to an inertial frame-invariant,a compact and unified description for rigid bodies and spatial revolute joints(SRJs).The geometric constraint of the bearing is covered by four open semi-cylinders,which can be treated as bilateral constraints assuming that the impact effects are negligible.The frictional contact problem is formulated as a horizontal linear complementary problem(HLCP),which is embedded in the Lie-group integration scheme.Error of the antenna pointing mechanism is modeled by means of the adjoint transformation and POE-based formula.The evolution of errors is obtained through the solution of non-smooth dynamics.The obtained numerical results illustrate the influences of FSRJs in dynamics modeling and error analysis of the antenna pointing mechanism.展开更多
X-ray phase-contrast imaging is one of the novel techniques,and has potential to enhance image quality and provide the details of inner structures nondestructively.In this work,we investigate quantitatively signal-to-...X-ray phase-contrast imaging is one of the novel techniques,and has potential to enhance image quality and provide the details of inner structures nondestructively.In this work,we investigate quantitatively signal-to-noise ratio（SNR） of grating-based x-ray phase contrast imaging（GBPCI） system by employing angular signal radiography（ASR）.Moreover,photon statistics and mechanical error that is a major source of noise are investigated in detail.Results show the dependence of SNR on the system parameters and the effects on the extracted absorption,refraction and scattering images.Our conclusions can be used to optimize the system design for upcoming practical applications in the areas such as material science and biomedical imaging.展开更多
Mechanical errors can not be avoided in fabrication. They will cause geometry errors and have impacts on the cavity performance. This paper systematically analyzes the impacts of mechanical errors on the RF performanc...Mechanical errors can not be avoided in fabrication. They will cause geometry errors and have impacts on the cavity performance. This paper systematically analyzes the impacts of mechanical errors on the RF performance of Peking University single spoke cavity. The various kinds of shape and size errors are considered, the influences on the resonation frequency and field flatness are studied by numerical simulation and the theoretical models are analyzed. The results show that the single spoke cavity is robust with respect to the mechanical tolerance. It also indicates the most essential factors for fabrication.展开更多
基金supported by the National Natural Science Foundation of China(No.51635002 Key Program,52075016,U20A20281)。
文摘This paper presents a non-smooth multibody dynamic formulation and error analysis of an antenna pointing mechanism including frictional spatial revolute joints(FSRJs)with small clearance in the framework of the special Euclidian group SE(3).The formulation leads to an inertial frame-invariant,a compact and unified description for rigid bodies and spatial revolute joints(SRJs).The geometric constraint of the bearing is covered by four open semi-cylinders,which can be treated as bilateral constraints assuming that the impact effects are negligible.The frictional contact problem is formulated as a horizontal linear complementary problem(HLCP),which is embedded in the Lie-group integration scheme.Error of the antenna pointing mechanism is modeled by means of the adjoint transformation and POE-based formula.The evolution of errors is obtained through the solution of non-smooth dynamics.The obtained numerical results illustrate the influences of FSRJs in dynamics modeling and error analysis of the antenna pointing mechanism.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11535015,11305173,and 11375225)
文摘X-ray phase-contrast imaging is one of the novel techniques,and has potential to enhance image quality and provide the details of inner structures nondestructively.In this work,we investigate quantitatively signal-to-noise ratio（SNR） of grating-based x-ray phase contrast imaging（GBPCI） system by employing angular signal radiography（ASR）.Moreover,photon statistics and mechanical error that is a major source of noise are investigated in detail.Results show the dependence of SNR on the system parameters and the effects on the extracted absorption,refraction and scattering images.Our conclusions can be used to optimize the system design for upcoming practical applications in the areas such as material science and biomedical imaging.
文摘Mechanical errors can not be avoided in fabrication. They will cause geometry errors and have impacts on the cavity performance. This paper systematically analyzes the impacts of mechanical errors on the RF performance of Peking University single spoke cavity. The various kinds of shape and size errors are considered, the influences on the resonation frequency and field flatness are studied by numerical simulation and the theoretical models are analyzed. The results show that the single spoke cavity is robust with respect to the mechanical tolerance. It also indicates the most essential factors for fabrication.
