Five-hundred-meter Aperture Spherical radio Telescope( FAST) is the largest sensitive single dish radio telescope in the world,in which the control and measurement of the feed is one crucial section of the FAST contro...Five-hundred-meter Aperture Spherical radio Telescope( FAST) is the largest sensitive single dish radio telescope in the world,in which the control and measurement of the feed is one crucial section of the FAST control system. Trilateration is presented to obtain three-dimensional coordinate for tracking feed focus cabin. Every three total stations chase prism movement to be attached on feed focus cabin and the prism position is determined from the measured distances based on the principle of trilateration. Therefore,feed position is determined from three prisms on the focus cabin. This study is to assess the accuracy and reliability of trilateration calculation on tracking focus cabin of FAST. Different arrangement of total stations on trilateration is theoretically studied. Through experiment,the proposed method shows that the accuracy is better than that of the polar coordinate measurement. The average root mean square error is lower than 0. 6 mm,which is found to have high accuracy and reliability.展开更多
This work employed an inductively coupled plasma wind tunnel to study the dynamic oxidation mechanisms of carbon fiber reinforced SiC matrix composite(C_(f)/SiC)in high-enthalpy and high-speed plasmas.The results high...This work employed an inductively coupled plasma wind tunnel to study the dynamic oxidation mechanisms of carbon fiber reinforced SiC matrix composite(C_(f)/SiC)in high-enthalpy and high-speed plasmas.The results highlighted a transition of passive/active oxidations of SiC at 800–1600℃and 1–5 kPa.Specially,the active oxidation led to the corrosion of the SiC coating and interruption of the SiO_(2) growth.The transition borders of active/passive oxidations were thus defined with respect to oxidation temperature and partial pressure of atomic O in the high-enthalpy and high-speed plasmas.In the transition and passive domains,the SiC dissipation was negligible.By multiple dynamic oxidations of C_(f)/SiC in the domains,the SiO_(2) thickness was not monotonously increased due to the competing mechanisms of passive oxidation of SiC and dissipation of SiO_(2).In addition,the mechanical properties of the SiC coating/matrix and the C_(f)/SiC were maintained after long-term dynamic oxidations,which suggested an excellent thermal stability of C_(f)/SiC serving in thermal protection systems(TPSs)of reusable hypersonic vehicles.展开更多
基金Supported by the National Natural Science Foundation of China(No.11273001,11373001,11703046)
文摘Five-hundred-meter Aperture Spherical radio Telescope( FAST) is the largest sensitive single dish radio telescope in the world,in which the control and measurement of the feed is one crucial section of the FAST control system. Trilateration is presented to obtain three-dimensional coordinate for tracking feed focus cabin. Every three total stations chase prism movement to be attached on feed focus cabin and the prism position is determined from the measured distances based on the principle of trilateration. Therefore,feed position is determined from three prisms on the focus cabin. This study is to assess the accuracy and reliability of trilateration calculation on tracking focus cabin of FAST. Different arrangement of total stations on trilateration is theoretically studied. Through experiment,the proposed method shows that the accuracy is better than that of the polar coordinate measurement. The average root mean square error is lower than 0. 6 mm,which is found to have high accuracy and reliability.
基金This work was supported by the National Natural Science Foundation of China(Nos.11902333 and 51972027)the CARDC Fundamental and Frontier Technology Research Fund.
文摘This work employed an inductively coupled plasma wind tunnel to study the dynamic oxidation mechanisms of carbon fiber reinforced SiC matrix composite(C_(f)/SiC)in high-enthalpy and high-speed plasmas.The results highlighted a transition of passive/active oxidations of SiC at 800–1600℃and 1–5 kPa.Specially,the active oxidation led to the corrosion of the SiC coating and interruption of the SiO_(2) growth.The transition borders of active/passive oxidations were thus defined with respect to oxidation temperature and partial pressure of atomic O in the high-enthalpy and high-speed plasmas.In the transition and passive domains,the SiC dissipation was negligible.By multiple dynamic oxidations of C_(f)/SiC in the domains,the SiO_(2) thickness was not monotonously increased due to the competing mechanisms of passive oxidation of SiC and dissipation of SiO_(2).In addition,the mechanical properties of the SiC coating/matrix and the C_(f)/SiC were maintained after long-term dynamic oxidations,which suggested an excellent thermal stability of C_(f)/SiC serving in thermal protection systems(TPSs)of reusable hypersonic vehicles.
