The disturbance torque generated via solar array drive assembly(SADA) can significantly degrade the key performance of satellite.The discussed SADA is composed of a two-phase hybrid stepping motor and a set of two-sta...The disturbance torque generated via solar array drive assembly(SADA) can significantly degrade the key performance of satellite.The discussed SADA is composed of a two-phase hybrid stepping motor and a set of two-stage straight gear reducer. Firstly, the vibration equation of the two-phase hybrid stepping motor is established via simplifying and linearizing the electromagnetic torque.Secondly, based on the vibration equation established, the disturbance torque model of SADA is created via force analysis and force system simplification. Thirdly, for precisely ground measuring the disturbance torque aroused by SADA, a measurement system,including a strain micro-vibrations measurement platform(SMMP) and a set of gravity unloading device(GUD), is designed.Fourthly, the proposed disturbance torque model is validated by measuring and simulating the disturbance torque produced via SADA driving rigid load through GUD. The results indicate that, the proposed disturbance torque model holds the ability to describe the disturbance torque caused by SADA with high precision. Finally, the disturbance torque emitted by SADA driving a flexible load, designed to simulate solar array, is modeled and simulated via using fixed-interface mode synthesis method(FIMSM). All the conclusions drawn from this article do have a meaningful help for studying the disturbance torque produced by SADA driving solar array on orbit.展开更多
Instrumental and environmental disturbances do affect FG5 absolute gravimeter observations and the estimated gravity values, sometimes to the degree that entire measurement campaigns are discarded. We propose a method...Instrumental and environmental disturbances do affect FG5 absolute gravimeter observations and the estimated gravity values, sometimes to the degree that entire measurement campaigns are discarded. We propose a method which moves towards the re-assessment of previously discarded observations. Once an estimate of the frequency and amplitude of a disturbance in a FG5 data set exists, the proposed method can estimate its impact on the estimated gravity value. This is performed through a Gaussian Bell Summation approach of the functional relationship between disturbance frequency and standard deviation of gravity. The filtering of the identified disturbance is realized through a modification of the functional model of the equation of motion in the least squares adjustment of FG5 observations. The results reveal that the Gaussian Bell Summation approximates the frequency—gravity impact relationship sufficiently well with negligible uncertainties, while the accuracy of the detected disturbance frequency defines a limiting factor for the gravity impact estimation. A realistic disturbance of 15 Hz with an amplitude of 1.5 nm had an impact of ≈48 [μGal] on the gravity estimate. The proposed filter approach reduced the impact to ≈12 [μGal], with the remaining effect being almost entirely associated to the uncertainty in disturbance frequency detection.展开更多
The bending creep and its disturbance effects of red sandstone rock beam and oil shale rock beam were studied by adopting the self-developed gravitation level style rock creep test machine and bending creep test syste...The bending creep and its disturbance effects of red sandstone rock beam and oil shale rock beam were studied by adopting the self-developed gravitation level style rock creep test machine and bending creep test system,and the constitutive equations were established.It is found that fracture morphology of rock beams under no disturbance load is regular,cracking position of fractures is on part of loading concentration,the crack starts from a neutral plane.However,fracture morphology of rock beams under disturbance load is irregular,cracking position of fractures deviates from a neutral plane.Delayed instability of rock beam occurs for some time under constant disturbance load.When disturbance load is beyond a certain range,suddenly instability of occurs rock beam in a certain time.The results show that there is a guiding significance for creep stability in the geotechnical engineering fields.展开更多
How to determine the earth’s external gravity field with the accuracy of O(T2) by making use of GPS data and gravity values measured on the earth’s surface is dealt with in this paper. There are two main steps: to e...How to determine the earth’s external gravity field with the accuracy of O(T2) by making use of GPS data and gravity values measured on the earth’s surface is dealt with in this paper. There are two main steps: to extend these measured values on the earth’s surface onto the reference ellipsoid at first and then to seek for the integral solution of the external Neumann problem outside the ellipsoid. In addition, the corresponding judging criteria of accuracy to solve the GPS-gravity boundary value problem are established. The integral solution given in the paper not only contains all frequency-spectral information of the gravity field with the accuracy of O(T 2), but is also easily computed. In fact, the solution has great significance for both theory and prac- tice.展开更多
In this study,a neural adaptive controller is developed for a ground experiment with a spacecraft proximity operation.As the water resistance in the experiment is highly nonlinear and can significantly affect the fide...In this study,a neural adaptive controller is developed for a ground experiment with a spacecraft proximity operation.As the water resistance in the experiment is highly nonlinear and can significantly affect the fidelity of the ground experiment,the water resistance must be estimated accurately and compensated using an active force online.For this problem,a novel control algorithm combined with Chebyshev Neural Networks(CNN)and an Active Disturbance Rejection Control(ADRC)is proposed.Specifically,the CNN algorithm is used to estimate the water resistance.The advantage of the CNN estimation is that the coefficients of the approximation can be adaptively changed to minimize the estimation error.Combined with the ADRC algorithm,the total disturbance is compensated in the experiment to improve the fidelity.The dynamic model of the spacecraft proximity maneuver in the experiment is established.The ground experiment of the proximity maneuver that considers an obstacle is provided to verify the efficiency of the proposed controller.The results demonstrate that the proposed method outperforms the pure ADRC method and can achieve close-to-real-time performance for the spacecraft proximity maneuver.展开更多
By using NCEP reanalysis data,the formation reason of a disaster weather process which happened in Fujian Province on April 1,2007 was analyzed. The results showed that this strong convection weather process was cause...By using NCEP reanalysis data,the formation reason of a disaster weather process which happened in Fujian Province on April 1,2007 was analyzed. The results showed that this strong convection weather process was caused by the development of convective thunderstorm monomer in the warm zone of jet stream which was in front of ground front at afternoon. The invasion of cold advection in the middle-high layer had the major trigger effects on this strong convection weather occurrence. The tilt development of vorticity was easy to appear in θse tilted frontal zone,which made a large amount of latent heat release exist in the middle layer of troposphere. Meanwhile,it favored the potential vorticity in the middle layer to download. Thus,it made the important contributions to the development,maintenance of low-altitude vorticity in the strong convection zone and favored the development,maintenance of thunderstorm. In the middle-low layer of troposphere where the strong convection happened,the distribution of meso-scale wave train which was similar to the gravity wave appeared. Meanwhile,it also reflected the wave characteristics which the ascending motion alternated with the descending motion in the divergence. The westerly disturbance in the middle-low layer of troposphere,the southerly disturbance in the low altitude and the middle-upper layer of troposphere made the important contributions to the strong convection weather. The easterlies disturbance and the divergence effect in the tropopause strengthened the development of vertical motion. The strong vertical wind shear was the favorable condition of strong convection weather occurrence.展开更多
Satellite altimetry can provide the geoid in ocean areas with a level of precision of about 10 cm. Such a precise geoid offers a good opportunity for studying the marine gravity field. The basic mathematical model and...Satellite altimetry can provide the geoid in ocean areas with a level of precision of about 10 cm. Such a precise geoid offers a good opportunity for studying the marine gravity field. The basic mathematical model and theory of the satellite altimetry were introduced briefly and firstly. Then the inverse Hotine method to derive gravity disturbances from satellite altimetry was presented. Meanwhile the inversion of marine gravity in Chinese coastal waters from Topex/Poseidon satellite altimetry data was tested, and the RMS between the gravity disturbance from the OSU91A model and satellite altimetry data inversing is about 12.76 mGal. Finally, some problems which are in inversing procedure were discussed, i e, integration singularity, edge effect etc. And it is conluded that the accuracy of the inversing gravity method can reach only a few mGal if proper treatment of Fast Fourier Transform (FFT) edge effect is employed.展开更多
垂线偏差数据对于提高惯性导航精度具有重要意义,阐述了使用重力场球谐模型计算水平重力扰动的方法,使用EGM2008重力场球谐模型计算水平重力扰动,并将其与美国国家地理空间情报局提供的全球2.5′×2.5′垂线偏差网格数据进行对比,...垂线偏差数据对于提高惯性导航精度具有重要意义,阐述了使用重力场球谐模型计算水平重力扰动的方法,使用EGM2008重力场球谐模型计算水平重力扰动,并将其与美国国家地理空间情报局提供的全球2.5′×2.5′垂线偏差网格数据进行对比,验证了所述水平重力扰动计算方法的正确性。将水平重力扰动计算结果用于航空、车载惯性导航数据离线处理,结果表明EGM2008模型计算的水平重力扰动可用于补偿惯性导航;将水平重力扰动计算结果用于长航时船载惯性导航数据离线处理,结果表明惯性导航精度最大提升1.5 n mile,平均提升0.8 n mile。展开更多
文摘The disturbance torque generated via solar array drive assembly(SADA) can significantly degrade the key performance of satellite.The discussed SADA is composed of a two-phase hybrid stepping motor and a set of two-stage straight gear reducer. Firstly, the vibration equation of the two-phase hybrid stepping motor is established via simplifying and linearizing the electromagnetic torque.Secondly, based on the vibration equation established, the disturbance torque model of SADA is created via force analysis and force system simplification. Thirdly, for precisely ground measuring the disturbance torque aroused by SADA, a measurement system,including a strain micro-vibrations measurement platform(SMMP) and a set of gravity unloading device(GUD), is designed.Fourthly, the proposed disturbance torque model is validated by measuring and simulating the disturbance torque produced via SADA driving rigid load through GUD. The results indicate that, the proposed disturbance torque model holds the ability to describe the disturbance torque caused by SADA with high precision. Finally, the disturbance torque emitted by SADA driving a flexible load, designed to simulate solar array, is modeled and simulated via using fixed-interface mode synthesis method(FIMSM). All the conclusions drawn from this article do have a meaningful help for studying the disturbance torque produced by SADA driving solar array on orbit.
文摘Instrumental and environmental disturbances do affect FG5 absolute gravimeter observations and the estimated gravity values, sometimes to the degree that entire measurement campaigns are discarded. We propose a method which moves towards the re-assessment of previously discarded observations. Once an estimate of the frequency and amplitude of a disturbance in a FG5 data set exists, the proposed method can estimate its impact on the estimated gravity value. This is performed through a Gaussian Bell Summation approach of the functional relationship between disturbance frequency and standard deviation of gravity. The filtering of the identified disturbance is realized through a modification of the functional model of the equation of motion in the least squares adjustment of FG5 observations. The results reveal that the Gaussian Bell Summation approximates the frequency—gravity impact relationship sufficiently well with negligible uncertainties, while the accuracy of the detected disturbance frequency defines a limiting factor for the gravity impact estimation. A realistic disturbance of 15 Hz with an amplitude of 1.5 nm had an impact of ≈48 [μGal] on the gravity estimate. The proposed filter approach reduced the impact to ≈12 [μGal], with the remaining effect being almost entirely associated to the uncertainty in disturbance frequency detection.
基金Projects(50474029,50174035) supported by the National Natural Science Foundation of China
文摘The bending creep and its disturbance effects of red sandstone rock beam and oil shale rock beam were studied by adopting the self-developed gravitation level style rock creep test machine and bending creep test system,and the constitutive equations were established.It is found that fracture morphology of rock beams under no disturbance load is regular,cracking position of fractures is on part of loading concentration,the crack starts from a neutral plane.However,fracture morphology of rock beams under disturbance load is irregular,cracking position of fractures deviates from a neutral plane.Delayed instability of rock beam occurs for some time under constant disturbance load.When disturbance load is beyond a certain range,suddenly instability of occurs rock beam in a certain time.The results show that there is a guiding significance for creep stability in the geotechnical engineering fields.
基金supported by Chinese Science Fund(Grant No.40374001).
文摘How to determine the earth’s external gravity field with the accuracy of O(T2) by making use of GPS data and gravity values measured on the earth’s surface is dealt with in this paper. There are two main steps: to extend these measured values on the earth’s surface onto the reference ellipsoid at first and then to seek for the integral solution of the external Neumann problem outside the ellipsoid. In addition, the corresponding judging criteria of accuracy to solve the GPS-gravity boundary value problem are established. The integral solution given in the paper not only contains all frequency-spectral information of the gravity field with the accuracy of O(T 2), but is also easily computed. In fact, the solution has great significance for both theory and prac- tice.
基金supported by the National Natural Science Foundation of China (No. 11802238)。
文摘In this study,a neural adaptive controller is developed for a ground experiment with a spacecraft proximity operation.As the water resistance in the experiment is highly nonlinear and can significantly affect the fidelity of the ground experiment,the water resistance must be estimated accurately and compensated using an active force online.For this problem,a novel control algorithm combined with Chebyshev Neural Networks(CNN)and an Active Disturbance Rejection Control(ADRC)is proposed.Specifically,the CNN algorithm is used to estimate the water resistance.The advantage of the CNN estimation is that the coefficients of the approximation can be adaptively changed to minimize the estimation error.Combined with the ADRC algorithm,the total disturbance is compensated in the experiment to improve the fidelity.The dynamic model of the spacecraft proximity maneuver in the experiment is established.The ground experiment of the proximity maneuver that considers an obstacle is provided to verify the efficiency of the proposed controller.The results demonstrate that the proposed method outperforms the pure ADRC method and can achieve close-to-real-time performance for the spacecraft proximity maneuver.
基金Supported by Fujian Natural Science Fund Plan Project(W0650004)The Science and Technology Plan Project of Xiamen Technology Bureau(3502Z20064022)
文摘By using NCEP reanalysis data,the formation reason of a disaster weather process which happened in Fujian Province on April 1,2007 was analyzed. The results showed that this strong convection weather process was caused by the development of convective thunderstorm monomer in the warm zone of jet stream which was in front of ground front at afternoon. The invasion of cold advection in the middle-high layer had the major trigger effects on this strong convection weather occurrence. The tilt development of vorticity was easy to appear in θse tilted frontal zone,which made a large amount of latent heat release exist in the middle layer of troposphere. Meanwhile,it favored the potential vorticity in the middle layer to download. Thus,it made the important contributions to the development,maintenance of low-altitude vorticity in the strong convection zone and favored the development,maintenance of thunderstorm. In the middle-low layer of troposphere where the strong convection happened,the distribution of meso-scale wave train which was similar to the gravity wave appeared. Meanwhile,it also reflected the wave characteristics which the ascending motion alternated with the descending motion in the divergence. The westerly disturbance in the middle-low layer of troposphere,the southerly disturbance in the low altitude and the middle-upper layer of troposphere made the important contributions to the strong convection weather. The easterlies disturbance and the divergence effect in the tropopause strengthened the development of vertical motion. The strong vertical wind shear was the favorable condition of strong convection weather occurrence.
文摘Satellite altimetry can provide the geoid in ocean areas with a level of precision of about 10 cm. Such a precise geoid offers a good opportunity for studying the marine gravity field. The basic mathematical model and theory of the satellite altimetry were introduced briefly and firstly. Then the inverse Hotine method to derive gravity disturbances from satellite altimetry was presented. Meanwhile the inversion of marine gravity in Chinese coastal waters from Topex/Poseidon satellite altimetry data was tested, and the RMS between the gravity disturbance from the OSU91A model and satellite altimetry data inversing is about 12.76 mGal. Finally, some problems which are in inversing procedure were discussed, i e, integration singularity, edge effect etc. And it is conluded that the accuracy of the inversing gravity method can reach only a few mGal if proper treatment of Fast Fourier Transform (FFT) edge effect is employed.
文摘垂线偏差数据对于提高惯性导航精度具有重要意义,阐述了使用重力场球谐模型计算水平重力扰动的方法,使用EGM2008重力场球谐模型计算水平重力扰动,并将其与美国国家地理空间情报局提供的全球2.5′×2.5′垂线偏差网格数据进行对比,验证了所述水平重力扰动计算方法的正确性。将水平重力扰动计算结果用于航空、车载惯性导航数据离线处理,结果表明EGM2008模型计算的水平重力扰动可用于补偿惯性导航;将水平重力扰动计算结果用于长航时船载惯性导航数据离线处理,结果表明惯性导航精度最大提升1.5 n mile,平均提升0.8 n mile。
