The most challenging problem of navigation in three-axis stabilized geostationary satellite is accurate calculation of misalignment angles, deduced by orbit measurement error, attitude measurement error, thermal elast...The most challenging problem of navigation in three-axis stabilized geostationary satellite is accurate calculation of misalignment angles, deduced by orbit measurement error, attitude measurement error, thermal elastic deformation, time synchronization error, and so on. Before the satellite is launched, the misalignment model must be established and validated. But there were no observation data, which is a non-negligible risk of yielding the greatest returns on investment. On the basis of misalignment modeling using landmarks and stars, which is not available between different organizations and is developed by ourselves, experimental data are constructed to validate the navigation processing flow as well as misalignment calculation accuracy. In the condition of using landmarks, the maximum misalignment calculation errors of roll, pitch, and yaw axis are 2, 2, and 104 micro radians, respectively, without considering the accuracy of image edge detection. While in the condition of using stars, the maximum errors of roll, pitch, and yaw axis are 1, 1, and 3 micro radians, respectively, without considering the accuracy of star center extraction. Results are rather encouraging, which pave the way for high-accuracy image navigation of three-axis stabilized geostationary satellite. The misalignment modeling as well as calculation method has been used in the new generation of geostationary meteorological satellite in China, FY-4 series, the first satellite of which was launched at the end of 2016.展开更多
Most wind turbine blades are assembled piece-by-piece onto the hub of a monopile-type offshore wind turbine using jack-up crane vessels.Despite the stable foundation of the lifting cranes,the mating process exhibits s...Most wind turbine blades are assembled piece-by-piece onto the hub of a monopile-type offshore wind turbine using jack-up crane vessels.Despite the stable foundation of the lifting cranes,the mating process exhibits substantial relative responses amidst blade root and hub.These relative motions are combined effects of wave-induced monopile motions and wind-induced blade root motions,which can cause impact loads at the blade root’s guide pin in the course of alignment procedure.Environmental parameters including the wind-wave misalignments play an important role for the safety of the installation tasks and govern the impact scenarios.The present study investigates the effects of wind-wave misalignments on the blade root mating process on a monopile-type offshore wind turbine.The dynamic responses including the impact velocities between root and hub in selected wind-wave misalignment conditions are investigated using multibody simulations.Furthermore,based on a finite element study,different impact-induced failure modes at the blade root for sideways and head-on impact scenarios,developed due to wind-wave misalignment conditions,are investigated.Finally,based on extreme value analyses of critical responses,safe domain for the mating task under different wind-wave misalignments is compared.The results show that although misaligned wind-wave conditions develop substantial relative motions between root and hub,aligned wind-wave conditions induce largest impact velocities and develop critical failure modes at a relatively low threshold velocity of impact.展开更多
Misalignment angle error model describing the SINS mathematical platform error is presented in this paper following the idea of small misalignment angle error model and large azimuth misalignment angle error model.It ...Misalignment angle error model describing the SINS mathematical platform error is presented in this paper following the idea of small misalignment angle error model and large azimuth misalignment angle error model.It can be considered that the three misalignment angles are independent of the rotational sequence in the misalignment error model,but not suitable in the large misalignment error model.The error angle of Euler platform is used to represent the three misalignment angles from theoretical navigation coordinate system to computational navigation coordinate system.The Euler platform error angle is utilized to represent the mathematical platform error and its physical meaning is very clear.The SINS nonlinear error model is deduced by using the error angle of Euler platform and is simplified under the condition of large azimuth error and small error.The simplified results are more comprehensive and accurate than the large azimuth misalignment error model.The damping SINS algorithm and its error model are proposed to change the structure of the strapdown inertial navigation algorithm by using the external damping information.The accuracy of SINS error model of large Euler platform error angle is simulated,and has strong practicability in initial alignment and is conducive to reducing the amount of calculation.展开更多
为探究风波浪耦合作用下张力腿浮式平台(tension leg platform,TLP)动力学特性,提出适用于我国东海平均水深的系泊最优线径。该文以美国可再生能源实验室(national renewable energy laboratory,NREL)5 MW海上风力机和TLP浮式平台为研...为探究风波浪耦合作用下张力腿浮式平台(tension leg platform,TLP)动力学特性,提出适用于我国东海平均水深的系泊最优线径。该文以美国可再生能源实验室(national renewable energy laboratory,NREL)5 MW海上风力机和TLP浮式平台为研究对象,根据IEC 61400-3标准生成Kaimal湍流风谱和P-M不规则波浪谱,参考中国船级社海上浮式风机平台指南较系统地研究系泊线径、风浪错位角及海水深度对TLP浮式平台的影响,并通过高斯混合模型(Gaussian mixture model,GMM)和期望最大(expectation maximization,EM)迭代法优化系泊线径。研究发现,增大缆绳直径会使浮式平台在纵荡和横荡方向的初始位置与位移幅值减小,风浪失调时平台运动分量同纵荡方向一致与横荡方向相反;风浪错位角度增大致使平台横荡响应更加敏感,横摇呈现先增大后减小的趋势;海洋深度增加浮式平台纵荡位移峰值随之增加,但平台艏摇方向运动响应无明显变化;300~370 m深度海域系泊线径最优值为0.134 m。结果可为我国近海张力腿浮式平台及系泊系统的优化设计、性能评估及规模化开发提供理论指导。展开更多
In the traditional unscented Kalman filter（UKF）,accuracy and robustness decline when uncertain disturbances exist in the practical system.To deal with the problem,a robust UKF algorithm based on an H-infinity norm i...In the traditional unscented Kalman filter（UKF）,accuracy and robustness decline when uncertain disturbances exist in the practical system.To deal with the problem,a robust UKF algorithm based on an H-infinity norm is proposed.In Krein space,a robust element is added in the simplified UKF so as to improve the algorithm.The filtering gain is adjusted by the robust element and in this way the performance of the robustness of the filtering algorithm is promoted.In the initial alignment process of the large heading misalignment angle of the strapdown inertial navigation system（SINS）,comparative studies are conducted on the robust UKF and the simplified UKF.The simulation results illustrate that compared with the simplified UKF,the robust UKF is more accurate,and the estimation error of heading misalignment decreases from 16.9＇ to 4.3＇.In short,the robust UKF can reduce the sensitivity to the system disturbances resulting in better performance.展开更多
文摘The most challenging problem of navigation in three-axis stabilized geostationary satellite is accurate calculation of misalignment angles, deduced by orbit measurement error, attitude measurement error, thermal elastic deformation, time synchronization error, and so on. Before the satellite is launched, the misalignment model must be established and validated. But there were no observation data, which is a non-negligible risk of yielding the greatest returns on investment. On the basis of misalignment modeling using landmarks and stars, which is not available between different organizations and is developed by ourselves, experimental data are constructed to validate the navigation processing flow as well as misalignment calculation accuracy. In the condition of using landmarks, the maximum misalignment calculation errors of roll, pitch, and yaw axis are 2, 2, and 104 micro radians, respectively, without considering the accuracy of image edge detection. While in the condition of using stars, the maximum errors of roll, pitch, and yaw axis are 1, 1, and 3 micro radians, respectively, without considering the accuracy of star center extraction. Results are rather encouraging, which pave the way for high-accuracy image navigation of three-axis stabilized geostationary satellite. The misalignment modeling as well as calculation method has been used in the new generation of geostationary meteorological satellite in China, FY-4 series, the first satellite of which was launched at the end of 2016.
基金The study is a part of SFI MOVE projects funded by the Research Council of Norway,NFR project number 237929.
文摘Most wind turbine blades are assembled piece-by-piece onto the hub of a monopile-type offshore wind turbine using jack-up crane vessels.Despite the stable foundation of the lifting cranes,the mating process exhibits substantial relative responses amidst blade root and hub.These relative motions are combined effects of wave-induced monopile motions and wind-induced blade root motions,which can cause impact loads at the blade root’s guide pin in the course of alignment procedure.Environmental parameters including the wind-wave misalignments play an important role for the safety of the installation tasks and govern the impact scenarios.The present study investigates the effects of wind-wave misalignments on the blade root mating process on a monopile-type offshore wind turbine.The dynamic responses including the impact velocities between root and hub in selected wind-wave misalignment conditions are investigated using multibody simulations.Furthermore,based on a finite element study,different impact-induced failure modes at the blade root for sideways and head-on impact scenarios,developed due to wind-wave misalignment conditions,are investigated.Finally,based on extreme value analyses of critical responses,safe domain for the mating task under different wind-wave misalignments is compared.The results show that although misaligned wind-wave conditions develop substantial relative motions between root and hub,aligned wind-wave conditions induce largest impact velocities and develop critical failure modes at a relatively low threshold velocity of impact.
基金This work is funded by Natural Science Foundation of Jiangsu Province under Grant BK20160955a project funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions and Science Research Foundation of Nanjing University of Information Science and Technology under Grant20110430+1 种基金Open Foundation of Jiangsu Key Laboratory of Meteorological Observation and Information Processing(KDXS1304)Open Foundation of Jiangsu Key Laboratory of Ocean Dynamic Remote Sensing and Acoustics(KHYS1405).
文摘Misalignment angle error model describing the SINS mathematical platform error is presented in this paper following the idea of small misalignment angle error model and large azimuth misalignment angle error model.It can be considered that the three misalignment angles are independent of the rotational sequence in the misalignment error model,but not suitable in the large misalignment error model.The error angle of Euler platform is used to represent the three misalignment angles from theoretical navigation coordinate system to computational navigation coordinate system.The Euler platform error angle is utilized to represent the mathematical platform error and its physical meaning is very clear.The SINS nonlinear error model is deduced by using the error angle of Euler platform and is simplified under the condition of large azimuth error and small error.The simplified results are more comprehensive and accurate than the large azimuth misalignment error model.The damping SINS algorithm and its error model are proposed to change the structure of the strapdown inertial navigation algorithm by using the external damping information.The accuracy of SINS error model of large Euler platform error angle is simulated,and has strong practicability in initial alignment and is conducive to reducing the amount of calculation.
基金The National Basic Research Program of China (973 Program) (No. 613121010202)
文摘In the traditional unscented Kalman filter（UKF）,accuracy and robustness decline when uncertain disturbances exist in the practical system.To deal with the problem,a robust UKF algorithm based on an H-infinity norm is proposed.In Krein space,a robust element is added in the simplified UKF so as to improve the algorithm.The filtering gain is adjusted by the robust element and in this way the performance of the robustness of the filtering algorithm is promoted.In the initial alignment process of the large heading misalignment angle of the strapdown inertial navigation system（SINS）,comparative studies are conducted on the robust UKF and the simplified UKF.The simulation results illustrate that compared with the simplified UKF,the robust UKF is more accurate,and the estimation error of heading misalignment decreases from 16.9＇ to 4.3＇.In short,the robust UKF can reduce the sensitivity to the system disturbances resulting in better performance.
