A numerical model is developed to simulate fully nonlinear extreme waves in finite and infinite water-depth wave tanks. A semi-mixed Enlerian-Lagrangian formulation is adopted and a higher-order boundary element metho...A numerical model is developed to simulate fully nonlinear extreme waves in finite and infinite water-depth wave tanks. A semi-mixed Enlerian-Lagrangian formulation is adopted and a higher-order boundary element method in conjunction with an image Green function is used for the fluid domain. The botmdary values on the free surface are updated at each time step by a fourth-order Runga-Kutta time-marching scheme at each time step. Input wave characteristics are specified at the upstream boundary by an appropriate wave theory. At the downstream boundary, an artificial damping zone is used to prevent wave reflection back into the computational domain. Using the image Green function in the whole fluid domain, the integrations on the two lateral walls and bottom are excluded. The simulation results on extreme wave elevations in finite and infinite water-depths are compared with experimental results and second-order analytical solutions respectively. The wave kinematics is also discussed in the present study.展开更多
Background:To evaluate the precision of corneal higher-order aberrations measurements after small incision lenticule extraction(SMILE)using the Sirius Scheimpfug-Placido topographer(CSO,Italy).Methods:Seventy-fve eyes...Background:To evaluate the precision of corneal higher-order aberrations measurements after small incision lenticule extraction(SMILE)using the Sirius Scheimpfug-Placido topographer(CSO,Italy).Methods:Seventy-fve eyes from 75 postoperative subjects were included in this prospective study.Three consecutive corneal aberrometric measurements were obtained with the Scheimpfug-Placido topographer by two experienced operators to assess intra-and inter-observer reproducibility.The within-subject standard deviation(Sw),test-retest repeatability(TRT)and the intraclass correlation coefcient(ICC)were calculated.Results:For intraobserver repeatability of anterior and total corneal aberrations,all ICCs were more than 0.922,except for trefoil(0.722 to 0.768).The ICCs of total root mean square(RMS),coma Z(3,±1),and spherical aberration Z(4,0)were over 0.810 while higher-order RMS,trefoil Z(3,±3),and astigmatism II Z(4,±2)were below 0.634 for posterior corneal surface aberrations.All Sw values for all types of aberrations were equal to or below 0.07μm.Regarding interobserver reproducibility,all TRT values were no more than 0.12μm,0.05μm,and 0.11μm for anterior,posterior,and total corneal aberrations,respectively.The ICC values ranged from 0.875 to 0.989,from 0.686 to 0.976 and over 0.834 for anterior,posterior,and total corneal aberrations,respectively.Conclusions:The repeatability of measurements of anterior and total corneal aberrations with the Sirius system in corneas after SMILE surgery was high,except for trefoil.There was some variability in posterior corneal aberrometric measurements.High reproducibility of corneal aberrometric measurements was observed between measurements of both examiners,except for trefoil,with poor to moderate reproducibility.展开更多
为了研究频率、幅值下垂特性对直驱型永磁风电系统小扰动稳定性的影响,建立了包含永磁同步电机(permanent magnet synchronous generator,PMSG)的单机无穷大系统小扰动稳定性分析的数学模型;采用最大功率点跟踪控制(maximum power point...为了研究频率、幅值下垂特性对直驱型永磁风电系统小扰动稳定性的影响,建立了包含永磁同步电机(permanent magnet synchronous generator,PMSG)的单机无穷大系统小扰动稳定性分析的数学模型;采用最大功率点跟踪控制(maximum power point tracking,MPPT),保证风力发电机输出功率最大;研究了网侧变换器基于下垂特性的控制方案,理论分析表明,下垂特性对系统的小扰动稳定性有较大影响;利用Matlab建模,对系统在不同下垂特性系数条件下进行了时域分析。仿真结果验证了理论分析的正确性,为采用下垂特性控制的直驱型永磁风力发电系统安全稳定的并网运行提供了一些可借鉴的理论依据。展开更多
基金supported by the National Natural Science Foundation of China (Grant Nos .50709005 ,50639030 and 10772040)the National High Technology Research and Development Program of China (Grant No.2006AA09A109-3) UK EPSRC(Grant Nos . GR/T07220/01 and GR/T07220/02)
文摘A numerical model is developed to simulate fully nonlinear extreme waves in finite and infinite water-depth wave tanks. A semi-mixed Enlerian-Lagrangian formulation is adopted and a higher-order boundary element method in conjunction with an image Green function is used for the fluid domain. The botmdary values on the free surface are updated at each time step by a fourth-order Runga-Kutta time-marching scheme at each time step. Input wave characteristics are specified at the upstream boundary by an appropriate wave theory. At the downstream boundary, an artificial damping zone is used to prevent wave reflection back into the computational domain. Using the image Green function in the whole fluid domain, the integrations on the two lateral walls and bottom are excluded. The simulation results on extreme wave elevations in finite and infinite water-depths are compared with experimental results and second-order analytical solutions respectively. The wave kinematics is also discussed in the present study.
基金the Medical and Health Science and Technology Program of Zhejiang Province(2019KY111)Foundation of Wenzhou City Science&Technology Bureau(Y2020037)+1 种基金EYE&ENT Hospital of Fudan University High-level Talents Program(2021318)Clinical Research Plan of SHDC(SHDC2020CR1043B)。
文摘Background:To evaluate the precision of corneal higher-order aberrations measurements after small incision lenticule extraction(SMILE)using the Sirius Scheimpfug-Placido topographer(CSO,Italy).Methods:Seventy-fve eyes from 75 postoperative subjects were included in this prospective study.Three consecutive corneal aberrometric measurements were obtained with the Scheimpfug-Placido topographer by two experienced operators to assess intra-and inter-observer reproducibility.The within-subject standard deviation(Sw),test-retest repeatability(TRT)and the intraclass correlation coefcient(ICC)were calculated.Results:For intraobserver repeatability of anterior and total corneal aberrations,all ICCs were more than 0.922,except for trefoil(0.722 to 0.768).The ICCs of total root mean square(RMS),coma Z(3,±1),and spherical aberration Z(4,0)were over 0.810 while higher-order RMS,trefoil Z(3,±3),and astigmatism II Z(4,±2)were below 0.634 for posterior corneal surface aberrations.All Sw values for all types of aberrations were equal to or below 0.07μm.Regarding interobserver reproducibility,all TRT values were no more than 0.12μm,0.05μm,and 0.11μm for anterior,posterior,and total corneal aberrations,respectively.The ICC values ranged from 0.875 to 0.989,from 0.686 to 0.976 and over 0.834 for anterior,posterior,and total corneal aberrations,respectively.Conclusions:The repeatability of measurements of anterior and total corneal aberrations with the Sirius system in corneas after SMILE surgery was high,except for trefoil.There was some variability in posterior corneal aberrometric measurements.High reproducibility of corneal aberrometric measurements was observed between measurements of both examiners,except for trefoil,with poor to moderate reproducibility.
文摘为了研究频率、幅值下垂特性对直驱型永磁风电系统小扰动稳定性的影响,建立了包含永磁同步电机(permanent magnet synchronous generator,PMSG)的单机无穷大系统小扰动稳定性分析的数学模型;采用最大功率点跟踪控制(maximum power point tracking,MPPT),保证风力发电机输出功率最大;研究了网侧变换器基于下垂特性的控制方案,理论分析表明,下垂特性对系统的小扰动稳定性有较大影响;利用Matlab建模,对系统在不同下垂特性系数条件下进行了时域分析。仿真结果验证了理论分析的正确性,为采用下垂特性控制的直驱型永磁风力发电系统安全稳定的并网运行提供了一些可借鉴的理论依据。
