In the pitching motion,the unsteady transition and relaminarization position plays an important role in the dynamic characteristics of the airfoil.In order to facilitate the computer to automatically and accurately ca...In the pitching motion,the unsteady transition and relaminarization position plays an important role in the dynamic characteristics of the airfoil.In order to facilitate the computer to automatically and accurately calculate the position of the transition and relaminarization,a Variable Slip Window Technology(VSWT)suitable for airfoil dynamic data processing was developed using the S809 airfoil experimental data in this paper and two calculation strategies,i.e.,global strategy and single point strategy,were proposed:global strategy and single point strategy.The core of the VSWT is the selection of the window function h and the parameters setting in the h function.The effect of the VSWT was evaluated using the dimensionless pulse strength value(INB),which can be used to evaluate the signal characteristics,of the root mean square(RMS)value of the fluctuating pressure.It is found that:the h function characteristics have a significant influence on the VSWT.The suitable functions are Hn function constructed in this paper and step function.For the left boundary of the magnified area,the step function can obtain the largest INB value,but the robustness is not good.The H1 function(Gaussian-like function,n=1)can show higher robustness while ensuring a large INB value.The two computing strategies,which are single point strategy and global strategy,have their own advantages and disadvantages.The former strategy,that is the single point strategy,can achieve a higher INB value,but the RMS magnification at the feature position needs to be known in advance.Although the INB value obtained by the latter strategy,that is the global strategy,is slightly smaller than the calculation results of the former strategy,it is not necessary to know the RMS magnification at the feature position in advance.So the global strategy has better robustness.The experimental data of NACA0012 airfoil was used to further validate the developed VSWT in this paper,and the results show that the VSWT developed in this paper can still double the INB value of the transition/relaminarization position.The VSWT developed in this paper has certain practicability,which is convenient for the computer to automatically determine the transition/relaminarization characteristics.展开更多
Channel estimation is very important for MIMO (Multiple Input Multiple Output) OFDM (Or-thogonal Frequency Division Multiplexing) systems, but its precision is reduced due to the noise in channel. In this letter, circ...Channel estimation is very important for MIMO (Multiple Input Multiple Output) OFDM (Or-thogonal Frequency Division Multiplexing) systems, but its precision is reduced due to the noise in channel. In this letter, circularly slipping window is introduced to resist the noise. It can be proved by simulation that with the same channel model, optimal slipping window length is the same with different vehicle speed. MSE (Minimum Square Error) of channel is greatly reduced with circularly slipping window, and performance of the system is closed to that with correct channel estimation.展开更多
近几年来,Internet 上频繁发生的蠕虫爆发和大规模分布式拒绝服务事件使网络服务的安全性面临严重的威胁。本文介绍了一个基于异常流量检测的 Internet 骨干网流量早期预警系统 ESTAB(Early-warning System ofTraffic Anomaly Based)。...近几年来,Internet 上频繁发生的蠕虫爆发和大规模分布式拒绝服务事件使网络服务的安全性面临严重的威胁。本文介绍了一个基于异常流量检测的 Internet 骨干网流量早期预警系统 ESTAB(Early-warning System ofTraffic Anomaly Based)。它基于 Internet 骨干网异常流量发现原理,通过对端口、长度分布、TCP 标志等直接变量(Direct Variable)的监测,并结合统计学中的时间序列分析方法,实时分析发现流量异常,并提出告警。文中提出了多种事件联合监测的概念,从流量监测角度有效地对付已知流量威胁(如已知蠕虫),并对未知流量威胁提供了相应的监测策略。展开更多
基金the Youth Science Foundation(No.20181111502212)for their support。
文摘In the pitching motion,the unsteady transition and relaminarization position plays an important role in the dynamic characteristics of the airfoil.In order to facilitate the computer to automatically and accurately calculate the position of the transition and relaminarization,a Variable Slip Window Technology(VSWT)suitable for airfoil dynamic data processing was developed using the S809 airfoil experimental data in this paper and two calculation strategies,i.e.,global strategy and single point strategy,were proposed:global strategy and single point strategy.The core of the VSWT is the selection of the window function h and the parameters setting in the h function.The effect of the VSWT was evaluated using the dimensionless pulse strength value(INB),which can be used to evaluate the signal characteristics,of the root mean square(RMS)value of the fluctuating pressure.It is found that:the h function characteristics have a significant influence on the VSWT.The suitable functions are Hn function constructed in this paper and step function.For the left boundary of the magnified area,the step function can obtain the largest INB value,but the robustness is not good.The H1 function(Gaussian-like function,n=1)can show higher robustness while ensuring a large INB value.The two computing strategies,which are single point strategy and global strategy,have their own advantages and disadvantages.The former strategy,that is the single point strategy,can achieve a higher INB value,but the RMS magnification at the feature position needs to be known in advance.Although the INB value obtained by the latter strategy,that is the global strategy,is slightly smaller than the calculation results of the former strategy,it is not necessary to know the RMS magnification at the feature position in advance.So the global strategy has better robustness.The experimental data of NACA0012 airfoil was used to further validate the developed VSWT in this paper,and the results show that the VSWT developed in this paper can still double the INB value of the transition/relaminarization position.The VSWT developed in this paper has certain practicability,which is convenient for the computer to automatically determine the transition/relaminarization characteristics.
文摘Channel estimation is very important for MIMO (Multiple Input Multiple Output) OFDM (Or-thogonal Frequency Division Multiplexing) systems, but its precision is reduced due to the noise in channel. In this letter, circularly slipping window is introduced to resist the noise. It can be proved by simulation that with the same channel model, optimal slipping window length is the same with different vehicle speed. MSE (Minimum Square Error) of channel is greatly reduced with circularly slipping window, and performance of the system is closed to that with correct channel estimation.
文摘近几年来,Internet 上频繁发生的蠕虫爆发和大规模分布式拒绝服务事件使网络服务的安全性面临严重的威胁。本文介绍了一个基于异常流量检测的 Internet 骨干网流量早期预警系统 ESTAB(Early-warning System ofTraffic Anomaly Based)。它基于 Internet 骨干网异常流量发现原理,通过对端口、长度分布、TCP 标志等直接变量(Direct Variable)的监测,并结合统计学中的时间序列分析方法,实时分析发现流量异常,并提出告警。文中提出了多种事件联合监测的概念,从流量监测角度有效地对付已知流量威胁(如已知蠕虫),并对未知流量威胁提供了相应的监测策略。
