Burst event detection in wall turbulence by WVITA method

Wavelet Variable Interval Time Average (WVITA) is introduced as a method incorporating burst event detection in wall turbulence. Wavelet transform is performed to unfold the longitudinal fluctuating velocity time series measured in the near wall region of a turbulent boundary layer using hot-film anemometer. This unfolding is both in time and in space simultaneously. The splitted kinetic of the longitudinal fluctuating velocity time series among different scales is obtained by integrating the square of wavelet coefficient modulus over temporal space. The time scale that related to burst events in wall turbulence passing through the fixed probe is ascertained by maximum criterion of the kinetic energy evolution across scales. Wavelet transformed localized variance of the fluctuating velocity time series at the maximum kinetic scale is put forward instead of localized short time average variance in Variable Interval Time Average (VITA) scheme. The burst event detection result shows that WVITA scheme can avoid erroneous judgement and solve the grouping problem more effectively which is caused by VITA scheme itself and can not be avoided by adjusting the threshold level or changing the short time average interval.

reuse strategies in distributed complex event detection

Software Engineering Society of Korean; Institute for Information Scientists and Engineers; IEEE Reliability Society; KAIST (Korea Advanced Institute of Science and Technology); Korea Information Promotion Agency; Samsung SDS

Pub/Sub系统中分布式复合事件检测技术研究

随着信息技术的发展，Pub/Sub系统由于具有异步和松耦合的特点，被越来越广泛的应用到金融、供应链管理、物流等领域。在这些应用中，用户对具有各种特定逻辑或时序关系的复合事件的订阅需求越来越迫切，这使得Pub/Sub系统中的分布式复合事件检测技术成为研究的热点，分布式复合事件检测技术包括复合订阅语言、复合匹配算法、以及订阅和事件的路由算法。 目前已有的Pub/Sub系统提供的复合订阅语言比较简单，对时序支持较弱，不能满足实际应用的需要，已有的复合匹配算法也不能有效的支持具有丰富时序关系的复合事件的检测。在路由方面，基于内容的Pub/Sub系统大都是在树结构或者无环图结构的覆盖网络上，采用基于过滤的原子路由方法，该路由方法需要将原子订阅传遍几乎整个网络，以减少订阅匹配的延迟，但这种路由方法很难适应网络的拓扑变化。而目前基于事件空间划分的路由方法不支持事件空间的动态划分和事件空间在不同服务器之间的移动，并且没有提供专门针对事件空间划分的复合事件检测方法。 本文在调研了各种应用需求的基础上，提出了能够表达事件丰富的时序关系、逻辑关系和事件实例关系的复合订阅语言，并且定义了两种事件排序方式。在消费语义采用配对模式的情况下，给出了该语言在两种事件排序方式下的检测结果集的定义。针对该复合订阅语言提出并实现了图结构和时间事件发生器相结合的复合匹配算法，该匹配算法使图结构可以有效的支持时序关系和非触发式事件的检测。在路由方面，首先实现了基于过滤的逆向路径转发的原子路由方法，并在此基础上，实现了就近检测协议，该协议优化了复合订阅匹配结构在网络中的部署。最后，设计和实现了基于事件空间划分的原子路由方法，该路由方法实现了事件空间的动态划分，并可以根据系统中服务器的负载情况实现事件空间的移动，从而有效的平衡服务器的负载。在此基础上，通过对复合订阅的拆分，并利用可移动的复合事件检测器实现了复合订阅的分布式部署和复合事件的分布式检测，同时通过对复合事件检测器的复用，进一步减少了网络负载和服务器的匹配负载。本文还通过实验验证了匹配算法和两种路由方法的性能和开销。

Assessment of bursting detection methods with LES database of turbulent channel flows

Validated by comparison with DNS, numerical database of turbulent channel flows is yielded by Large Eddy Simulation (LES). Three conventional techniques: uv quadrant 2, VITA and mu-level techniques for detecting turbulent bursts are applied to the identification of turbulent bursts. With a grouping parameter introduced by Bogard & Tiedemann (1986) or Luchik & Tiederman (1987), multiple ejections detected by these techniques which originate from a single burst can be grouped into a single-burst event. The results are compared with experimental results, showing that all techniques yield reasonable average burst period. However, uv quadrant 2 and mu-level are found to be superior to VITA in having large threshold-independent range.