Time-Frequency Analysis.

Data-driven discovery is revolutionizing the modeling, prediction, and control of complex systems. This textbook brings together machine learning, engineering mathematics, and mathematical physics to integrate modeling and control of dynamical systems with modern methods in data science. It highlights many of the recent advances in scientific computing that enable data-driven methods to be applied to a diverse range of complex systems, such as turbulence, the brain, climate, epidemiology, finance, robotics, and autonomy. Aimed at advanced undergraduate and beginning graduate students in the engineering and physical sciences, the text presents a range of topics and methods from introductory to state of the art.

Data-Driven Science and Engineering: Machine Learning, Dynamical Systems, and Control

conferencia sobre "Particle Image Velocimetry" de les 13:00-14:00 a la Sala de Juntes de l'FNB impartida pel professor Peter Bueken da l'Antwerp Maritime Acedemy (Belgica)

Particle Image Velocimetry

Quadrant analysis is a simple, but quite useful, turbulence data-processing technique that has been widely used, principally in the investigation of turbulent shear flows. This article traces the origins of the technique and reviews how it has been applied during the more than 40 years since it was conceived. Applications are highlighted that have expanded the technique beyond its original formulation.

Quadrant Analysis in Turbulence Research: History and Evolution

This article reviews past studies of airborne transmission between occupants in indoor environments, focusing on the spread of expiratory droplet nuclei from mouth/nose to mouth/nose for non-specific diseases. Special attention is paid to summarizing what is known about the influential factors, the inappropriate simplifications of the thermofluid boundary conditions of thermal manikins, the challenges facing the available experimental techniques, and the limitations of available evaluation methods. Secondary issues are highlighted, and some new ways to improve our understanding of airborne transmission indoors are provided. The characteristics of airborne spread of expiratory droplet nuclei between occupants, which are influenced correlatively by both environmental and personal factors, were widely revealed under steady-state conditions. Owing to the different boundary conditions used, some inconsistent findings on specific influential factors have been published. The available instrumentation was too slow to provide accurate concentration profiles for time-dependent evaluations of events with obvious time characteristics, while computational fluid dynamics (CFD) studies were mainly performed in the framework of inherently steady Reynolds-averaged Navier-Stokes modeling. Future research needs in 3 areas are identified: the importance of the direction of indoor airflow patterns, the dynamics of airborne transmission, and the application of CFD simulations.

/pdf/airborne-spread-of-expiratory-droplet-nuclei-between-the-dq7fw1tgym.pdf

Airborne spread of expiratory droplet nuclei between the occupants of indoor environments: A review.

Particle image velocimetry measurement of indoor airflow field: A review of the technologies and applications

The drag-reducing property of a superhydrophobic surface is investigated along with its mechanism. A superhydrophobic surface with micro–nanotextures is fabricated and tested using SEM and contact angle measurement. Velocity distributions in the turbulent boundary layer with a superhydrophobic surface and a smooth surface are measured by particle image velocimetry at Re
 θ
  = 810, 990, and 1220. An upward lift effect on the velocity profile caused by the rugged air layer on the superhydrophobic surface is observed, which indicates drag reduction. Estimated by the wall shear stress, a drag reduction of 10.1, 20.7, and 24.1 % is observed for Re
 θ
 equal to 810, 990, and 1220, respectively. The drag reduction is caused mainly by slip on the interface and modifications in the turbulent structures, and the latter plays a more important role as Re
 θ
 increases. Suppressions are observed in turbulence intensities, and reductions in the total Reynolds shear stress T
 turb
 +
 are 2.5, 18.5, and 23.1 % for Re
 θ
  = 810, 990, and 1220, respectively. Vortex fields above the superhydrophobic and smooth surfaces at Re
 θ
  = 990 are investigated. Vortexes are weakened and lifted upward by the superhydrophobic surface, and the position of the maximum swirling strength is lifted 0.17δ (δ is the boundary layer thickness) upward in the wall-normal direction. This modification in turbulence structures contributes significantly to the drag reduction in the turbulent boundary layer flow.

Mechanisms of drag reduction of superhydrophobic surfaces in a turbulent boundary layer flow

We present dynamic mode decomposition (DMD) for studying the hairpin vortices generated by hemisphere protuberance measured by two-dimensional (2D) time-resolved (TR) particle image velocimetry (PIV) in a water channel. The hairpins dynamic information is extracted by identifying their dominant frequencies and associated spatial structures. For this quasi-periodic data system, the resulting main Dynamic modes illustrate the different spatial structures associated with the wake vortex region and the near-wall region. By comparisons with proper orthogonal decomposition (POD), it can be concluded that the dynamic mode concentrates on a certain frequency component more effectively than the mode determined by POD. During the analysis, DMD has proven itself a robust and reliable algorithm to extract spatial-temporal coherent structures.

Nan Jiang

Papers

Particle image velocimetry measurement of indoor airflow field: A review of the technologies and applications

Mechanisms of drag reduction of superhydrophobic surfaces in a turbulent boundary layer flow

Dynamic mode decomposition of hairpin vortices generated by a hemisphere protuberance

Influence of spatial arrangements of roughness elements on turbulent Rayleigh-Bénard convection

Experimental study of transient air distribution of a jet collision region in an aircraft cabin mock-up