On the need for a nonlinear subscale turbulence term in POD models as exemplified for a high Reynolds number flow over an Ahmed body

We investigate a hierarchy of eddy-viscosity terms in POD Galerkin models to account for a large fraction of unresolved fluctuation energy. These Galerkin methods are applied to Large Eddy Simulation data for a flow around the vehicle-like bluff body call Ahmed body. This flow has three challenges for any reduced-order model: a high Reynolds number, coherent structures with broadband frequency dynamics, and meta-stable asymmetric base flow states. The Galerkin models are found to be most accurate with modal eddy viscosities as proposed by Rempfer & Fasel (1994). Robustness of the model solution with respect to initial conditions, eddy viscosity values and model order is only achieved for state-dependent eddy viscosities as proposed by Noack, Morzynski & Tadmor (2011). Only the POD system with state-dependent modal eddy viscosities can address all challenges of the flow characteristics. All parameters are analytically derived from the Navier-Stokes based balance equations with the available data. We arrive at simple general guidelines for robust and accurate POD models which can be expected to hold for a large class of turbulent flows.Comment: Submitted to the Journal of Fluid Mechanic

Cluster-based reduced-order modelling of a mixing layer

We propose a novel cluster-based reduced-order modelling (CROM) strategy of unsteady flows. CROM combines the cluster analysis pioneered in Gunzburger's group (Burkardt et al. 2006) and and transition matrix models introduced in fluid dynamics in Eckhardt's group (Schneider et al. 2007). CROM constitutes a potential alternative to POD models and generalises the Ulam-Galerkin method classically used in dynamical systems to determine a finite-rank approximation of the Perron-Frobenius operator. The proposed strategy processes a time-resolved sequence of flow snapshots in two steps. First, the snapshot data are clustered into a small number of representative states, called centroids, in the state space. These centroids partition the state space in complementary non-overlapping regions (centroidal Voronoi cells). Departing from the standard algorithm, the probabilities of the clusters are determined, and the states are sorted by analysis of the transition matrix. Secondly, the transitions between the states are dynamically modelled using a Markov process. Physical mechanisms are then distilled by a refined analysis of the Markov process, e.g. using finite-time Lyapunov exponent and entropic methods. This CROM framework is applied to the Lorenz attractor (as illustrative example), to velocity fields of the spatially evolving incompressible mixing layer and the three-dimensional turbulent wake of a bluff body. For these examples, CROM is shown to identify non-trivial quasi-attractors and transition processes in an unsupervised manner. CROM has numerous potential applications for the systematic identification of physical mechanisms of complex dynamics, for comparison of flow evolution models, for the identification of precursors to desirable and undesirable events, and for flow control applications exploiting nonlinear actuation dynamics.Comment: 48 pages, 30 figures. Revised version with additional material. Accepted for publication in Journal of Fluid Mechanic

Hassan Hemida Transient Simulation of the Aerodynamic Response of a Double-Deck Bus in Gusty Winds

The purpose of the research reported in this paper was to investigate the aerodynamic response of a double-deck bus in gusty winds using a detached-eddy simulation (DES

Managing knowledge transfer in research and development in the area of information and communication technology

Istraživačko-razvojne organizacije u području informacijske i komunikacijske tehnologije ogledni su predstavnik gospodarstva temeljenog na znanju. Poslovna izvrsnost, kvaliteta i inovacije temelji su poslovnih strategija globalnih centara znanja, a uspješna organizacija nužno mora osigurati mogućnost učinkovitog i efikasnog prijenosa znanja unutar organizacije, kao i između pojedenih organizacija kao dijelova globalne korporacije. U disertaciji je definirana formalna specifikacija prijenosa znanja unutar organizacijskog okružja istraživačko-razvojnog centra na području informacijske i komunikacijske tehnologije, kao i model prijenosa znanja zasnovan na projektnoj organizaciji i učenju iz iskustva. Definirani model prijenosa znanja može se primjeniti i za vrednovanje uspješnosti prijenosa znanja i za potencijalno poboljšanje uspješnosti prijenosa znanja. Na osnovi rezultata istraživanja predloženi su čimbenici uspješnosti prijenosa znanja i organizacijska načela upravljanja prijenosom znanja te je provedena njihova provjera na temelju usporedbe rezultata simulacije s iskustvenim pokazateljima.Research and development organizations in the field of information and communication technology are a model representative of knowledge based economy. Business excellence, quality and innovation are the key components of the business strategies of global knowledge centers. A successful organization has to ensure efficient and effective knowledge transfer within organization, as well as between organizations as part of a global corporation. In the thesis a formal specification of knowledge transfer within research and development centers in the field of information and communication technology, as well as a model of knowledge transfer based on project organization and learning from experience are being defined. The specified model of knowledge transfer can be used for the evaluation of the knowledge transfer effectiveness and for a potential improvement of the same. On the basis of the research results, factors of knowledge transfer effectiveness, as well as organizational criteria of knowledge transfer management are being proposed. These factors are also being verified through a comparison of simulations' results and experiential evidence

Managing knowledge transfer in research and development in the area of information and communication technology

Istraživačko-razvojne organizacije u području informacijske i komunikacijske tehnologije ogledni su predstavnik gospodarstva temeljenog na znanju. Poslovna izvrsnost, kvaliteta i inovacije temelji su poslovnih strategija globalnih centara znanja, a uspješna organizacija nužno mora osigurati mogućnost učinkovitog i efikasnog prijenosa znanja unutar organizacije, kao i između pojedenih organizacija kao dijelova globalne korporacije. U disertaciji je definirana formalna specifikacija prijenosa znanja unutar organizacijskog okružja istraživačko-razvojnog centra na području informacijske i komunikacijske tehnologije, kao i model prijenosa znanja zasnovan na projektnoj organizaciji i učenju iz iskustva. Definirani model prijenosa znanja može se primjeniti i za vrednovanje uspješnosti prijenosa znanja i za potencijalno poboljšanje uspješnosti prijenosa znanja. Na osnovi rezultata istraživanja predloženi su čimbenici uspješnosti prijenosa znanja i organizacijska načela upravljanja prijenosom znanja te je provedena njihova provjera na temelju usporedbe rezultata simulacije s iskustvenim pokazateljima.Research and development organizations in the field of information and communication technology are a model representative of knowledge based economy. Business excellence, quality and innovation are the key components of the business strategies of global knowledge centers. A successful organization has to ensure efficient and effective knowledge transfer within organization, as well as between organizations as part of a global corporation. In the thesis a formal specification of knowledge transfer within research and development centers in the field of information and communication technology, as well as a model of knowledge transfer based on project organization and learning from experience are being defined. The specified model of knowledge transfer can be used for the evaluation of the knowledge transfer effectiveness and for a potential improvement of the same. On the basis of the research results, factors of knowledge transfer effectiveness, as well as organizational criteria of knowledge transfer management are being proposed. These factors are also being verified through a comparison of simulations' results and experiential evidence

Managing knowledge transfer in research and development in the area of information and communication technology

Istraživačko-razvojne organizacije u području informacijske i komunikacijske tehnologije ogledni su predstavnik gospodarstva temeljenog na znanju. Poslovna izvrsnost, kvaliteta i inovacije temelji su poslovnih strategija globalnih centara znanja, a uspješna organizacija nužno mora osigurati mogućnost učinkovitog i efikasnog prijenosa znanja unutar organizacije, kao i između pojedenih organizacija kao dijelova globalne korporacije. U disertaciji je definirana formalna specifikacija prijenosa znanja unutar organizacijskog okružja istraživačko-razvojnog centra na području informacijske i komunikacijske tehnologije, kao i model prijenosa znanja zasnovan na projektnoj organizaciji i učenju iz iskustva. Definirani model prijenosa znanja može se primjeniti i za vrednovanje uspješnosti prijenosa znanja i za potencijalno poboljšanje uspješnosti prijenosa znanja. Na osnovi rezultata istraživanja predloženi su čimbenici uspješnosti prijenosa znanja i organizacijska načela upravljanja prijenosom znanja te je provedena njihova provjera na temelju usporedbe rezultata simulacije s iskustvenim pokazateljima.Research and development organizations in the field of information and communication technology are a model representative of knowledge based economy. Business excellence, quality and innovation are the key components of the business strategies of global knowledge centers. A successful organization has to ensure efficient and effective knowledge transfer within organization, as well as between organizations as part of a global corporation. In the thesis a formal specification of knowledge transfer within research and development centers in the field of information and communication technology, as well as a model of knowledge transfer based on project organization and learning from experience are being defined. The specified model of knowledge transfer can be used for the evaluation of the knowledge transfer effectiveness and for a potential improvement of the same. On the basis of the research results, factors of knowledge transfer effectiveness, as well as organizational criteria of knowledge transfer management are being proposed. These factors are also being verified through a comparison of simulations' results and experiential evidence