Modelling vortex formation in an unbaffled stirred tank reactors

Agitating liquids in unbaffled stirred tank leads to the formation of a vortex in the region of the impeller shaft when operating in the turbulent flow regime. A numerical model is presented here that captures such a vortex. The volume of fluid model, a multiphase flow model was employed in conjunction with a multiple reference frame model and the shear stress turbulence model. The dimensions of the tank considered here, were 0.585 m for the liquid depth and tank diameter with a 0.2925 m diameter impeller at a height of 0.2925 m. The impeller considered was an eight-bladed paddle type agitator that was rotating with an angular velocity of 7.54 rad s (72 rpm) giving a Reynolds number of 10 and Froude number of 0.043. Preliminary results of a second investigation into the effect of liquid phase properties on the vortex formed are also presented. © 2006 Elsevier B.V. All rights reserved.

Institutions and social entrepreneurship:the role of institutional voids, institutional support, and institutional configurations

We develop the institutional configuration perspective to understand which national contexts facilitate social entrepreneurship (SE). We confirm joint effects on SE of formal regulatory (government activism), informal cognitive (postmaterialist cultural values), and informal normative (socially supportive cultural norms, or weak-tie social capital) institutions in a multilevel study of 106,484 individuals in 26 nations. We test opposing propositions from the institutional void and institutional support perspectives. Our results underscore the importance of resource support from both formal and informal institutions, and highlight motivational supply side influences on SE. They advocate greater consideration of institutional configurations in institutional theory and comparative entrepreneurship research.

Vortex shedding from a row of square bars

Interactions of wakes in a flow past a row of square bars, which is placed across a uniform flow, are investigated by numerical simulations and experiments on the tassumption that the flow is two-dimensional and incompressible. At small Reynolds numbers the flow is steady and symmetric with respect not only to streamwise lines through the center of each square bar but also to streamwise centerlines between adjacent square bars. However, the steady symmetric flow becomes unstable at larger Reynolds numbers and make a transition to a steady asymmetric flow with respect to the centerlines between adjacent square bars in some cases or to an oscillatory flow in other cases. It is found that vortices are shed synchronously from adjacent square bars in the same phase or in anti-phase depending upon the distance between the bars when the flow is oscillatory. The origin of the transition to the steady asymmetric flow is identified as a pitchfork bifurcation, while the oscillatory flows with synchronous shedding of vortices are clarified to originate from a Hopf bifurcation. The critical Reynolds numbers of the transitions are evaluated numerically and the bifurcation diagram of the flow is obtained.

Some generalization of Desargues and Veronese configurations

2000 Mathematics Subject Classification: 51E14, 51E30.

Predegree Polynomials of Plane Configurations in Projective Space

2000 Mathematics Subject Classification: 14N10, 14C17.

A note on the propagation of quantized vortex rings through a quantum turbulence tangle:energy transport or energy dissipation?

We investigate quantum vortex ring dynamics at scales smaller than the inter-vortex spacing in quantum turbulence. Through geometrical arguments and high-resolution numerical simulations, we examine the validity of simple estimates for the mean free path and the structure of vortex rings post-reconnection. We find that a large proportion of vortex rings remain coherent objects where approximately 75% of their energy is preserved. This leads us to consider the effectiveness of energy transport in turbulent tangles. Moreover, we show that in low density tangles, appropriate for the ultra-quantum regime, ring emission cannot be ruled out as an important mechanism for energy dissipation. However at higher vortex line densities, typically associated with the quasi-classical regime, loop emission is expected to make a negligible contribution to energy dissipation, even allowing for the fact that our work shows rings can survive multiple reconnection events. Hence the Kelvin wave cascade seems the most plausible mechanism leading to energy dissipation

Universal profile of the vortex condensate in two-dimensional turbulence

An inverse turbulent cascade in a restricted two-dimensional periodic domain creates a condensate—a pair of coherent system-size vortices. We perform extensive numerical simulations of this system and carry out theoretical analysis based on momentum and energy exchanges between the turbulence and the vortices. We show that the vortices have a universal internal structure independent of the type of small-scale dissipation, small-scale forcing, and boundary conditions. The theory predicts not only the vortex inner region profile, but also the amplitude, which both perfectly agree with the numerical data.

Vortex-density fluctuations, energy spectra, and vortical regions in superfluid turbulence

Measurements of the energy spectrum and of the vortex-density fluctuation spectrum in superfluid turbulence seem to contradict each other. Using a numerical model, we show that at each instance of time the total vortex line density can be decomposed into two parts: one formed by metastable bundles of coherent vortices, and one in which the vortices are randomly oriented. We show that the former is responsible for the observed Kolmogorov energy spectrum, and the latter for the spectrum of the vortex line density fluctuations.

Kelvin-wave cascade in the vortex filament model

The small-scale energy-transfer mechanism in zero-temperature superfluid turbulence of helium-4 is still a widely debated topic. Currently, the main hypothesis is that weakly nonlinear interacting Kelvin waves (KWs) transfer energy to sufficiently small scales such that energy is dissipated as heat via phonon excitations. Theoretically, there are at least two proposed theories for Kelvin-wave interactions. We perform the most comprehensive numerical simulation of weakly nonlinear interacting KWs to date and show, using a specially designed numerical algorithm incorporating the full Biot-Savart equation, that our results are consistent with the nonlocal six-wave KW interactions as proposed by L'vov and Nazarenko.

Vállalati stratégiák, konfigurációk Magyarországon 1992 és 2010 között – 1. rész (Corporate strategies, configurations in Hungary between 1992 and 2010)

A vállalatok közvetlen versenytársaikkal összevetett eredményei alapján képzett teljesítményértékelési dimenziók, és az azok szerint képzett vállalati stratégiai archetípusok, konfigurációk azonosítása, leírása áll az empirikus kutatás fókuszában. Ezek során a szerző azonosítja a vállalati stratégiák archetípusait, felhasználva a konfigurációs iskola módszertanát. A kutatás az 1992 és 2010 között felvett magyarországi adatsorok alkalmazásával, több mint 1200 felsővezetői vélemény alapján készült. A válaszok alapján a vállalatok teljesítményét hét, egymástól független dimenzió mentén különíti el, melyek alapján különböző vállalatistratégia-típusok azonosíthatók. A kiemelkedő vállalati teljesítmény elérése érdekében a szerző konkrét ajánlásokat fogalmaz meg cikkében ______________ The identification and description of the strategic archetypes (configurations) are the focus of the empirical research. The author identifies and describes the archetypes of the adaptation strategies by using the methodology of the configuration school. The dataset of the research consists of more than 1200 CEO’s responses from Hungary between 1992 to 2010. Based on the responses, corporate performance has 7 independent dimensions, and they are suitable to identify and descripe different strategic archetypes. Based on the results, the article has practical advices how to deliver superior corporate performance.

Versenyképes stratégiák Magyarországon 1992 és 2010 között = Corporate Strategies, Configurations in Hungary between 1992 and 2010

Az empirikus kutatás fókuszában a vállalatok közvetlen versenytársaihoz képest realizált teljesítményei alapján képzett teljesítményértékelési dimenziók, és azok alapján képzett vállalati stratégiai archetípusok, konfigurációk azonosítása, leírása áll. A konfigurációs iskola módszertanát felhasználva azonosítom az empirikus kutatások során a vállalati stratégiák archetípusait. A kutatás 1992 és 2010 közötti Magyarországi adatsorok felhasználásával, több mint 1200 felsővezetői vélemény alapján készült. A válaszok alapján a vállalatok teljesítményét 7 egymástól független dimenzió mentén különíthetjük el, melyek alapján különböző vállalati stratégia típusok azonosíthatók. A műhelytanulmányben a gyakorlati tapasztalatok alapján, konkrét ajánlások kerülnek megfogalmazásra a kiemelkedő vállalati teljesítmény elérése érdekében. _______ The identification and description of the strategic archetypes (configurations) are the focus of the empirical research. I identify and describe the archetypes of the adaptation strategies by using the methodology of the configuration school. The dataset of the research consists of more than 1200 CEO’s responses from Hungary between 1992 to 2010. Based on the responses, corporate performance has 7 independent dimensions, and they are suitable to identify and descripe different strategic archetypes. Based on the results, the article has practical advices how to deliver superior corporate performance.

Multi-modes approach to modelling of vortex-induced vibration

Acknowledgements A.P. would like to acknowledge the support of the National Subsea Research Institute (NSRI) UK. E.P. and M.W. are grateful for partial support provided by the Italian Ministry of Education, University and Research (MIUR) by the PRIN funded program 2010/11 N.2010MBJK5B

2DOF CFD Calibrated Wake Oscillator Model to Investigate Vortex-Induced Vibrations

ACKNOWLEDGMENTS This work is supported by the National Subsea Research Institute (NSRI) UK.

Énergétique des vortex et comportement magnétique de la supraconductivité SO(5)

Mémoire numérisé par la Direction des bibliothèques de l'Université de Montréal.