Absolute and convective secondary instabilities in spatially periodic shear flows

The generic problem of the spatiotemporal instability of a periodic basic flow (Stuart vortices) is considered in order to interpret the sequence of bifurcations observed in open shear flows. Using a novel numerical technique, we show that the more concentrated the vortices, the smaller the backflow needed to trigger absolute instability. These results allow us to propose an alternative interpretation for the subharmonic resonance observed in forced shear flows, which is classically attributed to an acoustic feedbac

Towards an SDN network control application for differentiated traffic routing

In the last years, Software Defined Networking has emerged as a promising paradigm to foster network innovation and address the issues coming from the ossification of the TCP/IP architecture. The clean separation between control and data plane, the definition of northbound and southbound interfaces are key features of the Software Defined Networking paradigm. Moreover, a centralised control plane allows network operators to deploy advanced control and management strategies. Effective traffic engineering and resources management policies allow to achieve a better utilisation of network resources and improve endto- end service performance. This paper deals with the architectural design and experimental validation of a control application that enables differentiated routing for traffic flows belonging to different service classes. The new control application makes routing decisions leveraging on OpenFlow network statistics, i.e., taking advantage of real-time network status information. Moreover, a Deep Packet Inspection module has been developed and integrated in the control application to detect VoIP traffic with Session Initiation Protocol signalling, enforcing this way policies for a differentiated treatment of VoIP traffic. Finally, a functional validation is performed in emulated environment.This work was supported by the EPSRC INTERNET Project EP/H040536/1.This is the author accepted manuscript. The final version is available from IEEE via http://dx.doi.org/10.1109/ICC.2015.724925

The importance of phytoplankton trait variability in spring bloom formation

About 60 years ago, the critical depth hypothesis was proposed to describe the occurrence of spring phytoplankton blooms and emphasized the role of stratification for the timing of onset. Since then, several alternative hypotheses appeared focusing on the role of grazing and mixing processes such as turbulent convection or wind activity. Surprisingly, the role of community composition—and thus the distribution of phytoplankton traits—for bloom formation has not been addressed. Here, we discuss how trait variability between competing species might influence phytoplankton growth during the onset of the spring bloom. We hypothesize that the bloom will only occur if there are species with a combination of traits fitting to the environmental conditions at the respective location and time. The basic traits for formation of the typical spring bloom are high growth rates and photoadaptation to low light conditions, but other traits such as nutrient kinetics and grazing resistance might also be important. We present concise ideas on how to test our theoretical considerations experimentally. Furthermore, we suggest that future models of phytoplankton blooms should include both water column dynamics and variability of phytoplankton traits to make realistic projections instead of treating the phytoplankton bloom as an aggregate community phenomenon

Technological innovations and financial viability in brazilian water distribution system: a case study of GS Inima SAMAR and strategic guidelines for digital transformation

LAUREA MAGISTRALEQuesta tesi analizza l'applicazione, le prestazioni e la fattibilità economica delle innovazioni tecnologiche nel settore della distribuzione idrica, con un focus specifico sul contesto brasiliano. Attraverso una revisione della letteratura e uno studio di caso dettagliato relativo alla società GS Inima SAMAR di Araçatuba-SP, viene esplorata la transizione dalla gestione tradizionale dell’acqua a pratiche di gestione intelligente, che includono l’adozione di software per la modellazione idraulica (OpenFlows WaterGEMS), sensori avanzati, sistemi SCADA e strategie di setorizzazione. Lo studio descrive tutti i componenti chiave di un moderno Sistema di Distribuzione Idrica (WDS), come misuratori di portata, trasduttori di pressione, valvole di controllo e pompe, valutando il loro contributo all’efficienza operativa. Analizzando gli indicatori di prestazione e i costi operativi prima e dopo l’implementazione delle innovazioni, la tesi fornisce una valutazione basata sui dati dell’impatto della digitalizzazione e dell’ottimizzazione della rete. Tecniche finanziarie come il Valore Attuale Netto (VAN), il Rapporto Benefici/Costi (B/C) e il Tasso Interno di Rendimento (TIR) sono utilizzate per supportare le decisioni d’investimento. Lo studio di caso dimostra che, sebbene l’infrastruttura attuale presenti ancora limiti di maturità—soprattutto in termini di monitoraggio in tempo reale—le tecnologie implementate hanno già mostrato benefici misurabili, come la riduzione delle perdite idriche e il miglioramento del margine lordo e del ROI parziale. Infine, la tesi consolida il passaggio a una nuova piattaforma di modellazione sostituendo il precedente sistema GSWaterS con OpenFlows WaterGEMS di Bentley, consentendo simulazioni più avanzate e una maggiore capacità d’integrazione. Questo cambiamento supporta la continuazione della strategia di gestione intelligente dell’acqua, fornendo la base tecnica necessaria per miglioramenti futuri nel monitoraggio, nell’analisi e nelle decisioni operative all’interno dell’azienda.This thesis investigates the application, performance, and financial viability of technological innovations in the water distribution sector, with a focus on the Brazilian context. Through a detailed literature review and a case study of GS Inima SAMAR in Araçatuba-SP, it explores the transition from traditional to smart water management practices, including the adoption of hydraulic modeling software (GSWAterS and OpenFlows WaterGEMS), advanced sensors, SCADA systems, and sectorization strategies. The study describes all key components of a modern Water Distribution System (WDS), including flow meters, pressure transducers, control valves, and pumps, and evaluates their contribution to operational efficiency. By analyzing the performance indicators and operational costs before and after the implementation of innovations, the thesis provides a data-driven assessment of the impacts of digitalization and network optimization. Financial techniques such as Net Present Value (NPV), Benefit-Cost Ratio (B/C), and Internal Rate of Return (IRR) were applied to support investment decisions. The case study demonstrates that although the current infrastructure still lacks full maturity—especially in terms of real-time monitoring—the implemented technologies have already shown measurable benefits, including reduction in water losses and improvements in gross margin and partial ROI. Finally, the thesis consolidates the transition to a new modeling platform by replacing the previous GSWaterS system with Bentley’s OpenFlows WaterGEMS, enabling more advanced simulation and integration capabilities. This shift supports the continuation of the smart water management strategy, providing the necessary technical foundation for future improvements in monitoring, analysis, and operational decision-making within the utility

Direct and adjoint global modes of a recirculation bubble: Lift-up and convective non-normalities

International audienceThe stability of the recirculation bubble behind a smoothed backward-facing step is numerically computed. Destabilization occurs first through a stationary three-dimensional mode. Analysis of the direct global mode shows that the instability corresponds to a deformation of the recirculation bubble in which streamwise vortices induce low- and high-speed streaks as in the classical lift-up mechanism. Formulation of the adjoint problem and computation of the adjoint global mode show that both the lift-up mechanism associated with the transport of the base flow by the perturbation and the convective non-normality associated with the transport of the perturbation by the base flow explain the properties of the flow. The lift-up non-normality differentiates the direct and adjoint modes by their component: the direct is dominated by the streamwise component and the adjoint by the cross-stream component. The convective non-normality results in a different localization of the direct and adjoint global modes, respectively downstream and upstream. The implications of these properties for the control problem are considered. Passive control, to be most efficient, should modify the flow inside the recirculation bubble where direct and adjoint global modes overlap, whereas active control, by for example blowing and suction at the wall, should be placed just upstream of the separation point where the pressure of the adjoint global mode is maximum. © 2009 Cambridge University Press

Culvert Design and Roadway Restoration of Cavett Road at Damon Creek

Cavett Road is a small, two lane rural road located in Kirksey, Kentucky. This road faces the issue of flooding during light-to-moderate rain, posing risk to those who use the road, especially those living along Cavett Road. This flooding is also capable of washing away the surface of Cavett Road and the adjacent banks and soil wall of the creek, creating a risk of erosion and soil subsidence. To reduce the risk of flooding and erosion and improve roadway function, this project outlines a potential solution using newly-installed reinforced concrete box culverts and soil fill above them to improve the hydrology along Damon Creek and raise the roadway of Cavett Road to above the level of flooding using principles of various civil engineering disciplines, including hydrologic, hydraulic, structural, geotechnical, and transportation engineering, as well as cost analysis of these disciplines

Instability of a free-shear layer in the vicinity of a viscosity-stratified layer

The stability of a mixing layer made up of two miscible fluids, with a viscosity-stratified layer between them, is studied. The two fluids are of the same density. It is shown that unlike other viscosity-stratified shear flows, where species diffusivity is a dominant factor determining stability, species diffusivity variations over orders of magnitude do not change the answer to any noticeable degree in this case. Viscosity stratification, however, does matter, and can stabilize or destabilize the flow, depending on whether the layer of varying velocity is located within the less or more viscous fluid. By making an inviscid model flow with a slope change across the 'viscosity' interface, we show that viscous and inviscid results are in qualitative agreement. The absolute instability of the flow can also be significantly altered by viscosity stratification