Simulation of a shut-down transient in the Francis-99 turbine model

Due to the new intermittent electric energy sources, hydropower is forced to run more and more at off-design conditions and to regulate the operating conditions. This causes flow instabilities with pressure fluctuations, and load variations that may deteriorate the machine. Previous numerical research on the flow in water turbines has mainly focused on steady operating conditions at BEP and off-design. More knowledge is needed on transients between operating conditions, and start-up and shut-down procedures. This requires dynamic meshes that both rotate the runner, using a coupling interface to the non-rotating part of the mesh, and morph the guide vane mesh due to the change in guide vane angle during the transient. Special care needs to be taken to apply boundary conditions that resemble the experimental condition to be used for validation. The present work addresses a shut-down transient of the Francis-99 turbine (https://www.ntnu.edu/nvks/francis-99), using OpenFOAM-2.3.x. Turbulence is modelled by LES based on the dynamic one-equation eddy viscosity sub-grid model and the cube root volume filter width, although the temporal and spatial resolution requirements have not been assessed in these preliminary results. The inlet and outlet boundary conditions are set using pressure conditions. The outlet static pressure is taken from the experiment at BEP. The inlet total pressure is adjusted to yield the same flow rate as in the experiment at BEP. The flow rate is given by the solution. The runner region of the mesh rotates with a solid-body rotation, while the guide vane region of the mesh is morphing due to the continuous change in guide vane angle. Rotating and stationary parts of the mesh are coupled with an arbitrary mesh interface (AMI). The results show that the methodology can be used to capture the experimentally observed flow features during transients

Lady and the Trump: Status and Wealth in the Marriage Market

We examine a relatively neglected aspect of intergenerational transmission of economic standing, namely culturally determined status markers and their valuation in the marriage market. We take nobility to be such a status marker. Using data on Swedish marriages, we test the hypothesis that nobility have a greater probability of marrying up in terms of wealth. We find a large and statistically significant positive effect for nobility. This finding has important implications for the intergenerational transmission of inequality, and for the longevity of the institution of nobility itself

Forum sull’Health check e la PAC dopo il 2013 (parte 3)

Questo articolo collettivo raccoglie una terza serie di contributi alla riflessione sulle conclusioni dell’Health check e sulle prospettive della PAC per il dopo-2013, introdotta da un articolo di Franco Sotte pubblicato nel numero 15 di Agriregionieuropa (Sotte, 2008). Nei numeri scorsi sono state pubblicate le opinioni di altri autorevoli esperti (Cioffi, Corsi, De Filippis, Frascarelli, Salvatici, Scoppola, Agriregionieuropa, n.16, 2009; Boatto, Brunori, Henke, Mantino, Pupo D’Andrea, Sckokai, Agriregionieuropa, n.17, 2009). In questo numero della rivista sono riportate le opinioni di altri autorevoli economisti agrari. Tra di essi, anche quella di Erik Fahlbeck dell’Università di Uppsala

An Introduction to Special Issue: The Causes and Consequences of Secret Ballot Reform

This article introduces a collection of papers that explore two understudied but critical questions of enduring concern for the study of democratization. Was the secret ballot driven by the same forces that drove the rise of democracy more generally? Did the secret ballot end electoral fraud, or was its effect merely endogenous to economic modernization more generally? This article provides historical context for the rise of the secret ballot, systematizing some of the complexities and ambiguities of the concept of the “secret ballot” itself. Second, we summarize the approach and some of the main findings of the papers in the volume, offering an outline of the broader lessons that emerge from the papers. Finally, we reflect upon the significance of a historical study of the secret ballot for technological and institutional reforms for contemporary democrac