On the effect of compressibility on the impact of a falling jet

At the first World Sloshing Dynamics Symposium that took place during the Nineteenth (2009) International Offshore and Polar Engineering (ISOPE) Conference in Osaka, Japan, it was made clear that simplified academic problems have an important role to play in the understanding of liquid impacts. The problem of the impact of a mass of liquid on a solid structure is considered. First the steady two-dimensional and irrotational flow of an inviscid and incompressible fluid falling from a vertical pipe, hitting a horizontal plate and flowing sideways, is considered. A parametric study shows that the flow can either leave the pipe tangentially or detach from the edge of the pipe. Two dimensionless numbers come into play: the Froude number and the aspect ratio between the falling altitude and the pipe width. When the flow leaves tangentially, it can either be diverted immediately by the plate or experience squeezing before being diverted. The profile of the pressure exerted on the plate is computed and discussed. Then the same problem is revisited with the inclusion of compressibility effects, both for the falling liquid and for the gas surrounding it. An additional dimensionless number comes into play, namely the Mach number. Finally, a discussion on the differences between the incompressible and compressible cases is provided

International Competition between Public or Mixed Enterprises

We develop a model in which two firms from different countries compete on each other domestic market. Each firm is jointly owned by the residents and the government of its country. The extent of the government's stake in the public enterprise is endogenous and it determines the weight given to domestic consumers' surplus in the firm's payoff function. We show that the choice of each government's stake depends on a trade-off between allocative efficiency on the domestic market and profitability of foreign markets. We also highlight the fact that the government's stake in one country has an impact on firms' behavior in both countries.Regulation, public enterprises, duopoly

International Competition Between Public or Mixed Enterprises

We develop a model in which two firms from different countries compete on each other domestic market. Each firms is jointly owned by the residents and the government of its country. The extent of the government's stake in the public enterprise is endogenous and it determines the weight given the domestic consumers' surplus inithe firm's payoff function. We show that the choice of each government's stake depends on a trade-off between allocative efficiency on the domestic market and profitability of foreign markets. We also highlight the fact that the government's stake in on country has an impact of firms' behavior in both countries.Regulation, Public Enterprises, Duopoly

Meshless modelling of dynamic behaviour of glasses under intense shock loadings: application to matter ejection during high velocity impacts on thin brittle targets

The purpose of this study is to present a new material model adapted to SPH modelling of dynamic behaviour of glasses under shock loadings. This model has the ability to reproduce fragmentation and densification of glasses under compression as well as brittle tensile failure. It has been implemented in Ls-Dyna software and coupled with a SPH code. By comparison with CEA-CESTA experimental data the model has been validated for fused silica and Pyrex glass for stress level up to 35GPa. For Laser MegaJoule applications, the present material model was applied to 3D high velocity impacts on thin brittle targets with good agreement in term of damages and matter ejection with experimental data obtained using CESTA’s double stage light gas gun

Benchmark-Studie Wallis-Tirol bezüglich Massnahmen im Bereich Zweitwohnungen

Thema Tourismus polarisierte in der Schweiz in den letzten Jahren. Die Annahme der Zweitwohnungsinitiative im Jahre 2012 durch das Schweizer Stimmvolk hat die Walliser Tou-rismusbranche aufgemischt. Der Anteil der Gemeinden, die im Wallis in den Geltungsbereich der neuen Gesetzgebung fallen, beträgt 78 Prozent. Während sich in anderen Regionen der Tourismus seit der Finanzkrise langsam zu erholen scheint, war das Wallis im August 2013 der einzige Tourismuskanton mit einem Rückgang bei den Hotellogiernächten. Das Tirol hat die Zweitwohnungsproblematik bereits zu Beginn der 90er-Jahre erkannt, wes-halb die Region als „best-practise“ Beispiel dienen soll. Die Tiroler machen vieles anders, um nicht zu sagen, besser. In einer von BAKBASEL im Jahr 2011 veröffentlichen Studie stammen fünf der erfolgreichsten alpinen Destinationen aus Tirol und mit Zermatt nur eine aus dem Wallis. Die Zahlen sprechen für die Tiroler, was nicht allein am starken Schweizer Franken liegen kann. Für den Walliser Tourismus stellt sich nun die Frage, was geändert werden muss, um wieder einen konkurrenzfähigen Standort darzustellen

Hypervelocity impacts on thin brittle targets: experimental data and SPH simulations

The meteoroids and debris environment play an important role in the reduction of spacecraft life time. Ejecta or secondary debris, are produced when a debris or a meteoroid impact a spacecraft surface. These ejecta can contribute to a modification of the debris environment: either locally by the occurrence of secondary impacts on the component of complex and large space structures, or at long distance by formation of small orbital debris. This double characteristic underlines the necessity to model the damages caused by an HVI as well as the material ejection caused by the impact. Brittle materials are particularly sensitive to hypervelocity impacts because they produce features larger than those observed on ductile targets and the ejected fragments total mass including ejectas and spalls is in the order of 100 times bigger than the impacting mass. The main aim of this paper is to study the damaging and ejection processes that occur during hypervelocity impacts on thin brittle targets (dp = 500 microns for velocities ranging from 1 to 5 km/s). The two stage light gas gun “MICA” available at CEA-CESTA has been used to impact thin fused silica debris shields and the impacted samples have been analysed with environmental SEM microscopy and perthometer. Experimental characterization of ejected matter has also been performed on the MICA facility. The severe deformations occurring in any hypervelocity impact event are best described by meshless methods since they offer clear advantages for modeling large deformations and failure of solids as compared to mesh-based methods. Numerical simulation using the SPH method of Ls-Dyna and the Johnson Holmquist material model adapted for fused silica were performed at ENSICA. The results of these calculations are compared to experimental data obtained with MICA. Experimental data include the damage features in the targets (front and back spalled zone, perforation hole and cracks observed in the target) and the clouds and fragments ejected during the impact