Wake transition in the flow around two circular cylinders in staggered arrangements

Accepted versio

Benchmark on the Aerodynamics of a Rectangular 5:1 Cylinder: An overview after the first four years of activity

In July 2008, a benchmark study on the aerodynamics of a stationary rectangular cylinder with chord-to- depth ratio equal to 5 (BARC) was launched. This paper gives an outline of the state of the art on the aerodynamics of 5:1 rectangular cylinders prior to the starting of BARC, and summarizes the results obtained by the contributors during the first four years of activity. The results of about 70 realizations of the BARC flow configuration obtained under a nominally common set-up in both wind tunnel experiments and numerical simulations are compared among themselves and with the data available in the literature prior to BARC, in terms of bulk parameters, flow and aerodynamic load statistics, pressure and force spanwise correlations. It is shown that the near wake flow, the base pressure and, hence, the drag coefficient obtained in the different flow realizations are in very good agreement. Conversely, the flow features along the cylinder lateral surfaces and, hence, the lift, are strongly sensitive to set-up and modelling, leading to a significant dispersion of both wind tunnel measurements and numerical predictions. Finally, a possible asymmetry of the time averaged flow has been recognized both in wind tunnel tests and in numerical simulation

A parallel cellular automata Lattice Boltzmann Method for convection-driven solidification

This article presents a novel coupling of numerical techniques that enable three-dimensional convection-driven microstructure simulations to be con- ducted on practical time scales appropriate for small-size components or experiments. On the microstructure side, the cellular automata method is efficient for relatively large-scale simulations, while the lattice Boltzmann method provides one of the fastest transient computational fluid dynamics solvers. Both of these methods have been parallelized and coupled in a single code, allowing resolution of large-scale convection-driven solidification problems. The numerical model is validated against benchmark cases, extended to capture solute plumes in directional solidification and finally used to model alloy solidification of an entire differentially heated cavity capturing both microstructural and meso-/macroscale phenomena

Theory and sensitivity of wave-digital filter.

http://archive.org/details/theorysensitivit00pos

Verwendung des BSIM2-Modells bei höheren Frequenzen

Alle modernen Netzwerksimulationsprogramme enthalten für MOS-Transistoren mindestens die Modelle MOS1 bis MOS3, BSIM1 und BSIM2. Das BSIM2-Modell zeichnet sich durch eine relativ gute Widerspiegelung der DC-Eigenschaften einschließlich vieler Nebeneffekte des MOS-Transistors aus. Im Beitrag wird untersucht, inwieweit das BSIM2-Modell sich im unteren GHz-Bereich verwenden läßt

Zuverlässigkeitsuntersuchungen an MOS-Strukturen auf Wafer-Ebene

Zur Charakterisierung der Hot-Carrier-Resistenz der Transistoren in CMOS-Schaltungen und für die Lösung von Prozeßmonitoraufgaben eignet sich die Anwendung eines Gateimpulsstreßverfahrens auf Wafer-Ebene. Mit den Programmen "ARON8" und "OPTIKON" können durch Hot-Carrier-Streß deformierte Transistorkennlinien modelliert werden. Auf dieser Grundlage ermöglicht die Netzwerksimulation Veränderungen von Schaltungsparametern vorauszuberechnen, die durch Hot-Carrier-Effekte ausgelöst werden können. Durch TDDB-Messungen auf Wafer-Ebene kann die defektinduzierte Verringerung der Ausfallzeiten an Gateoxidkapazitäten ebenso nachgewiesen werden, wie durch aufwendige Ofentests. Das Testsystem muß die Registrierung der Ausfallereignisse parallel an möglichst vielen Strukturen und mit hoher Zeitauflösung gestatten

Status and market opportunities of solid oxide fuel cells based cogeneration systems

The most sustainable technology for conversion of natural gas into electricity and heat in the low to medium power levels, is a Solid Oxide Fuel Cell (SOFC) based Combined Heat and Power (CHP) unit. Electrical efficiencies of up to 60 % and total efficiencies of more than 90 % down to electrical powers of only 1 kW, makes these systems attractive for applications in varying power classes. The range between 10 and 50 kWel is especially promising for competition with conventional CHP units and the electrical grid. Different system layouts options exist to meet the technical requirements of specific applications as well as the cost targets for a early market entry. Main distinguishing features are the method of processing natural gas into a hydrogen-rich reformate (i.e. partial oxidation vs. steam reforming) and the cell stack technology used. As a result, electrical efficiencies, system complexity, and costs vary. Applied to cogeneration, the overall efficiency has the ma in impact on the profitability of the CHP unit, provided there is existence of a sufficient heat demand. Electrical efficiencies are dominated by power to heat ratios or the utilization factor, this means the number of operation hours needs to be increased. The calculation of CHP cost saving potentials is impeded strongly by application dependent parameters like profiles of heat and electricity demand as well as local gas and electricity prices. For Germany, payback periods can be calculated since typical load profiles of single and multi-family homes are available. Here, the choice of SOFC system layout depends on the economic viability of electricity feed-in to the grid. If funding is available, high electrical efficiencies are clearly favored. This is also valid for applications where only domestic hot water heating is required. Small base load power generators are profitable provided that the system cost targets can be met. Larger SOFC system in a power range of >100 kWel face a strong compe