55,850 research outputs found
Sybistroma crinipes Staeger 1842
No full textSybistroma crinipes Staeger, 1842 Distribution. Type locality: Denmark: “Ellemosen, Charlottenlund”. The species is known from Austria, Belgium, Czech, Denmark, France, Germany, Hungary, Iran, Italy, Netherlands, Romania, Russia (Alania), Sweden, Switzerland, Turkey (Uşak), UK, Ukraine (Uzhgorod).Published as part of Grichanov, Igor Ya. & Kazerani, Farzaneh, 2014, A new species of Sybistroma Meigen (Diptera: Dolichopodidae) from the Middle East with a key to West-Palaearctic species of the genus, pp. 572-582 in Zootaxa 3866 (4) on page 579, DOI: 10.11646/zootaxa.3866.4.7, http://zenodo.org/record/22760
Oxycera meigenii Staeger 1844
No full textOxycera meigenii Staeger, 1844 (fig. 2, b–c) Material examined: Iran, East Azerbaijan, Mekidi valley (located in center of Arasbaran forest): 38°50ʹ8.11˝ N, 46°54ʹ3.15˝ E, 1656 m, 19.07.2011, 3}, 1 {(Khaghaninia leg.). D i s t r i b u t i o n: Central and western parts of Europe, Afghanistan, Azerbaijan, Iran, Mongolia, Russia, Tajikistan, Turkey, Turkmenistan, Uzbekistan (Woodley, 2001). R e m a r k: In this species longitudinal yellow stripes on mesonoturn present in both sexes and connected to humeral spots, in female abrupt at the middle; abdominal tergites 2–4 with oblique yellow side-markings (fig 2, b–c)Published as part of Khaghaninia, S., Kazerani, F. & Hauser, M., 2015, The Genera Nemotelus And Oxycera (Diptera, Stratiomyidae) In The Arasbaran Forests, pp. 401-406 in Vestnik Zoologii 49 (5) on page 405, DOI: 10.1515/vzoo-2015-0045, http://zenodo.org/record/644924
A Dynamic Subfilter-scale Stress Model for Large Eddy Simulations Based on Physical Flow Scales
No full textWe propose a new definition of the length scale in an eddy-viscosity model for large-eddy simulations (LES). This formulation extends and generalizes a previous proposal [Piomelli, Rouhi and Geurts, Proc. ETMM10, 2014], in which the LES length scale was expressed in terms of the integral length-scale of turbulence determined by the flow characteristics and explicitly decoupled from the simulation grid; this approach was named Integral Length-Scale Approximation (ILSA). As in the original ILSA, the model coefficient was determined by the user, and required to maintain a desired contribution of the unresolved, subfilter scales (SFS) to the global transport. We propose a local formulation (local ILSA) in which the model coefficient is local in space, allowing a precise control over SFS activity as a function of location. This new formulation preserves the properties of the global model; application to channel flow and backward-facing step verifies its features and accuracy
Large-eddy simulation of a separated flow with a sub-filter scale model based on the integral length-scale
No full textA new sub-filter scale model for large-eddy simulations, which uses a length-scale proportional to the integral scale of the turbulence instead of the grid resolution to parametrize the modelled stresses, will be assessed in the prediction of the flow of a boundary-layer over a rough surface, which includes separation and reattachment
Near Wall PIV-Measurements on the Windward Slope of a Hill
No full textThe turbulent flow over periodic hills was measured near to the wall, using planar Particle-Image-Velocimetry (PIV) at high spatial resolution. Our focus is on the near wall turbulence structure on the windward slope of the hill. For large-eddy simulation (LES) we suspect that, if this was not predicted accurately, it affects the prediction of the velocity profiles over the hill crest which in turn will affect the recirculation length downstream of the hill. Regarding the time averaged velocities, we were able to resolve the linear viscous region of the boundary layer. The velocity distribution and also the Reynolds stress does not comply with the law of the wall as it is valid for a turbulent boundary layer at equilibrium
Energy dissipation and flux laws for unsteady turbulence
No full textDirect Numerical Simulations of spatially periodic unsteady turbulence show that the high Reynolds number scalings of the instantaneous energy dissipation rate and interscale energy flux at intermediate wavenumbers are qualitatively different from the well-known cornerstone scalings of equilibrium turbulence where and are time-dependent rms velocity and integral length-scales. Instead, they both scale as where and are length and velocity scales characterizing initial/overall unsteady turbulence conditions
Direct numerical simulation of turbulent Couette-Poiseuille flow with zero skin friction
No full textThe near-wall scaling of mean velocity U(y) is addressed for the case of zero skin friction on one wall of a fully turbulent channel flow. The present DNS results can be added to the evidence in support of the conjecture that U is proportional to √yw in the region just above the wall at which the mean shear dU/dy = 0
Real-space Manifestations of Bottlenecks in Turbulence Spectra
No full textAn energy-spectrum bottleneck, a bump in the turbulence spectrum between the inertial and dissipation ranges, is shown to occur in the non-turbulent, one-dimensional, hyperviscous Burgers equation and found to be the Fourier-space signature of oscillations in the real-space velocity, which are explained by boundary-layer-expansion techniques. Pseudospectral simulations are used to show that such oscillations occur in velocity correlation functions in one- and three-dimensional hyperviscous hydrodynamical equations that display genuine turbulence
Braid Entropy of Faraday Waves driven 2D Turbulence
No full textWe report new experimental results that use tools from braid theory to characterize two-dimensional turbulent flows driven by Faraday waves. The average topological length of the material fluid lines is found to grow exponentially with time. It allows us to compute the braid’s topological entropy SBraid. We show that SBraid increases as the square root of the turbulence kinetic energy E ~ u^2, where u^2 is the horizontal velocity variance . At long times, the PDFs of Lbraid are positively skewed and present strong exponential tails
Statistical separation of observed global and European climate data into natural and anthropogenic signals
No full textObserved global and European spatiotemporal related fields of surface air temperature, mean-sea-level pressure and precipitation are analyzed statistically with respect to their response to external forcing factors such as anthropogenic greenhouse gases, anthropogenic sulfate aerosol, solar variations and explosive volcanism, and known internal climate mechanisms such as the El Niño-Southern Oscillation (ENSO) and the North Atlantic Oscillation (NAO). As a first step, a principal component analysis (PCA) is applied to the observed spatiotemporal related fields to obtain spatial patterns with linear independent temporal structure. In a second step, the time series of each of the spatial patterns is subject to a stepwise regression analysis in order to separate it into signals of the external forcing factors and internal climate mechanisms as listed above as well as the residuals. Finally a back-transformation leads to the spatiotemporally related patterns of all these signals being intercompared. Two kinds of significance tests are applied to the anthropogenic signals. First, it is tested whether the anthropogenic signal is significant compared with the complete residual variance including natural variability. This test answers the question whether a significant anthropogenic climate change is visible in the observed data. As a second test the anthropogenic signal is tested with respect to the climate noise component only. This test answers the question whether the anthropogenic signal is significant among others in the observed data. Using both tests, regions can be specified where the anthropogenic influence is visible (second test) and regions where the anthropogenic influence has already significantly changed climate (first test)
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