Search results for "Drag"
showing 10 items of 179 documents
CFD simulations of dense solid–liquid suspensions in baffled stirred tanks: Prediction of solid particle distribution
2013
Abstract Industrial tanks devoted to the mixing of solid particles into liquids are often operated at an impeller speed N less than Njs (defined as the lowest speed allowing the suspension of all particles): under such conditions the distribution of solid-particles is very far from being homogeneous and very significant concentration gradients exist. The present work is devoted to assessing the capability of Computational Fluid Dynamics (CFD) in predicting the particle distribution throughout the tank. The CFD model proposed by Tamburini et al. [58] and successfully applied to the prediction of the sediment amount and shape was adopted here to simulate the particle distribution under partia…
On the induced drag reduction due to propeller-wing interaction
1995
AbstractThe aerodynamic interaction between a wing and a couple of propellers in tractor configuration is investigated by means of a model based on the lifting line concept and under the assumption of quasi-steady incompressible motion of inviscid fluid. The ways the propellers influence the wing performances, particularly the induced drag, are analysed. It turns out that the lift increase and the possible drag reduction depend strongly on the direction of the blade rotation and on the propeller distances from midspan, and result from two main effects: the direct propeller induction on the wing and the modification of the lift distribution along the span. An additional nonlinear (mixed) con…
Optimization of a Vehicle Shape by CFD Code
2005
In this paper, fluid dynamics simulations have been executed using a CFD (Computational Fluid Dynamics) commercial code, on a Maserati Biturbo mod. 222 - 1988. At first some surfaces are optimised, choosing the more important ones for the reduction of the resistance, by a manual variation of their geometry, hence a large surface is optimised in an automatic way, by means of an own software, developed in the MatLab environment, returning the optimised surface according to a specific objective function (the resistance in this paper). The aerodynamics resistance results are given under the form of aerodynamics penetration coefficient CD, taking into account the vehicle shape effect, the speed,…
Second-order hydrodynamic effects on the response of three semisubmersible floating offshore wind turbines
2020
Abstract Floating structures have become the most feasible solution for supporting wind turbines when offshore wind project move to deeper water. In this paper, a hydrodynamic analysis of three different semisubmersible floating offshore wind turbines is carried out including second-order hydrodynamic effects. The three examined platforms are V-shaped semisubmersible, Braceless semisubmersible and OC4-DeepCwind semisubmersible and are used to support the NREL 5 MW reference wind turbine. The main objective of the present study is to investigate and compare the hydrodynamic response of the three different semisubmersible floaters in two water depths (100 m, and 200 m) under different load co…
Polymeric microcontainers improve oral bioavailability of furosemide.
2016
Microcontainers with an inner diameter of 223 μm are fabricated using the polymer SU-8, and evaluated in vitro, in situ and in vivo for their application as an advanced oral drug delivery system for the poorly water soluble drug furosemide. An amorphous sodium salt of furosemide (ASSF) is filled into the microcontainers followed by applying a lid using Eudragit L100. It is possible to control the drug release in vitro, and in vitro absorption studies show that the microcontainers are not a hindrance for absorption of ASSF. In situ perfusion studies in rats are performed with ASSF-filled microcontainers coated with Eudragit and compared to a furosemide solution. The absorption rate constant …
Local Extinction of Dragonfly and Damselfly Populations in Low- and High-Quality Habitat Patches
2010
Understanding the risk of extinction of a single population is an important problem in both theoretical and applied ecology. Local extinction risk depends on several factors, including population size, demographic or environmental stochasticity, natural catastrophe, or the loss of genetic diversity. The probability of local extinction may also be higher in low-quality sink habitats than in high-quality source habitats. We tested this hypothesis by comparing local extinction rates of 15 species of Odonata (dragonflies and damselflies) between 1930-1975 and 1995-2003 in central Finland. Local extinction rates were higher in low-quality than in high-quality habitats. Nevertheless, for the thre…
Farmland versus forest: comparing changes in Odonata species composition in western and eastern Sweden
2013
Despite the loss of natural ecosystems in the developed world dur- ing the past millennia, anthropogenic landscapes still sustain much biodiversity. Our question was, whether ten year changes in regional Odonata faunas are comparable between farmland and forested areas, or if the species pool of farm- land areas respond in other ways than that of forest. 2. We used data of dragonfly larvae collected from 16 lakes in a farmland area in south-western Sweden in the years 2002 and 2011/12, and compared these to data from 34 lakes in a forest area in south-eastern Sweden in the years 1996 and 2006. 3. The species-richness in the agricultural region increased by 17% but decreased by 13% in the fo…
Reverse and normal drag along a fault
2005
An analysis of the theoretical displacement field around a single dip-slip fault at depth reveals that normal and reverse fault drag develop by perturbation flow induced by fault slip. We analytically model the heterogeneous part of the instantaneous displacement field of an isolated two-dimensional mode II fault in an infinite, homogeneous elastic body in response to fault slip. Material on both sides of the fault is displaced and ‘opposing circulation cells’ arise on opposite sides of the fault, with displacement magnitudes increasing towards the center of the fault. Both normal and reverse drag can develop at the fault center depending on the angle between the markers and the fault; norm…
Flow resistance in gravel-bed channels with large-scale roughness
2003
A previously published mixing length (ML) model for evaluating the Darcy–Weisbach friction factor for a large-scale roughness condition (depth to sediment height ratio ranging from 1 to 4) is briefly reviewed and modified (MML). Then the MML model and a modified drag (MD) model are experimentally tested using laboratory measurements carried out for gravel-bed channels and large-scale roughness condition. This analysis showed that the MML gives accurate estimates of the Darcy–Weisbach coefficient and for Froude number values greater than 0·5 the MML model coincides with the ML one. Testing of the MD model shows limited accuracy in estimating flow resistance. Finally, the MML and MD models are com…
Hand feeding: a method to increase the survival rate ofOrthetrum coerulescens(Odonata: Libellulidae) in outdoor enclosures
2014
Food intake rate and diet composition have a high impact on all organisms and affect individual fitness, fecundity and mortality. Specimens in enclosures have to be fed in an adequate way and with minimum stress for the specimens. Adult dragonflies are flying hunters. In enclosures, they are usually fed by adding different kinds of adult dipterans. In this study, I additionally fed specimens of Orthetrum coerulescens by hand. Each specimen received one house fly or up to six fruit flies per day. This was less than an adult dragonfly would normally consume; however, this additional hand feeding was enough to significantly increase the survival rate of individuals, especially within the first…