29 research outputs found
Using TurbSim stochastic simulator to improve accuracy of computational modelling of wind in the built environment
Small wind turbines are often sited in more complex environments than in open terrain. These sites include locations near buildings, trees and other obstacles, and in such situations, the wind is normally highly three-dimensional, turbulent, unstable and weak. There is a need to understand the turbulent flow conditions for a small wind turbine in the built environment. This knowledge is crucial for input into the design process of a small wind turbine to accurately predict blade fatigue loads and lifetime and to ensure that it operates safely with a performance that is optimized for the environment. Computational fluid dynamics is a useful method to provide predictions of local wind flow patterns and to investigate turbulent flow conditions at small wind turbine sites, in a manner that requires less time and investment than actual measurements. This article presents the results of combining a computational fluid dynamics package (ANSYS CFX software) with a stochastic simulator (TurbSim) as an approach to investigate the turbulent flow conditions on the rooftop of a building where small wind turbines are sited. The findings of this article suggest that the combination of a computational fluid dynamics package with the TurbSim stochastic simulator is a promising tool to assess turbulent flow conditions for small wind turbines on the roof of buildings. In particular, in the prevailing wind direction, the results show a significant gain in accuracy in using TurbSim to generate wind speed and turbulence kinetic energy profiles for the inlet of the computational fluid dynamics domain rather than using a logarithmic wind-speed profile and a pre-set value of turbulence intensity in the computational fluid dynamics code. The results also show that small wind turbine installers should erect turbines in the middle of the roof of the building and avoid the edges of the roof as well as areas on the roof close to the windward and leeward walls of the building in the prevailing wind direction
Effect of temperature on impact properties of hybrid fiberglass/Kevlar laminate composites
This paper demonstrates results of an experimental study on Kevlar/fiberglass composite laminates subjected to impact loading at variable temperatures. The effect of temperature on maximum energy, maximum impact force, and compression after impact was studied at several low velocity impact energy levels (8J, 15J, 25J). The temperatures considered were in the range of -50C to 120C. Results indicated that impact performance of these composites was affected over the range of temperature considered. Testing at ambient temperature is not fully sufficient and therefore additional testing must be performed for full understanding of composite laminate properties
The role of temperature on impact properties of Kevlar/fiberglass composite laminates
This paper demonstrates results of an experimental study on Kevlar/fiberglass composite laminates subjected to impact loading at variable temperatures. The effect of temperature on maximum energy, elastic energy, maximum deflection, maximum impact force, ductility, and compression after impact was studied at several low velocity impact energy levels (8, 15 and 25 J). The temperatures considered were in the range of -50 to 120°C. Results indicated that impact performance of these composites was affected over the range of temperature considered. Testing at ambient temperature is not fully sufficient and therefore additional testing must be performed for full understanding of composite laminate properties
Cholesterol and bile acids regulate cholesterol 7 alpha-hydroxylase expression at the transcriptional level in culture and in transgenic mice.
Cholesterol 7 alpha-hydroxylase (7 alpha-hydroxylase) is the rate-limiting enzyme in bile acid biosynthesis. It is subject to a feedback control, whereby high levels of bile acids suppress its activity, and cholesterol exerts a positive control. It has been suggested that posttranscriptional control plays a major part in that regulation. We have studied the mechanisms by which cholesterol and bile acids regulate expression of the 7 alpha-hydroxylase gene and found it to be solely at the transcriptional level by using two different approaches. First, using a tissue culture system, we localized a liver-specific enhancer located 7 kb upstream of the transcriptional initiation site. We also showed that low-density lipoprotein mediates transcriptional activation of chimeric genes, containing either the 7 alpha-hydroxylase or the albumin enhancer in front of the 7 alpha-hydroxylase proximal promoter, to the same extent as the in vivo cholesterol-mediated regulation of 7 alpha-hydroxylase mRNA. In a second approach, using transgenic mice, we have found that expression of an albumin enhancer-7 alpha-hydroxylase-lacZ fusion gene is restricted to the liver and is regulated by cholesterol and bile acids in a manner quantitatively similar to that of the endogenous gene. We also found, that a liver-specific enhancer is necessary for expression of the rat 7 alpha-hydroxylase gene, in agreement with the tissue culture experiments. Together, these results demonstrate that cholesterol and bile acids regulate the expression of the 7 alpha-hydroxylase gene solely at the transcriptional level
Visualization and Experimental Characterization of Wrapping Layer Using Planar Laser-Induced Fluorescence
Droplets on nanotextured oil-impregnated surfaces have
high mobility
due to record-low contact angle hysteresis (∼1–3°),
attributed to the absence of solid–liquid contact. Past studies
have utilized the ultralow droplet adhesion on these surfaces to improve
condensation, reduce hydrodynamic drag, and inhibit biofouling. Despite
their promising utility, oil-impregnated surfaces are not fully embraced
by industry because of the concern for lubricant depletion, the source
of which has not been adequately studied. Here, we use planar laser-induced
fluorescence (PLIF) to not only visualize the oil layer encapsulating
the droplet (aka wrapping layer) but also measure its thickness since
the wrapping layer contributes to lubricant depletion. Our PLIF visualization
and experiments show that (a) due to the imbalance of interfacial
forces at the three-phase contact line, silicone oil forms a wrapping
layer on the outer surface of water droplets, (b) the thickness of
the wrapping layer is nonuniform both in space and time, and (c) the
time-average thickness of the wrapping layer is ∼50 ±
10 nm, a result that compares favorably with our scaling analysis
(∼50 nm), which balances the curvature-induced capillary force
with the intermolecular van der Waals forces. Our experiments show
that, unlike silicone oil, mineral oil does not form a wrapping layer,
an observation that can be exploited to mitigate oil depletion of
nanotextured oil-impregnated surfaces. Besides advancing our mechanistic
understanding of the wrapping oil layer dynamics, the insights gained
from this work can be used to quantify the lubricant depletion rate
by pendant droplets in dropwise condensation and water harvesting