An experimental study of tip shape effects on the flutter of aft-swept, flat-plate wings

The effects of tip chord orientation on wing flutter are investigated experimentally using six cantilever-mounted, flat-plate wing models. Experimentally determined flutter characteristics of the six models are presented covering both the subsonic and transonic Mach number ranges. While all models have a 60 degree leading edge sweep, a 40.97 degree trailing edge sweep, and a root chord of 34.75 inches, they are subdivided into two series characterized by a higher aspect ratio and a lower aspect ratio. Each series is made up of three models with tip chord orientations which are parallel to the free-stream flow, perpendicular to the model mid-chord line, and perpendicular to the free-stream flow. Although planform characteristics within each series of models are held constant, structural characteristics such as mode shapes and natural frequencies are allowed to vary

Acute effects of Hibiscus sabdariffa calyces on postprandial blood pressure, vascular function, blood lipids, biomarkers of insulin resistance and inflammation in humans

The acute impact of Hibiscus sabdariffa calyces (HSC) extract on postprandial vascular function and other cardiometabolic risk factors have not been studied previously. This study investigated the acute impact of HSC extract consumption on blood pressure (BP), vascular function and other cardiometabolic risk markers. Twenty-five men with 1% to 10% cardiovascular disease (CVD) risk (determined by QRISK 2) were randomised to consume either 250 mL of the aqueous extract of HSC or water with breakfast in a randomised, controlled, single-blinded, 2-meal cross-over study (ClinicalTrials.gov, NTC02165553) with a two weeks washout period between study days. BP was measured at baseline and hourly for 4 h. Flow mediated dilatation (FMD) of the branchial artery was measured at baseline, 2 and 4 h post intervention drink consumption. Acute consumption of aqueous extract of HSC caused a significant increase in % FMD ( < 0.001), a non-significant decrease in systolic BP (SBP) and diastolic BP (DBP); non-significant increase in urinary and plasma nitric oxide (NOx) and reduced response of serum glucose, plasma insulin, serum triacylglycerol and C-reactive protein (CRP) levels; significant ( = 0.026) improvement in the area under systemic antioxidant response curve (0 to 2 h); no significant changes in arterial stiffness following the acute consumption of the extract of HSC. Gallic acid, 4-O-methylgallic acid, 3-O-methylgallic acid and hippuric acid reached a maximum plasma concentration at 1 to 2 h post consumption of the extract of HSC. The extract of HSC improved postprandial vascular function and may be a useful dietary strategy to reduce endothelial dysfunction and CVD risk, although this requires confirmation

EVIDENCE OF POSITIONAL DOPING EFFECTS ON THE OPTICAL PROPERTIES OF DOPED TIN DIOXIDE (SnO2) WITH ZINC (Zn)

Films of pure SnO2 were doped with zinc (Zn.SnO2) via chemical spray pyrolysis method. Its deposition on the glass slide with different doping concentration values of 1 wt.%, 2 wt.%, 3 wt.% and 4 wt.% Zn on SnO2. The optical properties were investigated. The average transmittance, reflectance intensity and optical band gap of the Zn doped SnO2, showed that the results gotten were due to the dopant affinity for any sites on the sample structure which defines the properties of the doped samples. This concept explains the strange functionality noticed in some metallic oxides

Experimental Evidence of Quantum Confinement Impairment In The Optical Properties of Annealed Lead Sulphide Thin Film

Recent characterizations of compounds are undoubtedly one of the avenues for the emergence of new semiconducting-light emitting diode (LED) devices. The industrial application of the lead sulphide thin film has been proposed. The lead sulphide thin film was grown by Chemical Bathe Deposition Technique (CBDT) and annealed at four temperatures of 100oC, 150oC, 200oC and 250oC. The samples were analyzed via the 6045 U-V spectrometer. The results shows that PbS thin film has a low transmittance value ranging from 0.204709% to 0.85722%; absorbance value ranging between 3.026% and 3.564%; reflectance value ranging from 81% to 114%; direct band gap was between 1.66eV to 1.78eV. Hence, the calculated refractive index ranges from 1.67 to 1.669. The evidence of quantum confinement impairment in each annealed samples was proofed. This shows that the optical tuning of the lead sulphide is dependent on the thermal control of its constituent's diamete

Transonic shock-induced dynamics of a flexible wing with a thick circular-arc airfoil

Transonic shock boundary layer oscillations occur on rigid models over a small range of Mach numbers on thick circular-arc airfoils. Extensive tests and analyses of this phenomena have been made in the past but essentially all of them were for rigid models. A simple flexible wing model with an 18 pct. circular arc airfoil was constructed and tested in the Langley Transonic Dynamics Tunnel to study the dynamic characteristics that a wing might have under these circumstances. In the region of shock boundary layer oscillations, buffeting of the first bending mode was obtained. This mode was well separated in frequency from the shock boundary layer oscillations. A limit cycle oscillation was also measured in a third bending like mode, involving wind vertical bending and splitter plate motion, which was in the frequency range of the shock boundary layer oscillations. Several model configurations were tested, and a few potential fixes were investigated

Experimental flutter boundaries with unsteady pressure distributions for the NACA 0012 Benchmark Model

The Structural Dynamics Div. at NASA-Langley has started a wind tunnel activity referred to as the Benchmark Models Program. The objective is to acquire test data that will be useful for developing and evaluating aeroelastic type Computational Fluid Dynamics codes currently in use or under development. The progress is described which was achieved in testing the first model in the Benchmark Models Program. Experimental flutter boundaries are presented for a rigid semispan model (NACA 0012 airfoil section) mounted on a flexible mount system. Also, steady and unsteady pressure measurements taken at the flutter condition are presented. The pressure data were acquired over the entire model chord located at the 60 pct. span station

Modeling the Effects of Steel Catenary Riser (SCR) Wall Thickness on Its Structural and Fatigue Performances for Wave-Induced Load

The Steel Catenary Riser (SCR) exhibits significant bending and oscillation owing to undue vessel (which the riser is attached to) movements. The prevalent hydrodynamic loads (wave, current, hydrostatic pressure) are the leading causes of this structural behavior. These initiate a motion - related fatigue phenomenon. This study evaluates the feasibility of increasing the SCR Wall Thickness (WT) for better fatigue performance and structural responses when subjected to the dominant wave spectrum (Ochi Hubble) in deep water West Africa. Relevant data were acquired from an offshore facility in the study area and managed empirically through the use of marine structural analysis software- ORCAFLEX®. Following Det Norske Veritas (DNV, 2010) methodology, 4 SCRs of uniform Internal Diameters (ID) were designated (SCR1, SCR2, SCR3, SCR4), modeled with different WTs (0.0626ft, 0.1876ft, 0.3126ft, 0.4376ft) and analyzed under eight wave load cases. Before the fatigue assessments, the systems were analyzed for static and dynamic responses. Results showed that increasing the WT increases the Fatigue Life (FL) only along each riser arc length - from top to bottom. It was also observed from the systems’ structural response analyses that the effective tension at the Hang off Point (HOP) increases with increase in WT and a compromise in the capacity of the SCRs to flex alongside the hydrodynamic loads due to cumulative rise in the weight of the system. This eventually lowered the FL at the HOP below the DNV’s minimum FL for design purposes – 200 years.Keywords: Steel Catenary Riser, Wall thickness, Fatigue Performance, Ochi-Hubble, Structural response.DOI: 10.7176/ISDE/10-6-03Publication date:July 31st 201