On the use of linear-elastic local stresses to design load-carrying fillet-welded steel joints against static loading

This paper uses local linear-elastic stresses to estimate the static strength of steel arc welded joints. The proposed design methodology was developed by taking as a starting point the fundamental concepts on which the Theory of Critical Distances (TCD) is based. The overall accuracy of the devised approach was checked against a number of experimental results taken from the literature and generated by testing a variety of welded geometries. Such a systematic validation exercise demonstrated that the TCD is highly accurate in estimating the static strength of arc welded joints irrespective of the complexity of the assessed welded detail’s geometry

Facile, Efficient Routes to Diverse Protected Thiols and to Their Deprotection and Addition to Create Functional Polymers by Thiol−Ene Coupling

Carbazole, dinitrobenzoate, phenol, pyridine, and 4-cyano-4‘-alkoxybiphenyl side groups were grafted onto pendant vinyl groups of polybutadiene (PB) by thiol−ene addition to yield functional polymer of polydispersity equal to that of the precursor material. Synthesis protocols that are clean (>90% conversion to desired product) and scalable were developed to incorporate a protected thiol group into functional precursors. The resulting acetyl or benzoyl thioesters are suitable for long-term storage, and are conveniently deprotected and added to polymer in a matter of hours in a straightforward procedure that does not require isolation of the thiol intermediate. Alternatively, PB functionalization could be achieved with equal success by reaction with β-mercaptoethanol (BME), and subsequent esterification of the incorporated hydroxyl groups with a suitable acyl halide. The chemistry described can potentially be applied to add any side group onto any polymer, copolymer, or block copolymer displaying pendant vinyl groups

The Mw 6.3, 2009 L’Aquila earthquake: source, path and site effects from spectral analysis of strong motion data

The strong motion data of 2009 April 6 L’Aquila (Central Italy) earthquake (Mw = 6.3) and of 12 aftershocks (4.1 ≤ Mw ≤ 5.6) recorded by 56 stations of the Italian strong motion network are spectrally analysed to estimate the source parameters, the seismic attenuation, and the site amplification effects. The obtained source spectra for S wave have stress drop values ranging from 2.4 to 16.8 MPa, being the stress drop of the main shock equal to 9.2 MPa. The spectral curves describing the attenuation with distance show the presence of shoulders and bumps, mainly around 50 and 150 km, as consequence of significant reflected and refracted arrivals from crustal interfaces. The attenuation in the first 50 km is well described by a quality factor equal to Q( f ) = 59 f 0.56 obtained by fixing the geometrical spreading exponent to 1. Finally, the horizontal-to-vertical spectral ratio provides unreliable estimates of local site effects for those stations showing large amplifications over the vertical component of motion

Internal Passage Heat Transfer Prediction Using Multiblock Grids and a Kappa-Omega Turbulence Model

Numerical simulations of the three-dimensional flow and heat transfer in a rectangular duct with a 180 C bend were performed. Results are presented for Reynolds numbers of 17,000 and 37,000 and for aspect ratios of 0.5 and I.O. A kappa-omega turbulence model with no reference to distance to a wall is used. Direct comparison between single block and multiblock grid calculations are made. Heat transfer and velocity distributions are compared to available literature with good agreement. The multi-block grid system is seen to produce more accurate results compared to a single-block grid with the same number of cells

Effects of Tip Clearance and Casing Recess on Heat Transfer and Stage Efficiency in Axial Turbines

Calculations were performed to assess the effect of the tip leakage flow on the rate of heat transfer to blade, blade tip and casing. The effect on exit angle and efficiency was also examined. Passage geometries with and without casing recess were considered. The geometry and the flow conditions of the GE-E 3 first stage turbine, which represents a modem gas turbine blade were used for the analysis. Clearance heights of 0%, 1%, 1.5% and 3% of the passage height were considered. For the two largest clearance heights considered, different recess depths were studied. There was an increase in the thermal load on all the heat transfer surfaces considered due to enlargement of the clearance gap. Introduction of recessed casing resulted in a drop in the rate of heat transfer on the pressure side but the picture on the suction side was found to be more complex for the smaller tip clearance height considered. For the larger tip clearance height the effect of casing recess was an orderly reduction in the suction side heat transfer as the casing recess height was increased. There was a marked reduction of heat load and peak values on the blade tip upon introduction of casing recess, however only a small reduction was observed on the casing itself. It was reconfirmed that there is a linear relationship between the efficiency and the tip gap height. It was also observed that the recess casing has a small effect on the efficiency but can have a moderating effect on the flow underturning at smaller tip clearances

Simulations of Turbine Cooling Flows Using a Multiblock-Multigrid Scheme

Results from numerical simulations of air flow and heat transfer in a 'branched duct' geometry are presented. The geometry contains features, including pins and a partition, as are found in coolant passages of turbine blades. The simulations were performed using a multi-block structured grid system and a finite volume discretization of the governing equations (the compressible Navier-Stokes equations). The effects of turbulence on the mean flow and heat transfer were modeled using the Baldwin-Lomax turbulence model. The computed results are compared to experimental data. It was found that the extent of some regions of high heat transfer was somewhat under predicted. It is conjectured that the underlying reason is the local nature of the turbulence model which cannot account for upstream influence on the turbulence field. In general, however, the comparison with the experimental data is favorable

A Three-Dimensional Coupled Internal/External Simulation of a Film-Cooled Turbine Vane

A three-dimensional Navier-Stokes simulation has been performed for a realistic film-cooled turbine vane using the LeRC-HT code. The simulation includes the flow regions inside the coolant plena and film cooling holes in addition to the external flow. The vane is the subject of an upcoming NASA Glenn Research Center experiment and has both circular cross-section and shaped film cooling holes. This complex geometry is modeled using a multi-block grid which accurately discretizes the actual vane geometry including shaped holes. The simulation matches operating conditions for the planned experiment and assumes periodicity in the spanwise direction on the scale of one pitch of the film cooling hole pattern. Two computations were performed for different isothermal wall temperatures, allowing independent determination of heat transfer coefficients and film effectiveness values. The results indicate separate localized regions of high heat transfer coefficient values, while the shaped holes provide a reduction in heat flux through both parameters. Hole exit data indicate rather simple skewed profiles for the round holes, but complex profiles for the shaped holes with mass fluxes skewed strongly toward their leading edges

Comparison between empirical predictive equations calibrated at global and national scale and the Italian strong-motion data

In Italy in the last years many ground motion prediction equations (hereinafter GMPEs) were calibrated both at national and regional scale using weak and strong motion data recorded in the last 30 years by several networks. Moreover many of the Italian strongest earthquakes were included in global datasets in order to calibrate GMPEs suitable to predict ground-motion at very large scale. In the last decade the Sabetta and Pugliese (1996) relationships represented a reference for the ground motion predictions in Italy. At present all Italian strong-motion data, recorded from 1972 by RAN (Italian Accelerometric Network), and more recently by other regional networks (e.g. RAIS, Strong motion network of Northern Italy), are collected in ITACA (ITalian ACcelerometric Archive). Considering Italian strong-motion data with Mw  4.0 and distance (Joyner-Boore or epicentral) up to 100 km, new GMPEs were developed by Bindi et al. (2009), aimed at replacing the older Italian relationships. The occurrence of the recent 23rd December 2008, Mw 5.4, Parma (Northern Italy) earthquake and the 6th April 2009, Mw 6.3, L’Aquila earthquake, allowed to upgrade the ITACA data set and gave us the possibility to validate the predictive capability of many GMPEs, developed using Italian, European and global data sets. The results are presented in terms of quality of performance (fit between recorded and predicted values) using the maximum likelihood approach as explained in Spudich et al. (1999). Considering the strong-motion data recorded during the L’Aquila sequence the considered GMPEs, in average, overestimate the observed data, showing a dependence of the residuals with distance in particular at higher frequencies. An improvement of fit is obtained comparing all Italian strong-motion data included in ITACA with the European GMPEs calibrated by Akkar and Bommer (2007 a,b) and the global models calibrated by Cauzzi and Faccioli (2008). In contrast, Italian data seem to attenuate faster than the NGA models calibrated by Boore and Atkinson (2008), in particular at higher frequencies

Ground Motion Prediction Equations Derived from the Italian Strong Motion Database

We present a set of ground motion prediction equations (GMPEs) derived for the geometrical mean of the horizontal components and the vertical, considering the latest release of the strong motion database for Italy. The regressions are performed over the magnitude range 4–6.9 and considering distances up to 200 km. The equations are derived for peak ground acceleration (PGA), peak ground velocity (PGV) and 5%-damped spectral acceleration at periods between 0.04 and 2 s. The total standard deviation (sigma) varies between 0.34 and 0.38 log10 unit, confirming the large variability of ground shaking parameters when regional data sets containing small to moderate magnitude events (M < 6) are used. The between-stations variability provides the largest values for periods shorter than 0.2 s while, for longer periods, the between-events and between-stations distributions of error provide similar contribution to the total variabilit

Role of Diffusion-Weighted MRI (DWI-MRI) in the Diagnosis of Brain Complications caused by Heroin Substance Abuse

Background: Magnetic resonance imaging (MRI) offers higher diagnostic accuracy for brain lesions caused by heroin abuse compared to compute tomography (CT) scan. These lesions have a low signal on T1-weighted (T1W) images and a high signal on T2-weighted (T2W) and fluid-attenuated inversion recovery (FLAIR) images. This study aimed to evaluate the role of diffusion-weighted MRI (DWI-MRI) in heroin addicts.Methods: This cross-sectional study was conducted on 20 patients with heroin addiction (vapor inhalation/injection) referring to Imam Reza Hospital of Mashhad, Iran. Patients in whom heroin abuse was only cause of consciousness, loss and neurological symptoms were enrolled in this study. Demographic data of the patients were recorded, including MRI, FLAIR, T1W and T2W images. In addition, DWI of axial and sagittal sections of the brain was performed in the following sequences.Results: In this study, mean age of patients was 40.15±7.673 years, and 95% of patients were male. The most common mode of heroin use was inhalation, and mean duration of addiction was 5.48±3.393 years. Mean daily intake of heroin was 13.4±15.30 grams, and mean duration of heroin abuse was 10.3 and 4.6 years in patients with and without MRI changes, respectively. A significant correlation was observed between MRI changes and duration of heroin use (r=0.721) (p=0.001). In addition, a significant correlation was observed between MRI changes and daily intake of heroin (p=0.006).Conclusion: According to the results of this study, brain lesions caused by heroin abuse have a low signal on T1W images and a high signal on T2W and FLAIR images. Therefore, it could be concluded that heroin intake has significant effects on the brain of users