An intercomparison exercise on the capabilities of CFD models to reproduce a large-scale hydrogen deflagration in open atmosphere

Within the HySafe Network of Excellence, several organizations with experience in numerical combustion modeling participated to Standard Benchmark Exercise Problem 2 (SBEP-V2), trying to reproduce numerically the explosion of a stoichiometric hydrogen-air mixture in a 10 m radius balloon. Different codes and models have been applied in the validation exercise. The simulation results and experimental data for the flame speed, the maximum pressures, the rate of pressure rise and the maximum impulse are discussed and compared by means of statistical analysis. An overall satisfactory agreement for the flame speed and maximum pressure is found.     

Friction pressure correlations for turbulent flow of drag reducing polymer solutions in straight and coiled tubing

Accurate determination of friction pressure losses of dilute drag reducing polymer solutions remains to be a challenge in many practical applications. These include a wide variety of hydraulic operations performed on a daily basis in the oil and gas industry. Most drilling, completions, and stimulation jobs require pumping fluids at high flow rates, which in turn generates high frictional pressure losses, enhanced by the use of small diameter tubing or coiled tubing. Curvature in this latter is believed to generate secondary flows and thus extra flow resistance. Therefore, good drag reduction characteristics of fluids are desirable.In this study, energy dissipation by eddies in turbulent flow of viscoelastic fluids is assumed to be the mechanism causing drag reduction. Various concentrations of Nalco ASP-700 and Nalco ASP-820 dilute polymer solutions are tested at ambient temperature in laboratory-scale and full-scale flow loops installed with straight and coiled tubing sections exhibiting different values of diameter, curvature ratio and pipe roughness. In addition, flow tests are conducted at 100 °F and 130 °F using the laboratory-scale flow loop.Effects of concentration, temperature, curvature ratio, and pipe roughness on drag reduction are discussed in light of Fanning friction factor versus solvent Reynolds number plots. Results show that drag reduction in coiled tubing is lower than in straight tubing. As curvature ratio increases, drag reduction decreases. The effect of increasing temperature is to decrease drag reduction in straight tubing and increase it in coiled tubing. In turn, the effect of increasing pipe roughness is to slightly decrease drag reduction in straight tubing up to a certain Reynolds number value and then it starts to increase. For coiled tubing, the effect of increasing pipe roughness is to decrease drag reduction.In this study, generalized correlations for the prediction of drag reduction in dilute polymer solutions flowing in straight and coiled tubing are developed on the basis of the energy dissipation of eddies in turbulent flow field and a shear rate dependent relaxation time. In addition, correlations are validated using experimental data for a low concentration guar fluid flowing through full-scale flow loop.     

Measurement of spectra over the Bolund hill in wind tunnel

We have determined the normal Reynolds stresses and spectra of the wind velocity over a 1:115 scale mock‐up of the Bolund hill. The experiment was run in a neutral boundary layer wind tunnel using 3‐component hot‐wire velocimetry, 2‐component particle image velocimetry, and a high‐precision traversing system. Spectra have been determined at different points along transects at 2 and 5 m height above ground level. The experiment was run for 270° wind direction and for two Reynolds numbers, and , based on the maximum height of the hill and the free wind speed at this height. Our results show how the normalized power spectral density changes over the hill. The analysis of the normalized streamwise spectrum at 2 m height, just after the escarpment, reveals that part of the energy is concentrated in the interval of normalized frequencies n_h≈0.01?0.02, which could be a signature of a weakened “flapping” phenomenon described in the literature for flows over forward facing steps. The departure of the spectra slope in the inertial subrange, from the value ?5/3, was found to be correlated with the hill geometry.     

A fast and efficient contact algorithm for fretting problems applied to fretting modes I,II and III

A computational contact algorithm is presented to solve both the normal and tangential contact problems that describe fretting contacts between two elastic half-spaces. The coupling between the normal and tangential contact problems can or not be taken into account. Nevertheless the coupling should be introduced when materials are dissimilar. Fast and efficient methods are used. The contact solver is based on a conjugate gradient method and acceleration techniques based on the Fast Fourier transforms (FFT) are employed. Very good agreements are found with analytical solutions of three fretting examples representing each fretting mode. However it is shown that these analytical solutions are based on approximations that can be too strong when materials are dissimilar.     

Advances in centerless grinding technology

This paper reviews the history of centerless grinding and its contribution to industry. It summarizes the evolution of centerless grinding theory including advanced modeling and simulation. Then, it discusses the design of main elements of a centerless grinding machine such as spindles, bed, guideways and positioning system, and provides design guidelines for future machines. The paper presents the state-of-the-art centerless grinding technologies: advanced machines, advanced process monitoring and the latest developments in grinding wheels. Finally, in conclusion, future trends and research work in centerless grinding technology are discussed.     

Leydig cell tumor with pseudoprecocious puberty (author's transl)

Authors present a case of a Leydig cell testicular tumor in a boy aged three years with a six-month follow-up. This type of tumor which is usually hormone-producing has in children a virilizing effect giving signs of pseudoprecocious puberty. Hormonal tests before and after surgery are described as well as the histological study. The various possibilities of differential diagnosis, treatment and prognosis in the presence of a unilateral testis enlargement in a boy are commented.     

Nets and filters in intuitionistic fuzzy topological spaces

The basic concept of intuitionistic fuzzy point has been defined by Çoker and Demirci. Also, Çoker constructed the fundamental theory on intuitionistic fuzzy topological spaces. In this paper, we define the notions of net and filter in the intuitionistic fuzzy sense, and obtain some results on convergence, in particular we establish the correspondence between net convergence and filter convergence in the intuitionistic fuzzy sense.     

Effect of electrical stunning on meat quality of lamb

The effects of stunning on both initial and up to 2 weeks post mortem storage meat quality of Spanish Manchega breed lamb were studied. Twenty-four lambs were distributed into two groups. The first group (US; n =12) were slaughtered without previous stunning. In the second group (ES; n =12) animals were electrically stunned. Meat quality was assessed by examining pH, colour as L*, a*, b* values, water holding capacity (WHC) and shear force (SF). Stunning did not affect any parameter studied in the first 24 h post mortem. There were increasing differences between groups in pH (P<0.001) from 5 days onwards. In general stunning did not have an effect on WHC, SF and colour parameters. Ageing of meat affected SF in the ES group but not in the US one; however, there were no significant differences between treatments at any of the ageing times.     

Holographic characteristics of a 1-mm-thick photopolymer to be used in holographic memories

Poly(vinyl alcohol-acrylamide) photopolymers are materials of interest in the field of digital information storage (holographic memories). We analyzed the behavior of a 1-mm-thick photopolymer. Using a standard holographic setup, we recorded unslanted diffraction gratings. The material has high angular selectivity (0.4 degrees), good sensitivity (88 mJ/cm2), and small losses caused by absorption and scattering of light. It also has a high maximum diffraction efficiency (70%). A significant induction period was seen in the material. The authors hypothesize that, during most of this induction period, polymerization does in fact take place but is not reflected in the appearance of the diffracted light until a certain threshold value of exposure is reached.     

Association between conscious knowledge and performance in normal subjects: Reply to Cohen and Curran (1993) and Willingham, Greeley, and Bardone (1993).

Several studies (e.g., M. J. Nissen & P. Bullemer, 1987) have claimed that reaction times (RTs) to a repeating sequence may improve although Ss are not aware of the repeating sequence. P. Perruchet and M. A. Amorim (see record 1992-37919-001) pointed out that the measure of awareness involved in these studies was inadequate (e.g., Ss were not even explicitly asked to retrieve the repeating sequence), and they showed that the dissociation in normal Ss no longer held when awareness was assessed by recall or recognition tests. In this reply, it is shown that A. Cohen and T. Curran's (1993) criticisms of the validity of Perruchet and Amorim's tests and of the theoretical implications of their results are either without foundation or unfalsifiable. Further, it is shown that the new experiment by D. B. Willingham et al (1993) does not demonstrate dissociation. Both comments further illustrate the widespread uncritical acceptance of dissociation, which probably originates from, but is not theoretically justified by, evidence available for dissociation in amnesic patients. (PsycINFO Database Record (c) 2010 APA, all rights reserved)