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Numerical Predictions (numerical + prediction)
Selected AbstractsNumerical prediction of the hydrodynamic performance of a centrifugal pump in cavitating flowsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING, Issue 5 2007Jun Li Abstract A computational modelling for the prediction of the hydrodynamic performance of a centrifugal pump in cavitating flows is presented in this paper. The cavitation model is implemented in a viscous Reynolds-averaged Navier,Stokes solver. The cavity interface and shape are determined using an iterative procedure matching the cavity surface to a constant pressure boundary. The pressure distribution, as well as its gradient on the wall, is taken into account in updating the cavity shape iteratively. Numerical validation of the present cavitation model and algorithms is performed on different headform/cylinder bodies for a range of cavitation numbers through comparing with the experimental data. Flow characteristics trends associated with off-design flow and twin cavities in the blade channel are observed using the presented cavitation prediction. The rapid drop in head coefficient at low cavitation number is captured for two different flow coefficients. Local flow field solution illustrates the principle physical mechanisms associated with the onset of breakdown. Copyright © 2006 John Wiley & Sons, Ltd. [source] Numerical prediction of severe convection: comparison with operational forecastsMETEOROLOGICAL APPLICATIONS, Issue 1 2003Milton S. Speer The prediction of severe convection is a major forecasting problem in Australia during the summer months. In particular, severe convection in the Sydney basin frequently produces heavy rain or hail, flash flooding, and destructive winds. Convective activity is a forecasting challenge for the Sydney basin, mainly from October to April. Currently, there is a need for improved numerical model guidance to supplement the official probabilistic convective outlooks, issued by the operational forecasters. In this study we assess the performance of a very high resolution (2 km) numerical weather prediction (NWP) model in terms of how well it performed in providing guidance on heavy rainfall and hail, as well as other mesoscale features such as low level convergence lines. Two cases are described in which the operational forecasts were incorrect on both occasions. Non-severe thunderstorms were predicted on 1 December 2000 but severe convection occurred. Severe convection was predicted on 8 December 2000, but no convection was reported. In contrast, the numerical model performed well, accurately predicting severe convection on 1 December and no convection on 8 December. These results have encouraged a program aimed at providing an enhanced numerical modelling capability to the operational forecasters for the Sydney basin. Copyright © 2003 Royal Meteorological Society [source] Prediction of turbulent flow and heat transfer within rotating U-shaped passagesHEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 6 2006Liu Chuan Kai Abstract Numerical predictions of three-dimensional flow and heat transfer are presented for rotating serpentine passages with and without rib turbulators. The coolant air is pressurized and its operating conditions are selected closely to match actual turbine operating parameters. Two different arrangements of rib turbulators were studied: (1) transverse ribs on the leading and trailing walls and (2) transverse ribs on all four walls. The rib height-to-hydraulic diameter ratio (e/Dh) is 0.143; the rib pitch-to-height ratio (s/e) is 7. Results for the rib-roughened serpentine passages were compared with those of smooth ones calculated in the literature. It was shown that a significant enhancement is achieved by means of rib turbulators in a serpentine passage at a stationary state as well as in a rotating state. In the radially-outward flow passages, the effect of rotation on heat transfer is relatively prominent. The secondary flows induced by the Coriolis forces are most intensive in the channel with four ribbed surfaces. The heat transfer after a 180° sharp turn in the smooth channel is influenced more by the sharp-turn-induced flow than the rib-roughened ones. © 2006 Wiley Periodicals, Inc. Heat Trans Asian Res, 35(6): 410,420, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.20125 [source] Mode I crack propagation in concrete under fatigue: microscopic observations and modellingINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 13 2002A. Toumi Abstract In this study, three-point bending tests were carried out on notched beams to investigate mode I crack propagation in plain concrete under fatigue. The first part of the study focused on microscopic observations of the crack growth features. Microscopic observations were made using the replica method associated with scanning electron microscopy (SEM). Observations of fatigue crack growth both on the surface and inside the specimens are presented as a comparison between the observed crack lengths and those estimated by the compliance calibration method. In the second part, a finite element model of mode I crack propagation under fatigue is presented. According to the cohesive crack concept, a cohesive force distribution on the crack at various loading stages is assumed, according to both the stress-crack opening relation worked out by Hordijk (1991; Thesis, Technische Universiteit) and a new proposed relation with hysteresis loop. Finite element computation is used to evaluate the crack extension in the bending beams. Numerical predictions are discussed in comparison with experimental results. Copyright © 2002 John Wiley & Sons, Ltd. [source] Model study of time-dependent muscle response to pulsed electrical stimulationBIOELECTROMAGNETICS, Issue 5 2010Ravindra P. Joshi Abstract A systems-level model analysis of neuromuscular response to external electrical stimulation is presented. Action potential (AP) generation, dynamics of voltage-based calcium release at the motor endplates controlled by the arrival of APs, and muscle force production are all comprehensively included. Numerical predictions exhibit trends that are qualitatively similar to measurements of muscle response in rats from a burst of cortical stimulation and a nanosecond impulse. Modulation of neural membrane conductances (including possible electroporation) that alters the neural impulse generation frequency is hypothesized as a possible mechanism leading to observed changes in muscle force production. Other possibilities such as calcium release at nerve end endings also exist. It is also proposed that multipulsing strategies and changing the electric field direction by using multielectrode systems would be useful. Bioelectromagnetics 31:361,370, 2010. © 2010 Wiley-Liss, Inc. [source] Fatigue life prediction and failure analysis of a gas turbine disc using the finite-element methodFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 9 2004R. A. CLÁUDIO ABSTRACT A numerical prediction of the life of a gas turbine model disc by means of the finite-element technique is presented and the solution is compared with an experimental rim-spinning test. The finite-element method was used to obtain the K solution for a disc with two types of cracks, both at the notch root of the blade insert and located in the corner and in the centre. A crack aspect ratio of (a/c) = 1 was assumed. The fracture mechanics parameters J -integral and K were used in the assessment, which were computed with linear elastic and elastic,plastic material behaviour. Using a crack propagation program with appropriate fatigue-creep crack growth-rate data, previously obtained in specimens for the nickel-based superalloy IN718 at 600 °C, fatigue life predictions were made. The predicted life results were checked against experimental data obtained in real model discs. The numerical method, based on experimental fatigue data obtained in small laboratory specimens, shows great potential for development, and may be able to reduce the enormous costs involved in the testing of model and full-size components. [source] Adaptive through-thickness integration for accurate springback predictionINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 5 2008I. A. Burchitz Abstract Accurate numerical prediction of springback in sheet metal forming is essential for the automotive industry. Numerous factors influence the accuracy of prediction of this complex phenomenon by using the finite element method. One of them is the numerical integration through the thickness of shell elements. It is known that the traditional numerical schemes are very inefficient in elastic,plastic analysis and even for simple problems they require up to 50 integration points for an accurate springback prediction. An adaptive through-thickness integration strategy can be a good alternative. The main characteristic feature of the strategy is that it defines abscissas and weights depending on the integrand's properties and, thus, can adapt itself to improve the accuracy of integration. A concept of an adaptive through-thickness integration strategy for shell elements is presented in this paper. Its potential is demonstrated using two examples. Calculations of a simple test,bending a beam under tension,show that for a similar set of material and process parameters the adaptive rule with seven integration points performs significantly better than the traditional trapezoidal rule with 50 points. Simulations of an unconstrained cylindrical bending problem demonstrate that the adaptive through-thickness integration strategy for shell elements can guarantee an accurate springback prediction at minimal costs. Copyright © 2007 John Wiley & Sons, Ltd. [source] 3D tangentially injected swirling recirculating flow in a nozzle with a slotted-tube,Effects of groove parametersINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 11 2010Hui-Fen Guo Abstract A numerical prediction for 3D swirling recirculating flow in an air-jet spinning nozzle with a slotted-tube is carried out with the realizable k,, turbulence model. The effects of the groove parameters on the flow and yarn properties are investigated. The simulation results show that some factors, such as reverse flow upstream of the injector, vortex breakdown downstream of the injector, corner recirculation zone (CRZ) behind the step and vortex ring in the groove caused by the groove geometric variation, are significantly related to fluid flow, and consequently to yarn properties. With increasing groove height, the length of the CRZ increases, while the initial vortex ring in the groove decreases and a same direction rotating vortex forms in the bottom of the groove. Similarly, as the groove width increases, the extent of both vortex breakdown in downstream of the injectors and the vortex ring in the groove increases slightly, whereas the CRZ lengths in stream-wise direction decrease. Some factors, such as the negative tangential velocities, the size of the vortex rings in the grooves and the CRZ, are constant for nozzles with different groove lengths. Copyright © 2009 John Wiley & Sons, Ltd. [source] Behaviour modelling of a PEMFC operating on diluted hydrogen feedINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 14 2008M. Minutillo Abstract The polymer electrolyte membrane fuel cell (PEMFC) using reformate gas as fuel is regarded as an attractive solution for the near-term introduction of fuel cells in stationary or mobile power generation market. With respect to hydrogen feeding, the reformate gas fuelling involves additional polarization losses because of the hydrogen dilution and the impurities contained in the gas. In this paper a one-dimensional model has been developed to investigate the behaviour of a PEMFC operating with reformate gas mixture. The model, based on a semi-empirical approach, considers the kinetic reactions in the anode side taking into account the effect of reverse water,gas shift (RWGS) due to the presence of CO2 in the fuel. As it is well known, the exhaust stream from fuel reformers can contain a high carbon dioxide concentration (>20%) that can have a detrimental effect on the fuel cell performance because of the combination of the dilution and the formation of CO by the RWGS reaction. The numerical simulation results have been compared with the experimental data, obtained in the test room of Industrial Engineering Department of Cassino University, and a good match has been observed. The model has been developed by using a simplified approach that, nevertheless, can allow to obtain a good numerical prediction of the fuel cell performance reducing the simulation time and computational efforts. Copyright © 2008 John Wiley & Sons, Ltd. [source] Overall numerical simulation of extrusion blow molding processPOLYMER ENGINEERING & SCIENCE, Issue 8 2000Shin-Ichiro Tanifuji This paper focuses on the overall numerical simulation of the parison formation and inflation process of extrusion blow molding. The competing effects due to swell and drawdown in the parison formation process were analyzed by a Lagrangian Eulerian (LE) finite element method (FEM) using an automatic remeshing technique. The parison extruded through an annular die was modeled as an axisymmetric unsteady nonisothermal flow with free surfaces and its viscoelastic properties were described by a K-BKZ integral constitutive equation. An unsteady die-swell simulation was performed to predict the time course of the extrudate parison shape under the influence of gravity and the parison controller. In addition, an unsteady large deformation analysis of the parison inflation process was also carried out using a three-dimensional membrane FEM for viscoelastic material. The inflation sequence for the parison molded into a complex-shaped mold cavity was analyzed. The numerical results were verified using experimental data from each of the sub-processes. The greatest advantage of the overall simulation is that the variation in the parison dimension caused by the swell and drawdown effect can be incorporated into the inflation analysis, and consequently, the accuracy of the numerical prediction can be enhanced. The overall simulation technique provides a rational means to assist the mold design and the determination of the optimal process conditions. [source] Fibonacci grids: A novel approach to global modellingTHE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 619 2006Richard Swinbank Abstract Recent years have seen a resurgence of interest in a variety of non-standard computational grids for global numerical prediction. The motivation has been to reduce problems associated with the converging meridians and the polar singularities of conventional regular latitude,longitude grids. A further impetus has come from the adoption of massively parallel computers, for which it is necessary to distribute work equitably across the processors; this is more practicable for some non-standard grids. Desirable attributes of a grid for high-order spatial finite differencing are: (i) geometrical regularity; (ii) a homogeneous and approximately isotropic spatial resolution; (iii) a low proportion of the grid points where the numerical procedures require special customization (such as near coordinate singularities or grid edges); (iv) ease of parallelization. One family of grid arrangements which, to our knowledge, has never before been applied to numerical weather prediction, but which appears to offer several technical advantages, are what we shall refer to as ,Fibonacci grids'. These grids possess virtually uniform and isotropic resolution, with an equal area for each grid point. There are only two compact singular regions on a sphere that require customized numerics. We demonstrate the practicality of this type of grid in shallow-water simulations, and discuss the prospects for efficiently using these frameworks in three-dimensional weather prediction or climate models. © Crown copyright, 2006. Royal Meteorological Society [source] Experimental and theoretical simulations of seismic poundings between two adjacent structuresEARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 4 2003K. T. Chau Abstract Shaking table tests have been carried out to investigate the pounding phenomenon between two steel towers of different natural frequencies and damping ratios, subject to different combinations of stand-off distance and seismic excitations. Both harmonic waves and ground motions of the 1940 El Centro earthquake are used as input. Subjected to sinusoidal excitations, poundings between the two towers could appear as either periodic or chaotic. For periodic poundings, impact normally occurs once within each excitation cycle or within every other excitation cycle. A type of periodic group poundings was also observed for the first time (i.e. a group of non-periodic poundings repeating themselves periodically). Chaotic motions develop when the difference of the natural frequency of the two towers become larger. Under sinusoidal excitations, the maximum relative impact velocity always develops at an excitation frequency between the natural frequencies of the two towers. Both analytical and numerical predictions of the relative impact velocity, the maximum stand-off distance, and the excitation frequency range for pounding occurrences were made and found to be comparable with the experimental observations in most of the cases. The stand-off distance attains a maximum when the excitation frequency is close to that of the more flexible tower. Pounding appears to amplify the response of the stiffer structure but suppress that of the more flexible structure; and this agrees qualitatively with previous shaking table tests and theoretical studies. Copyright © 2003 John Wiley & Sons, Ltd. [source] A discrete thermodynamic approach for anisotropic plastic,damage modeling of cohesive-frictional geomaterialsINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 12 2010Q. Z. Zhu Abstract A discrete plastic,damage model is developed for cohesive-frictional geomaterials subjected to compression-dominated stresses. Macroscopic plastic strains of material are physically generated by frictional sliding along weakness planes. The evolution of damage is related to the evolution of weakness planes physically in connection with the propagation of microcracks. A discrete approach is used to account for anisotropic plastic flow and damage evolution, by introducing two stress invariants and one plastic hardening variable for each family of sliding weakness planes. Plastic flow in each family is coupled with damage evolution. The proposed model is applied to typical geomaterials and comparisons between numerical predictions and experimental data are presented. Copyright © 2009 John Wiley & Sons, Ltd. [source] Homogenization-based analysis of anisotropic damage in brittle materials with unilateral effect and interactions between microcracksINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 6 2009Q. Z. Zhu Abstract This paper is devoted to micromechanical modeling of induced anisotropic damage in brittle geomaterials. The formulation of the model is based on a proper homogenization procedure by taking into account unilateral effects and interactions between microcracks. The homogenization procedure is developed in the framework of Eshelby's inclusion solution and Ponte-Castaneda and Willis (J. Mech. Phys. Solids 1995; 43:1919,1951) estimate. The homogenization technique is combined with the thermodynamics framework at microscopic level for the determination of damage evolution law. A rigorous crack opening,closure transition condition is established and an energy-release-rate-based damage criterion is proposed. Computational aspects on the implementation of micromechanical model are also discussed. The proposed model is evaluated by comparing numerical predictions with experimental data for various laboratory tests on concrete. Parametric studies on unilateral effects and influences of microcracks interactions are finally performed and analyzed. Copyright © 2008 John Wiley & Sons, Ltd. [source] Influence of size on the constitutive equations of concrete or rock dowelsINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 15 2008Letícia Fleck Fadel Miguel Abstract The numerical fracture analysis of non-homogeneous rock or concrete dowels subjected to shear and compression is described in detail. The method of analysis allows the consideration of scale and rate effects due to material non-homogeneity and fracture. The proposed approach is verified by comparing numerical predictions with experimental results reported in the literature for a series of small rock samples, since experimental evidence for large bodies is not yet available (2007). Results generated by Monte Carlo simulation using the so-called discrete element method to model the dowels suggest that a simple three parameters law can be used to predict the relationship between tangential stress at the base and lateral distortion. It is observed that the larger the size of the cubes, the smaller both the peak tangential stress and the rupture distortion. Size effects are also evaluated in samples with vertical restraint. The influence of loading rate is likewise numerically assessed for two sample sizes. The effect is compatible with experimental evidence available for concrete using small samples. Copyright © 2008 John Wiley & Sons, Ltd. [source] The influence of the construction process on the deformation behaviour of diaphragm walls in soft clayey groundINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 7 2006R. Schäfer Abstract Conventional numerical predictions of deep excavations normally neglect the construction process of the retaining structure and choose the earth pressure at rest as initial condition at the beginning of the simulation. The presented results of simulation and measurements during the construction process of the Taipei National Enterprise Center show, that such an assumption leads to an underestimation of the horizontal wall deflection, the surface ground settlements as well as the loading of the struts in case of normally to slightly over-consolidated clayey soil deposits. The stepwise installation process of the individual diaphragm wall panels results in a substantial modification of the lateral effective stresses in the adjacent ground. Especially the pouring process of the panel and the fresh concrete pressure causes a partial mobilization of the passive earth pressure and a distinct stress level increase in the upper half of the wall. As a consequence of the increased stresses prior to the pit excavation, up to 15% greater ground and wall movements are predicted. Moreover, the increased stress level due to the installation process of the diaphragm wall leads to substantial higher strut loadings during the excavation of the pit. Copyright © 2006 John Wiley & Sons, Ltd. [source] The modelling of anchors using the material point methodINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 9 2005C. J. Coetzee Abstract The ultimate capacity of anchors is determined using the material point method (MPM). MPM is a so-called meshless method capable of modelling large displacements, deformations and contact between different bodies. A short introduction to MPM is given and the derivation of the discrete governing equations. The analysis of a vertically loaded anchor and one loaded at 45° is presented. The load,displacement curves are compared to that obtained from experiments and the effect of soil stiffness and anchor roughness is investigated. The results of the vertically loaded anchor are also compared to an analytical solution. The displacement of the soil surface above the anchor was measured and compared to the numerical predictions. Convergence with mesh refinement is demonstrated and the effect of mesh size and dilatancy angle on the shear band width and orientation is indicated. The results show that MPM can model anchor pull out successfully. No special interface elements are needed to model the anchor,soil interface and the predicted ultimate capacities were within 10% of the measured values. Copyright © 2005 John Wiley & Sons, Ltd. [source] 1-D numerical modelling of shallow flows with variable horizontal densityINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 11 2010Feifei Zhang Leighton Abstract A1-D numerical model is presented for vertically homogeneous shallow flows with variable horizontal density. The governing equations represent depth-averaged mass and momentum conservation of a liquid,species mixture, and mass conservation of the species in the horizontal direction. Here, the term ,species' refers to material transported with the liquid flow. For example, when the species is taken to be suspended sediment, the model provides an idealized simulation of hyper-concentrated sediment-laden flows. The volumetric species concentration acts as an active scalar, allowing the species dynamics to modify the flow structure. A Godunov-type finite volume scheme is implemented to solve the conservation laws written in a deviatoric, hyperbolic form. The model is verified for variable-density flows, where analytical steady-state solutions are derived. The agreement between the numerical predictions and benchmark test solutions illustrates the ability of the model to capture rapidly varying flow features over uniform and non-uniform bed topography. A parameter study examines the effects of varying the initial density and depth in different regions. Copyright © 2009 John Wiley & Sons, Ltd. [source] Numerical simulation of turbulent flow through series stenosesINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 7 2003T. S. Lee Abstract The flow fields in the neighbourhoods of series vascular stenoses are studied numerically for the Reynolds numbers from 100 to 4000, diameter constriction ratios of 0.2,0.6 and spacing ratios of 1, 2, 3, 4 and ,. In this study, it has been further verified that in the laminar flow region, the numerical predictions by k,, turbulence model matched those by the laminar-flow modelling very well. This suggests that the k,, turbulence model is capable of the prediction of the laminar flow as well as the prediction of the turbulent stenotic flow with good accuracy. The extent of the spreading of the recirculation region from the first stenosis and its effects on the flow field downstream of the second stenosis depend on the stenosis spacing ratio, constriction ratio and the Reynolds number. For c1 = 0.5 with c2 , c1, the peak value of wall vorticity generated by the second stenosis is always less than that generated by the first stenosis. However, the maximum centreline velocity and turbulence intensity at the second stenosis are higher than those at the first stenosis. In contrast, for c1 = 0.5 with c2 = 0.6, the maximum values at the second stenosis are much higher than those at the first stenosis whether for centreline velocity and turbulence intensity or for wall vorticity. The peak values of the wall vorticity and the centreline disturbance intensity both grow up with the Reynolds number increasing. The present study shows that the more stenoses can result in a lower critical Reynolds number that means an earlier occurrence of turbulence for the stenotic flows. Copyright © 2003 John Wiley & Sons, Ltd. [source] Simulation of shockwave propagation with a thermal lattice Boltzmann modelINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 11 2003ShiDe Feng Abstract A two-dimensional 19-velocity (D2Q19) lattice Boltzmann model which satisfies the conservation laws governing the macroscopic and microscopic mass, momentum and energy with local equilibrium distribution order O(u4) rather than the usual O(u3) has been developed. This model is applied to simulate the reflection of shockwaves on the surface of a triangular obstacle. Good qualitative agreement between the numerical predictions and experimental measurements is obtained. As the model contains the higher-order terms in the local equilibrium distribution, it performs much better in terms of numerical accuracy and stability than the earlier 13-velocity models with the local equilibrium distribution accurate only up to the second order in the velocity u. Copyright © 2003 John Wiley & Sons, Ltd. [source] Kinetics of microbubble,solid surface interaction and attachmentAICHE JOURNAL, Issue 4 2003Chun Yang Microbubble,solid surface interaction and attachment under the influence of hydrodynamic and physicochemical forces were studied experimentally and theoretically. An impinging-jet technique was developed to measure bubble-attachment flux onto a flat solid surface in an impinging-jet stagnation flow. A video imaging system enables direct observation of the attachment behavior of hydrogen microbubbles onto two different collector surfaces: hydrophilic untreated glass and hydrophobic methylated glass. Experimental results showed that the attachment flux depends on both hydrodynamic flow and electrolyte concentration. A mass-transfer model developed computes bubble-attachment flux, considering hydrodynamic convection, Brownian diffusion, migration under gravitational buoyancy, and DLVO surface forces (that is, van der Waals and electric double-layer forces). At high flow rates, the numerical predictions for attachment rates onto methylated glass generally agreed well with the experimental data. However, a difference exists between theoretical and experimentally determined attachment rates for both untreated and methylated glass when the Reynolds number of the flow is low. Several mechanisms are proposed to account for this discrepancy. [source] Investigation of the combustion process in an auxiliary heating system using dual-pump CARSJOURNAL OF RAMAN SPECTROSCOPY, Issue 6 2006A. Braeuer Abstract A dual-pump coherent anti-Stokes Raman spectroscopy (CARS) setup was used for the simultaneous determination of temperature and oxygen/nitrogen ratio in an automotive auxiliary heating system. The auxiliary heating system was equipped with eight windows to provide four line-of-sight optical accesses at two different downstream levels. The usable laser pulse energies, which are essentially limited by the damage threshold of the glass windows, were increased by the application of an optical pulse stretcher. Measurements were performed for standard diesel fuel for full- and part-load operation as well as for the model fuel n -dodecane for full-load operation. The n -dodecane measurements can directly be compared with numerical predictions, whereas the results for diesel fuel provide information about the possibility of transfer of the n -dodecane simulations to real fuel conditions. Copyright © 2006 John Wiley & Sons, Ltd. [source] On a test bench for studying lubrication in a spherical bearing: simulations and experimental validationLUBRICATION SCIENCE, Issue 4 2006N.P. Belfiore In this paper a test bench dedicated to the analysis of a lubricated spherical pair is presented. The experimental set-up has been used to validate a numerical code that has been developed by the authors in order to simulate a complex lubricated spherical pair that affects the reliability of a novel continuous variable transmission (CVT). The test bench is modular and can be adapted to other lubricated pairs, either cylindrical or spherical. The stand is equipped with an I/O control card and allows the on-line acquisition of some important parameters. As for the numerical code, the finite-difference method has been used to solve the indirect problem in the lubricated spherical pad, under the condition of hydrodynamic regime, with externally pressurized inlets. Two simulators are needed since the physical properties of the test bench and the real system are different. The one that simulates the behavior of the spherical pair in the test stand has been used to ascertain the numeric approach prediction capability. Indeed, the experimental tests gave results which are in very good correspondence with the numerical predictions. Hence, the second simulator, which has been tailored on the particular spherical pair the CVT is equipped with, gained reliability in predicting the behavior of the real system under different load and speed conditions. These predictions have been useful in achieving new insights into the novel CVT, which, under this new light, has been criticized by making the point that its range of application in automotive is, at the actual state of the art, rather limited, in spite of a high intrinsic complexity. Copyright © 2006 John Wiley & Sons, Ltd. [source] From linear to non-linear scales: analytical and numerical predictions for weak-lensing convergenceMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2004Andrew J. Barber ABSTRACT Weak-lensing convergence can be used directly to map and probe the dark-mass distribution in the Universe. Building on earlier studies, we recall how the statistics of the convergence field are related to the statistics of the underlying mass distribution, in particular to the many-body density correlations. We describe two model-independent approximations which provide two simple methods to compute the probability distribution function (pdf) of the convergence. We apply one of these to the case where the density field can be described by a lognormal pdf. Next, we discuss two hierarchical models for the high-order correlations which allow us to perform exact calculations and evaluate the previous approximations in such specific cases. Finally, we apply these methods to a very simple model for the evolution of the density field from linear to highly non-linear scales. Comparisons with the results obtained from numerical simulations, obtained from a number of different realizations, show excellent agreement with our theoretical predictions. We have probed various angular scales in the numerical work and considered sources at 14 different redshifts in each of two different cosmological scenarios, an open cosmology and a flat cosmology with non-zero cosmological constant. Our simulation technique employs computations of the full three-dimensional shear matrices along the line of sight from the source redshift to the observer and is complementary to more popular ray-tracing algorithms. Our results therefore provide a valuable cross-check for such complementary simulation techniques, as well as for our simple analytical model, from the linear to the highly non-linear regime. [source] Forecasting futures returns in the presence of price limitsTHE JOURNAL OF FUTURES MARKETS, Issue 2 2005Arie Harel In a futures market with a daily price-limit rule, trading occurs only at prices within limits determined by the previous day's settlement price. Price limits are set in dollars but can be expressed as return limits. When the daily return limit is triggered, the true equilibrium futures return (and price) is unobservable. In such a market, investors may suffer from information loss if the return "moves the limit." Assuming normally distributed futures returns with unknown means but known volatilities, we develop a Bayesian forecasting model in the presence of return limits and provide some numerical predictions. Our innovation is the derivation of the predictive density for futures returns in the presence of return limits. © 2005 Wiley Periodicals, Inc. Jrl Fut Mark 25:199,210, 2005 [source] | ||||||||||||||||||||||||||||||||||