Numerical

Distribution by Scientific Domains
Distribution within Engineering

Kinds of Numerical

  • several numerical

  • Terms modified by Numerical

  • numerical aberration
  • numerical abundance
  • numerical accuracy
  • numerical algorithm
  • numerical algorithms
  • numerical analysis
  • numerical analysis method
  • numerical aperture
  • numerical application
  • numerical approach
  • numerical approximation
  • numerical aspect
  • numerical calculation
  • numerical change
  • numerical chromosomal abnormality
  • numerical code
  • numerical comparison
  • numerical computation
  • numerical data
  • numerical density
  • numerical determination
  • numerical difficulty
  • numerical diffusion
  • numerical discretization
  • numerical dispersion
  • numerical dissipation
  • numerical effects
  • numerical efficiency
  • numerical error
  • numerical estimate
  • numerical estimation
  • numerical evaluation
  • numerical evidence
  • numerical example
  • numerical experiment
  • numerical experimentation
  • numerical flexibility
  • numerical flux
  • numerical illustration
  • numerical implementation
  • numerical instability
  • numerical integration
  • numerical integration procedure
  • numerical integration scheme
  • numerical inversion
  • numerical investigation
  • numerical magnitude
  • numerical method
  • numerical methodology
  • numerical methods
  • numerical model
  • numerical model simulation
  • numerical modeling
  • numerical modelling
  • numerical models
  • numerical optimization
  • numerical parameter
  • numerical performance
  • numerical point
  • numerical prediction
  • numerical problem
  • numerical procedure
  • numerical quadrature
  • numerical rating
  • numerical rating scale
  • numerical representation
  • numerical resolution
  • numerical response
  • numerical result
  • numerical results.
  • numerical scale
  • numerical scheme
  • numerical score
  • numerical simulation
  • numerical simulation model
  • numerical simulation result
  • numerical simulation study
  • numerical solution
  • numerical stability
  • numerical strategy
  • numerical studies
  • numerical study
  • numerical system
  • numerical taxonomy
  • numerical technique
  • numerical techniques
  • numerical test
  • numerical test case
  • numerical tool
  • numerical treatment
  • numerical validation
  • numerical value
  • numerical verification
  • numerical weather prediction
  • numerical weather prediction model
  • numerical weather prediction models
  • numerical work

  • Selected Abstracts


    Output-only structural identification in time domain: Numerical and experimental studies

    EARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 4 2008
    M. J. Perry
    Abstract By identifying changes in stiffness parameters, structural damage can be detected and monitored. Although considerable progress has been made in this research area, many challenges remain in achieving robust structural identification based on incomplete and noisy measurement signals. The identification task is made even more difficult if measurement of input force is to be eliminated. To this end, an output-only structural identification strategy is proposed to identify unknown stiffness and damping parameters. A non-classical approach based on genetic algorithms (GAs) is adopted. The proposed strategy makes use of the recently developed GA-based method of search space reduction, which has shown to be able to accurately and reliably identify structural parameters from measured input and output signals. By modifying the numerical integration scheme, input can be computed as the parameter identification task is in progress, thereby eliminating the need to measure forces. Numerical and experimental results demonstrate the power of the strategy in accurate and efficient identification of structural parameters and damage using only incomplete acceleration measurements. Copyright 2007 John Wiley & Sons, Ltd. [source]


    Numerical and dietary responses of a predator community in a temperate zone of Europe

    ECOGRAPHY, Issue 2 2009
    Gilles Dupuy
    The generalist predation hypothesis predicts that the functional responses of generalist predator species should be quicker than those of specialist predators and have a regulating effect on vole populations. New interpretations of their role in temperate ecosystems have, however, reactivated a debate suggesting generalist predators may have a destabilizing effect under certain conditions (e.g. landscape homogeneity, low prey diversity, temporary dominance of 1 prey species associated with a high degree of dietary specialization). We studied a rich predator community dominated by generalist carnivores (Martes spp., Vulpes vulpes, Felis catus) over a 6 yr period in farmland and woodland in France. The most frequent prey were small rodents (mostly Microtus arvalis, a grassland species, and Apodemus spp., a woodland species). Alternative prey were diverse and dominated by lagomorphs (Oryctolagus cuniculus, Lepus europeus). We detected a numerical response among specialist carnivores but not among generalist predators. The dietary responses of generalist predators were fairly complex and most often dependent on variation in density of at least 1 prey species. These results support the generalist predation hypothesis. We document a switch to alternative prey, an increase of diet diversity, and a decrease of diet overlap between small and medium-sized generalists during the low density phase of M. arvalis. In this ecosystem, the high density phases of small mammal species are synchronous and cause a temporary specializing of several generalist predator species. This rapid functional response may indicate the predominant role of generalists in low amplitude population cycles of voles observed in some temperate areas. [source]


    Stochastic approach for output SINR computation at SC diversity systems with correlated Nakagami- m fading

    EUROPEAN TRANSACTIONS ON TELECOMMUNICATIONS, Issue 5 2009
    Daniela M. Milovi
    In this paper, we derive the cumulative distribution function of the signal-to-interference,+,,noise ratio (SINR) achieved by the selection combining (SC) diversity receiver operating over correlated Nakagami- m channel in the presence of co-channel interference. Numerical and simulation results are presented to show the effects of fading severity and signal and interference imbalance on the system's performance. Copyright 2009 John Wiley & Sons, Ltd. [source]


    The Influence of Magnetic Fields on the Mechanical Behaviour of Granular Materials Used for Foundry Moulding: Numerical and Experimental Analysis,

    ADVANCED ENGINEERING MATERIALS, Issue 8 2006
    P.-M. Geffroy
    Understanding the mechanical behaviour of granular materials is of financial importance in many industries, including the geotechnical [1], pharmaceutical and foundry sectors. In the latter, granular materials are used as mould elements for lost foam (sand) and magnetic moulding (steel shot) processes. This study focuses on optimising mould geometry and magnetic field characteristics (intensity and orientation) to obtain the desired dimensions of the final product. [source]


    The Collapse Response of Sandwich Beams with Aluminium Face Sheets and a Metal Foam Core,

    ADVANCED ENGINEERING MATERIALS, Issue 6 2004
    V.L. Tagarielli
    Abstract Plastic collapse modes of simply supported and clamped sandwich beams have been investigated experimentally and theoretically, for aluminium face sheets and Alporas foam core. The effect of clamped boundary conditions is to induce axial stretching after the initial yield mechanism. Hence, face sheet ductility dictates the level of energy absorption of the beam. Numerical and analytical predictions are validated by the available experimental evidence. [source]


    Numerical and experimental investigation of mixed-mode fracture parameters on silicon nitride using the Brazilian disc test

    FATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 8 2010
    G. LEVESQUE
    ABSTRACT Engineering applications of ceramics can often involve mixed-mode conditions involving both tensile and shear loading. Mixed-mode fracture toughness parameters are evaluated for applicability to ceramics using the Brazilian disc test on silicon nitride. Semi-elliptical centrally located surface flaws are induced on the disc specimens using Vickers indentation and compression loaded to fracture with varying levels of mode mixity. The disc specimens are modelled via 3D finite element analysis and all three modes of stress intensity factors computed along the crack front, at failure load. We present a numerical and experimental investigation of four widely used mixed-mode fracture criteria and conclude that the critical strain energy release rate criterion is simple to implement and effective for silicon nitride under mixed-mode conditions. [source]


    Numerical and experimental investigation of heat and mass transfer in unsaturated porous media with low convective drying intensity

    HEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 5 2008
    Tao Lu
    Abstract The heat and mass transfer in an unsaturated wet cylindrical bed packed with quartz particles was investigated theoretically and experimentally for relatively low convective drying rates. The medium was dried by blowing dry air over the top of the porous bed which was insulated by impermeable, adiabatic material on the bottom and sides. Local thermodynamic equilibrium was assumed in the mathematical model describing the multi-phase flow in the unsaturated porous medium using the energy and mass conservation equations for heat and mass transfer during the drying. The drying model included convection and capillary transport of the moisture, and convection and diffusion of the gas. The wet and dry regions were coupled with a dynamic boundary condition at the evaporation front. The numerical results indicated that the drying process could be divided into three periods: the initial temperature rise period, the constant drying rate period, and the reduced drying rate period. The numerical results agreed well with the experimental data, verifying that the mathematical model can evaluate the drying performance of porous media for low drying rates. 2008 Wiley Periodicals, Inc. Heat Trans Asian Res, 37(5): 290,312, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.20205 [source]


    Combining interface damage and friction in a cohesive-zone model

    INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 5 2006
    Giulio Alfano
    Abstract A new method to combine interface damage and friction in a cohesive-zone model is proposed. Starting from the mesomechanical assumption, typically made in a damage-mechanics approach, whereby a representative elementary area of the interface can be additively decomposed into an undamaged and a fully damaged part, the main idea consists of assuming that friction occurs only on the fully damaged part. The gradual increase of the friction effect is then a natural outcome of the gradual increase of the interface damage from the initial undamaged state to the complete decohesion. Suitable kinematic and static hypotheses are made in order to develop the interface model whereas no special assumptions are required on the damage evolution equations and on the friction law. Here, the Crisfield's interface model is used for the damage evolution and a simple Coulomb friction relationship is adopted. Numerical and analytical results for two types of constitutive problem show the effectiveness of the model to capture all the main features of the combined effect of interface damage and friction. A finite-step interface law has then been derived and implemented in a finite-element code via interface elements. The results of the simulations made for a fibre push-out test and a masonry wall loaded in compression and shear are then presented and compared with available experimental results. They show the effectiveness of the proposed model to predict the failure mechanisms and the overall structural response for the analysed problems. Copyright 2006 John Wiley & Sons, Ltd. [source]


    A new approach to reduce membrane and transverse shear locking for one-point quadrature shell elements: linear formulation

    INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 2 2006
    Rui P. R. Cardoso
    Abstract In the last decade, one-point quadrature shell elements attracted many academic and industrial researchers because of their computational performance, especially if applied for explicit finite element simulations. Nowadays, one-point quadrature finite element technology is not only applied for explicit codes, but also for implicit finite element simulations, essentially because of their efficiency in speed and memory usage as well as accuracy. In this work, one-point quadrature shell elements are combined with the enhanced assumed strain (EAS) method to develop a finite element formulation for shell analysis that is, simultaneously, computationally efficient and more accurate. The EAS method is formulated to alleviate locking pathologies existing in the stabilization matrices of one-point quadrature shell elements. An enhanced membrane field is first constructed based on the quadrilateral area coordinate method, to improve element's accuracy under in-plane loads. The finite element matrices were projected following the work of Wilson et al. (Numerical and Computer Methods in Structural Mechanics, Fenven ST et al. (eds). Academic Press: New York, 1973; 43,57) for the incompatible modes approach, but the present implementation led to more accurate results for distorted meshes because of the area coordinate method for quadrilateral interpolation. The EAS method is also used to include two more displacement vectors in the subspace basis of the mixed interpolation of tensorial components (MITC) formulation, thus increasing the dimension of the null space for the transverse shear strains. These two enhancing vectors are shown to be fundamental for the Morley skew plate example in particular, and in improving the element's transverse shear locking behaviour in general. Copyright 2005 John Wiley & Sons, Ltd. [source]


    Behaviour control of modern composite structures

    INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 14 2004
    Alexander Tesar
    Abstract Numerical and experimental assessment of modern composite structures provided with knowledge-based joints for their behaviour control is treated in the present paper. Special connection strip, joining composite materials, is adopted. The wave approach of the back propagation neural network in micro- and macromechanical modelling is used for the numerical analysis of the problem. Some numerical and experimental results are given in order to demonstrate the efficiency of the control joint suggested. Copyright 2004 John Wiley & Sons, Ltd. [source]


    Feasibility Study of a Thick-Film PZT Resonant Pressure Sensor Made on a PreFired 3D LTCC Structure

    INTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, Issue 1 2009
    Marina Santo Zarnik
    This paper discusses the feasibility of a piezoelectric resonant pressure sensor made of lead,zirconate,titanate (PZT) thick films on a preprocessed 3D low-temperature co-fired ceramic structure with a deformable diaphragm. Numerical and experimental analyses were carried out. Two different thick-film PZT compositions were characterized. Using experimentally evaluated material properties, a finite-element analysis showed the trends and facilitated the decisions in the design phase of the sensor. [source]


    Numerical and analytical calculations of the temperature and flow field in the upwind power plant

    INTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 6 2004
    Henry Pastohr
    Abstract The upwind power plant is an interesting system to generate electrical power from free solar energy. The authors have carried out an analysis to improve the description of the operation mode and efficiency. The pressure drop at the turbine and the mass flow rate have a decisive influence on the efficiency. This can be determined only by coupling of all parts of an upwind power plant. In this study the parts ground, collector, chimney and turbine are modelled together numerically. The basis for all sections is the numerical CFD programme FLUENT. This programme solves the basic equations of the thermal fluid dynamics. Model development and parameter studies particularly arise with this tool. Additional to the calculations using FLUENT a simple model is developed for comparison purposes and parameter studies. The numerical results with FLUENT compare well with the results given by the simple model, therefore, we can use the simple model for parameter studies. The basis for the geometry is the prototype Manzanares. Copyright 2004 John Wiley & Sons, Ltd. [source]


    Reliable memory feedback design for a class of non-linear time-delay systems

    INTERNATIONAL JOURNAL OF ROBUST AND NONLINEAR CONTROL, Issue 1 2004
    Dong Yue
    Abstract This paper is concerned with the robust controller design of uncertain time-delay systems with unknown nonlinearity and actuators failures. New methods for designing stabilizing controllers and reliable controllers are proposed. The stability criteria of the closed-loop system, which are dependent on the magnitudes of the delay and its derivative, are derived in the form of linear matrix inequalities. Numerical and simulation results are provided to demonstrate the effectiveness of the proposed results, as well as the reduction of conservativeness when compared with existing ones. Copyright 2004 John Wiley & Sons, Ltd. [source]


    On the high-density polyethylene extrusion: Numerical, analytical and experimental modeling

    ADVANCES IN POLYMER TECHNOLOGY, Issue 3 2010
    A. G. Mamalis
    Abstract A three-dimensional numerical model was developed to investigate the nonisothermal, non-Newtonian polymer flow through a cone cylindrical die used in the HDPE (high-density polyethylene) extrusion process. The numerical model was based on the computational fluid dynamics code COMSOL 3.4 the finite element method, and it was used to calculate pressure, flow, and temperature distributions in a cone cylindrical die used for industrial-scale extrusion of an HDPE rod. The model also accounted for viscous heating. In addition, pressure and temperature data were derived using an analytical solution. The numerical approach agrees fairly well with the experimental data recorded during the extrusion process of the material. 2010 Wiley Periodicals, Inc. Adv Polym Techn 29:173,184, 2010; View this article online at wileyonlinelibrary. DOI 10.1002/adv.20185 [source]


    An alternative analytical reduction scheme in the time-domain layered finite element reduction recovery method for high-frequency IC design

    MICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 9 2008
    Houle Gan
    Abstract An alternative analytical reduction scheme was proposed in the time-domain layered finite element reduction recovery (LAFE-RR) method for the analysis of high-frequency integrated circuits. This alternative reduction scheme permits the use of general absorbing boundary conditions in the framework of a time-domain LAFE-RR method. In addition, it allows for an application of the LAFE-RR method to circuit problems in which the system matrices in multiple regions need to be reduced separately. Numerical and experimental results are given to demonstrate its validity. 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 2337,2341, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23630 [source]


    A broadband, circular switched parasitic array for portable and vehicular mobile DVB-T applications at the V UHF band

    MICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 7 2008
    Stylianos C. Panagiotou
    Abstract A broadband, circular switched parasitic array with two active elements, suitable for DVB-T applications at the V-UHF band is designed with the aid of a genetic algorithm. Numerical as well as measurements results are presented for a single switch position. Simulation results are also presented for switched-beam array operation, using the measured antenna radiation patterns. 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 1727,1732, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23494 [source]


    Phaseless antenna characterization by prolate function expansion of the aperture field

    MICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 10 2006
    A. Capozzoli
    Abstract To be of actual interest for practical applications, phaseless antenna characterization must be reliable and accurate. This inverse problem suffers from the ill-posedeness, and its solution is very sensitive to the adopted formulation that should be able to incorporate all the available information. An "effective" representation of the unknowns is able to reduce the overall number of parameters to be sought for and therefore to have significant beneficial effects on both accuracy and reliability. This aim is attained by means of a prolate spheroidal wave function expansion of the aperture field, which allows accounting for the finite dimensions of the antenna aperture with the least possible number of parameters. Numerical and experimental results point out the accuracy and reliability of the proposed algorithm, also in comparison with other available methods. 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 2060,2064, 2006; Published online in Wiley Inter-Science (www.interscience.wiley.com). DOI 10.1002/mop.21852 [source]


    Numerical and experimental investigation of the deformational behaviour of plastic containers

    PACKAGING TECHNOLOGY AND SCIENCE, Issue 5 2001
    D. Karalekas
    Abstract A numerical and experimental study was undertaken to investigate the deformational behaviour of a plastic grooved container used to store agrochemical solutions when loaded under columnar crush conditions. Finite element analysis was implemented to calculate stresses and deformations at various critical points of the container. A non-linear elastoplastic analysis was performed, based on the ABAQUS FEM computer program. The results of the stress analysis were coupled with a yield criterion to predict the initiation of plastic deformation. The numerically obtained results are compared to those obtained experimentally. It was found that the numerically calculated strains at predetermined locations of the plastic container were in good agreement with the experimentally measured ones. Copyright 2001 John Wiley & Sons, Ltd. [source]


    Numerical and experimental investigation of shrinkage behavior of precision injection molded articles.

    POLYMER ENGINEERING & SCIENCE, Issue 8 2008

    In the accompanying paper, Part I, presented are the physical modeling and numerical formulation of new lateral motion modelings. In Part II, new models developed in Part I are validated by the successful comparison of calculated residual stress profile with the literature data. The predicted results of the birefringence, residual stress distribution, and shrinkage from new lateral motion modeling are in better agreement with corresponding experimental data than those from the conventional ones. The new model prediction falls between those of two extreme cases corresponding to conventional models. As a result of extensive parametric study of processing conditions, the developed analysis system is found to be capable of successfully predicting the tendency of shrinkage behavior varying with most of processing conditions. In this regard, the new model enables better analysis based design and optimization of precision injection-molded products. POLYM. ENG. SCI., 2008. 2008 Society of Plastics Engineers [source]


    Fixed-point type iterations in numerical simulations for static and dynamic elastoplasticity

    PROCEEDINGS IN APPLIED MATHEMATICS & MECHANICS, Issue 1 2003
    Yury Vetyukov Mag.
    Dynamics of the elastoplastic media is stated in terms of plastic eigenstrains acting upon a background elastic problem with fixed (initial) stiffness. The plastic flow is described by specifically introduced plastic multipliers, which minimizes the number of unknown variables to be determined within the time step. A fixed-point type iteration strategy is suggested for the computation of the plastic multipliers, which has been implemented for the finite element spatial discretization. Numerical experiments show the correctness and the effectiveness of the developed algorithm. [source]


    Influence of Incompressibility on Different Wave Types in Porous Media

    PROCEEDINGS IN APPLIED MATHEMATICS & MECHANICS, Issue 1 2003
    Dobromil Pryl Dipl.-Ing.
    There are three wave types in poroelastic continua, the fast compressional wave, with solid and fluid moving inphase, the shear wave, and the second (slow) compressional wave, which has no equivalent in elastic materials, with solid and fluid moving in opposite directions. The fast compressional wave propagates with infinite speed if both constituents are modelled incompressible. Numerical results of BEM calculations showing the influence of incompressible constituents will be presented as well as elements employing different shape functions for the solid displacements and the pore pressure. [source]


    Extension of the time-dependent dynamical diffraction theory to `optical phonon'-type distortions: application to diffraction from coherent acoustic and optical phonons

    ACTA CRYSTALLOGRAPHICA SECTION A, Issue 1 2003
    Peter Sondhauss
    An extension of the time-dependent Takagi,Taupin theory to `optical phonon'-type distortions is presented. By splitting the susceptibility into the contributions from each atom in a unit cell, modifications to the structure factor as well as lattice parameter are taken into account. The result is a compact, surprisingly simple, equation with a strong formal similarity to the classical Takagi,Taupin equation, with the latter included as a special case. Time dependence is explicitly retained and thus the analysis is applicable to situations where the crystal is modified on time scales comparable with that for the X-rays to traverse an extinction depth. A comparison is made between the influence of coherent acoustic and optical phonons on the diffraction of X-rays. Numerical and perturbative analytical solutions of the generalized Takagi,Taupin equation are presented in the presence of such phonons. [source]


    Charge density and electrostatic potential analyses in paracetamol

    ACTA CRYSTALLOGRAPHICA SECTION B, Issue 3 2009
    Nouzha Bouhmaida
    The electron density of monoclinic paracetamol was derived from high-resolution X-ray diffraction at 100,K. The Hansen,Coppens multipole model was used to refine the experimental electron density. The topologies of the electron density and the electrostatic potential were carefully analyzed. Numerical and analytical procedures were used to derive the charges integrated over the atomic basins. The highest charge magnitude (,1.2,e) was found for the N atom of the paracetamol molecule, which is in agreement with the observed nucleophilic attack occurring in the biological media. The electric field generated by the paracetamol molecule was used to calculate the atomic charges using the divergence theorem. This was simultaneously applied to estimate the total electrostatic force exerted on each atom of the molecule by using the Maxwell stress tensor. The interaction electrostatic energy of dimers of paracetamol in the crystal lattice was also estimated. [source]


    Numerical study of the equilibrium thermodynamics of the Coulomb glass

    ANNALEN DER PHYSIK, Issue 12 2009
    M. Goethe
    We discuss the results of large-scale Monte Carlo simulations of the lattice Coulomb glass model. Using the Exchange Monte Carlo algorithm we are able to equilibrate the system to very low temperature and obtain evidence against the existence of an equilibrium glass transition in three dimensions (3D). We also discuss results for the 3D Random Field Ising model that highlight the role of the interaction range. Finally, we report results for the 2D Coulomb glass, which show a behaviour very similar to the 3D case. [source]


    Improving calibration without training: the role of task information

    APPLIED COGNITIVE PSYCHOLOGY, Issue 4 2003
    Tim Rakow
    Medical students estimated probabilities that medical school applicants selected randomly from a defined population would be offered a place on the basis of information about eight characteristics of each one. Estimates were biased in favour of acceptance and this was unaffected by mere provision of base rate information. However, a first experiment showed that provision of this information reduced miscalibration after each candidate had been discussed within small groups of participants. A second experiment showed beneficial effects of providing people with the range of probability responses derived from a statistical model of how candidates' characteristics influenced whether or not they were offered a place. Numerical and graphical representations of this information both improved calibration but did so by having different effects on the distribution of participants' probability responses. Copyright 2003 John Wiley & Sons, Ltd. [source]


    Numerical and Experimental Analysis of an Axial Flow Left Ventricular Assist Device: The Influence of the Diffuser on Overall Pump Performance

    ARTIFICIAL ORGANS, Issue 7 2005
    Alexandrina Untaroiu
    Abstract:, Thousands of adult cardiac failure patients may benefit from the availability of an effective, long-term ventricular assist device (VAD). We have developed a fully implantable, axial flow VAD (LEV-VAD) with a magnetically levitated impeller as a viable option for these patients. This pump's streamlined and unobstructed blood flow path provides its unique design and facilitates continuous washing of all surfaces contacting blood. One internal fluid contacting region, the diffuser, is extremely important to the pump's ability to produce adequate pressure but is challenging to manufacture, depending on the complex blade geometries. This study examines the influence of the diffuser on the overall LEV-VAD performance. A combination of theoretical analyses, computational fluid (CFD) simulations, and experimental testing was performed for three different diffuser models: six-bladed, three-bladed, and no-blade configuration. The diffuser configurations were computationally and experimentally investigated for flow rates of 2,10 L/min at rotational speeds of 5000,8000 rpm. For these operating conditions, CFD simulations predicted the LEV-VAD to deliver physiologic pressures with hydraulic efficiencies of 15,32%. These numerical performance results generally agreed within 10% of the experimental measurements over the entire range of rotational speeds tested. Maximum scalar stress levels were estimated to be 450 Pa for 6 L/min at 8000 rpm along the blade tip surface of the impeller. Streakline analysis demonstrated maximum fluid residence times of 200 ms with a majority of particles exiting the pump in 80 ms. Axial fluid forces remained well within counter force generation capabilities of the magnetic suspension design. The no-bladed configuration generated an unacceptable hydraulic performance. The six-diffuser-blade model produced a flow rate of 6 L/min against 100 mm Hg for 6000 rpm rotational speed, while the three-diffuser-blade model produced the same flow rate and pressure rise for a rotational speed of 6500 rpm. The three-bladed diffuser configuration was selected over the six-bladed, requiring only an incremental adjustment in revolution per minute to compensate for and ease manufacturing constraints. The acceptable results of the computational simulations and experimental testing encourage final prototype manufacturing for acute and chronic animal studies. [source]


    Extension of a combined analytical/numerical initial value problem solver for unsteady periodic flow

    INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 9 2002
    Lawrence J. De Chant
    Abstract Here we describe analytical and numerical modifications that extend the Differential Reduced Ejector/ mixer Analysis (DREA), a combined analytical/numerical, multiple species ejector/mixing code developed for preliminary design applications, to apply to periodic unsteady flow. An unsteady periodic flow modelling capability opens a range of pertinent simulation problems including pulse detonation engines (PDE), internal combustion engine ICE applications, mixing enhancement and more fundamental fluid dynamic unsteadiness, e.g. fan instability/vortex shedding problems. Although mapping between steady and periodic forms for a scalar equation is a classical problem in applied mathematics, we will show that extension to systems of equations and, moreover, problems with complex initial conditions are more challenging. Additionally, the inherent large gradient initial condition singularities that are characteristic of mixing flows and that have greatly influenced the DREA code formulation, place considerable limitations on the use of numerical solution methods. Fortunately, using the combined analytical,numerical form of the DREA formulation, a successful formulation is developed and described. Comparison of this method with experimental measurements for jet flows with excitation shows reasonable agreement with the simulation. Other flow fields are presented to demonstrate the capabilities of the model. As such, we demonstrate that unsteady periodic effects can be included within the simple, efficient, coarse grid DREA implementation that has been the original intent of the DREA development effort, namely, to provide a viable tool where more complex and expensive models are inappropriate. Copyright 2002 John Wiley & Sons, Ltd. [source]


    A MATLAB toolbox for solving acid-base chemistry problems in environmental engineering applications

    COMPUTER APPLICATIONS IN ENGINEERING EDUCATION, Issue 4 2005
    Chetan T. Goudar
    Abstract A MATLAB toolbox incorporating several computer programs has been developed in an attempt to automate laborious calculations in acid-base chemistry. Such calculations are routinely used in several environmental engineering applications including the design of wastewater treatment systems and for predicting contaminant fate and transport in the subsurface. The computer programs presented in this study do not replace student thinking involved in formulating the problem solving strategy but are merely tools that simplify the actual problem solving process. They encompass a wide variety of acid-base chemistry topics including equilibrium constant calculations, construction of distribution diagrams for mono and multiprotic systems, ionic strength and activity coefficient calculations, and buffer index calculations. All programs are characterized by an intuitive graphical user interface where the user supplies input information. Program outputs are either numerical or graphical depending upon the nature of the problem. The application of this approach to solving actual acid-base chemistry problems is illustrated by computing the pH and equilibrium composition of a 0.1 M Na2CO3 system at 30C using several programs in the toolbox. As these programs simplify lengthy computations such as ionization fraction and activity coefficient calculations, it is hoped they will help bring more complicated problems to the environmental engineering classroom and enhance student understanding of important concepts that are applicable to real-world systems. The programs are available free of charge for academic use from the authors. 2005 Wiley Periodicals, Inc. Comput Appl Eng Educ 13: 257,265, 2005; Published online in Wiley InterScience (www.interscience.wiley.com); DOI 10.1002/cae.20051 [source]


    Meltwater discharge through the subglacial bed and its land-forming consequences from numerical experiments in the Polish lowland during the last glaciation

    EARTH SURFACE PROCESSES AND LANDFORMS, Issue 4 2009
    Jan A. Piotrowski
    Abstract Numerical experiments suggest that the last glaciation severely affected the upper lithosphere groundwater system in NW Poland: primarily its flow pattern, velocities and fluxes. We have simulated subglacial groundwater flow in two and three spatial dimensions using finite difference codes for steady-state and transient conditions. The results show how profoundly the ice sheet modifies groundwater pressure heads beneath and some distance beyond the ice margin. All model runs show water discharge at the ice forefield driven by ice-sheet-thickness-modulated, down-ice-decreasing hydraulic heads. In relation to non-glacial times, the transient 3D model shows significant changes in the groundwater flow directions in a regionally extensive aquifer ca. 90 m below the ice,bed interface and up to 40 km in front of the glacier. Comparison with empirical data suggests that, depending on the model run, only between 5 and 24% of the meltwater formed at the ice sole drained through the bed as groundwater. This is consistent with field observations documenting abundant occurrence of tunnel valleys, indicating that the remaining portion of basal meltwater was evacuated through a channelized subglacial drainage system. Groundwater flow simulation suggests that in areas of very low hydraulic conductivity and adverse subglacial slopes water ponding at the ice sole was likely. In these areas the relief shows distinct palaeo-ice lobes, indicating fast ice flow, possibly triggered by the undrained water at the ice,bed interface. Owing to the abundance of low-permeability strata in the bed, the simulated groundwater flow depth is less than ca. 200 m. Copyright 2009 John Wiley & Sons, Ltd. [source]


    Network-scale dynamics of grain-size sorting: implications for downstream fining, stream-profile concavity, and drainage basin morphology

    EARTH SURFACE PROCESSES AND LANDFORMS, Issue 4 2004
    Nicole M. Gasparini
    Abstract We explore the link between channel-bed texture and river basin concavity in equilibrium catchments using a numerical landscape evolution model. Theory from homogeneous sediment transport predicts that river basin concavity directly increases with bed sediment size. If the effective grain size on a river bed governs its concavity, then natural phenomena such as grain-size sorting and channel armouring should be linked to concavity. We examine this hypothesis by allowing the bed sediment texture to evolve in a transport-limited regime using a two grain-size mixture of sand and gravel. Downstream ,ning through selective particle erosion is produced in equilibrium. As the channel-bed texture adjusts downstream so does the local slope. Our model predicts that it is not the texture of the original sediment mixture that governs basin concavity. Rather, concavity is linked to the texture of the sorted surface layer. Two different textural regimes are produced in the experiments: a transitional regime where the mobility of sand and gravel changes with channel-bed texture, and a sand-dominated region where the mobility of sand and gravel is constant. The concavity of these regions varies depending on the median gravel- or sand-grain size, erosion rate, and precipitation rate. The results highlight the importance of adjustments in both surface texture and slope in natural rivers in response to changes in ,uvial and sediment inputs throughout a drainage network. This adjustment can only be captured numerically using multiple grain sizes or empirical downstream ,ning rules. Copyright 2004 John Wiley & Sons, Ltd. [source]