bluuebunny/crossref_metadata_2025_split huggingface dataset:
Enhancement of fixed‐grid methods towards complex fluid–structure interaction applications
Authors: Gerstenberger Axel , Wall Wolfgang A. 
Published: April 2008

AbstractFixed‐grid methods for moving interface problems offer a number of attractive properties and have therefore gained quite some popularity in recent time. However, moving mesh approaches still have their advantages when the physical problem requires special treatment or accurate representation of the interface. This is, for example, the case in complex fluid–structure interaction (FSI) problems when state‐of‐the‐art boundary layer meshing is essential. This paper explores two enhancements of fixed‐grid methods that allow the improved solution of such complex FSI problems. The two enhancements are a straightforward approach based on local adaptivity and a hybrid method that combines ideas from fixed‐grid methods and arbitrary Lagrangean–Eulerian formulations. Although both enhancements could be used with most available fixed‐grid approaches they are given here against the background of a recently developed extended finite element method (XFEM)/Lagrange multiplier (LM) (Comp. Meth. Appl. Mech. Eng. 2007. DOI: 10.1016/j.cma.2007.07.002) fixed‐grid method. It is shown that the hybrid scheme perfectly fits into the presented XFEM/LM framework in a consistent way. Copyright © 2008 John Wiley & Sons, Ltd.
Blood flow dynamics and fluid–structure interaction in patient‐specific bifurcating cerebral aneurysms
Authors: Valencia Alvaro , Ledermann Darren , Rivera Rodrigo , Bravo Eduardo , Galvez Marcelo 
Published: April 2008

AbstractHemodynamics plays an important role in the progression and rupture of cerebral aneurysms. The current work describes the blood flow dynamics and fluid–structure interaction in seven patient‐specific models of bifurcating cerebral aneurysms located in the anterior and posterior circulation regions of the circle of Willis. The models were obtained from 3D rotational angiography image data, and blood flow dynamics and fluid–structure interaction were studied under physiologically representative waveform of inflow. The arterial wall was assumed to be elastic, isotropic and homogeneous. The flow was assumed to be laminar, non‐Newtonian and incompressible. In one case, the effects of different model suppositions and boundary conditions were reported in detail. The fully coupled fluid and structure models were solved with the finite elements package ADINA. The vortex structure, pressure, wall shear stress (WSS), effective stress and displacement of the aneurysm wall showed large variations, depending on the morphology of the artery, aneurysm size and position. The time‐averaged WSS, effective stress and displacement at the aneurysm fundus vary between 0.17 and 4.86 Pa, 4.35 and 170.2 kPa and 0.16 and 0.74 mm, respectively, for the seven patient‐specific models of bifurcating cerebral aneurysms. Copyright © 2008 John Wiley & Sons, Ltd.
Convergence of MPFA on triangulations and for Richards' equation
Authors: Klausen R. A. , Radu F. A. , Eigestad G. T. 
Published: April 2008

AbstractSpatial discretization of transport and transformation processes in porous media requires techniques that handle general geometry, discontinuous coefficients and are locally mass conservative. Multi‐point flux approximation (MPFA) methods are such techniques, and we will here discuss some formulations on triangular grids with further application to the nonlinear Richards equation. The MPFA methods will be rewritten to mixed form to derive stability conditions and error estimates. Several MPFA versions will be shown, and the versions will be discussed with respect to convergence, symmetry and robustness when the grids are rough. It will be shown that the behavior may be quite different for challenging cases of skewness and roughness of the simulation grids. Further, we apply the MPFA discretization approach for the Richards equation and derive new error estimates without extra regularity requirements. The analysis will be accompanied by numerical results for grids that are relevant for practical simulation. Copyright © 2008 John Wiley & Sons, Ltd.
Stabilized finite element methods to predict ventilation efficiency and thermal comfort in buildings
Authors: Lube G. , Knopp T. , Rapin G. , Gritzki R. , Rösler M. 
Published: April 2008

AbstractThe non‐isothermal, incompressible Navier–Stokes equations with Boussinesq approximation are considered as a model of turbulent indoor air flows. The transient calculation is based on the Reynolds‐averaged Navier–Stokes problem using the k/ε‐turbulence model or improved variants such as the $\overline{v^2}-f$ model. The model is first discretized in time using backward‐differencing schemes and then linearized using a Newton‐type method per time step with emphasis on the proper calculation of (non‐negative) turbulence quantities. The resulting auxiliary problems of Oseen type and of advection–diffusion–reaction type are solved using stabilized finite element method of residual type. Here we summarize some of our recent analytical results for higher‐order methods and shock‐capturing techniques. The numerical solution to the model in boundary layer regions is obtained using either adaptive wall functions if the k‐ε model is used or a hybrid mesh with anisotropic refinement if the $\overline{v^2}-f$ model is applied. Besides the standard flow quantities, it is possible to calculate quantities such as the age of the air. Such quantities are used to develop criteria for the evaluation of the efficiency of air exchange in a room. The quality of the numerical simulations is demonstrated for typical benchmark problems. Copyright © 2008 John Wiley & Sons, Ltd.
A vortex axis and vortex core border grid adaptation algorithm
Authors: Rütten Markus , Alrutz Thomas , Wendland Holger 
Published: April 2008

AbstractIn the design process of hydrodynamical and aerodynamical technical applications, the numerical simulation of massively separated vortical flow is crucial for predicting, for example, lift or drag. To obtain reliable numerical results, it is mandatory to accurately predict the physical behavior of vortices. Thus, the dominant vortical flow structures have to be resolved in detail, which requires a local grid refinement and certain adaptation techniques. In this paper, a vortex flow structure adaptation algorithm is presented, which is particularly designed for local grid refinement at vortex axes positions and associated vortex core border locations. To this end, a fast and efficient vortex axis detection scheme is introduced and the algorithm for the vortex core border determination is explained. As the interaction between vortices makes the assignment of grid points to a certain vortex axis difficult, a helicity‐based vortex distinction approach in combination with a geometrical rotational sensor is developed. After describing the combined different techniques in detail, the vortex feature adaptation algorithm is applied to analytical and more realistic examples, which show that the described grid adaptation algorithm is able to enhance the grid cell resolution locally such that all significant vortical flow phenomena are resolved. Copyright © 2008 John Wiley & Sons, Ltd.
Energy norm a posteriori error estimation for divergence‐free discontinuous Galerkin approximations of the Navier–Stokes equations
Authors: Kanschat Guido , Schötzau Dominik 
Published: April 2008

AbstractWe develop the energy norm a posteriori error analysis of exactly divergence‐free discontinuous RTk/Qk Galerkin methods for the incompressible Navier–Stokes equations with small data. We derive upper and local lower bounds for the velocity–pressure error measured in terms of the natural energy norm of the discretization. Numerical examples illustrate the performance of the error estimator within an adaptive refinement strategy. Copyright © 2008 John Wiley & Sons, Ltd.
On the use of anisotropic a posteriori error estimators for the adaptative solution of 3D inviscid compressible flows
Authors: Bourgault Y. , Picasso M. , Alauzet F. , Loseille A. 
Published: April 2008

AbstractThis paper describes the use of an a posteriori error estimator to control anisotropic mesh adaptation for computing inviscid compressible flows. The a posteriori error estimator and the coupling strategy with an anisotropic remesher are first introduced. The mesh adaptation is controlled by a single‐parameter tolerance (TOL) in regions where the solution is regular, whereas a condition on the minimal element size hmin is enforced across solution discontinuities. This hmin condition is justified on the basis of an asymptotic analysis. The efficiency of the approach is tested with a supersonic flow over an aircraft. The evolution of a mesh adaptation/flow solution loop is shown, together with the influence of the parameters TOL and hmin. We verify numerically that the effect of varying hmin is concordant with the conclusions of the asymptotic analysis, giving hints on the selection of hmin with respect to TOL. Finally, we check that the results obtained with the a posteriori error estimator are at least as accurate as those obtained with anisotropic a priori error estimators. All the results presented can be obtained using a standard desktop computer, showing the efficiency of these adaptative methods. Copyright © 2008 John Wiley & Sons, Ltd.
Assessment of algorithms for the no‐slip boundary condition in the lattice Boltzmann equation of BGK model
Authors: Suh Yong Kweon , Kang Jinfen , Kang Sangmo 
Published: April 2008

AbstractThree kinds of algorithms for the lattice Boltzmann equation of the BGK model in the implementation of the no‐slip boundary condition on the wall are assessed by using the analytical formula for the slip velocity of the fully developed pressure‐driven channel flow. It is shown that the bounce‐back algorithm results in the spatial accuracy of 1st order, except for the case when the wall is located at half way between the two grid lines. The interpolation scheme proposed by Yu et al. (Prog. Aerospace Sci. 2003; 39:329–367) and the similar one by Bouzidi et al. (Phys. Fluids 2001; 13(11):3452–3459) are of 2nd order, but the error increases quadratically with the relaxation time. The extrapolation scheme of Guo et al. (Phys. Fluids 2002; 14(6):2007–2010) is also shown to be of 2nd order, and the error level increases linearly with the relaxation time, but it turns out that this scheme is unstable for a certain range of parameter values. Numerical experiments with various parameter sets have been performed to obtain the stability diagram. Three algorithms are then applied to a circular‐Couette flow and their performance is also studied in terms of the numerical accuracy and stability. Copyright © 2008 John Wiley & Sons, Ltd.
Non‐Newtonian flow in branched pipes and artery models
Authors: Barth William L. , Branets Larisa V. , Carey Graham F. 
Published: April 2008

AbstractThis work concerns finite element analysis for a class of generalized Newtonian flows through branching pipe or tube junctions in industrial applications or blood flow through arterial branches, prosthetic tube implants or in biomedical engineering devices. A two‐step morphing transformation is developed and implemented to map a generic coplanar 3D branching flow configuration to general out‐of‐plane deformed geometry including local constriction/dilation ‘defects’ suitable for modeling specific arterial flow and industrial flow applications. Unstructured 3D meshes may be generated in the reference configuration and morphed to the application configuration. The resulting meshes may be tangled and exhibit mesh quality degradation. Algorithms integrating mesh generation, morphing, untangling and cell shape control strategies are presented.Phenomenological studies are conducted with the Powell–Eyring class as a representative model to determine local details of shear‐thinning flow behavior as well as the nature and location of high shear stress regions on artery branch walls. The supporting simulations are carried out using a parallel finite element scheme with domain decomposition by a sectional partitioning that takes advantage of the medial curve shape and specialized ILU preconditioning. Copyright © 2008 John Wiley & Sons, Ltd.
Steady flow through a realistic human upper airway geometry
Authors: Nithiarasu P. , Hassan O. , Morgan K. , Weatherill N. P. , Fielder C. , Whittet H. , Ebden P. , Lewis K. R. 
Published: April 2008

AbstractAir flow through a human upper airway (central part) has been carried out using a realistic geometry. In addition to explaining the anatomy, problems and importance of patient‐specific study of human upper airways, this article also presents some qualitative and quantitative simulation results. As expected, the shear and pressure forces are large in the oropharynx and laryngopharynx, where the flow passage is narrow. This clearly indicates that these locations should be the focus of any study aimed at understanding the human upper airway collapse in a patient‐specific manner. Copyright © 2008 John Wiley & Sons, Ltd.
Stress, social support, and outcomes in two probability samples of homeless adults
Authors: Toro Paul A. , Tulloch Elizabeth , Ouellette Nicole 
Published: April 2008

AbstractThis study investigated the main effects of social support measures and their stress‐buffering effects in two samples of homeless adults (Ns=249 and 219) obtained in the same large county (surrounding Detroit) at different points in time over an 8‐year period (1992–1994 and 2000–2002). The findings suggest that the construct of social support, commonly applied to broad community and student samples, can also be usefully applied to at‐risk groups such as the homeless. Although the study's main effects and stress‐buffering effects were generally consistent with existing research on social support, the findings point out that expected results do not consistently emerge even when similar sampling and measurement techniques are employed. For example, a measure of perceived support showed consistent main and stress‐buffering effects on psychological symptoms (but not other outcomes) and social network measures showed less consistent effects on outcomes (e.g., alcohol and drug abuse symptoms). © 2008 Wiley Periodicals, Inc.
Using discourse analysis and psychological sense of community to understand school transitions
Authors: Fyson Stephen J. 
Published: April 2008

AbstractThe research involved examining the nature of the transition that students experienced in progressing to junior high school from primary school. Students' experiences were chosen as the focus of the research because the issue of substance being investigated was that of alienation. The main methodology that was used was the qualitative procedure of discourse analysis, implemented over a 3‐year period. This report describes the findings from the first year of the study.The key findings of the research include the establishment of critical concerns of students. These critical concerns were articulated as psychological sense of community categories of interest, with positive and negative discourse descriptors being developed according to an analysis of students' descriptions of social regularities. The categories of interest were arranged into a sequential pattern that described pathways to increasing commitment or alienation. © 2008 Wiley Periodicals, Inc.
A commentary on Newbrough's Third Position
Authors: Newbrough J. R. , McMillan David W. , Lorion Raymond P. 
Published: April 2008

AbstractNewbrough's Third Position is discussed in terms of its utility as a framework within which to understand and resolve interpersonal differences, seemingly irresolvable diametric differences, and conflictual situations. The framework's essential elements and its application is illustrated through the presentation of a series of fictitious scenarios that open with conflict and close with a resolution in which the interested parties feel heard and satisfied. The intent of the commentary is to re‐introduce community psychologists to this framework and encourage its consideration, application, and investigation in responding to community‐based conflicts and the resolution of seeming impasses. The Third Position is presented as a valuable tool for the community psychologist involved with conflict resolution, community consultation, and community development. © 2008 Wiley Periodicals, Inc.
Community involvement and adolescent mental health: moderating effects of race/ethnicity and neighborhood disadvantage
Authors: Hull Pamela , Kilbourne Barbara , Reece Michelle , Husaini Baqar 
Published: April 2008

AbstractSocial development and stress process theories suggest that participation in one's community can function as a protective factor for mental health, especially for youth from socioeconomically disadvantaged areas. However, the effects of community involvement on adolescent mental health could vary across racial/ethnic groups and levels of neighborhood disadvantage. The objectives of this paper are to: (1) examine the effects of various types of community involvement on adolescent mental health, and (2) assess the extent to which race/ethnicity and neighborhood disadvantage moderate the effects of community involvement on adolescent mental health. Using data from two waves (1994/95 and 1996) of the National Longitudinal Study of Adolescent Health (“Add Health,” N=7,863), multilevel (hierarchical) linear models were estimated that tested for interaction effects of race/ethnicity and neighborhood disadvantage. The types of community participation that impacted adolescent mental health varied across racial/ethnic groups. Neighborhood interaction and religious participation were salient for both White and Hispanic teens, but the impact of religious participation for Whites was moderated by neighborhood disadvantage. Non‐sport extracurricular activities and employment were the salient factors for Black teens, both of which were moderated by neighborhood disadvantage. The findings from this study have implications for community‐level and clinical interventions to prevent and/or treat mental health problems among adolescents. Social integration interventions should take into account adolescents' cultural backgrounds and socioeconomic contexts in order to be effective. © 2008 Wiley Periodicals, Inc.
Eucalyptus globulus kraft process modifications: Effect on pulping and bleaching performance and papermaking properties of bleached pulps
Authors: Santiago AS , Neto C Pascoal 
Published: April 2008

AbstractBACKGROUND: Increasing the yield of the wood pulping process allows the reduction of specific wood costs. Process modifications with a great impact on pulp yield are the profiling of chemical charges and addition of anthraquinone (AQ). The aim of the present work is to investigate the influence of effective alkali (EA) profiling and addition of anthraquinone on E. globulus kraft pulping performance. The impact of such process modifications on the ECF bleaching process and on the papermaking properties of the resulting bleached pulps is also evaluated.RESULTS: An EA profiling cook may lead to a pulp yield gain, which is more significant as the total EA charge used in the kraft cook increases. AQ addition to kraft pulping leads to a significant yield increase. The ClO2 charge required to fully bleach the pulps is lower for EA profiling and higher for kraft + AQ unbleached pulps. Bleached AQ pulp presents a high beatability due to high pulp xylan retention.CONCLUSION: A low total EA charge is the key parameter for high polysaccharide retention on pulp. AQ addition constitutes a feasible strategy to increase pulp yield. Bleaching performance and papermaking properties of pulps produced with the three different methods may be affected by the kraft pulping modifications. Copyright © 2008 Society of Chemical Industry
Direct injection LC/ESI‐MS horse urine analysis for the quantification and identification of threshold substances for doping control. I. Determination of hydrocortisone
Authors: Vonaparti A. , Lyris E. , Panderi I. , Koupparis M. , Georgakopoulos C. 
Published: April 2008

AbstractTwo simple and rapid LC/MS methods with direct injection analysis were developed and validated for the quantification and identification of hydrocortisone in equine urine using the same sample preparation but different mass spectrometric systems: ion trap mass spectrometry (IT‐MS) and time‐of‐flight mass spectrometry (TOF‐MS). The main advantage of the proposed methodology is the minimal sample preparation procedure, as particle‐free diluted urine samples were directly injected into both LC/MS systems. Desonide was used as internal standard (IS). The linear range was 0.25–2.5 µg ml−1 for both methods. Matrix effects were evaluated by preparing and analyzing calibration curves in water solutions and different horse urine samples. A great variation of the signal both for hydrocortisone and the internal standard was observed in different matrices. To overcome matrix effects, the unavailability of blank matrix and the excessive cost of the isotopically labeled internal standard, standard additions calibration method was applied. This work is an exploration of the performance of the standard additions approach in a method where neither nonisotopic internal standards nor extensive sample preparation is utilized and no blank matrix is available. The relative standard deviations of intra and interday analysis of hydrocortisone in horse urine were lower than 10.2 and 5.4%, respectively, for the LC/IT‐MS method and lower than 8.4 and 4.4%, respectively, for the LC/TOF‐MS method. Accuracy (bias percentage) was less than 9.7% for both methods. Copyright © 2008 John Wiley & Sons, Ltd.
Effect of lyophilisation, refrigerated storage and frozen storage on the coagulant activity and microbiological quality of Cynara cardunculus L. extracts
Authors: Tejada Luis , Vioque Montserrat , Gómez Rafael , Fernández‐Salguero José 
Published: April 2008

AbstractBACKGROUND:Cheese‐makers have traditionally kept vegetable coagulants refrigerated until use, even though little was known of their microbiological quality or coagulant activity during storage. This study aimed to assess the efficacy of lyophilisation, refrigerated storage and frozen storage of fresh vegetable extract as a means of standardising coagulant activity in terms of coagulation times, pH and microbiological quality.RESULTS:Neither the pH nor the coagulation time of lyophilised extracts was significantly modified during 1 year; however, changes were observed following frozen storage, and more notable following refrigerated storage. Lyophilisation of aqueous extracts prompted the destruction of most micro‐organisms; low counts initially noted for total mesophiles, lactic acid bacteria and yeasts disappeared during the first few days of storage, due to low water activity. There was a generalised decrease in micro‐organism counts during frozen storage. Refrigeration was found to be unsuitable for storing of cardoon extract; an increase of roughly 2 log unit counts was recorded in total mesophile, lactic acid bacteria, yeast and mould counts after 1 year of refrigerated storage.CONCLUSION:Refrigerated storage cannot be considered a suitable method for prolonged conservation of aqueous cardoon extract. Both lyophilisation and frozen storage of aqueous extracts proved ideal for prolonged storage of vegetable coagulant. Lyophilisation additionally had certain advantages over frozen storage. Copyright © 2008 Society of Chemical Industry