Search

The rheological behaviour of dilute soil-water mixtures, such as hyperconcentrated mixtures and interstitial fluids in debris flows, can significantly affect the flow dynamics of flow-type landslides. These mixtures often contain clay, silt, and sandy particles. Despite great efforts, the effects of soil type and texture on the rheological behaviour of these mixtures are still not well understood. To tackle this issue, an experimental investigation is carried out using a narrow-gap rotational viscometer to evaluate the interactions from colloidal (clay) and non-colloidal (silt and sand) particles and possibility of flow regime change. The flow curves of dilute mixtures are determined with and without a dispersion agent. A functional curve between spindle speed and Reynolds Number or Froud Number is proposed to distinguish different flow regimes in the narrow-gap rotational viscometer. Results demonstrate the applicability of the Bingham model for describing the bulk rheological behaviour of dilute mixtures. The mixture viscosity governs the contribution of the hydrodynamic effects from all particles, while the yield stress governs the contribution of the colloidal effects from colloidal particles. Results also reveal that for dilute mixtures containing particles up to medium sand size, the main cause of the flow regime change is the flow boundary conditions. Key words: soil-water mixtures, rheological behaviour, debris flows, viscosity, colloidal particles, dispersion agent, Introduction The study of the rheological behaviour of soil-water mixtures is important as it affects the flow dynamics of flow-type landslides. Dilute mixtures often contain fine particles (clay and silt) [...]

The destructive nature of debris flows is mainly caused by flow bulking from entrainment of an erodible channel bed. To arrest these flows, multiple flexible barriers are commonly installed along the predicted flow path. Despite the importance of an erodible bed, its effects are generally ignored when designing barriers. In this study, three unique experiments were carried out in a 28 m long flume to investigate the impact of a debris flow on both single and dual flexible barriers installed in a channel with a 6 m long erodible soil bed. Initial debris volumes of 2.5 and 6 [m.sup.3] were modelled. For the test setting adopted, a small upstream flexible barrier before the erodible bed separates the flow into several surges via overflow. The smaller surges reduce bed entrainment by 70% and impact force on the terminal barrier by 94% compared to the case without an upstream flexible barrier. However, debris overflowing the deformed flexible upstream barrier induces a centrifugal force that results in a dynamic pressure coefficient that is up to 2.2 times higher than those recommended in guidelines. This suggests that although compact upstream flexible barriers can be effective for controlling bed entrainment, they should be carefully designed to withstand higher impact forces. Key words: landslide, debris flow, flexible barrier, entrainment, flume. La nature destructrice des coulees de debris est principalement causee par le gonflement du debit resultant de l'entrainement d'un lit de canal erodable. Pour arreter ces coulees, de multiples barrieres flexibles sont generalement installees tout au long de la trajectoire prevue des coulees. Malgre l'importance d'un lit erodable, ses effets sont generalement ignores lors de la conception des barrieres. Dans cette etude, trois experiences uniques ont ete realisees dans un canal de 28 m de long pour etudier l'impact d'une coulee de debris sur des barrieres flexibles simples et doubles installees dans un canal avec un lit de sol erodable de 6 m de long. Des volumes initiaux de debris de 2,5 et 6 [m.sup.3] ont ete modelises. Dans le cadre de l'essai adopte, une petite barriere flexible en amont du lit erodable separe l'ecoulement en plusieurs poussees par surverse. Les poussees plus petites reduisent l'entrainement du lit de 70 % et la force d'impact sur la barriere terminale de 94 % par rapport au cas sans barriere flexible en amont. Cependant, les debris qui debordent de la barriere flexible deformee en amont induisent une force centrifuge qui entraine un coefficient de pression dynamique jusqu'a 2,2 fois superieur a ceux recommandes dans les lignes directrices. Cela suggere que, bien que les barrieres flexibles compactes en amont puissent etre efficaces pour controler l'entrainement du lit, elles doivent etre concues avec soin pour resister a des forces d'impact plus elevees. [Traduit par la Redaction] Mots-cles : glissement de terrain, coulee de debris, barriere flexible, entrainement, canal d'ecoulement., 1. Introduction Debris flows may increase in scale by entraining bed material along the flow path (Hungr et al. 2005; Iverson and Ouyang 2015). Entrainment occurs when a debris flow [...]

This study considered numerical applications of smoothed particle hydrodynamics (SPH) to non-Newtonian flow in filled or partially filled conveying elements of twin-screw extruders (TSEs). The algorithms were validated by using a plane Poiseuille flow. Two geometrical configurations with different gap were investigated. A large sound speed was used to prevent particles penetrating the wall boundary of the complex geometry. The velocity field and flow rate of Newtonian flow and non-Newtonian flow (power law) in filled model and partially filled model were analyzed. The distribution of particles in partially filled conveying element in one rotation is introduced. The rheological properties of material take important effect on the flow in fully filled and partially filled cases. For the fully filled cases, the screw-barrel clearance takes important effect on the flow due to the leakage flow reducing the flow rate. For the partially filled case, the clearance affects the non-Newtonian flow by changing the rheological properties of the fluid. The effect of clearance on Newtonian flow is very limited due to no back pressure in the partially filled case. This work prepared a groundwork for the accurate analysis of real extrusion by SPH. KEYWORDS complex geometry, meshfree method, partially filled flow, power law fluid, twin-screw extruder, 1 | INTRODUCTION Corotating, intermeshing twin-screw extruders (TSEs) are used extensively in polymers, food, and pharmaceutical industries because it has a good mixing and self-cleaning property. Flows in TSE often [...]

The concept of complexity for dynamical spherically symmetric dissipative self-gravitating configuration (Herrera et al. Phys. Rev. D, 98,104059 (2018). doi:10.1103/PhysRevD.98.104059) is generalized in the scenario of modified Gauss-Bonnet gravity. For this purpose, a spherically symmetric fluid with locally anisotropic, dissipative, and non-dissipative configurations is considered. We choose the same complexity factor for the structure as we did for the static case, while we consider the homologous condition for the simplest pattern of evolution. In this approach, we formulate structure scalars that demonstrate the essential properties of the system. A fluid distribution that fulfills the vanishing complexity constraint and proceeds homologously corresponds to isotropic, geodesic, homogeneous, and shear-free fluid. In the dissipative case, the fluid is still geodesic but it is shearing, and there is a wide range of solutions. In the last, the stability of vanishing complexity is examined. Key words: self-gravitating system, anisotropy, hydrodynamics, tilted space-time, complexity. Nous generalisons le concept de complexite pour une configuration autogravitante, dissipative, spheriquement symetrique et dynamique (Herrera et al. Phys. Rev. D, 98, 104059 (2018). doi:10.1103/PhysRevD.98.104059), dans le scenario de la gravite de Gauss-Bonnet. A cette fin, nous considerons un fluide spheriquement symetrique avec une configuration localement anisotrope, dissipative et non dissipative. Nous choisissons le meme facteur de complexite pour la structure que pour le cas statique, pendant que nous considerons la condition homologue pour le schema d'evolution le plus simple. Dans cette approche, nous formulons des scalaires de structure qui demontrent les proprietes essentielles du systeme. Une distribution de fluide qui satisfait la contrainte de disparition de la complexite et procede de facon homologue correspond a un fluide sans cisaillement, homogene, geodesique et isotrope. Dans le cas dissipatif, le fluide demeure geodesique, mais montre un cisaillement et il y a une large gamme de solutions. Finalement, nous examinons la stabilite de la disparition de la complexite. [Traduit par la Redaction] Mots-cles : systeme autogravitant, anisotropie, hydrodynamique, espace-temps incline, complexite., 1. Introduction There are many works in the literature in which the definition of complexity has been proposed by using different approaches [1-6]. Lopez-Ruiz and collaborators [7, 8] established this [...]

Lagrangian particle-based smoothed particle hydrodynamics (SPH) is increasingly widely used in landslide modelling. This paper investigates four important issues not addressed by previous studies on SPH modelling of large-scale landslides, i.e., convergence property, influence of constitutive parameters, scale effect and friction reduction, and influence of different treatments of the viscous effect. The GPU-acceleration technique is employed to achieve high-resolution three-dimensional (3D) modelling. The Baige landslide is investigated by comparing numerical results with field data, and detailed analyses on the four issues are provided. Suggestions on particle resolution, constitutive parameter, and formulations of viscous discretization are also presented for future SPH modelling of large-scale landslides. Key words: large-scale landslides, smoothed particle hydrodynamics, constitutive model, graphics processing unit (GPU) acceleration, convergence. L'hydrodynamique particulaire lissee (SPH) basee sur des particules lagrangiennes est de plus en plus utilisee dans la modelisation des glissements de terrain. Cet article analyse quatre questions importantes qui n'ont pas ete abordees par les etudes precedentes sur la modelisation SPH des glissements de terrain a grande echelle, a savoir la propriete de convergence, l'influence des parametres constitutifs, de l'effet d'echelle et de la reduction du frottement, et l'influence de differents traitements de l'effet visqueux. La technique d'acceleration par GPU est utilisee pour realiser une modelisation 3D a haute resolution. Le glissement de terrain de Baige est etudie en comparant les resultats numeriques avec les donnees de terrain, et des analyses detaillees sur les quatre questions sont fournies. Des suggestions sur la resolution des particules, les parametres constitutifs et les formulations de la discretisation visqueuse sont egalement presentees pour la modelisation SPH future des glissements de terrain a grande echelle. [Traduit par la Redaction] Mots-cles : glissements de terrain a grande echelle, hydrodynamique des particules lissees, modele constitutif, acceleration par processeur graphique (GPU), convergence., 1. Introduction Large-scale landslides are a major socio-economic threat in mountainous regions, as they usually lead to continuous damage of infrastructures and, in many cases, causalities. Various numerical methods were [...]

Characteristics of turbulent flow around a braided bar are much more complex as compared to the straight and meandering rivers. The impact of a mid-channel bar on the turbulent flow structure has been investigated in this research. A new dominance function [S.sub.i,H] is proposed in this study as a measure of the relative dominance of ejection and sweep events in turbulent flow structure. Occurrence of the kolk-boil phenomenon is observed due to interaction of ejection and sweep events. The kolk-boil phenomenon generates negative pressure gradients which result in suspension of bed sediment particles in the flow domain. The transition probability of bursting event movements is computed using the first Markov chain. A new parameter movement ratio is formulated in this study, which is found to faithfully reflect the fluvial processes of sedimentation and scouring on the channel bed. Acceleration of flow is seen to occur at adjoining regions close to the upstream end of the bar. Due to the presence of the bar, the flow area in its proximity decreases which has caused increment in the velocity at sections located near the upstream end of the mid-channel bar. For model runs with bars, a distinct bulge in the turbulent intensity graph is observed. The mid-channel bar effect is mainly discernible in the lower layers of flow. Key words: kolk-boil phenomenon, bursting events, mid-channel bar, transitional movements, hole size, fluid-bar interaction. Les caracteristiques de l'ecoulement turbulent autour d'un banc anastomose sont beaucoup plus complexes que celles des rivieres droites et sinueuses. Dans le cadre de cette recherche, l'impact du banc median d'alluvionnement sur la structure de l'ecoulement turbulent a ete etudie. Une nouvelle fonction de dominance [S.sub.i,H] est proposee comme mesure de la dominance relative des evenements d'ejection et de balayage dans la structure de l'ecoulement turbulent. Le phenomene d'ebullition du << kolk >> est observe en raison de l'interaction des evenements d'ejection et de balayage. Le phenomene d'ebullition du kolk genere des gradients de pression negatifs qui entrainent la suspension de particules de sediments du lit dans le domaine d'ecoulement. La probabilite de transition des mouvements d'evenements d'eclatement est calculee a l'aide de la premiere chaine de Markov. Un nouveau parametre, soit le rapport de mouvement, est formule et s'avere refleter fidelement les processus fluviaux de sedimentation et d'affouillement sur le lit du canal. L'acceleration de l'ecoulement se produit dans les regions adjacentes pres de l'extremite en amont du banc. En raison de la presence du banc, la zone d'ecoulement dans sa proximite diminue, ce qui entraine une augmentation de la vitesse dans les sections situees pres de l'extremite amont du banc median d'alluvionnement. Pour les analyses de modele avec des bancs, un gonflement distinct dans le graphique d'intensite turbulente est observe. L'effet du banc median d'alluvionnement est principalement perceptible dans les couches inferieures de l'ecoulement. [Traduit par la Redaction] Mots-cles : phenomene d'ebullition de << kolk >>, evenements d'eclatement, banc median d'alluvionnement, mouvements de transition, taille de trou, interaction fluide-banc., Introduction There exist in nature several patterns of river planforms such as meandering and braiding. The flow structure and secondary currents in the meandering channels have been studied by many [...]

To assess and predict the direction and range of a dredging induced contaminated sediment plume on the surrounding environment, a three-dimensional hydrodynamic and mud transport modeling system MIKE 3-FM was used in the Randle Reef area of Hamilton Harbour. Simulations were carried out with the typical local and maximum winds under which the dredging operation would proceed. The dredge plume travel pattern and range in both horizontal and vertical planes are examined under various wind conditions and model mesh resolutions. It was found that the simulated plume extents were very sensitive to transport model mesh resolution due to the additional numerical advection induced in the calculations. Detailed discussion of this particular issue has not been observed in other publications. The results of this simulation provide useful information for remediation project managers in planning and guiding the environmental monitoring of dredging operations. In addition, the methodology used in this study can be adapted to other dredging projects. Key words: contaminated sediment plume, water quality monitoring, sediment remediation, Randle Reef, hydrodynamic and transport modeling. Afin d'evaluer et de prevoir la direction et l'etendue d'un panache de sediments contamines cause par le dragage dans le milieu environnant, un systeme de modelisation tridimensionnelle hydrodynamique et de transport de boue MIKE 3-FM a ete utilise dans la region du recif Randle du port de Hamilton. Des simulations ont ete effectuees avec les vents locaux et maximaux typiques sous lesquels l'operation de dragage devait se derouler. La trajectoire et l'etendue du panache de dragage dans les plans horizontal et vertical sont examinees dans diverses conditions de vent et dans diverses resolutions de maillage. Il a ete constate que les etendues simulees du panache etaient tres sensibles a la resolution du maillage du modele de transport en raison de l'advection numerique supplementaire induite dans les calculs. On n'a pas observe de discussion detaillee sur cette question particuliere dans d'autres publications. Les resultats de cette simulation donnent aux gestionnaires de projet de restauration des renseignements utiles quant a la planification et l'orientation de la surveillance environnementale des operations de dragage. De plus, la methodologie utilisee dans cette etude peut etre adaptee a d'autres projets de dragage. [Traduit par la Redaction] Mots-cles : panache de sediments contamines, surveillance de la qualite de l'eau, assainissement des sediments, recif Randle, modelisation hydrodynamique et de transport., Introduction During dredging, suspended sediment plumes are generated and can potentially spread over a large area. Therefore, it is important to understand these ranges are under different operation conditions. In [...]

Coalescence-induced droplet jumping on superhydrophobic surfaces has been observed at microscale and even nanoscale. The enhancement in jumping velocity of coalescing droplets is crucial for condensation heat transfer enhancement, antiicing, self-cleaning, and so forth. However, the research on how to acquire a higher jumping velocity is really very limited. In this paper, we use molecular dynamics simulations to study the coalescence-induced jumping of two equally sized nanodroplets on chemically heterogeneous surfaces composed of alternating stripes with different hydrophobicity. We show that the jumping velocity is closely related to the stripe width and wettability contrast, and it can even exceed that on an ideal superhydrophobic surface with 180 [degrees] contact angle when the striped surfaces are properly designed. We also demonstrate that there is always an optimal stripe width yielding the maximum jumping velocity, whereas its value is independent of the wettability contrast. We reveal that the dominant factor to determine the jumping velocity is the apparent contact angle of equilibrated droplets over heterogeneous surfaces for small stripe widths; it changes to the time of liquid bridges impacting surfaces for moderate stripe widths and to the contact area between equilibrated droplets and relatively hydrophobic stripes for large stripe widths. We believe the present simulations can provide useful guidance to design self-jumping superhydrophobic surfaces. Key words: mixed-wettability, superhydrophobic surfaces, coalescence, jumping velocity, molecular dynamics simulations. Les sauts de gouttelettes induits par coalescence sur une surface super-hydrophobe s'observent aux echelles micro et nano. L'accroissement de la vitesse de saut des gouttelettes se fusionnant est cruciale pour l'augmentation du transfert de chaleur par condensation, pour l'antigivrage, l'auto-nettoyage, etc. Cependant, il n'y a que tres peu de recherche sur le moyen d'augmenter la vitesse de saut. Nous utilisons ici des simulations de dynamique moleculaire pour etudier le sautillement, induit par leur fusion, de deux nano-gouttelettes de meme grosseur sur des surfaces chimiquement heterogenes composees de bandes alternees de differente hydrophobicite. Nous montrons que la vitesse de saut est etroitement reliee a la largeur de ces bandes et du contraste de mouillabilite et qu'elle peut meme exceder celle sur une surface superhydrophobe continue ideale avec un angle de surface de 180 [degrees], a condition que les surfaces striees soient concues de facon appropriees. Nous annoncons aussi qu'il y a une largeur de bande optimale produisant une vitesse de saut maximale, et que sa valeur est independante du contraste de mouillabilite. Nous revelons que, sur les surfaces heterogenes avec des bandes de petites largeurs, le facteur dominant pour determiner la vitesse de saut est l'angle de contact apparent des gouttelettes en equilibre, mais pour des bandes de largeur moyenne, ce facteur dominant devient le temps du pont liquide impactant la surface, alors que pour des bandes de grande largeur, il devient la surface de contact entre les gouttelettes equilibrees et les bandes relativement hydrophobes. Nous croyons que les resultats de ces simulations fourniront des guides utiles dans la conception des surfaces super-hydrophobes auto-sautillantes. [Traduit par la Redaction] Mots-cles : mouillabilite mixte, super-hydrophobe, coalescence/fusion, vitesse de saut, simulations de dynamique moleculaire., 1. Introduction Coalescence-induced droplet jumping on superhydrophobic surfaces was first discovered by Boreyko and Chen in 2009 [1]. Over the past decade, this phenomenon has received more and more attention [...]

The hydrodynamic erosion generated by the pumping action of the wheel load during rain and snow is the main cause of the semi-rigid base failure. Unfortunately, however, very few experimental methods and damage models can reasonably describe and predict the moisture damage performance of semi-rigid base materials under the pumping action. To address this issue, a hydrodynamic pressure erosion test was conducted firstly. Then, the compressive test was performed on the eroded specimens to evaluate the damage mechanism of semi-rigid base materials subjected to hydrodynamic erosion. Finally, a moisture-induced damage model that is applicable to the semi-rigid base materials was established by the concept of damage mechanics. The results indicated that the presented damage model encapsulates the complex behavior of the semi-rigid base materials under the hydrodynamic pressure and provides a more rational method for predicting the moisture damage performance of semi-rigid base materials. Key words: moisture damage, semi-rigid base materials, stress state, damage model. L'erosion hydrodynamique generee par l'effet de pompage de la charge sur roues pendant la pluie et la neige est la principale cause de la rupture de base semi-rigide. Malheureusement, tres peu de methodes experimentales et de modules de dommages peuvent raisonnablement decrire et predire le comportement des materiaux de base semi-rigides par rapport aux dommages par l'humidite sous l'effet de pompage. Pour remedier a ce probleme, un essai d'erosion sous pression hydrodynamique a d'abord ete effectue. Ensuite, l'essai de compression a ete effectue sur les echantillons erodes pour evaluer le mecanisme d'endommagement des materiaux de base semi-rigides soumis a l'erosion hydrodynamique. Enfin, un modele de dommages induits par l'humidite applicable aux materiaux de base semi-rigides a ete etabli par le concept de mecanique des dommages. Les resultats ont indique que le modele de dommages presente reproduit le comportement complexe des materiaux de base semi-rigides sous la pression hydrodynamique et fournit une methode plus rationnelle pour predire les resultats des dommages causes aux materiaux de base semi-rigides par l'humidite. [Traduit par la Redaction] Mots-cles: dommages par l'humidite, materiaux de base semi-rigides, etat de contrainte, modele de dommages., Introduction Moisture damage is one of the most common distresses for asphalt pavement, which has been a research topic among investigators for many years (Hamedi and Moghadas 2015). Numerous studies [...]

The computation of total flow in a flooded river is very crucial work in designing economical flood defense schemes and drainage systems. Further, under non-uniform flow conditions like in converging and diverging compound channel, the traditional methods provide poor results with high errors. The analytical methods require the system of nonlinear equations to be solved, which is very complex. So, mathematical models that prompt in taking care of a complex system of problems are solved here through an artificial neural network (ANN) and adaptive neuro-fuzzy inference system (ANFIS). By utilizing ANN and ANFIS, an attempt is made to predict the discharge in converging and diverging compound channels. In the analysis, the most influencing dimensionless parameters such as friction factor ratio, area ratio, hydraulic radius ratio, bed slope, width ratio, relative flow depth, angle of converging or diverging, relative longitudinal distance, and flow aspect ratio are taken into consideration for computation of discharge. Gamma test and M-test have been performed to achieve the best combinations of input parameters and training length respectively. The significant input parameters that influence the discharge are found to be friction factor ratio, hydraulic radius ratio, relative flow depth, and bed slope. A suitable performance is achieved by the ANFIS model as compared to ANN model with a high coefficient of determination of 0.86 and low root mean square error of 0.005 in predicting the discharge of non-prismatic compound channels taken under consideration. Key words: non-prismatic compound channels, Gamma test, M-test, relative flow depth, width ratio, artificial neural network (ANN), adaptive neuro-fuzzy inference system (ANFIS). Le calcul d'ecoulement total dans une riviere inondee constitue un travail primordial pour la conception de projets de defense contre les inondations et de systemes de drainage economiques. De plus, dans des conditions d'ecoulement non uniformes comme dans les chenaux composes convergents et divergents, les methodes traditionnelles donnent de mauvais resultats avec des niveaux d'erreurs eleves. Les methodes d'analyse requierent la resolution de systeme d'equations non lineaires, lesquelles sont tres complexes. Ainsi, les modeles mathematiques susceptibles de solutionner un systeme complexe de problemes sont resolus ici par un reseau de neurones artificiels (RNA) et un systeme d'inference neuro-floue adaptatif (SINFA). En utilisant un RNA et un SINFA, on tente de predire le debit dans des chenaux composes convergents et divergents. Dans l'analyse, les parametres adimensionnels les plus determinants tels que le rapport de facteur de frottement, le rapport de surface, le rapport de rayon hydraulique, la pente du lit, le rapport de largeur, la profondeur d'ecoulement relative, l'angle de convergence ou de divergence, la distance longitudinale relative, le facteur de forme d'ecoulement sont pris en consideration pour le calcul du debit. Le test gamma et le test M ont ete realises pour obtenir les meilleures combinaisons de parametres d'entree et de duree d'entrainement, respectivement. Les principaux parametres d'entree qui influent sur le debit sont le rapport de facteur de frottement, le rapport du rayon hydraulique, la profondeur relative d'ecoulement et la pente du lit. Une performance appropriee est obtenue par le modele SINFA comparativement au modele RNA avec un coefficient de determination eleve de 0,86 et un ecart quadratique moyen bas de 0,005 dans la prediction du debit de chenaux composes non-prismatiques pris en consideration. [Traduit par la Redaction] Mots-cles : chenaux composes non-prismatiques, test gamma, test M, profondeur relative de l'ecoulement, rapport de largeur, reseau de neurones artificiels (RNA), systeme d'inference neuro-floue adaptatif (SINFA)., Introduction The sustainability of human civilization depends on rivers due to the availability of water for their day-to-day activity. But the same river has the potential to devastate everything and [...]

Hydrodynamics, which generally describes the flow of a fluid, is expected to hold even for fundamental particles such as electrons when inter-particle interactions dominate.sup.1. Although various aspects of electron hydrodynamics have been revealed in recent experiments.sup.2-11, the fundamental spatial structure of hydrodynamic electrons--the Poiseuille flow profile--has remained elusive. Here we provide direct imaging of the Poiseuille flow of an electronic fluid, as well as a visualization of its evolution from ballistic flow. Using a scanning carbon nanotube single-electron transistor.sup.12, we image the Hall voltage of electronic flow through channels of high-mobility graphene. We find that the profile of the Hall field across the channel is a key physical quantity for distinguishing ballistic from hydrodynamic flow. We image the transition from flat, ballistic field profiles at low temperatures into parabolic field profiles at elevated temperatures, which is the hallmark of Poiseuille flow. The curvature of the imaged profiles is qualitatively reproduced by Boltzmann calculations, which allow us to create a 'phase diagram' that characterizes the electron flow regimes. Our results provide direct confirmation of Poiseuille flow in the solid state, and enable exploration of the rich physics of interacting electrons in real space. The emergence of a liquid-like electronic flow from ballistic flow in graphene is imaged, and an almost-ideal viscous hydrodynamic fluid of electrons exhibiting a parabolic Poiseuille flow profile is observed., Author(s): Joseph A. Sulpizio [sup.1] , Lior Ella [sup.1] , Asaf Rozen [sup.1] , John Birkbeck [sup.2] [sup.3] , David J. Perello [sup.2] [sup.3] , Debarghya Dutta [sup.1] , Moshe [...]

In this research we use a generalized hydrodynamic model to numerically investigate the quasi-neutral expansion and compression of an electron-ion plasma with nonextensive electron velocity distribution into or from vacuum. We study the effects of kinematic viscosity and electron-ion collisions on the expansion profile and compare our results to the numerical solutions of the standard Korteweg--de Vries (KdV) equation. It is found that the quasi-neutrality assumption in the hydrodynamic approach in the absence of viscosity and collisions, which leads to elimination of Poisson's equation, sets the weak dispersion limit and becomes equivalent to the standard weakly dispersive KdV model. In the weak dispersion limit our model, as well as the KdV with small dispersion effect, predicts that a pulse-like initial profile evolves into solitary wave train. We further show that in a plasma expansion different shock profiles, such as purely dispersive, diffusive-dispersive, and dissipative ones, with significantly different characters may form. Finally, the effect of electron nonextensivity on oscillatory shock waves shows that the expansion profile is affected by changes of q-parameter. Our numerical solution is in qualitative agreement with some distinguished experiments showing the possibility of dispersive shock wave formation in rarefied plasma during an expansion into vacuum. Key words: plasma expansion, nonextensive plasma, shock waves, dispersive shock waves, hydrodynamic. Cette recherche utilise une generalisation du modele hydrodynamique pour etudier numeriquement l'expansion/ compression vers/du vide d'un plasma quasi-neutre avec une distribution de vitesse electronique non extensive (a parametre q). Nous etudions les effets de la viscosite cinematique et des collisions electron-ion sur le profil d'expansion et comparons nos resultats avec la solution numerique de l'equation Korteweg - de Vries (KdV) standard. Nous trouvons que l'hypothese de quasi-neutralite, dans l'approche hydrodynamique en absence de viscosite et de collision qui mene a l'elimination de l'equations de Poisson, etablit la limite de dispersion faible et devient equivalente au modele KdV standard faiblement dispersif. Dans la limite de faible dispersion, notre modele, comme KdV dans les memes conditions, predit qu'un profil initial de type impulsion evolue vers un train d'ondes solitaires. Nous montrons aussi que dans un plasma peuvent se former, avec des caracteres significativement differents, des profils de choc a expansion differente, de type purement dispersif ou diffusif-dispersif ou dissipatif. Finalement, l'effet du caractere non extensif des electrons sur les ondes de choc oscillantes montre que le profil d'expansion est affecte par la variation du parametre q. Notre solution numerique est en accord qualitatif avec des experiences reconnues, montrant la possibilite de formation d'ondes de choc dispersives dans des plasmas rarefies en expansion vers le vide. [Traduit par la Redaction] Mots-cles: expansion du plasma, plasma non extensive, ondes de choc, ondes de choc dispersives, hydrodynamique., 1. Introduction Shock waves are among the important nonlinear excitations that play an essential role in natural phenomena. They are characterized as sudden change in a physical quantity of a [...]

Thermo-active diaphragm walls that combine load bearing ability with a ground source heat pump (GSHP) are considered to be one of the new technologies in geotechnical engineering. Despite the vast range of potential applications, current thermo-active diaphragm wall designs have very limited use from a geotechnical aspect. This paper investigates the wall-soil interaction behaviour of a thermo-active diaphragm wall by conducting a thermo-hydro-mechanical finite element analysis. The GSHP operates by circulating cold coolant into the thermo-active diaphragm wall during winter. Soil contraction and small changes in the earth pressures acting on the wall are observed. The strain reversal effect makes the soil stiffness increase when the wall moves in the unexcavated side direction, and hence gives different trends for long-term wall movements compared to the linear elastic model. The GSHP operation makes the wall move in a cyclic manner, and the seasonal variation is approximately 0.5-1 mm, caused by two factors: the thermal effects on the deformation of the diaphragm wall itself and the thermally induced volume change of the soil and pore water. In addition, it is found that the change in bending moment of the wall due to the seasonal GSHP cycle is caused mainly by the thermal differential across the wall during the winter, because the seasonal changes in earth pressures acting on the diaphragm wall are very limited. Key words: thermo-hydro-mechanical analysis, thermo-active diaphragm wall, finite element. Les parois moulees thermoactives qui allient la capacite de charge et les pompes a chaleur geothermiques (GSHP) sont considerees comme l'une des nouvelles technologies dans l'ingenierie geotechnique. Malgre la vaste gamme d'applications potentielles, les parois diaphragme thermoactifs actuels conus ont tres peu de l'utilisation d'un aspect geotechnique. Cet article etudie le comportement d'interaction sol-paroi d'une paroi diaphragme thermoactif en effectuant une analyse thermo- hydromecaniques par elements finis. La chaleur geothermique fonctionne par circulation d'eau froide dans les parois diaphragme thermoactif pendant l'hiver. La contraction du sol et de petits changements dans les pressions de la terre agissant sur la paroi sont observes. L'effet d'inversion de souche augmente la rigidite du sol lorsque la paroi se deplace dans le sens du cote non excave, et donc donne des differentes tendances a long terme pour les mouvements du mur par rapport au modele elastique lineaire. La chaleur geothermique permet de deplacer la paroi d'une maniere cyclique, et la variation saisonniere est d'environ 0,5-1 mm, cause par deux facteurs: les effets thermiques sur la deformation de la paroi membrane elle-meme et le changement de volume induit par la chaleur du sol et de l'eau interstitielle. En outre, il est constate que le changement dans le moment de flexion de la paroi en raison de la nature saisonniere du cycle GSHP est cause principalement par le differentiel thermique a travers la paroi au cours de l'hiver, parce que les changements saisonniers de pressions sur la paroi du diaphragme sont tres limites. [Traduit par la Redaction] Mots-cles: analyse thermo-hydro-mecaniques, paroi diaphragme thermoactif, elements finis., Introduction Ground source heat pump (GSHP) technology can offer low-carbon heating and cooling and hot water provision. Their electrical consumption and maintenance requirements can be lower than those of conventional [...]

We propose a generalization of quantum mechanical equations in the hydrodynamic form by introducing, into the Lagrangian density, terms taking into account the diffusion velocity at zero and finite temperatures and the diffusion pressure energy of the warm vacuum. Based on this, for the model of one-dimensional hydrodynamics, we construct a system of equations that are analogous to the Euler equations, but with the inclusion of quantum and thermal effects. They are a generalization of the equations of the Nelson stochastic mechanics. The numerical analysis of the system's solutions' behavior determined that this system can be used to describe the process of quantum-thermal fluctuation relaxation. Key words: quantum stochastic influence, thermal stochastic influence, effective influence, self-diffusion, density of diffusion pressure energy, drift and diffusion velocities, fluctuations, numerical analysis. Nous proposons une generalisation des equations de mecanique quantique sous leur forme hydrodynamique en introduisant dans la densite lagrangienne des termes qui tiennent compte de la vitesse de diffusion aux temperatures nulle et finies et de l'energie de pression de diffusion du vide chaud. Sur cette base, pour le modele unidimensionnel de l'hydrodynamique, nous construisons un systeme d'equations qui sont analogues aux equations d'Euler, mais avec l'inclusion d'effets quantiques et thermiques. Ces equations sont une generalisation des equations de la mecanique stochastique de Nelson. L'analyse numerique du comportement des solutions de ce systeme permet de conclure que ce systeme peut etre utilise pour decrire le processus de relaxation des fluctuations thermiques quantiques. [Traduit par la Redaction] Mots-cles : influence stochastique quantique, influence stochastique thermique, influence efficace, autodiffusion, densite d'energie de pression de diffusion, vitesses de derive et de diffusion, fluctuations, analyse numerique. PACS No.: 02.60.Dc, 03.65.-w., 1. Introduction Thermal fluctuations in hydrodynamics have been taken into account for 50 years; however, there is still no consistent quantum statistical theory that accounts for quantum and thermal effects [...]

We derive a microscopic version of the successful phenomenological hydrodynamic model of Bohr-Davydov-Faessler-Greiner for collective rotation-vibration motion of an axially symmetric deformed nucleus. The derivation is not limited to small oscillation amplitudes. The nuclear Schrodinger equation is canonically transformed to collective coordinates, and then linearized using a constrained variational method. The associated constraints are imposed on the wave-function rather than on the particle coordinates. This approach yields three self-consistent, time-reversal invariant, cranking-type Schrodinger equations for the rotation-vibration and intrinsic motions, and a self-consistency equation. For harmonic oscillator mean-field potentials, these equations are solved in closed forms and applied to the ground-state rotational bands in some axially symmetric nuclei. The results are compared with those of other models and related measured data. Key words: multi-particle rotation, multi-particle vibration, intrinsic motion, angular momentum, moments of inertia, canonical transformation, constrained variational method, time-reversal invariance, self-consistency, cranking model, axial symmetry, rotational-band termination or cutoff. Nous derivons une version microscopique du modele hydrodynamique phenomenologique reussi de Bohr-DavydovFaesler-Greiner pour le mouvement de rotation-vibration d'un noyau deforme de symetrie axiale. La derivation n'est pas limitee aux oscillations de faible amplitude. L'equation nucleaire de Schrodinger est canoniquement transformee en coordonnees collectives et ensuite linearisee via une methode variationnelle contrainte. Les contraintes associees sont imposees aux fonctions d'onde plutot qu'aux coordonnees. L'approche donne trois equations de Schrodinger de type cranking, invariantes sous renversement du temps et auto-coherentes. Pour un champ moyen d'oscillateur harmonique, ces equations peuvent etre solutionnees analytiquement et appliquees aux bandes de rotation de noyaux de symetrie axiale. Les resultats sont compares a ceux d'autres modeles et a des valeurs mesurees. [Traduit par la Redaction] Mots-cles: rotation multi-particules, vibration multi-particules, mouvement intrinseque, moment angulaire, moment d'inertie, transformation canonique, methode variationnelle contrainte, invariance sous renversement du temps, auto-coherence, modele de cranking, symetrie axiale, fin de bande de rotation. PACS Nos.: 21.60.Ev, 21.60.FW, 21.60.Jz., 1. Introduction The phenomenological hydrodynamic rotation-vibration model of Bohr-Davydov-Faessler-Greiner (BDFG) [1-5] has been remarkably successful in predicting the properties of low-lying collective rotation and vibration states in deformed nuclei. The [...]

Algal blooms caused by the stalk-forming diatom Didymosphenia geminata impact the habitat structure and functioning of stream ecosystems. We evaluated site-specific geomorphic controls on D. geminata in a cobble bed river in the Front Range of the Rocky Mountains. Entrainment potential, defined as the ratio of mean bed shear stress to the critical shear stress, was found to be the most important control on total abundance. A comparison with critical thresholds for sediment transport showed that the requirements for flushing flows to control D. geminata blooms are similar to that required for channel maintenance. Environmental parameters influencing the morphology of the algal mats and the potential for D. geminata to dominate the benthic algal community were also investigated. The results not only contribute to understanding of the controls on benthic algal growth in dynamic streams but also for management of water releases as mitigation for the control of future blooms of D. geminata. Les proliferations d'algues causees par la diatomee formant des tiges Didymosphenia geminata ont une incidence sur la structure de l'habitat et la fonction des ecosystemes fluviaux. Nous avons evalue les controles geomorphologiques propres au site sur D. geminata dans une riviere a lit caillouteux du chainon frontal des montagnes Rocheuses. Nous avons constate que le potentiel d'entrainement, defini comme etant le rapport de la contrainte de cisaillement moyenne sur le lit et de la contrainte de cisaillement critique, est le parametre qui exerce le plus grand controle sur l'abondance totale. Une comparaison avec des seuils critiques pour le transport de sediments a demontre que les exigences quant aux debits de lessivage comme mesure de controle des proliferations de D. geminata sont semblables aux exigences pour le maintien du chenal. Les parametres environnementaux qui influencent la morphologie des tapis algaires et le potentiel pour D. geminata d'etre dominante dans la communaute d'algues benthiques ont egalement ete etudies. Les resultats aident non seulement a comprendre les facteurs qui controlent la croissance des algues benthiques dans les cours d'eau dynamiques, mais sont aussi utiles pour la gestion des lachers d'eau comme mesure d'attenuation dans la lutte contre les proliferations futures de D. geminata. [Traduit par la Redaction], Introduction Didymosphenia geminata is a freshwater diatom of primarily lotic habitats that has emerged in the past decade as a major threat to stream ecosystems globally (Blanco and Ector 2009). [...]

The nonequilibrium adaptation parameters of a depth-averaged two-dimensional hydrodynamic and sediment transport model were examined in the study. Calculated results were compared to data measured in two sets of published laboratory experiments that investigated mining-pit migration under well-controlled boundary conditions including steady flow and uniform rectangular cross sections along the flume except in the vicinity of the experimental mining area. The two sets of experiments were chosen as representatives of bed-load-dominated and suspended-load-dominated cases, respectively. A sensitivity analysis was conducted to estimate the influence of the nonequilibrium adaptation parameters on mining-pit migration simulation. Calculated results indicate that appropriate selection of the adaptation parameters is critical in order to close the nonequilibrium sediment transport formulas when modeling mining-pit migration. DOI: 10.1061/(ASCE)HY.1943-7900.0000242 CE Database subject headings: Sediment transport; Rivers; Hydraulic models. Author keywords: Sediment transport; River engineering; Modeling; Fluvial morphology; Gravel mining.

An engineered thermal management is fundamental to the application of gas foil bearings (GFBs) as turboshaft supports in rotorcraft propulsion systems. The paper presents a model for the thermal energy transport in a rotor-GFB system operating at high temperature with typical inner and/or outer cooling flows. Predicted film temperatures agree with published test data, demonstrating the effectiveness of an outer cooling stream to remove heat and to control the operating temperature. The inner flow stream is not as efficient. The analysis shows paths of thermal energy by conduction and convection to assist in the design and troubleshooting of rotor-GFB systems operating hot. Bearing temperatures and shaft motions measurements are obtained in a test rotor electrically heated to 132[degrees]C. In speed-up tests to 26 krpm, the rotor motion amplitude drops suddenly just above the critical speed, thus, evidencing the typical hardening of compliant bearings. At the hottest test condition, since air is more viscous, the rotor peak motion amplitude decreases, not showing a jump. The coastdown tests show the critical speed increases slightly as the temperature increases. [DOI: 10.1115/1.4000279]

The flow behavior in hydrocyclones is quite complex. The computational fluid dynamics method was used to simulate the flow fields inside a hydrocyclone in order to investigate its separation efficiency. In the computational fluid dynamics study of hydrocyclones, the air-core dimension is a key to predicting the mass split between the underflow and overflow. In turn, the mass split influences the prediction of the size classification curve. Generally in hydrocyclone simulations, assuming low particle volume fractions, the discrete phase effects on the continuous phase have been excluded; therefore, one-way coupling method has been used. Due to high particle consistencies, regions in some cases, especially in underflow areas, excluding discrete phase effects on continuous phase may be ineligible. In this study for an example case by consisting discrete phase effects and using two-way coupling method, simulation accuracy noticeably has been improved. Three models, the k - [epsilon] model the Reynolds stress model (RSM) without considering air core, and Reynolds stress turbulence model with volume of fluid multiphase model for simulating air core, were compared for the predictions of velocity, axial and tangential velocity distributions and separation proportion. Results by the RSM with air-core simulation and two-way coupling model since it produces some detailed features of the turbulence and discrete phase mode effects, are clearly closer in predicting the experimental data than the other two. [DOI: 10.1115/1.3130445] Keywords: hydrocyclone, VOF multiphase, Lagrangian approach, particles trajectory, air core, one-way coupling, two-way coupling

A spherical drop of viscosity [[mu].sup.(1)] and radius [a.sub.1] is surrounded by a spherical shell of viscosity [[mu].sup.(2)], internal radius [a.sub.1], and external radius [a.sub.2], beyond which there is an unbounded matrix fluid of viscosity [[mu].sup.(3)]. An arbitrary axisymmetric singularity acts inside or outside the viscous spherical shell. It is established that the Stokes' stream function induced in this heterogeneous medium is explicitly expressible solely in terms of the corresponding stream function for the unperturbed homogeneous unbounded medium. As an application of the general solution, it is shown that there exists a homogeneous spherical drop of viscosity [mu] and radius [a.sub.2], which is equivalent to the spherical drop of viscosity [[mu].sup.(1)] and radius [a.sub.1], surrounded by the spherical shell of viscosity [[mu].sup.(2)] and outer radius [a.sub.2]. A new formula is also established for the effective viscosity of a multiphase medium comprising an incompressible fluid of viscosity [[mu].sup.(3)] in which are embedded N small identical spherical drops of viscosity [[mu].sup.(1)], surrounded by spherical shells of viscosity [[mu].sup.(2)], assuming that the interference effects of these coated spherical drops are negligible, and that their arrangement is axisymmetrical. The corresponding two-dimensional results are also presented, by slightly modifying the three-dimensional results. [DOI: 10.1115/1.3130450] Keywords: spherical drops, spherical shells, incompressible fluids, heterogeneous medium, Stokes' stream function

Basin-scale internal waves are inherently nonhydrostatic; however, they are frequently resolved features in three- dimensional hydrostatic lake and coastal ocean models. Comparison of hydrostatic and nonhydrostatic formulations of the Centre for Water Research Estuary and Lake Computer Model provides insight into the similarities and differences between these representations of internal waves. Comparisons to prior laboratory experiments are used to demonstrate the expected wave evolution. The hydrostatic model cannot replicate basin-scale wave degeneration into a solitary wave train, whereas a nonhydrostatic model does represent the downscaling of energy. However, the hydrostatic model produces a nonlinear traveling borelike feature that has similarities to the mean evolution of the nonhydrostatic wave. CE Database subject headings: Coastal processes; Hydrodynamics; Internal waves; Hydrologic models.

A three-dimensional hydrodynamic model, MIKE 3, was used to assess the effects of the cooling water thermal plume from the 877 MW Charles Poletti power plant that discharges to the East River in Queens, New York City. The East River is a tidal strait that connects New York Harbor and Long Island Sound--two large, out of phase estuaries with complex hydrodynamics. The study was additionally required to account for the thermal discharge of a larger, 1253 MW power plant adjacent to Poletti. The model used a flexible mesh formulation based on unstructured triangular elements and was successfully calibrated with triaxial thermal field survey data. After calibration, the model was used to demonstrate that under worst case conditions the resulting thermal plume did not exceed the regulatory thermal criteria. CE Database subject headings: Three-dimensional models; Powerplants; Thermal factors; Hydrodynamics; New York; New York City.

Results from combined laboratory experimental and turbulent numerical modeling studies are presented to investigate the effects of bed roughness (discrete square strips) and slope on the flow over a free overfall in a rectangular channel. A broad range of model parameters such as the bed roughness, channel slope, and incoming upstream Froude number is investigated. The water surface profiles upstream of the brink of the channel, the velocity fields in cavity between two strips, and end depth (water depth at the brink of the channel) are simulated, measured, and discussed for various input conditions. The results show that for a given dimension of bed roughness the relative spacing of roughness (defined as the ratio of the center to center distance to the height of the strip) has a significant effect on the flow. The computational results are in good agreement with the experimental measurements. CE Database subject headings: Stream improvement; Channel design; Geomorphology; Water discharge.

This paper presents the application of hydrostatic and nonhydrostatic three-dimensional hydrodynamic models to a stratified lake. Focus was given to the multiscale response of the internal wave field to strong wind gusts exceeding 20 m [s.sup.-1]. Simulations were performed using different horizontal grid resolutions with uniform grid sizes varying from 100x 100 to 10 x 10 m. Results of the hydrostatic models were used to investigate the large-scale features of the internal wave motion. With the intent of investigating the high-frequency waves, observed results of these simulations were used as initial conditions for nonhydrostatic simulations using smaller grids. Wavelength of the high frequency waves decreased with grid resolution. However, none of the uniform grids were sufficiently fine to capture the waves of the highest frequency. Simulations performed using a nonuniform grid produced internal waves of similar frequency of the waves observed in the field. The simulations showed that these waves were shear unstable modes and that their vertical and horizontal length scales were in close agreement with results from linear stability analysis. DOI: 10.1061/(ASCE)0733-9429(2007)133:11(1206) CE Database subject headings: Internal waves; Three-dimensional model; Lakes; Hydrodynamic pressure; Wind gusts; Stratified flow.

There has been substantial development in computer codes for three-dimensional linear hydroelasticity, but to the authors' knowledge, there are no problems of sufficient complexity put forth in the open literature to serve as appropriate benchmark problems for a floating structure. We present in this paper detailed descriptions of two such problems for three-dimensional hydroelastic computer codes. The first structure is a rectangular, boxshaped 'barge' with dimensions 100 mX 10 mX2 m. The second is a Wigley hull with dimensions 100 mX 10 mX 4.5 m. In both cases, the deformational response is primarily global. Detailed descriptions of each structure, the finite element structural shell models, and the hydrodynamic fluid models, based on the constant panel Green's function method, are provided. Fine meshes are used to minimize discretization errors. Detailed results, including dry natural periods and modes, wet natural periods, and wave-induced displacements and stresses, are presented. The detail is sufficient for others to use the problems as benchmarks for computer codes. [DOI: 10.1115/1.2746397]