Energy Technology Data Exchange (ETDEWEB)
Grison, E [Commissariat a l' Energie Atomique, Lab. de Physique-Chimie et basses temperatures, Grenoble (France).Centre d' Etudes Nucleaires; Commissariat a l' Energie Atomique, Saclay (France).Centre d' Etudes Nucleaires
1960-07-01
The introduction of a small volume of liquid into a turbulent gas stream used as cooling agent improves considerably the heat transfer coefficient of the gas. When the turbulent regime is established, one observes in a cylindrical tube two types of flow whether the liquid wets or does not wet the wall. In the first case, one gets on the wall an annular liquid film and droplets in suspension are in the gas stream. In the second case, a fog of droplets is formed without any liquid film on the wall. Experiments were performed with the following mixtures: water-hydrogen, water-nitrogen, ethanol-nitrogen (wetting liquids) introduced into a stainless steel tube of 4 mm ID, electrically heated on 320 mm of length. We varied the gas flow rate (Reynolds until 50000), the rate of the liquid flow rate to gas flow rate (until 15), the pressure (until 10 kg/cm{sup 2}), the temperature (until the boiling point) and the heat flux (until 250 W/cm{sup 2}). Two types of burnout were observed. A formula of correlation of the burnout heat flux is given. Making use of the analogy between mass transfer and heat transfer, a dimensionless formula of correlation of the local heat transfer coefficients is established. (author) [French] L'introduction d'un faible volume de liquide dans un ecoulement gazeux turbulent utilise comme fluide refrigerant permet une amelioration considerable des coefficients d'echanges thermiques que l'on aurait si le gaz etait employe seul (nous avons obtenu un facteur d'amelioration superieur a 10). En regime turbulent etabli, on observe dans un tube deux modes d'ecoulements selon que le liquide mouille ou ne mouille pas la paroi. Dans le premier cas, on obtient sur la paroi un film annulaire liquide et des gouttelettes en suspension dans le coeur gazeux. Dans le deuxieme cas, il se forme un veritable brouillard sans film liquide sur la paroi. Les etudes experimentales ont ete effectuees avec les melanges eau-hydrogene, eau-azote, ethanol-azote (liquides
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Jullien, F [Commissariat a l' Energie Atomique, Saclay (France). Centre d' Etudes Nucleaires, Direction des piles atomiques
1968-02-01
In this thesis are presented the experimental results obtained during the study of the turbulent diffusion of heat using a wire source in a flat air flow. The Taylor statistical theory laws are well respected in the domain studied. The experiments have made it possible to evaluate the influence of the Reynolds number and of the distance from the wall on the quadratic values of velocity fluctuations and on the Lagrange turbulence scales. In particular, the author has found a correlation between the Lagrange scales and the friction coefficient when the Reynolds number varies. A diffusion law is derived from the Taylor theory; it makes it possible to explain more clearly the idea of turbulent conductivity. (author) [French] Cette these presente les resultats experimentaux de l'etude de la diffusion turbulente de la chaleur a partir d'un fil source dans un ecoulement d'air plan. Les lois de la theorie statistique de Taylor sont bien verifiees dans le domaine d'etude. Les experiences ont permis d'evaluer l'influence du nombre de Reynolds et de la distance a la paroi sur les valeurs quadratiques des fluctuations de vitesse et les echelles lagrangiennes de turbulence. En particulier, l'auteur a trouve une correlation entre les echelles lagrangiennes et le coefficient de frottement lorsque le nombre de Reynolds varie. Comme consequences de la theorie de Taylor, une loi de diffusion est etablie et permet de preciser la notion de conductibilite turbulente. (auteur)
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Galinat, S.
2005-04-15
This work presents the drop breakup phenomenon in a turbulent flow induced by a cross-section restriction in a pipe. A global analysis of single-drop breakup, in a finite volume downstream of the orifice, has allowed deriving statistical quantities such as the break-up probability and the daughter-drop distribution. These parameters are function of a global Weber number based on the maximal pressure drop through the orifice. At a local scale, the locations of breakup events are distributed heterogeneously and depend on the flow Reynolds number. The local hydrodynamic study in downstream of the orifice, which has been done by using Particle Image Velocimetry, reveals the specific breakup zones. Otherwise, this analysis has proved that the turbulence is the predominant external stress at the drop scale. The relation between drop deformation and the external stress along the trajectory has been simulated numerically by the response of a damped oscillator to the locally measured instantaneous turbulence forcing. The results of statistical analysis have allowed to introduce a breakup criterion, based on a unique deformation threshold value for all experiments. This multi-scale approach has been conducted to study drop breakup mechanisms in a concentrated dispersion. The breakup probability decrease with the increase of dispersed phase concentration, which influences the turbulent Weber number distribution in downstream of the orifice. (author)
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Ravelet, F
2005-09-15
We report experimental studies of the turbulent von Karman flow, inertially stirred between counter-rotating impellers. We first study the flow and its transition from laminar to turbulent regime. We highlight the role of slowly varying large scales, due to the presence of an azimuthal mixing layer. The large scales of this flow can be unstable in turbulent regime. We study the statistics of the transitions between the different mean states. The second part is dedicated to an experiment in liquid sodium, called VKS2. We optimize the time-averaged flow in order to allow kinematic dynamo action. We report the very first results of the experiment, and discuss the role of the large scales temporal non-stationariness. (author)
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Bidart, A.; Caltagirone, J.P.; Parneix, S. [Laboratoire MASTER-ENSCPB, 33 - Talence (France)
1997-12-31
The MASTER laboratory has been involved since several years in the creation and utilization of modeling tools for the prediction of 3-D turbulent flows and heat transfers in turbine blades in order to optimize the cooling systems of turbo-machineries. This paper describes one of the test-cases that has been used for the validation of the `Aquilon` calculation code developed in this aim. Then, the modeling performed with the `Fluent` industrial code in order to evaluate the possible improvements of the Aquilon code, is presented. (J.S.) 5 refs.
Energy Technology Data Exchange (ETDEWEB)
Leconte, M.
2008-11-15
The H confinement regime is set when the heating power reaches a threshold value P{sub c} and is linked to the formation of a transport barrier in the edge region of the plasma. Such a barrier is characterized by a high pressure gradient and is submitted to ELM (edge localized mode) instabilities. ELM instabilities trigger violent quasi-periodical ejections of matter and heat that induce quasi-periodical relaxations of the transport barrier called relaxation oscillations. In this work we studied the interaction between sheared flows and turbulence in fusion plasmas. In particular, we studied the complex dynamics of a transport barrier and we show through a simulation that resonant magnetic perturbations could control relaxation oscillations without a significant loss of confinement
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Graber, H [Commissariat a l' Energie Atomique, 91 - Saclay (France). Centre d' Etudes Nucleaires
1969-04-01
champ de temperature ainsi que le nombre de Nusselt en ecoulement laminaire et flux de chaleur constant. En ecoulement turbulent, les lois concernant la repartition de la diffusivite de quantite de mouvement dans un tube, etablies par H. Reichardt et adaptees a l'espace annulaire et au faisceau tubulaire, permettent la determination du champ de vitesse et du coefficient de perte de charge et consequemment la solution des equations de transfert de chaleur. Les resultats du calcul numerique sont rassembles dans des tableaux et representes par des diagrammes pour un domaine etendu des differents parametres et compares avec des resultats experimentaux. Par un procede simple, on peut determiner la valeur minimale de la longueur d'etablissement du regime thermique. (auteur)
Energy Technology Data Exchange (ETDEWEB)
Graber, H. [Commissariat a l' Energie Atomique, 91 - Saclay (France). Centre d' Etudes Nucleaires
1969-04-01
indiquees les equations pour le calcul explicite du champ de temperature ainsi que le nombre de Nusselt en ecoulement laminaire et flux de chaleur constant. En ecoulement turbulent, les lois concernant la repartition de la diffusivite de quantite de mouvement dans un tube, etablies par H. Reichardt et adaptees a l'espace annulaire et au faisceau tubulaire, permettent la determination du champ de vitesse et du coefficient de perte de charge et consequemment la solution des equations de transfert de chaleur. Les resultats du calcul numerique sont rassembles dans des tableaux et representes par des diagrammes pour un domaine etendu des differents parametres et compares avec des resultats experimentaux. Par un procede simple, on peut determiner la valeur minimale de la longueur d'etablissement du regime thermique. (auteur)
Energy Technology Data Exchange (ETDEWEB)
Viollet, P.L.
1995-06-01
The turbulent flows encountered in nuclear reactor thermal hydraulic studies or fossil-fired plant thermo-aerodynamic analyses feature widely varying characteristics, frequently entailing heat transfers and two-phase flows so that modelling these phenomena tends more and more to involve coupling between several branches of engineering. Multi-scale geometries are often encountered, with complex wall shapes, such as a PWR vessel, a reactor coolant pump impeller or a circulating fluidized bed combustion chamber. When it comes to validating physical models of these flows, the analytical process highlights the main descriptive parameters of local flow conditions: tensor characterizing the turbulence anisotropy, characteristic time scales for turbulent flow particle dynamics. Cooperative procedures implemented between national or international working parties can accelerate validation by sharing and exchanging results obtained by the various organizations involved. With this principle accepted, we still have to validate the products themselves, i.e. the software used for the studies. In this context, the ESTET, ASTRID and N3S codes have been subjected to a battery of test cases covering their respective fields of application. These test cases are re-run for each new version, so that the sets of test cases systematically benefit from the gradually upgraded functionalities of the codes. (author). refs., 3 figs., 6 tabs.
Energy Technology Data Exchange (ETDEWEB)
Burnage, H
1962-07-01
A theoretical study has been made of a fully developed turbulent flow in cylindrical tubing of circular cross-section subjected to a uniform suction through the walls. This study has made it possible to find a relationship giving the friction coefficient at the wall in terms of the amount of local suction and of the longitudinal static pressure gradient. A method for calculating the Reynolds tensions from the pressure measurements has been devised. An experimental system has been developed. Pressure measurements have been made. By using experimental results it has been possible to obtain a semi empirical expression for the friction coefficient at the wall, in terms of the amount of suction of the inlet Reynolds number, and of the abscissa. (author) [French] Une etude theorique de refoulement turbulent pleinement developpe dans une conduite cylindrique de section circulaire soumise a une aspiration parietale uniforme a ete entreprise. Elle a permis de trouver une relation donnant le coefficient de frottement a la paroi en fonction du taux d'aspiration local et du gradient de pression statique longitudinal. Une methode de calcul des tensions de Reynolds a partir des mesures de pression a ete etablie. Un dispositif experimental a ete realise et mis au point. Des mesures de pression ont ete effectuees. L'utilisation des resultats experimentaux a permis d'obtenir une expression semi-empirique du coefficient de frottement a la paroi en fonction du taux d'aspiration, du nombre de Reynolds d'entree et de l'abscisse. (auteur)
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Vermorel, O
2003-11-15
This work is devoted to the numerical and theoretical study of turbulence modulation by particles using direct numerical simulation for the continuous phase coupled with a Lagrangian prediction of trajectories of discrete particles. The configuration corresponds to a slab of particles injected at high velocity into an isotropic decaying turbulence. The motion of a particle is supposed to be governed only by the drag force. The particle mass loading is large so that momentum exchange between particles and fluid results in a significant modulation of the turbulence. Collisions are neglected. The momentum transfer between particles and gas causes a strong acceleration of the gas in the slab. In the periphery of the slab, the turbulence is enhanced due to the production by the mean gas velocity gradients. The analysis of the interphase transfer terms in the gas turbulent kinetic energy equation shows that the direct effect of the particles is to damp the turbulence in the core of the slab but to enhance it in the periphery. This last effect is due to a strong correlation between the particle distribution and the instantaneous gas velocity. Another issue concerns the k-{epsilon} model and the validity of its closure assumptions in two phase flows. A new eddy viscosity expression, function of particle parameters, is used to model the Reynolds stress tensor. The modelling of the gas turbulent dissipation rate is questioned. A two-phase Langevin equation is also tested to model drift velocity and fluid-particles velocity covariance equations. (author)
1991-07-01
Is 0.12- - -- often focussed on complex turbulent flows and the A -0.4y deficiencies of turbulence models in these cir- cumstances. However, turbulent...inherent deficiencies in stress discrepancies which have been traced to numer- ical errors, and as the collaboration and interac- LASHER, W.C.; TAULBEE, D.B...nIliio K I A ( tK2 .iWA Notiwcwiar Ivitit: 1kiciii. I’ stabi.in t \\MAIU(Attn: Itilioickrt DI11 :ni~h I ).Ih oItii li o I’.t ll) ’kOE 25 - \\cd Iitacispa
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Chandesris, M
2006-12-15
This work deals with the numerical simulation of turbulent flows in the whole nuclear reactor core, using multi-scale approaches. First, a macroscopic turbulence model is built, based on a porous media approach, to describe the flow in the fuel assemblies part of the nuclear core. Then, we study the jump conditions that have to be applied at a free fluid/porous interface. A thorough analytical study is carried out for laminar flows. This study allows to answer some fundamental questions about the physical meaning of the jump conditions, the values of the jump parameters and the location of the interface. Using these results, jump conditions for turbulent flows are proposed. The model is then applied to the simulation of a turbulent flow in a simplified model of a reactor core. (author)
Energy Technology Data Exchange (ETDEWEB)
Moussiere, S
2006-12-15
Supercritical water oxidation is an innovative process to treat organic liquid waste which uses supercritical water properties to mix efficiency the oxidant and the organic compounds. The reactor is a stirred double shell reactor. In the step of adaptation to nuclear constraints, the computational fluid dynamic modeling is a good tool to know required temperature field in the reactor for safety analysis. Firstly, the CFD modeling of tubular reactor confirms the hypothesis of an incompressible fluid and the use of k-w turbulence model to represent the hydrodynamic. Moreover, the EDC model is as efficiency as the kinetic to compute the reaction rate in this reactor. Secondly, the study of turbulent flow in the double shell reactor confirms the use of 2D axisymmetric geometry instead of 3D geometry to compute heat transfer. Moreover, this study reports that water-air mixing is not in single phase. The reactive turbulent flow is well represented by EDC model after adaptation of initial conditions. The reaction rate in supercritical water oxidation reactor is mainly controlled by the mixing. (author)
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Bastin, G.
2004-09-15
The aim of this study concerns the use of numerical methods for the resolution of the Reynolds Averaged Navier Stokes equations adapted to the simulation of the cooling of the trailing edge of a stator in a high pressure turbine. These methods, based on the elsA solver developed at ONERA, use a four steps Runge Kutta time discretization scheme and a Jameson centered space discretization scheme. The scheme is applied through a finite volume approach on control volume centered on the cells of a multi-block structured mesh. Turbulence is simulated either through the algebraic Michel model, or through the one-transport-equation Spalart-Allmaras model, or through the two-transport-equations k 1, k {omega} and k {epsilon} models, and through ASM model. A simulation of the flow in a bidimensional stator, without cooling, is carried out. The cooling, which is realized with trailing edge slots, is then simulated on a bidimensional stator. Because the slot is represented by meshes overlapping the mesh of the smooth blade, the Chimera method is chosen. This method makes it possible computations with overlapping meshes. The comparison with the experimental data, on these two first computations has validated this strategy to represent such slots. The tridimensional simulation of a single stator with taking account of the cooling is then realized. It showed the complex and tridimensional aspects of the main flow with focus on the influence of the cooling system. Finally two steady computations, without and with cooling, and an unsteady computation without cooling are carried out on a high pressure turbine stage. The comparison with the experimental data obtained in the frame of the European Brite-Euram program is made. These results make it possible to determine the effect of the cooling on the flow in a turbine stage. (authors)
Energy Technology Data Exchange (ETDEWEB)
Perroud, P; De La Harpe, A; Rebiere, J [Commissariat a l' Energie Atomique, Grenoble (France). Centre d' Etudes Nucleaires
1960-12-15
Two stainless steel tubes were used (with diameters of 5 and 10 mm, lengths 400 and 600 mm respectively), heated electrically (50 Hz). The mixture flows from top to bottom. The work was carried out mainly on mixtures of high concentration (x > 0.1), at pressures between 50 and 60 kg/cm{sup 2}, flowing as a liquid film on the walls of the tube with droplets suspended in the central current of steam. By analysis of the heat transfer laws the exchange mechanisms were established, and the conditions under which the critical heat flux may be exceeded without danger of actual burnout were determined. In this way high output concentrations (x{sub s} > 0.9) may be obtained. An attempt has been made to find out to what extent existing correlation formulae can be used to account for the phenomena observed. It is shown that those dealing with exchange coefficients can only be applied in a first approximation in cases where exchange by convection is preponderant, and only below the critical flux. The formulae proposed by WAPD and CISE do not give a satisfactory estimation of the critical heat flux, and the essential reasons for this inadequacy are explained. Lastly, the Martinelli and Nelson method may be used to an approximation of 30 per cent for the calculation of charge losses. (author) [French] On a utilise deux tubes en acier inox (avec des diametres de 5 et 10 mm, et des longueurs respectives 400 et 600 mm) chauffes electriquement (50 Hz). Le melange s'ecoule de haut en bas. Les etudes ont porte plus specialement sur des melanges de titres eleves (x > 0,1) a des pressions comprises entre 60 et 90 kg/cm{sup 2} dont l'ecoulement se fait avec film liquide annulaire et gouttelettes en suspension dans le coeur de vapeur. Par l'analyse des lois de transfert de chaleur, on a precise les mecanismes d'echanges et l'on a d'autre part determine dans quelles conditions le flux de chaleur critique peut etre depasse sans danger de 'burnout' proprement dit. On peut ainsi obtenir des
Popov, Andrei Vladimir
The aerospace industry is motivated to reduce fuel consumption in large transport aircraft, mainly through drag reduction. The main objective of the global project is the development of an active control system of wing airfoil geometry during flight in order to allow drag reduction. Drag reduction on a wing can be achieved through modifications in the laminar-to-turbulent flow transition point position, which should be situated as close as possible to the trailing edge of the airfoil wing. As the transition point plays a crucial part in this project, this work focuses on the control of its position on the airfoil, as an effect of controlling the deflection of a morphing wing airfoil equipped with a flexible skin. The paper presents the modeling and the experimental testing of the aerodynamic performance of a morphing wing, starting from the design concept phase all the way to the bench and wind tunnel tests phases. Several wind tunnel test runs for various Mach numbers and angles of attack were performed in the 6 x 9 ft2 wind tunnel at the Institute for Aerospace Research at the National Research Council Canada. A rectangular finite aspect ratio wing, having a morphing airfoil cross-section due to a flexible skin installed on the upper surface of the wing, was instrumented with Kulite transducers. The Mach number varied from 0.2 to 0.3 and the angle of attack between -1° and 2°. Unsteady pressure signals were recorded and analyzed and a thorough comparison, in terms of mean pressure coefficients and their standard deviations, was performed against theoretical predictions, using the XFoil computational fluid dynamics code. The acquired pressure data was analyzed through custom-made software created with Matlab/Simulink in order to detect the noise magnitude in the surface airflow and to localize the transition point position on the wing upper surface. This signal processing was necessary in order to detect the Tollmien-Schlichting waves responsible for triggering
Modeling of turbulent bubbly flows; Modelisation des ecoulements turbulents a bulles
Energy Technology Data Exchange (ETDEWEB)
Bellakhal, Ghazi
2005-03-15
The two-phase flows involve interfacial interactions which modify significantly the structure of the mean and fluctuating flow fields. The design of the two-fluid models adapted to industrial flows requires the taking into account of the effect of these interactions in the closure relations adopted. The work developed in this thesis concerns the development of first order two-fluid models deduced by reduction of second order closures. The adopted reasoning, based on the principle of decomposition of the Reynolds stress tensor into two statistically independent contributions turbulent and pseudo-turbulent parts, allows to preserve the physical contents of the second order relations closure. Analysis of the turbulence structure in two basic flows: homogeneous bubbly flows uniform and with a constant shear allows to deduce a formulation of the two-phase turbulent viscosity involving the characteristic scales of bubbly turbulence, as well as an analytical description of modification of the homogeneous turbulence structure induced by the bubbles presence. The Eulerian two-fluid model was then generalized with the case of the inhomogeneous flows with low void fractions. The numerical results obtained by the application of this model integrated in the computer code MELODIF in the case of free sheared turbulent bubbly flow of wake showed a satisfactory agreement with the experimental data and made it possible to analyze the modification of the characteristic scales of such flow by the interfacial interactions. The two-fluid first order model is generalized finally with the case of high void fractions bubbly flows where the hydrodynamic interactions between the bubbles are not negligible any more. (author)
Etude aerodynamique d'un jet turbulent impactant une paroi concave
LeBlanc, Benoit
Etant donne la demande croissante de temperatures elevees dans des chambres de combustion de systemes de propulsions en aerospatiale (turbomoteurs, moteur a reaction, etc.), l'interet dans le refroidissement par jets impactant s'est vu croitre. Le refroidissement des aubes de turbine permet une augmentation de temperature de combustion, ce qui se traduit en une augmentation de l'efficacite de combustion et donc une meilleure economie de carburant. Le transfert de chaleur dans les au bages est influence par les aspects aerodynamiques du refroidissement a jet, particulierement dans le cas d'ecoulements turbulents. Un manque de comprehension de l'aerodynamique a l'interieur de ces espaces confinees peut mener a des changements de transfert thermique qui sont inattendus, ce qui augmente le risque de fluage. Il est donc d'interet pour l'industrie aerospatiale et l'academie de poursuivre la recherche dans l'aerodynamique des jets turbulents impactant les parois courbes. Les jets impactant les surfaces courbes ont deja fait l'objet de nombreuses etudes. Par contre des conditions oscillatoires observees en laboratoire se sont averees difficiles a reproduire en numerique, puisque les structures d'ecoulements impactants des parois concaves sont fortement dependantes de la turbulence et des effets instationnaires. Une etude experimentale fut realisee a l'institut PPRIME a l'Universite de Poitiers afin d'observer le phenomene d'oscillation dans le jet. Une serie d'essais ont verifie les conditions d'ecoulement laminaires et turbulentes, toutefois le cout des essais experimentaux a seulement permis d'avoir un apercu du phenomene global. Une deuxieme serie d'essais fut realisee numeriquement a l'Universite de Moncton avec l'outil OpenFOAM pour des conditions d'ecoulement laminaire et bidimensionnel. Cette etude a donc comme but de poursuivre l'enquete de l'aerodynamique oscillatoire des jets impactant des parois courbes, mais pour un regime d'ecoulement transitoire, turbulent
Energy Technology Data Exchange (ETDEWEB)
Delayre, R; Saunier, J P [Commissariat a l' Energie Atomique, Saclay (France).Centre d' Etudes Nucleaires
1961-07-01
Experimental investigations of the instable behavior of a pressurized water flow in forced convection in a heating channel, with subcooled or bulk boiling have been carried. Tests were conducted at 1140, 850 and 570 psi. The test section was 35 in. high, surmounted by a 25.4 in. riser, these sections were by-passed by a pipe where the flow was between 1 and 4 times the flow in the test section. The water velocity (in the test section) was between 1.6 and 6.6 ft/s. Under certain conditions oscillations with a period of several seconds and perfectly stable have been observed. A mathematical model has been defined and a good agreement obtained for the main characteristics of the oscillations. It seems that the dimensions of the riser have a determining effect: the inception of bulk boiling gives an important variation of the driving head which can generate oscillations due to the non-zero delay for the system to reach its equilibrium. (author) [French] Une investigation experimentale des risques d'instabilite d'ecoulement d'eau sous pression dans un canal chauffant, avec ebullition sous refroidie ou en masse a ete faite. Les essais ont ete effectues a des pressions de 40, 60 et 80 kg/cm{sup 2}. La section d'essais d'une hauteur de 1,37m etait surmontee d'une cheminee de 1 m, le tout by-passe par une conduite ou le debit pouvait varier entre 1 et 4 fois le debit dans la section d'essais. La vitesse dans la section variait entre 0,5 et 2 m/s. Dans certaines conditions, des oscillations de periode de l'ordre de quelques secondes et parfaitement stables sont apparues. Un modele mathematique a permis de retrouver les principales caracteristiques de ces oscillations. Il semble que l'influence des dimensions de la cheminee soit determinante: en effet, l'apparition de l'ebullition de masse entraine une importante variation de la hauteur motrice qui peut engendrer des oscillations entretenues a cause du retard non nul a la mise en equilibre du systeme. (auteur)
Energy Technology Data Exchange (ETDEWEB)
Huyghe, J; Mondin, G [Commissariat a l' Energie Atomique, Grenoble (France). Centre d' Etudes Nucleaires
1962-07-01
The present study deals with measures of heat transfer and pressure drop in two-phase liquid flow. The stream is of annular dispersed type, obtained by introducing a small quantity of liquid in a gas turbulent flow. The heat transfer experiments are performed without vaporization of the liquid phase. A notable improvement of the heat transfer coefficient of such a stream is observed, compared with a gas-alone or liquid-alone flow. The improvement concerning the gas-alone is of about 20 when it is compared with the same gas Reynolds's number, of about 8 when it is compared with the same total mass flow rate. A hydrodynamic study of the flow pattern lets us know the original structure of the flow, and allows to foresee the experimental results by means of a simplified theory. (authors) [French] II est fait etat de mesures de transfert thermique et de perte de charge dans un ecoulement en double phase gaz-liquide. L'ecoulement est du type annulaire disperse, obtenu par injection d'une faible quantite de liquide dans un ecoulement gazeux en regime turbulent. Les experiences de transfert thermique sont menees sans vaporisation de la phase liquide. On note une amelioration sensible du coefficient de transfert thermique dans un tel ecoulement par rapport a un ecoulement de gaz seul ou de liquide seul. L'augmentation est de l'ordre de 20 par rapport au gaz seul si on opere a meme nombre de REYNOLDS du gaz, de l'ordre de 8 si on opere a meme debit massique total. Une etude hydrodynamique rapide de l'ecoulement permet de connaitre la structure originale de l'ecoulement, puis de prevoir par une theorie simplifiee le phenomene thermique observe. (auteurs)
Energy Technology Data Exchange (ETDEWEB)
Dano, C.
2003-01-15
The objective of this thesis is to evaluate k-e, k-l and k-w low Reynolds two equation turbulence models for. A quadratic nonlinear k-l model is also implemented in this study. We analyze the two equation turbulence models capacity to predict the turbomachinery flows and the wakes. We are interested more particularly in the unsteady three dimensional configuration with rotor-stator interactions. A Gaussian distribution reproduces the upstream wake. This analysis is carried out in term of prediction quality but also in term of numerical behavior. Turbines and compressors configurations are tested. (author)
Algorithmes de couplage RANS et ecoulement potentiel
Gallay, Sylvain
Dans le processus de developpement d'avion, la solution retenue doit satisfaire de nombreux criteres dans de nombreux domaines, comme par exemple le domaine de la structure, de l'aerodynamique, de la stabilite et controle, de la performance ou encore de la securite, tout en respectant des echeanciers precis et minimisant les couts. Les geometries candidates sont nombreuses dans les premieres etapes de definition du produit et de design preliminaire, et des environnements d'optimisations multidisciplinaires sont developpes par les differentes industries aeronautiques. Differentes methodes impliquant differents niveaux de modelisations sont necessaires pour les differentes phases de developpement du projet. Lors des phases de definition et de design preliminaires, des methodes rapides sont necessaires afin d'etudier les candidats efficacement. Le developpement de methodes ameliorant la precision des methodes existantes tout en gardant un cout de calcul faible permet d'obtenir un niveau de fidelite plus eleve dans les premieres phases de developpement du projet et ainsi grandement diminuer les risques associes. Dans le domaine de l'aerodynamisme, les developpements des algorithmes de couplage visqueux/non visqueux permettent d'ameliorer les methodes de calcul lineaires non visqueuses en methodes non lineaires prenant en compte les effets visqueux. Ces methodes permettent ainsi de caracteriser l'ecoulement visqueux sur les configurations et predire entre autre les mecanismes de decrochage ou encore la position des ondes de chocs sur les surfaces portantes. Cette these se focalise sur le couplage entre une methode d'ecoulement potentiel tridimensionnelle et des donnees de section bidimensionnelles visqueuses. Les methodes existantes sont implementees et leurs limites identifiees. Une methode originale est ensuite developpee et validee. Les resultats sur une aile elliptique demontrent la capacite de l'algorithme a de grands angles d'attaques et dans la region post
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Chatelain, A.
2004-09-15
LES of turbulent flows with heat transfer was used within the framework of conjugate heat transfer problems. The objective of this work lies not only in identifying the various elements likely to impair temperature fluctuations estimations at the fluid/solid interface but also to introduce adequate wall modeling. The choice of a proper convection scheme for the transport of passive scalars led to the adoption of a high order upwind scheme with slope limiter. The use of classical wall models having shown some weaknesses as for the estimation of parietal temperature fluctuations, two new approaches are proposed and tested. The first one relies on a complete resolution of the Navier-Stokes equations on a refined grid close to the wall making it possible to rebuild the temperature fluctuations near the wall. The second one relies on the simultaneous and one dimensional resolution of a turbulent boundary layer equation and a variance transport equation near the wall. (author)
Energy Technology Data Exchange (ETDEWEB)
Rieger, M [Commissariat a l' Energie Atomique, 91 - Saclay (France). Centre d' Etudes Nucleaires
1968-06-01
The heat transfer parameters were determined experimentally in electrically heated tube bundles for turbulent flow parallel to the axis. The tubes were arranged in a pattern of equilateral triangles. The ratios of the distance between the axes of the tubes to their external diameter were 1.60 and 1.25 in the two test sections studied. The experiments were carried out with distilled water and with a mixture of 60 per cent ethylene glycol and 40 per cent water. The values obtained for the Prandtl numbers in this way fell within the range from 2.3 to 18. The Reynolds numbers were varied between 10{sup 4} and 2.10{sup 5}. The relation between the mean heat transfer coefficients and the friction factor in the tube bundles was found from the experiments as: Nu = [Re Pr {zeta}/8]/[1+{radical}({zeta}/8) 8.8 (Pr-1.3) Pr{sup -0.22}]. The experimentally determined mean Nusselt numbers were also given by the following function: Nu = (0.0122 + 0.00245 p/d) Re{sup 0.86} Pr{sup 0.4}, with a maximum deviation of {+-}4 per cent. For certain local Nusselt numbers, deviations of up to 20 per cent with respect to the relations given were observed. (author) [French] Dans des faisceaux tubulaires a chauffage electrique parcourus par un ecoulement turbulent parallele a l'axe, on a determine experimentalement les parametres du transfert de chaleur. Les centres des sections droites des tubes etaient des sommets de triangles equilateraux. Les rapports de la distance a l'axe des tubes et leur diametre exterieur dans les deux veines de mesure etudiees etaient de 1.60 et 1.25. Des essais furent effectues avec de l'eau distillee ainsi qu'avec un melange de 60 pour cent de glycol ethylenique et 40 pour cent d'eau. Les valeurs des nombres de Prandtl obtenues ainsi etaient situees entre 2.3 a 18. On a fait varier les nombres de Reynolds entre 10{sup 4} et 2.10{sup 5}. La relation entre les nombres caracteristiques de transfert de chaleur moyens et la perte de charge dans les faisceaux tabulaires
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Reinhardt, B.; Duhamel, Ph.; Cordonnier, A. [FCB Centre de Recherches, 59 - Lille (France); Florent, P. [LAMIH/LMFE, 59 - Valenciennes (France)
1997-12-31
The cyclones used in cement industry generally have a diameter of 4 to 6 m. However, tests on cyclones bigger than 4 m can hardly be performed and thus, it is important to study the influence of the size of the apparatus on the development of the generated vortex. A study of the structure and characteristics of the suspension inside a cyclone has been carried out. The results of the characterization of two cyclones (400 and 800 mm diameter) running without load are presented first in order to study the vortex behaviour. In parallel with this experimental study, a numerical study has been carried out and a calculation code called CYCLOP has been developed. The code, the equations of the gas flow inside the cyclone and the modifications given to the turbulent model are presented. (J.S.) 4 refs.
On turbulence and the formation of riffle-pools in gravel-bed rivers
MacVicar, Bruce J.
Cette these doctorale porte sur l'organisation des rivieres a lit de graviers. La formation du lit en sequences a grande echelle---les sequences seuil-mouille---est une caracteristique de ces rivieres qui controle la stabilite et la productivite ecologique. Malgre son importance, le mecanisme qui genere les seuil-mouilles reste obscur. Ce probleme est lie a trois facteurs: les donnees de terrain qui existent ne sont pas suffisantes pour accepter ou rejeter les hypotheses qui existent, la complexite des interactions entre l'ecoulement, le transport des sediments, et les formes du lit; et le role de la turbulence qui n'est pas considere de facon adequate. L'approche de cette these est d'aborder ces facteurs simultanement avec des methodes innovatrices pour mesurer les parametres importants sur le terrain et de modeliser des processus non lineaires dans une riviere. Les objectifs sont: (a) de developper un modele qui est capable de simuler le transport des sediments et les interactions avec l'ecoulement turbulent, (b) en utilisant le modele, de montrer le role des mecanismes de retroaction dans le developpement des formes du lit, (c) de tester les velocimetres dans des ecoulements a fortes vitesses et fortes intensites turbulente, (d) de mesurer et caracteriser les dynamiques de l'ecoulement dans un seuil-mouille force, (e) de mesurer et caracteriser les dynamiques de la sedimentologie et la morphologie dans un seuil-mouille force, et (f) en utilisant le modele et l'analyse des donnees de terrain, d'identifier les mecanismes qui contribuent a la formation des seuils-mouilles. En considerant une riviere comme un systeme complexe, nous avons cree un modele qui simule le transport des sediments individuellement, c'est-a-dire un modele 'discret'. Les particules repondent aux parametres locaux de l'ecoulement et des boucles de retroaction sont possibles. Les processus physiques sont simplifies afin de permettre la consideration des mecanismes qui generent les formes du lit
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Boure, J [Commissariat a l' Energie Atomique, Grenoble (France). Centre d' Etudes Nucleaires
1963-07-01
A small disturbance is, shown to give rise to two waves: a pressure (sonic) wave and a continuity wave. Their propagation velocities are calculated. These velocities are independent of the disturbance amplitude. The sonic velocity is primarily a function of that one corresponding to the same medium with no flow and of the liquid phase velocity. It is also a function of the physical properties of the phases on the saturation line, of the slip laws and of the void fraction. The continuity wave velocity is only a function of the slip laws, of the void fraction and of the velocity of either phase. It appears two kinds of critical flow rates which are calculated. The void fraction and the liquid and gas velocities variations are calculated. These results are extended to the case of a real loop and an approximative method is given for the treatment of this case. (author) [French] On montre qu'une petite perturbation donne naissance a deux ondes: une onde de pression (onde sonique) et une onde de continuite. On calcule leurs vitesses de propagation qui sont independantes de l'amplitude de la perturbation. La vitesse du son depend des proprietes physiques des phases le long de la courbe de saturation, des lois du glissement, de la fraction volumique de vapeur. Elle depend surtout de la vitesse qu'il aurait dans le milieu immobile de meme fraction volumique de vapeur, et de la vitesse de la phase liquide. La vitesse de l'onde de continuite depend des lois du glissement, de la fraction volumique de vapeur et de la vitesse d'une des phases. Il apparait deux types de debits critiques que l'on calcule. On calcule egalement les variations de la fraction volumique de vapeur et des vitesses des phases dans la perturbation. On generalise des resultats precedents dans le cas d'un circuit reel et on propose une methode approchee pour traiter le probleme dans ce cas. (auteur)
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Pinson, F
2006-03-15
- This work deals with the macroscopic modeling of turbulence in porous media. It concerns heat exchangers, nuclear reactors as well as urban flows, etc. The objective of this study is to describe in an homogenized way, by the mean of a spatial average operator, turbulent flows in a solid matrix. In addition to this first operator, the use of a statistical average operator permits to handle the pseudo-aleatory character of turbulence. The successive application of both operators allows us to derive the balance equations of the kind of flows under study. Two major issues are then highlighted, the modeling of dispersion induced by the solid matrix and the turbulence modeling at a macroscopic scale (Reynolds tensor and turbulent dispersion). To this aim, we lean on the local modeling of turbulence and more precisely on the k - {epsilon} RANS models. The methodology of dispersion study, derived thanks to the volume averaging theory, is extended to turbulent flows. Its application includes the simulation, at a microscopic scale, of turbulent flows within a representative elementary volume of the porous media. Applied to channel flows, this analysis shows that even within the turbulent regime, dispersion remains one of the dominating phenomena within the macro-scale modeling framework. A two-scale analysis of the flow allows us to understand the dominating role of the drag force in the kinetic energy transfers between scales. Transfers between the mean part and the turbulent part of the flow are formally derived. This description significantly improves our understanding of the issue of macroscopic modeling of turbulence and leads us to define the sub-filter production and the wake dissipation. A
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Viollet, P L; Goussebaile, J [E.D.F, Laboratoire National d' Hydraulique, Chatou (France)
1983-07-01
Finite-difference methods have been developed for the two-dimensional computation of non-isothermal unsteady flows inside cavities with curved boundaries. The algorithm uses either u, v, P or u, v, {psi} formulations, and arbitrary non orthogonal curvilinear grids may be used. The turbulence modelling is tested for the case of a stratified two-layer flow with shear and the k-{epsilon} eddy viscosity and algebraic-stress models are compared. An example of unsteady density currents in a U-shaped pipe is given with comparison of experimental results. (author) [French] Cette note decrit succinctement les methodes de differences finies qui ont ete developpees pour le calcul bidimensionnel d'ecoulements non isothermes dans les cavites presentant des frontieres courbes. L'algorithme utilise les variables u, v, P ou u, v, {psi} et des maillages curvilignes non orthogonaux quelconques peuvent etre utiliss. La simulation de turbulence a deux equations est testee pour le cas d'un ecoulement horizontal stratifie: le modele k-{epsilon} standard est compare au modele avec expressions algebriques des flux turbulents. Enfin, un exemple de courants de densite instationnaires dans une tuyauterie en forme de U, pour lequel des resultats experimentaux sont disponibles, est presente. (author)
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NONE
1999-12-31
This conference day was organized by the `radiations` section of the French association of thermal engineers. This book of proceedings contains 8 papers entitled: `simultaneous temperature and NO concentration measurements in a hydrogen-air turbulent flame`; `application of iodine laser induced fluorescence to temperature, pressure and velocity measurements`; `Doppler phase measurement of refractive index and temperature`; `experimental and numerical study of temperature fields of particulates in plasma jets`; `measurement and determination of temperatures and concentrations of hot exhaust gases with FTIR emission spectroscopy`; `combustion control in gas turbines using CO{sub 2} emission spectroscopy`; `analysis of gases temperature fields and particulate jets. Application to hydrogen-air, kerosene stato-reactors and to solid propellant jets`; `restitution of temperature and species profiles in pre-mixing flames by inversion of transmission and IR emission data. (J.S.)
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NONE
1998-12-31
This conference day was organized by the `radiations` section of the French association of thermal engineers. This book of proceedings contains 8 papers entitled: `simultaneous temperature and NO concentration measurements in a hydrogen-air turbulent flame`; `application of iodine laser induced fluorescence to temperature, pressure and velocity measurements`; `Doppler phase measurement of refractive index and temperature`; `experimental and numerical study of temperature fields of particulates in plasma jets`; `measurement and determination of temperatures and concentrations of hot exhaust gases with FTIR emission spectroscopy`; `combustion control in gas turbines using CO{sub 2} emission spectroscopy`; `analysis of gases temperature fields and particulate jets. Application to hydrogen-air, kerosene stato-reactors and to solid propellant jets`; `restitution of temperature and species profiles in pre-mixing flames by inversion of transmission and IR emission data. (J.S.)
Directory of Open Access Journals (Sweden)
A KORICHI
2007-06-01
Full Text Available L’objet de cette publication est de présenter une étude de la caractéristique courant-tension d’une cellule solaire organique à base d’un composite poly (2-methoxy-5-(2’- ethylhexyloxy-1, 4-phenylenevinylene (MEH-PPV avec [6, 6]-phenyl C60 butyric acid methyl ester (PCBM en fonction de l’intensité d’illumination. La variation du photocourant, du facteur de forme, de la tension en circuit ouvert, du courant de saturation ainsi que de la puissance maximale de sortie sous différentes intensités lumineuses (100 mW/cm2, 60 mW/cm2 et 24 mW/cm2, sont examinés expérimentalement. Il est observé que pour des valeurs données de la résistance série et/ou la résistance shunt, le facteur de forme est déterminé par le courant inverse de saturation et le facteur d’idéalité de la cellule solaire. Les effets de ces composants, dans l’ensemble de performance photovoltaïque, sont discutés.
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Ravet, F. [Rouen Univ., 76 - Mont-Saint-Aignan (France)]|[SNECMA, 77 - Moissy-Cramayel (France); Baudoin, Ch.; Schultz, J.L. [SNECMA, 77 - Moissy-Cramayel (France)
1996-12-31
Simplifying hypotheses are required when combustion and aerodynamic phenomena are considered simultaneously. In this paper, a turbulent combustion model is proposed, in which the combustion chemistry is reduced to a single reaction. In this way, only two variables are needed to describe the problem and combustion can be characterized by the consumption of one of the two reactive species. In a first step, the instantaneous consumption rate is obtained using the Lagrangian form of the mass fraction equation of the species under consideration, and by considering the equilibrium state only. This state is determined in order to preserve the consistency with results that should be obtained using a complete kinetics scheme. In a second step, the average rate is determined using the instantaneous consumption term and a probabilistic density function. This model was tested on various configurations and in particular on an experimental main chamber and on a reheating chamber. Results indicate that this model could be used to predict temperature levels inside these combustion chambers. Other applications, like the prediction of pollutant species emission can be considered. (J.S.) 12 refs.
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Mhiri, H.; Habli, S.; El Golli, S. [Ecole Nationale d' Ingenieurs de Monastir (Tunisia); Le Palec, G.; Bournot, Ph. [Institut de Mecanique de Marseille (France)
1999-11-01
We intend to solve equations governing turbulent plane-vertical isotherm and non isotherm jets by taking into account inflow conditions at the exit of the nozzle. The analysis is focused on the influence of these conditions on this type of flow. Two cases are considered (uniform and parabolic velocity and temperature profiles). A finite difference scheme is developed to solve the governing equations. This numeric model allows us to show that the region of fully developed regime begins much nearer the nozzle for the turbulent case than for the laminar flow case. Indeed, the turbulence increases the mixing between the incoming gas from the nozzle and the ambient fluid, and consequently the size of the potential core zone decreases. The results are compared to other works introducing mathematical variables based on the energy conservation for the case of the mixed convection and the momentum conservation for the forced convection, which allows the validation of our results. (authors)
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Rambaud, P.
2001-11-01
The theme of this numerical thesis is on the behavior of solid particles embedded in a non-homogeneous and non-isotropic turbulent gas flow as the one tacking place in a plane channel. The turbulence is generated through the direct numerical simulation of Navier-Stokes equations discretized by formally second order in time and space finite difference operators. This Eulerian vision of the incompressible gas flow is completed by a Lagrangian formulation allowing to follow solid particles. In this formulation, the considered forces are the non-linear drag and the Saffman lift both corrected for wall effects. Furthermore, depending on the test cases studied, particle bouncing forces on the wall, gravity or electrostatic forces are taken into account. A three-dimensional Hermitian interpolation highlight the special care spend on the determination of the fluid velocity at the solid particle location. The first code application is dedicated to solid particles dispersion inside an horizontal channel, or in a channel operated in a weightlessness state. The huge amount of data from the Lagrangian tracking is reduced to the integral times of the turbulence seen by the solid particles on their trajectories. Those times are crucial in Lagrangian methods associated with a low numerical cost compared with the ones used in the present study. Among those methods, the one based on Langevin type equations have the best potential to handle industrial type problems. Nevertheless, this method needs to rebuild the fluid velocity fluctuations seen by the solid particles on their trajectories. This technic is able to reproduce the crossing trajectory effect, the inertial effect and the continuity effect, only if the integral times of the turbulence seen are known. Till now, those times were known thanks to a semi-empirical correlation from direct numerical simulation in homogeneous and isotropic turbulence (Wang and Stock 1993). However, although these conditions, this correlation was
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Chagras, V.
2004-03-15
The aim of this work is to contribute to the numerical modeling of turbulent gas-solid flows in vertical or horizontal non isothermal pipes, which can be found in many industrial processes (pneumatic transport, drying, etc). The model is based on an Eulerian-Lagrangian approach allowing a fine description of the interactions between the two phases (action of the fluid upon the particles (dispersion), action of the particles upon the fluid (two way coupling) and between particles (collisions)), more or less influential according to the characteristics of the flow. The influence of the gas phase turbulence on the particle motion is taken into account using a non-isotropic dispersion model, which allows the generation of velocity and temperature fluctuations of the fluid seen by the particles. The numerical developments brought to the model for vertical and horizontal pipe flow have been validated by comparison with available experimental results from the literature. The sensitivity tests highlight the influence of the dispersion model, collisions and turbulence modulation (direct and non direct modifications ) on the dynamic and thermal behavior of the suspension. The model is able to predict the heat exchanges in the presence of particles for a wide range of flows in vertical and horizontal pipes. However numerical problems still exist in two-way coupling for very small particles and loading ratios above one. This is related to the problems encountered when modeling the coupling terms between the two phases (parameters C{sub {epsilon}}{sub 2} and C{sub {epsilon}}{sub 3} ) involved in the turbulence dissipation balance. (author)
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Belletre, J.; Bataille, F.; Lallemaned, A. [Institut National des Sciences Appliquees (INSA), 69 - Villeurbanne (France)
1997-12-31
The effusion of a cold gas through a porous wall submitted to a hot turbulent parietal flow is studied in order to reduce the convective heat fluxes between the wall and the hot fluid. A modeling of the turbulent dynamical and thermal boundary layer is obtained using a RNG k-{epsilon} model. The cold gas injection through the porous plate and the fluid-wall friction are taken into account using a discrete succession of pores and solid elements. For a 1% injection rate, the modeling results agree with experiments performed in a test-duct. On the other hand, convective heat fluxes on the porous plate are calculated using semi-empirical correlations and different injection rates and temperatures of the hot flow. (J.S.) 23 refs.
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Jacques, R.; Le Quere, P.; Daube, O. [Centre National de la Recherche Scientifique (CNRS), 91 - Orsay (France)
1997-12-31
Turbulent flows between a fixed disc and a rotating disc are encountered in various applications like turbo-machineries or torque converters of automatic gear boxes. These flows are characterised by particular physical phenomena mainly due to the effects of rotation (Coriolis and inertia forces) and thus, classical k-{epsilon}-type modeling gives approximative results. The aim of this work is to study these flows using direct numerical simulation in order to provide precise information about the statistical turbulent quantities and to improve the k-{epsilon} modeling in the industrial MATHILDA code of the ONERA and used by SNECMA company (aerospace industry). The results presented are restricted to the comparison between results obtained with direct simulation and results obtained with the MATHILDA code in the same configuration. (J.S.) 8 refs.
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Benarafa, Y
2005-12-15
The main issue to perform a computational study of high Reynolds numbered turbulent flows consists on predicting their unsteadiness without implying a tremendous computational cost. First, the main drawbacks of large-eddy simulation with standard wall model on a coarse mesh for a plane channel flow are highlighted. To correct these drawbacks two coupling RANS/LES methods have been proposed. The first one relies on a sophisticated wall model (TBLE) which consists on solving Thin Boundary Layer Equations with a RANS type turbulent closure in the near wall region. The second one consists on a RANS/LES methods have been proposed. The second one consists on a RANS/LES coupling method using a forcing term approach. These various approaches have been implemented in the TRIO-U code developed at CEA (French Atomic Center) at Grenoble, France. The studied flow configurations are the fully developed plane channel flow and a flow around a surface-mounted cubical obstacle. Both approaches provide encouraging results and allow a surface-mounted cubical obstacle. Both approaches provide encouraging results and allow unsteady simulations for a low computational cost. (author)
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Garbet, X
2001-06-01
The purpose of this work is to introduce the main processes that occur in a magnetized plasma. During the last 2 decades, the understanding of turbulence has made great progress but analytical formulas and simulations are far to produce reliable predictions. The values of transport coefficients in a tokamak plasma exceed by far those predicted by the theory of collisional transport. This phenomenon is called abnormal transport and might be due to plasma fluctuations. An estimation of turbulent fluxes derived from the levels of fluctuations, is proposed. A flow description of plasma allows the understanding of most micro-instabilities. The ballooning representation deals with instabilities in a toric geometry. 3 factors play an important role to stabilize plasmas: density pinch, magnetic shear and speed shear. The flow model of plasma gives an erroneous value for the stability threshold, this is due to a bad description of the resonant interaction between wave and particle. As for dynamics, flow models can be improved by adding dissipative terms so that the linear response nears the kinetic response. The kinetic approach is more accurate but is complex because of the great number of dimensions involved. (A.C.)
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Lackme, C [Commissariat a l' Energie Atomique, Grenoble (France). Centre d' Etudes Nucleaires
1967-07-01
This report deals with the components and use of resistivity probes in bubble flow. With a single probe, we have studied the longitudinal and radial structure of the flow. The very complicated evolution of the radial structure is shown by the measurement of the mean bubble flux at several points in the tube. A double probe associated with a device the principle of which is given in this report, permits the measure of the local velocity of bubbles. Unlike the mean bubble flux profile, the change in the velocity profile along the tube is not significant. We have achieved the synthesis of these two pieces of information, mean local bubble flux and local velocity, by computing the mean weighed velocity in the tube. This weighed velocity compares remarkably with the velocity computed from the volumetric gas flow rate and the mean void fraction. (author) [French] Ce rapport traite d'une etude methodologique des ecoulements diphasiques a bulles. Les fluides sont l'air et l'eau, ils circulent du bas vers le haut dans un tube vertical de 32 mm de diametre et 2 metres de long. Cette etude a pour but de permettre une description fine de l'ecoulement. Pour cela, il a ete necessaire de developper des appareillages nouveaux et de mettre au point les methodes d'analyses correspondantes. La valeur des mesures effectuees et des methodes utilisees apparait dans une comparaison concluante et conclusive entre des resultats de mesures globales et des resultats integres de mesures locales. (auteur)
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Pelce, J [Commissariat a l' Energie Atomique, Saclay (France). Centre d' Etudes Nucleaires
1960-02-15
This report deals with the experimental study of forced heat convection in annular spaces through which flow of air is passing when a uniform heat flux is dissipated across the inner wall. These observations took place chiefly in the region where thermal equilibrium are not yet established. Amongst other things it became apparent that, both in the region where thermal equilibrium conditions are on the way to establishment and where they are already established, the following relationship held good: the longitudinal temperature gradient, either on the wall or in the fluid stream, is proportional to the heat flux dissipated q, and inversely proportional to the average flow rate V: dT/dx = B (q/V). From this result the next step is to express the variations of the local convection coefficient {alpha} (or of the Margoulis number M) in a relationship of the form: 1/M = {psi}(V) + F(x). If this relationship is compared with the classical empirical relationship {alpha} = KV{sup n} (where n is close to 0.8), the relationship: 1/M = {xi}V{sup 1-n} + F(x) is obtained ({xi} is a constant for a given annular space); from this it was possible to coordinate the whole set of experimental results. (author) [French] Il s'agit precisement de l'etude experimentale de la convection forcee de la chaleur dans des espaces annulaires parcourus par de l'air en ecoulement turbulent, lorsqu'on dissipe a travers la paroi interieure un flux de chaleur uniforme. Ces observations ont eu lieu principalement dans la region ou le regime thermique n'est pas encore etabli. Il est apparu, entre autre, qu'il existait, tant dans la region ou le regime thermique est en voie d'etablissement qu'en regime etabli, la relation suivante: le gradient longitudinal des temperatures, que ce soit sur la paroi ou dans l'ecoulement fluide, est proportionnel au flux de la chaleur dissipee q, et inversement proportionnel a la vitesse moyenne V de l'ecoulement: dT/dx = B (q/V). Ce resultat a pour consequence de traduire
Bailly, Christophe
2015-01-01
This book covers the major problems of turbulence and turbulent processes, including physical phenomena, their modeling and their simulation. After a general introduction in Chapter 1 illustrating many aspects dealing with turbulent flows, averaged equations and kinetic energy budgets are provided in Chapter 2. The concept of turbulent viscosity as a closure of the Reynolds stress is also introduced. Wall-bounded flows are presented in Chapter 3, and aspects specific to boundary layers and channel or pipe flows are also pointed out. Free shear flows, namely free jets and wakes, are considered in Chapter 4. Chapter 5 deals with vortex dynamics. Homogeneous turbulence, isotropy, and dynamics of isotropic turbulence are presented in Chapters 6 and 7. Turbulence is then described both in the physical space and in the wave number space. Time dependent numerical simulations are presented in Chapter 8, where an introduction to large eddy simulation is offered. The last three chapters of the book summarize remarka...
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Pietri, L.; Amielh, M.; Anselmet, F.; Fulachier, L. [Institut de Recherche sur les Phinomenes Hors Equilibre Equipe Turbulence, 13 - Marseille (France)
1997-12-31
Turbulent flows with strong density variations, like helium jets in the ambient air, have specific properties linked with the difference of gas densities. This paper presents some experimental results of turbulence properties inside such flows: the Reynolds tensions and the associated turbulent viscosity, and some characteristics linked with the statistical properties of the different turbulence scales. These last results allows to show the complexity of such flows characterized by the influence of external parameters (Reynolds number, initial density ratio, initial momentum flux) that govern the evolution of these parameters inside the jet from the nozzle up to regions where similarity properties are reached. (J.S.) 12 refs.
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Dubuit, N
2006-10-15
This work deals with the transport of impurities in magnetically confined thermonuclear plasmas. The accumulation of impurities in the core of the plasma would imply dramatic losses of energy that may lead to the extinction of the plasma. On the opposite, the injection of impurities in the plasma edge is considered as an efficient means to extract heat without damaging the first wall. The balance between these 2 contradictory constraints requires an accurate knowledge of the impurity transport inside the plasma. The effect of turbulence, the main transport mechanism for impurities is therefore a major issue. In this work, the complete formula of a turbulent flow of impurities for a given fluctuation spectrum has been inferred. The origin and features of the main accumulation processes have been identified. The main effect comes from the compressibility of the electrical shift speed in a plane perpendicular to the magnetic field. This compressibility appears to be linked to the curvature of the magnetic field. A less important effect is a thermal-diffusion process that is inversely proportional to the number of charges and then disappears for most type of impurities except the lightest. This effect implies an impurity flux proportional to the temperature gradient and its direction can change according to the average speed of fluctuations. A new version of the turbulence code TRB has been developed. This new version allows the constraints of the turbulence not by the gradients but by the flux which is more realistic. The importance of the processes described above has been confirmed by a comparison between calculation and experimental data from Tore-supra and the Jet tokamak. The prevailing role of the curvature of the magnetic field in the transport impurity is highlighted. (A.C.)
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Sarazin, Y
1997-11-21
The aim of this work is to propose a new frame to study turbulent transport in plasmas. In order to avoid the restraint of scale separability the forcing by flux is used. A critical one-dimension self-organized cellular model is developed. In keeping with experience the average transport can be described by means of diffusion and convection terms whereas the local transport could not. The instability due to interchanging process is thoroughly studied and some simplified equations are derived. The proposed model agrees with the following experimental results: the relative fluctuations of density are maximized on the edge, the profile shows an exponential behaviour and the amplitude of density fluctuations depends on ionization source strongly. (A.C.) 103 refs.
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Delhaye, J. [Commissariat a l' Energie Atomique, Grenoble (France). Centre d' Etudes Nucleaires
1968-07-01
The experimental knowledge of the local void-fraction is basic for the derivation of the constitutive equations of two-phase flows. This report deals with measurements of the local void-fraction based on the use of a constant temperature hot-film anemometer associated with a multichannel analyser. After determining the void-fraction profile along a diameter of a vertical pipe (40 mm I.D.), in which air and water flow upwards, we compare the void-fraction averaged over the diameter with the average value measured directly by a {gamma}-ray method. Two runs were made in bubble flow and a third in slug flow. The two methods give results in a good agreement especially for bubble flow. The void-fraction averaged over the cross-section was also calculated from the different profiles and compared in a good manner with the experimental results of R. ROUMY. For bubble flow we verified the theory of S.G. BANKOFF about the shape of the void-fraction profiles. (author) [French] Nous proposons une methode de mesure du taux de vide local a en ecoulement diphasique, basee sur l'emploi d'un anemometre a film chaud a temperature constante dont on etudie la repartition du signal en amplitude dans un analyseur multicanaux. Ayant trace un profil de taux de vide local suivant un diametre d'une conduite verticale de section circulaire parcourue par un ecoulement ascendant d'eau et d'air, nous avons compare la moyenne de {alpha} sur ce diametre a la valeur obtenue par une methode d'absorption de rayons {gamma}. Les essais ont ete faits en ecoulements a bulles et a bouchons. Les deux methodes donnent des resultats concordants en particulier pour les ecoulements a bulles. Le taux de vide moyenne dans la section, calcule a partir des differents profils, a egalement ete compare avec succes aux resultats experimentaux de R. ROUMY. Dans l'etude de la structure radiale des ecoulements a bulles, nous avons verifie l'hypothese de S.G. BAJMKOFF. (auteur)
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Delhaye, J [Commissariat a l' Energie Atomique, Grenoble (France). Centre d' Etudes Nucleaires
1968-07-01
The experimental knowledge of the local void-fraction is basic for the derivation of the constitutive equations of two-phase flows. This report deals with measurements of the local void-fraction based on the use of a constant temperature hot-film anemometer associated with a multichannel analyser. After determining the void-fraction profile along a diameter of a vertical pipe (40 mm I.D.), in which air and water flow upwards, we compare the void-fraction averaged over the diameter with the average value measured directly by a {gamma}-ray method. Two runs were made in bubble flow and a third in slug flow. The two methods give results in a good agreement especially for bubble flow. The void-fraction averaged over the cross-section was also calculated from the different profiles and compared in a good manner with the experimental results of R. ROUMY. For bubble flow we verified the theory of S.G. BANKOFF about the shape of the void-fraction profiles. (author) [French] Nous proposons une methode de mesure du taux de vide local a en ecoulement diphasique, basee sur l'emploi d'un anemometre a film chaud a temperature constante dont on etudie la repartition du signal en amplitude dans un analyseur multicanaux. Ayant trace un profil de taux de vide local suivant un diametre d'une conduite verticale de section circulaire parcourue par un ecoulement ascendant d'eau et d'air, nous avons compare la moyenne de {alpha} sur ce diametre a la valeur obtenue par une methode d'absorption de rayons {gamma}. Les essais ont ete faits en ecoulements a bulles et a bouchons. Les deux methodes donnent des resultats concordants en particulier pour les ecoulements a bulles. Le taux de vide moyenne dans la section, calcule a partir des differents profils, a egalement ete compare avec succes aux resultats experimentaux de R. ROUMY. Dans l'etude de la structure radiale des ecoulements a bulles, nous avons verifie l'hypothese de S.G. BAJMKOFF. (auteur)
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Roumy, R [Commissariat a l' Energie Atomique, Grenoble (France). Centre d' Etudes Nucleaires
1969-07-01
This report deals with experimental work on a two phase air-water mixture in vertical tubes of different diameters. The average void fraction was measured in a 2 metre long test section by means of quick-closing valves. Using resistive probes and photographic techniques, we have determined the flow patterns and developed diagrams to indicate the boundaries between the various patterns: independent bubbles, agglomerated bubbles, slugs, semi-annular, annular. In the case of bubble flow and slug flow, it is shown that the relationship between the average void fraction and the superficial velocities of the phases is given by: V{sub sg} = f(<{alpha}>) * g(V{sub sl}). The function g(V{sub sl}) for the case of independent bubbles has been found to be: g(V{sub sl}) = V{sub sl} + 20. For semi-annular and annular flow conditions; it appears that the average void fraction depends, to a first approximation only on the ratio V{sub sg}/V{sub sl}. (author) [French] Ce rapport est une etude experimentale d'un melange diphasique eau-air dans des tubes verticaux de differents diametres. Nous avons mesure la fraction de vide moyenne dans une portion de canal de longueur 2 m, au moyen d'un systeme de vannes a fermeture rapide et simultanee. Au moyen de sondes resistives et de photographies nous avons determine la configuration de l'ecoulement et trace des cartes donnant les frontieres entre les differentes configurations d'ecoulement: bulles independantes, bulles agglomerees, bouchons, semi-annulaire, annulaire. Nous montrons que pour les regimes a bulles et a bouchons, une equation de la forme V{sub sg} = f(<{alpha}>) * g(V{sub sl}) relie la fraction de vide moyenne aux vitesses superficielles de chacune des phases. Nous avons pu determiner la fonction g(V{sub sl}) dans le cas du regime a bulles independantes, et nous trouvons g(V{sub sl}) = V{sub sl} + 20. Pour les regimes semi-annulaire et annulaire, il semble qu'en premiere approximation, la fraction de vide moyenne ne depende que
Directory of Open Access Journals (Sweden)
Hemeidia A. M.
2006-11-01
puissances. Les calculs pour la conception de la canalisation ont été effectués sur ordinateur, à l'aide d'un programme, dans des conditions d'écoulement turbulent.
Energy Technology Data Exchange (ETDEWEB)
La Harpe, A de; Perroud, P [Commissariat a l' Energie Atomique, Grenoble (France).Centre d' Etudes Nucleaires
1961-07-01
Three different dispositions were used: a tube (diameter 4 mm, length 320 mm) and two annular spaces (3 x 8.8 and 5 x 8.8 mm, length 260 mm). The tubes are of stainless steel and are heated by a 50 cycle alternating current. The Reynolds number varied from 4000 to 120000, the wall temperature up to 700 deg. C, and the exit-temperature up to 500 deg. C. Heat flows of up to 170 W/cm{sup 2} were observed. All the experimental results can be summed up by a correlation expression of the Colburn type Nu = 0,020 Re{sup 0.8} Pr{sup 0.4}, as long as the physical properties of the gas are expressed at the film temperature t{sub 0.3} = t{sub m} + 0.3 (t{sub p} - t{sub m}). For each particular disposition, a more exact correlation has however been obtained. A variation of the film temperature index with the ratio of the heated to the wetted perimeters has been observed. The pressure loss coefficients measured are lightly higher than those calculated using von Karman formula for smooth tubes. (author) [French] On a utilise trois geometries differentes: tube (diametre 4 mm, longueur 320 mm) et deux espaces annulaires (3 x 8,8 et 5 x 8,8 mm, longueur 260 mm). Les tubes sont en acier inoxydable et chauffes en courant alternatif 50 Hz. Le nombre de Reynolds a varie de 4000 a 120000, la temperature de paroi jusqu'a 700 deg. C et la temperature de sortie de l'hydrogene jusqu'a 500 deg. C. On a observe des flux de chaleur atteignant 170 W/cm{sup 2}. L'ensemble des resultats experimentaux peut etre resume par la formule de correlation, type Colburn, Nu = 0,020 Re{sup 0,8} Pr{sup 0,4} a condition d'evaluer les proprietes physiques du gaz a la temperature de film t{sub 0.3} = t{sub m} + 0.3 (t{sub p} - t{sub m}). Pour chaque geometrie particuliere, une correlation plus precise a cependant pu etre obtenue. On note une variation de l'indice de la temperature de film avec le rapport du perimetre chauffant au perimetre mouille. Les coefficients de perte de charge mesures sont legerement plus grands que ceux calcules par la formule de von Karman valable pour les tubes lisses. (auteur)
Energy Technology Data Exchange (ETDEWEB)
Sarazin, Y
2004-03-01
This document gathers the lectures made in the framework of a Ph.D level physics class dedicated to plasma physics. This course is made up of 3 parts : 1) collisions and transport, 2) transport and turbulence, and 3) study of a few exchange instabilities. More precisely the first part deals with the following issues: thermonuclear fusion, Coulomb collisions, particles trajectories in a tokamak, neo-classical transport in tokamaks, the bootstrap current, and ware pinch. The second part involves: particle transport in tokamaks, quasi-linear transport, resonance islands, resonance in tokamaks, from quasi to non-linear transport, and non-linear saturation of turbulence. The third part deals with: shift velocities in fluid theory, a model for inter-change instabilities, Rayleigh-Benard instability, Hasegawa-Wakatani model, and Hasegawa-Mima model. This document ends with a series of appendices dealing with: particle-wave interaction, determination of the curvature parameter G, Rossby waves.
Energy Technology Data Exchange (ETDEWEB)
Payan, J
1994-05-01
After a review of turbulence and transport phenomena in tokamak plasmas and the radial electric field shear effect in various tokamaks, experimental measurements obtained at Tore Supra by the means of the ALTAIR plasma diagnostic technique, are presented. Electronic drift waves destabilization mechanisms, which are the main features that could describe the experimentally observed microturbulence, are then examined. The effect of a radial electric field shear on electronic drift waves is then introduced, and results with ohmic heating are studied together with relations between turbulence and transport. The possible existence of ionic waves is rejected, and a spectral frequency modelization is presented, based on the existence of an electric field sheared radial profile. The position of the inversion point of this field is calculated for different values of the mean density and the plasma current, and the modelization is applied to the TEXT tokamak. The radial electric field at Tore Supra is then estimated. The effect of the ergodic divertor on turbulence and abnormal transport is then described and the density fluctuation radial profile in presence of the ergodic divertor is modelled. 80 figs., 120 refs.
Energy Technology Data Exchange (ETDEWEB)
Urbin, Gerald [Institut National Polytechnique, 38 - Grenoble (France)
1998-02-02
This study highlights the potentialities of the numerical technique of large scale simulation in describing and understanding the turbulent flows in a complex geometry. Particularly, it is focussed on flows of free jet, confined jets and multiple jets of high solidity grid. Spatial simulations of the circular zone close to a free jet, of high Reynolds number were performed. In spite of an evident sensitivity to upstream conditions good agreement between our statistical predictions and different experimental measurements was obtained. The multiple coherent vortical structures implied in the transition to turbulence of the jet were found. At the same time, helical or annular axisymmetric vortices were observed. Also, an original vortical arrangement was evidenced, resulting from the alternating inclination and local pairing of these rings. It could been forced through an ad-hoc excitation which modifies subsequently drastically the jet development. When an axisymmetric excitation is imposed after formation of annular structures, pairs of counter-rotative longitudinal vortices occur and generate lateral jets. Their nature and presence in case of a helical excitation are discussed. An efficient method for controlling their number is developed. Then, one is studied the very low frequency periodic phenomenon of backward-facing transition to turbulence which develops in the confined jet and grid multiple jets (a phenomenon generic in numerous flows). It was found to depend not only on the characteristic of the re-circulation (pre-transition) zones but also on the upstream flow (zone of post-transition stagnation, pressure effect). Large scale transversal motions of the fluid have been found beginning from the grid. An interpretation of this phenomenon is suggested 193 refs., 109 figs.
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Rousseau, J C [Commissariat a l' Energie Atomique, Saclay (France). Centre d' Etudes Nucleaires
1965-07-01
A study is made of the problem of the flow-rate and pressure distributions along the length of two volumes, internal and external, bounded by a series of non-continuous annular elements placed along the channel axis. It is observed that the phenomenon can easily be represented by equations. The theoretical expressions observed are particularly simple when the distances between the elements are above a certain minimum value. The experimental work has made it possible to show that the theoretical formulation derived is valid with a very great accuracy. The experimental study has also been carried out in the case of a very small spacing between the elements. It has been possible to show in this case that the hypothesis made for deriving the theoretical expressions was perfectly justified. In the last part finally, we consider the practical problem of evaluating the pressure-drops between the ends of a series of annular elements. (author) [French] On etudie le probleme de la repartition des debits et des pressions le long des deux espaces, interne et externe, delimites par une succession d'elements annulaires non jointifs, disposes suivant l'axe d'un canal. On constate que le phenomene peut etre mis aisement en equation. Les relations theoriques obtenues prennent en particulier une forme simple lorsque les intervalles entre elements sont superieurs a une valeur minimum. L'etude experimentale a permis de constater que cette formulation theorique etablie etait alors valable avec une precision excellente. L'etude experimentale a ete egalement effectuee dans le cas de tres faibles intervalles entre elements consecutifs. On a pu alors verifier que l'hypothese adoptee dans l'etablissement des relations theoriques etait parfaitement justifiee. Dans un dernier chapitre enfin, nous abordons le point de vue pratique de l'evaluation des pertes de charge aux bornes d'un train d'elements annulaires. (auteur)
Energy Technology Data Exchange (ETDEWEB)
Rousseau, J.C. [Commissariat a l' Energie Atomique, Saclay (France). Centre d' Etudes Nucleaires
1965-07-01
A study is made of the problem of the flow-rate and pressure distributions along the length of two volumes, internal and external, bounded by a series of non-continuous annular elements placed along the channel axis. It is observed that the phenomenon can easily be represented by equations. The theoretical expressions observed are particularly simple when the distances between the elements are above a certain minimum value. The experimental work has made it possible to show that the theoretical formulation derived is valid with a very great accuracy. The experimental study has also been carried out in the case of a very small spacing between the elements. It has been possible to show in this case that the hypothesis made for deriving the theoretical expressions was perfectly justified. In the last part finally, we consider the practical problem of evaluating the pressure-drops between the ends of a series of annular elements. (author) [French] On etudie le probleme de la repartition des debits et des pressions le long des deux espaces, interne et externe, delimites par une succession d'elements annulaires non jointifs, disposes suivant l'axe d'un canal. On constate que le phenomene peut etre mis aisement en equation. Les relations theoriques obtenues prennent en particulier une forme simple lorsque les intervalles entre elements sont superieurs a une valeur minimum. L'etude experimentale a permis de constater que cette formulation theorique etablie etait alors valable avec une precision excellente. L'etude experimentale a ete egalement effectuee dans le cas de tres faibles intervalles entre elements consecutifs. On a pu alors verifier que l'hypothese adoptee dans l'etablissement des relations theoriques etait parfaitement justifiee. Dans un dernier chapitre enfin, nous abordons le point de vue pratique de l'evaluation des pertes de charge aux bornes d'un train d'elements annulaires. (auteur)
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Santon, L; Vernier, Ph [Commissariat a l' Energie Atomique, Grenoble (France). Centre d' Etudes Nucleaires
1961-07-01
For heat transfer studies in certain cases of cooling in swimming-pool type nuclear reactors, a knowledge of the distribution of the velocities between two heating elements is of prime importance. A Pitot tube and a micro-manometer have been developed for making these measurements on an experimental model. (authors) [French] Pour l'etude du transfert de chaleur dans certains cas de refroidissement des reacteurs nucleaires du type piscine, la connaissance de la repartition des vitesses entre deux elements chauffants est primordiale. On a mis au point un tube de Pitot et un micromanometre pour effectuer ces mesures sur une maquette experimentale. (auteurs)
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Louahlia, H.; Panday, P.K. [Institut de Genie Energetique, 90 - Belfort (France)
1997-12-31
This paper presents a comparison between turbulence models based on Prandtl theory and applied to the problem of pure fluids condensation. A theoretical model is defined which allows to determine the physical characteristics of condensation between two vertical or horizontal flat plates. The total heat flux exchanged at the wall and the mean Nusselt number are calculated using several closure models in the liquid and vapor phases. Calculation results obtained for the R123 condensation between two vertical plates show that the Pletcher`s model or the Groenwald and Kroeger`s one applied to the vapor flow and the Von Karman`s model used for the liquid film predict thermal fluxes close to the measured ones. It has been noticed also that the condensation heat transfer is underestimated in the laminar model. In the case of the R113 condensation on an horizontal flat plate, the mean Nusselt numbers estimated in the Pletcher`s model applied to both phases are close to the measurements performed by Lu and Suryanarayana. (J.S.) 12 refs.
Energy Technology Data Exchange (ETDEWEB)
Dondainas, N
1998-07-01
This study concerns the calculation methods relative to wall heat transfers in the simulation of air flows inside rooms. Today, there is a real need for a low cost predictive and reliable tool for the prediction of air flows inside buildings or air-conditioned rooms. However, the validity of results is highly dependent to the models used, in particular for the heat and pulse exchanges on walls. This study comprises 3 parts. The first part concerns the convective exchanges. An evaluation of 5 wall turbulence models is made (logarithmic functions model, non-equilibrium model, two-layers model, Lam and Bremhorst low-Reynolds model and modified Lam model). Comparison with experiment is performed on two test cases of the literature: the Cheesewright cavity in natural convection and the Blay cavity in mixed convection. A particular attention is paid to the mesh dependence of results and to the convergence of calculations. The second part concerns the radiant heat transfers between the walls of a room. A new method, called scale change method, is developed for the evaluation of radiant transfers. This method generalizes the fictive cell and radiosity methods. The energy conservation and exchange reciprocity principles are respected. The new method is not a zonal but a field method because net radiant fluxes calculated for each cell wall are variable (the walls are not isothermal). An evaluation of three methods is performed (ray tracing, fictive cell, and the new method) on 4 test cases in 2-D and 3-D geometry with and without mask effect. A particular attention is paid to the processing cost. The third part deals with the study of a real scale atrium. Three air-conditioning configurations are studied. An important part of the study concerns the convection-radiation coupling. Its advantage is to reject the boundary conditions outside the room. (J.S.)
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Grangers, S.; Campistron, R.; Lebret, J.
1994-09-01
This paper deals with the physical mechanisms inducing motion-development dynamic fluid forces in a tube array subject to water cross-flow. Three configurations have been tested. In the first one, a single flexible tube was positioned in the middle of an array of rigid cylinders; in the second one, a single flexible tube was positioned in the first row of an array of rigid cylinders; in the third one, the first three rows of the array were flexible, the other cylinders being rigid. Tube response measurements were analyzed by the inverse methodology developed at EDF/R and D D/HTA and implemented into the IMENE and MEIDEE softwares. This methodology allows for studying the variation of the fluid-structure system eigenvalues with flow velocity. From the information, motion-dependent fluid forces can also be estimated. The results of these analyses are compared to previously published data and to the theoretical results obtained with a slightly extended version of the Lever and Weaver analytical model. The main conclusions which can be drawn are as follows: -for each configuration tested, dynamic instabilities occur which induce sudden large amplitude motions for certain flow velocities; -these instabilities seem to result from the interaction of various physical mechanisms; two of them have been clearly identified: they are (i) a single mode flutter phenomenon and (ii) a complex interaction between tube motion and a symmetric vortex shedding; in the last case, tube oscillations regenerate a flow periodicity which had been damped out by flow turbulence when the tube was motionless, then the shed vortices act in turn on tube motion and precipitate the dynamic instability; -in the configurations tested, the location of the flexible tube within the array has a major influence on the development of low-structure interaction; -the Lever and Weaver model gives interesting qualitative trends but the quantitative results are not good. (authors). 22 refs., 20 figs., 1 appendix.
1999-02-01
traitement du signal fournit effectivement un effort nul. La pression initiale dans la fosse pi est mesuree par un capteur statique eau - eau . Pour...est de plusieurs minutes en presence d’ecoulement et avec une interface air- eau de grande surface. L’hypothese principale du modele elementaire...fonction des parametres de similitude. A l’aide d’un traitement d’images on peut extraire des visualisations le contour exterieur des bulles et en
Directory of Open Access Journals (Sweden)
Dullien F. A. L.
2006-12-01
Full Text Available The main classes of separators of particulates from gases comprise inertial separators, filters, (wet scrubbers and electrostatic precipitators, each of which technique has its proper niche and each has its advantages and its disadvantages. In the present paper a new class of equipment, the turbulent flow precipitator (TFP for gas cleaning is described that, though at the present only in its infancy, is rapidly gaining popularity because it has some advantages over each and every known type of separator and it has very few limitations. TFPs are far more efficient for the removal of fine particles than inertial separators, unlike filters they do not plug up, they do not present secondary disposal problems and they require less maintenance (and are less expensive than electrostatic precipitators. They can be very efficient also in the submicron range of particle size and there are no practical limitations as far as high temperatures and/or corrosive atmospheres are concerned. They are equally suitable for the removal of solid and liquid particles from gases. Turbulent flow precipitators work on the principle of turbulent eddy penetration into deep regions where there is no net flow, where the eddies die out and where the fine particulates carried by the eddies deposit on collector surfaces. TFPs comprise two well defined regions:- straight, uniform and unobstructed flow passages in which the gas carrying the suspended fine particulates is passed in turbulent flow;- and adjacent collection regions where there is no net gas flow and where all of the separation of particles from the gas takes place. Hence, a TFP is a filter in which the separation of the particulates from the gas takes place outside the passages where the gas flows. Les principaux séparateurs de particules dans un courant de gaz existants sur le marché sont les séparateurs par inertie, les filtres, les laveurs et les électrofiltres. Chaque type de séparateur est destiné à une
Ecoulement et mise en structure de suspensions macroscopiques
Petit, L.
In this review, we report the various experimental studies performed on suspensions of solid particules in liquids, and concerning the rheological behaviour of such systems and the ordering of particules under the applied velocity fields. The number of materials which are flowing suspensions (reagents in chemical engineering, paints while spreading, blood flow, muds in oil reservoir) gave rise to a number of experimental studies, especially in the last twenty years. The results show a wide variety of behaviour, even for systems of intermediate concentration. In addition, even for identical systems, the results depend of the type of flow. Then, it is clear that, in addition of the standard parameters which are to be taken into account, it is necessary to consider the type of flow the suspension is submitted to. The flow influences the spatial distribution of the particules, leading to their ordering or migration. These ordering or motions influence the flow, and then, the rheological behaviour of the whole system. So, there is a feedback mechanism from the ordering to the flow, which explains the experimental observations. Nous reportons dans cette revue les différentes études expérimentales réalisées sur les suspensions de particules solides dans un liquide et qui concernent le comportement rhéologique de ces systèmes ainsi que les mouvements des particules sous l'effet des champs de vitesse imposés. Ces mouvements peuvent conduire soit à des mises en structure, ou encore à des migrations des particules. L'importance du nombre de matériaux qui se présentent sous forme de suspension et qui sont mis en écoulement (réactif en génie chimique, peintures lors de leur mise en place, écoulement sanguin, boues dans les forages pétroliers,...) a motivé un grand nombre de travaux expérimentaux plus fondamentaux sur le sujet, particulièrement dans les vingt dernières années. Les résultats correspondants montrent une très grande diversité des
Energy Technology Data Exchange (ETDEWEB)
Lusseyran, Francois
1990-12-13
This research thesis reports the study and description of the structure of a slug flow regime in a co-current vertical cylindrical duct, and the characterization and prediction of its transition towards a slug-churn (de-structured) regime. Flow physical mechanisms highlighted by the measurement of two important dynamics variables (wall friction and thickness of liquid films) are related to hypotheses of cellular models. The author first proposes an overview of slug flow regimes: theoretical steady and one-dimensional analysis, mass assessment equations of cellular models, application to the assessment of the flow rate and of the thickness of the film surrounding the gas slug. In the second part, the author addresses the slug flow regime transition towards the slug-churn regime: assessment of the evolution of flow dynamic properties, use of average wall friction analysis to obtain a relevant transition criterion. The third part presents experimental conditions, and measurement methods: conductometry for thickness measurement, polarography for wall friction measurement, and gas phase detection by using an optic barrier or optic fibres [French] Les ecoulements gaz-liquide en conduite verticale presentent quatre configurations ou regimes d'ecoulement. Ce travail porte sur le regime a poches et sur la transition vers la configuration qui lui succede: le regime destructure (churn flow). Les mesures sont effectuees a 200D du point d'injection du gaz, dans une conduite de 12.2 mm de diametre et pour le couple de fluides eau-azote. Les deux principales grandeurs mesurees en fonction des flux d'entree sont: le frottement parietal instantane (methode electrochimique) et l'epaisseur de film instantanee (methode conductimetrique). Une detection optique simultanee de la presence des phases permet un traitement conditionnel de la base de donnees. Les caracteristiques de la cellule moyenne representative de chaque point de fonctionnement en sont deduites: longueur de la cellule
Stirring turbulence with turbulence
Cekli, H.E.; Joosten, R.; van de Water, W.
2015-01-01
We stir wind-tunnel turbulence with an active grid that consists of rods with attached vanes. The time-varying angle of these rods is controlled by random numbers. We study the response of turbulence on the statistical properties of these random numbers. The random numbers are generated by the
Energy Technology Data Exchange (ETDEWEB)
Delhaye, J M [Commissariat a l' Energie Atomique, 38 - Grenoble (France). Centre d' Etudes Nucleaires
1968-12-01
equations concerning different methods of presenting two-phase flows with those proposed in the literature. As a result a detailed study has been made of the work of C.G. TELETOV, S.S. KUTATELADZE, M.A. STYRIKOVICH and N. ZUBER; a summary of this work presented. (author) [French] Ce rapport traite des equations generales de conservation de la masse, de la quantite de mouvement et de l'energie pour un ecoulement diphasique. Ces equations sont presentees sous plusieurs formes a partir des equations integrales qui sont posees a priori. 1. Equations aux variables locales instantanees et conditions d'interface; 2. Equations aux variables instantanees moyennees dans une section et applications pratiques: ces equations renferment une donnee experimentale interessante qui est le rapport de la section de passage d'une phase sur la section totale d'une conduite. 3. Equations aux moyennes statistiques locales et equations moyennees dans le temps: une tentative plus poussee pour relier experience et theorie consiste a prendre les moyennes statistiques des equations locales. On obtient alors des equations ou interviennent des variables moyennees dans le temps par application d'une hypothese ergodique. 4. Combinaisons des moyennes statistiques et des moyennes dans une section: on considere dans cette etude des variables locales moyennees statistiquement, puis moyennees dans la section et egalement des variables moyennees dans la section puis moyennees statistiquement. 5. Equations generales relatives aux emulsions: dans ce cas, une phase se presente (localement sous un aspect tres divise. Cette particularite permet de definir une concentration volumique locale et d'etablir des equations aux applications multiples. On a complete et precise certains points de la premiere partie de ce rapport concernant les equations generales de conservation des ecoulements diphasiques. On a introduit dans les equations generales les termes correspondant a la tension interfaciale. Les conditions d
Energy Technology Data Exchange (ETDEWEB)
Delhaye, J.M. [Commissariat a l' Energie Atomique, 38 - Grenoble (France). Centre d' Etudes Nucleaires
1968-12-01
equations concerning different methods of presenting two-phase flows with those proposed in the literature. As a result a detailed study has been made of the work of C.G. TELETOV, S.S. KUTATELADZE, M.A. STYRIKOVICH and N. ZUBER; a summary of this work presented. (author) [French] Ce rapport traite des equations generales de conservation de la masse, de la quantite de mouvement et de l'energie pour un ecoulement diphasique. Ces equations sont presentees sous plusieurs formes a partir des equations integrales qui sont posees a priori. 1. Equations aux variables locales instantanees et conditions d'interface; 2. Equations aux variables instantanees moyennees dans une section et applications pratiques: ces equations renferment une donnee experimentale interessante qui est le rapport de la section de passage d'une phase sur la section totale d'une conduite. 3. Equations aux moyennes statistiques locales et equations moyennees dans le temps: une tentative plus poussee pour relier experience et theorie consiste a prendre les moyennes statistiques des equations locales. On obtient alors des equations ou interviennent des variables moyennees dans le temps par application d'une hypothese ergodique. 4. Combinaisons des moyennes statistiques et des moyennes dans une section: on considere dans cette etude des variables locales moyennees statistiquement, puis moyennees dans la section et egalement des variables moyennees dans la section puis moyennees statistiquement. 5. Equations generales relatives aux emulsions: dans ce cas, une phase se presente (localement sous un aspect tres divise. Cette particularite permet de definir une concentration volumique locale et d'etablir des equations aux applications multiples. On a complete et precise certains points de la premiere partie de ce rapport concernant les equations generales de conservation des ecoulements diphasiques. On a introduit dans les equations generales les termes correspondant a la tension
Energy Technology Data Exchange (ETDEWEB)
El Kabiri, M.; Paranthoen, P.; Rosset, L.; Lecordier, J.C. [Rouen Univ., 76 - Mont-Saint-Aignan (France)
1997-12-31
An experimental study of heat transport downstream of a linear source installed in a turbulent boundary layer is performed. Second and third order momenta of velocity and temperature fields are presented and compared to gradient-type modeling. (J.S.) 7 refs.
Energy Technology Data Exchange (ETDEWEB)
Maille, C.; Moinard, J. [Societe Steinet Roubaix, Paris (France); Blanc, D.; Fontan, J. [Faculte des Sciences, Toulouse (France)
1963-03-15
The circulation inside an industrial boiler depends cm the flow-rate and on the specific gravity of the water-steam emulsion. Conventional methods for measuring flow-rate in screen tubes require complex devices and may disturb the phenomenon under study. The employment of an external radioactive source and detector for densitometry measurements is simple and in common use. Unfortunately, it is difficult to use in the present case. The authors have therefore developed a method consisting of the introduction of a calculated amount of sodium-24 into the boiler water. This very simple device does not disturb the flow. The experimental design, built up at die test station of Stein and Roubaix Co., is described. Sodium-24 gives consistent results, although less accurate than the densitometric process using an external source of Co{sup 60}. Investigations are now being made on a series of parallel tubes with the geometry, used in industrial boilers. (author) [French] La circulation a l'interieur d'une chaudiere industrielle est conditionnee par la vitesse d'ecoulement et le poids specifique, de l'emulsion (eau - vapeur). Les procedes classiques de mesure de la vitesse d'ecoulement dans les tubes d'ecrans necessitent des montages difficiles et risquent de perturber le phenomene a mesurer. L'emploi d'une source radioactive externe est un procede simple et courant de densimetrie; il est helas difficile a adapter dans le cas actuel. C'est pourquoi les auteurs ont adopte une technique qui consiste a Introduire dans l'eau de la chaudiere une quantite calculee de sodium-24. Ce procede, tres simple, ne perturbe pas l'ecoulement. Les auteurs decrivent le montage experimental realise a la station d'essais de la Societe Stein et Roubaix. La methode du sodium-24 conduit a des resultats coherents, bien que moins precis que le procede densime- trique employant une source externe de MCo. Les etudes en cours concernent une serie de tubes paralleles, disposes selon la geometrie adoptee
Energy Technology Data Exchange (ETDEWEB)
Sapet, J C [Commissariat a l' Energie Atomique, Saclay (France). Centre d' Etudes Nucleaires
1962-12-15
The research which makes up this thesis is concerned both with the problems of adsorption an chromatographic columns and of catalysis, which involve the surface properties of these solids, and with problems of isotope separation by gaseous diffusion. In this latter case, the flow in the two-dimensional adsorbed phase is a secondary phenomenon but it is nevertheless necessary to know its influence on the separation factor. Up to the present time very little work has been published on this subject, the importance of which needs no stressing. The author has devised very sensitive techniques making it possible to study the flow of two-dimensional phases in micro-porous bodies. He has demonstrated not only the role of the relative pressure and of the nature of the components (gas and solid) but also the relationship between the mobility of the adsorbate and the thermodynamic characteristics of the adsorption. The author has treated numerous examples involving the diffusion either of pure gases (n-butane, n-pentane, isopentane), or of binary mixtures, and has shown on the one hand that the separative effect of the two-dimensional flow at the interface is a maximum in the neighbourhood of the monolayer, and on the other hand that the mass effect is of the second order with respect to the structural factor of the diffusing molecule. The problem considered is of importance both from a fundamental point of view and from that of its industrial applications. (author) [French] Le sujet de travail de cette these interesse aussi bien les problemes d'adsorption sur colonne de chromatographie et de catalyse, qui font intervenir directement les proprietes superficielles des solides, que ceux concernant la separation isotopique par diffusion gazeuse. Dans ce dernier cas l'ecoulement en phase adsorbee bidimensiormelle est un phenomene secondaire dont i1 faut cependant connaitre l'effet sur le facteur de separation. Pratiquement aucun travail fondamental n'a encore ete publie sur ce
Energy Technology Data Exchange (ETDEWEB)
Labit, B
2002-10-01
In a fusion machine, understanding plasma turbulence, which causes a degradation of the measured energy confinement time, would constitute a major progress in this field. In tokamaks, the measured ion and electron thermal conductivities are of comparable magnitude. The possible sources of turbulence are the temperature and density gradients occurring in a fusion plasma. Whereas the heat losses in the ion channel are reasonably well understood, the origin of the electron losses is more uncertain. In addition to the radial velocity associated to the fluctuations of the electric field, electrons are more affected than ions by the magnetic field fluctuations. In experiments, the confinement time can be conveniently expressed in terms of dimensionless parameters. Although still somewhat too imprecise, these scaling laws exhibit strong dependencies on the normalized pressure {beta} or the normalized Larmor radius, {rho}{sub *}. The present thesis assesses whether a tridimensional, electromagnetic, nonlinear fluid model of plasma turbulence driven by a specific instability can reproduce the dependence of the experimental electron heat losses on the dimensionless parameters {beta} and {rho}{sub *}. The investigated interchange instability is the Electron Temperature Gradient driven one (ETG). The model is built by using the set of Braginskii equations. The developed simulation code is global in the sense that a fixed heat flux is imposed at the inner boundary, leaving the gradients free to evolve. From the nonlinear simulations, we have put in light three characteristics for the ETG turbulence: the turbulent transport is essentially electrostatic; the potential and pressure fluctuations form radially elongated cells called streamers; the transport level is very low compared to the experimental values. The thermal transport dependence study has shown a very small role of the normalized pressure, which is in contradiction with the Ohkama's formula. On the other hand
Energy Technology Data Exchange (ETDEWEB)
Sanders, H.; Gokalp, I. [Centre National de la Recherche Scientifique (CNRS), 45 - Orleans-la-Source (France). Laboratoire de Combustion Systemes Reactifs
1996-12-31
The suitability of the turbulent combustion flamelets model in order to predict the index of NO{sub x} production in turbulent flames of hydrogen diffusion is analyzed. In the flamelet approach, the turbulent flame is equivalent to a group of laminar flames submitted to a mechanical stretching which generates a chemical disequilibrium. This effect can be described by the stretching or by the scalar dissipation ratio. A numerical modeling is performed in order to evaluate the advantages of both approaches and to compare the behaviour of the NO{sub x} emission index with the experiments of Chen and Driscoll. This study shows that predictions of NO{sub x} emission indexes have a correct behaviour with respect to the Damkoehler number only when the scalar dissipation ratio is used as a parameter to describe the chemical state outside equilibrium. Predictions of the flamelet models are improving when the Damkoehler number increases. On the other hand, the absolute NO{sub x} concentrations are overestimated and can be due to the effects of differential diffusion. (J.S.) 14 refs.
Energy Technology Data Exchange (ETDEWEB)
Coste, D. [Commissariat a l' Energie Atomique, Saclay (France). Centre d' Etudes Nucleaires
1964-07-01
With a view to determining the changes occurring in gas reactors after cooling accidents, a calculation programme is established for unidimensional gas flows with pressure drops, heat exchanges and in certain cases blowing, in a reticulated lattice. Any schematization can be taken into account by the use of a set of indices. This programme, of which the FORTRAN list is given, is applied to particular cases of sudden pressure drops in the circuits. The results obtained are in good agreement with those obtained both from the graphical method using the characteristics and from experimental recorded data. (author) [French] En vue de determiner les evolutions des reacteurs a gaz apres accident de refroidissement, on etablit un programme de calcul pour les ecoulements gazeux unidimensionnels avec pertes de charge, echanges thermiques et eventuellement soufflage, en reseau maille. Toute schematisation peut etre prise en compte grace a un jeu d'indices. Ce programme, dont la liste FORTRAN est presentee, est applique a des cas particuliers de degonflage brutal de circuits. Ses resultats sont en bon accord, d'une part avec ceux de la methode graphique des caracteristiques, d'autre part avec des enregistrements experimentaux. (auteur)
Energy Technology Data Exchange (ETDEWEB)
Coste, D [Commissariat a l' Energie Atomique, Saclay (France). Centre d' Etudes Nucleaires
1964-07-01
With a view to determining the changes occurring in gas reactors after cooling accidents, a calculation programme is established for unidimensional gas flows with pressure drops, heat exchanges and in certain cases blowing, in a reticulated lattice. Any schematization can be taken into account by the use of a set of indices. This programme, of which the FORTRAN list is given, is applied to particular cases of sudden pressure drops in the circuits. The results obtained are in good agreement with those obtained both from the graphical method using the characteristics and from experimental recorded data. (author) [French] En vue de determiner les evolutions des reacteurs a gaz apres accident de refroidissement, on etablit un programme de calcul pour les ecoulements gazeux unidimensionnels avec pertes de charge, echanges thermiques et eventuellement soufflage, en reseau maille. Toute schematisation peut etre prise en compte grace a un jeu d'indices. Ce programme, dont la liste FORTRAN est presentee, est applique a des cas particuliers de degonflage brutal de circuits. Ses resultats sont en bon accord, d'une part avec ceux de la methode graphique des caracteristiques, d'autre part avec des enregistrements experimentaux. (auteur)
Magnetohydrodynamic turbulence
Biskamp, Dieter
2003-01-01
This book presents an introduction to, and modern account of, magnetohydrodynamic (MHD) turbulence, an active field both in general turbulence theory and in various areas of astrophysics. The book starts by introducing the MHD equations, certain useful approximations and the transition to turbulence. The second part of the book covers incompressible MHD turbulence, the macroscopic aspects connected with the different self-organization processes, the phenomenology of the turbulence spectra, two-point closure theory, and intermittency. The third considers two-dimensional turbulence and compressi
International Nuclear Information System (INIS)
Donnelly, R.J.
1988-01-01
Most flows of fluids, in nature and in technology, are turbulent. Since much of the energy expended by machines and devices that involve fluid flows is spent in overcoming drag caused by turbulence, there is a strong motivation to understand the phenomena. Surprisingly, the peculiar, quantum-mechanical form of turbulence that can form in superfluid helium may turn out to be much simpler to understand that the classical turbulence that forms in normal fluids. It now seems that the study of superfluid turbulence may provide simplified model systems for studying some forms of classical turbulence. There are also practical motivations for studying superfluid turbulence. For example, superfuid helium is often used as a coolant in superconducting machinery. Superfluid turbulence is the primary impediment to the transfer of heat by superfluid helium; an understanding of the phenomena may make it possible to design more efficient methods of refrigeration for superconducting devices. 8 figs
Energy Technology Data Exchange (ETDEWEB)
Duplat, F
1998-10-26
In the frame of nuclear safety studies about corium and water interactions, we address spreading and cooling stage of corium fragments in a liquid pool. Considering the complexity of encountered flow regimes and mechanical and thermal interactions coupling, modelling validation is based on a thermal-hydraulic computer code (MC3D). A bibliographical study shows that classical modelling of three phase flow is based on constitutive laws already established in the case of two phase flow. The present study states a complete analysis of BILLEAU experiments and defines a characterisation method for a sphere cloud. Some complementary QUEOS experiments are also described. Mechanical interaction terms such as added mass, lift and turbulent dispersion have been presented in the frame of a three phase flow and their influence has been tested in numerical simulations of BILLEAU tests. The effect of film vapour overheat, as well as particle diameter evolution have been studied. Moreover a radiative heat transfer modelling developed in Karlsruhe research centre (FZK) has been analysed and completed. Numerical simulations achieved for this study show that mechanical and thermal behaviour of the system are actually coupled. Taking into account lift and turbulent dispersion terms as well as heat transfer modifications all wed better results. This study also presents some considerations about flow regimes identification as a preliminary for studies about numerical diffusion that was already estimated in the present state of the computer code MC3D. (author)
Energy Technology Data Exchange (ETDEWEB)
Boure, J [Commissariat a l' Energie Atomique, Grenoble (France).Centre d' Etudes Nucleaires
1961-07-01
It is shown, for a swimming-pool type pile cooled by forced convection (general flow downwards), that a permanently stable regime with downward flow in all the channels is not possible when the flow is below a critical value for a given power. In the hot channels the natural convection then becomes preponderant, the direction of the flow is reversed and a permanently stable regime exists for which the flow is upwards in the hot channels. Calculations are made, with simplifying hypotheses in the case of Melusine. (author) [French] Pour une pile piscine refrigeree en convection forcee (ecoulement global descendant), on montre qu'un regime permanent stable avec ecoulement descendant dans tous les canaux est impossible lorsque le debit est inferieur a une valeur critique pour une puissance donnee. Dans les canaux chauds, la convection naturelle l'emporte alors, le sens du courant s'inverse et un regime permanent stable existe, pour lequel le courant est ascendant dans les canaux chauds. On fait les calculs, avec des hypotheses simplificatrices, dans le cas de Melusine. (auteur)
Energy Technology Data Exchange (ETDEWEB)
Grandotto Biettoli, M
2006-04-15
The report presents globally the works done by the author in the thermohydraulic applied to nuclear reactors flows. It presents the studies done to the numerical simulation of the two phase flows in the steam generators and a finite element method to compute these flows. (author)
Energy Technology Data Exchange (ETDEWEB)
Adoua, S.R
2007-07-15
This work is devoted to the study of an oblate spheroidal bubble of prescribed shape set fixed in a linear shear flow using direct numerical simulation. The three dimensional Navier-Stokes equations are solved in orthogonal curvilinear coordinates using a finite volume method. The bubble response is studied over a wide range of the aspect ratio (1-2.7), the bubble Reynolds number (50-2000) and the non-dimensional shear rate (0.-1.2). The numerical simulations shows that the shear flow imposes a plane symmetry of the wake whatever the parameters of the flow. The trailing vorticity is organized into two anti-symmetrical counter rotating tubes with a sign imposed by the competition of two mechanisms (the Lighthill mechanism and the instability of the wake). Whatever the Reynolds number, the lift coefficient reaches the analytical value obtained in an inviscid, weakly sheared flow corresponding to a lift force oriented in the same direction as that of a spherical bubble. For moderate Reynolds numbers, the direction of the lift force reverses when the bubble aspect ratio is large enough as observed in experiments. This reversal occurs for aspect ratios larger than 2.225 and is found to be directly linked to the sign of the trailing vorticity which is concentrated within two counter-rotating threads which propel the bubble in a direction depending of their sign of rotation. The behavior of the drag does not revel any significant effect induced by the wake structure and follows a quadratic increase with the shear rate. Finally, the torque experienced by the bubble also reverses for the same conditions inducing the reversal of the lift force. By varying the orientation of the bubble in the shear flow, a stable equilibrium position is found corresponding to a weak angle between the small axis of the bubble and the flow direction. (author)
EuHIT, Collaboration
2015-01-01
As a member of the EuHIT (European High-Performance Infrastructures in Turbulence - see here) consortium, CERN is participating in fundamental research on turbulence phenomena. To this end, the Laboratory provides European researchers with a cryogenic research infrastructure (see here), where the first tests have just been performed.
International Nuclear Information System (INIS)
Horton, W.
1998-07-01
The origin of plasma turbulence from currents and spatial gradients in plasmas is described and shown to lead to the dominant transport mechanism in many plasma regimes. A wide variety of turbulent transport mechanism exists in plasmas. In this survey the authors summarize some of the universally observed plasma transport rates
Energy Technology Data Exchange (ETDEWEB)
Nazarenko, Sergey [Warwick Univ., Coventry (United Kingdom). Mathematics Inst.
2011-07-01
Wave Turbulence refers to the statistical theory of weakly nonlinear dispersive waves. There is a wide and growing spectrum of physical applications, ranging from sea waves, to plasma waves, to superfluid turbulence, to nonlinear optics and Bose-Einstein condensates. Beyond the fundamentals the book thus also covers new developments such as the interaction of random waves with coherent structures (vortices, solitons, wave breaks), inverse cascades leading to condensation and the transitions between weak and strong turbulence, turbulence intermittency as well as finite system size effects, such as ''frozen'' turbulence, discrete wave resonances and avalanche-type energy cascades. This book is an outgrow of several lectures courses held by the author and, as a result, written and structured rather as a graduate text than a monograph, with many exercises and solutions offered along the way. The present compact description primarily addresses students and non-specialist researchers wishing to enter and work in this field. (orig.)
Hanratty, Thomas J.
1980-01-01
This paper gives an account of research on the structure of turbulence close to a solid boundary. Included is a method to study the flow close to the wall of a pipe without interferring with it. (Author/JN)
CERN. Geneva. Audiovisual Unit
2005-01-01
Understanding turbulence is vital in astrophysics, geophysics and many engineering applications, with thermal convection playing a central role. I shall describe progress that has recently been made in understanding this ubiquitous phenomenon by making controlled experiments using low-temperature helium, and a brief account of the frontier topic of superfluid turbulence will also be given. CERN might be able to play a unique role in experiments to probe these two problems.
Tchen, C. M.
1986-01-01
Theoretical and numerical works in atmospheric turbulence have used the Navier-Stokes fluid equations exclusively for describing large-scale motions. Controversy over the existence of an average temperature gradient for the very large eddies in the atmosphere suggested that a new theoretical basis for describing large-scale turbulence was necessary. A new soliton formalism as a fluid analogue that generalizes the Schrodinger equation and the Zakharov equations has been developed. This formalism, processing all the nonlinearities including those from modulation provided by the density fluctuations and from convection due to the emission of finite sound waves by velocity fluctuations, treats large-scale turbulence as coalescing and colliding solitons. The new soliton system describes large-scale instabilities more explicitly than the Navier-Stokes system because it has a nonlinearity of the gradient type, while the Navier-Stokes has a nonlinearity of the non-gradient type. The forced Schrodinger equation for strong fluctuations describes the micro-hydrodynamical state of soliton turbulence and is valid for large-scale turbulence in fluids and plasmas where internal waves can interact with velocity fluctuations.
Graphite suspension in carbon dioxide; Suspension de graphite dans le gaz carbonique
Energy Technology Data Exchange (ETDEWEB)
Roche, R [Commissariat a l' Energie Atomique, Saclay (France). Centre d' Etudes Nucleaires; Moussez, C; Rouvillois, X; Brevet, R [Societe Nationale d' Etude et de Construction de Moteurs d' Aviation (SNECMA), 75 - Paris (France)
1965-07-01
Since 1963 the Atomic Division of SNECMA has been conducting, under a contract with the CEA, an experimental work with a two-component fluid comprised of carbon dioxide and small graphite particles. The primary purpose was the determination of basic engineering information pertaining to the stability and the flowability of the suspension. The final form of the experimental loop consists mainly of the following items: a light-phase compressor, a heavy-phase pump, an electrical-resistance type heater section, a cooling heat exchanger, a hairpin loop, a transparent test section and a separator. During the course of the testing, it was observed that the fluid could be circulated quite easily in a broad range of variation of the suspension density and velocity - density from 30 to 170 kg/m{sup 3} and velocity from 2 to 24 m/s. The system could be restarted and circulation maintained without any difficulty, even with the heavy-phase pump alone. The graphite did not have a tendency to pack or agglomerate during operation. No graphite deposition was observed on the wall of the tubing. A long period run (250 hours) has shown the evolution of the particle dimensions. Starting with graphite of surface area around 20 m{sup 2}/g (graphite particles about 1 {mu}), the powder surface area reaches an asymptotic value of 300 m{sup 2}/g (all the particles less than 0.3 {mu}). Moisture effect on flow stability, flow distribution between two parallel channels, pressure drop in straight tubes, recompression ratio in diffusers were also investigated. (author) [French] Depuis 1963 la Division Atomique de la SNECMA conduit, dans le cadre d'un contrat avec le Commissariat A l'Energie Atomique, l'etude experimentale d'une suspension de fines particules de graphite dans le gaz carbonique. L'objectif principal est d'obtenir des informations d'ordre mecanique et technologique sur la mise en oeuvre de l'ecoulement de ce fluide diphase. Le circuit experimental comprend principalement: un
International Nuclear Information System (INIS)
Drury, L.O.; Stewart, J.M.
1976-01-01
A generalization of a transformation due to Kurskov and Ozernoi is used to rewrite the usual equations governing subsonic turbulence in Robertson-Walker cosmological models as Navier-Stokes equations with a time-dependent viscosity. This paper first rederives some well-known results in a very simple way by means of this transformation. The main result however is that the establishment of a Kolmogorov spectrum at recombination appears to be incompatible with subsonic turbulence. The conditions after recombination are also discussed briefly. (author)
Energy Technology Data Exchange (ETDEWEB)
Sarh, B.; Gokalp, I.; Sanders, H. [Centre National de la Recherche Scientifique (CNRS), 45 - Orleans-la-Source (France)
1997-12-31
In the framework of the studies carried out by the LCSR on variable density flows and diffusion turbulent flames, this paper deals with the study of the influence of density variation on the characteristics of a heated rectangular turbulent jet emerging in a stagnant surrounding atmosphere and more particularly on the determination of turbulent viscosity. The dynamical field is measured using laser-Doppler anemometry while the thermal field is measured using cold wire anemometry. A numerical predetermination of the characteristics of this jet, based on a k-{epsilon} modeling, is carried out. (J.S.) 6 refs.
DEFF Research Database (Denmark)
Nielsen, Mogens Peter; Shui, Wan; Johansson, Jens
2011-01-01
term with stresses depending linearly on the strain rates. This term takes into account the transfer of linear momentum from one part of the fluid to another. Besides there is another term, which takes into account the transfer of angular momentum. Thus the model implies a new definition of turbulence...
Strongly coupled dispersed two-phase flows; Ecoulements diphasiques disperses fortement couples
Energy Technology Data Exchange (ETDEWEB)
Zun, I.; Lance, M.; Ekiel-Jezewska, M.L.; Petrosyan, A.; Lecoq, N.; Anthore, R.; Bostel, F.; Feuillebois, F.; Nott, P.; Zenit, R.; Hunt, M.L.; Brennen, C.E.; Campbell, C.S.; Tong, P.; Lei, X.; Ackerson, B.J.; Asmolov, E.S.; Abade, G.; da Cunha, F.R.; Lhuillier, D.; Cartellier, A.; Ruzicka, M.C.; Drahos, J.; Thomas, N.H.; Talini, L.; Leblond, J.; Leshansky, A.M.; Lavrenteva, O.M.; Nir, A.; Teshukov, V.; Risso, F.; Ellinsen, K.; Crispel, S.; Dahlkild, A.; Vynnycky, M.; Davila, J.; Matas, J.P.; Guazelli, L.; Morris, J.; Ooms, G.; Poelma, C.; van Wijngaarden, L.; de Vries, A.; Elghobashi, S.; Huilier, D.; Peirano, E.; Minier, J.P.; Gavrilyuk, S.; Saurel, R.; Kashinsky, O.; Randin, V.; Colin, C.; Larue de Tournemine, A.; Roig, V.; Suzanne, C.; Bounhoure, C.; Brunet, Y.; Tanaka, A.T.; Noma, K.; Tsuji, Y.; Pascal-Ribot, S.; Le Gall, F.; Aliseda, A.; Hainaux, F.; Lasheras, J.; Didwania, A.; Costa, A.; Vallerin, W.; Mudde, R.F.; Van Den Akker, H.E.A.; Jaumouillie, P.; Larrarte, F.; Burgisser, A.; Bergantz, G.; Necker, F.; Hartel, C.; Kleiser, L.; Meiburg, E.; Michallet, H.; Mory, M.; Hutter, M.; Markov, A.A.; Dumoulin, F.X.; Suard, S.; Borghi, R.; Hong, M.; Hopfinger, E.; Laforgia, A.; Lawrence, C.J.; Hewitt, G.F.; Osiptsov, A.N.; Tsirkunov, Yu. M.; Volkov, A.N.
2003-07-01
This document gathers the abstracts of the Euromech 421 colloquium about strongly coupled dispersed two-phase flows. Behaviors specifically due to the two-phase character of the flow have been categorized as: suspensions, particle-induced agitation, microstructure and screening mechanisms; hydrodynamic interactions, dispersion and phase distribution; turbulence modulation by particles, droplets or bubbles in dense systems; collective effects in dispersed two-phase flows, clustering and phase distribution; large-scale instabilities and gravity driven dispersed flows; strongly coupled two-phase flows involving reacting flows or phase change. Topic l: suspensions particle-induced agitation microstructure and screening mechanisms hydrodynamic interactions between two very close spheres; normal stresses in sheared suspensions; a critical look at the rheological experiments of R.A. Bagnold; non-equilibrium particle configuration in sedimentation; unsteady screening of the long-range hydrodynamic interactions of settling particles; computer simulations of hydrodynamic interactions among a large collection of sedimenting poly-disperse particles; velocity fluctuations in a dilute suspension of rigid spheres sedimenting between vertical plates: the role of boundaries; screening and induced-agitation in dilute uniform bubbly flows at small and moderate particle Reynolds numbers: some experimental results. Topic 2: hydrodynamic interactions, dispersion and phase distribution: hydrodynamic interactions in a bubble array; A 'NMR scattering technique' for the determination of the structure in a dispersion of non-brownian settling particles; segregation and clustering during thermo-capillary migration of bubbles; kinetic modelling of bubbly flows; velocity fluctuations in a homogeneous dilute dispersion of high-Reynolds-number rising bubbles; an attempt to simulate screening effects at moderate particle Reynolds numbers using an hybrid formulation; modelling the two
Energy Technology Data Exchange (ETDEWEB)
Boudjemadi, R.
1996-03-01
The main objectives of this thesis are the direct numerical simulation of natural convection in a vertical differentially heated slot and the improvements of second-order turbulence modelling. A three-dimensional direct numerical simulation code has been developed in order to gain a better understanding of turbulence properties in natural convection flows. This code has been validated in several physical configurations: non-stratified natural convection flows (conduction solution), stratified natural convection flows (double boundary layer solution), transitional and turbulent Poiseuille flows. For the conduction solution, the turbulent regime was reached at a Rayleigh number of 1*10{sup 5} and 5.4*10{sup 5}. A detailed analysis of these results has revealed the principal qualities of the available models but has also pointed our their shortcomings. This data base has been used in order to improve the triple correlations transport models and to select the turbulent time scales suitable for such flows. (author). 122 refs., figs., tabs., 4 appends.
National Oceanic and Atmospheric Administration, Department of Commerce — Forecast turbulence hazards identified by the Graphical Turbulence Guidance algorithm. The Graphical Turbulence Guidance product depicts mid-level and upper-level...
Graphical Turbulence Guidance - Composite
National Oceanic and Atmospheric Administration, Department of Commerce — Forecast turbulence hazards identified by the Graphical Turbulence Guidance algorithm. The Graphical Turbulence Guidance product depicts mid-level and upper-level...
Magnetohydrodynamic Turbulence
Montgomery, David C.
2004-01-01
Magnetohydrodynamic (MHD) turbulence theory is modeled on neutral fluid (Navier-Stokes) turbulence theory, but with some important differences. There have been essentially no repeatable laboratory MHD experiments wherein the boundary conditions could be controlled or varied and a full set of diagnostics implemented. The equations of MHD are convincingly derivable only in the limit of small ratio of collision mean-free-paths to macroscopic length scales, an inequality that often goes the other way for magnetofluids of interest. Finally, accurate information on the MHD transport coefficients-and thus, the Reynolds-like numbers that order magnetofluid behavior-is largely lacking; indeed, the algebraic expressions used for such ingredients as the viscous stress tensor are often little more than wishful borrowing from fluid mechanics. The one accurate thing that has been done extensively and well is to solve the (strongly nonlinear) MHD equations numerically, usually in the presence of rectangular periodic boundary conditions, and then hope for the best when drawing inferences from the computations for those astrophysical and geophysical MHD systems for which some indisputably turbulent detailed data are available, such as the solar wind or solar prominences. This has led to what is perhaps the first field of physics for which computer simulations are regarded as more central to validating conclusions than is any kind of measurement. Things have evolved in this way due to a mixture of the inevitable and the bureaucratic, but that is the way it is, and those of us who want to work on the subject have to live with it. It is the only game in town, and theories that have promised more-often on the basis of some alleged ``instability''-have turned out to be illusory.
Energy Technology Data Exchange (ETDEWEB)
Fenzi, Ch
1999-10-29
In magnetic fusion devices, the optimisation of the power deposition profile on plasma facing components crucially depends on the heat diffusivity across the magnetic field fines, which is determined by the plasma edge turbulence. In this regard, spatial asymmetries of plasma edge turbulence are of great interest. In this work, we interest in up-down asymmetries of density fluctuations which are usually observed in Tore Supra, using a coherent light scattering experiment. It is shown that these asymmetries are correlated to the plasma edge geometrical configuration (plasma facing components, limiters). In fact, the plasma-limiter interaction induces locally in the plasma edge and the SOL (r/a > 0.9) an additional turbulence with short correlation length along the magnetic field fines, which spreads in the plasma core (0.9 {>=} r/a {>=} 0.5). The resultant up-down asymmetry weakly depends on density, increases with the edge safety factor, and inverts when the plasma current direction is reversed. Such up-down asymmetry observations bring strong impact on edge turbulence and transport models, which usually predict a ballooning of the turbulence in the high-field side but not an up-down asymmetry. A possible model is proposed here, based on the Kelvin Helmholtz instability. (author)
High Reynolds Number Turbulence
National Research Council Canada - National Science Library
Smits, Alexander J
2007-01-01
The objectives of the grant were to provide a systematic study to fill the gap between existing research on low Reynolds number turbulent flows to the kinds of turbulent flows encountered on full-scale vehicles...
DEFF Research Database (Denmark)
Brand, Arno J.; Peinke, Joachim; Mann, Jakob
2011-01-01
The nature of turbulent flow towards, near and behind a wind turbine, the effect of turbulence on the electricity production and the mechanical loading of individual and clustered wind turbines, and some future issues are discussed.......The nature of turbulent flow towards, near and behind a wind turbine, the effect of turbulence on the electricity production and the mechanical loading of individual and clustered wind turbines, and some future issues are discussed....
International Nuclear Information System (INIS)
Goldman, M.V.
1984-01-01
After a brief discussion of beam-excited Langmuir turbulence in the solar wind, we explain the criteria for wave-particle, three-wave and strong turbulence interactions. We then present the results of a numerical integration of the Zakharov equations, which describe the strong turbulence saturation of a weak (low-density) high energy, bump-on-tail beam instability. (author)
Progress in turbulence research
International Nuclear Information System (INIS)
Bradshaw, P.
1990-01-01
Recent developments in experiments and eddy simulations, as an introduction to a discussion of turbulence modeling for engineers is reviewed. The most important advances in the last decade rely on computers: microcomputers to control laboratory experiments, especially for multidimensional imaging, and supercomputers to simulate turbulence. These basic studies in turbulence research are leading to genuine breakthroughs in prediction methods for engineers and earth scientists. The three main branches of turbulence research: experiments, simulations (numerically-accurate three-dimensional, time-dependent solutions of the Navier-Stokes equations, with any empiricism confined to the smallest eddies), and modeling (empirical closure of time-averaged equations for turbulent flow) are discussed. 33 refs
Homogeneous turbulence dynamics
Sagaut, Pierre
2018-01-01
This book provides state-of-the-art results and theories in homogeneous turbulence, including anisotropy and compressibility effects with extension to quantum turbulence, magneto-hydodynamic turbulence and turbulence in non-newtonian fluids. Each chapter is devoted to a given type of interaction (strain, rotation, shear, etc.), and presents and compares experimental data, numerical results, analysis of the Reynolds stress budget equations and advanced multipoint spectral theories. The role of both linear and non-linear mechanisms is emphasized. The link between the statistical properties and the dynamics of coherent structures is also addressed. Despite its restriction to homogeneous turbulence, the book is of interest to all people working in turbulence, since the basic physical mechanisms which are present in all turbulent flows are explained. The reader will find a unified presentation of the results and a clear presentation of existing controversies. Special attention is given to bridge the results obta...
DEFF Research Database (Denmark)
Gilling, Lasse
of resolved inflow turbulence on airfoil simulations in CFD. The detached-eddy simulation technique is used because it can resolve the inflow turbulence without becoming too computationally expensive due to its limited requirements for mesh resolution in the boundary layer. It cannot resolve the turbulence......Wind turbines operate in inflow turbulence whether it originates from the shear in the atmospheric boundary layer or from the wake of other wind turbines. Consequently, the airfoils of the wings experience turbulence in the inflow. The main topic of this thesis is to investigate the effect...... that is formed in attached boundary layers, but the freestream turbulence can penetrate the boundary layer. The idea is that the resolved turbulence from the freestream should mix high momentum flow into the boundary layer and thereby increase the resistance against separation and increase the maximum lift...
Energy Technology Data Exchange (ETDEWEB)
Betata, S.A.
1998-02-13
During the production phase of an oil reservoir, a pressure drawdown occurs in the near wellbore region. This may lower the pressure below the bubble-point pressure, leading to the appearance of a gas phase, thus decreasing the oil relative permeability and the well productivity. The main goal of this study is the development of an appropriate laboratory procedure and its modeling, so as to derive gas-oil relative permeabilities at conditions representative of the near wellbore region, e.g. for a dispersed gas phase. A set of depressurization tests in porous media are performed for various conditions of pressure gradient and supersaturation. They are interpreted using a model relating the gas saturation to the supersaturation, as well as the nucleation rate J. Gas-oil relative permeabilities and average gas saturation versus time are measured. Oil relative permeabilities are found to be a function of both the gas saturation and the supersaturation. In addition to that, above a given threshold pressure drop part of the gas is mobilized. The value of J, obtained from the oil production curve leads to the description of the bubble population, in terms of their number and size. It is shown that oil-phase flow impairment is caused more by a limited number of large bubbles rather than by the presence of regularly distributed small ones. The procedure thus established allows the description of the behavior of oil and gas, not only above the critical gas saturation (defined as the saturation above which the gas phase becomes continuous), but also in the early stage of the nucleation, when the gas, even in a dispersed form, can flow depending on the applied pressure gradient. (author) 39 refs.
Energy Technology Data Exchange (ETDEWEB)
Artus, V.
2003-11-01
For two-phase flow in heterogeneous media, the emergence of different flow regimes at large-scale is driven by local interactions between the viscous coupling and the heterogeneity. In particular, when the viscosity ratio is favorable, viscous effects induce a transverse flow that stabilizes the front while flooding. However, most of recent stochastic models neglect the influence of the viscous coupling. We developed a stochastic model for the dynamics of the front, taking the viscous coupling into account. For stable cases, this model relates the statistical properties of the front to the statistical properties of the permeability field. For stable flow in stratified media, we show that the front is stationary by parts in the reservoir. These parts can be identified as large-scale hydrodynamic layers and separately coarsened in the large-scale simulation model. For flows with favorable viscosity ratios in isotropic reservoirs, we show that a stationary front occurs, in a statistical sense. For unfavorable viscosity ratios, the flow is driven by the development of viscous fingering. These different regimes lead to different large-scale saturation profiles that can be matched with a macro-dispersion equation, if the effective convective flux is modified to take into account stabilizing or destabilizing viscous effects. (author)
Energy Technology Data Exchange (ETDEWEB)
Boscary, J [CEA Centre d` Etudes de Cadarache, 13 - Saint-Paul-lez-Durance (France). Direction des Sciences de la Matiere; [Association Euratom-CEA, Centre d` Etudes Nucleaires de Cadarache, 13 - Saint-Paul-lez-Durance (France). Dept. de Recherches sur la Fusion Controlee
1997-03-01
The design of plasma facing components is crucial for plasma performance in next fusion reactors. These elements will be submitted to very high heat flux. They will be actively water-cooled by swirl tubes in the subcooled boiling regime. High heat flux experiments were conducted in order to analyse the heat transfer and to evaluate the critical heat flux. Water-cooled mock-ups were one-side heated by an electron beam gun for different thermal-hydraulic conditions. The critical heat flux was detected by an original method based on the isotherm modification on the heated surface. The wall heat transfer law including forced convection and subcooled boiling regimes was established. Numerical calculations of the material heat transfer conduction allowed the non-homogeneous distribution of the wall temperature and of the wall heat flux to be evaluated. The critical heat flux value was defined as the wall maximum heat flux. A critical heat flux model based on the liquid sublayer dryout under a vapor blanket was established. A good agreement with test results was found. (author) 197 refs.
Energy Technology Data Exchange (ETDEWEB)
Boscary, J
1995-10-01
The design of plasma facing components is crucial for plasma performance in next fusion reactors. These elements will be submitted to very high heat flux. They will be actively water-cooled by swirl tubes in the subcooled boiling regime. High heat flux experiments were conducted in order to analyse the heat transfer and to evaluate the critical heat flux. Water-cooled mock-ups were one-side heated by an electron beam gun for different thermal-hydraulic conditions. The critical heat flux was detected by an original method based on the isotherm modification on the heated surface. The wall heat transfer law including forced convection and subcooled boiling regimes was established. Numerical calculations of the material heat transfer conduction allowed the non-homogeneous distribution of the wall temperature and of the wall heat flux to be evaluated. The critical heat flux value was defined as the wall maximum heat flux. A critical heat flux model based on the liquid sublayer dryout under a vapor blanket was established. A good agreement with test results was found. (author). 198 refs., 126 figs., 21 tabs.
Energy Technology Data Exchange (ETDEWEB)
Feraille, Th.; Casalis, G. [Aerodynamics and Energetics Modeling Dept., 31 - Toulouse (France)
2003-12-01
The Taylor flow is the laminar single phase flow induced by gas injection through porous walls, and is assumed to represent the flow inside solid propellant motors. Such a flow is intrinsically unstable, and the generated instabilities are probably responsible for the thrust oscillations observed in the aforesaid motors. However particles are embedded in the propellants usually used, and are released in the fluid by the lateral walls during the combustion, so that there are two heterogeneous phases in the flow. The purpose of this paper is to study the influence of these particles on stability by comparison with stability results from the single phase studies, in a plane two-dimensional configuration. The particles are supposed to be chemically inert and of a uniform size. In order to carry out a linear stability study for this flow modified by the presence of particles, the mean particle velocity field is first determined, assuming that only the gas exerts forces on the particles. This field is sought in a self similar form, which imposes a limit on the size of the particles. However, the particle mass concentration cannot be obtained in a self similar form, but can only, be described by a partial differential equation. The mean flow characteristics being determined, the spectrum of the discretized linear stability operator shows first that particle addition does not trigger any new 'dangerous' modes compared with the single phase flow case. It also shows that the most amplified mode in the case of the single phase flow remains the most amplified mode in the case of the two phase flow. Moreover, the addition of particles acts continuously upon stability results, behaving linearly with respect to the particle mass concentration when the latter is small. The linear correction to the monophasic mode, as well as the evolution of the modes with weak values of the particle mass concentration at the wall, are shown to be proportional to the ejection velocity of the particles. Then, the evolution of the Eigenmodes from a given injection speed of the particles to another one is deduced by affinity, all other parameters being fixed. With a fixed Stokes number, stability results for a finite Reynolds number and results for the inviscid flow bring together when augmenting the particle mass concentration at the wall. Therefore, by knowing single phase flow results and the evolution of stability characteristics of the two phase flow in the inviscid case, it it easy to determine whether particle-laden Taylor flow is more or less stable than the monophasic Taylor flow for large particle mass concentration. (authors)
Energy Technology Data Exchange (ETDEWEB)
Vinay, G.
2005-11-15
Pipelining crude oils that contain large proportions of paraffins can cause many specific difficulties. These oils, known as waxy crude oils, usually exhibit high 'pour point', where this temperature is higher than the external temperature conditions surrounding the pipeline. During the shutdown, since the temperature decreases in the pipeline, the gel-like structure builds up and the main difficulty concerns the issue of restarting. This PhD attempts to improve waxy crude oil behaviour understanding thanks to experiment, modelling and numerical simulation in order to predict more accurately time and pressure required to restart the flow. Using various contributions to the literature, waxy crude oils are described as viscoplastic, thixotropic and compressible fluid. Strong temperature history dependence plays a prevailing role in the whole shutdown and restart process. Thus, waxy crude oils under flowing conditions correspond to the non-isothermal flow of a viscoplastic material with temperature-dependent rheological properties. Besides, the restart of a waxy crude oil is simulated by the isothermal transient flow of a weakly compressible thixotropic fluid in axisymmetric pipe geometry. We retain the Houska model to describe the thixotropic/viscoplastic feature of the fluid and compressibility is introduced in the continuity equation. The viscoplastic constitutive equation is involved using an augmented Lagrangian method and the resulting equivalent saddle-point problem is solved thanks to an Uzawa-like algorithm. Governing equations are discretized using a Finite Volume method and the convection terms are treated thanks to a TVD (Total Variation Diminishing) scheme. The Lagrangian functional technique usually used for incompressible viscoplastic flows, is adapted to compressible situations. Several numerical results attest the good convergence properties of the proposed transient algorithm. The non-isothermal results highlight the strong sensitivity of the flow pattern to the temperature changes in terms of yielded/un-yielded regions. Then, the combined effects of compressibility and thixotropy have beneficial influence on the restart issue. In fact, a thixotropic flow, not able to start up in compressible situations, could be restarted thanks to compressibility. At last, comparison between numerical and experimental results allows to validate the numerical code. (author)
Energy Technology Data Exchange (ETDEWEB)
Dumont, N.
2004-12-15
Combustion quality in Direct Injection Diesel engine depends strongly on the jet atomization in the combustion chamber. Atomization is due to aerodynamic interaction, but it is also influenced by the liquid flow characteristics at the injector exit. As the phenomena are extremely rapid and they take place in very small geometries, experimental investigations are pretty hard to manage. Consequently, our purpose is to develop a simulation code which has two goals: a better comprehension of the flow in the injector in order to optimize the injector geometry, and the prediction of the flow characteristics at the injector exit, in order to provide boundary conditions to combustion simulation codes. At first, we describe phenomena occurring in the injector and their influence on atomization. Their we make a revue of the two-phase models, defining their validity domains. We present the model that we use, based on a homogeneous flow assumption in each mesh cell, and its implementation in KIVA-MB. We show that a particular attention has been focused on exit boundary conditions: we used non-reflective conditions. Simulations results are then described and validated for a one-hole injector and a multi-hole injector, showing the code possibilities to get a better understanding of the liquid flow in an injector during the whole injection. (author)
Energy Technology Data Exchange (ETDEWEB)
Selle, L.
2004-01-15
Swirl flows exhibit a large variety of topologies, depending on the ratio of the flux axial momentum to the axial flux of tangential momentum: this ratio is called swirl number. Above a given critical value for the swirl number, the pressure gradient reverses the flow on the axis of rotation. This central recirculation zone is used in turbines for flame stabilization. And yet, reacting-swirled flows can exhibit combustion instabilities resulting from the coupling between acoustics and unsteady heat release. Combustion instabilities can lead to loss of control or even complete destruction of the system. Their prediction is impossible with standard engineering tools. The work presented here investigates the capabilities of numerical research tools for the prediction of combustion instabilities. Large-Eddy Simulation (LES) is implemented in a code solving the Navier-Stokes equations for compressible-multi-components fluids (code AVBP developed at CERFACS). This method takes into account for the major ingredients of combustion instabilities such as acoustics and flame / vortex interaction. The LES methodology is validated in the swirled flow from a complex industrial burner (SIEMENS PG). Both reactive and non-reactive regimes are successfully compared with experimental data in terms of mean temperature and mean and RMS velocities. Experimental measurements were performed at the university of Karlsruhe (Germany). A detailed analysis of the acoustics and its interaction with the flame front is performed with the code AVSP, also developed at CERFACS. (author)
Studi Eksperimen dan Numerik Pengaruh Penambahan Vortex Generator pada Airfoil NASA LS-0417
Directory of Open Access Journals (Sweden)
Ulul Azmi
2017-03-01
Full Text Available Separasi boundary layer merupakan fenomena penting yang mempengaruhi performansi airfoil. Salah satu upaya untuk menunda atau menghilangkan separasi aliran adalah meningkatkan momentum fluida untuk melawan adverse pressure dan tegangan geser permukaan. Hal ini mengakibatkan separasi aliran akan tertunda lebih ke belakang. Upaya tersebut dapat dilakukan dengan penambahan turbulent generator pada upper surface airfoil. Vortex generator (VG merupakan salah satu jenis turbulent generator yang dapat mempercepat transisi dari laminar boundary layer menjadi turbulent boundary layer. Oleh karena itu, penelitian ini bertujuan untuk mengetahui pengaruh jarak penempatan dan ketinggian VG terhadap perkembangan turbulent boundary layer sehingga dapat meningkatkan performansi airfoil. Penelitian ini dilakukan dengan eksperimen dan numerik pada Re = 1.41x105 dengan angle of attack 16°. Benda uji yang digunakan adalah airfoil NASA LS-0417 dengan dan tanpa VG. Variasi jarak penempatan dan ketinggian VG yaitu x/c = 0.1; 0.2; 0.3; 0.4 (h = 1 mm; 3 mm; 5 mm. Hasil yang didapatkan adalah variasi vortex generator paling optimal adalah vortex generator dengan x/c = 0.3 dan h = 1 mm dimana Nilai CL/CD mengalami kenaikan sebesar 14.337%.
Turbulence generation by waves
Energy Technology Data Exchange (ETDEWEB)
Kaftori, D.; Nan, X.S.; Banerjee, S. [Univ. of California, Santa Barbara, CA (United States)
1995-12-31
The interaction between two-dimensional mechanically generated waves, and a turbulent stream was investigated experimentally in a horizontal channel, using a 3-D LDA synchronized with a surface position measuring device and a micro-bubble tracers flow visualization with high speed video. Results show that although the wave induced orbital motion reached all the way to the wall, the characteristics of the turbulence wall structures and the turbulence intensity close to the wall were not altered. Nor was the streaky nature of the wall layer. On the other hand, the mean velocity profile became more uniform and the mean friction velocity was increased. Close to the free surface, the turbulence intensity was substantially increased as well. Even in predominantly laminar flows, the introduction of 2-D waves causes three dimensional turbulence. The turbulence enhancement is found to be proportional to the wave strength.
Plasma Turbulence General Topics
Energy Technology Data Exchange (ETDEWEB)
Kadomtsev, B. B. [Nuclear Energy Institute, Academy of Sciences of the USSR, Moscow, USSR (Russian Federation)
1965-06-15
It is known that under experimental conditions plasma often shows chaotic motion. Such motion, when many degrees of freedom are excited to levels considerably above the thermal level, will be called turbulent. The properties of turbulent plasma in many respects differ from the properties of laminar plasma. It can be said that the appearance of various anomalies in plasma behaviour indicates the presence of turbulence in plasma. In order to verify directly the presence of turbulent motion in plasma we must, however, measure the fluctuation of some microscopic parameters in plasma.
International Nuclear Information System (INIS)
Duri, D.
2012-01-01
This experimental work is focused on the statistical study of the high Reynolds number turbulent velocity field in an inertially driven liquid helium axis-symmetric round jet at temperatures above and below the lambda transition (between 2.3 K and 1.78 K) in a cryogenic wind tunnel. The possibility to finely tune the fluid temperature allows us to perform a comparative study of the quantum He II turbulence within the classical framework of the Kolmogorov turbulent cascade in order to have a better understanding of the energy cascade process in a superfluid. In particular we focused our attention on the intermittency phenomena, in both He I and He II phases, by measuring the high order statistics of the longitudinal velocity increments by means of the flatness and the skewness statistical estimators. A first phase consisted in developing the cryogenic facility, a closed loop pressurized and temperature regulated wind tunnel, and adapting the classic hot-wire anemometry technique in order to be able to work in such a challenging low temperature environment. A detailed calibration procedure of the fully developed turbulent flow was the carried out at 2.3 K at Reynolds numbers based on the Taylor length scale up to 2600 in order to qualify our testing set-up and to identify possible facility-related spurious phenomena. This procedure showed that the statistical properties of the longitudinal velocity increments are in good agreement with respect to previous results. By further reducing the temperature of the working fluid (at a constant pressure) below the lambda point down to 1.78 K local velocity measurements were performed at different superfluid density fractions. The results show a classic behaviour of the He II energy cascade at large scales while, at smaller scales, a deviation has been observed. The occurrence of this phenomenon, which requires further investigation and modelling, is highlighted by the observed changing sign of the third order structure
EPA’s Dan Nelson is the Director of the Human Research Protocol Office at the National Health and Environmental Effect Research Laboratory, Dan works to protect the rights and welfare of EPA’s research participants.
Supriyadi, Supriyadi
1999-01-01
Manusia sering disebut sebagai makhluk sosial, makhluk berakal, makhluk berseni, dan sebagainya. Tulisan ini secara tidak langsung membicarakan manusia sebagai makhluk berbahasa, bersimbol, dan bereligi . Meskipun demikian, titik tolaknya bukan pada manusia itu sendiri, tetapi pada bahasa, simbol, dan religinya, terutama pada hubungan di antara ketiganya . Hubungan antara bahasa dan simbol tidak diragukan lagi karena bahasa merupakan jenis simbol . Demikian juga hubungan antara simbol dengan ...
PDF Modeling of Turbulent Combustion
National Research Council Canada - National Science Library
Pope, Stephen B
2006-01-01
.... The PDF approach to turbulent combustion has the advantages of fully representing the turbulent fluctuations of species and temperature, and of allowing realistic combustion chemistry to be implemented...
International Nuclear Information System (INIS)
Vorotyntsev, M.A.
1991-01-01
Key problems of turbulent mass transfer at a solid wall are reviewed: closure problem for the concentration field, information on wall turbulence, applications of microelectrodes to study the structure of turbulence, correlation properties of current fluctuations. (author). 26 refs
Turbulence modelling; Modelisation de la turbulence isotherme
Energy Technology Data Exchange (ETDEWEB)
Laurence, D. [Electricite de France (EDF), Direction des Etudes et Recherches, 92 - Clamart (France)
1997-12-31
This paper is an introduction course in modelling turbulent thermohydraulics, aimed at computational fluid dynamics users. No specific knowledge other than the Navier Stokes equations is required beforehand. Chapter I (which those who are not beginners can skip) provides basic ideas on turbulence physics and is taken up in a textbook prepared by the teaching team of the ENPC (Benque, Viollet). Chapter II describes turbulent viscosity type modelling and the 2k-{epsilon} two equations model. It provides details of the channel flow case and the boundary conditions. Chapter III describes the `standard` (R{sub ij}-{epsilon}) Reynolds tensions transport model and introduces more recent models called `feasible`. A second paper deals with heat transfer and the effects of gravity, and returns to the Reynolds stress transport model. (author). 37 refs.
Nagendra Prakash, Vivek
2013-01-01
This thesis deals with the broad topic of particles in turbulence, which has applications in a diverse number of fields. A vast majority of fluid flows found in nature and in the industry are turbulent and contain dispersed elements. In this thesis, I have focused on light particles (air bubbles in
Dynamic paradigm of turbulence
International Nuclear Information System (INIS)
Mukhamedov, Alfred M.
2006-01-01
In this paper a dynamic paradigm of turbulence is proposed. The basic idea consists in the novel definition of chaotic structure given with the help of Pfaff system of PDE associated with the turbulent dynamics. A methodological analysis of the new and the former paradigm is produced
Behaviour of turbulence models near a turbulent/non-turbulent interface revisited
International Nuclear Information System (INIS)
Ferrey, P.; Aupoix, B.
2006-01-01
The behaviour of turbulence models near a turbulent/non-turbulent interface is investigated. The analysis holds as well for two-equation as for Reynolds stress turbulence models using Daly and Harlow diffusion model. The behaviour near the interface is shown not to be a power law, as usually considered, but a more complex parametric solution. Why previous works seemed to numerically confirm the power law solution is explained. Constraints for turbulence modelling, i.e., for ensuring that models have a good behaviour near a turbulent/non-turbulent interface so that the solution is not sensitive to small turbulence levels imposed in the irrotational flow, are drawn
Directory of Open Access Journals (Sweden)
Line A.
2006-11-01
Full Text Available Le modèle présenté ici permet la pré-détermination du gradient de pression, du taux global de gaz, et de grandeurs caractéristiques de l'intermittence, dans un écoulement à poches et bouchons en conduite verticale. L'écriture des lois de conservation en moyenne phasique conditionnelle conduit à la définition d'une cellule moyenne équivalente. La fermeture du modèle est assurée par des lois de contrainte de cisaillement film-paroi, film-poche, bouchon-paroi, par une loi d'arrachage du gaz au culot de la poche, une loi de glissement du gaz dans les bouchons et par une loi de la vitesse moyenne de propagation des fronts de poches. Le calibrage et la qualification du modèle s'appuient sur deux banques de données, dont l'une a été obtenue avec des fluides pétroliers dans des conditions proches des situations industrielles (boucle diphasique de Boussens. The model described here can be used to predetermine the pressure gradient, the overall gas rate and the characteristic intermittence magnitudes in pocket and slug flow in a vertical pipe. The way governing equations in the conditional phase average are written defines an equivalent average cell. The model is closed by film/wall, film/pocket and slug/wall shear-stress laws, by a pulloff law for the gas at the bottom of the pocket, a slippage law for the gas in the slugs, and a mean propagation velocity law for the pocket fronts. The calibration and qualification of the model are based on two data banks, one of which contains data on petroleum fluids under conditions close to industrial situations (two-phase loop at Boussens.
1993-04-01
vibrationicl (fans des tuNZ~rcs tesi pri~sentee. Pour les conditions g~n~iatr-iccs consid~r~es, 1 onisation I es tenoes tie flux die Moude parfait son...lenus figures possibles, deux initialisations du champ valcurs de Y/delta (Y ktant Is distance A Ia peau wont disponibles : et DELTA , I’kpaissenr de...maillage support on calcule Plus de details sont disponibles dans les les distances des nocuds A la peau tres references . prkciskment. Le code N.S
Turbulent current drive mechanisms
McDevitt, Christopher J.; Tang, Xian-Zhu; Guo, Zehua
2017-08-01
Mechanisms through which plasma microturbulence can drive a mean electron plasma current are derived. The efficiency through which these turbulent contributions can drive deviations from neoclassical predictions of the electron current profile is computed by employing a linearized Coulomb collision operator. It is found that a non-diffusive contribution to the electron momentum flux as well as an anomalous electron-ion momentum exchange term provide the most efficient means through which turbulence can modify the mean electron current for the cases considered. Such turbulent contributions appear as an effective EMF within Ohm's law and hence provide an ideal means for driving deviations from neoclassical predictions.
Belotserkovskii, OM; Chechetkin, VM
2005-01-01
The authors present the results of numerical experiments carried out to examine the problem of development of turbulence and convection. On the basis of the results, they propose a physical model of the development of turbulence. Numerical algorithms and difference schema for carrying out numerical experiments in hydrodynamics, are proposed. Original algorithms, suitable for calculation of the development of the processes of turbulence and convection in different conditions, even on astrophysical objects, are presented. The results of numerical modelling of several important phenomena having both fundamental and applied importance are described.
Energy Technology Data Exchange (ETDEWEB)
Hoejstrup, J [NEG Micon Project Development A/S, Randers (Denmark); Hansen, K S [Denmarks Technical Univ., Dept. of Energy Engineering, Lyngby (Denmark); Pedersen, B J [VESTAS Wind Systems A/S, Lem (Denmark); Nielsen, M [Risoe National Lab., Wind Energy and Atmospheric Physics, Roskilde (Denmark)
1999-03-01
The pdf`s of atmospheric turbulence have somewhat wider tails than a Gaussian, especially regarding accelerations, whereas velocities are close to Gaussian. This behaviour is being investigated using data from a large WEB-database in order to quantify the amount of non-Gaussianity. Models for non-Gaussian turbulence have been developed, by which artificial turbulence can be generated with specified distributions, spectra and cross-correlations. The artificial time series will then be used in load models and the resulting loads in the Gaussian and the non-Gaussian cases will be compared. (au)
Modeling of turbulent chemical reaction
Chen, J.-Y.
1995-01-01
Viewgraphs are presented on modeling turbulent reacting flows, regimes of turbulent combustion, regimes of premixed and regimes of non-premixed turbulent combustion, chemical closure models, flamelet model, conditional moment closure (CMC), NO(x) emissions from turbulent H2 jet flames, probability density function (PDF), departures from chemical equilibrium, mixing models for PDF methods, comparison of predicted and measured H2O mass fractions in turbulent nonpremixed jet flames, experimental evidence of preferential diffusion in turbulent jet flames, and computation of turbulent reacting flows.
Aviation turbulence processes, detection, prediction
Lane, Todd
2016-01-01
Anyone who has experienced turbulence in flight knows that it is usually not pleasant, and may wonder why this is so difficult to avoid. The book includes papers by various aviation turbulence researchers and provides background into the nature and causes of atmospheric turbulence that affect aircraft motion, and contains surveys of the latest techniques for remote and in situ sensing and forecasting of the turbulence phenomenon. It provides updates on the state-of-the-art research since earlier studies in the 1960s on clear-air turbulence, explains recent new understanding into turbulence generation by thunderstorms, and summarizes future challenges in turbulence prediction and avoidance.
Turbulent buoyant jets and plumes
Rodi, Wolfgang
The Science & Applications of Heat and Mass Transfer: Reports, Reviews, & Computer Programs, Volume 6: Turbulent Buoyant Jets and Plumes focuses on the formation, properties, characteristics, and reactions of turbulent jets and plumes. The selection first offers information on the mechanics of turbulent buoyant jets and plumes and turbulent buoyant jets in shallow fluid layers. Discussions focus on submerged buoyant jets into shallow fluid, horizontal surface or interface jets into shallow layers, fundamental considerations, and turbulent buoyant jets (forced plumes). The manuscript then exami
Analisis Kebijakan dan Efektivitas Organisasi
Directory of Open Access Journals (Sweden)
Amir Syarifudin Kiwang
2015-05-01
Full Text Available Penerapan Peraturan Gubernur Nusa Tenggara Timur Nomor 8 Tahun 2011 tentang Organisasi dan Tata Kerja Unit Pelaksana Teknis Pendidikan dan Pelatihan Koperasi dan Usaha Mikro Kecil dan Menengah pada Dinas Koperasi dan Usaha Mikro Kecil dan Menengah Provinsi Nusa Tenggara Timur adalah dalam rangka untuk meningkatkan efektivitas kerja organisasi pada UPT Diklat Koperasi dan UMKM. Penelitian ini berusaha untuk melihat dampak kebijakan organisasi terhadap efektivitas organisasi dengan menggunakan enam elemen variabel dari kebijakan dan praktik manajemen. Keenam elemen tersebut adalah penetapan tujuan strategis, pencarian dan pemanfaatan sumber daya, lingkungan prestasi, proses komunikasi, kepemimpinan dan pengambilan keputusan, serta adaptasi dan inovasi organisasi. Penelitian kualitatif ini menggunakan pendekatan studi kasus. Teknik analisis data yang digunakan adalah analisis data model Miles dan Huberman, yang terdiri atas reduksi data, display/penyajian data, dan kesimpulan/verifikasi. Hasil penelitian menunjukkan bahwa efektivitas organisasi pada UPT Diklat koperasi dan UMKM belum berjalan secara baik, hal ini dapat dilihat dari beberapa hal antara lain, belum adanya tenaga spesialisasi pengelola diklat dan tenaga khusus (sarjana di bidang perkoperasian dan kondisi lingkungan kerja (lingkungan prestasi pada UPT Diklat koperasi dan UMKM yang belum efektif. Penempatan pegawai juga belum tepat, mutasi ke UPT Diklat Koperasi dan UMKM tidak memperhatikan latar belakang pendidikan dan spesialisasi/keahlian pegawai sehingga membutuhkan waktu dalam proses penyesuaian serta menurunkan jumlah pelaksanaan diklat dikarenakan keterbatasan alokasi dana.
Containerless Ripple Turbulence
Putterman, Seth; Wright, William; Duval, Walter; Panzarella, Charles
2002-11-01
One of the longest standing unsolved problems in physics relates to the behavior of fluids that are driven far from equilibrium such as occurs when they become turbulent due to fast flow through a grid or tidal motions. In turbulent flows the distribution of vortex energy as a function of the inverse length scale [or wavenumber 'k'] of motion is proportional to 1/k5/3 which is the celebrated law of Kolmogorov. Although this law gives a good description of the average motion, fluctuations around the average are huge. This stands in contrast with thermally activated motion where large fluctuations around thermal equilibrium are highly unfavorable. The problem of turbulence is the problem of understanding why large fluctuations are so prevalent which is also called the problem of 'intermittency'. Turbulence is a remarkable problem in that its solution sits simultaneously at the forefront of physics, mathematics, engineering and computer science. A recent conference [March 2002] on 'Statistical Hydrodynamics' organized by the Los Alamos Laboratory Center for Nonlinear Studies brought together researchers in all of these fields. Although turbulence is generally thought to be described by the Navier-Stokes Equations of fluid mechanics the solution as well as its existence has eluded researchers for over 100 years. In fact proof of the existence of such a solution qualifies for a 1 M millennium prize. As part of our NASA funded research we have proposed building a bridge between vortex turbulence and wave turbulence. The latter occurs when high amplitude waves of various wavelengths are allowed to mutually interact in a fluid. In particular we have proposed measuring the interaction of ripples [capillary waves] that run around on the surface of a fluid sphere suspended in a microgravity environment. The problem of ripple turbulence poses similar mathematical challenges to the problem of vortex turbulence. The waves can have a high amplitude and a strong nonlinear
Inflow Turbulence Generation Methods
Wu, Xiaohua
2017-01-01
Research activities on inflow turbulence generation methods have been vigorous over the past quarter century, accompanying advances in eddy-resolving computations of spatially developing turbulent flows with direct numerical simulation, large-eddy simulation (LES), and hybrid Reynolds-averaged Navier-Stokes-LES. The weak recycling method, rooted in scaling arguments on the canonical incompressible boundary layer, has been applied to supersonic boundary layer, rough surface boundary layer, and microscale urban canopy LES coupled with mesoscale numerical weather forecasting. Synthetic methods, originating from analytical approximation to homogeneous isotropic turbulence, have branched out into several robust methods, including the synthetic random Fourier method, synthetic digital filtering method, synthetic coherent eddy method, and synthetic volume forcing method. This article reviews major progress in inflow turbulence generation methods with an emphasis on fundamental ideas, key milestones, representative applications, and critical issues. Directions for future research in the field are also highlighted.
Containerless Ripple Turbulence
Putterman, Seth; Wright, William; Duval, Walter; Panzarella, Charles
2002-01-01
One of the longest standing unsolved problems in physics relates to the behavior of fluids that are driven far from equilibrium such as occurs when they become turbulent due to fast flow through a grid or tidal motions. In turbulent flows the distribution of vortex energy as a function of the inverse length scale [or wavenumber 'k'] of motion is proportional to 1/k(sup 5/3) which is the celebrated law of Kolmogorov. Although this law gives a good description of the average motion, fluctuations around the average are huge. This stands in contrast with thermally activated motion where large fluctuations around thermal equilibrium are highly unfavorable. The problem of turbulence is the problem of understanding why large fluctuations are so prevalent which is also called the problem of 'intermittency'. Turbulence is a remarkable problem in that its solution sits simultaneously at the forefront of physics, mathematics, engineering and computer science. A recent conference [March 2002] on 'Statistical Hydrodynamics' organized by the Los Alamos Laboratory Center for Nonlinear Studies brought together researchers in all of these fields. Although turbulence is generally thought to be described by the Navier-Stokes Equations of fluid mechanics the solution as well as its existence has eluded researchers for over 100 years. In fact proof of the existence of such a solution qualifies for a 1 M$ millennium prize. As part of our NASA funded research we have proposed building a bridge between vortex turbulence and wave turbulence. The latter occurs when high amplitude waves of various wavelengths are allowed to mutually interact in a fluid. In particular we have proposed measuring the interaction of ripples [capillary waves] that run around on the surface of a fluid sphere suspended in a microgravity environment. The problem of ripple turbulence poses similar mathematical challenges to the problem of vortex turbulence. The waves can have a high amplitude and a strong nonlinear
Turbulence Generation in Combustion.
1987-07-22
flame length . This work is summarized in this section. I1.1 Model for Turbulent Burning Velocity For a range of turbulence conditions including...Variable density effects have been added in an approximation, and an expression for the length of jet flames has been developed. The flame length expression...of jet mixing and jet flame length data using fractals, College of Engineering, Energy Report E-86-02, Comell University, Ithaca, NY, 1986. Results
Stochastic tools in turbulence
Lumey, John L
2012-01-01
Stochastic Tools in Turbulence discusses the available mathematical tools to describe stochastic vector fields to solve problems related to these fields. The book deals with the needs of turbulence in relation to stochastic vector fields, particularly, on three-dimensional aspects, linear problems, and stochastic model building. The text describes probability distributions and densities, including Lebesgue integration, conditional probabilities, conditional expectations, statistical independence, lack of correlation. The book also explains the significance of the moments, the properties of the
Magnetohydrodynamic turbulence revisited
International Nuclear Information System (INIS)
Goldreich, P.; Sridhar, S.
1997-01-01
In 1965, Kraichnan proposed that MHD turbulence occurs as a result of collisions between oppositely directed Alfvacute en wave packets. Recent work has generated some controversy over the nature of nonlinear couplings between colliding Alfvacute en waves. We find that the resolution to much of the confusion lies in the existence of a new type of turbulence, intermediate turbulence, in which the cascade of energy in the inertial range exhibits properties intermediate between those of weak and strong turbulent cascades. Some properties of intermediate MHD turbulence are the following: (1) in common with weak turbulent cascades, wave packets belonging to the inertial range are long-lived; (2) however, components of the strain tensor are so large that, similar to the situation in strong turbulence, perturbation theory is not applicable; (3) the breakdown of perturbation theory results from the divergence of neighboring field lines due to wave packets whose perturbations in velocity and magnetic fields are localized, but whose perturbations in displacement are not; (4) three-wave interactions dominate individual collisions between wave packets, but interactions of all orders n≥3 make comparable contributions to the intermediate turbulent energy cascade; (5) successive collisions are correlated since wave packets are distorted as they follow diverging field lines; (6) in common with the weak MHD cascade, there is no parallel cascade of energy, and the cascade to small perpendicular scales strengthens as it reaches higher wavenumbers; (7) for an appropriate weak excitation, there is a natural progression from a weak, through an intermediate, to a strong cascade. copyright 1997 The American Astronomical Society
MULTIFLUID MAGNETOHYDRODYNAMIC TURBULENT DECAY
International Nuclear Information System (INIS)
Downes, T. P.; O'Sullivan, S.
2011-01-01
It is generally believed that turbulence has a significant impact on the dynamics and evolution of molecular clouds and the star formation that occurs within them. Non-ideal magnetohydrodynamic (MHD) effects are known to influence the nature of this turbulence. We present the results of a suite of 512 3 resolution simulations of the decay of initially super-Alfvenic and supersonic fully multifluid MHD turbulence. We find that ambipolar diffusion increases the rate of decay of the turbulence while the Hall effect has virtually no impact. The decay of the kinetic energy can be fitted as a power law in time and the exponent is found to be -1.34 for fully multifluid MHD turbulence. The power spectra of density, velocity, and magnetic field are all steepened significantly by the inclusion of non-ideal terms. The dominant reason for this steepening is ambipolar diffusion with the Hall effect again playing a minimal role except at short length scales where it creates extra structure in the magnetic field. Interestingly we find that, at least at these resolutions, the majority of the physics of multifluid turbulence can be captured by simply introducing fixed (in time and space) resistive terms into the induction equation without the need for a full multifluid MHD treatment. The velocity dispersion is also examined and, in common with previously published results, it is found not to be power law in nature.
Directory of Open Access Journals (Sweden)
Sri Soewasti Soesanto
2012-10-01
Full Text Available Manusia yang sehat tiap hari membuang tinja yang harus ditampung dan/atau diolah secara saniter. Meskipun Indonesia telah 55 tahun merdeka dan telah memiliki banyak ahli sanitasi/teknik penyehatan baik lulusan dalam maupun luar negeri, namun cara pengelolaan tinja yang ada kebanyakan masih belum memenuhi syarat kesehatan. Tangki septik dianggap sebagai cara penampungan tinja yang terbaik, padahal sebenarnya masih terjadi pencemaran tanah dan air melalui saluran perembesan.Tangki septik (septic tank merupakan salah satu macam sarana pengolahan tinja manusia yang pada garis besarnya terdiri dari sebuah tangki pembusukan lumpur (sludge digester dan saluran perembesan efluen. Tangki pembusukan harus memenuhi syarat mengenai perbandingan panjang dan lebar serta syarat kedalaman maksimum dan minimum, agar pembusukan lumpur dari tinja manusia dapat berjalan sempurna malahan tidak berbau busuk lagi.
Directory of Open Access Journals (Sweden)
Wayan Eko Radityo
2012-12-01
Full Text Available Depresi merupakan gangguan mood berupa kesedihan yang intens, berlangsung dalamwaktu lama, dan mengganggu kehidupan normal yang insidennya semakin meningkatseiring dengan meningkatnya tekanan hidup. Tahun 2020, depresi diperkirakanmenempati urutan kedua penyakit di dunia. Gejala-gejala depresi terdiri dari gangguanemosi, gangguan kognitif, keluhan somatik, gangguan psikomotor, dan gangguanvegetatif. Salah satu gejala depresi yang muncul adalah gangguan tidur yang bisaberupa insomnia, bangun secara tiba-tiba, dan hipersomnia. Hal ini disebabkan olehgangguan neurotransmiter dan regulasi hormon. Selain sebagai gejala depresi, gangguantidur juga bisa merupakan penyebab depresi. Beberapa penelitian memberikanhubungan gangguan tidur dapat meningkatkan risiko depresi di kemudian hari.
Tearing instabilities in turbulence
International Nuclear Information System (INIS)
Ishizawa, A.; Nakajima, N.
2009-01-01
Full text: Effects of micro-turbulence on tearing instabilities are investigated by numerically solving a reduced set of two-fluid equations. Micro-turbulence excites both large-scale and small-scale Fourier modes through energy transfer due to nonlinear mode coupling. The energy transfer to large scale mode does not directly excite tearing instability but it gives an initiation of tearing instability. When tearing instability starts to grow, the excited small scale mode plays an important role. The mixing of magnetic flux by micro-turbulence is the dominant factor of non-ideal MHD effect at the resonant surface and it gives rise to magnetic reconnection which causes tearing instability. Tearing instabilities were investigated against static equilibrium or flowing equilibrium so far. On the other hand, the recent progress of computer power allows us to investigate interactions between turbulence and coherent modes such as tearing instabilities in magnetically confined plasmas by means of direct numerical simulations. In order to investigate effects of turbulence on tearing instabilities we consider a situation that tearing mode is destabilized in a quasi-equilibrium including micro-turbulence. We choose an initial equilibrium that is unstable against kinetic ballooning modes and tearing instabilities. Tearing instabilities are current driven modes and thus they are unstable for large scale Fourier modes. On the other hand kinetic ballooning modes are unstable for poloidal Fourier modes that are characterized by ion Larmor radius. The energy of kinetic ballooning modes spreads over wave number space through nonlinear Fourier mode coupling. We present that micro-turbulence affects tearing instabilities in two different ways by three-dimensional numerical simulation of a reduced set of two-fluid equations. One is caused by energy transfer to large scale modes, the other is caused by energy transfer to small scale modes. The former is the excitation of initial
Turbulence introduction to theory and applications of turbulent flows
Westerweel, Jerry; Nieuwstadt, Frans T M
2016-01-01
This book provides a general introduction to the topic of turbulent flows. Apart from classical topics in turbulence, attention is also paid to modern topics. After studying this work, the reader will have the basic knowledge to follow current topics on turbulence in scientific literature. The theory is illustrated with a number of examples of applications, such as closure models, numerical simulations and turbulent diffusion, and experimental findings. The work also contains a number of illustrative exercises.
Keragaman dan Peran Biologi Arthrophoda pada Sawah Irigasi dan Tegalan
Suwarno, Suwarno
2016-01-01
Penelitian ini bertujuan untuk mengetahui keragaman arthropoda dan peran biologinya pada tanah sawah irigasi dan tegalan. Penelitian ini dilaksanakan di daerah persawahan di daerah Sragen pada bulan Maret – Mei 2016. Metode Penelitian dengan menggunakan pitfall trap atau perangkap jebakan yang diletakkan area persawahan dan tegalan. Teknik pengumpulan data dengan menggunakan purposive sampling. Sampel arthropoda yang diperoleh diidentifikasi dan dianalisis di Laboratorium pendidikan Biologi. ...
Implications of Navier-Stokes turbulence theory for plasma turbulence
International Nuclear Information System (INIS)
Montgomery, David
1977-01-01
A brief discussion of Navier-Stokes turbulence theory is given with particular reference to the two dimensional case. The MHD turbulence is introduced with possible applications of techniques developed in Navier-Stokes theory. Turbulence in Vlasov plasma is also discussed from the point of view of the ''direct interaction approximation'' (DIA). (A.K.)
A mathematical model of turbulence for turbulent boundary layers
International Nuclear Information System (INIS)
Pereira Filho, H.D.V.
1977-01-01
Equations to the so called Reynolds stress-tensor (kinetic turbulent energy) and dissipation rate are developed and a turbulence flux approximation used. Our ideia here is to use those equations in order to develop an economical and fast numeircal procedure for computation of turbulent boundary layer. (author) [pt
Yang, Huan; Zimmerman, Aaron; Lehner, Luis
2015-02-27
We demonstrate that rapidly spinning black holes can display a new type of nonlinear parametric instability-which is triggered above a certain perturbation amplitude threshold-akin to the onset of turbulence, with possibly observable consequences. This instability transfers from higher temporal and azimuthal spatial frequencies to lower frequencies-a phenomenon reminiscent of the inverse cascade displayed by (2+1)-dimensional fluids. Our finding provides evidence for the onset of transitory turbulence in astrophysical black holes and predicts observable signatures in black hole binaries with high spins. Furthermore, it gives a gravitational description of this behavior which, through the fluid-gravity duality, can potentially shed new light on the remarkable phenomena of turbulence in fluids.
Energy Technology Data Exchange (ETDEWEB)
Caldas, Ibere L.; Heller, M.V.A.P.; Brasilio, Z.A. [Sao Paulo Univ., SP, RJ (Brazil). Inst. de Fisica
1997-12-31
Full text. In this work we summarize the results from experiments on electrostatic and magnetic fluctuations in tokamak plasmas. Spectral analyses show that these fluctuations are turbulent, having a broad spectrum of wavectors and a broad spectrum of frequencies at each wavector. The electrostatic turbulence induces unexpected anomalous particle transport that deteriorates the plasma confinement. The relationship of these fluctuations to the current state of plasma theory is still unclear. Furthermore, we describe also attempts to control this plasma turbulence with external magnetic perturbations that create chaotic magnetic configurations. Accordingly, the magnetic field lines may become chaotic and then induce a Lagrangian diffusion. Moreover, to discuss nonlinear coupling and intermittency, we present results obtained by using numerical techniques as bi spectral and wavelet analyses. (author)
Energy Technology Data Exchange (ETDEWEB)
Mann, Jakob [Risoe National Lab., Wind Energy and Atmosheric Physics Dept., Roskilde (Denmark)
1999-03-01
The purpose of this work is to develop a model of the spectral velocity-tensor in neutral flow over complex terrain. The resulting equations are implemented in a computer code using the mean flow generated by a linear mean flow model as input. It estimates turbulence structure over hills (except on the lee side if recirculation is present) in the so-called outer layer and also models the changes in turbulence statistics in the vicinity roughness changes. The generated turbulence fields are suitable as input for dynamic load calculations on wind turbines and other tall structures and is under implementation in the collection of programs called WA{sup s}P Engineering. (au) EFP-97; EU-JOULE-3. 15 refs.
Evaluasi Sifat Morpologi dan Teknologi Pengolahan pada Gabah dan Beras
Santosa, Susilo
2017-01-01
Penelitian evaluasi dan beras terhadap mutu dan jumlah hasil ditekankan pada lr36 , lr38 dan Cisadane. Penelitian dilakukan di laboratorium Balai Penelitian Tanaman Pangan Karawang. Hasil studi menunjukkan diantara ketiga varitas, Cisadane mempunyai ukuran dimensi butiran yang lebih besar daripada Ir36 dan Ir38. Di antara ketiga varitas, persen kulit sekam yang tertinggi didapat 23,57 % pada lr38 diikuti 22,32% pada Ir36 dan 19,5% pada Cisadane. Persen beras pecah kulit tertinggi diperoleh pa...
Evaluasi Sifat Morpologi Dan Teknologi Pengolahan Pada Gabah Dan Beras
Santosa, Susilo
1982-01-01
Penelitian evaluasi dan beras terhadap mutu dan jumlah hasil ditekankan pada lr36 , lr38 dan Cisadane. Penelitian dilakukan di laboratorium Balai Penelitian Tanaman Pangan Karawang. Hasil studi menunjukkan diantara ketiga varitas, Cisadane mempunyai ukuran dimensi butiran yang lebih besar daripada Ir36 dan Ir38. Di antara ketiga varitas, persen kulit sekam yang tertinggi didapat 23,57 % pada lr38 diikuti 22,32% pada Ir36 dan 19,5% pada Cisadane. Persen beras pecah kulit tertinggi diperoleh pa...
Turbulence Intensity Scaling: A Fugue
Basse, Nils T.
2018-01-01
We study streamwise turbulence intensity definitions using smooth- and rough-wall pipe flow measurements made in the Princeton Superpipe. Scaling of turbulence intensity with the bulk (and friction) Reynolds number is provided for the definitions. The turbulence intensity is proportional to the square root of the friction factor with the same proportionality constant for smooth- and rough-wall pipe flow. Turbulence intensity definitions providing the best description of the measurements are i...
Turbulent wakes of fractal objects
Staicu, A.D.; Mazzi, B.; Vassilicos, J.C.; Water, van de W.
2003-01-01
Turbulence of a windtunnel flow is stirred using objects that have a fractal structure. The strong turbulent wakes resulting from three such objects which have different fractal dimensions are probed using multiprobe hot-wire anemometry in various configurations. Statistical turbulent quantities are
Plasma turbulence calculations on supercomputers
International Nuclear Information System (INIS)
Carreras, B.A.; Charlton, L.A.; Dominguez, N.; Drake, J.B.; Garcia, L.; Leboeuf, J.N.; Lee, D.K.; Lynch, V.E.; Sidikman, K.
1991-01-01
Although the single-particle picture of magnetic confinement is helpful in understanding some basic physics of plasma confinement, it does not give a full description. Collective effects dominate plasma behavior. Any analysis of plasma confinement requires a self-consistent treatment of the particles and fields. The general picture is further complicated because the plasma, in general, is turbulent. The study of fluid turbulence is a rather complex field by itself. In addition to the difficulties of classical fluid turbulence, plasma turbulence studies face the problems caused by the induced magnetic turbulence, which couples field by itself. In addition to the difficulties of classical fluid turbulence, plasma turbulence studies face the problems caused by the induced magnetic turbulence, which couples back to the fluid. Since the fluid is not a perfect conductor, this turbulence can lead to changes in the topology of the magnetic field structure, causing the magnetic field lines to wander radially. Because the plasma fluid flows along field lines, they carry the particles with them, and this enhances the losses caused by collisions. The changes in topology are critical for the plasma confinement. The study of plasma turbulence and the concomitant transport is a challenging problem. Because of the importance of solving the plasma turbulence problem for controlled thermonuclear research, the high complexity of the problem, and the necessity of attacking the problem with supercomputers, the study of plasma turbulence in magnetic confinement devices is a Grand Challenge problem
2012-01-01
Dagobert, and C. Franchis . Atmospheric tur- bulence restoration by diffeomorphic image registration and blind deconvolution. In ACIVS, 2008. 1 [4] S...20] V. Tatarskii. Wave Propagation in a Turbulent Medium. McGraw-Hill Books, 1961. 2 [21] Y. Tian and S. Narasimhan. A globally optimal data-driven
van der Veen, Roeland
2016-01-01
In this thesis, several questions related to drop impact and Taylor-Couette turbulence are answered. The deformation of a drop just before impact can cause a bubble to be entrapped. For many applications, such as inkjet printing, it is crucial to control the size of this entrapped bubble. To study
Turbulence and Flying Machines
Indian Academy of Sciences (India)
other to make the aircraft roll. For example, a downward dis- placement of the left aileron causes the airplane to roll to the right. In Figure 4 the elevators have been deflected downwards, giving rise to a 'nose-down' moment about the pitch axis. Delaying Turbulence. In the last few decades, flying machines have proliferated ...
Turbulence and particle acceleration
International Nuclear Information System (INIS)
Scott, J.S.
1975-01-01
A model for the production of high energy particles in the supernova remnant Cas A is considered. The ordered expansion of the fast moving knots produce turbulent cells in the ambient interstellar medium. The turbulent cells act as magnetic scattering centers and charged particles are accelerated to large energies by the second order Fermi mechanism. Model predictions are shown to be consistent with the observed shape and time dependence of the radio spectrum, and with the scale size of magnetic field irregularities. Assuming a galactic supernova rate at 1/50 yr -1 , this mechanism is capable of producing the observed galactic cosmic ray flux and spectrum below 10 16 eV/nucleon. Several observed features of galactic cosmic rays are shown to be consistent with model predictions. A model for the objects known as radio tall galaxies is also presented. Independent blobs of magnetized plasma emerging from an active radio galaxy into an intracluster medium become turbulent due to Rayleigh--Taylor and Kelvin--Helmholz instabilities. The turbulence produces both in situ betatron and 2nd order Fermi accelerations. Predictions of the dependence of spectral index and flux on distance along the tail match observations well. Fitting provides values of physical parameters in the blobs. The relevance of this method of particle acceleration for the problem of the origin of x-ray emission in clusters of galaxies is discussed
Nature of interstellar turbulence
International Nuclear Information System (INIS)
Altunin, V.
1981-01-01
A significant role in producing the pattern of interstellar scintillation observed in discrete radio sources may be played by the magnetoacoustic turbulence that will be generated as shock waves are propagated at velocity V/sub sh/roughly-equal 20--100 km/sec through the interstellar medium, as well as by irregularities in stellar wind emanating from type OB stars
Stochastic modelling of turbulence
DEFF Research Database (Denmark)
Sørensen, Emil Hedevang Lohse
previously been shown to be closely connected to the energy dissipation. The incorporation of the small scale dynamics into the spatial model opens the door to a fully fledged stochastic model of turbulence. Concerning the interaction of wind and wind turbine, a new method is proposed to extract wind turbine...
Analysis of turbulent boundary layers
Cebeci, Tuncer
1974-01-01
Analysis of Turbulent Boundary Layers focuses on turbulent flows meeting the requirements for the boundary-layer or thin-shear-layer approximations. Its approach is devising relatively fundamental, and often subtle, empirical engineering correlations, which are then introduced into various forms of describing equations for final solution. After introducing the topic on turbulence, the book examines the conservation equations for compressible turbulent flows, boundary-layer equations, and general behavior of turbulent boundary layers. The latter chapters describe the CS method for calculati
Magnetosheath electrostatic turbulence
International Nuclear Information System (INIS)
Rodriguez, P.
1979-01-01
By using measurements with the University of Iowa plasma wave experiment on the Imp 6 satellite a study has been conducted of the spectrum of electrostatic plasma waves in the terrestrial magnetosheath. Electrostatic plasma wave turbulence is almost continuously present throughout the magnetosheath with broadband (20 Hz to 70 kHz) rms field intensities typically 0.01--1.0 mV m -1 . Peak intensities of about 1.0 mV m -1 near the electron plasma frequency (30--60 kHz) have been detected occasionally. Two or three components can usually be identified in the spectrum of magnetosheath electrostatic turbulence: a high-frequency (> or =30kHz) component peaking at the electron plasma frequency f/sub p/e, a low-frequency component with a broad intensity maximum below the nominal ion plasma frequency f/sub p/i (approx. f/sub p/e/43), and a less well defined intermediate component in the range f/sub p/i < f< f/sub p/e. The intensity distribution of magnetosheath electrostatic turbulence clearly shows that the low-frequency component is associated with the bow shock, suggesting that the ion heating begun at the shock continues into the downstream magnetosheath. Electrostatic waves below 1 kHz are polarized along the magnetic field direction, a result consistent with the polarization of electrostatic waves at the shock. The high- and intermediate-frequency components are features of the magnetosheath spectrum which are not characteristic of the shock spectrum but are often detected in the upstream solar wind. The intensity distribution of electrostatic turbulence at the magnetosheath plasma frequency has no apparent correlation with the shock, indicating that electron plasma oscillations are a general feature of the magnetosheath. The plasma wave noise shows a tendency to decrease toward the dawn and dusk regions, consistent with a general decrease in turbulence away from the subsolar magnetosheath
Turbulence measurements in fusion plasmas
International Nuclear Information System (INIS)
Conway, G D
2008-01-01
Turbulence measurements in magnetically confined toroidal plasmas have a long history and relevance due to the detrimental role of turbulence induced transport on particle, energy, impurity and momentum confinement. The turbulence-the microscopic random fluctuations in particle density, temperature, potential and magnetic field-is generally driven by radial gradients in the plasma density and temperature. The correlation between the turbulence properties and global confinement, via enhanced diffusion, convection and direct conduction, is now well documented. Theory, together with recent measurements, also indicates that non-linear interactions within the turbulence generate large scale zonal flows and geodesic oscillations, which can feed back onto the turbulence and equilibrium profiles creating a complex interdependence. An overview of the current status and understanding of plasma turbulence measurements in the closed flux surface region of magnetic confinement fusion devices is presented, highlighting some recent developments and outstanding problems.
Destabilizing turbulence in pipe flow
Kühnen, Jakob; Song, Baofang; Scarselli, Davide; Budanur, Nazmi Burak; Riedl, Michael; Willis, Ashley P.; Avila, Marc; Hof, Björn
2018-04-01
Turbulence is the major cause of friction losses in transport processes and it is responsible for a drastic drag increase in flows over bounding surfaces. While much effort is invested into developing ways to control and reduce turbulence intensities1-3, so far no methods exist to altogether eliminate turbulence if velocities are sufficiently large. We demonstrate for pipe flow that appropriate distortions to the velocity profile lead to a complete collapse of turbulence and subsequently friction losses are reduced by as much as 90%. Counterintuitively, the return to laminar motion is accomplished by initially increasing turbulence intensities or by transiently amplifying wall shear. Since neither the Reynolds number nor the shear stresses decrease (the latter often increase), these measures are not indicative of turbulence collapse. Instead, an amplification mechanism4,5 measuring the interaction between eddies and the mean shear is found to set a threshold below which turbulence is suppressed beyond recovery.
Transitional-turbulent spots and turbulent-turbulent spots in boundary layers.
Wu, Xiaohua; Moin, Parviz; Wallace, James M; Skarda, Jinhie; Lozano-Durán, Adrián; Hickey, Jean-Pierre
2017-07-03
Two observations drawn from a thoroughly validated direct numerical simulation of the canonical spatially developing, zero-pressure gradient, smooth, flat-plate boundary layer are presented here. The first is that, for bypass transition in the narrow sense defined herein, we found that the transitional-turbulent spot inception mechanism is analogous to the secondary instability of boundary-layer natural transition, namely a spanwise vortex filament becomes a [Formula: see text] vortex and then, a hairpin packet. Long streak meandering does occur but usually when a streak is infected by a nearby existing transitional-turbulent spot. Streak waviness and breakdown are, therefore, not the mechanisms for the inception of transitional-turbulent spots found here. Rather, they only facilitate the growth and spreading of existing transitional-turbulent spots. The second observation is the discovery, in the inner layer of the developed turbulent boundary layer, of what we call turbulent-turbulent spots. These turbulent-turbulent spots are dense concentrations of small-scale vortices with high swirling strength originating from hairpin packets. Although structurally quite similar to the transitional-turbulent spots, these turbulent-turbulent spots are generated locally in the fully turbulent environment, and they are persistent with a systematic variation of detection threshold level. They exert indentation, segmentation, and termination on the viscous sublayer streaks, and they coincide with local concentrations of high levels of Reynolds shear stress, enstrophy, and temperature fluctuations. The sublayer streaks seem to be passive and are often simply the rims of the indentation pockets arising from the turbulent-turbulent spots.
Liever kraanwater dan bronwater
Kole, A.P.W.
2011-01-01
Een test in het Restaurant van de Toekomst van de invloed van CO2-labels op het aankoopgedrag van consumenten, heeft nog geen duidelijk beeld opgeleverd. Wel pakten mensen vaker kraanwater dan bronwater.
DEFF Research Database (Denmark)
Risum, Janne
2010-01-01
The convention of performing female characters (dan characters) in Beijing opera, as practised by its most prominent male performer of female characters Mei Lanfang, and its and his cultural context and aesthetic aim...
Anaïs Schaeffer
2015-01-01
As a member of the EuHIT (European High-Performance Infrastructures in Turbulence - see here) consortium, CERN is participating in fundamental research on turbulence phenomena. To this end, the Laboratory provides European researchers with a cryogenic research infrastructure (see here), where the first tests have just been performed. The last day of data collection, tired but satisfied after seven intense days of measurements. Around the cryostat, from left to right: Philippe-E. Roche, Éléonore Rusaouen (CNRS), Olivier Pirotte, Jean-Marc Quetsch (CERN), Nicolas Friedlin (CERN), Vladislav Benda (CERN). Not in the photo: Laurent Le Mao (CERN), Jean-Marc Debernard (CERN), Jean-Paul Lamboy (CERN), Nicolas Guillotin (CERN), Benoit Chabaud (Grenoble Uni), and Gregory Garde (CNRS). CERN has a unique cryogenic facility in hall SM18, consisting of 21 liquid-helium-cooled test stations. While this equipment was, of course, designed for testing parts of CERN's acce...
Suppression of turbulent resistivity in turbulent Couette flow
Si, Jiahe; Colgate, Stirling A.; Sonnenfeld, Richard G.; Nornberg, Mark D.; Li, Hui; Colgate, Arthur S.; Westpfahl, David J.; Romero, Van D.; Martinic, Joe
2015-07-01
Turbulent transport in rapidly rotating shear flow very efficiently transports angular momentum, a critical feature of instabilities responsible both for the dynamics of accretion disks and the turbulent power dissipation in a centrifuge. Turbulent mixing can efficiently transport other quantities like heat and even magnetic flux by enhanced diffusion. This enhancement is particularly evident in homogeneous, isotropic turbulent flows of liquid metals. In the New Mexico dynamo experiment, the effective resistivity is measured using both differential rotation and pulsed magnetic field decay to demonstrate that at very high Reynolds number rotating shear flow can be described entirely by mean flow induction with very little contribution from correlated velocity fluctuations.
Suppression of turbulent resistivity in turbulent Couette flow
Energy Technology Data Exchange (ETDEWEB)
Si, Jiahe, E-mail: jsi@nmt.edu; Sonnenfeld, Richard G.; Colgate, Arthur S.; Westpfahl, David J.; Romero, Van D.; Martinic, Joe [New Mexico Institute of Mining and Technology, Socorro, New Mexico 87801 (United States); Colgate, Stirling A.; Li, Hui [Los Alamos National Laboratory, Los Alamos, New Mexico 87544 (United States); Nornberg, Mark D. [University of Wisconsin-Madison, Madison, Wisconsin 53706 (United States)
2015-07-15
Turbulent transport in rapidly rotating shear flow very efficiently transports angular momentum, a critical feature of instabilities responsible both for the dynamics of accretion disks and the turbulent power dissipation in a centrifuge. Turbulent mixing can efficiently transport other quantities like heat and even magnetic flux by enhanced diffusion. This enhancement is particularly evident in homogeneous, isotropic turbulent flows of liquid metals. In the New Mexico dynamo experiment, the effective resistivity is measured using both differential rotation and pulsed magnetic field decay to demonstrate that at very high Reynolds number rotating shear flow can be described entirely by mean flow induction with very little contribution from correlated velocity fluctuations.
Suppression of turbulent resistivity in turbulent Couette flow
International Nuclear Information System (INIS)
Si, Jiahe; Sonnenfeld, Richard G.; Colgate, Arthur S.; Westpfahl, David J.; Romero, Van D.; Martinic, Joe; Colgate, Stirling A.; Li, Hui; Nornberg, Mark D.
2015-01-01
Turbulent transport in rapidly rotating shear flow very efficiently transports angular momentum, a critical feature of instabilities responsible both for the dynamics of accretion disks and the turbulent power dissipation in a centrifuge. Turbulent mixing can efficiently transport other quantities like heat and even magnetic flux by enhanced diffusion. This enhancement is particularly evident in homogeneous, isotropic turbulent flows of liquid metals. In the New Mexico dynamo experiment, the effective resistivity is measured using both differential rotation and pulsed magnetic field decay to demonstrate that at very high Reynolds number rotating shear flow can be described entirely by mean flow induction with very little contribution from correlated velocity fluctuations
Turbulence and fossil turbulence lead to life in the universe
International Nuclear Information System (INIS)
Gibson, Carl H
2013-01-01
Turbulence is defined as an eddy-like state of fluid motion where the inertial-vortex forces of the eddies are larger than all the other forces that tend to damp the eddies out. Fossil turbulence is a perturbation produced by turbulence that persists after the fluid ceases to be turbulent at the scale of the perturbation. Because vorticity is produced at small scales, turbulence must cascade from small scales to large, providing a consistent physical basis for Kolmogorovian universal similarity laws. Oceanic and astrophysical mixing and diffusion are dominated by fossil turbulence and fossil turbulent waves. Observations from space telescopes show turbulence and vorticity existed in the beginning of the universe and that their fossils persist. Fossils of big bang turbulence include spin and the dark matter of galaxies: clumps of ∼10 12 frozen hydrogen planets that make globular star clusters as seen by infrared and microwave space telescopes. When the planets were hot gas, they hosted the formation of life in a cosmic soup of hot-water oceans as they merged to form the first stars and chemicals. Because spontaneous life formation according to the standard cosmological model is virtually impossible, the existence of life falsifies the standard cosmological model. (paper)
Bruno, Roberto
2016-01-01
This book provides an overview of solar wind turbulence from both the theoretical and observational perspective. It argues that the interplanetary medium offers the best opportunity to directly study turbulent fluctuations in collisionless plasmas. In fact, during expansion, the solar wind evolves towards a state characterized by large-amplitude fluctuations in all observed parameters, which resembles, at least at large scales, the well-known hydrodynamic turbulence. This text starts with historical references to past observations and experiments on turbulent flows. It then introduces the Navier-Stokes equations for a magnetized plasma whose low-frequency turbulence evolution is described within the framework of the MHD approximation. It also considers the scaling of plasma and magnetic field fluctuations and the study of nonlinear energy cascades within the same framework. It reports observations of turbulence in the ecliptic and at high latitude, treating Alfvénic and compressive fluctuations separately in...
4th European Turbulence Conference
1993-01-01
The European Turbulence Conferences have been organized under the auspices of the European Mechanics Committee (Euromech) to provide a forum for discussion and exchange of recent and new results in the field of turbulence. The first conference was organized in Lyon in 1986 with 152 participants. The second and third conferences were held in Berlin (1988) and Stockholm (1990) with 165 and 172 participants respectively. The fourth was organized in Delft from 30 June to 3 July 1992 by the J.M. Burgers Centre. There were 214 participants from 22 countries. This steadily growing number of participants demonstrates both the success and need for this type of conference. The main topics of the Fourth European Turbulence Conference were: Dynamical Systems and Transition; Statistical Physics and Turbulence; Experiments and Novel Experimental Techniques; Particles and Bubbles in Turbulence; Simulation Methods; Coherent Structures; Turbulence Modelling and Compressibility Effects. In addition a special session was held o...
2016-06-23
AFRL-AFOSR-VA-TR-2016-0277 Experimental Investigation of Turbulence-Chemistry Interaction in High- Reynolds -Number Turbulent Partially Premixed...4. TITLE AND SUBTITLE [U] Experimental investigation of turbulence-chemistry interaction in high- Reynolds -number 5a. CONTRACT NUMBER turbulent...for public release Final Report: Experimental investigation of turbulence-chemistry interaction in high- Reynolds -number turbulent partially premixed
PREFERENSI PEMBIAYAAN USAHA MIKRO DAN KECIL : PERSPEKTIF GENDER DAN ENTREPRENEURABILITY
Directory of Open Access Journals (Sweden)
Khaira Amalia Fachrudin
2013-06-01
Full Text Available Preferensi pembiayaan dalam perusahaan besar lebih didasarkan pada karakteristik perusahaan tersebut. Namun dalam usaha mikro dan kecil hal ini mungkin berbeda dan bergantung pada karakteristik pemiliknya seperti gender dan entrepreneurability. Perbedaan gender mungkin juga membedakan entrepreneurability dan dukungan yang diterima. Penelitian ini akan menguji apakah terdapat perbedaan preferensi pembiayaan berdasarkan gender, entrepreneurability berdasarkan gender dan berdasarkan preferensi pembiayaan, serta perbedaan dukungan berdasarkan gender. Sampel dari usaha mikro dan kecil yang bergerak dalam bidang kuliner diuji dengan uji beda Independent Sample t Test dan kemudian dengan Crosstabulation untuk lebih memperinci hasilnya. Hasil uji menunjukkan bahwa tidak terdapat perbedaan yang signifikan preferensi pembiayaan berdasarkan gender dan berdasarkan entrepreneurability, namun entrepreneurability berbeda signifikan berdasarkan gender dan juga ditemukan bahwa dukungan moral, tenaga, dan modal yang diterima pemilik usaha pria dan wanita tidak berbeda signifikan (p value lebih kecil dari 0.05. Hasil ini menunjukkan bahwa terdapat kesetaraan gender dalam pembiayaan usaha dan entrepreneurability lebih tinggi pada pria. Pria pemilik usaha juga mendapatkan dukungan tenaga kerja yang lebih banyak daripada wanita. Dukungan tenaga ini adalah salah satu bentuk financial bootstrapping karena dapat mengurangi pembiayaan usaha
Wave turbulence in magnetized plasmas
Directory of Open Access Journals (Sweden)
S. Galtier
2009-02-01
Full Text Available The paper reviews the recent progress on wave turbulence for magnetized plasmas (MHD, Hall MHD and electron MHD in the incompressible and compressible cases. The emphasis is made on homogeneous and anisotropic turbulence which usually provides the best theoretical framework to investigate space and laboratory plasmas. The solar wind and the coronal heating problems are presented as two examples of application of anisotropic wave turbulence. The most important results of wave turbulence are reported and discussed in the context of natural and simulated magnetized plasmas. Important issues and possible spurious interpretations are also discussed.
DETEKSI DAN MANAJEMEN REFEEDING SYNDROME
Darmadi Darmadi; Riska Habriel Ruslie
2012-01-01
AbstrakRefeeding syndrome (RFS) dideskripsikan sebagai perubahan biokimiawi, manifestasi klinis dan komplikasi sebagai konsekuensi pemberian nutrisi pada pasien kurang gizi. Refeeding syndrome ini menyebabkan dampak buruk dan kematian. Sindroma ini lebih sering terjadi pada kelompok risiko. Refeeding syndrome merupakan suatu sindroma yang sering tak terdiagnosis oleh karena itu perlu peningkatan pengetahuan dan kesadaran dari tenaga medis untuk mengurangi morbiditas dan mortalitas dari RFS. K...
Directory of Open Access Journals (Sweden)
H. Z. Baumert
2009-03-01
Full Text Available This paper extends a turbulence closure-like model for stably stratified flows into a new dynamic domain in which turbulence is generated by internal gravity waves rather than mean shear. The model turbulent kinetic energy (TKE, K balance, its first equation, incorporates a term for the energy transfer from internal waves to turbulence. This energy source is in addition to the traditional shear production. The second variable of the new two-equation model is the turbulent enstrophy (Ω. Compared to the traditional shear-only case, the Ω-equation is modified to account for the effect of the waves on the turbulence time and space scales. This modification is based on the assumption of a non-zero constant flux Richardson number in the limit of vanishing mean shear when turbulence is produced exclusively by internal waves. This paper is part 1 of a continuing theoretical development. It accounts for mean shear- and internal wave-driven mixing only in the two limits of mean shear and no waves and waves but no mean shear, respectively.
The new model reproduces the wave-turbulence transition analyzed by D'Asaro and Lien (2000b. At small energy density E of the internal wave field, the turbulent dissipation rate (ε scales like ε~E^{2}. This is what is observed in the deep sea. With increasing E, after the wave-turbulence transition has been passed, the scaling changes to ε~E^{1}. This is observed, for example, in the highly energetic tidal flow near a sill in Knight Inlet. The new model further exhibits a turbulent length scale proportional to the Ozmidov scale, as observed in the ocean, and predicts the ratio between the turbulent Thorpe and Ozmidov length scales well within the range observed in the ocean.
INOVASI DAN STRATEGI PENCAPAIANNYA
Directory of Open Access Journals (Sweden)
Liem Ferryanto
2009-01-01
Full Text Available Innovation is the way of life of any institution to profitably sustain its life. It starts with empathy, the ability to reach outside of ourselves and walk in someone else’s shoes, and optimal implementation of the newly advanced technology. Innovation shows its results through continuously hard working efforts known as "10 Thousand Hours Rule". As world uncertainty creates complexity we, instead of predicting, should therefore anticipate the future by creating and managing real options on contingent projects or elements of alternative optimal strategies. This should reflect into our portfolio strategy. Abstract in Bahasa Indonesia: Inovasi merupakan darah bagi suatu institusi untuk bisa hidup berkelanjutan serta menguntungkan. Inovasi berupa penemuan baru secara sistematis yang berawal dari empati, kemampuan untuk melihat dunia melalui mata orang lain, dan pemanfaatan secara optimal kemajuan teknologi yang ada. Inovasi baru menghasilkan buahnya melalui kerja keras, yaitu dengan mengikuti “Aturan 10 Ribu Jam” secara berkesinambungan. Ketidakpastian, interaksi, keterbatasan dan degradasi menciptakan kompleksitas tentang kebutuhan dan solusi di masa depan. Oleh sebab itu daripada meramalkan risiko yang bakal terjadi, kita sebaiknya memasang strategi berupa skenario untuk mereduksi akibat dari risiko masa depan yang tidak kita mengerti. Skenario ini dapat diperoleh lewat penciptaan dan penanganan beberapa pilihan nyata atas semua proyek antisipatif yang ada. Kata kunci: Inovasi, ketidakpastian dan kompleksitas, aturan 10 ribu jam, paradoks strategi, peta jalan, empati, kerja berkesinambungan.
Energy Technology Data Exchange (ETDEWEB)
Rodier, J.; Marichal, M. [Commissariat a l' energie atomique et aux energies alternatives - CEA, Centre de production de plutonium de Marcoule, Service de protection contre les radiations (France)
1961-07-01
The process whereby waste from the Marcoule plant mixes with the water in the Rhone was followed in tests with rhodamine as a chemical tracer. Satisfactory dispersion was noted less than 4 km downstream from the waste discharge duct outlet, and the degree of homogeneity was considered to be satisfactory at the bridge of Roquemaure, und perfect at Avignon. This investigation not only revealed a complete absence of any preferential flow paths containing high radioactive waste concentrations, but it also enabled the most representative points to be selected at which to take Rhone water samples during future radioactive waste discharges. Reprint of a paper published in 'La Houille Blanche' N. 5 - Aug 196, p. 636-641 [French] L'emploi de la rhodamine comme traceur chimique a permis de suivre l'evolution du melange des effluents du Centre de Marcoule aux eaux du Rhone. La dispersion est deja satisfaisante a moins de 4 km en aval de la conduite des rejets, et l'homogeneite peut etre consideree comme atteinte au pont de Roquemaure et parfaite a Avignon. Cette etude a montre que les veines preferentielles ou se concentrait l'ecoulement des effluents radioactifs n'existent pas. Elle a permis de preciser en outre les emplacements les plus representatifs des points d'echantillonnage des eaux du Rhone au cours des rejets. Reproduction d'un article publie dans 'La houille blanche' N. 5 - Aug 196, p. 636-641.
PENGELOLAAN PENELITIAN DAN PENGEMBANGAN KESEHATAN DI THAILAND, MYANMAR, DAN INDIA
Directory of Open Access Journals (Sweden)
Anorital, SKM Anorital, SKM
2012-09-01
Full Text Available Dalam bulan Januari 1991 yang lalu, Sdr. Anorital, SKM (Ka. Subbag. Pengumpulan dan PengolahanData Badan Litbangkes dan H. Syafwani Mirin, SKM (Ka. Bag. Keuangan Badan Litbangkes memperoleh fellowship dari WHO untuk melakukan studi perbandingan ke institusi-institusi penelitian kesehatan di Thailand,Myanmar, dan India.Berikut di bawah ini tulisan bersangkutan yang menggambarkan secara garis besar pengelolaan penelitian dan pengembangan kesehatan pada masing-masing negara obyek studi. Semoga informasi yang terkandung pada tulisan ini dapat bermanfaat bagi pengembangan Badan Penelitian dan Pengembangan Kesehatan.
Large Eddy Simulation of turbulence
International Nuclear Information System (INIS)
Poullet, P.; Sancandi, M.
1994-12-01
Results of Large Eddy Simulation of 3D isotropic homogeneous turbulent flows are presented. A computer code developed on Connexion Machine (CM5) has allowed to compare two turbulent viscosity models (Smagorinsky and structure function). The numerical scheme influence on the energy density spectrum is also studied [fr
Advances in compressible turbulent mixing
International Nuclear Information System (INIS)
Dannevik, W.P.; Buckingham, A.C.; Leith, C.E.
1992-01-01
This volume includes some recent additions to original material prepared for the Princeton International Workshop on the Physics of Compressible Turbulent Mixing, held in 1988. Workshop participants were asked to emphasize the physics of the compressible mixing process rather than measurement techniques or computational methods. Actual experimental results and their meaning were given precedence over discussions of new diagnostic developments. Theoretical interpretations and understanding were stressed rather than the exposition of new analytical model developments or advances in numerical procedures. By design, compressibility influences on turbulent mixing were discussed--almost exclusively--from the perspective of supersonic flow field studies. The papers are arranged in three topical categories: Foundations, Vortical Domination, and Strongly Coupled Compressibility. The Foundations category is a collection of seminal studies that connect current study in compressible turbulent mixing with compressible, high-speed turbulent flow research that almost vanished about two decades ago. A number of contributions are included on flow instability initiation, evolution, and transition between the states of unstable flow onset through those descriptive of fully developed turbulence. The Vortical Domination category includes theoretical and experimental studies of coherent structures, vortex pairing, vortex-dynamics-influenced pressure focusing. In the Strongly Coupled Compressibility category the organizers included the high-speed turbulent flow investigations in which the interaction of shock waves could be considered an important source for production of new turbulence or for the enhancement of pre-existing turbulence. Individual papers are processed separately
Interstellar turbulence and shock waves
International Nuclear Information System (INIS)
Bykov, A.M.
1982-01-01
Random deflections of shock fronts propagated through the turbulent interstellar medium can produce the strong electro-density fluctuations on scales l> or approx. =10 13 cm inferred from pulsar radio scintillations. The development of turbulence in the hot-phase ISM is discussed
Conditional Eddies in Plasma Turbulence
DEFF Research Database (Denmark)
Johnsen, Helene; Pécseli, Hans; Trulsen, J.
1986-01-01
Conditional structures, or eddies, in turbulent flows are discussed with special attention to electrostatic turbulence in plasmas. The potential variation of these eddies is obtained by sampling the fluctuations only when a certain condition is satisfied in a reference point. The resulting...
Memory effects in turbulent diffusion
International Nuclear Information System (INIS)
Zagorodny, A.G.; Weiland, J.; Wilhelmsson, H.
1993-01-01
A non-Markovian approach is proposed for the derivation of the diffusion coefficient of saturated turbulence. A memory term accounting for nonlocal coherence effects is introduced in a new attempt to describe the transition between weak and strong turbulence. The result compares favourably with recent experiments as well as mode coupling simulations of fusion plasmas. (14 refs.)
Advances in compressible turbulent mixing
Energy Technology Data Exchange (ETDEWEB)
Dannevik, W.P.; Buckingham, A.C.; Leith, C.E. [eds.
1992-01-01
This volume includes some recent additions to original material prepared for the Princeton International Workshop on the Physics of Compressible Turbulent Mixing, held in 1988. Workshop participants were asked to emphasize the physics of the compressible mixing process rather than measurement techniques or computational methods. Actual experimental results and their meaning were given precedence over discussions of new diagnostic developments. Theoretical interpretations and understanding were stressed rather than the exposition of new analytical model developments or advances in numerical procedures. By design, compressibility influences on turbulent mixing were discussed--almost exclusively--from the perspective of supersonic flow field studies. The papers are arranged in three topical categories: Foundations, Vortical Domination, and Strongly Coupled Compressibility. The Foundations category is a collection of seminal studies that connect current study in compressible turbulent mixing with compressible, high-speed turbulent flow research that almost vanished about two decades ago. A number of contributions are included on flow instability initiation, evolution, and transition between the states of unstable flow onset through those descriptive of fully developed turbulence. The Vortical Domination category includes theoretical and experimental studies of coherent structures, vortex pairing, vortex-dynamics-influenced pressure focusing. In the Strongly Coupled Compressibility category the organizers included the high-speed turbulent flow investigations in which the interaction of shock waves could be considered an important source for production of new turbulence or for the enhancement of pre-existing turbulence. Individual papers are processed separately.
Nondissipative gravitational turbulence
International Nuclear Information System (INIS)
Gurevich, A.V.; Zybin, K.P.
1988-01-01
The nonlinear stage of development of the Jeans instability in a cold nondissipative gravitating gas is considered. It is shown that for a time exceeding the Jeans time a nondissipative gravitational singularity (NGS) is formed in the vicinity of a local density maximum. The NGS is a stationary dynamic structure, the basis of which is the singularity. The density of the gas at the center of the NGS (for r → 0) tends to infinity, and the field potential and the mean velocity of the trapped gas, possess a power singularity. The turbulent state arises as the result of development of the instability in the case of an irregular initial density distribution. It is an hierarchic structure consisting of nested moving NGS of various sizes, the NGS of smaller dimensions being trapped in the field of a NGS of larger dimensions. The scaling relations for each given NGS in this case hold for both the gas density and density of smaller size trapped NGS. A brief comparison with the observational data shows that the real hierarchic structure of the Universe ranging from scales pertaining to spherical stellar clusters up to those of rich galaxy clusters is apparently a developed gravitational turbulence
Kinerja Dan Efisiensi Bank Pemerintah (Bumn) Dan Busn Yang Go Publik Di Indonesia
Haryanto, Sugeng
2012-01-01
Penelitian ini menganalisis kinerja dan tingkat efisiensi bank-bank BUMN dan BUSN yang go Publik di Bursa Efek Indonesia. Sample penelitian ini mengambil tiga bank BUMN Bank BNI 46, Bank Mandiri dan Bank BRI) dan tiga bank BUSN (Bank BCA, Bank Niaga dan Bank Panin) dengan periode analisis tahun 2005-2011. Varibael yang digunakan meliputi ROA, ROE, LAR. LDR, NPL dan BOPO. Tujuan dari penelitian ini adalah melihat dan menganalisis perbedaan kinerja antara Bank BUMN dan BUSN yang go public di...
Prawira, Albert
2011-01-01
Perbedaan pola makan antara vegetarian dan non vegetarian dapat mempengaruhi kesehatan gigi dan mulut. Tujuan penelitian adalah untuk mengetahui kondisi oral higiene dan karies gigi pada umat vegetarian dan non vegetarian di Maha Vihara Maitreya Medan. Jenis penelitian adalah survei deskriptif. Sampel terdiri atas 74 vegetarian dan 65 non vegetarian. Pemeriksaan oral higiene dan karies gigi masing-masing menggunakan indeks OHIS Greene dan Vermillion dan indeks DMFT Klein, se...
Turbulent premixed flames on fractal-grid-generated turbulence
Energy Technology Data Exchange (ETDEWEB)
Soulopoulos, N; Kerl, J; Sponfeldner, T; Beyrau, F; Hardalupas, Y; Taylor, A M K P [Mechanical Engineering Department, Imperial College London, London SW7 2AZ (United Kingdom); Vassilicos, J C, E-mail: ns6@ic.ac.uk [Department of Aeronautics, Imperial College London, London SW7 2AZ (United Kingdom)
2013-12-15
A space-filling, low blockage fractal grid is used as a novel turbulence generator in a premixed turbulent flame stabilized by a rod. The study compares the flame behaviour with a fractal grid to the behaviour when a standard square mesh grid with the same effective mesh size and solidity as the fractal grid is used. The isothermal gas flow turbulence characteristics, including mean flow velocity and rms of velocity fluctuations and Taylor length, were evaluated from hot-wire measurements. The behaviour of the flames was assessed with direct chemiluminescence emission from the flame and high-speed OH-laser-induced fluorescence. The characteristics of the two flames are considered in terms of turbulent flame thickness, local flame curvature and turbulent flame speed. It is found that, for the same flow rate and stoichiometry and at the same distance downstream of the location of the grid, fractal-grid-generated turbulence leads to a more turbulent flame with enhanced burning rate and increased flame surface area. (paper)
Turbulent Fluid Motion 6: Turbulence, Nonlinear Dynamics, and Deterministic Chaos
Deissler, Robert G.
1996-01-01
Several turbulent and nonturbulent solutions of the Navier-Stokes equations are obtained. The unaveraged equations are used numerically in conjunction with tools and concepts from nonlinear dynamics, including time series, phase portraits, Poincare sections, Liapunov exponents, power spectra, and strange attractors. Initially neighboring solutions for a low-Reynolds-number fully developed turbulence are compared. The turbulence is sustained by a nonrandom time-independent external force. The solutions, on the average, separate exponentially with time, having a positive Liapunov exponent. Thus, the turbulence is characterized as chaotic. In a search for solutions which contrast with the turbulent ones, the Reynolds number (or strength of the forcing) is reduced. Several qualitatively different flows are noted. These are, respectively, fully chaotic, complex periodic, weakly chaotic, simple periodic, and fixed-point. Of these, we classify only the fully chaotic flows as turbulent. Those flows have both a positive Liapunov exponent and Poincare sections without pattern. By contrast, the weakly chaotic flows, although having positive Liapunov exponents, have some pattern in their Poincare sections. The fixed-point and periodic flows are nonturbulent, since turbulence, as generally understood, is both time-dependent and aperiodic.
Directory of Open Access Journals (Sweden)
Priscilia Yunita Wijaya
1999-01-01
Full Text Available We have seen many desain all around our everyday living. Design exist in the form of brochures%2C posters%2C banners%2C signages%2C book covers%2C and etcetera. Some are nice and easy to understand%2C some are ok%2C and some look like they are not fully develop and thought. A word that run across our mind whrn we enjoying a design is idea . A good design almost always associated with a good idea%2C is it tru? This paper is going to discuss about desain and its relationship to idea. Abstract in Bahasa Indonesia : Banyak desain yang diamati dalam kehidupan kita sehari-hari. Desain hadir dalam bentuk brosur%2C poster%2C spanduk%2C tanda-tanda%2C sampul buku%2C dan lain sebagainya. Ada beberapa yang bagus dan mudah untuk dimengerti%2C beberapa yang biasa%2C dan beberapa yang tampak asal dibuat. Sebuah kata yang terlintas dalam pemikiran kita dalam menikmati sebuah desain adalah ide . Sebuah desain yang baik selalu di identikan dengan ide yang baik%2C benarkah hal ini? Apakah desain dan apa hubungannya dengan ide akan dibahas pada tulisan ini.
Turbulent/non-turbulent interfaces detected in DNS of incompressible turbulent boundary layers
Watanabe, T.; Zhang, X.; Nagata, K.
2018-03-01
The turbulent/non-turbulent interface (TNTI) detected in direct numerical simulations is studied for incompressible, temporally developing turbulent boundary layers at momentum thickness Reynolds number Reθ ≈ 2000. The outer edge of the TNTI layer is detected as an isosurface of the vorticity magnitude with the threshold determined with the dependence of the turbulent volume on a threshold level. The spanwise vorticity magnitude and passive scalar are shown to be good markers of turbulent fluids, where the conditional statistics on a distance from the outer edge of the TNTI layer are almost identical to the ones obtained with the vorticity magnitude. Significant differences are observed for the conditional statistics between the TNTI detected by the kinetic energy and vorticity magnitude. A widely used grid setting determined solely from the wall unit results in an insufficient resolution in a streamwise direction in the outer region, whose influence is found for the geometry of the TNTI and vorticity jump across the TNTI layer. The present results suggest that the grid spacing should be similar for the streamwise and spanwise directions. Comparison of the TNTI layer among different flows requires appropriate normalization of the conditional statistics. Reference quantities of the turbulence near the TNTI layer are obtained with the average of turbulent fluids in the intermittent region. The conditional statistics normalized by the reference turbulence characteristics show good quantitative agreement for the turbulent boundary layer and planar jet when they are plotted against the distance from the outer edge of the TNTI layer divided by the Kolmogorov scale defined for turbulent fluids in the intermittent region.
Turbulent deflagrations, autoignitions, and detonations
Bradley, Derek
2012-09-01
Measurements of turbulent burning velocities in fan-stirred explosion bombs show an initial linear increase with the fan speed and RMS turbulent velocity. The line then bends over to form a plateau of high values around the maximum attainable burning velocity. A further increase in fan speed leads to the eventual complete quenching of the flame due to increasing localised extinctions because of the flame stretch rate. The greater the Markstein number, the more readily does flame quenching occur. Flame propagation along a duct closed at one end, with and without baffles to increase the turbulence, is subjected to a one-dimensional analysis. The flame, initiated at the closed end of the long duct, accelerates by the turbulent feedback mechanism, creating a shock wave ahead of it, until the maximum turbulent burning velocity for the mixture is attained. With the confining walls, the mixture is compressed between the flame and the shock plane up to the point where it might autoignite. This can be followed by a deflagration to detonation transition. The maximum shock intensity occurs with the maximum attainable turbulent burning velocity, and this defines the limit for autoignition of the mixture. For more reactive mixtures, autoignition can occur at turbulent burning velocities that are less than the maximum attainable one. Autoignition can be followed by quasi-detonation or fully developed detonation. The stability of ensuing detonations is discussed, along with the conditions that may lead to their extinction. © 2012 by Pleiades Publishing, Ltd.
Comparison of turbulence mitigation algorithms
Kozacik, Stephen T.; Paolini, Aaron; Sherman, Ariel; Bonnett, James; Kelmelis, Eric
2017-07-01
When capturing imagery over long distances, atmospheric turbulence often degrades the data, especially when observation paths are close to the ground or in hot environments. These issues manifest as time-varying scintillation and warping effects that decrease the effective resolution of the sensor and reduce actionable intelligence. In recent years, several image processing approaches to turbulence mitigation have shown promise. Each of these algorithms has different computational requirements, usability demands, and degrees of independence from camera sensors. They also produce different degrees of enhancement when applied to turbulent imagery. Additionally, some of these algorithms are applicable to real-time operational scenarios while others may only be suitable for postprocessing workflows. EM Photonics has been developing image-processing-based turbulence mitigation technology since 2005. We will compare techniques from the literature with our commercially available, real-time, GPU-accelerated turbulence mitigation software. These comparisons will be made using real (not synthetic), experimentally obtained data for a variety of conditions, including varying optical hardware, imaging range, subjects, and turbulence conditions. Comparison metrics will include image quality, video latency, computational complexity, and potential for real-time operation. Additionally, we will present a technique for quantitatively comparing turbulence mitigation algorithms using real images of radial resolution targets.
International Nuclear Information System (INIS)
Kahn, F.D.
1983-01-01
A relativistic plasma flow can explain many of the observations on the one-sided jets, which are associated with radio sources that show superluminal motions in their cores. The pressure from the ambient medium will communicate across the jet in a relatively short distance, typically 30 kpc. The friction between the jet and the external medium then makes the flow go turbulent. As a result the jet dissipates energy and will be brought to rest within a few hundred kpc, if it does not strike an obstacle before. The mean flow in the jet is strongly sheared and stretches the lines of force of any magnetic field frozen into the plasma. The dominant field direction, as seen from the rest frame of the plasma, is therefore parallel to the length of the jet. Polarization measurements have shown that this is in fact the case. (author)
International Nuclear Information System (INIS)
Pomeau, Y.
1981-07-01
In this work it is reviewed a few known types of transition to turbulence, as the cascade of period doubling and the intermittent transition. This happens in dynamical systems with a few degrees of freedom, as modelled by the iteration of non linear maps. Then it is presented specific transitions for systems with many degrees of freedom. It is condidered first the occurence of a low frequency broadband noise in large cells at the onset of Rayleigh-Benard convection; then the transition by intermittent bursts in parallel flows. In this last case, one is concerned with localized and finite amplitude perturbations. Simple geometric arguments show that these fluctuations, when they are isolated and with a well definite relative speed, exist for a single value of the Reynolds number only [fr
Saturation of the turbulent dynamo.
Schober, J; Schleicher, D R G; Federrath, C; Bovino, S; Klessen, R S
2015-08-01
The origin of strong magnetic fields in the Universe can be explained by amplifying weak seed fields via turbulent motions on small spatial scales and subsequently transporting the magnetic energy to larger scales. This process is known as the turbulent dynamo and depends on the properties of turbulence, i.e., on the hydrodynamical Reynolds number and the compressibility of the gas, and on the magnetic diffusivity. While we know the growth rate of the magnetic energy in the linear regime, the saturation level, i.e., the ratio of magnetic energy to turbulent kinetic energy that can be reached, is not known from analytical calculations. In this paper we present a scale-dependent saturation model based on an effective turbulent resistivity which is determined by the turnover time scale of turbulent eddies and the magnetic energy density. The magnetic resistivity increases compared to the Spitzer value and the effective scale on which the magnetic energy spectrum is at its maximum moves to larger spatial scales. This process ends when the peak reaches a characteristic wave number k☆ which is determined by the critical magnetic Reynolds number. The saturation level of the dynamo also depends on the type of turbulence and differs for the limits of large and small magnetic Prandtl numbers Pm. With our model we find saturation levels between 43.8% and 1.3% for Pm≫1 and between 2.43% and 0.135% for Pm≪1, where the higher values refer to incompressible turbulence and the lower ones to highly compressible turbulence.
Statistical properties of turbulence: An overview
Indian Academy of Sciences (India)
the turbulent advection of passive scalars, turbulence in the one-dimensional Burgers equation, and fluid turbulence in the presence of polymer ... However, it is not easy to state what would consti- tute a solution of the turbulence ...... flow with Lagrangian tracers and use a cubic spline interpolation method to calculate their ...
Scale separation closure and Alfven wave turbulence
International Nuclear Information System (INIS)
Chen, C.Y.; Mahajan, S.M.
1985-04-01
Based on the concept of scale separation between coherent response function and incoherent source for renormalized turbulence theories, a closure scheme is proposed. A model problem dealing with shear-Alfven wave turbulence is numerically solved; the solution explicitly shows expected turbulence features such as frequency shift from linear modes, band-broadening, and a power law dependence for the turbulence spectrum
Strong Turbulence in Low-beta Plasmas
DEFF Research Database (Denmark)
Tchen, C. M.; Pécseli, Hans; Larsen, Søren Ejling
1980-01-01
An investigation of the spectral structure of turbulence in a plasma confined by a strong homogeneous magnetic field was made by means of a fluid description. The turbulent spectrum is divided into subranges. Mean gradients of velocity and density excite turbulent motions, and govern the production......-cathode reflex arc, Stellarator, Zeta discharge, ionospheric plasmas, and auroral plasma turbulence....
Effects of premixed flames on turbulence and turbulent scalar transport
Energy Technology Data Exchange (ETDEWEB)
Lipatnikov, A.N.; Chomiak, J. [Department of Applied Mechanics, Chalmers University of Technology, 412 75 Goeteborg (Sweden)
2010-02-15
Experimental data and results of direct numerical simulations are reviewed in order to show that premixed combustion can change the basic characteristics of a fluctuating velocity field (the so-called flame-generated turbulence) and the direction of scalar fluxes (the so-called countergradient or pressure-driven transport) in a turbulent flow. Various approaches to modeling these phenomena are discussed and the lack of a well-elaborated and widely validated predictive approach is emphasized. Relevant basic issues (the transition from gradient to countergradient scalar transport, the role played by flame-generated turbulence in the combustion rate, the characterization of turbulence in premixed flames, etc.) are critically considered and certain widely accepted concepts are disputed. Despite the substantial progress made in understanding the discussed effects over the past decades, these basic issues strongly need further research. (author)
Effect of turbulent collisions on diffusion in stationary plasma turbulence
International Nuclear Information System (INIS)
Xia, H.; Ishihara, O.
1990-01-01
Recently the velocity diffusion process was studied by the generalized Langevin equation derived by the projection operator method. The further study shows that the retarded frictional function plays an important role in suppressing particle diffusion in the velocity space in stronger turbulence as much as the resonance broadening effect. The retarded frictional effect, produced by the effective collisions due to the plasma turbulence is assumed to be a Gaussian, but non-Markovian and non-wide-sense stationary process. The relations between the proposed formulation and the extended resonance broadening theory is discussed. The authors also carry out test particle numerical experiment for Langmuir turbulence to test the theories. In a stronger turbulence a deviation of the diffusion rate from the one predicted by both the quasilinear and the extended resonance theories has been observed and is explained qualitatively by the present formulation
Wind energy impact of turbulence
Hölling, Michae; Ivanell, Stefan
2014-01-01
This book presents the results of the seminar ""Wind Energy and the Impact of Turbulence on the Conversion Process"" which was supported from three societies, namely the EUROMech, EAWE and ERCOFATC and took place in Oldenburg, Germany in spring 2012.The seminar was one of the first scientific meetings devoted to the common topic of wind energy and basic turbulence. The established community of researchers working on the challenging puzzle of turbulence for decades met the quite young community of researchers, who face the upcoming challenges in the fast growing field of wind energy application
Outer scale of atmospheric turbulence
Lukin, Vladimir P.
2005-10-01
In the early 70's, the scientists in Italy (A.Consortini, M.Bertolotti, L.Ronchi), USA (R.Buser, Ochs, S.Clifford) and USSR (V.Pokasov, V.Lukin) almost simultaneously discovered the phenomenon of deviation from the power law and the effect of saturation for the structure phase function. During a period of 35 years we have performed successively the investigations of the effect of low-frequency spectral range of atmospheric turbulence on the optical characteristics. The influence of the turbulence models as well as a outer scale of turbulence on the characteristics of telescopes and systems of laser beam formations has been determined too.
Quantum Turbulence ---Another da Vinci Code---
Tsubota, M.
Quantum turbulence comprises a tangle of quantized vorticeswhich are stable topological defects created by Bose-Einstein condensation, being realized in superfluid helium and atomic Bose-Einstein condensates. In recent years there has been a growing interest in quantum turbulence. One of the important motivations is to understand the relation between quantum and classical turbulence. Quantum turbulence is expected to be much simpler than usual classical turbulence and give a prototype of turbulence. This article reviews shortly the recent research developments on quantum turbulence.
Directory of Open Access Journals (Sweden)
Lilik Mulyadi
2015-07-01
Full Text Available UU Contempt of Court merupakan kebutuhan yang bersifat urgent, segera dan mendesak, sehingga perlu dilakukan kajian dan penelitian secara kritis, akademis dan bersifat komprehensif untuk menjaga keluhuran dan menegakkan martabat dan wibawa peradilan.
Epistemologi dan Keterbatasan Teori Gravitasi
Directory of Open Access Journals (Sweden)
Erwin Erwin
2017-08-01
Full Text Available Peristiwa tentang kecenderungan jatuhnya benda-benda menuju pusat bumi dan keteraturan peredaran planet dan benda-benda langit lainnya dalam tata surya dahulu dianggap dua fenomena yang berbeda. Mekanika benda langit dan mekanika bumi yang sebelumnya merupakan dua pengetahuan yang terpisah, dianggap satu kesatuan oleh Sir Isaac Newton. Newton mengemukakan hukum gravitasi umum yaitu gaya tarik menarik antara dua benda besarnya sebanding dengan massa masing-masing benda dan berbanding terbalik dengan kuadrat jarak antara kedua benda. Hukum gravitasi ini sukses menjalaskan bagaimana benda cendrung jatuh menuju pusat bumi dan peredaran planet dan benda-benda langit lain mengelilingi matahari dalam sistem tata surya. Namun hukum gravitasi Newton ternyata tidak sepenuhnya tepat, beberapa hal dapat dijelaskan dengan hukum relativitas Einstein, namun demikian hukum relativitas Einstein juga dicurigai masih perlu diamandemen agar dapat menjelaskan fenomena alam dengan tepat.
EPISTEMOLOGI DAN KETERBATASAN TEORI GRAVITASI
Directory of Open Access Journals (Sweden)
Erwin Erwin
2017-08-01
Full Text Available Peristiwa tentang kecenderungan jatuhnya benda-benda menuju pusat bumi dan keteraturan peredaran planet dan benda-benda langit lainnya dalam tata surya dahulu dianggap dua fenomena yang berbeda. Mekanika benda langit dan mekanika bumi yang sebelumnya merupakan dua pengetahuan yang terpisah, dianggap satu kesatuan oleh Sir Isaac Newton. Newton mengemukakan hukum gravitasi umum yaitu gaya tarik menarik antara dua benda besarnya sebanding dengan massa masing-masing benda dan berbanding terbalik dengan kuadrat jarak antara kedua benda. Hukum gravitasi ini sukses menjalaskan bagaimana benda cendrung jatuh menuju pusat bumi dan peredaran planet dan benda-benda langit lain mengelilingi matahari dalam sistem tata surya. Namun hukum gravitasi Newton ternyata tidak sepenuhnya tepat, beberapa hal dapat dijelaskan dengan hukum relativitas Einstein, namun demikian hukum relativitas Einstein juga dicurigai masih perlu diamandemen agar dapat menjelaskan fenomena alam dengan tepat.
ECOULEMENT MAMELONNAIRE SANGLANT UNILATERAL ET ...
African Journals Online (AJOL)
22 déc. 2009 ... However malignant forms can be individualized and their short- term prognosis is very reserved. KEYS WORDS: Bloody nipple discharge - Breast cancer - Prognosis ... lever le doute de la malignité, sauf en cas d'association à des signes locaux suspects. Les pièces opératoires sont analysées, archivées et ...
ISLAM DAN RADIKALISME: Upaya Antisipasi dan Penanggulangannya
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Idrus Ruslan
2017-02-01
Full Text Available Sejak tragedi pemboman WTC tanggal 11 September 2001 yang disusul dengan rangkaian peledakan bom di sejumlah negara, banyak orang non Muslim yang berasumsi bahwa ajaran Islam identik dengan radikalisme. Walaupun assumsi yang berkembang itu dapat dimaklumi, namun keyakinan tersebut tentu saja tidak sepenuhnya benar. Karena meskipun terdapat sekelompok orang Islam yang berbuat radikal, akan tetapi mayoritas Muslim justru bertentangan dengan mereka. Lagi pula, jika dicermati secara mendalam, sesungguhnya Islam sama sekali tidak mentolerir tindakan radikal. Ia adalah agama kasih sayang yang sangat mendodrong penganutnya untuk berbuat baik terhadap orang lain, termasuk kepada orang-orang non-Muslim. Artikel ini menawarkan beberapa upaya strategis dalam mengantisipasi dan menanggulangi bahaya radikalisme-terorisme.
Turbulence optimisation in stellarator experiments
Energy Technology Data Exchange (ETDEWEB)
Proll, Josefine H.E. [Max-Planck/Princeton Center for Plasma Physics (Germany); Max-Planck-Institut fuer Plasmaphysik, Wendelsteinstr. 1, 17491 Greifswald (Germany); Faber, Benjamin J. [HSX Plasma Laboratory, University of Wisconsin-Madison, Madison, WI 53706 (United States); Helander, Per; Xanthopoulos, Pavlos [Max-Planck/Princeton Center for Plasma Physics (Germany); Lazerson, Samuel A.; Mynick, Harry E. [Plasma Physics Laboratory, Princeton University, P.O. Box 451 Princeton, New Jersey 08543-0451 (United States)
2015-05-01
Stellarators, the twisted siblings of the axisymmetric fusion experiments called tokamaks, have historically suffered from confining the heat of the plasma insufficiently compared with tokamaks and were therefore considered to be less promising candidates for a fusion reactor. This has changed, however, with the advent of stellarators in which the laminar transport is reduced to levels below that of tokamaks by shaping the magnetic field accordingly. As in tokamaks, the turbulent transport remains as the now dominant transport channel. Recent analytical theory suggests that the large configuration space of stellarators allows for an additional optimisation of the magnetic field to also reduce the turbulent transport. In this talk, the idea behind the turbulence optimisation is explained. We also present how an optimised equilibrium is obtained and how it might differ from the equilibrium field of an already existing device, and we compare experimental turbulence measurements in different configurations of the HSX stellarator in order to test the optimisation procedure.
Optimizing Stellarators for Turbulent Transport
International Nuclear Information System (INIS)
Mynick, H.E.; Pomphrey, N.; Xanthopoulos, P.
2010-01-01
Up to now, the term 'transport-optimized' stellarators has meant optimized to minimize neoclassical transport, while the task of also mitigating turbulent transport, usually the dominant transport channel in such designs, has not been addressed, due to the complexity of plasma turbulence in stellarators. Here, we demonstrate that stellarators can also be designed to mitigate their turbulent transport, by making use of two powerful numerical tools not available until recently, namely gyrokinetic codes valid for 3D nonlinear simulations, and stellarator optimization codes. A first proof-of-principle configuration is obtained, reducing the level of ion temperature gradient turbulent transport from the NCSX baseline design by a factor of about 2.5.
Structure and modeling of turbulence
International Nuclear Information System (INIS)
Novikov, E.A.
1995-01-01
The open-quotes vortex stringsclose quotes scale l s ∼ LRe -3/10 (L-external scale, Re - Reynolds number) is suggested as a grid scale for the large-eddy simulation. Various aspects of the structure of turbulence and subgrid modeling are described in terms of conditional averaging, Markov processes with dependent increments and infinitely divisible distributions. The major request from the energy, naval, aerospace and environmental engineering communities to the theory of turbulence is to reduce the enormous number of degrees of freedom in turbulent flows to a level manageable by computer simulations. The vast majority of these degrees of freedom is in the small-scale motion. The study of the structure of turbulence provides a basis for subgrid-scale (SGS) models, which are necessary for the large-eddy simulations (LES)
Modeling Compressed Turbulence with BHR
Israel, Daniel
2011-11-01
Turbulence undergoing compression or expansion occurs in systems ranging from internal combustion engines to supernovae. One common feature in many of these systems is the presence of multiple reacting species. Direct numerical simulation data is available for the single-fluid, low turbulent Mach number case. Wu, et al. (1985) compared their DNS results to several Reynolds-averaged Navier-Stokes models. They also proposed a three-equation k - ɛ - τ model, in conjunction with a Reynolds-stress model. Subsequent researchers have proposed alternative corrections to the standard k - ɛ formulation. Here we investigate three variants of the BHR model (Besnard, 1992). BHR is a model for multi-species variable-density turbulence. The three variants are the linear eddy-viscosity, algebraic-stress, and full Reynolds-stress formulations. We then examine the predictions of the model for the fluctuating density field for the case of variable-density turbulence.
Premixed autoignition in compressible turbulence
Konduri, Aditya; Kolla, Hemanth; Krisman, Alexander; Chen, Jacqueline
2016-11-01
Prediction of chemical ignition delay in an autoignition process is critical in combustion systems like compression ignition engines and gas turbines. Often, ignition delay times measured in simple homogeneous experiments or homogeneous calculations are not representative of actual autoignition processes in complex turbulent flows. This is due the presence of turbulent mixing which results in fluctuations in thermodynamic properties as well as chemical composition. In the present study the effect of fluctuations of thermodynamic variables on the ignition delay is quantified with direct numerical simulations of compressible isotropic turbulence. A premixed syngas-air mixture is used to remove the effects of inhomogeneity in the chemical composition. Preliminary results show a significant spatial variation in the ignition delay time. We analyze the topology of autoignition kernels and identify the influence of extreme events resulting from compressibility and intermittency. The dependence of ignition delay time on Reynolds and turbulent Mach numbers is also quantified. Supported by Basic Energy Sciences, Dept of Energy, United States.
Workshop on Engineering Turbulence Modeling
Povinelli, Louis A. (Editor); Liou, W. W. (Editor); Shabbir, A. (Editor); Shih, T.-H. (Editor)
1992-01-01
Discussed here is the future direction of various levels of engineering turbulence modeling related to computational fluid dynamics (CFD) computations for propulsion. For each level of computation, there are a few turbulence models which represent the state-of-the-art for that level. However, it is important to know their capabilities as well as their deficiencies in order to help engineers select and implement the appropriate models in their real world engineering calculations. This will also help turbulence modelers perceive the future directions for improving turbulence models. The focus is on one-point closure models (i.e., from algebraic models to higher order moment closure schemes and partial differential equation methods) which can be applied to CFD computations. However, other schemes helpful in developing one-point closure models, are also discussed.
Toy models of developed turbulence
Directory of Open Access Journals (Sweden)
M.Hnatich
2005-01-01
Full Text Available We have investigated the advection of a passive scalar quantity by incompressible helical turbulent flow within the framework of extended Kraichnan model. Turbulent fluctuations of velocity field are assumed to have the Gaussian statistics with zero mean and defined noise with finite time-correlation. Actual calculations have been done up to two-loop approximation within the framework of field-theoretic renormalization group approach. It turned out that space parity violation (helicity of turbulent environment does not affect anomalous scaling which is a peculiar attribute of the corresponding model without helicity. However, stability of asymptotic regimes, where anomalous scaling takes place, strongly depends on the amount of helicity. Moreover, helicity gives rise to the turbulent diffusivity, which has been calculated in one-loop approximation.
Stochastic Subspace Modelling of Turbulence
DEFF Research Database (Denmark)
Sichani, Mahdi Teimouri; Pedersen, B. J.; Nielsen, Søren R.K.
2009-01-01
positive definite cross-spectral density matrix a frequency response matrix is constructed which determines the turbulence vector as a linear filtration of Gaussian white noise. Finally, an accurate state space modelling method is proposed which allows selection of an appropriate model order......, and estimation of a state space model for the vector turbulence process incorporating its phase spectrum in one stage, and its results are compared with a conventional ARMA modelling method.......Turbulence of the incoming wind field is of paramount importance to the dynamic response of civil engineering structures. Hence reliable stochastic models of the turbulence should be available from which time series can be generated for dynamic response and structural safety analysis. In the paper...
Turbulence in unmagnetized Vlasov plasmas
International Nuclear Information System (INIS)
Kuo, S.P.
1985-01-01
The classical technique of transformation and characteristics is employed to analyze the problem of strong turbulence in unmagnetized plasmas. The effect of resonance broadening and perturbation expansion are treated simultaneously, without time secularities. The renormalization procedure of Dupree and Tetreault is used in the transformed Vlasov equation to analyze the turbulence and to derive explicitly a diffusion equation. Analyses are extended to inhomogeneous plasmas and the relationship between the transformation and ponderomotive force is obtained. (author)
Turbulent effective absorptivity and refractivity
International Nuclear Information System (INIS)
Rax, J.M.
1984-09-01
The problem of wave propagation in a turbulent magnetized plasma is investigated. Considering small scale, low frequency density fluctuations we solve the Maxwell equations and show that the eikonal approximation remains valid with an effective refractivity and an effective absorptivity taking into account the energy diffusion due to the turbulent motion. Then the result is applied to the problem of lower hybrid waves scattering by drift waves density fluctuations in tokamaks
Quantify the complexity of turbulence
Tao, Xingtian; Wu, Huixuan
2017-11-01
Many researchers have used Reynolds stress, power spectrum and Shannon entropy to characterize a turbulent flow, but few of them have measured the complexity of turbulence. Yet as this study shows, conventional turbulence statistics and Shannon entropy have limits when quantifying the flow complexity. Thus, it is necessary to introduce new complexity measures- such as topology complexity and excess information-to describe turbulence. Our test flow is a classic turbulent cylinder wake at Reynolds number 8100. Along the stream-wise direction, the flow becomes more isotropic and the magnitudes of normal Reynolds stresses decrease monotonically. These seem to indicate the flow dynamics becomes simpler downstream. However, the Shannon entropy keeps increasing along the flow direction and the dynamics seems to be more complex, because the large-scale vortices cascade to small eddies, the flow is less correlated and more unpredictable. In fact, these two contradictory observations partially describe the complexity of a turbulent wake. Our measurements (up to 40 diameters downstream the cylinder) show that the flow's degree-of-complexity actually increases firstly and then becomes a constant (or drops slightly) along the stream-wise direction. University of Kansas General Research Fund.
DIVERSITAS DAN KERAPATAN MANGROVE, GASTROPODA DAN BIVALVIA DI ESTUARI PERANCAK, BALI
Susiana; Ali, Syamsu Alam; Rukminasari, Nita
2011-01-01
Penelitian ini bertujuan membandingkan diversitas dan kerapatan mangrove dengan kepadatan gastropoda dan bivalvia di mangrove alami dan rehabilitasi. Pengukuran ekosistem mangrove menggunakan transek kuadrat 10 m x 10 m. Kelimpahan dan kepadatan gastropoda dan bialvia menggunakan transek kuadrat berukuran 1 m x 1 m. Analisis nMDS, cluster untuk melihat hubungan karekteristik mangrove alami dan rehabilitasi dianalisis secara deskriptif dan analisis regresi untuk mendetermi...
Recent developments in plasma turbulence and turbulent transport
Energy Technology Data Exchange (ETDEWEB)
Terry, P.W. [Univ. of Wisconsin, Madison, WI (United States)
1997-09-22
This report contains viewgraphs of recent developments in plasma turbulence and turbulent transport. Localized nonlinear structures occur under a variety of circumstances in turbulent, magnetically confined plasmas, arising in both kinetic and fluid descriptions, i.e., in either wave-particle or three-wave coupling interactions. These structures are non wavelike. They cannot be incorporated in the collective wave response, but interact with collective modes through their shielding by the plasma dielectric. These structures are predicted to modify turbulence-driven transport in a way that in consistent with, or in some cases are confirmed by recent experimental observations. In kinetic theory, non wavelike structures are localized perturbations of phase space density. There are two types of structures. Holes are self-trapped, while clumps have a self-potential that is too weak to resist deformation and mixing by ambient potential fluctuations. Clumps remain correlated in turbulence if their spatial extent is smaller than the correlation length of the scattering fields. In magnetic turbulence, clumps travel along stochastic magnetic fields, shielded by the plasma dielectric. A drag on the clump macro-particle is exerted by the shielding, inducing emission into the collective response. The emission in turn damps back on the particle distribution via Landau dampling. The exchange of energy between clumps and particles, as mediated by the collective mode, imposes constraints on transport. For a turbulent spectrum whose mean wavenumber along the equilibrium magnetic field is nonzero, the electron thermal flux is proportional to the ion thermal velocity. Conventional predictions (which account only for collective modes) are larger by the square root of the ion to electron mass ratio. Recent measurements are consistent with the small flux. In fluid plasma,s localized coherent structures can occur as intense vortices.
DAKWAH DAN PEMBERDAYAAN PEREMPUAN
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Siti Nurmahyati
2017-02-01
Full Text Available Da’wah is an attempt to persuade and influence others in realizing the teachings of Islam, to achieve worldly prosperity and welfare of the hereafter. The success was fueled by propaganda aspects are interrelated, anatara preachers, propaganda material, propaganda strategy, mad’u (target da’wah. The number of women in this country nearly half of people (49.36. therefore, it is important to empower women in da’wah to build their own people in consciousness and religious activities that provide the basics of life prosperous world and hereafter. Dakwah merupakan suatu upaya untuk mengajak dan mempengaruhi orang lain dalam merealisasikan ajaran Islam, untuk mencapai tujuan kesejahteraan duniawi maupun kesejahteraan ukhrawi. Keberhasilan tersebut pun dipicu oleh berbagai aspek dakwah yang saling terkait, antara juru dakwah, materi dakwah, strategi dakwah, mad’u (sasaran dakwah. Jumlah kaum perempuan di negara ini hampir mencapai separuh dari jumlah masyarakatnya (49,36. Oleh karena itu, sangat penting sekali pemberdayaan perempuan dalam dakwah untuk membangun kaumnya sendiri dalam kesadaran dan aktivitas-aktivitas keagamaan yang memberikan dasar kehidupan sejahtera duniawi dan ukhrawi.
ASIMETRI INFORMASI DAN UNDERPRICING
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Tety Anggita Safitri
2013-03-01
Full Text Available Tujuan penelitian ini adalah untuk menguji pengaruh asimetri informasi terhadap underpricing. Penelitian ini menggunakan sampel 63 perusahaan yang melakukan penawaran umum perdana di Bursa Efek Indonesia dalam kurun waktu 2005-2010. Analisis data menggunakan regresi linier berganda, yaitu menguji proksi asimetri informasi yang terdiri atas ukuran perusahaan, umur perusahaan, proporsi saham yang ditawarkan kepada masyarakat, reputasi underwriter dan reputasi auditor terhadap underpricing. Hasil penelitian ini mengindikasikan bahwa reputasi underwriter dan reputasi auditor berpengaruh terhadap underpricing. Ukuran perusahaan, umur perusahaan dan proporsi saham yang ditawarkan tidak berpengaruh terhadap underpricing.The aim of this research is to examine the effect of assymetric information on underpricing. This research used a sample of 63 companies that make initial public offering on the Indonesia Stock Exchange in the period of 2005-2010. The data analysis is using multiple linear regression, which is testing the proxy of asymmetric information which consists of the firm size, the firm age, the proportion of shares offered to the public, underwriter reputation and auditor reputation on underpricing. This research indicates that underwriter reputation and auditor reputation have a significant effect on underpricing. The firm size, the firm age and the proportion of shares offered to the public have no significant effect on underpricing.
Bominaar, Jeroen; Pashtrapanska, Mira; Elenbaas, Thijs; Dam, Nico; ter Meulen, Hans; van de Water, Willem
2008-04-01
We describe a scheme of molecular tagging velocimetry in air in which nitric oxide (NO) molecules are created out of O2 and N2 molecules in the focus of a strong laser beam. The NO molecules are visualized a while later by laser-induced fluorescence. The precision of the molecular tagging velocimetry of gas flows is affected by the gradual blurring of the written patterns through molecular diffusion. In the case of turbulent flows, molecular diffusion poses a fundamental limit on the resolution of the smallest scales in the flow. We study the diffusion of written patterns in detail for our tagging scheme which, at short (micros) delay times is slightly anomalous due to local heating by absorption of laser radiation. We show that our experiments agree with a simple convection-diffusion model that allows us to estimate the temperature rise upon writing. Molecular tagging can be a highly nonlinear process, which affects the art of writing. We find that our tagging scheme is (only) quadratic in the intensity of the writing laser.
Energy Technology Data Exchange (ETDEWEB)
Soubbaramayer, [Commissariat a l' Energie Atomique, Saclay (France). Centre d' Etudes Nucleaires
1967-03-01
This work deals with detonation and deflagration waves in magnetogasdynamics. Four types of detonations and four types of deflagration are considered. We point out that the propagation of these waves is not always completely determined by the initial boundary conditions and the conservation laws across the discontinuity. To fix the ideas we consider the piston problem and we show that in some cases more conditions must be added to the conservation laws in order to provide sufficient data for the unique determination of the propagation process. We then show that the needed additional conditions may be derived from an investigation of the internal structure of the detonation and deflagration process in magneto gas dynamics. This internal structure is investigated for the eight types of process under the influence of the combustion mechanism and the dissipative coefficients (viscosities, electrical and thermal conductivity). Finally all the possible solutions for the piston problem are discussed in a simple case. The methods developed here may be extended to ionizing shocks. (author) [French] On considere dans ce travail les ondes de detonation et de deflagration en magneto-dynamique. Quatre types de detonation et quatre types de deflagration sont etudies. On montre d'abord que la propagation de ces ondes n'est pas toujours completement determinee par les conditions initiales, les conditions aux limites et les conditions de choc. Pour fixer les idees nous considerons le probleme du piston et nous montrons que, dans certains cas, des conditions supplementaires doivent etre jointes aux conditions de choc pour determiner l'ecoulement d'une facon unique. Nous montrons ensuite que ces conditions supplementaires peuvent etre deduites de l'analyse de la structure interne des detonations et des deflagrations magnetodynamiques. Cette structure interne est etudiee en tenant compte du mecanisme de combustion et des coefficients de dissipation (viscosites, conductivites
DAMPAK NEGATIF PERKEMBANGAN TEKNOLOGI INFORMATIKA DAN KOMUNIKASI DAN CARA ANTISIFASINYA
Directory of Open Access Journals (Sweden)
I Gede Ratnaya
2011-03-01
Full Text Available Sampai saat ini perkembangan ilmu pengetahuan telah menghantarkan masyarakat menuju babak baru yaitu babak yang memanfaatkan peralatan-peralatan yang merupakan hasil dari teknologi. Penggunaan tenaga manusia yang semakin hari semakin kecil volumenya sering kali menyebabkan orang kehilangan pekerjaannya karena tugasnya telah tergantikan oleh peralatan atau mesin. Sebagai sarana penyampaian informasi dan komunikasi, komputer bisa dipakai sebagai sarana berinternetan. Lewat internet orang bisa mencari bermacam-macam informasi dan berkomunikasi. Peran yang dapat diberikan oleh aplikasi teknologi informasi ini adalah mendapatkan informasi untuk kehidupan pribadi seperti informasi tentang kesehatan, hobi, rekreasi, dan rohani. Selain memberikan keuntungan, ternyata peralatan teknologi informasi dan komunikasi juga memberikan dampak negatif bagi penggunanya. Dampak negatif tersebut muncul sebagai akibat dari penggunaan yang salah atau tidak bertanggung jawab dari yang menggunakan. Beberapa dampak negatif tersebut adalah 1. Anak lebih banyak menghabiskan waktu menonton TV ketimbang melakukan hal lainnya (seperti belajar dan olah raga, 2. Anak kehilangan kemampuan berbaur dengan masyarakat dan cenderung nyaman dengan kehidupan online, 3 Adanya pelanggaran hak cipta, 4. Kejahatan di internet, 5. Penyebaran virus komputer, dan 6. Pornografi, perjudian, penipuan, tayangan kekerasan. Adapun cara mengatasi dampak-dampak negatif tersebut adalah : 1. Gunakan teknologi untuk menjalin hubungan dengan orang yang sudah dikenal, 2. Cari komunitas positif yang sering melakukan pertemuan didunia nyata, 3. Perlunya penegakkan hukum yang berlaku dengan dibentuknya polisi internet, 4. Menghindari pemakaian telepon seluler yang berfitur canggih oleh anak-anak dibawah umur dan lebih mengawasi penggunaan telepon seluler, 5. Perbanyak membaca buku-buku yang bersifat edukatif dan bersifat keimanan serta aplikasi komputer yang bersifat mendidik, dan 6. Perlunya pengaturan
KETERGANTUNGAN ONLINE GAME DAN PENANGANANNYA
Directory of Open Access Journals (Sweden)
Ridwan Syahran
2015-06-01
Full Text Available Penelitian ini dimaksudkan untuk mengetahui perilaku yang ditimbulkan dari kecanduan bermaian online game pada siswa SMP Negeri 1 Palu yang meliputi faktor-faktor penyebab kecanduan, keadaan psikologis yang ditimbulkan dari kecanduan bermain online game dan dampak-dampak yang ditimbulkan dari kecanduan bermain online game.Pendekatan penelitian ini adalah penelitian kualitatif dengan jenis penelitian studi kasus dengan berdasarkan responden dan informan sebagai bahan sumber data. Dalam proses pengumpulan data digunakan teknik observasi dan wawancara, dimana setelah data diperoleh selanjutnya dianalisis dengan menggunakan analisis deskriptif kualitatif.Berdasarkan hasil penelitian ini, bahwa subyek (RZ dan (MT, kedua subyek penelitian menjadi ketergantungan atau kecanduan untuk bermain online game yang dikarenakan tersedianya beberapa fasilitas pendukung untuk bermain game di rumah, adanya faktor sosial dari pertemanan dengan teman bermain dan keingintahuan yang sangat besar terhadap suatu jenis game. Penanganan ketergantungan game online dengan bantuan dari berbagai pihak terutama pihak sekolah memberikan kepercayaan kepada konselor sekolah atau guru BK untuk mengadakan seminar kepada orang tua siswa tentang game online dan masalah yang akan ditimbulkan, mengatur waktu belajar dan bermain anak, memasukkan materi tentang game online dan dampaknya kepada siswa serta memberikan penyaluran yang baik dalam memilih game yang edukatif serta Menjalin komunikasi interpersonal agar anak dapat terbuka dengan orang tua.
Modeling of Turbulent Swirling Flows
Shih, Tsan-Hsing; Zhu, Jiang; Liou, William; Chen, Kuo-Huey; Liu, Nan-Suey; Lumley, John L.
1997-01-01
Aircraft engine combustors generally involve turbulent swirling flows in order to enhance fuel-air mixing and flame stabilization. It has long been recognized that eddy viscosity turbulence models are unable to appropriately model swirling flows. Therefore, it has been suggested that, for the modeling of these flows, a second order closure scheme should be considered because of its ability in the modeling of rotational and curvature effects. However, this scheme will require solution of many complicated second moment transport equations (six Reynolds stresses plus other scalar fluxes and variances), which is a difficult task for any CFD implementations. Also, this scheme will require a large amount of computer resources for a general combustor swirling flow. This report is devoted to the development of a cubic Reynolds stress-strain model for turbulent swirling flows, and was inspired by the work of Launder's group at UMIST. Using this type of model, one only needs to solve two turbulence equations, one for the turbulent kinetic energy k and the other for the dissipation rate epsilon. The cubic model developed in this report is based on a general Reynolds stress-strain relationship. Two flows have been chosen for model evaluation. One is a fully developed rotating pipe flow, and the other is a more complex flow with swirl and recirculation.
Advancements in engineering turbulence modeling
Shih, T.-H.
1991-01-01
Some new developments in two-equation models and second order closure models are presented. Two-equation models (k-epsilon models) have been widely used in computational fluid dynamics (CFD) for engineering problems. Most of low-Reynolds number two-equation models contain some wall-distance damping functions to account for the effect of wall on turbulence. However, this often causes the confusion and difficulties in computing flows with complex geometry and also needs an ad hoc treatment near the separation and reattachment points. A set of modified two-equation models is proposed to remove the aforementioned shortcomings. The calculations using various two-equation models are compared with direct numerical simulations of channel flow and flat boundary layers. Development of a second order closure model is also discussed with emphasis on the modeling of pressure related correlation terms and dissipation rates in the second moment equations. All the existing models poorly predict the normal stresses near the wall and fail to predict the 3-D effect of mean flow on the turbulence (e.g. decrease in the shear stress caused by the cross flow in the boundary layer). The newly developed second order near-wall turbulence model is described and is capable of capturing the near-wall behavior of turbulence as well as the effect of 3-D mean flow on the turbulence.
TRIAM-1 turbulent heating experiment
Energy Technology Data Exchange (ETDEWEB)
Nakamura, Yukio; Hiraki, Naoji; Nakamura, Kazuo; Kikuchi, Mitsuru; Nagao, Akihiro [Kyushu Univ., Fukuoka (Japan). Research Inst. for Applied Mechanics
1983-02-01
The experimental studies on the containment of high temperature plasma and turbulent heating using the tokamak device with strong magnetic field (TRIAM-1) started in 1977 have achieved much results up to fiscal 1979, and the anticipated objectives were almost attained. The results of these studies were summarized in the ''Report of the results of strong magnetic field tokamak TRIAM-1 experiment''. In this report, the results obtained by the second stage project of the TRIAM-1 project are summarized. The second stage was the two-year project for fiscal 1980 and 81. In the second stage project, by the complete preparation of measuring instrument and the improvement of the experimental setup, the carefully planned experiment on turbulent heating was performed, in particular, the clarification of the mechanism of turbulent heating was the central theme. As the important results obtained, the detection of ion sound waves at the time of turbulent heating, the formation of high energy ions by wave-particle interaction and the clarification of the process of their energy relaxation, and the verification of the effectiveness of double pulse turbulent heating are enumerated.
TRIAM-1 turbulent heating experiment
International Nuclear Information System (INIS)
Nakamura, Yukio; Hiraki, Naoji; Nakamura, Kazuo; Kikuchi, Mitsuru; Nagao, Akihiro
1983-01-01
The experimental studies on the containment of high temperature plasma and turbulent heating using the tokamak device with strong magnetic field (TRIAM-1) started in 1977 have achieved much results up to fiscal 1979, and the anticipated objectives were almost attained. The results of these studies were summarized in the ''Report of the results of strong magnetic field tokamak TRIAM-1 experiment''. In this report, the results obtained by the second stage project of the TRIAM-1 project are summarized. The second stage was the two-year project for fiscal 1980 and 81. In the second stage project, by the complete preparation of measuring instrument and the improvement of the experimental setup, the carefully planned experiment on turbulent heating was performed, in particular, the clarification of the mechanism of turbulent heating was the central theme. As the important results obtained, the detection of ion sound waves at the time of turbulent heating, the formation of high energy ions by waveparticle interaction and the clarification of the process of their energy relaxation, and the verification of the effectiveness of double pulse turbulent heating are enumerated. (Kako, I.)
PDF turbulence modeling and DNS
Hsu, A. T.
1992-01-01
The problem of time discontinuity (or jump condition) in the coalescence/dispersion (C/D) mixing model is addressed in probability density function (pdf). A C/D mixing model continuous in time is introduced. With the continuous mixing model, the process of chemical reaction can be fully coupled with mixing. In the case of homogeneous turbulence decay, the new model predicts a pdf very close to a Gaussian distribution, with finite higher moments also close to that of a Gaussian distribution. Results from the continuous mixing model are compared with both experimental data and numerical results from conventional C/D models. The effect of Coriolis forces on compressible homogeneous turbulence is studied using direct numerical simulation (DNS). The numerical method used in this study is an eight order compact difference scheme. Contrary to the conclusions reached by previous DNS studies on incompressible isotropic turbulence, the present results show that the Coriolis force increases the dissipation rate of turbulent kinetic energy, and that anisotropy develops as the Coriolis force increases. The Taylor-Proudman theory does apply since the derivatives in the direction of the rotation axis vanishes rapidly. A closer analysis reveals that the dissipation rate of the incompressible component of the turbulent kinetic energy indeed decreases with a higher rotation rate, consistent with incompressible flow simulations (Bardina), while the dissipation rate of the compressible part increases; the net gain is positive. Inertial waves are observed in the simulation results.
Two-dimensional turbulent convection
Mazzino, Andrea
2017-11-01
We present an overview of the most relevant, and sometimes contrasting, theoretical approaches to Rayleigh-Taylor and mean-gradient-forced Rayleigh-Bénard two-dimensional turbulence together with numerical and experimental evidences for their support. The main aim of this overview is to emphasize that, despite the different character of these two systems, especially in relation to their steadiness/unsteadiness, turbulent fluctuations are well described by the same scaling relationships originated from the Bolgiano balance. The latter states that inertial terms and buoyancy terms balance at small scales giving rise to an inverse kinetic energy cascade. The main difference with respect to the inverse energy cascade in hydrodynamic turbulence [R. H. Kraichnan, "Inertial ranges in two-dimensional turbulence," Phys. Fluids 10, 1417 (1967)] is that the rate of cascade of kinetic energy here is not constant along the inertial range of scales. Thanks to the absence of physical boundaries, the two systems here investigated turned out to be a natural physical realization of the Kraichnan scaling regime hitherto associated with the elusive "ultimate state of thermal convection" [R. H. Kraichnan, "Turbulent thermal convection at arbitrary Prandtl number," Phys. Fluids 5, 1374-1389 (1962)].
TEM turbulence optimisation in stellarators
Proll, J. H. E.; Mynick, H. E.; Xanthopoulos, P.; Lazerson, S. A.; Faber, B. J.
2016-01-01
With the advent of neoclassically optimised stellarators, optimising stellarators for turbulent transport is an important next step. The reduction of ion-temperature-gradient-driven turbulence has been achieved via shaping of the magnetic field, and the reduction of trapped-electron mode (TEM) turbulence is addressed in the present paper. Recent analytical and numerical findings suggest TEMs are stabilised when a large fraction of trapped particles experiences favourable bounce-averaged curvature. This is the case for example in Wendelstein 7-X (Beidler et al 1990 Fusion Technol. 17 148) and other Helias-type stellarators. Using this knowledge, a proxy function was designed to estimate the TEM dynamics, allowing optimal configurations for TEM stability to be determined with the STELLOPT (Spong et al 2001 Nucl. Fusion 41 711) code without extensive turbulence simulations. A first proof-of-principle optimised equilibrium stemming from the TEM-dominated stellarator experiment HSX (Anderson et al 1995 Fusion Technol. 27 273) is presented for which a reduction of the linear growth rates is achieved over a broad range of the operational parameter space. As an important consequence of this property, the turbulent heat flux levels are reduced compared with the initial configuration.
Energy Technology Data Exchange (ETDEWEB)
Bataillon, D
1996-12-11
The determination of the role of liquid films in three phase flows in porous media is very important for enhanced oil recovery by gas injection in a petroleum reservoir. The existence of liquid films (water, oil), their thickness and their stability, control the distribution of fluids and the displacement of these fluids in the reservoir. The target of this research is to obtain, from experimental observations, the microscopic rules of flow by films taking into account the elementary mechanisms controlling the displacement of fluids. For this, a method of liquid film flow thickness measurement is developed in a quartz Hele-Shaw cell. It is based on infrared spectrometry, used for the first time to our knowledge for such an application, which gives the possibility to follow the drainage kinetics of oil and water in the presence of gas. When the thick oil film is initially stable on water in the presence of gas, it slowly drains until it reaches a constant thickness of about 20 nm. This film may breaks down into micro droplets of less than few micrometers in diameter. When this thick oil film is not initially stable, it immediately breaks down into droplets of 10 to 20 {mu}m in diameter prevents any oil flow. For spreading conditions, the initial oil thickness of about 200 nm is calculated form the Ca capillary number. The flow kinetics of this film is then determined when macroscopic forces are predominant. Finally, for the estimation of the stabilisation thickness, disjoining pressure isotherms, based on long-scale intermolecular forces (VdW), are calculated for pure n-alkanes. In order to study the macroscopic flow parameters, gravity drainage experiments are carried out in a 2D glass network (micro-model). Measurements of oil production (weight) and residual saturations (image analysis) show clearly the influence of the initial stability of oil, coating water in the presence of gas, on the flow mechanisms. (author) 73 refs.
Energy Technology Data Exchange (ETDEWEB)
Perrin, S.
1998-06-11
The aim of this study is to propose a packed column characterization method in the form of phases flows and mass transfer model, in which the parameters are estimated by transient technique. After a bibliographic study a model is performed and validated. It allows efficiency and precision in the parameters choice. Two tracer techniques have been implemented: they show interesting possibilities of flow diagnosis. (A.L.B.)
Energy Technology Data Exchange (ETDEWEB)
Delay, G
2005-03-15
The aim of this study is to determine instantaneous liquid flow rate oscillations effect on non stationary air entrainment of an injector conical spray (Gasoline Direct Injection). The tools we use are either experimental or numerical ones. An instantaneous flow rate determination method is used. It is based on pulsated flows physics and only requires the velocity at the centerline of a pipe mounted just before the injector. So, it is possible to 'rebuild' the instantaneous velocity distributions and then to get the instantaneous liquid flow rate (Laser Doppler Anemometry measurements). A mechanical and hydraulics modeling software (AMESim) is necessary to get injector outlet flow rate. Simulations are validated by both 'rebuilding' method results and common rail pressure measurements. Fluorescent Particle Image Velocimetry (FPIV), suited to dense two -phase flows, is used to measure air flow around and inside the conical spray. Velocity measurements close to the spray frontier are used to compute instantaneous air entrainment. Considering droplets momentum exchange with air and thanks to droplets diameters and liquid velocities measurements at the nozzle exit, a transient air entrainment model is proposed according to FPIV measurements. (author)
Energy Technology Data Exchange (ETDEWEB)
Picot, D
1998-07-01
The problems with the optimization and design of proton exchange membrane fuel cells (PEMFC) are mainly based on the mastery of water and heat transfers inside the active cells. A theoretical and experimental discussion about this topic is proposed. The average sharing coefficients of the generated water are measured for 3 Nora fuel cells (1, 5 and 10 kW). The values obtained with nafion 117 are in agreement with the data of the literature, while the 40% generated water recovered inside the anode compartment with nafion 115 are unexpected. The difficulty to obtain a physical formulation of electro-osmosis does not allow to quantify this coefficient and leads to justify the limitations of use of the numerical codes on this topic. However, by separating the intrinsic parameters of the electrodes/membrane system and the global operation parameters of a cell, it is possible to extrapolate realistic humidification strategies. In the framework of the European project 'Fever', a systemic model of a 30 kW module for electric-powered vehicle has been developed. For an optimum energy integration of Nora fuel cells in volume-limited applications, it is necessary to separate the humidification sections of these modules. In the case where air is used as oxidant, the presence of nitrogen inside the anode compartment has been evidenced both in close and recirculation modes. In agreement with the literature data about nafion permeability, the nitrogen migration through the electrolyte is explained by the diffusion theory. A discussion about the interest of using both operational modes to maximize the energy efficiency is proposed. Finally, a simple-phase and double-phase numerical study with interface reconstruction is carried out using the resolution of Navier-Stokes equations in Eulerian formalism in order to consider the problems linked with the internal flows inside the collectors of Nora cells. (J.S.)
Energy Technology Data Exchange (ETDEWEB)
Ercolino, J.
2001-01-15
In this study, a fast analysis code for the meridian flow inside turbo-machineries has been developed. This code is based on the resolution of the averaged dynamical equations controlling the internal stationary and non-viscous flow in the relative reference frame. A linear combination of momentum equations has been used in the axial and radial directions to avoid the source term of the equations to become singular. The model developed is particularly adapted to the general case of compression machines, i.e.the mixed machines. Starting with the hypothesis of a finite number of blading and assuming an axisymmetric flow, the equations allowing to calculate the blading forces and the simplified kinematics of blade-to-blade flow have been developed. This kinematics takes into consideration the geometrical data supplied by manufacturers or by global design softwares. This last approach ensures a very efficient link in the framework of turbomachine design projects where the blades geometry is introduced in a very simple way for a first optimization approach. The results obtained seem to be very consistent in nominal flow but also in partial flow conditions as shown by the qualitative comparisons with test results. (J.S.)
Energy Technology Data Exchange (ETDEWEB)
Zakarian, E.
2000-03-10
Recent estimations predict that over half the remaining offshore oil and gas reserves are located in deep water and marginal fields. For such reserves, economic recovery methods are required. Then, multiphase flows are transported within pipelines and separated on treatment platforms built in shallow water or processed in onshore facilities. Unfortunately, hydrodynamic instabilities may occur whenever gas and liquid flow in a pipeline, generating serious operating problems. This dissertation presents a new way to model two-phase flows in pipelines such as pipeline-riser systems. Equations are algebraic and differential. Their smoothness depends on the closure laws of the problem such as slip or friction laws. Smooth forms of these closure laws are presented for the first time in this dissertation. Therefore, a mathematical analysis of our model fits into a classical frame: a linear analysis leads to an analytical expression of the boundary between stable and unstable flows. A nonlinear analysis provides for the first time, the bifurcation curves of gas-liquid flows in pipe-riser systems, locally round their stability boundary. (author)
Energy Technology Data Exchange (ETDEWEB)
Cartaud, F
2004-11-15
Composite liner at the bottom of waste landfill is based, in France, on a geo-membrane overlapping a compacted clay liner. Defects exist in geo-membranes and leachates, provided by water percolation through the waste, then flow in the interface between the two components of the lining system. The present work consisted in analysis, quantification and modelling of the leakage process in the interface. The experimental study has been carried out on a one-meter scale device in laboratory and allowed to assess the role of normal stress on the flow rate in interface. The case where a geo-textile is present beneath the geo-membrane has been also studied. The modelling allows to take into account more accurately the geometry of the interface and ensures a better quantification of leachate flow rates than using existing methods. (author)
Energy Technology Data Exchange (ETDEWEB)
Labois, M
2008-10-15
This thesis deals with hyperbolic models for the simulation of compressible two-phase flows, to find alternatives to the classical bi-fluid model. We first establish a hierarchy of two-phase flow models, obtained according to equilibrium hypothesis between the physical variables of each phase. The use of Chapman-Enskog expansions enables us to link the different existing models to each other. Moreover, models that take into account small physical unbalances are obtained by means of expansion to the order one. The second part of this thesis focuses on the simulation of flows featuring velocity unbalances and pressure balances, in two different ways. First, a two-velocity two-pressure model is used, where non-instantaneous velocity and pressure relaxations are applied so that a balancing of these variables is obtained. A new one-velocity one-pressure dissipative model is then proposed, where the arising of second-order terms enables us to take into account unbalances between the phase velocities. We develop a numerical method based on a fractional step approach for this model. (author)
Energy Technology Data Exchange (ETDEWEB)
Brossard, C.; Gicquel, P.; Barat, M.; Ristori, A.
2002-07-01
A three dimensional mock-up has been realized at the ONERA, to study the combustion in conditions of pressure, speed and temperatures similar as real temperatures in ramjet. The first step of the tests program allows to study the cold and non reactive flows, by an hydraulic simulation. In the second step, the hot reactive and non reactive flows have been studied in more realistic tests. This paper presents the results obtained in non reactive flow and on high speed reactive flow. (A.L.B.)
Energy Technology Data Exchange (ETDEWEB)
Lapuerta, C
2006-10-15
During an hypothetical major accident in a pressurized water reactor, the deterioration of the core can produce a stratified pool crossed by a bubbly flow. This latter strongly impacts the heat transfers, whose intensities are crucial in the progression of the accident. In this context, this work is devoted to the diffuse interface modelling for the study of an-isothermal incompressible flows, composed of three immiscible components, with no phase change. In the diffuse interface methods, the system evolution is driven by the minimization of a free energy. The originality of our approach, derived from the Cahn-Hilliard model, is based on the particular form of the energy we proposed, which enables to have an algebraically and dynamically consistent model, in the following sense: on the one hand, the triphasic free energy is equal to the diphasic one when only two phases are present; on the other, if a phase is not initially present then it will not appear during system evolution, this last property being stable with respect to numerical errors. The existence and the uniqueness of weak and strong solutions are proved in two and three dimensions as well as a stability result for metastable states. The modelling of an an-isothermal three phase flow is further accomplished by coupling the Cahn-Hilliard equations with the energy balance and Navier-Stokes equations where surface tensions are taken into account through volume capillary forces. These equations are discretized in time and space in order to preserve properties of continuous model (volume conservation, energy estimate). Different numerical results are given, from the validation case of the lens spreading between two phases, to the study of the heat and mass transfers through a liquid/liquid interface crossed by a single bubble or a series of bubbles. (author)
Résilience organisationnelle rebondir face aux turbulences
Koninckx, Guy
2010-01-01
Toutes les organisations traversent des turbulences et des crises. Ces situations conduisent à des pertes de repères et de sens. Les identités ne sont pas épargnées. Dans de telles circonstances, comment rebondir ? Quels moyens mettre en oeuvre pour favoriser la résilience, cette capacité à faire face à l'adversité ? Les auteurs présentent ici le cadre conceptuel de la résilience, différents modèles, une démarche opérationnelle et un ensemble d'outils appropriés. Le modèle CIRERO permet de positionner les organisations sur les trajectoires de résilience. Des stratégies particulières sont recommandées en fonction des situations de crise. Toute personne amenée à mettre en place des conditions favorables à l'émergence de la résilience trouvera, dans ce livre, un guide, une " boîte à outils " et une abondante source d'informations constituées par des retours d'expériences et des études de cas d'organisations amenées à affronter de sérieux bouleversements.
Turbulence models in supersonic flows
International Nuclear Information System (INIS)
Shirani, E.; Ahmadikia, H.; Talebi, S.
2001-05-01
The aim of this paper is to evaluate five different turbulence models when used in rather complicated two-dimensional and axisymmetric supersonic flows. They are Baldwin-Lomax, k-l, k-ε, k-ω and k-ζ turbulence models. The compressibility effects, axisymmetric correction terms and some modifications for transition region are used and tested in the models. Two computer codes based on the control volume approach and two flux-splitting methods. Roe and Van Leer, are developed. The codes are used to simulate supersonic mixing layers, flow behind axisymmetric body, under expanded jet, and flow over hollow cylinder flare. The results are compared with experimental data and behavior of the turbulence models is examined. It is shown that both k-l and k-ζ models produce very good results. It is also shown that the compressibility correction in the model is required to obtain more accurate results. (author)
Atmospheric turbulence and diffusion research
International Nuclear Information System (INIS)
Hosker, R.P. Jr.
1993-01-01
The Atmospheric Turbulence and Diffusion Division (well known in the atmospheric dispersion community as the Atmospheric Turbulence and Diffusion Laboratory, ATDL) is one of several field facilities of NOAAs Air Resources Laboratory, headquartered in Silver Spring, Maryland. The laboratory conducts research on matters of atmospheric diffusion and turbulent exchange, concerning air quality. ATDD focuses attention on the physics of the lower atmosphere, with special emphasis on the processes contributing to atmospheric transport, dispersion, deposition, and air-surface exchange, and on the development of predictive capabilities using the results of this research. Research is directed toward issues of national and global importance related to the missions of DOE, to DOE's Oak Ridge Field Office, and to NOAA. The program is divided into four major projects: plume transport and diffusion in the planetary boundary layer, complex topography, canopy micrometeorology, and air-surface exchange
ANISOTROPIC INTERMITTENCY OF MAGNETOHYDRODYNAMIC TURBULENCE
International Nuclear Information System (INIS)
Osman, K. T.; Kiyani, K. H.; Chapman, S. C.; Hnat, B.
2014-01-01
A higher-order multiscale analysis of spatial anisotropy in inertial range magnetohydrodynamic turbulence is presented using measurements from the STEREO spacecraft in fast ambient solar wind. We show for the first time that, when measuring parallel to the local magnetic field direction, the full statistical signature of the magnetic and Elsässer field fluctuations is that of a non-Gaussian globally scale-invariant process. This is distinct from the classic multiexponent statistics observed when the local magnetic field is perpendicular to the flow direction. These observations are interpreted as evidence for the weakness, or absence, of a parallel magnetofluid turbulence energy cascade. As such, these results present strong observational constraints on the statistical nature of intermittency in turbulent plasmas
Resonant quasiparticles in plasma turbulence
International Nuclear Information System (INIS)
Mendonca, J.T.; Bingham, R.; Shukla, P.K.
2003-01-01
A general view is proposed on wave propagation in fluids and plasmas where the resonant interaction of monochromatic waves with quasiparticles is considered. A kinetic equation for quasiparticles is used to describe the broadband turbulence interacting with monochromatic waves. Resonant interactions occur when the phase velocity of the long wavelength monochromatic wave is nearly equal to the group velocity of short wavelength wave packets, or quasiparticles, associated with the turbulent spectrum. It is shown that quasiparticle Landau damping can take place, as well as quasiparticle beam instabilities, thus establishing a direct link between short and large wavelength perturbations of the medium. This link is distinct from the usual picture of direct and inverse energy cascades, and it can be used as a different paradigm for the fluid and plasma turbulence theories
Turbulent breakage of ductile aggregates.
Marchioli, Cristian; Soldati, Alfredo
2015-05-01
In this paper we study breakage rate statistics of small colloidal aggregates in nonhomogeneous anisotropic turbulence. We use pseudospectral direct numerical simulation of turbulent channel flow and Lagrangian tracking to follow the motion of the aggregates, modeled as sub-Kolmogorov massless particles. We focus specifically on the effects produced by ductile rupture: This rupture is initially activated when fluctuating hydrodynamic stresses exceed a critical value, σ>σ(cr), and is brought to completion when the energy absorbed by the aggregate meets the critical breakage value. We show that ductile rupture breakage rates are significantly reduced with respect to the case of instantaneous brittle rupture (i.e., breakage occurs as soon as σ>σ(cr)). These discrepancies are due to the different energy values at play as well as to the statistical features of energy distribution in the anisotropic turbulence case examined.
Orbital-angular-momentum entanglement in turbulence
CSIR Research Space (South Africa)
Hamadou Ibrahim, A
2013-06-01
Full Text Available The turbulence-induced decay of orbital-angular-momentum (OAM) entanglement between two photons is investigated numerically and experimentally. To compare our resultswith previouswork,we simulate the turbulent atmosphere with a single phase screen...
Particle Settling in Low Energy Turbulence
Allen, Rachel; MacVean, Lissa; Tse, Ian; Mazzaro, Laura; Stacey, Mark; Variano, Evan
2014-11-01
Particle settling velocities can be altered by turbulence. In turbulence, dense particles may get trapped in convergent flow regions, and falling particles may be swept towards the downward side of turbulent eddies, resulting in enhanced settling velocities. The degree of velocity enhancement may depend on the Stokes number, the Rouse number, and the turbulent Reynolds number. In a homogeneous, isotropic turbulence tank, we tested the effects of particle size and type, suspended sediment concentration, and level of turbulence on the settling velocities of particles typically found in muddy estuaries. Two Acoustic Doppler Velocimeters (ADVs), separated vertically, measured turbulent velocities and suspended sediment concentrations, which yield condition dependent settling velocities, via ∂/á C ñ ∂ t = -∂/∂ z (ws á C ñ + á w ' C ' ñ) . These results are pertinent to fine sediment transport in estuaries, where high concentrations of suspended material are transported and impacted by low energy turbulence.
PDF methods for turbulent reactive flows
Hsu, Andrew T.
1995-01-01
Viewgraphs are presented on computation of turbulent combustion, governing equations, closure problem, PDF modeling of turbulent reactive flows, validation cases, current projects, and collaboration with industry and technology transfer.
Frontogenesis and turbulent mixing
Zhang, S.; Chen, F.; Shang, Q.
2017-12-01
ageostrophic secondary circulation together with the cross-frontal ageostrophic speed. The mixed characteristic is weak in summer, but the large turbulent dissipation and mixing rate measured in the frontal region, which show that the front promoted exchange of material and energy in the upper ocean.
Molecular mixing in turbulent flow
International Nuclear Information System (INIS)
Kerstein, A.R.
1993-01-01
The evolution of a diffusive scalar field subject to turbulent stirring is investigated by comparing two new modeling approaches, the linear-eddy model and the clipped-laminar-profile representation, to results previously obtained by direct numerical simulation (DNS) and by mapping-closure analysis. The comparisons indicate that scalar field evolution is sensitive to the bandwidth of the stirring process, and they suggest that the good agreement between DNS and mapping closure reflects the narrowband character of both. The new models predict qualitatively new behaviors in the wideband stirring regime corresponding to high-Reynolds-number turbulence
Plasma turbulence effects on aurorae
International Nuclear Information System (INIS)
Mishin, E.V.; Telegin, V.A.
1989-01-01
Analysis of modern state of microprocesses physics in plasma of aurorare, initiated by energetic electron flow intrusion, is presented. It is shown that there is a number of phenomena, which cannot be explained under non-collision (collective) mechanisms of interaction are applied. Effects of plasma turbulence in the area of auroral arcs are considered. Introduction of a new structural element to auroral arc - plasma-turbulence (PT) layer is substantiated. Numerical simulation of electron kinetics, changes in neutral composition, as well as generation of IR- and UV-radiation in PT layer has been realized
Ion-acoustic plasma turbulence
International Nuclear Information System (INIS)
Bychenkov, V.Y.; Silin, V.P.
1982-01-01
A theory is developed of the nonlinear state that is established in a plasma as a result of development of ion-acoustic instability. Account is taken simultaneously of the linear induced scattering of the waves by the ions and of the quasilinear relaxation of the electrons by the ion-acoustic pulsations. The distribution of the ion-acoustic turbulence in frequency and in angle is obtained. An Ohm's law is established and expressions are obtained for the electronic heat flux and for the relaxation time of the electron temperature in a turbulent plasma. Anomalously large absorption and scattering of the electromagnetic waves by the ion-acoustic pulsations is predicted
The roles of turbulence on plasma heating
International Nuclear Information System (INIS)
Kawamura, Takaichi; Kawabe, Takaya
1976-01-01
The relation between the heating rate of plasma particles and the thermalization frequency is established, and the important role of plasma turbulence in the fast thermalization process is underlined. This relation can be applied not only in the case of high current turbulent heating but also when turbulent phenomena occur with other heating means. The experimental results on ion and electron heating during the Mach II experiment are presented. The role of turbulence on particle losses accross the magnetic field is analyzed
Exploiting similarity in turbulent shear flows for turbulence modeling
Robinson, David F.; Harris, Julius E.; Hassan, H. A.
1992-01-01
It is well known that current k-epsilon models cannot predict the flow over a flat plate and its wake. In an effort to address this issue and other issues associated with turbulence closure, a new approach for turbulence modeling is proposed which exploits similarities in the flow field. Thus, if we consider the flow over a flat plate and its wake, then in addition to taking advantage of the log-law region, we can exploit the fact that the flow becomes self-similar in the far wake. This latter behavior makes it possible to cast the governing equations as a set of total differential equations. Solutions of this set and comparison with measured shear stress and velocity profiles yields the desired set of model constants. Such a set is, in general, different from other sets of model constants. The rational for such an approach is that if we can correctly model the flow over a flat plate and its far wake, then we can have a better chance of predicting the behavior in between. It is to be noted that the approach does not appeal, in any way, to the decay of homogeneous turbulence. This is because the asymptotic behavior of the flow under consideration is not representative of the decay of homogeneous turbulence.
Exploiting similarity in turbulent shear flows for turbulence modeling
Robinson, David F.; Harris, Julius E.; Hassan, H. A.
1992-12-01
It is well known that current k-epsilon models cannot predict the flow over a flat plate and its wake. In an effort to address this issue and other issues associated with turbulence closure, a new approach for turbulence modeling is proposed which exploits similarities in the flow field. Thus, if we consider the flow over a flat plate and its wake, then in addition to taking advantage of the log-law region, we can exploit the fact that the flow becomes self-similar in the far wake. This latter behavior makes it possible to cast the governing equations as a set of total differential equations. Solutions of this set and comparison with measured shear stress and velocity profiles yields the desired set of model constants. Such a set is, in general, different from other sets of model constants. The rational for such an approach is that if we can correctly model the flow over a flat plate and its far wake, then we can have a better chance of predicting the behavior in between. It is to be noted that the approach does not appeal, in any way, to the decay of homogeneous turbulence. This is because the asymptotic behavior of the flow under consideration is not representative of the decay of homogeneous turbulence.
Suryanti, Rut; Jafar, Nurhaedar; Syam, Aminuddin
2013-01-01
Konsumsi fast food dan soft drink dapat menyebabkan kelebihan berat badan dan obesitas.Penelitian ini bertujuan untuk mengetahui gambaran jenis dan jumlah zat gizi makro dari konsumsi fast food dan soft drink pada mahasiswa yang obesitas.Jenis penelitian adalah deskriptif, dilaksanakan pada bulan Mei-Juni 2013 di Universitas Hasanuddin dengan jumlah responden 60 orang. Instrument penelitian adalah kuesioner identitas diri dan food frekuensiSemiQuantitatif fast food dan soft drink, food pictur...
PERSEPSI DAN TRANSFORMASI VISI DAN MISI PADA CIVITAS AKADEMIKA STAIN PEKALONGAN
Directory of Open Access Journals (Sweden)
Imam Khanafi
2013-05-01
Full Text Available Penelitian ini mengukur tingkat persepsi visi dan misi civitas akademika STAIN Pekalongan, dan mengukur juga tingkat implementasi sebagai transformasi visi misi tersebut serta menemukan hubungan antara persepsi dengan implementasinya. Kajian ini memiliki signifikan yang strategis dalam konteks manajemen dan pengembangan Pendidikan di STAIN Pekalongan dan lembaga pendidikan lainnya. Hal ini karena posisi visi dan misi sebagai kerangka acuan (frame of reference yang mengarahkan dan menjelaskan kepada keseluruh unsur civitas akademika dalam setiap program kerjanya.
Plasma Soliton Turbulence and Statistical Mechanics
International Nuclear Information System (INIS)
Treumann, R.A.; Pottelette, R.
1999-01-01
Collisionless kinetic plasma turbulence is described approximately in terms of a superposition of non-interacting solitary waves. We discuss the relevance of such a description under astrophysical conditions. Several types of solitary waves may be of interest in this relation as generators of turbulence and turbulent transport. A consistent theory of turbulence can be given only in a few particular cases when the description can be reduced to the Korteweg-de Vries equation or some other simple equation like the Kadomtsev-Petviashvili equation. It turns out that the soliton turbulence is usually energetically harder than the ordinary weakly turbulent plasma description. This implies that interaction of particles with such kinds of turbulence can lead to stronger acceleration than in ordinary turbulence. However, the description in our model is only classical and non-relativistic. Transport in solitary turbulence is most important for drift wave turbulence. Such waves form solitary drift wave vortices which may provide cross-field transport. A more general discussion is given on transport. In a model of Levy flight trapping of particles in solitons (or solitary turbulence) one finds that the residence time of particles in the region of turbulence may be described by a generalized Lorentzian probability distribution. It is shown that under collisionless equilibrium conditions far away from thermal equilibrium such distributions are natural equilibrium distributions. A consistent thermodynamic description of such media can be given in terms of a generalized Lorentzian statistical mechanics and thermodynamics. (author)
Wall roughness induces asymptotic ultimate turbulence
Zhu, Xiaojue; Verschoof, Ruben Adriaan; Bakhuis, Dennis; Huisman, Sander Gerard; Verzicco, Roberto; Sun, Chao; Lohse, Detlef
2018-01-01
Turbulence governs the transport of heat, mass and momentum on multiple scales. In real-world applications, wall-bounded turbulence typically involves surfaces that are rough; however, characterizing and understanding the effects of wall roughness on turbulence remains a challenge. Here, by
Analysis of chaos in plasma turbulence
DEFF Research Database (Denmark)
Pedersen, T.S.; Michelsen, Poul; Juul Rasmussen, J.
1996-01-01
-stationary turbulent state is reached in a finite time, independent of the initial conditions. Different regimes of the turbulent state can be obtained by varying the coupling parameter C, related to the parallel electron dynamics. The turbulence is described by using particle tracking and tools from chaos analysis...
PROTOSTELLAR OUTFLOW EVOLUTION IN TURBULENT ENVIRONMENTS
International Nuclear Information System (INIS)
Cunningham, Andrew J.; Frank, Adam; Carroll, Jonathan; Blackman, Eric G.; Quillen, Alice C.
2009-01-01
The link between turbulence in star-forming environments and protostellar jets remains controversial. To explore issues of turbulence and fossil cavities driven by young stellar outflows, we present a series of numerical simulations tracking the evolution of transient protostellar jets driven into a turbulent medium. Our simulations show both the effect of turbulence on outflow structures and, conversely, the effect of outflows on the ambient turbulence. We demonstrate how turbulence will lead to strong modifications in jet morphology. More importantly, we demonstrate that individual transient outflows have the capacity to re-energize decaying turbulence. Our simulations support a scenario in which the directed energy/momentum associated with cavities is randomized as the cavities are disrupted by dynamical instabilities seeded by the ambient turbulence. Consideration of the energy power spectra of the simulations reveals that the disruption of the cavities powers an energy cascade consistent with Burgers'-type turbulence and produces a driving scale length associated with the cavity propagation length. We conclude that fossil cavities interacting either with a turbulent medium or with other cavities have the capacity to sustain or create turbulent flows in star-forming environments. In the last section, we contrast our work and its conclusions with previous studies which claim that jets cannot be the source of turbulence.
Global Turbulence Decision Support for Aviation
Williams, J.; Sharman, R.; Kessinger, C.; Feltz, W.; Wimmers, A.
2009-09-01
Turbulence is widely recognized as the leading cause of injuries to flight attendants and passengers on commercial air carriers, yet legacy decision support products such as SIGMETs and SIGWX charts provide relatively low spatial- and temporal-resolution assessments and forecasts of turbulence, with limited usefulness for strategic planning and tactical turbulence avoidance. A new effort is underway to develop an automated, rapid-update, gridded global turbulence diagnosis and forecast system that addresses upper-level clear-air turbulence, mountain-wave turbulence, and convectively-induced turbulence. This NASA-funded effort, modeled on the U.S. Federal Aviation Administration's Graphical Turbulence Guidance (GTG) and GTG Nowcast systems, employs NCEP Global Forecast System (GFS) model output and data from NASA and operational satellites to produce quantitative turbulence nowcasts and forecasts. A convective nowcast element based on GFS forecasts and satellite data provides a basis for diagnosing convective turbulence. An operational prototype "Global GTG” system has been running in real-time at the U.S. National Center for Atmospheric Research since the spring of 2009. Initial verification based on data from TRMM, Cloudsat and MODIS (for the convection nowcasting) and AIREPs and AMDAR data (for turbulence) are presented. This product aims to provide the "single authoritative source” for global turbulence information for the U.S. Next Generation Air Transportation System.
The PDF method for turbulent combustion
Pope, S. B.
1991-01-01
Probability Density Function (PDF) methods provide a means of calculating the properties of turbulent reacting flows. They have been successfully applied to many turbulent flames, including some with finite rate kinetic effects. Here the methods are reviewed with an emphasis on computational issues and their application to turbulent combustion.
Turbulence, Magnetic Reconnection in Turbulent Fluids and Energetic Particle Acceleration
Lazarian, A.; Vlahos, L.; Kowal, G.; Yan, H.; Beresnyak, A.; de Gouveia Dal Pino, E. M.
2012-11-01
Turbulence is ubiquitous in astrophysics. It radically changes many astrophysical phenomena, in particular, the propagation and acceleration of cosmic rays. We present the modern understanding of compressible magnetohydrodynamic (MHD) turbulence, in particular its decomposition into Alfvén, slow and fast modes, discuss the density structure of turbulent subsonic and supersonic media, as well as other relevant regimes of astrophysical turbulence. All this information is essential for understanding the energetic particle acceleration that we discuss further in the review. For instance, we show how fast and slow modes accelerate energetic particles through the second order Fermi acceleration, while density fluctuations generate magnetic fields in pre-shock regions enabling the first order Fermi acceleration of high energy cosmic rays. Very importantly, however, the first order Fermi cosmic ray acceleration is also possible in sites of magnetic reconnection. In the presence of turbulence this reconnection gets fast and we present numerical evidence supporting the predictions of the Lazarian and Vishniac (Astrophys. J. 517:700-718, 1999) model of fast reconnection. The efficiency of this process suggests that magnetic reconnection can release substantial amounts of energy in short periods of time. As the particle tracing numerical simulations show that the particles can be efficiently accelerated during the reconnection, we argue that the process of magnetic reconnection may be much more important for particle acceleration than it is currently accepted. In particular, we discuss the acceleration arising from reconnection as a possible origin of the anomalous cosmic rays measured by Voyagers as well as the origin cosmic ray excess in the direction of Heliotail.
Energy Technology Data Exchange (ETDEWEB)
Lardjane, N.
2002-05-15
The subject of this work concerns the application of large-eddy simulation to the mixing of two fluids with different thermodynamical properties. Numerical errors in the discretization of Navier-Stokes equations and their interaction with sub-grid models are investigated on a self decaying isotropic homogeneous turbulence. A high resolution numerical code is then developed for the simulation of binary mixing layers. Reduction of early acoustic waves amplitude is achieved by use of a temporal self-similar initial condition. The relative magnitude of sub-grid terms arising from filtered equations is investigated on explicit filtering of direct numerical simulation results of temporal N{sub 2}/O{sub 2} and H{sub 2}/O{sub 2} mixing layers. Implicit closure (MILES) is then evoked on the basis of WENO schemes. (author)
Energy Technology Data Exchange (ETDEWEB)
Avalon, G. [Office National d' Etudes et de Recherches Aerospatiales (ONERA), 91 - Palaiseau (France); Casalis, G. [Office National d' Etudes et de Recherches Aerospatiales (ONERA), 91 - Palaiseau (France)
1998-07-01
Aero-acoustic coupling that occurs inside solid propellant rocket engines can lead to a longitudinal acoustic mode resonance of the combustion chamber. This phenomenon, which can have various origins, in analyzed using the Vecla test facility and the theory of linear stability of flows. Different comparisons between the hot-wire measurements performed and the theory of stability confirm the presence of intrinsic instabilities for this type of flow. The instability allows to selectively amplify a given range of frequencies which depends on the injection velocity and on the conduit height. The results obtained seem to indicate that when this frequency range does not comprise the longitudinal acoustic mode or the first harmonics, the flow becomes turbulent downstream. (J.S.)
Etude du transfert thermique entre un jet rond turbulent et une paroi ...
African Journals Online (AJOL)
Dans ce travail, on s\\'intéresse à l\\'étude du transfert de chaleur d\\'une plaque plane soumise à l\\'action d\\'un jet d\\'air perpendiculaire. L\\'étude de la possibilité d\\'améliorer le transfert de chaleur est effectuée en fonction des paramètres caractéristiques de l\\'interaction jet - paroi. Le problème du jet rond turbulent frappant ...
Perancangan dan Analisis Redistribution Routing Protocol OSPF dan EIGRP
Directory of Open Access Journals (Sweden)
DWI ARYANTA
2016-02-01
Full Text Available Abstrak OSPF (Open Shortest Path First dan EIGRP (Enhanced Interior Gateway Routing Protocol adalah dua routing protokol yang banyak digunakan dalam jaringan komputer. Perbedaan karakteristik antar routing protokol menimbulkan masalah dalam pengiriman paket data. Teknik redistribution adalah solusi untuk melakukan komunikasi antar routing protokol. Dengan menggunakan software Cisco Packet Tracer 5.3 pada penelitian ini dibuat simulasi OSPF dan EIGRP yang dihubungkan oleh teknik redistribution, kemudian dibandingkan kualitasnya dengan single routing protokol EIGRP dan OSPF. Parameter pengujian dalam penelitian ini adalah nilai time delay dan trace route. Nilai trace route berdasarkan perhitungan langsung cost dan metric dibandingkan dengan hasil simulasi. Hasilnya dapat dilakukan proses redistribution OSPF dan EIGRP. Nilai delay redistribution lebih baik 1% dibanding OSPF dan 2-3% di bawah EIGRP tergantung kepadatan traffic. Dalam perhitungan trace route redistribution dilakukan 2 perhitungan, yaitu cost untuk area OSPF dan metric pada area EIGRP. Pengambilan jalur utama dan alternatif pengiriman paket berdasarkan nilai cost dan metric yang terkecil, hal ini terbukti berdasarkan perhitungan dan simulasi. Kata kunci: OSPF, EIGRP, Redistribution, Delay, Cost, Metric. Abstract OSPF (Open Shortest Path First and EIGRP (Enhanced Interior Gateway Routing Protocol are two routing protocols are widely used in computer networks. Differences between the characteristics of routing protocols pose a problem in the delivery of data packets. Redistribution technique is the solution for communication between routing protocols. By using the software Cisco Packet Tracer 5.3 in this study were made simulating OSPF and EIGRP redistribution linked by technique, then compared its quality with a single EIGRP and OSPF routing protocols. Testing parameters in this study is the value of the time delay and trace route. Value trace route based on direct calculation of cost
5th European Turbulence Conference
1995-01-01
Under the auspices of the Euromech Committee, the Fifth European Turbulence Conference was held in Siena on 5-8 July 1994. Following the previous ETC meeting in Lyon (1986), Berlin (1988), Stockholm (1990) and Delft (1992), the Fifth ETC was aimed at providing a review of the fundamental aspects of turbulence from a theoretical, numerical and experimental point of view. In the magnificent town of Siena, more than 250 scientists from all over the world, spent four days discussing new ideas on turbulence. As a research worker in the field of turbulence, I must say that the works presented at the Conference, on which this book is based, covered almost all areas in this field. I also think that this book provides a major opportunity to have a complete overview of the most recent research works. I am extremely grateful to Prof. C. Cercignani, Dr. M. Loffredo, and Prof. R. Piva who, as members of the local organizing committee, share the success of the Conference. I also want to thank Mrs. Liu' Catena, for her inva...
Stochastic acceleration by hydromagnetic turbulence
International Nuclear Information System (INIS)
Kulsrud, R.M.
1979-03-01
A general theory for particle acceleration by weak hydromagnetic turbulence with a given spectrum of waves is described. Various limiting cases, corresponding to Fermi acceleration and magnetic pumping, are discussed and two numerical examples illustrating them are given. An attempt is made to show that the expression for the rate of Fermi acceleration is valid for finite amplitudes
Topology optimization of turbulent flows
DEFF Research Database (Denmark)
Dilgen, Cetin B.; Dilgen, Sumer B.; Fuhrman, David R.
2018-01-01
The aim of this work is to present a fast and viable approach for taking into account turbulence in topology optimization of complex fluid flow systems, without resorting to any simplifying assumptions in the derivation of discrete adjoints. Topology optimization is an iterative gradient...
Dissipative structures in magnetorotational turbulence
Ross, Johnathan; Latter, Henrik N.
2018-03-01
Via the process of accretion, magnetorotational turbulence removes energy from a disk's orbital motion and transforms it into heat. Turbulent heating is far from uniform and is usually concentrated in small regions of intense dissipation, characterised by abrupt magnetic reconnection and higher temperatures. These regions are of interest because they might generate non-thermal emission, in the form of flares and energetic particles, or thermally process solids in protoplanetary disks. Moreover, the nature of the dissipation bears on the fundamental dynamics of the magnetorotational instability (MRI) itself: local simulations indicate that the large-scale properties of the turbulence (e.g. saturation levels, the stress-pressure relationship) depend on the short dissipative scales. In this paper we undertake a numerical study of how the MRI dissipates and the small-scale dissipative structures it employs to do so. We use the Godunov code RAMSES and unstratified compressible shearing boxes. Our simulations reveal that dissipation is concentrated in ribbons of strong magnetic reconnection that are significantly elongated in azimuth, up to a scale height. Dissipative structures are hence meso-scale objects, and potentially provide a route by which large scales and small scales interact. We go on to show how these ribbons evolve over time — forming, merging, breaking apart, and disappearing. Finally, we reveal important couplings between the large-scale density waves generated by the MRI and the small-scale structures, which may illuminate the stress-pressure relationship in MRI turbulence.
Turbulent magnetohydrodynamics in liquid metals
International Nuclear Information System (INIS)
Berhanu, Michael
2008-01-01
In electrically conducting fluids, the electromagnetic field is coupled with the fluid motion by induction effects. We studied different magnetohydrodynamic phenomena, using two experiments involving turbulent flows of liquid metal. The first mid-sized uses gallium. The second, using sodium, is conducted within the VKS (Von Karman Sodium) collaboration. It has led to the observation of the dynamo effect, namely converting a part of the kinetic energy of the fluid into magnetic energy. We have shown that, depending on forcing conditions, a statistically stationary dynamo, or dynamical regimes of magnetic field can be generated. In particular, polarity reversals similar to those of Earth's magnetic field were observed. Meanwhile, experiment with Gallium has been developed to study the effects of electromagnetic induction by turbulent flows in a more homogeneous and isotropic configuration than in the VKS experiment. Using data from these two experiments, we studied the advection of magnetic field by a turbulent flow and the induced fluctuations. The development of probes measuring electrical potential difference allowed us to further highlight the magnetic braking of a turbulent flow of Gallium by Lorentz force. This mechanism is involved in the saturation of the dynamo instability. (author) [fr
Nonuniform quantum turbulence in superfluids
Nemirovskii, Sergey K.
2018-04-01
The problem of quantum turbulence in a channel with an inhomogeneous counterflow of superfluid turbulent helium is studied. The counterflow velocity Vns x(y ) along the channel is supposed to have a parabolic profile in the transverse direction y . Such statement corresponds to the recent numerical simulation by Khomenko et al. [Phys. Rev. B 91, 180504 (2015), 10.1103/PhysRevB.91.180504]. The authors reported about a sophisticated behavior of the vortex-line density (VLD) L (r ,t ) , different from L ∝Vns x(y) 2 , which follows from the straightforward application of the conventional Vinen theory. It is clear that Vinen theory should be refined by taking into account transverse effects, and the way it ought to be done is the subject of active discussion in the literature. In this work, we discuss several possible mechanisms of the transverse flux of VLD L (r ,t ) which should be incorporated in the standard Vinen equation to describe adequately the inhomogeneous quantum turbulence. It is shown that the most effective among these mechanisms is the one that is related to the phase-slippage phenomenon. The use of this flux in the modernized Vinen equation corrects the situation with an unusual distribution of the vortex-line density, and satisfactorily describes the behavior L (r ,t ) both in stationary and nonstationary situations. The general problem of the phenomenological Vinen theory in the case of nonuniform and nonstationary quantum turbulence is thoroughly discussed.
Turbulent transport in magnetized plasmas
Horton, Wendell
2012-01-01
This book explains how magnetized plasmas self-organize in states of electromagnetic turbulence that transports particles and energy out of the core plasma faster than anticipated by the fusion scientists designing magnetic confinement systems in the 20th century. It describes theory, experiments and simulations in a unified and up-to-date presentation of the issues of achieving nuclear fusion power.
Magnetohydrodynamics turbulence: An astronomical perspective
Indian Academy of Sciences (India)
MHD turbulence in the solar wind are described in §6, and a theory of ..... on plasmas are very difficult to perform, and so experimental verification was not forth- .... checks of self-consistency regarding the assumed weakness of the cascade.
Turbulent jet in confined counterflow
Indian Academy of Sciences (India)
framework for presenting the results of the flowfield and jet penetration length. ... A turbulent jet is a basic free shear flow and has received research attention (see, .... MBE76 identify this to be a transitional zone and for. √ .... higher return flow and also higher velocity from counterflow due to a narrower gap thus leading.
Statistical description of turbulent dispersion
Brouwers, J.J.H.
2012-01-01
We derive a comprehensive statistical model for dispersion of passive or almost passive admixture particles such as fine particulate matter, aerosols, smoke and fumes, in turbulent flow. The model rests on the Markov limit for particle velocity. It is in accordance with the asymptotic structure of
Magnetic fluctuations in turbulent flow
International Nuclear Information System (INIS)
Ruzmaikin, A.A.
1990-01-01
For dynamo excitation of the magnetic fluctuations in infinite fluid only a sufficient large magnetic Reynolds number is needed. In a infinite region an additional condition appears. Due to the diffusion of the magnetic field through the boundaries a size of the region must be large enough compare with a correlation length of the turbulence. Author)
Turbulent flows over sparse canopies
Sharma, Akshath; García-Mayoral, Ricardo
2018-04-01
Turbulent flows over sparse and dense canopies exerting a similar drag force on the flow are investigated using Direct Numerical Simulations. The dense canopies are modelled using a homogeneous drag force, while for the sparse canopy, the geometry of the canopy elements is represented. It is found that on using the friction velocity based on the local shear at each height, the streamwise velocity fluctuations and the Reynolds stress within the sparse canopy are similar to those from a comparable smooth-wall case. In addition, when scaled with the local friction velocity, the intensity of the off-wall peak in the streamwise vorticity for sparse canopies also recovers a value similar to a smooth-wall. This indicates that the sparse canopy does not significantly disturb the near-wall turbulence cycle, but causes its rescaling to an intensity consistent with a lower friction velocity within the canopy. In comparison, the dense canopy is found to have a higher damping effect on the turbulent fluctuations. For the case of the sparse canopy, a peak in the spectral energy density of the wall-normal velocity, and Reynolds stress is observed, which may indicate the formation of Kelvin-Helmholtz-like instabilities. It is also found that a sparse canopy is better modelled by a homogeneous drag applied on the mean flow alone, and not the turbulent fluctuations.
Wind effect in turbulence parametrization
Colombini, M.; Stocchino, A.
2005-09-01
The action of wind blowing over a closed basin ultimately results in a steady shear-induced circulation pattern and in a leeward rising of the free surface—and a corresponding windward lowering—known as wind set-up. If the horizontal dimensions of the basin are large with respect to the average flow depth, the occurrence of local quasi-equilibrium conditions can be expected, i.e. the flow can be assumed to be locally driven only by the wind stress and by the opposing free surface gradient due to set-up. This wind-induced flow configuration shows a strong similarity with turbulent Couette-Poiseuille flow, the one dimensional flow between parallel plates generated by the simultaneous action of a constant pressure gradient and of the shear induced by the relative motion of the plates. A two-equation turbulence closure is then employed to perform a numerical study of turbulent Couette-Poiseuille flows for different values of the ratio of the shear stresses at the two walls. The resulting eddy viscosity vertical distributions are analyzed in order to devise analytical profiles of eddy viscosity that account for the effect of wind. The results of this study, beside allowing for a physical insight on the turbulence process of this class of flows, will allow for a more accurate description of the wind effect to be included in the formulation of quasi-3D and 3D models of lagoon hydrodynamics.
Turbulent jet in confined counterflow
Indian Academy of Sciences (India)
The mean flowfield of a turbulent jet issuing into a confined, uniform counterflow was investigated computationally. Based on dimensional analysis, the jet penetration length was shown to scale with jet-to-counterflow momentum flux ratio. This scaling and the computational results reproduce the well-known correct limit of ...
Magnetic turbulence and anomalous transport
International Nuclear Information System (INIS)
Garbet, X.; Mourgues, F.; Samain, A.
1990-01-01
The self consistency conditions for magnetic turbulence are reviewed. The main features of magnetic topology involving stochastic flux lines are summarized. Two driving sources are considered: thermal effects which require large scale residual islands and electron diamagnetism which involves fluctuation scales smaller than the ion Larmor radius and a β p threshold of order one. Stability criteria and transport coefficients are given
Group-kinetic theory and modeling of atmospheric turbulence
Tchen, C. M.
1989-01-01
A group kinetic method is developed for analyzing eddy transport properties and relaxation to equilibrium. The purpose is to derive the spectral structure of turbulence in incompressible and compressible media. Of particular interest are: direct and inverse cascade, boundary layer turbulence, Rossby wave turbulence, two phase turbulence; compressible turbulence, and soliton turbulence. Soliton turbulence can be found in large scale turbulence, turbulence connected with surface gravity waves and nonlinear propagation of acoustical and optical waves. By letting the pressure gradient represent the elementary interaction among fluid elements and by raising the Navier-Stokes equation to higher dimensionality, the master equation was obtained for the description of the microdynamical state of turbulence.
An introduction to turbulence and its measurement
Bradshaw, P
1971-01-01
An Introduction to Turbulence and Its Measurement is an introductory text on turbulence and its measurement. It combines the physics of turbulence with measurement techniques and covers topics ranging from measurable quantities and their physical significance to the analysis of fluctuating signals, temperature and concentration measurements, and the hot-wire anemometer. Examples of turbulent flows are presented. This book is comprised of eight chapters and begins with an overview of the physics of turbulence, paying particular attention to Newton's second law of motion, the Newtonian viscous f
On the prediction of turbulent secondary flows
Speziale, C. G.; So, R. M. C.; Younis, B. A.
1992-01-01
The prediction of turbulent secondary flows, with Reynolds stress models, in circular pipes and non-circular ducts is reviewed. Turbulence-driven secondary flows in straight non-circular ducts are considered along with turbulent secondary flows in pipes and ducts that arise from curvature or a system rotation. The physical mechanisms that generate these different kinds of secondary flows are outlined and the level of turbulence closure required to properly compute each type is discussed in detail. Illustrative computations of a variety of different secondary flows obtained from two-equation turbulence models and second-order closures are provided to amplify these points.
Topics in strong Langmuir turbulence
International Nuclear Information System (INIS)
Skoric, M.M.
1981-01-01
This thesis discusses certain aspects of the turbulence of a fully ionised non-isothermal plasma dominated by the Langmuir mode. Some of the basic properties of strongly turbulent plasmas are reviewed. In particular, interest is focused on the state of Langmuir turbulence, that is the turbulence of a simple externally unmagnetized plasma. The problem of the existence and dynamics of Langmuir collapse is discussed, often met as a non-linear stage of the modulational instability in the framework of the Zakharov equations (i.e. simple time-averaged dynamical equations). Possible macroscopic consequences of such dynamical turbulent models are investigated. In order to study highly non-linear collapse dynamics in its advanced stage, a set of generalized Zakharov equations are derived. Going beyond the original approximation, the author includes the effects of higher electron non-linearities and a breakdown of slow-timescale quasi-neutrality. He investigates how these corrections may influence the collapse stabilisation. Recently, it has been realised that the modulational instability in a Langmuir plasma will be accompanied by the collisionless-generation of a slow-timescale magnetic field. Accordingly, a novel physical situation has emerged which is investigated in detail. The stability of monochromatic Langmuir waves in a self-magnetized Langmuir plasma, is discussed, and the existence of a novel magneto-modulational instability shown. The wave collapse dynamics is investigated and a physical interpretation of the basic results is given. A problem of the transient analysis of an interaction of time-dependent electromagnetic pulses with linear cold plasma media is investigated. (Auth.)
Experiments in turbulent pipe flow
Energy Technology Data Exchange (ETDEWEB)
Torbergsen, Lars Even
1998-12-31
This thesis reports experimental results for the mean velocity and turbulence statistics in two straight pipe sections for bulk Reynolds numbers in the range 22000 to 75000. The flow was found consistent with a fully developed state. Detailed turbulence spectra were obtained for low and moderate turbulent Reynolds number. For the pipe centre line location at R{sub {lambda}} = 112, a narrow range in the streamwise power spectrum applied to the -5/3 inertial subrange. However this range was influenced both by turbulence production and viscous dissipation, and therefore did not reflect a true inertial range. The result indicates how the intermediate range between the production and dissipative scales can be misinterpreted as an inertial range for low and moderate R{sub {lambda}}. To examine the universal behaviour of the inertial range, the inertial scaling of the streamwise power spectrum is compared to the inertial scaling of the second order longitudinal velocity structure function, which relate directly by a Fourier transform. Increasing agreement between the Kolmogorov constant C{sub K} and the second order structure function scaling constant C{sub 2} was observed with increasing R{sub {lambda}}. The result indicates that a true inertial range requires several decades of separation between the energy containing and dissipative scales. A method for examining spectral anisotropy is reported and applied to turbulence spectra in fully developed pipe flow. It is found that the spectral redistribution from the streamwise to the two lateral spectra goes primarily to the circumferential component. Experimental results are reported for an axisymmetric contraction of a fully developed pipe flow. 67 refs., 75 figs., 9 tabs.
Directory of Open Access Journals (Sweden)
Rudi Riyanto
2007-12-01
Full Text Available Penelitian pengaruh perebusan, penggaraman dan penjemuran pada udang dan cumi terhadap pembentukan 7‑ketokolesterol telah dilakukan. Dalam penelitian ini, udang dan cumi masing masing dibagi dalam dua kelompok. Pada kelompok pertama diberikan perlakuan perebusan dalam air, dan pada kelompok kedua diberikan perlakuan perebusan dalam air garam (3% air garam untuk udang dan 20% air garam untuk cumi. Setelah perebusan, dilakukan pengeringan di bawah matahari (udang dikupas dahulu sebelum dijemur. Pengambilan sampel dilakukan saat kondisi segar, setelah direbus dan setelah dijemur. Pengamatan dilakukan terhadap kandungan 7‑ketokolesterol, kolesterol, nilai TBA, dan kadar air. Hasil penelitian menunjukkan bahwa perebusan, penggaraman dan penjemuran berpengaruh terhadap pembentukan 7‑ketokolesterol sampai konsentrasi 20,82 ppm pada udang dan 15,05 ppm pada cumi sebagai konsentrasi tertinggi produk hasil oksidasi kolesterol yang terbentuk. Penelitian ini dapat dijadikan bukti bahwa pemanasan (perebusan dan penjemuran, serta penggaraman berpengaruh dalam proses oksidasi kolesterol pada udang dan cumi.
Electron acceleration by turbulent plasmoid reconnection
Zhou, X.; Büchner, J.; Widmer, F.; Muñoz, P. A.
2018-04-01
In space and astrophysical plasmas, like in planetary magnetospheres, as that of Mercury, energetic electrons are often found near current sheets, which hint at electron acceleration by magnetic reconnection. Unfortunately, electron acceleration by reconnection is not well understood yet, in particular, acceleration by turbulent plasmoid reconnection. We have investigated electron acceleration by turbulent plasmoid reconnection, described by MHD simulations, via test particle calculations. In order to avoid resolving all relevant turbulence scales down to the dissipation scales, a mean-field turbulence model is used to describe the turbulence of sub-grid scales and their effects via a turbulent electromotive force (EMF). The mean-field model describes the turbulent EMF as a function of the mean values of current density, vorticity, magnetic field as well as of the energy, cross-helicity, and residual helicity of the turbulence. We found that, mainly around X-points of turbulent reconnection, strongly enhanced localized EMFs most efficiently accelerated electrons and caused the formation of power-law spectra. Magnetic-field-aligned EMFs, caused by the turbulence, dominate the electron acceleration process. Scaling the acceleration processes to parameters of the Hermean magnetotail, electron energies up to 60 keV can be reached by turbulent plasmoid reconnection through the thermal plasma.
CORPORATE IDENTITY SEJARAH DAN APLIKASINYA
Directory of Open Access Journals (Sweden)
Christine Suharto Cenadi
1999-01-01
Full Text Available In the recent globalization era%2C and the developed market%2C many companies compete to attract consumers to buy their products. One of the keys to compete and survive in this developing market is by creating an image and graphic identity. This paper will discuss about corporate identity%2C image%2C its purpose and applications. Abstract in Bahasa Indonesia : Dalam era globalisasi dewasa ini%2C dan dengan berkembangnya pasar (market%2C banyak perusahaan bersaing untuk menarik perhatian konsumen untuk membeli produknya. Salah satu cara untuk bersaing dan dapat bertahan di dalam pasar yang terus berkembang ini adalah dengan menciptakan suatu image dan identitas graphic. Tulisan ini akan membahas tentang corporate identity%2C image%2C fungsi dan aplikasinya
ADIABATIC HEATING OF CONTRACTING TURBULENT FLUIDS
International Nuclear Information System (INIS)
Robertson, Brant; Goldreich, Peter
2012-01-01
Turbulence influences the behavior of many astrophysical systems, frequently by providing non-thermal pressure support through random bulk motions. Although turbulence is commonly studied in systems with constant volume and mean density, turbulent astrophysical gases often expand or contract under the influence of pressure or gravity. Here, we examine the behavior of turbulence in contracting volumes using idealized models of compressed gases. Employing numerical simulations and an analytical model, we identify a simple mechanism by which the turbulent motions of contracting gases 'adiabatically heat', experiencing an increase in their random bulk velocities until the largest eddies in the gas circulate over a Hubble time of the contraction. Adiabatic heating provides a mechanism for sustaining turbulence in gases where no large-scale driving exists. We describe this mechanism in detail and discuss some potential applications to turbulence in astrophysical settings.
Contribution to the study of turbulence spectra
Dumas, R.
1979-01-01
An apparatus suitable for turbulence measurement between ranges of 1 to 5000 cps and from 6 to 16,000 cps was developed and is described. Turbulence spectra downstream of the grills were examined with reference to their general characteristics, their LF qualities, and the effects of periodic turbulence. Medium and HF are discussed. Turbulence spectra in the boundary layers are similarly examined, with reference to their fluctuations at right angles to the wall, and to lateral fluctuations. Turbulence spectra in a boundary layer with suction to the wall is discussed. Induced turbulence, and turbulence spectra at high Reynolds numbers. Calculations are presented relating to the effect of filtering on the value of the correlations in time and space.
Profil Sensori dan Nilai Gizi Beberapa Jenis Ikan Patin dan Hibrid Nasutus
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Theresia Dwi Suryaningrum
2010-11-01
Full Text Available Penelitian mengenai profil sensori dan nilai gizi filet patin Siam (Pangasius hypopthalmus, Jambal (Pangasius djambal Bleeker, Pasupati, Nasutus serta hasil silangan Siam dan Nasutus (hibrid Nasutus telah dilakukan. Analisis sensori dilakukan dengan uji pembeda menyeluruh, uji pembeda atribut, uji kesukaan, dan uji rangking. Pengamatan lainnya dilakukan terhadap edible portion dan nilai gizi (proksimat dan profil asam amino. Hasil penelitian menunjukkan bahwa filet patin hibrid Nasutus lebih memiliki kesamaan warna dengan filet patin Nasutus daripada filet patin Siam. W arna daging filet patin hibrid Nasutus berbeda nyata dengan induknya yaitu patin Nasutus dan patin Siam. Panelis lebih menyukai warna filet patin hibrid Nasutus dibandingkan dengan patin Pasupati. Patin hibrid Nasutus mempunyai tekstur yang berbeda nyata dengan Nasutus dan Jambal yang kompak dan padat, tetapi mempunyai kesamaan dengan patin Siam dan Pasupati yang agak kompak dan agak padat. Berdasarkan intensitas warna, hasil uji pembeda atribut dan uji kesukaan, maka secara berturut-turut panelis menyukai filet patin Jambal, Nasutus, hibrid Nasutus, Pasupati, dan Siam. Hibrid Nasutus mempunyai edible portionpaling tinggi (49% dibandingkan dengan patin lainnya tetapi mempunyai kadar air, kadar lemak, dan kadar protein yang lebih rendah dan berbeda nyata dengan induknya (patin Siam dan Nasutus. Patin Siam mengandung asam amino esensial paling tinggi di antara berbagai jenis patin yang diteliti. Profil asam amino patin hibrid Nasutus, Jambal, Pasupati, dan Nasutus hampir sama, kecuali pada patin Siam yang mengandung glisin, leusin, isoleusin, histidin, serin, treonin, dan prolin yang lebih tinggi dibandingkan dengan patin lainnya
MENGENALI GEJALA TINITUS DAN PENATALAKSANAANNYA
Directory of Open Access Journals (Sweden)
Dewi Purwita Agustini
2016-05-01
Full Text Available Telinga berdenging atau dikenal dalam bahasa medis sebagai tinitus, banyak dikeluhkan sebagai suatu bising atau bunyi yang muncul di kepala tanpa adanya rangsangan dari luar. Adapun keluhan yang dialami ini seperti bunyi mendengung, mendesis, menderu, atau berbagai variasi bunyi yang lain. Tinitus bukanlah penyakit atau sindroma, tapi hanya merupakan gejala yang mungkin berasal dari satu atau sejumlah kelainan. Sebetulnya suara yang terdengar oleh telinga tersebut belum tentu bersifat kelainan atau patologis. Jika orang sehat yang terbukti telinganya normal, berada dalam ruang kedap (anehoic chamber, maka ia akan dapat mendengar berbagai macam suara yang berasal dari berbagai organ tubuhnya sendiri yang memang bekerja setiap saat, contohnya: pernapasan, kontraksi jantung, dan aliran darah. Kenyataannya, dalam kehidupan sehari-hari, suasana yang memungkinkan suara fisiologis atau normal tersebut terdengar oleh seseorang sangat jarang tercipta dan bahkan dalam kamar yang sunyi di malam hari sekalipun. Hal ini dikarenakan, bunyi masking dari lingkungan dengan berintensitas bunyi sekitar 25 – 30 dB. Tinitus baru menjadi gejala jika suara organ tubuh intensitasnya melebihi bunyi masking lingkungan tadi. Tinitus kerap diderita terutama orang pada kelompok usia pertengahan dan usia tua. Menurut data statistic dari pusat kesehatan di Amerika, sekitar 32% orang dewasa pernah mengalami tinitus pada suatu saat tertentu dalam hidupnya, dan 6 % nya sangat menganggu dan cukup sulit disembuhkan. Di Inggris, 17% populasi juga memiliki masalah tinitus. Sayangnya di Indonesia belum ada data statistic yang memadai, namun berdasarkan pengalaman empiris, penderita tinitus cukup banyak dan sering ditemui di tempat praktek, klinik, maupun rumah sakit. Meski tinitus bukanlah keadaan yang membahayakan, munculnya gejala ini pada hampir kebanyakan orang sangat mengganggu dan sering mempengaruhi kualitas hidup dan pekerjaannya. Kata Kunci: Tinitus, berdenging, telinga
International Development Research Centre (IDRC) Digital Library (Canada)
Le CRDI appuie la recherche dans les. Philippines depuis 1972. Le travail qu'y ont accompli des universités et des instituts de recherche vigoureux et la participation active de la société civile ont entraîné d'importantes améliorations dans les domaines de l'agriculture, du suivi de la pauvreté et de la gestion des forêts.
DEFF Research Database (Denmark)
2009-01-01
XML specifications for DanRIS (Danish Registration- og InformationsSystem), where the the aim is: Improved exchange of data Improved data processing Ensuring future access to all gathered data from the year 1999 until now......XML specifications for DanRIS (Danish Registration- og InformationsSystem), where the the aim is: Improved exchange of data Improved data processing Ensuring future access to all gathered data from the year 1999 until now...
Ketergantungan Online Game Dan Penanganannya
Syahran, Ridwan
2015-01-01
Penelitian ini dimaksudkan untuk mengetahui perilaku yang ditimbulkan dari kecanduan bermaian online game pada siswa SMP Negeri 1 Palu yang meliputi faktor-faktor penyebab kecanduan, keadaan psikologis yang ditimbulkan dari kecanduan bermain online game dan dampak-dampak yang ditimbulkan dari kecanduan bermain online game.Pendekatan penelitian ini adalah penelitian kualitatif dengan jenis penelitian studi kasus dengan berdasarkan responden dan informan sebagai bahan sumber data. Dalam proses ...
Directory of Open Access Journals (Sweden)
Ferschneider G.
2006-11-01
Full Text Available Les écoulements diphasiques gaz-liquide ont été étudiés afin de contribuer à développer des modèles de calculs prédictifs des pertes de charge dans les conduites de production des bruts pétroliers. Les expériences nécessaires ont été réalisées sur la boucle diphasique de Boussens dans les conditions suivantes représentatives des conditions industrielles : diamètre 6 , longueur 120 m, disposition de la conduite horizontale ou faiblement ascendante, couple de fluide gaz naturel-huile légère. Le gradient de pression, le contenu global, et la distribution locale des phases ont été mesurés. Le traitement des équations de conservation phasique intégrées sur la section par différents types de moyennes a permis de développer un modèle cellulaire qui inclue un nombre limité d'équations constitutives nécessaires à sa fermeture. Ce modèle prédétermine convenablement le gradient de pression, le contenu gaz global et la longueur des poches et des bouchons. Two-phase gas-liquid flows were analyzed so as to develop models for prediction of pressure drops in crude-oil production lines. The experiments were performed on the two-phase loop at Boussens under the following representative industrial conditions: 6 diameter, 120 m length, horizontal or slightly rising pipe, couple of fluids natural gas and light oil. The pressure gradient, average content and local phase distribution were measured. Conservation phase equations integrated along the cross-section were processed by different time-averaged operators so as to develop a cellular model including a limited number of constitutive equations required for its closure. This model suitably predetermines the pressure gradient, the average gas content and the length of gas and liquid slug.
Statistical Mechanics of Turbulent Dynamos
Shebalin, John V.
2014-01-01
Incompressible magnetohydrodynamic (MHD) turbulence and magnetic dynamos, which occur in magnetofluids with large fluid and magnetic Reynolds numbers, will be discussed. When Reynolds numbers are large and energy decays slowly, the distribution of energy with respect to length scale becomes quasi-stationary and MHD turbulence can be described statistically. In the limit of infinite Reynolds numbers, viscosity and resistivity become zero and if these values are used in the MHD equations ab initio, a model system called ideal MHD turbulence results. This model system is typically confined in simple geometries with some form of homogeneous boundary conditions, allowing for velocity and magnetic field to be represented by orthogonal function expansions. One advantage to this is that the coefficients of the expansions form a set of nonlinearly interacting variables whose behavior can be described by equilibrium statistical mechanics, i.e., by a canonical ensemble theory based on the global invariants (energy, cross helicity and magnetic helicity) of ideal MHD turbulence. Another advantage is that truncated expansions provide a finite dynamical system whose time evolution can be numerically simulated to test the predictions of the associated statistical mechanics. If ensemble predictions are the same as time averages, then the system is said to be ergodic; if not, the system is nonergodic. Although it had been implicitly assumed in the early days of ideal MHD statistical theory development that these finite dynamical systems were ergodic, numerical simulations provided sufficient evidence that they were, in fact, nonergodic. Specifically, while canonical ensemble theory predicted that expansion coefficients would be (i) zero-mean random variables with (ii) energy that decreased with length scale, it was found that although (ii) was correct, (i) was not and the expected ergodicity was broken. The exact cause of this broken ergodicity was explained, after much
ENERGI DAN DAMPAKNYA TERHADAP LINGKUNGAN
Directory of Open Access Journals (Sweden)
I Made Astra
2010-11-01
Full Text Available Energi dapat berubah dari satu bentuk ke bentuk yang lainnya, perubahannya sering mempengaruhi lingkungan dan udara yang kita hirup dengan berbagai cara. Energy kimia dalam bahan bakar fosil diubah menjadi energy panas, mekanik, atau listrik melalui pembakaran dan ini sebagai penghasil polutan terbesar. Dan dengan demikian pembangkit listrik, kendaraan bermotor, dan kompor adalah penyebab utama terjadinya polusi udara. Polutan yang dikeluarkan biasanya dikelompokan menjadi hidrokarbon (HC, nitrogen oksida (NOx, dan karbon monoksida (CO. Polutan yang dihasilkan pada pembakaran fosil merupakan faktor terbesar terjadinya asap, hujan asam, pemanasan global dan perubahan iklim. The conversion of energy from one form to another often affects the environment and the air we breath in many ways. Pollutants are emitted as the chemical energy in fossil fuels is converten to thermal, mechanical, or electrical energy via combustion, and thus power plants, motor vehicles, and even stoves take the blame for air pollution, and the pollutants released by the vehicles are usually grouped as hydrocarbons (HC, nitrogen oxides (NOx, and carbon monoxide (CO. Pollutans emitted during the combustion of fossil fuels are responsible for smog, acid rain, and global warming and climate change.
Isolasi dan Karakterisasi Ralstonia syzygii
Directory of Open Access Journals (Sweden)
Yanuar Danaatmadja
2009-07-01
Full Text Available Ralstonia syzygii is one of important pathogens of cloves. This study was aimed at obtaining pure culture of R. syzygi from diseased plant tissue samples. The acterium was isolated from infected clove plantations in Ungaran, Central Java. It had the ability to make clove seedlings show symptoms and then die 41 days after inoculation. The reisolated bacterium also showed its ability to kill clove seedlings after 17 days. The bacterium is gram negative, able to ultilize glucose, sucrose, maltose, mannitol, sorbitol, dulcitol, and glycerol, able to hydrolyze starch, grow well at 27oC, able to catalyze and release water and oxygen from hydrogen peroxyde (H2O2 and aerobically. Ralstonia syzygii merupakan salah satu patogen penting pada tanaman cengkeh. Penelitian ini dilakukan untuk mendapakan isolat murni R syzygii dari jaringan tanaman terinfeksi. Bakteri diisolasi dari pertanaman cengkeh sakit yang berasal dari daerah Ungaran, Jawa Tengah. Bakteri menunjukkan kemampuan untuk menyebabkan bibit tanaman cangkeh sakit dan kemudian mati 41 hsi. Bakteri hasil reisolasi juga menunjukkan kemampuannya menyebabkan sakit dan kematian pada bibit tanaman cengkeh setelah 17 hsi. Bakteri yang diperoleh bersifat gram negatif, mampu memanfaatkan glukosa, sukrosa, maltosa, manitol, sorbitol, dulsitol, dan gliserol, mampu menghidrolisis pati, tumbuh baik pada suhu 27o C, mampu mengkatalisis dan melepaskan air dan oksigen dari hydrogen peroxide (H2O2 dan bersifat aerob.
PREFACE: Turbulent Mixing and Beyond Turbulent Mixing and Beyond
Abarzhi, Snezhana I.; Gauthier, Serge; Rosner, Robert
2008-10-01
The goals of the International Conference `Turbulent Mixing and Beyond' are to expose the generic problem of Turbulence and Turbulent Mixing in Unsteady Flows to a wide scientific community, to promote the development of new ideas in tackling the fundamental aspects of the problem, to assist in the application of novel approaches in a broad range of phenomena, where the non-canonical turbulent processes occur, and to have a potential impact on technology. The Conference provides the opportunity to bring together scientists from the areas which include, but are not limited to, high energy density physics, plasmas, fluid dynamics, turbulence, combustion, material science, geophysics, astrophysics, optics and telecommunications, applied mathematics, probability and statistics, and to have their attention focused on the long-standing formidable task. The Turbulent Mixing and Turbulence in Unsteady Flows, including multiphase flows, plays a key role in a wide variety of phenomena, ranging from astrophysical to nano-scales, under either high or low energy density conditions. Inertial confinement and magnetic fusion, light-matter interaction and non-equilibrium heat transfer, properties of materials under high strain rates, strong shocks, explosions, blast waves, supernovae and accretion disks, stellar non-Boussinesq and magneto-convection, planetary interiors and mantle-lithosphere tectonics, premixed and non-premixed combustion, oceanography, atmospheric flows, unsteady boundary layers, hypersonic and supersonic flows, are a few examples to list. A grip on unsteady turbulent processes is crucial for cutting-edge technology such as laser-micromachining and free-space optical telecommunications, and for industrial applications in aeronautics. Unsteady Turbulent Processes are anisotropic, non-local and multi-scale, and their fundamental scaling, spectral and invariant properties depart from the classical Kolmogorov scenario. The singular aspects and similarity of the
Comparison of turbulent particle dispersion models in turbulent shear flows
Directory of Open Access Journals (Sweden)
S. Laín
2007-09-01
Full Text Available This work compares the performance of two Lagrangian turbulent particle dispersion models: the standard model (e.g., that presented in Sommerfeld et al. (1993, in which the fluctuating fluid velocity experienced by the particle is composed of two components, one correlated with the previous time step and a second one randomly sampled from a Wiener process, and the model proposed by Minier and Peirano (2001, which is based on the PDF approach and performs closure at the level of acceleration of the fluid experienced by the particle. Formulation of a Langevin equation model for the increments of fluid velocity seen by the particle allows capturing some underlying physics of particle dispersion in general turbulent flows while keeping the mathematical manipulation of the stochastic model simple, thereby avoiding some pitfalls and simplifying the derivation of macroscopic relations. The performance of both dispersion models is tested in the configurations of grid-generated turbulence (Wells and Stock (1983 experiments, simple shear flow (Hyland et al., 1999 and confined axisymmetric jet flow laden with solids (Hishida and Maeda (1987 experiments.
Penskalaan Butir Format Respons Pilihan dan Respons Bebas Berdasarkan Model Rasch dan Partial Credit
Eko Hariadi
2007-01-01
Penelitian melihat pengaruh jumlah parameter butir, kategori respons bebas (RB), pengaruh sampel terhadap akurasi estimasi parameter kemampuan untuk menghasilkan estimasi yang stabil dan pengaruh pembobotan butir RP dan butir RB terhadap kesalahan baku. Penelitian dalam dua tahap, simulasi menggunakan 30 kondisi dengan replikasi 50 dengan variabel panjang tes, jumlah kategori, dan jumlah parameter butir, dan analisis deskriptif, dilanjutkan penerapan penskalaan gabungan butir tipe res...
Kurniawan, Andi; Fadjar, Mohamad; Sukoso, Sukoso; Prihanto, Asep Awaludin
2015-01-01
Mikroorganisme yang mampu menghasilkan biofim menimbulkan masalah yang serius dalam bidang kesehatan dan pangan. Penelitian biofim bagi sebagian peneliti sangat identik dengan kerumitan proses penghitungan dan visualisasi penutupan permukaan substrat penempelan bakteri. Penelitian ini ditujukan untuk mengetahui efiiensi metode alternatif untuk menghitung dan memvisualisasikan biofimVibrio cholera. Pada penelitian ini beberapa faktor lingkungan seperti pH, suhu, dan kondisi kultur diujicobakan...
Turbulent equipartitions in two dimensional drift convection
International Nuclear Information System (INIS)
Isichenko, M.B.; Yankov, V.V.
1995-01-01
Unlike the thermodynamic equipartition of energy in conservative systems, turbulent equipartitions (TEP) describe strongly non-equilibrium systems such as turbulent plasmas. In turbulent systems, energy is no longer a good invariant, but one can utilize the conservation of other quantities, such as adiabatic invariants, frozen-in magnetic flux, entropy, or combination thereof, in order to derive new, turbulent quasi-equilibria. These TEP equilibria assume various forms, but in general they sustain spatially inhomogeneous distributions of the usual thermodynamic quantities such as density or temperature. This mechanism explains the effects of particle and energy pinch in tokamaks. The analysis of the relaxed states caused by turbulent mixing is based on the existence of Lagrangian invariants (quantities constant along fluid-particle or other orbits). A turbulent equipartition corresponds to the spatially uniform distribution of relevant Lagrangian invariants. The existence of such turbulent equilibria is demonstrated in the simple model of two dimensional electrostatically turbulent plasma in an inhomogeneous magnetic field. The turbulence is prescribed, and the turbulent transport is assumed to be much stronger than the classical collisional transport. The simplicity of the model makes it possible to derive the equations describing the relaxation to the TEP state in several limits
Relation of astrophysical turbulence and magnetic reconnection
Energy Technology Data Exchange (ETDEWEB)
Lazarian, A. [Department of Astronomy, University of Wisconsin, 475 North Charter Street, Madison, Wisconsin 53706 (United States); Eyink, Gregory L. [Department of Applied Mathematics and Statistics, Johns Hopkins University, Baltimore, Maryland 21218 (United States); Vishniac, E. T. [Department of Physics and Astronomy, McMaster University, 1280 Main Street West, Hamilton, Ontario L8S 4M1 (Canada)
2012-01-15
Astrophysical fluids are generically turbulent and this must be taken into account for most transport processes. We discuss how the preexisting turbulence modifies magnetic reconnection and how magnetic reconnection affects the MHD turbulent cascade. We show the intrinsic interdependence and interrelation of magnetic turbulence and magnetic reconnection, in particular, that strong magnetic turbulence in 3D requires reconnection and 3D magnetic turbulence entails fast reconnection. We follow the approach in Eyink et al.[Astrophys. J. 743, 51 (2011)] to show that the expressions of fast magnetic reconnection in A. Lazarian and E. T. Vishniac [Astrophys. J. 517, 700 (1999)] can be recovered if Richardson diffusion of turbulent flows is used instead of ordinary Ohmic diffusion. This does not revive, however, the concept of magnetic turbulent diffusion which assumes that magnetic fields can be mixed up in a passive way down to a very small dissipation scales. On the contrary, we are dealing the reconnection of dynamically important magnetic field bundles which strongly resist bending and have well defined mean direction weakly perturbed by turbulence. We argue that in the presence of turbulence the very concept of flux-freezing requires modification. The diffusion that arises from magnetic turbulence can be called reconnection diffusion as it based on reconnection of magnetic field lines. The reconnection diffusion has important implications for the continuous transport processes in magnetized plasmas and for star formation. In addition, fast magnetic reconnection in turbulent media induces the First order Fermi acceleration of energetic particles, can explain solar flares and gamma ray bursts. However, the most dramatic consequence of these developments is the fact that the standard flux freezing concept must be radically modified in the presence of turbulence.
Electromotive force in strongly compressible magnetohydrodynamic turbulence
Yokoi, N.
2017-12-01
Variable density fluid turbulence is ubiquitous in geo-fluids, not to mention in astrophysics. Depending on the source of density variation, variable density fluid turbulence may be divided into two categories: the weak compressible (entropy mode) turbulence for slow flow and the strong compressible (acoustic mode) turbulence for fast flow. In the strong compressible turbulence, the pressure fluctuation induces a strong density fluctuation ρ ', which is represented by the density variance ( denotes the ensemble average). The turbulent effect on the large-scale magnetic-field B induction is represented by the turbulent electromotive force (EMF) (u': velocity fluctuation, b': magnetic-field fluctuation). In the usual treatment in the dynamo theory, the expression for the EMF has been obtained in the framework of incompressible or weak compressible turbulence, where only the variation of the mean density , if any, is taken into account. We see from the equation of the density fluctuation ρ', the density variance is generated by the large mean density variation ∂ coupled with the turbulent mass flux . This means that in the region where the mean density steeply changes, the density variance effect becomes relevant for the magnetic field evolution. This situation is typically the case for phenomena associated with shocks and compositional discontinuities. With the aid of the analytical theory of inhomogeneous compressible magnetohydrodynamic (MHD) turbulence, the expression for the turbulent electromotive force is investigated. It is shown that, among others, an obliqueness (misalignment) between the mean density gradient ∂ and the mean magnetic field B may contribute to the EMF as ≈χ B×∂ with the turbulent transport coefficient χ proportional to the density variance (χ ). This density variance effect is expected to strongly affect the EMF near the interface, and changes the transport properties of turbulence. In the case of an interface under the MHD slow
Model for Simulation Atmospheric Turbulence
DEFF Research Database (Denmark)
Lundtang Petersen, Erik
1976-01-01
A method that produces realistic simulations of atmospheric turbulence is developed and analyzed. The procedure makes use of a generalized spectral analysis, often called a proper orthogonal decomposition or the Karhunen-Loève expansion. A set of criteria, emphasizing a realistic appearance...... eigenfunctions and estimates of the distributions of the corresponding expansion coefficients. The simulation method utilizes the eigenfunction expansion procedure to produce preliminary time histories of the three velocity components simultaneously. As a final step, a spectral shaping procedure is then applied....... The method is unique in modeling the three velocity components simultaneously, and it is found that important cross-statistical features are reasonably well-behaved. It is concluded that the model provides a practical, operational simulator of atmospheric turbulence....
Langmuir turbulence in space plasmas
Energy Technology Data Exchange (ETDEWEB)
Goldman, M.V. [Colorado Univ., Boulder, CO (United States); Newman, D.L. [Colorado Univ., Boulder, CO (United States); Wang, J.G. [Colorado Univ., Boulder, CO (United States); Muschietti, L. [California Univ., Berkeley (United States). Space Sciences Lab.
1996-11-01
Recent developments in theoretical and numerical modeling of Langmuir turbulence in space and laboratory plasmas are addressed. Kinetic effects, which have been missing from (fluid) traditional Zakharov equation models are explored using Vlasov code simulations. These studies are motivated by beam-driven Langmuir waves and particle distributions measured in earth`s foreshock region, and by beam-driven Langmuir waves and beams that underlie type III solar radio emission in the solar wind. The nonlinear physical processes studied in these 1-D Vlasov simulations include both wave-wave interactions and acceleration of particles by waves-leading to electron-beam flattening. We study bump-on-tail instabilities as boundary value problems, and determine the interplay in space and time between beam plateau formation, stimulated wave-wave backscatter cascades, and strong turbulence wave-packet collapse. (orig.).
Transition and turbulence (hydrodynamic visualizations)
Werle, Henri
The very extensive Reynolds number domain (10 to the 4th power less than or equal to Re sub L greater than or equal to 10 to the 6th power) of the TH2 water tunnel at Chatillon, allowed for laminar-turbulent transition phenomena to be studied systematically by visualizations and with methods previously developed in the TH1 water tunnel. These tests concern a wide variety of models including, Flate plate type models (smooth or grooved, with curved afterbody or right base), cylindrical pod type models (smooth or grooved, with curved afterbody or plane base), and models of different shapes (recall). The purpose of these tests is to provide a visualization of these transition and turbulence phenomena in order to better understand the phenomena.
Flux driven turbulence in tokamaks
International Nuclear Information System (INIS)
Garbet, X.; Ghendrih, P.; Ottaviani, M.; Sarazin, Y.; Beyer, P.; Benkadda, S.; Waltz, R.E.
1999-01-01
This work deals with tokamak plasma turbulence in the case where fluxes are fixed and profiles are allowed to fluctuate. These systems are intermittent. In particular, radially propagating fronts, are usually observed over a broad range of time and spatial scales. The existence of these fronts provide a way to understand the fast transport events sometimes observed in tokamaks. It is also shown that the confinement scaling law can still be of the gyroBohm type in spite of these large scale transport events. Some departure from the gyroBohm prediction is observed at low flux, i.e. when the gradients are close to the instability threshold. Finally, it is found that the diffusivity is not the same for a turbulence calculated at fixed flux than at fixed temperature gradient, with the same time averaged profile. (author)
John Leask Lumley: Whither Turbulence?
Leibovich, Sidney; Warhaft, Zellman
2018-01-01
John Lumley's contributions to the theory, modeling, and experiments on turbulent flows played a seminal role in the advancement of our understanding of this subject in the second half of the twentieth century. We discuss John's career and his personal style, including his love and deep knowledge of vintage wine and vintage cars. His intellectual contributions range from abstract theory to applied engineering. Here we discuss some of his major advances, focusing on second-order modeling, proper orthogonal decomposition, path-breaking experiments, research on geophysical turbulence, and important contributions to the understanding of drag reduction. John Lumley was also an influential teacher whose books and films have molded generations of students. These and other aspects of his professional career are described.
Statistical theory of plasmas turbulence
International Nuclear Information System (INIS)
Kim, Eun-jin; Anderson, Johan
2009-01-01
We present a statistical theory of intermittency in plasma turbulence based on short-lived coherent structures (instantons). In general, the probability density functions (PDFs) of the flux R are shown to have an exponential scaling P(R) ∝ exp (-cR s ) in the tails. In ion-temperature-gradient turbulence, the exponent takes the value s=3/2 for momentum flux and s=3 for zonal flow formation. The value of s follows from the order of the highest nonlinear interaction term and the moments for which the PDFs are computed. The constant c depends on the spatial profile of the coherent structure and other physical parameters in the model. Our theory provides a powerful mechanism for ubiquitous exponential scalings of PDFs, often observed in various tokamaks. Implications of the results, in particular, on structure formation are further discussed. (author)
Heat flux driven ion turbulence
International Nuclear Information System (INIS)
Garbet, X.
1998-01-01
This work is an analysis of an ion turbulence in a tokamak in the case where the thermal flux is fixed and the temperature profile is allowed to fluctuate. The system exhibits some features of Self-Organized Critical systems. In particular, avalanches are observed. Also the frequency spectrum of the thermal flux exhibits a structure similar to the one of a sand pile automaton, including a 1/f behavior. However, the time average temperature profile is found to be supercritical, i.e. the temperature gradient stays above the critical value. Moreover, the heat diffusivity is lower for a turbulence calculated at fixed flux than a fixed temperature gradient, with the same time average temperature. This behavior is attributed to a stabilizing effect of avalanches. (author)
Multifractal Modeling of Turbulent Mixing
Samiee, Mehdi; Zayernouri, Mohsen; Meerschaert, Mark M.
2017-11-01
Stochastic processes in random media are emerging as interesting tools for modeling anomalous transport phenomena. Applications include intermittent passive scalar transport with background noise in turbulent flows, which are observed in atmospheric boundary layers, turbulent mixing in reactive flows, and long-range dependent flow fields in disordered/fractal environments. In this work, we propose a nonlocal scalar transport equation involving the fractional Laplacian, where the corresponding fractional index is linked to the multifractal structure of the nonlinear passive scalar power spectrum. This work was supported by the AFOSR Young Investigator Program (YIP) award (FA9550-17-1-0150) and partially by MURI/ARO (W911NF-15-1-0562).
Microstructures (clumps) in turbulent plasmas
International Nuclear Information System (INIS)
Balescu, R.; Misguich, J.H.
1977-01-01
A general analysis of binary correlations in a turbulent plasma leads to a functional relation relating correlations to the one-particle distribution function. Such a relation allows to understand the mechanism of generation of the microstructures or clumps introduced by Dupree. The expressions introduced by this author appear as a lowest approximation of the general equation. The features and interpretation of these microstructures are briefly discussed [fr
Geometry Dependence of Stellarator Turbulence
International Nuclear Information System (INIS)
Mynick, H.E.; Xanthopoulos, P.; Boozer, A.H.
2009-01-01
Using the nonlinear gyrokinetic code package GENE/GIST, we study the turbulent transport in a broad family of stellarator designs, to understand the geometry-dependence of the microturbulence. By using a set of flux tubes on a given flux surface, we construct a picture of the 2D structure of the microturbulence over that surface, and relate this to relevant geometric quantities, such as the curvature, local shear, and effective potential in the Schrodinger-like equation governing linear drift modes
Shell Models of Superfluid Turbulence
International Nuclear Information System (INIS)
Wacks, Daniel H; Barenghi, Carlo F
2011-01-01
Superfluid helium consists of two inter-penetrating fluids, a viscous normal fluid and an inviscid superfluid, coupled by a mutual friction. We develop a two-fluid shell model to study superfluid turbulence and investigate the energy spectra and the balance of fluxes between the two fluids in a steady state. At sufficiently low temperatures a 'bottle-neck' develops at high wavenumbers suggesting the need for a further dissipative effect, such as the Kelvin wave cascade.
Turbulent diffusion of small particles
International Nuclear Information System (INIS)
Margolin, L.G.
1977-11-01
The diffusion of small, spherical, rigid particles suspended in an incompressible turbulent fluid, but not interacting with each other, was studied. As a stochastic process, the turbulent fluid velocity field is assumed to be homogeneous, isotropic and stationary. Assuming the Stokes regime, a particle of equation of motion is used which includes only the effects of Stokes drag and a virtual mass force and an exact solution is found for the particle velocity correlation function, for all times and initial conditions, in terms of a fluid velocity correlation function measured along the motion of the particle. This shows that for times larger than a certain time scale, the particle velocity correlation becomes stationary. The effect of small shears in the fluid velocity was considered, under the additional restrictions of a certain high frequency regime for the turbulence. The shears convected past the particle much faster than the growth of the boundary layer. New force terms due to the presence of such shears are calculated and incorporated into the equation of motion. A perturbation solution to this equation is constructed, and the resultant particle velocity correlation function and diffusion coefficient are calculated. To lowest order, the particle diffusivity is found to be unaltered by the presence of small mean flow shears. The last model treated is one in which particles traverse a turbulent fluid with a large mean velocity. Among other restrictions, linearized form drag is assumed. The diffusion coefficient for such particles was calculated, and found to be much smaller than the passive scalar diffusion coefficient. This agrees within 5 percent with the experimental results of Snyder and Lumley
Conditional Eddies in Plasma Turbulence
DEFF Research Database (Denmark)
Johnsen, H.; Pécseli, H.L.; Trulsen, J.
1987-01-01
Low‐frequency electrostatic turbulence generated by the ion–ion beam instability was investigated experimentally in a double‐plasma device. Real time signals were recorded and examined by a conditional statistical analysis. Conditionally averaged potential distributions reveal the formation...... and propagation of structures with a relatively long lifetime. Various methods for making a conditional analysis are discussed and compared. The results are discussed with reference to ion phase space vortices and clump formation in collisionless plasmas....
Plankton Dynamics and Mesoscale Turbulence
2010-06-29
transformation of inorganic materials and light into living matter by photosynthesis) is operated mainly by small, unicellular algae that float freely in the...Aquatic ecosystems are characterized by the essential role played by fluid dynamics. The small organisms which compose the plankton are advected by the...surrounding flow and must cope with environmental currents, turbulence, and waves. And those organisms which anchor themselves to the rocks and to the
Information Theory and Plasma Turbulence
International Nuclear Information System (INIS)
Dendy, R. O.
2009-01-01
Information theory, applied directly to measured signals, yields new perspectives on, and quantitative knowledge of, the physics of strongly nonlinear and turbulent phenomena in plasmas. It represents a new and productive element of the topical research programmes that use modern techniques to characterise strongly nonlinear signals from plasmas, and that address global plasma behaviour from a complex systems perspective. We here review some pioneering studies of mutual information in solar wind and magnetospheric plasmas, using techniques tested on standard complex systems.
Turbulent Liquid Metal Dynamo Experiments
International Nuclear Information System (INIS)
Forest, Cary
2007-01-01
The self-generation of magnetic fields in planets and stars--the dynamo effect--is a long-standing problem of magnetohydrodynamics and plasma physics. Until recently, research on the self-excitation process has been primarily theoretical. In this talk, I will begin with a tutorial on how magnetic fields are generated in planets and stars, describing the 'Standard Model' of self-excitation known as the alpha-omega dynamo. In this model, axisymmetric differential rotation can produce the majority of the magnetic field, but some non-axisymmetric, turbulence driven currents are also necessary. Understanding the conversion of turbulent kinetic energy in the fluid motion into electrical currents and thus magnetic fields, is a major challenge for both experiments and theory at this time. I will then report on recent results from a 1 meter diameter, spherical, liquid sodium dynamo experiment at the University of Wisconsin, in which the first clear evidence for these turbulence driven currents has been observed.
Conformal invariance in hydrodynamic turbulence
International Nuclear Information System (INIS)
Falkovich, Gregory
2007-01-01
This short survey is written by a physicist. It contains neither theorems nor precise definitions. Its main content is a description of the results of numerical solution of the equations of fluid mechanics in the regime of developed turbulence. Due to limitations of computers, the results are not very precise. Despite being neither exact nor rigorous, the findings may nevertheless be of interest for mathematicians. The main result is that the isolines of some scalar fields (vorticity, temperature) in two-dimensional turbulence belong to the class of conformally invariant curves called SLE (Scramm-Loewner evolution) curves. First, this enables one to predict and find a plethora of quantitative relations going far beyond what was known previously about turbulence. Second, it suggests relations between phenomena that seemed unrelated, like the Euler equation and critical percolation. Third, it shows that one is able to get exact analytic results in statistical hydrodynamics. In short, physicists have found something unexpected and hope that mathematicians can help to explain it.
Application of some turbulence models
International Nuclear Information System (INIS)
Ushijima, Sho; Kato, Masanobu; Fujimoto, Ken; Moriya, Shoichi
1985-01-01
In order to predict numerically the thermal stratification and the thermal striping phenomena in pool-type FBRs, it is necessary to simulate adequately various turbulence properties of flows with good turbulence models. This report presents numerical simulations of two dimensional isothermal steady flows in a rectangular plenum using three types of turbulence models. Three models are general k-ε model and two Reynolds stress models. The agreements of these results are examined and the properties of these models are compared. The main results are summarized as follows. (1) Concerning the mean velocity distributions, although a little differences exist, all results of three models agree with experimental values. (2) It can be found that non-isotropy of normal Reynolds stresses (u' 2 , v' 2 ) distributions is qwite well simulated by two Reynolds stress models, but not adequately by k-ε model, shear Reynolds stress (-u', v') distribations of three models have little differences and agree good with experiments. (3) Balances of the various terms of Reynolds stress equations are examined. Comparing the results obtained by analyses and those of previous experiments, both distributions show qualitative agreements. (author)
Kinetic features of interchange turbulence
International Nuclear Information System (INIS)
Sarazin, Y; Grandgirard, V; Fleurence, E; Garbet, X; Ghendrih, Ph; Bertrand, P; Depret, G
2005-01-01
Non-linear gyrokinetic simulations of the interchange instability are discussed. The semi-Lagrangian numerical scheme allows one to address two critical points achieved with simulations lasting several confinement times: an accurate statistical analysis of the fluctuations and the back reaction of the turbulence on equilibrium profiles. Zonal flows are found to quench a 2D + 1D interchange turbulence when one of the species has a vanishing response to zonal modes. Conversely, when streamers dominate, the equilibrium profiles are found to be stiff. In the non-linear regime and steady-state turbulence, the distribution function exhibits a significant departure from a Maxwellian distribution. This property is characterized by an expansion on generalized Laguerre functions with a slow decay of the series of moments. This justifies the use of gyrokinetic simulations since a standard fluid approach, based on a limited number of moments, would certainly require a complex closure so as to take into account the impact of these non-vanishing high order moments
Turbulence modelling for incompressible flows
International Nuclear Information System (INIS)
Rodi, W.
1985-12-01
EUROMECH colloquium 180 was held at Karlsruhe from 4-6 July, 1984, with the aim of bringing together specialists working in the area of turbulence modelling and of reviewing the state-of-the-art in this field. 44 scientists from 12 countries participated and 28 papers were presented. The meeting started with a review of the performance of two-equation turbulence models employing transport equations for both the velocity and the length scale of turbulence. These models are now generally well established, but it was found that their application to certain flow situations remains problematic. The modelling assumptions involved in Reynolds stress-equation models were reviewed next, and new assumptions were proposed. It was generally agreed that, as computing power increases, these more complex models will become more popular also for practical applications. The increase in computing power also allows more and more to resolve the viscous sublayer with low Reynolds numbers models, and the capabilities and problems of these models were discussed. In this connection, special aspects of boundary layer calculations were also discussed, namely those associated with 3D boundary layers, converging and diverging flow and slightly detached boundary layers. The complex physical phenomena prevalent in situations under the influence of buoyancy and rotation were reviewed, and several papers were presented on models for simulating these effects. (orig./HP) [de
Energy Technology Data Exchange (ETDEWEB)
NONE
1962-07-01
The effects of electric fields on heat transfer to the following gases: air, argon, nitrogen, carbon dioxyde, helium, hydrogen, were studied in an annular channel, the inner part of which is the heating element. Experiments were made both in free convection and forced convection, the latter case with and without an external source of ionisation. Two causes of improvement of heat transfer were found: electro-convection and ionic convection; the influence of various parameters (electric fields, current of ionisation, temperatures, pressures, flow rate, etc...) is also investigated. Increasing of exchanged power was measured: in free convection this increasing reached 400 per cent and, in forced convection, it was found to be mainly dependent on stream velocity, decreasing from 300 per cent at Re = 6000 to few per cent for Re {>=} 30000 for a given gas pressure. Experiments in pile have shown that the use of an external source of ionisation allowed to obtain the same order of improvement as above but with a voltage much lower. This fact would make easier the use of this process of heat transfer in a channel of a reactor. (authors) [French] On a etudie l'action du champ electrique sur les echanges de chaleur dans les gaz suivants: air, argon, azote, anhydride carbonique, helium, hydrogene, avec un element chauffant cylindrique dans un canal concentrique. Des experiences ont ete effectuees en convection libre et en convection forcee en l'absence et en presence d'une source exterieure d'ionisation. On a distingue deux sortes de mecanismes d'accroissement des echanges, l'un d'electroconvection proprement dite et l'autre de convection ionique, et on precise l'influence des divers parametres (champ electrique, courant d'ionisation, temperature, pression, debit, etc...). On a pu chiffrer les ordres de grandeur des accroissements d'echanges observes qui, en convection libre, atteignent 300 a 400 pour cent et, en convection forcee, dependent beaucoup de la vitesse d'ecoulement
International Nuclear Information System (INIS)
Imaizumi, Ryota; Morikawa, Koichi; Higuchi, Masamori; Saito, Takayuki
2009-01-01
In this study, the interaction between a bubble swarm and homogeneous isotropic turbulence was experimentally investigated. The objective is to clarify the turbulence modulation induced by interaction between the bubble swarm and the homogeneous isotropic turbulence without mean flow. In order to generate simultaneously ideally homogeneous isotropic turbulence and a sufficiently controlled bubble swarm, we employed both oscillating grid and bubble generators equipped with audio speakers. First, the homogeneous isotropic turbulence was formed by operating the oscillating grid cylindrical acrylic pipe (height: 600 mm, inner diameter: 149 mm) filled with ion-exchanged and degassed water. Second, we stopped the oscillating-grid in arbitrary time after the homogeneous isotropic turbulence was achieved. A few moments later, the controlled bubble swarm (number of bubbles: 3, average equivalent diameter of bubble: 3 mm, bubble Reynolds number: 859, Weber number: 3.48) was launched into the decaying turbulence described above, using the bubble generators. The bubble formation, bubble size and bubble-launch timing are controlled arbitrarily and precisely by this device. In this study, we conducted the following experiments: 1) measurement of the motion of bubbles in rest water and oscillating grid turbulence via high-speed visualization, 2) measurement of the liquid phase motion around the bubbles in rest water via PIV system with LIF method, 3) measurement of the liquid phase motion around the bubbles in oscillating-grid turbulence via PIV system with LIF method. In the vitalization of the liquid-phase motion of both experiments, two high speed video cameras were employed in order to simultaneously film large- and small-scale interrogation areas. The liquid-phase ambient turbulence hastened the change of the bubble motion from zigzag mode to spiral mode. The interaction between the bubble swarm and liquid-phase turbulence increased decay-rate of the turbulence. (author)
Purwarupa Sistem Integrasi Quadcopter dan Mobile Robot
Dharmawan, Andi; Lusiarta Putera, Christian Antonia
2012-01-01
AbstrakQuadcopter, juga dikenal sebagai quadrotor, adalah helikopter dengan empat motor yang dilengkapi dengan empat buah propeller pada masing-masing motornya yang digunakan untuk terbang dan bermanuver. Pada quadcopter terdapat 3 variabel sudut yang menjadi element utama dalam pengendaliannya yaitu roll, pitch, dan yaw yang diperoleh dari penggabungan sensor accelerometer, gyroscope dan magnetometer dengan metode Direction Cosine Matrix. Pada sistem integrasi mobile robot dan quadcopter, d...
Review Dendrimer : Definisi, Sintesis, Aplikasi Dan Prospektif
Rahmi, Dwinna
2013-01-01
Dendrimer merupakan makrostruktur monodisperse dengan banyak cabang yang homogen dan degree of branching (DB) 100%. Dua cara sintesis dendrimer yaitu convergent dan divergent dilakukan. Convergent dilakukan dengan reaksi kovalen antara dua dan lebih monomer. Divergent dimulai dengan pembentukan inti dilanjutkan dengan pembentukan cabang yang merupakan group fungsional yang aktif. Sejauh ini dendrimer sudah banyak diterapkan pada bidang farmasi yaitu drug delivery dan non farmasi pada proses i...
Directory of Open Access Journals (Sweden)
Timothy John Pattiasina
2014-07-01
Full Text Available Advanced Encryption Standard (AES dan Knapsack adalah dua algoritma enkripsi simetris dan asimetris yang paling sering digunakan. Penelitian ini menganalisa kedua algoritma AES dan algoritma Knapsack. Prototipe aplikasi enkripsi email ini dirancang dengan menggabungkan karateristik algoritma AES dan Knapsack untuk memecahkan masalah keamanan email. Algoritma AES digunakan untuk mengenkripsi dan deskripsi email berupa teks atau file, sedangkan Algoritma Knapsack di gunakan untuk mengenkripsi kunci AES. Enkripsi hybrid yang diterapkan pada aplikasi bertujuan untuk menambah keamanan informasi dalam sebuah jaringan.
Compressibility, turbulence and high speed flow
Gatski, Thomas B
2009-01-01
This book introduces the reader to the field of compressible turbulence and compressible turbulent flows across a broad speed range through a unique complimentary treatment of both the theoretical foundations and the measurement and analysis tools currently used. For the computation of turbulent compressible flows, current methods of averaging and filtering are presented so that the reader is exposed to a consistent development of applicable equation sets for both the mean or resolved fields as well as the transport equations for the turbulent stress field. For the measurement of turbulent compressible flows, current techniques ranging from hot-wire anemometry to PIV are evaluated and limitations assessed. Characterizing dynamic features of free shear flows, including jets, mixing layers and wakes, and wall-bounded flows, including shock-turbulence and shock boundary-layer interactions, obtained from computations, experiments and simulations are discussed. Key features: * Describes prediction methodologies in...
Sudden viscous dissipation in compressing plasma turbulence
Davidovits, Seth; Fisch, Nathaniel
2015-11-01
Compression of a turbulent plasma or fluid can cause amplification of the turbulent kinetic energy, if the compression is fast compared to the turnover and viscous dissipation times of the turbulent eddies. The consideration of compressing turbulent flows in inviscid fluids has been motivated by the suggestion that amplification of turbulent kinetic energy occurred on experiments at the Weizmann Institute of Science Z-Pinch. We demonstrate a sudden viscous dissipation mechanism whereby this amplified turbulent kinetic energy is rapidly converted into thermal energy, which further increases the temperature, feeding back to further enhance the dissipation. Application of this mechanism in compression experiments may be advantageous, if the plasma can be kept comparatively cold during much of the compression, reducing radiation and conduction losses, until the plasma suddenly becomes hot. This work was supported by DOE through contract 67350-9960 (Prime # DOE DE-NA0001836) and by the DTRA.
Compressibility, turbulence and high speed flow
Gatski, Thomas B
2013-01-01
Compressibility, Turbulence and High Speed Flow introduces the reader to the field of compressible turbulence and compressible turbulent flows across a broad speed range, through a unique complimentary treatment of both the theoretical foundations and the measurement and analysis tools currently used. The book provides the reader with the necessary background and current trends in the theoretical and experimental aspects of compressible turbulent flows and compressible turbulence. Detailed derivations of the pertinent equations describing the motion of such turbulent flows is provided and an extensive discussion of the various approaches used in predicting both free shear and wall bounded flows is presented. Experimental measurement techniques common to the compressible flow regime are introduced with particular emphasis on the unique challenges presented by high speed flows. Both experimental and numerical simulation work is supplied throughout to provide the reader with an overall perspective of current tre...
Turbulence-Free Double-slit Interferometer
Smith, Thomas A.; Shih, Yanhua
2018-02-01
Optical turbulence can be detrimental for optical observations. For instance, atmospheric turbulence may reduce the visibility or completely blur out the interference produced by an interferometer in open air. However, a simple two-photon interference theory based on Einstein's granularity picture of light makes a turbulence-free interferometer possible; i.e., any refraction index, length, or phase variations along the optical paths of the interferometer do not have any effect on its interference. Applying this mechanism, the reported experiment demonstrates a two-photon double-slit interference that is insensitive to atmospheric turbulence. The turbulence-free mechanism and especially the turbulence-free interferometer would be helpful in optical observations that require high sensitivity and stability such as for gravitational-wave detection.
Current-driven turbulence in plasmas
International Nuclear Information System (INIS)
Kluiver, H. de.
1977-10-01
Research on plasma heating in linear and toroidal systems using current-driven turbulence is reviewed. The motivation for this research is presented. Relations between parameters describing the turbulent plasma state and macroscopic observables are given. Several linear and toroidal devices used in current-driven turbulence studies are described, followed by a discussion of special diagnostic methods used. Experimental results on the measurement of electron and ion heating, anomalous plasma conductivity and associated turbulent fluctuation spectra are reviewed. Theories on current-driven turbulence are discussed and compared with experiments. It is demonstrated from the experimental results that current-driven turbulence occurs not only for extreme values of the electric field but also for an experimentally much more accessible and wide range of parameters. This forms a basis for a discussion on possible future applications in fusion-oriented plasma research
Mathematical and physical theory of turbulence
Cannon, John
2006-01-01
Although the current dynamical system approach offers several important insights into the turbulence problem, issues still remain that present challenges to conventional methodologies and concepts. These challenges call for the advancement and application of new physical concepts, mathematical modeling, and analysis techniques. Bringing together experts from physics, applied mathematics, and engineering, Mathematical and Physical Theory of Turbulence discusses recent progress and some of the major unresolved issues in two- and three-dimensional turbulence as well as scalar compressible turbulence. Containing introductory overviews as well as more specialized sections, this book examines a variety of turbulence-related topics. The authors concentrate on theory, experiments, computational, and mathematical aspects of Navier-Stokes turbulence; geophysical flows; modeling; laboratory experiments; and compressible/magnetohydrodynamic effects. The topics discussed in these areas include finite-time singularities a...
Aperture averaging in strong oceanic turbulence
Gökçe, Muhsin Caner; Baykal, Yahya
2018-04-01
Receiver aperture averaging technique is employed in underwater wireless optical communication (UWOC) systems to mitigate the effects of oceanic turbulence, thus to improve the system performance. The irradiance flux variance is a measure of the intensity fluctuations on a lens of the receiver aperture. Using the modified Rytov theory which uses the small-scale and large-scale spatial filters, and our previously presented expression that shows the atmospheric structure constant in terms of oceanic turbulence parameters, we evaluate the irradiance flux variance and the aperture averaging factor of a spherical wave in strong oceanic turbulence. Irradiance flux variance variations are examined versus the oceanic turbulence parameters and the receiver aperture diameter are examined in strong oceanic turbulence. Also, the effect of the receiver aperture diameter on the aperture averaging factor is presented in strong oceanic turbulence.
National Research Council Canada - National Science Library
Lowe, Kevin T; Simpson, Roger L
2006-01-01
An advanced laser-Doppler velocimeter (LDV), deemed the 'comprehensive LDV', is designed to acquire fully-resolved turbulence structural measurements in high Reynolds number two- and three-dimensional turbulent boundary layers...
Energy Technology Data Exchange (ETDEWEB)
Martin, R [Commissariat a l' Energie Atomique, Grenoble (France). Centre d' Etudes Nucleaires
1969-07-01
Void fraction measurements were made in two phase flow boiling systems at high pressures in a uniformly heated, rectangular channel with a high aspect ratio. The local void fraction values were calculated from measurements of the absorption of a thin collimated X-ray beam (2 mm x 0.05 mm). The mean void fraction in a horizontal section results from integration of the local values across the section. At a fixed measuring station the quality and- void fraction were varied by changing the heat flux, flow rate and pressure systematically. Two channels were used differing in length and thickness (150.8 cm x 5.3 cm x 0.2 cm and the significant features of this study are: -1) The void fraction measurements are among the first obtained at such high pressure (80 to 140 kg/cm{sup 2}); -2) In the experimental region under consideration the measurements are systematic and numerous enough to allow accurate interpolations: mass velocity from 50 to 220 g/cm{sup 2}.s, heat flux from 40 to 170 W/cm{sup 2} and calculated steam quality from -0.2 to 0.2; -3) Many tests were performed under local boiling conditions with the mean temperature of the fluid below the saturation temperature; and -4) These results were compared to the predictions of certain models presented in the literature and simple empirical formulae were developed to fit the experimental results. (author) [French] Des mesures de taux de vide ont ete effectuees sur un ecoulement eau-vapeur a haute pression dans un canal vertical, de section rectangulaire tres allongee et chauffe a flux uniforme. Les valeurs du taux de vide local sont obtenues a partir des mesures de l'absorption d'un faisceau de rayons X finement collimate (2 mm x 0,05 mm). La valeur du taux de vide moyen dans une section droite s'en deduit par integration. Cette section droite ou sont realisees les mesures est fixe et, a pression, debit et flux donnes, les variations du titre et du taux de vide sont obtenues par variations de l'enthalpie d'entree. Deux
KORELASI ANTARA ISLAM DAN EKONOMI
Directory of Open Access Journals (Sweden)
Akmal Zainal Abidin
2015-03-01
Full Text Available CORELATION BETWEEN ISLAM AND ECONOMY. This paper aims to identifies about the correlation between economic and Islam. Islam is the perfect religion that governs all things in life, including the economy. This is evident with the concept of well-being which is described in the al-Quran and Sunnah. Basically the goal of every human life is to prosper, although humans make sense of well- being with a different perspective. Most understand economics assume that welfare is the welfare of earthly material. But to make sense of well-being with the term al-Falah, is meaning holistic wellbeing and balance between material and spiritual dimensions. al-Quran and Sunnah have taught that the human being will be achieved if living in balance between material and spiritual. This is because human life does not just stop in the life of this world, but there is still a second life that will be faced by humanity in the hereafter, and well-being will be achieved with the truth is that people can balance the needs of the world and the hereafter, and that is what is taught in Islamic economics. Keywords: Islam, Economy, Prosperity. Tulisan ini bertujuan untuk menjelasakn tentang korelasi antara ekonomi dan Islam. Islam adalah agama yang sempurna yang mengatur segala hal dalam kehidupan ini, termasuk juga ekonomi. Hal ini terbukti dengan konsep kesejahteraan yang dipaparkan dalam al-Quran dan Sunnah. Pada dasarnya tujuan hidup setiap manusia adalah untuk mencapai kesejahteraan, meskipun manusia memaknai kesejahteraan dengan perspektif yang berbeda-beda. Sebagian besar paham ekonomi menganggap bahwa kesejahteraan adalah kesejahteraan material duniawi. Namun Islam memaknai kesejahteraan dengan istilah Falah yang berarti kesejahteraan holistik dan seimbang antara dimensi material dan spiritual. Al-Quran dan Sunnah telah mengajarkan bahwa kesejahteraan akan tercapai jika manusia menjalani hidup secara seimbang antara material dan
Karakteristik Dan Spektrum Manajemen Pendidikan Islam
Jannah, Siti Raudhatul
2013-01-01
Artikel ini mendiskusikan mengenai manajemen pendidikan Islam, karakteristik, dan spektrumnya. Karakteristik manajemen pendidikan Islam harus didasarkan pada al-Qur'an dan Hadits serta pemikiran rasional yang telah diuji validitasnya. Spektrum manajemen pendidikan Islam meliputi lingkup manajemen personalia pendidikan Islam, manajemen peserta didik pendidikan Islam, maanjemen kurikulum pendidikan Islam, manajemen keuangan pendidikan Islam, manajemen sarana dan prasarana pendidikan Islam, mana...
PRODUKSI NANOFIBER DAN APLIKASINYA DALAM PENGOLAHAN AIR
Krisnandika, Vania Elita
2017-01-01
Abstrak Kebutuhan air meningkat seiring meningkatnya jumlah penduduk dan taraf kehidupan masyarakat. Pembangunan yang dilakukan secara terus-menerus dan sangat cepat di Indonesia mengakibatkan penurunan kualitas air permukaan. Teknologi membran merupakan salah satu teknologi pengolahan air yang menghasilkan produk dengan kualitas tinggi. Membran berstruktur nano, khususnya nanofiber, saat ini menjadi perhatian karena menjawab kebutuhan teknologi filtrasi yang efektif dan hemat biaya. Pr...
On the theory of turbulent flame velocity
Bychkov, Vitaly; Akkerman, Vyacheslav; Petchenko, Arkady
2012-01-01
The renormalization ideas of self-similar dynamics of a strongly turbulent flame front are applied to the case of a flame with realistically large thermal expansion of the burning matter. In that case a flame front is corrugated both by external turbulence and the intrinsic flame instability. The analytical formulas for the velocity of flame propagation are obtained. It is demonstrated that the flame instability is of principal importance when the integral turbulent length scale is much large...
DETEKSI DAN MANAJEMEN REFEEDING SYNDROME
Directory of Open Access Journals (Sweden)
Darmadi Darmadi
2012-09-01
Full Text Available AbstrakRefeeding syndrome (RFS dideskripsikan sebagai perubahan biokimiawi, manifestasi klinis dan komplikasi sebagai konsekuensi pemberian nutrisi pada pasien kurang gizi. Refeeding syndrome ini menyebabkan dampak buruk dan kematian. Sindroma ini lebih sering terjadi pada kelompok risiko. Refeeding syndrome merupakan suatu sindroma yang sering tak terdiagnosis oleh karena itu perlu peningkatan pengetahuan dan kesadaran dari tenaga medis untuk mengurangi morbiditas dan mortalitas dari RFS. Karena alasan tersebut ditulis tinjauan pustaka ini yang akan membahas mengenai patofisiologi, faktor risiko, manifestasi klinis, dan manajemennya.Kata kunci : refeeding syndrome, kurang gizi, hipofosfatemia, dukungan nutrisiAbstractRefeeding syndrome (RFS describel as biochemical changes, clinical manifestations, and complications that can occur as a consequence of feeding a malnourished individual. RFS can result in serious harm and death. RFS more commonly occurs in at-risk populations. Increased awareness amongst healthcare professionals is likely to reduce morbidity and mortality. This review examines the pathophysiology, risk factors, clinical manifestations, and management of RFS.Key word : refeeding syndrome, malnourished, hypophosphatemia, nutritional support
Islam, Media, dan Politik : Sebuah Perdebatan dan Kontempelasi Nilai Berdemokrasi
Directory of Open Access Journals (Sweden)
Idil Akbar
2016-10-01
Full Text Available Infact, press or media is one of pilar democracy. Media in democracy is a public sphere to communi-cation and makes relation, and a same time as public arena to gain information. But, media also could not release from streotypes and tendency that usually bring of interest, either the owner or ideology. It is meaning media can not released from perspective distorsion, values bias and take a side. Media also effective to become propaganda instrument for a political interest and an ideology. It is seen like how media in US, for example, stereotype of Islam in discourses contradiction and glob-al interest opposition. Then, Islam dominantly identified as doctrine teaches radicalism, fundamen-talism and terorism. Thus, it is often be justification for US to operate the military mission in the name of democracy. Tak dipungkiri pers atau media menjadi salah satu pilar bagi demokrasi. Media dalam demokrasi adalah sebagai ruang bagi publik berkomunikasi dan berinteraksi, sekaligus sarana publik mem-peroleh informasi tentang banyak hal. Namun, media juga tak bisa dilepaskan dari stereotip dan kecenderungan-kecenderungan, yang biasanya membawa kepentingan, baik pemilik maupun ide-ologi. Media karenanya tak lepas dari distorsi perspektif, bias nilai dan berpihak. Media juga efektif menjadi alat propaganda bagi sebuah kepentingan politik dan ideologi, seperti bagaimana media di negara Amerika, misalnya, menstereotipkan Islam dalam analisis pertentangan wacana dan kepent-ingan global. Sehingga, dominan Islam diidentikkan dengan sematan sebagai ajaran yang mengajarkan radikalisme, fundamentalisme dan terorisme. Karenanya pula seringkali menjadi alasan pembenar bagi Amerika untuk menjalankan misi militer atas nama demokrasi.
Directory of Open Access Journals (Sweden)
Benny Cristovel
2007-12-01
Full Text Available Menjadi seorang musisi tidak sekedar bermain musik atau menyanyi saja. Ada jenjang-jenjang yang akan dilewatidalam dunia musik, yang pada akhirnya setiap musisi dihadapkan kepada tanggung jawab dalam dunia tersebut. Di jaman ini, jika jenjang seorang musisi sudah tahap profesional, maka musik dan bisnis merupakan hal yang tidak terpisahkan. Jadi tidak heran jika ada banyak orang yang memimpikan untuk berkarier dalam bidang musik, bahkan telah men1adicita-cita sejak kecil.Jadi penting bagi musisi gerejawi benar-benar "mengkotakkan dirinya" terhadap persepsi yang dianut oleh musisi sekuler, bukan mencampurkannya. Hal ini sangat esensial, karena musisi gerejawi bukan melayani manusia melainkan oleh anugerah Tuhan dipercayakan pekerjaan ini. Dengan demikian pelayanan sebagai musisi gerejawi tidak tercemar oleh persepsi dari dunia musik sekuler. Selain itu musisi gerejawi dapat merefleksikan Tuhan yang disembahnya kepada dunia sekuler, karena tujuan dari semua yang dilakukannya adalah untuk kemuliaan nama Tuhan.
Modeling turbulence structure. Chemical kinetics interaction in turbulent reactive flows
Energy Technology Data Exchange (ETDEWEB)
Magnussen, B F [The Norwegian Univ. of Science and Technology, Trondheim (Norway)
1998-12-31
The challenge of the mathematical modelling is to transfer basic physical knowledge into a mathematical formulation such that this knowledge can be utilized in computational simulation of practical problems. The combustion phenomena can be subdivided into a large set of interconnected phenomena like flow, turbulence, thermodynamics, chemical kinetics, radiation, extinction, ignition etc. Combustion in one application differs from combustion in another area by the relative importance of the various phenomena. The difference in fuel, geometry and operational conditions often causes the differences. The computer offers the opportunity to treat the individual phenomena and their interactions by models with wide operational domains. The relative magnitude of the various phenomena therefore becomes the consequence of operational conditions and geometry and need not to be specified on the basis of experience for the given problem. In mathematical modelling of turbulent combustion, one of the big challenges is how to treat the interaction between the chemical reactions and the fluid flow i.e. the turbulence. Different scientists adhere to different concepts like the laminar flamelet approach, the pdf approach of the Eddy Dissipation Concept. Each of these approaches offers different opportunities and problems. All these models are based on a sound physical basis, however none of these have general validity in taking into consideration all detail of the physical chemical interaction. The merits of the models can only be judged by their ability to reproduce physical reality and consequences of operational and geometric conditions in a combustion system. The presentation demonstrates and discusses the development of a coherent combustion technology for energy conversion and safety based on the Eddy Dissipation Concept by Magnussen. (author) 30 refs.
Modeling turbulence structure. Chemical kinetics interaction in turbulent reactive flows
Energy Technology Data Exchange (ETDEWEB)
Magnussen, B.F. [The Norwegian Univ. of Science and Technology, Trondheim (Norway)
1997-12-31
The challenge of the mathematical modelling is to transfer basic physical knowledge into a mathematical formulation such that this knowledge can be utilized in computational simulation of practical problems. The combustion phenomena can be subdivided into a large set of interconnected phenomena like flow, turbulence, thermodynamics, chemical kinetics, radiation, extinction, ignition etc. Combustion in one application differs from combustion in another area by the relative importance of the various phenomena. The difference in fuel, geometry and operational conditions often causes the differences. The computer offers the opportunity to treat the individual phenomena and their interactions by models with wide operational domains. The relative magnitude of the various phenomena therefore becomes the consequence of operational conditions and geometry and need not to be specified on the basis of experience for the given problem. In mathematical modelling of turbulent combustion, one of the big challenges is how to treat the interaction between the chemical reactions and the fluid flow i.e. the turbulence. Different scientists adhere to different concepts like the laminar flamelet approach, the pdf approach of the Eddy Dissipation Concept. Each of these approaches offers different opportunities and problems. All these models are based on a sound physical basis, however none of these have general validity in taking into consideration all detail of the physical chemical interaction. The merits of the models can only be judged by their ability to reproduce physical reality and consequences of operational and geometric conditions in a combustion system. The presentation demonstrates and discusses the development of a coherent combustion technology for energy conversion and safety based on the Eddy Dissipation Concept by Magnussen. (author) 30 refs.
Measurement of beam driven hydrodynamic turbulence
International Nuclear Information System (INIS)
Norem, J.; Black, E.; Bandura, L.; Errede, D.; Cummings, M. A. C.
2003-01-01
Cooling intense muon beams in liquid hydrogen absorbers introduces kW of heating to the cold fluid, which will drive turbulent flow. The amount of turbulence may be sufficient to help cool the liquid, but calculations are difficult. We have used a 20 MeV electron beam in a water tank to look at the scale of the beam driven convection and turbulence. The density and flow measurements are made with schlieren and Ronchi systems. We describe the optical systems and the turbulence measured. These data are being used to calibrate hydrodynamic calculations of convection driven and forced flow cooling in muon cooling absorbers
Predator-prey encounters in turbulent waters
DEFF Research Database (Denmark)
Mann, J.; Ott, Søren; Pécseli, H.L.
2002-01-01
With reference to studies of predator-prey encounters in turbulent waters, we demonstrate the feasibility of an experimental method for investigations of particle fluxes to an absorbing surface in turbulent flows. A laboratory experiment is carried out, where an approximately homogeneous and isot......With reference to studies of predator-prey encounters in turbulent waters, we demonstrate the feasibility of an experimental method for investigations of particle fluxes to an absorbing surface in turbulent flows. A laboratory experiment is carried out, where an approximately homogeneous...
De-trending of turbulence measurements
DEFF Research Database (Denmark)
Hansen, Kurt Schaldemose; Larsen, Gunner Chr.
2006-01-01
contribution to the wind speed turbulence intensity for a number of representative locations. A linear de-trending process has been implemented during indexing of the time-series. The observed de-trended turbulence intensities are reduced 3 – 15 % compared to the raw turbulence intensity. This reduction...... depends primarily on site characteristics and local mean wind speed variations. Reduced turbulence intensity will result in lower design fatigue loads. This aspect of de-trending is discussed by use of a simple heuristic load model. Finally an empirical model for de-trending wind resource data...
Visible imaging of edge turbulence in NSTX
International Nuclear Information System (INIS)
Zweben, S.; Maqueda, R.; Hill, K.; Johnson, D.
2000-01-01
Edge plasma turbulence in tokamaks and stellarators is believed to cause the radical heat and particle flux across the separatrix and into the scrape-off-layers of these devices. This paper describes initial measurements of 2-D space-time structure of the edge density turbulence made using a visible imaging diagnostic in the National Spherical Torus Experiment (NSTX). The structure of the edge turbulence is most clearly visible using a method of gas puff imaging to locally illuminate the edge density turbulence
Nonexistence of two forms of turbulent bremsstrahlung
International Nuclear Information System (INIS)
Kuijpers, J.; Melrose, D.B.
1985-01-01
It is shown that the forms of turbulent bremsstrahlung proposed by Tsytovich, Stenflo, and Wilhelmsson and by Nambu do not exist. The proposed mechanisms involve upconversion of ion sound turbulence into Langmuir turbulence, with the ion sound waves being emitted and absorbed resonantly and the Langmuir waves being emitted and absorbed nonresonantly. It is pointed out that a symmetry implicit in a standard QED treatment implies that there is another contribution to turbulent bremsstrahlung in addition to that calculated by Tsytovich, Stenflo, and Wilhelmsson and that the two contributions cancel exactly, leading to the null result. (Our arguments on this point have proved controversial.) Nambu made an approximation inconsistently, and when this approximation is not made, two terms in his analytic treatment cancel exactly. We argue that turbulent bremsstrahlung is related to a radiative correction in which the resonant emission of ion sound turbulence is modified by the nonresonant emission and absorption of Langmuir waves. Physically we interpret the nonexistence of turbulent bremsstrahlung as being due to each emission of a Langmuir quantum being associated with an absorption of an identical Langmuir quantum so that the Langmuir turbulence is unchanged. Proposed astrophysical applications of turbulent bremsstrahlung need to be reconsidered
Oceanic turbulence - Big bangs or continuous creation?
Caldwell, D. R.
1983-01-01
A hypothesis concerning the turbulence characteristics of 'microstructure' patches in the ocean is proposed in which a turbulence field is driven at the same time and scale at which it is observed. The driving energy is converted into turbulence kinetic energy in such a way that the observed overturning thickness scale is linearly related to the length scale. This hypothesis is contrasted with that of Gibson (1982), in which the 'patches' are produced by rare, powerful turbulence generators that have 'fossilized' prior to their observation. Careful attention is given to the sampling process and its assumptions.
Anisotropy of turbulence in wind turbine wakes
Energy Technology Data Exchange (ETDEWEB)
Gomez-Elvira, Rafael [Comision Nacional de Energia (Spain); Crespo, Antonio; Migoya, Emilio; Manuel, Fernando [Departamento de Ingenieria Energetica y Fluidomecanica, Escuela Tecnica Superior de Ingenieros Industriales, Universidad Politecnica de Madrid, Jose Gutierrez Abascal, 2. 28006 Madrid (Spain); Hernandez, Julio [Departamento de Mecanica, ETSII, Universidad Nacional de Educacion a Distancia, Ciudad Universitaria, 28040 Madrid (Spain)
2005-10-01
This work is mainly dedicated to the study of non-isotropic characteristics of turbulence in wind turbine wakes, specifically the shear layer of the near wake. A calculation method based on an explicit algebraic model for the components of the turbulent stress tensor is proposed, and the results are found to be in acceptable agreement with experimental results. Analytical expressions for the estimation of an upper limit of the global turbulence kinetic energy, k, and the individual contributions of each diagonal term in the turbulent stress tensor are proposed. Their predictions are compared with experimental results.
Visible imaging of edge turbulence in NSTX
International Nuclear Information System (INIS)
S. Zweben; R. Maqueda; K. Hill; D. Johnson; S. Kaye; H. Kugel; F. Levinton; R. Maingi; L. Roquemore; S. Sabbagh; G. Wurden
2000-01-01
Edge plasma turbulence in tokamaks and stellarators is believed to cause the radial heat and particle flux across the separatrix and into the scrape-off-layers of these devices. This paper describes initial measurements of 2-D space-time structure of the edge density turbulence made using a visible imaging diagnostic in the National Spherical Torus Experiment (NSTX). The structure of the edge turbulence is most clearly visible using a method of ''gas puff imaging'' to locally illuminate the edge density turbulence
Energy Technology Data Exchange (ETDEWEB)
Morel, Ch
1997-10-31
The aim of this thesis is the 3-D modeling and numerical simulation of liquid/gas (water/vapor or water/air) two-phase flows in cooling circuits of nuclear power plants during normal and accidental situations. The development of a multidimensional dual-fluid model encounters two problems: the statistical effects of turbulence and the interface mass, momentum and energy transfers. The models developed in this study were introduced in the 3-D module of the CATHARE code developed by the CEA and the results were compared to experimental results available in the literature. The first chapter describes the equations of the local dual-fluid model for the 3-D description of two-phase flows. Closing relations adapted to dispersed flows with isothermal bubbles and without phase transformation are proposed and focus on the momentum transfer at the interfaces. The theoretical study of turbulence in the liquid phase of a bubble flow is modelled in chapter 2. Chapter 3 deals with the voluminal interface area used in the interface mass, momentum and energy transfers, and chapters 4 and 5 concern the application of the developed models to concrete situations. Chapter 4 describes in details the 3-D module of the CATHARE code while chapter 5 gives a comparison of numerical results obtained using the CATHARE code with other experimental results obtained at EdF. (J.S.) 109 refs.
Statistical Mechanics of Turbulent Flows
International Nuclear Information System (INIS)
Cambon, C
2004-01-01
This is a handbook for a computational approach to reacting flows, including background material on statistical mechanics. In this sense, the title is somewhat misleading with respect to other books dedicated to the statistical theory of turbulence (e.g. Monin and Yaglom). In the present book, emphasis is placed on modelling (engineering closures) for computational fluid dynamics. The probabilistic (pdf) approach is applied to the local scalar field, motivated first by the nonlinearity of chemical source terms which appear in the transport equations of reacting species. The probabilistic and stochastic approaches are also used for the velocity field and particle position; nevertheless they are essentially limited to Lagrangian models for a local vector, with only single-point statistics, as for the scalar. Accordingly, conventional techniques, such as single-point closures for RANS (Reynolds-averaged Navier-Stokes) and subgrid-scale models for LES (large-eddy simulations), are described and in some cases reformulated using underlying Langevin models and filtered pdfs. Even if the theoretical approach to turbulence is not discussed in general, the essentials of probabilistic and stochastic-processes methods are described, with a useful reminder concerning statistics at the molecular level. The book comprises 7 chapters. Chapter 1 briefly states the goals and contents, with a very clear synoptic scheme on page 2. Chapter 2 presents definitions and examples of pdfs and related statistical moments. Chapter 3 deals with stochastic processes, pdf transport equations, from Kramer-Moyal to Fokker-Planck (for Markov processes), and moments equations. Stochastic differential equations are introduced and their relationship to pdfs described. This chapter ends with a discussion of stochastic modelling. The equations of fluid mechanics and thermodynamics are addressed in chapter 4. Classical conservation equations (mass, velocity, internal energy) are derived from their
Directory of Open Access Journals (Sweden)
Atik Abidah
2010-12-01
Full Text Available Abstraks: Keberadaan lembaga zakat di Indonesia yang diakui oleh perundang-undangan ada dua, yaitu Badan Amil Zakat (BAZ dan Lembaga Amil Zakat (LAZ. BAZ adalah lembaga zakat yang dikelola oleh pemerintah, sedangkan LAZ adalah lembaga yang dikelola oleh masyarakat. Artikel ini merupakan merupakan hasil penelitian lapangan dengan menggunakan pendekatan kualitatif. Data digali langsung dari BAZ Kota Madiun dan LAZ dalam hal ini ada 2 lembaga, yaitu Lembaga Manajemen Infaq (LMI dan Baitul Maal Hidayatullah (BMH. Hasil penelitian BAZ lebih efektif dibanding LAZ, karena BAZ di bawah naungan Pemerintah Kota Madiun dan didukung dengan kebijakan dalam menjalankan progam kerjanya. Sedangkan pada LAZ (LMI dan BMH karena sifatnya mandiri, maka segala sesuatunya akan efektif jika mereka bekerja keras, dan itulah yang selama ini dilakukan oleh LMI dan BMH, sehingga sampai saat ini mereka masih eksis.
INTERAKSI DAN HARMONI UMAT BERAGAMA
Directory of Open Access Journals (Sweden)
Joko Tri Haryanto
2012-05-01
Masyarakat Singkawang adalah masyarakat yang terdiri atas berbagai kelompok suku bangsa dan agama. Secara historis, masyarakat Singkawang mampu mempertahankan harmoni antar agama. Model interaksi sosial yang bersifat asosiatif tampaknya potensial untuk mendukung harmoni di dalam masyarakat. Berdasarkan paradigma fungsional-struktural, masyarakat diasumsikan sebagai sistem organik yang memiliki huungan antar bagiannya untuk mempertahankan masyarakat. Interaksi sosial di dalam masyarakat Singkawang dikembangkan melalui interaksi di dalam lingkup keluarga, lingkungan sekitar, aktifitas ekonomi, para pimpinan agama, dan hubungan di dalam lingkup budaya dan tradisi. Meskipun demikian, hubungan antar unsur masyarakat masih kosmopolitan, yang di dalamnya anggota masyarakat kurang aktif dalam mengembangkan harmoni masyarakat.
Gyrokinetic simulation of microtearing turbulence
International Nuclear Information System (INIS)
Doerk, Hauke
2013-01-01
In modern fusion experiments, plasma turbulence is responsible for the radial heat transport and thus determines the plasma confinement within the magnetic field of tokamak devices. Deeper theoretical understanding is needed to explain today's and future fusion experiments. The goal of fusion research is to establish nuclear fusion as a safe and sustainable energy source. In future fusion power plants, and also in large fusion experiments like the presently constructed ITER, plasma heating predominantly affects the electron species. The reason is of fundamental nature: the collisional cross section of fast ions that are produced by the heating systems is larger for thermal electrons than for thermal ions. It is thus essential to correctly predict electron thermal transport, but the overall picture still continues to evolve. Besides microinstabilities on the electron gyroradius scales, also a stochastized magnetic field can contribute to enhanced electron transport. Already since the 1970's, the so-called microtearing instability is discussed as a source of stochastic fields. This microinstability deserves its name for breaking up the magnetic field structure by forming small-scale magnetic islands. The linear microtearing instability and its nonlinear, turbulent behavior is investigated in this thesis by means of numerical simulations with the gyrokinetic turbulence code Gene. The underlying gyrokinetic equations are not only appropriate to predict turbulent transport, but also describe neoclassical transport that is drift-kinetic in nature. Besides revealing interesting physics on long time scales, solving the neoclassical equation serves as an excellent test for the numerical implementation of the collision operator in Gene. Focusing on the local limit, it is found that a modification of this implementation that considers certain symmetries is necessary to obtain a satisfactory agreement with the well-established drift-kinetic neoclassical code Neo. Also the
ETIKA BISNIS AL-GHAZALI DAN ADAM SMITH DALAM PERSPEKTIF ILMU BISNIS DAN EKONOMI
Directory of Open Access Journals (Sweden)
AM. M. Hafidz MS.
2013-05-01
Full Text Available Penelitian ini adalah untuk mengeksplorasi: (1 pembangunan etika bisnis yang telah dirumuskan oleh al-Ghazali dan Adam Smith, (2 persamaan dan perbedaan antara dua etika bisnis pria, dan (3 relevansi bisnis mereka etika bisnis modern dunia dan ekonomi. Bisnis etika dibangun oleh al-Ghazali dan Smith di dataran praksis tidak jauh berbeda. Etika bisnis konstruksi dibangun oleh al-Ghazali didasarkan pada prinsip-prinsip seperti orientasi itikad baik tentang dunia dan akhirat, kejujuran, kepentingan pribadi dan social keseimbangan, dan perilaku / perbuatan yang tepat. Di sisi lain, etika bisnis konstruksi dibangun oleh Smith, berdasarkan keadilan, altruisme, keadilan dan liberal (kebebasan ekonomi. Baik etika bisnis yang diperkenalkan oleh kedua sangat relevan untuk menjadi digunakan sebagai bahan pokok acuan dalam etika bisnis modern.
Pengembangan Sistem Otomatisasi AC dan Lampu Menggunakan Fuzzy dan Raspberry Pi
Directory of Open Access Journals (Sweden)
Rudy Ariyanto
2017-11-01
Full Text Available Otomatisasi AC dan lampu dilakukan untuk menghemat energi yang digunakan pada kehidupan sehari-hari. Dalam pengembangan otomatisasi AC dan lampu perlu menerapkan sebuah perangkat yang memiliki fungsi maksimal dengan harga yang minimal. Raspberry Pi merupakan perangkat atau modul dengan harga rendah yang mampu melakukan komunikasi wireless tanpa bantuan modul lain. Dalam pengembangan otomatisasi AC dan lampu juga diperlukan sebuah metode yang mampu melakukan kontrol terhadap nyala AC dan lampu. Penerapan metode fuzzy dapat dilakukan untuk menghimpun informasi keadaan ruang yang didapat dari sensor untuk menentukan nyala AC dan lampu secara otomatis. Oleh sebab itu pada penelitian ini mengusulkan pengembangan otomatisasi AC dan lampu menggunakan Raspberry Pi dan Fuzzy. Otomatisasi AC dan lampu menggunakan Raspberry Pi yang menerapkan metode Fuzzy dapat menghemat energi hingga 59,87% dalam hal lama waktu nyala AC dan 57,47% untuk lumenasi lampu
Turbulent transport of energetic ions
International Nuclear Information System (INIS)
Dannert, Tilman; Hauff, Thilo; Jenko, Frank; Guenter, Sibylle
2006-01-01
Approaching ITER operation, the issue of anomalous transport of fast particles becomes more and more important. This is partly because the ITER heating and current drive system relies heavily on neutral beam injection. Moreover burning plasmas are heated by fast fusion α particles.Fusion α particles are characterised by a fixed energy and an isotropic velocity distribution. Therefore they have gyroradii one magnitude larger than the thermal ions. The dependency of the particle diffusion of α test particles on the Kubo number K = VExBτc/λc (VExB mean E x B velocity, τc, λc correlation time and length of the turbulent potential) is presented. For different turbulent regimes, different dependency of the diffusion on the gyroradius is found. For large Kubo numbers, the transport is found to remain constant for gyroradii up to the correlation length of the potential, whereas it is drastically reduced in the small Kubo number regime.In the second part, a model for beam ions injected along the equilibrium magnetic field is described. The beam ions are treated gyrokinetically in a self-consistent way with the equilibrium distribution function taken as a shifted Maxwellian. The implications of such a model for the Vlasov equation, the field equations, and the calculation of moments and fluxes are discussed. Linear and nonlinear results, obtained with the gyrokinetic flux tube code GENE show the existence of a new instability driven by fast beam ions. The instability has a maximum growth rate at perpendicular wave numbers of kyρs ∼ 0.15 and depends mainly on the beam velocity and the density gradient of the beam ions. This instability leads to a replacement of bulk ion particle transport by fast ion particle transport, connected to a strongly enhanced heat flux. In the presence of this instability, the turbulent particle and heat transport is dominated by fast ions
Sistem Informasi Penjualan dan Pemesanan Layanan Berbasis Web dan SMS Gateway di Petshop "PetZone"
Directory of Open Access Journals (Sweden)
Siska Fadhilah Wati
2013-09-01
Full Text Available Dewasa ini teknologi informasi sangat membantu dalam dunia bisnis. Kemudahan yang ditawarkan akan menjaring lebih banyak konsumen. Namun, perusahan tingkat menengah seperti PetZone saat ini masih jarang yang menawarkan kemudahan berbelanja atau pemesanan layanan secara online. Oleh karena itu diperlukan sebuah sistem berbasis web di perusahaan PetZone yang dapat memudahkan pemilik dan karyawan dalam apenjualan, pelayanan, dan pemasaran, serta memudahkan pelanggan dalam jual-beli barang dan jasa. Atas dasar masalah tersebut dibangun Sistem Informasi Penjualan dan Pemesanan Layanan Berbasis Web dan SMS Gateway untuk menunjang proses bisnis yang ada. Sistem informasi dibangun menggunakan bahasa pemrograman PHP framework Codeigniter, javascript untuk tampilan yang dinamis, dan database MySQL. Proses pembuatan dan pengembangan Sistem Informasi Penjualan ini menggunakan metode air terjun. Metode air terjun meliputi kebutuhan pengguna, analisis, rancangan, implementasi dan pengujian. Pemodelan Sistem Informasi yang dibangun menggunakan metode berorientasi objek UML (Unified Modeling Language yang terdiri dari Use case diagram, Class diagram dan Sequence diagram. Hasil pengujian Sistem Informasi Penjualan dan Pemesanan Layanan Berbasis Web dan SMS Gateway menunjukkan bahwa semua fitur yang terdapat baik dalam sistem informasi maupun SMS gateway dapat bekerja dengan baikdengan ratusan sample data, dan server SMS gateway dapat memproses lebih dari satu SMS secara bersamaan. Dalam perkembangan ke depannya nanti, Sistem Informasi Penjualan dan Pemesanan Layanan Berbasis Web dan SMS Gateway masih dapat dikembangkan lagi dengan menambah fitur-fitur pada SMS gateway sehingga lebih memudahkan konsumen.
Gyrokinetic simulations of ETG Turbulence*
Nevins, William
2005-10-01
Recent gyrokinetic simulations of electron temperature gradient (ETG) turbulence [1,2] produced different results despite similar plasma parameters. Ref.[1] differs from Ref.[2] in that [1] eliminates magnetically trapped particles ( r/R=0 ), while [2] retains magnetically trapped particles ( r/R 0.18 ). Differences between [1] and [2] have been attributed to insufficient phase-space resolution and novel physics associated with toroidicity and/or global simulations[2]. We have reproduced the results reported in [2] using a flux-tube, particle-in-cell (PIC) code, PG3EQ[3], thereby eliminating global effects as the cause of the discrepancy. We observe late-time decay of ETG turbulence and the steady-state heat transport in agreement with [2], and show this results from discrete particle noise. Discrete particle noise is a numerical artifact, so both the PG3EQ simulations reported here and those reported in Ref.[2] have little to say about steady-state ETG turbulence and the associated anomalous electron heat transport. Our attempts to benchmark PIC and continuum[4] codes at the plasma parameters used in Ref.[2] produced very large, intermittent transport. We will present an alternate benchmark point for ETG turbulence, where several codes reproduce the same transport levels. Parameter scans about this new benchmark point will be used to investigate the parameter dependence of ETG transport and to elucidate saturation mechanisms proposed in Refs.[1,2] and elsewhere[5-7].*In collaboration with A. Dimits (LLNL), J. Candy, C. Estrada-Mila (GA), W. Dorland (U of MD), F. Jenko, T. Dannert (Max-Planck Institut), and G. Hammett (PPPL). Work at LLNL performed for US DOE under Contract W7405-ENG-48.[1] F. Jenko and W. Dorland, PRL 89, 225001 (2002).[2] Z. Lin et al, 2004 Sherwood Mtg.; 2004 TTF Mtg.; Fusion Energy 2004 (IAEA, Vienna, 2005); Bull. Am. Phys. Soc. (November, 2004); 2005 TTF Mtg.; 2005 Sherwood Mtg.; Z. Lin, et al, Phys. Plasmas 12, 056125 (2005). [3] A.M. Dimits
Electromagnetic weak turbulence theory revisited
Energy Technology Data Exchange (ETDEWEB)
Yoon, P. H. [IPST, University of Maryland, College Park, Maryland 20742 (United States); Ziebell, L. F. [Instituto de Fisica, UFRGS, Porto Alegre, RS (Brazil); Gaelzer, R.; Pavan, J. [Instituto de Fisica e Matematica, UFPel, Pelotas, RS (Brazil)
2012-10-15
The statistical mechanical reformulation of weak turbulence theory for unmagnetized plasmas including fully electromagnetic effects was carried out by Yoon [Phys. Plasmas 13, 022302 (2006)]. However, the wave kinetic equation for the transverse wave ignores the nonlinear three-wave interaction that involves two transverse waves and a Langmuir wave, the incoherent analogue of the so-called Raman scattering process, which may account for the third and higher-harmonic plasma emissions. The present paper extends the previous formalism by including such a term.
Prediction of free turbulent mixing using a turbulent kinetic energy method
Harsha, P. T.
1973-01-01
Free turbulent mixing of two-dimensional and axisymmetric one- and two-stream flows is analyzed by a relatively simple turbulent kinetic energy method. This method incorporates a linear relationship between the turbulent shear and the turbulent kinetic energy and an algebraic relationship for the length scale appearing in the turbulent kinetic energy equation. Good results are obtained for a wide variety of flows. The technique is shown to be especially applicable to flows with heat and mass transfer, for which nonunity Prandtl and Schmidt numbers may be assumed.
International Nuclear Information System (INIS)
Eilek, J.A.
1989-01-01
Recent theories of magnetohydrodynamic turbulence are used to construct microphysical turbulence models, with emphasis on models of anisotropic turbulence. These models have been applied to the determination of the emergent polarization from a resolved uniform source. It is found that depolarization alone is not a unique measure of the turbulence, and that the turblence will also affect the total-intensity distributions. Fluctuations in the intensity image can thus be employed to measure turbulence strength. In the second part, it is demonstrated that a power-spectral analysis of the total and polarized intensity images can be used to obtain the power spectra of the synchrotron emission. 81 refs
Efikasi Kendiri: Perbandingan Antara Islam dan Barat
Directory of Open Access Journals (Sweden)
Noornajihan, J.
2014-12-01
Full Text Available Terminologi efikasi kendiri (EK merupakan terminologi yang diperkenalkan dalam ilmu psikologi sekitar tahun 70-an. Namun, istilah ini masih kurang difahami oleh kebanyakan individu terutama mereka yang bukan berlatar belakangkan bidang psikologi. Oleh itu, satu keperluan hasil penulisan ini diketengahkan, memandangkan konsep ini penting dalam diri setiap individu bagi memacu kecemerlangan diri. Justeru, kertas kerja ini akan mengupas serba ringkas mengenai konsep EK dari perspektif Islam dan Barat, dengan melihat kepada beberapa titik persamaan dan perbezaan antara kedua-dua pandangan. Islam dan Barat bersetuju bahawa individu yang memiliki EK yang tinggi merupakan individu yang berfikiran positif, berani mengambil risiko dan tidak mudah berputus. Namun pandangan Islam terhadap konsep ini lebih luas, kerana Islam mengaitkan konsep ini dengan konsep tauhid uluhiyyah dan konsep manusia sebagai ahsan al-taqwim. Oleh demikian, EK dari perspektif Islam lebih bersifat kekal dan umum, di samping individu yang berefikasi tinggi menurut Islam ialah individu yang memiliki sifat sabar, syukur, redha dan redha.
PERANCANGAN DAN PENGEMBANGAN PROTOTYPE SISTEM PARKIR
Directory of Open Access Journals (Sweden)
Indah Ayu Septriyaningrum
2016-10-01
Abstrak Sistem parkir manual pada pelayanan parkir mall memerlukan pengelolaan dan pengembangan sistem yang lebih rumit dan jauh dari kata efisien. Informasi yang didapatkan pengelola parkir terkait kondisi parkir di lapangan setiap harinya masih kurang. Tujuan dari penelitian ini adalah merancang dan mengembangkan prototype sistem parkir. Metode pengembangan dan perancangan sistem pada penelitian ini adalah metode Waterfall. Hasil yang didapatkan adalah sistem ini dapat mendeteksi keberadaan mobil pada slot parkir yang tersedia dengan bantuan Intel Galileo Board Gen 2 sebagai kontroler, sensor LDR (Light Dependent Resistor dan sensor ultrasonik (PING sebagai alat bantu pendeteksi keberadaan mobil. Sistem dapat menampilkan aktifitas parkir pada aplikasi web seperti kondisi lahan parkir kosong, lahan terisi, waktu masuk, waktu keluar, lama parkir dan kapasitas parkir yang tersedia serta grafik pemakaian lahan parkir. Dapat disimpulkan bahwa perancangan dan pengembangan sistem berhasil diimplementasikan. Kata Kunci : Sistem parkir, waterfall, Intel Galileo Board Gen 2,sensor LDR (Light Dependent Resistor, sensor ultrasonik
Premixed Turbulent Flames and Spectral Approach Flammes turbulentes de prémélange Approche spectrale
Directory of Open Access Journals (Sweden)
Mathieu J.
2006-11-01
the behaviour of flames developing in a turbulent field can be easily understood. This approach could also open the way to new modeling methods. Indépendamment de l'intérêt scientifique que présentent les flammes de prémélange, les applications industrielles sont nombreuses. Dans cet article la flamme est supposée se développer dans un milieu turbulent ce qui oblige à une comparaison précise des échelles associées à la flamme et de celles associées à la turbulence. Cette confrontation n'est pas nouvelle. Cet article montre que ces comparaisons peuvent s'enrichir si l'on accepte une description spectrale de la turbulence faisant largement référence à de nombreux travaux antérieurs. La notion de champ extérieur turbulent agissant sur la flamme et celle de champ turbulent envahissant la flamme apparaît clairement lors d'une représentation spectrale. On voit également comment l'on passe continûment d'une situation avec front de réaction à une autre où la réaction s'effectue en volume tandis que se développe une compétition entre une réaction chimique qui tend à générer une ségrégation des espèces et une diffusion turbulente qui provoque le mélange. Dans les moteurs à combustion avec prémélange il existe un grand nombre de situations possibles dépendant de la vitesse de rotation. On conçoit aisément qu'une modélisation unique valable quel que soit le régime ne soit guère envisageable. Il y a là aussi matière à réflexions. Autre sujet au demeurant ouvert est celui de la modélisation. Dans le présent article certaines structures turbulentes sont étudiées. Resterait à savoir si une architecture spécifique de moteur n'est pas capable de générer des structures turbulentes particulières. Jusqu'ici le rôle de tourbillons privilégiés avait été introduit par la voie de séquences de tourbillons. L'approche spectrale permet de considérer un ensemble continu de structures analogues intervenant dans un phénomène de
International Nuclear Information System (INIS)
Jeong, Hae Yong; Ha, Kwi Seok; Kwon, Young Min; Chang, Won Pyo; Lee, Yong Bum
2006-01-01
The existing experimental data related to the turbulent mixing factor in rod arrays is examined and a new definition of the turbulent mixing factor is introduced to take into account the turbulent mixing of fluids with various Prandtl numbers. The new definition of the mixing factor is based on the eddy diffusivity of energy. With this definition of the mixing factor, it was found that the geometrical parameter, δ ij /D h , correlates the turbulent mixing data better than S/d, which has been used frequently in existing correlations. Based on the experimental data for a highly turbulent condition in square rod arrays, a correlation describing turbulent mixing dependent on the parameter δ ij /D h has been developed. The correlation is insensitive to the Re number and it takes into account the effect of the turbulent Prandtl number. The proposed correlation predicts a reasonable mixing even at a lower S/d ratio
Turbulence models development and engineering applications
International Nuclear Information System (INIS)
Groetzbach, G.; Ammann, T.; Dorr, B.; Hiltner, I.; Hofmann, S.; Kampczyk, M.; Kimhi, Y.; Seiter, C.; Woerner, M.; Alef, M.; Hennemuth, A.
1995-01-01
The FLUTAN code is used for analyzing the decay heat removal in new reactor concepts. The turbulence models applied in FLUTAN are improved by the development of the TURBIT code. TURBIT serves for a numerical simulation of turbulent channel flow. (orig.)
Resistive drift wave turbulence and transport
International Nuclear Information System (INIS)
Wakatani, M.
1986-01-01
Our efforts for studying the properties of resistive drift wave turbulence by using model mode-coupling equations are shown. It may be related to the edge turbulence and the associated anomalous transport in tokamaks or in stellarator/heliotron. (author)
The roles of turbulence on plasma heating
International Nuclear Information System (INIS)
Kawamura, Takaichi; Kawabe, Takaya.
1976-06-01
In this paper, the characteristic features of the turbulent heating are reviewed, which is considered to be one of the strong candidates of the further heating method in fusion reactor systems, referring to the works in the Institute of Plasma Physics, Nagoya University. The roles of turbulence in plasma heating including toroidal plasma heating are discussed from several points of view. The relation between the heating rate of plasma particles and the thermalization (randomization) frequency is theoretically investigated and the role of plasma turbulence in the fast thermalization is shown. The experimental results on fluctuation and heating of electrons and ions in turbulently heated plasmas are presented. The influence of turbulence, which is responsible for the particle heating, on the diffusion across the confinement magnetic field is considered for the application in the toroidal plasmas. It is pointed out that the turbulent fields in the fast turbulent heating give only a minor effect to the loss of particles across the magnetic field. It can be said that the enhanced fluctuation in turbulent plasma gives its field energy to the plasma particles while it can play the role of the fast thermalization of the ordered motion of particles that is produced in the plasma by some acceleration process. (Kato, T.)
Flames in fractal grid generated turbulence
Energy Technology Data Exchange (ETDEWEB)
Goh, K H H; Hampp, F; Lindstedt, R P [Department of Mechanical Engineering, Imperial College, London SW7 2AZ (United Kingdom); Geipel, P, E-mail: p.lindstedt@imperial.ac.uk [Siemens Industrial Turbomachinery AB, SE-612 83 Finspong (Sweden)
2013-12-15
Twin premixed turbulent opposed jet flames were stabilized for lean mixtures of air with methane and propane in fractal grid generated turbulence. A density segregation method was applied alongside particle image velocimetry to obtain velocity and scalar statistics. It is shown that the current fractal grids increase the turbulence levels by around a factor of 2. Proper orthogonal decomposition (POD) was applied to show that the fractal grids produce slightly larger turbulent structures that decay at a slower rate as compared to conventional perforated plates. Conditional POD (CPOD) was also implemented using the density segregation technique and the results show that CPOD is essential to segregate the relative structures and turbulent kinetic energy distributions in each stream. The Kolmogorov length scales were also estimated providing values {approx}0.1 and {approx}0.5 mm in the reactants and products, respectively. Resolved profiles of flame surface density indicate that a thin flame assumption leading to bimodal statistics is not perfectly valid under the current conditions and it is expected that the data obtained will be of significant value to the development of computational methods that can provide information on the conditional structure of turbulence. It is concluded that the increase in the turbulent Reynolds number is without any negative impact on other parameters and that fractal grids provide a route towards removing the classical problem of a relatively low ratio of turbulent to bulk strain associated with the opposed jet configuration. (paper)
Statistical properties of transport in plasma turbulence
DEFF Research Database (Denmark)
Naulin, V.; Garcia, O.E.; Nielsen, A.H.
2004-01-01
The statistical properties of the particle flux in different types of plasma turbulence models are numerically investigated using probability distribution functions (PDFs). The physics included in the models range from two-dimensional drift wave turbulence to three-dimensional MHD dynamics...
Multiscale coherent structures in tokamak plasma turbulence
International Nuclear Information System (INIS)
Xu, G. S.; Wan, B. N.; Zhang, W.; Yang, Q. W.; Wang, L.; Wen, Y. Z.
2006-01-01
A 12-tip poloidal probe array is used on the HT-7 superconducting tokamak [Li, Wan, and Mao, Plasma Phys. Controlled Fusion 42, 135 (2000)] to measure plasma turbulence in the edge region. Some statistical analysis techniques are used to characterize the turbulence structures. It is found that the plasma turbulence is composed of multiscale coherent structures, i.e., turbulent eddies and there is self-similarity in a relative short scale range. The presence of the self-similarity is found due to the structural similarity of these eddies between different scales. These turbulent eddies constitute the basic convection cells, so the self-similar range is just the dominant scale range relevant to transport. The experimental results also indicate that the plasma turbulence is dominated by low-frequency and long-wavelength fluctuation components and its dispersion relation shows typical electron-drift-wave characteristics. Some large-scale coherent structures intermittently burst out and exhibit a very long poloidal extent, even longer than 6 cm. It is found that these large-scale coherent structures are mainly contributed by the low-frequency and long-wavelength fluctuating components and their presence is responsible for the observations of long-range correlations, i.e., the correlation in the scale range much longer than the turbulence decorrelation scale. These experimental observations suggest that the coexistence of multiscale coherent structures results in the self-similar turbulent state
The collapse of turbulence in the evening
Wiel, van de B.J.H.; Moene, A.F.; Jonker, H.J.J.; Baas, P.; Basu, S.; Sun, J.; Holtslag, A.A.M.
2012-01-01
A common experience in everyday weather is the fact that near-surface wind speeds tend to weaken in the evening, particularly in fair weather conditions. This cessation of wind usually coincides with the collapse of turbulence which leads to a quiet flow near the ground. As the absence of turbulent
Beyond scale separation in gyrokinetic turbulence
International Nuclear Information System (INIS)
Garbet, X.; Sarazin, Y.; Grandgirard, V.; Dif-Pradalier, G.; Darmet, G.; Ghendrih, Ph.; Angelino, P.; Bertrand, P.; Besse, N.; Gravier, E.; Morel, P.; Sonnendruecker, E.; Crouseilles, N.; Dischler, J.-M.; Latu, G.; Violard, E.; Brunetti, M.; Brunner, S.; Lapillonne, X.; Tran, T.-M.; Villard, L.; Boulet, M.
2007-01-01
This paper presents the results obtained with a set of gyrokinetic codes based on a semi-Lagrangian scheme. Several physics issues are addressed, namely, the comparison between fluid and kinetic descriptions, the intermittent behaviour of flux driven turbulence and the role of large scale flows in toroidal ITG turbulence. The question of the initialization of full-F simulations is also discussed
Dissipation range turbulent cascades in plasmas
International Nuclear Information System (INIS)
Terry, P. W.; Almagri, A. F.; Forest, C. B.; Nornberg, M. D.; Rahbarnia, K.; Sarff, J. S.; Fiksel, G.; Hatch, D. R.; Jenko, F.; Prager, S. C.; Ren, Y.
2012-01-01
Dissipation range cascades in plasma turbulence are described and spectra are formulated from the scaled attenuation in wavenumber space of the spectral energy transfer rate. This yields spectra characterized by the product of a power law and exponential fall-off, applicable to all scales. Spectral indices of the power law and exponential fall-off depend on the scaling of the dissipation, the strength of the nonlinearity, and nonlocal effects when dissipation rates of multiple fluctuation fields are different. The theory is used to derive spectra for MHD turbulence with magnetic Prandtl number greater than unity, extending previous work. The theory is also applied to generic plasma turbulence by considering the spectrum from damping with arbitrary wavenumber scaling. The latter is relevant to ion temperature gradient turbulence modeled by gyrokinetics. The spectrum in this case has an exponential component that becomes weaker at small scale, giving a power law asymptotically. Results from the theory are compared to three very different types of turbulence. These include the magnetic plasma turbulence of the Madison Symmetric Torus, the MHD turbulence of liquid metal in the Madison Dynamo Experiment, and gyrokinetic simulation of ion temperature gradient turbulence.
Turbulent viscosity in natural surf zones
Grasso, F.R.; Ruessink, B.G.
2012-01-01
Waves breaking in the shallow surf zone near the shoreline inject turbulence into the water column that may reach the bed to suspend sediment. Breaking-wave turbulence in the surf zone is, however, poorly understood, which is one of the reasons why many process-based coastal-evolution models
Imposing resolved turbulence in CFD simulations
DEFF Research Database (Denmark)
Gilling, L.; Sørensen, Niels N.
2011-01-01
In large‐eddy simulations, the inflow velocity field should contain resolved turbulence. This paper describes and analyzes two methods for imposing resolved turbulence in the interior of the domain in Computational Fluid Dynamics simulations. The intended application of the methods is to impose...
Power curve report - with turbulence intensity normalization
DEFF Research Database (Denmark)
Gómez Arranz, Paula; Wagner, Rozenn; Vesth, Allan
, additional shear and turbulence intensitity filters are applied on the measured data. Secondly, the method for normalization to a given reference turbulence intensity level (as described in Annex M of the draft of IEC 61400-12-1 Ed.2 [3]) is applied. The measurements have been performed using DTU...
Turbulence associated with the sawtooth internal disruption
International Nuclear Information System (INIS)
Andreoletti, J.; Laviron, C.; Olivain, J.; Pecquet, A.L.
1989-05-01
Specific turbulence associated with the sawtooth internal disruption has been observed on TFR tokamak plasmas by analyzing density fluctuations with CO 2 laser light scattering. The time localization is clearly connected with the successive phases of the relaxation process. Some specific turbulence appears in relation to the kink motion, but the main burst corresponds to the collapse phase. We concentrate our study on this strong burst and show first its frequency and wave number spectral properties and the corresponding pseudo dispersion relation. The specific turbulence is spatially localized. It is within the interior of the q = 1 surface and extends approximately 120 0 azimuthally. Taking into account the twisting of the central plasma during the turbulent kink phase, this location agrees with the azimuthal position of the ''sooner and faster'' outgoing heat flux. The power level of this turbulence is two orders of magnitude larger than the local quasi-stationary turbulence. These observations are in fair agreement with the predictions of the sawtooth disruption model previously proposed by Andreoletti. The observed specific turbulence shows several similarities with the so called ''magnetodrift turbulence'' described in the model
Prediction of turbulent shear layers in turbomachines
Bradshaw, P.
1974-01-01
The characteristics of turbulent shear layers in turbomachines are compared with the turbulent boundary layers on airfoils. Seven different aspects are examined. The limits of boundary layer theory are investigated. Boundary layer prediction methods are applied to analysis of the flow in turbomachines.
Stochastic models for turbulent reacting flows
Energy Technology Data Exchange (ETDEWEB)
Kerstein, A. [Sandia National Laboratories, Livermore, CA (United States)
1993-12-01
The goal of this program is to develop and apply stochastic models of various processes occurring within turbulent reacting flows in order to identify the fundamental mechanisms governing these flows, to support experimental studies of these flows, and to further the development of comprehensive turbulent reacting flow models.
Lagrangian properties of particles in turbulence
Toschi, F.; Bodenschatz, E.
2009-01-01
The Lagrangian description of turbulence is characterized by a unique conceptual simplicity and by an immediate connection with the physics of dispersion and mixing. In this article, we report some motivations behind the Lagrangian description of turbulence and focus on the statistical properties of
Efektivitas Weblog dan Facebook Terintegrasi untuk Pembelajaran Virtual
Hartono
2014-01-01
Abstrak: Saat ini, banyak mahasiswa menghabiskan waktu mereka di internet. Mereka melakukan kegiatan seperti membuat blog, mengunduh, mengunggah, chatting, dan berinteraksi melalui facebook. Mahasiswa sekarang ini hidup dengan teknologi. Penelitian menunjukkan bahwa weblog dan facebook berpotensi mendukung belajar dan mengajar. Guru dan pendidik menggunakan kegiatan tersebut untuk meningkatkan kualitas belajar. Penelitian ini bertujuan untuk mengetahui efektivitas weblog dan facebook ketika d...
Collaborative testing of turbulence models
Bradshaw, P.
1992-12-01
This project, funded by AFOSR, ARO, NASA, and ONR, was run by the writer with Profs. Brian E. Launder, University of Manchester, England, and John L. Lumley, Cornell University. Statistical data on turbulent flows, from lab. experiments and simulations, were circulated to modelers throughout the world. This is the first large-scale project of its kind to use simulation data. The modelers returned their predictions to Stanford, for distribution to all modelers and to additional participants ('experimenters')--over 100 in all. The object was to obtain a consensus on the capabilities of present-day turbulence models and identify which types most deserve future support. This was not completely achieved, mainly because not enough modelers could produce results for enough test cases within the duration of the project. However, a clear picture of the capabilities of various modeling groups has appeared, and the interaction has been helpful to the modelers. The results support the view that Reynolds-stress transport models are the most accurate.
Turbulent acceleration of auroral electrons
International Nuclear Information System (INIS)
Bryant, D.A.; Cook, A.C.; Wang, Z.-S.; Angelis, U. de; Perry, C.H.
1991-07-01
It is shown that the characteristic peak in the auroral electron velocity distribution can be generated stochastically through resonant interactions with lower-hybrid electrostatic turbulence. The peak itself is shown to be a direct consequence of restrictions imposed on reflexion of electron velocities in the frame of reference of individual wave packets by the limitation in group velocity. A Monte-Carlo model demonstrates how the various properties of the acceleration region are reflected in the resultant electron distribution. It is shown, in particular, that the width of the peak is governed by the amplitude of the turbulence, while the amplitude of the peak reflects the column density of wave energy. Electron distributions encountered within three auroral arcs are interpreted to yield order of magnitude estimates of the amplitude and rms electric field of lower-hybrid wave packets. The velocities and frequencies of the resonant waves, the net electric field, the column density of wave energy and the electric-field energy density are also estimated. The results are found to be consistent with available electric-field measurements. A general broadening of the electron distribution caused by less systematic interactions between electrons and wave packets is shown to have a negligible effect on the peak resulting from the reflexion process; it does, though, lead to the creation of a characteristic high-energy tail. (author)
Parallel plasma fluid turbulence calculations
International Nuclear Information System (INIS)
Leboeuf, J.N.; Carreras, B.A.; Charlton, L.A.; Drake, J.B.; Lynch, V.E.; Newman, D.E.; Sidikman, K.L.; Spong, D.A.
1994-01-01
The study of plasma turbulence and transport is a complex problem of critical importance for fusion-relevant plasmas. To this day, the fluid treatment of plasma dynamics is the best approach to realistic physics at the high resolution required for certain experimentally relevant calculations. Core and edge turbulence in a magnetic fusion device have been modeled using state-of-the-art, nonlinear, three-dimensional, initial-value fluid and gyrofluid codes. Parallel implementation of these models on diverse platforms--vector parallel (National Energy Research Supercomputer Center's CRAY Y-MP C90), massively parallel (Intel Paragon XP/S 35), and serial parallel (clusters of high-performance workstations using the Parallel Virtual Machine protocol)--offers a variety of paths to high resolution and significant improvements in real-time efficiency, each with its own advantages. The largest and most efficient calculations have been performed at the 200 Mword memory limit on the C90 in dedicated mode, where an overlap of 12 to 13 out of a maximum of 16 processors has been achieved with a gyrofluid model of core fluctuations. The richness of the physics captured by these calculations is commensurate with the increased resolution and efficiency and is limited only by the ingenuity brought to the analysis of the massive amounts of data generated
Compressibility effects on turbulent mixing
Panickacheril John, John; Donzis, Diego
2016-11-01
We investigate the effect of compressibility on passive scalar mixing in isotropic turbulence with a focus on the fundamental mechanisms that are responsible for such effects using a large Direct Numerical Simulation (DNS) database. The database includes simulations with Taylor Reynolds number (Rλ) up to 100, turbulent Mach number (Mt) between 0.1 and 0.6 and Schmidt number (Sc) from 0.5 to 1.0. We present several measures of mixing efficiency on different canonical flows to robustly identify compressibility effects. We found that, like shear layers, mixing is reduced as Mach number increases. However, data also reveal a non-monotonic trend with Mt. To assess directly the effect of dilatational motions we also present results with both dilatational and soleniodal forcing. Analysis suggests that a small fraction of dilatational forcing decreases mixing time at higher Mt. Scalar spectra collapse when normalized by Batchelor variables which suggests that a compressive mechanism similar to Batchelor mixing in incompressible flows might be responsible for better mixing at high Mt and with dilatational forcing compared to pure solenoidal mixing. We also present results on scalar budgets, in particular on production and dissipation. Support from NSF is gratefully acknowledged.
Dynamic structure in self-sustained turbulence
International Nuclear Information System (INIS)
Itoh, K.; Itoh, S.; Yagi, M.; Fukuyama, A.
1995-06-01
Dynamical equation for the self-sustained and pressure-driven turbulence in toroidal plasmas is derived. The growth rate of the dressed-test mode, which belongs to the subcritical turbulence, is obtained as a function of the turbulent transport coefficient. In the limit of the low fluctuation level, the mode has the feature of the nonlinear instability and shows the explosive growth. The growth rate vanishes when the driven transport reaches to the stationarily-turbulent level. The stationary solution is thermodynamically stable. The characteristic time, by which the stationary and self-sustained turbulence is established, scales with the ion-sound transit time and is accelerated by the bad magnetic curvature. Influences of the pressure gradient as well as the radial electric field inhomogeneity are quantified. (author)
Visualization of a Turbulent Jet Using Wavelets
Institute of Scientific and Technical Information of China (English)
Hui LI
2001-01-01
An application of multiresolution image analysis to turbulence was investigated in this paper, in order to visualize the coherent structure and the most essential scales governing turbulence. The digital imaging photograph of jet slice was decomposed by two-dimensional discrete wavelet transform based on Daubechies, Coifman and Baylkin bases. The best choice of orthogonal wavelet basis for analyzing the image of the turbulent structures was first discussed. It is found that these orthonormal wavelet families with index N＜10 were inappropriate for multiresolution image analysis of turbulent flow. The multiresolution images of turbulent structures were very similar when using the wavelet basis with the higher index number, even though wavelet bases are different functions. From the image components in orthogonal wavelet spaces with different scales, the further evident of the multi-scale structures in jet can be observed, and the edges of the vortices at different resolutions or scales and the coherent structure can be easily extracted.
Hydromagnetic turbulence in the direct interaction approximation
International Nuclear Information System (INIS)
Nagarajan, S.
1975-01-01
The dissertation is concerned with the nature of turbulence in a medium with large electrical conductivity. Three distinct though inter-related questions are asked. Firstly, the evolution of a weak, random initial magnetic field in a highly conducting, isotropically turbulent fluid is discussed. This was first discussed in the paper 'Growth of Turbulent Magnetic Fields' by Kraichnan and Nagargian. The Physics of Fluids, volume 10, number 4, 1967. Secondly, the direct interaction approximation for hydromagnetic turbulence maintained by stationary, isotropic, random stirring forces is formulated in the wave-number-frequency domain. Thirdly, the dynamical evolution of a weak, random, magnetic excitation in a turbulent electrically conducting fluid is examined under varying kinematic conditions. (G.T.H.)
Lõuka tuuliku restaureerimine / Dan Lukas
Lukas, Dan
2005-01-01
Hiiumaal Pühalepa vallas Vahtrepa külas Lõuka talu maadel asuva pukktuuliku ajaloost, restaureerimise käigust. Teostus: Dan Lukas. Muinsuskaitseline järelevalve: Tõnu Sepp, tema kommentaar. Ill.:pukktuuliku lõiked ja korruste plaanid, 7 värv. fotot
Internal Control: Peran Dan Perkembangannya
Murtin, Alek
2000-01-01
Perhatian terhadap pentingnya internal control dalam organisasi berjalan dari waktu ke waktu untuk meningkatkan fungsi internal control yang disesuaikan dengan perkembangan lingkungan organisasi, dimulai dengan adanya internal check, kemudian internal control system, internal control structure dan terakhir adalah internal control-integrated framework. Internal control system sempat berkembang beberapa tahun di Indonesia yang selanjutnya digantikan oleh internal control structure yang digunaka...
Asuransi Takaful: Prospek Dan Tantangannya
Sobirin, Achmad; Muhtar, Muchsin
1994-01-01
Dewasa ini perhatian terhadap nilai-nilai syariah Islam terhadap muamalah khususnya di bidang ekonomi menjadi besar. Lembaga perekonomian yang terjalin dengan pranata keagamaan makin menggejala dimana-mana dan kini sedang tumbuh mencari bentuk untuk dapat diterima di tengah-tengah masyarakat.
Directory of Open Access Journals (Sweden)
. Riyanti
2017-01-01
Hasil penelitian, ketentuan tentang standar pelayanan minimal bidang keluarga berencana, keluarga sejahtera dan asas perikemanusiaan dengan hak asasi manusia sangat berhubungan keterbatasan lingkup pelayanan dan standar pelaksanaan Komunikasi Informasi dan Edukasi yang tidak jelasberdampak pada tidak dipenuhinya hak asasi manusia untuk mendapatkan kesetaraan dan kebebasan dalam pelayanan keluarga berencana dan keluarga sejahtera.
KINERJA DAN EFISIENSI BANK PEMERINTAH (BUMN DAN BUSN YANG GO PUBLIK DI INDONESIA
Directory of Open Access Journals (Sweden)
Sugeng Haryanto
2012-06-01
Full Text Available Penelitian ini menganalisis kinerja dan tingkat efisiensi bank-bank BUMN dan BUSN yang go Publik di Bursa Efek Indonesia. Sample penelitian ini mengambil tiga bank BUMN Bank BNI 46, Bank Mandiri dan Bank BRI dan tiga bank BUSN (Bank BCA, Bank Niaga dan Bank Panin dengan periode analisis tahun 2005-2011. Varibael yang digunakan meliputi ROA, ROE, LAR. LDR, NPL dan BOPO. Tujuan dari penelitian ini adalah melihat dan menganalisis perbedaan kinerja antara Bank BUMN dan BUSN yang go public di Bursa Efek Indonesia tahun 2005-2011. Pendekatan pengukuran kinerja yang digunakan adalah Return on Asset (ROA, Return on Equity (ROE dan Loan to Deposit Ratio (LDR, Loan to Asset Ratio (LAR, dan efisiensi bank. Hasil dari penelitian menunjukkan bahwa 1 Bank-bank nasional, baik itu bank BUMN maupun BUSN menunjukkan kinerja yang semakin baik, 2 tidak terdapat perbedaan yang signifikan antara kinerja bank BUMN dan BUSN untuk variabel ROA, ROE, LAR, LDR, dan BOPO sedangkan variabel NPL yang merupakan indikator risiko kredit menunjukkan adanya perbedaan yang signifikan antara Bank BUMN dan BUSN
PREFACE Turbulent Mixing and Beyond
Abarzhi, Snezhana I.; Gauthier, Serge; Niemela, Joseph J.
2010-12-01
The goals of the International Conference 'Turbulent Mixing and Beyond', TMB-2009, are to expose the generic problem of non-equilibrium turbulent processes to a broad scientific community, to promote the development of new ideas in tackling the fundamental aspects of the problem, to assist in the application of novel approaches in a broad range of phenomena, where the turbulent processes occur, and to have a potential impact on technology. The Conference provides the opportunity to bring together researchers from different areas, which include but are not limited to fluid dynamics, plasmas, high energy density physics, astrophysics, material science, combustion, atmospheric and Earth sciences, nonlinear and statistical physics, applied mathematics, probability and statistics, data processing and computations, optics and telecommunications, and to have their attention focused on the long-standing formidable task of non-equilibrium processes. Non-equilibrium turbulent processes play a key role in a broad variety of phenomena spanning astrophysical to atomistic scales and high or low energy density regimes. Inertial confinement and magnetic fusion, light-matter interaction and non-equilibrium heat transfer, strong shocks and explosions, material transformation under high strain rate, supernovae and accretion disks, stellar non-Boussinesq and magneto-convection, planetary interiors and mantle-lithosphere tectonics, premixed and non-premixed combustion, non-canonical wall-bounded flows, hypersonic and supersonic boundary layers, dynamics of atmosphere and oceanography, are just a few examples. A grip on non-equilibrium turbulent processes is crucial for cutting-edge technology such as laser micro-machining, nano-electronics, free-space optical telecommunications, and for industrial applications in the areas of aeronautics and aerodynamics. Non-equilibrium turbulent processes are anisotropic, non-local, multi-scale and multi-phase, and often are driven by shocks or
PEMBINAAN DAN PENGEMBANGAN USAHA KECIL
Directory of Open Access Journals (Sweden)
Sentot Harman Glendoh
2001-01-01
Full Text Available Small business as an economic activity of society on a small scale, has a central role in the economy of Indonesia. Although the economic crisis has created a great disturbance in the live of large and middle-size business, apparently small business continues to function well in the lower levels of the economy. The main role of small business is: 1 use excess labor; 2 as a producer of goods and services at reachable prices for the lower economic levels of society; 3 as a potential producer of foreign exchange because of the success of this type of industry in producing non-oil commodities for export. Remembering that the role of small business is large and has great influence on the lower economic levels of society, it is quite necessary to pay attention to the development of this sector. Abstract in Bahasa Indonesia : Usaha kecil sebagai kegiatan ekonomi rakyat berskala kecil memiliki peran sentral dalam perekonomian Indonesia. Walaupun krisis ekonomi telah memporakporandakan kehidupan bidang usaha besar dan menengah, ternyata usaha kecil tetap tegar dan berjalan marak dikawasan kehidupan ekonomi tingkat bawah. Peran pokok usaha kecil ini adalah: (1 sebagai penyerap tenaga kerja, (2 sebagai penghasil barang dan jasa pada tingkat harga yang terjangkau bagi kebutuhan rakyat banyak yang berpenghasilan rendah, (3 sebagai penghasil devisa negara yang potensial kerena keberhasilannya dalam meproduksi komoditi ekspor non migas. Mengingat peran usaha kecil tersebut sangat besar andilnya bagi negara dan masyarakat kecil dilapisan bawah, maka pembinaan dan pengembangannya sangat perlu diperhatikan. Kata kunci: pembinaan, pengembangan, usaha kecil.
Dynamic method to study turbulence and turbulence transport
International Nuclear Information System (INIS)
Inagaki, S.; Itoh, S.-I.; Kasuya, N.; Sasaki, M.; Fujisawa, A.; Ida, K.; Itoh, K.; Tokuzawa, T.; Tamura, N.; Kubo, S.; Shimozuma, T.; Tanaka, K.; Tsuchiya, H.; Nagayama, Y.; Yamada, H.; Komori, A.; Kobayashi, T.; Kosuga, Y.; Kamiya, Kensaku
2014-10-01
Here we developed research methods of plasma turbulence transport associated with the non-local features. The ECH modulation experiment and the higher harmonic analysis of the heat wave indicated: (1) propagation of the change of T e at the time of switch-off/on of ECH power is about 5 times faster than that of perturbation itself, (2) propagation of the higher (7th) harmonic of the T e perturbation is 5 times faster than prediction by the diffusive model. New bi-spectral analysis of fluctuations demonstrated a non-linear coupling of micro-fluctuations at different radial locations. These results are beneficial for control of plasma dynamics in future fusion reactors. (author)
AGROFORESTRI UNTUK ADAPTASI DAN MITIGASI PERUBAHAN IKLIM
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Tigor Butarbutar
2017-01-01
Full Text Available Hilangnya tutupan lahan hutan karena konversi hutan untuk pemukiman, perkebunan, pertanian dan kebutuhan untuk pembangunan di sektor lain, telah menyebabkan perubahan pola cuaca/iklim di berbagai tempat. Perubahan iklim dapat diantisipasi dengan mitigasi dan adaptasi. Mitigasi berarti usahausaha pencegahan yang perlu dilakukan, sedangkan adaptasi merupakan kegiatan-kegiatan penyesuaian yang perlu dilakukan untuk dapat hidup dan bertahan dan meningkatkan ketahanan, kelenturan dan mengarahkemigrasikarenakondisiiklimyangberbeda.Agroforestridapatmemitigasidanmengadaptasi perubahaniklim dengan alasan-alasansebagaiberikut: aPencampuranjenis pohonpenghasilkayu,buah dan lain-lain, karena campuran jenis lebih baik dari tanaman murni; b Pencampuran jenis yang didasarkan pada sifat toleransi ( dan , sehingga akan memanfaatkan seluruh cahaya untuk fotosintesis; c Pencampuran perbedaan umur; d Pencampuran berdasarkan perbedaan waktu pemanenan; e Penggabungan nilai ekonomi, sosial dan budaya sehingga perubahan vegetasi dapat berjalan seiring dengan perubahan sosial dan budaya secara berangsur yang dapat disesuaikan dengan perubahan iklim; dan f Dapat digunakan sebagai model untuk memfasilitasi perubahan kelompok vegetasi menjadi kelompok yang baru (adaptasi, seperti teori perubahan vegetasi melalui perladangan berpindah-pindahyangteratur.
INDUSTRIALISASI DAN TANTANGANNYA PADA SEKTOR PENDIDIKAN
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Arif Unwanullah
2015-10-01
Full Text Available Abstrak: Industrialisasi dan Tantangannya pada Sektor Pendidikan. Sumbangan pendidikan dalam perubahan dan pembangunan masa lalu telah bergeser dengan kemajuan teknoekonomi dan komunikasi. Perubahan yang terjadi telah menggeser tatanan kehidupan dan pandangan masyarakat. Materialisme, kapitalisme, efisiensi, dan efektivitas telah menjadi tujuan dan semangat hidup. Pergeseran pandangan masyarakat telah mengubah pula pandangan keberhasilan dan mutu pendidikan, di mana pendidikan diukur dari keberhasilan dalam keterserapan lulusan dalam dunia kerja, oleh karenanya pendidikan dianalisis dari karakteristik sebagai investasi (capital-investment. Pergeseran makna dan tanggung jawab pendidikan mendorong dunia pendidikan melakukan pembaruan dengan alternatif: membangun pembaruan penalaran warganya menuju pemerdekaan dan pendewasaan, pendidikan dilaksanakan secara komprehensif dan bekerjasama dengan semua pihak secara kemitraan, dan membangun visi pendidikan secara komprehensif dan simultan dengan semua pihak. Kata kunci: perubahan sosial, materialistik, modernisasi dan kapitalis Abstract: Industrialization and its education Sector challenges. Contribution of education has shifted with the progress of technology, economy, and communication. The changes have shifted the society's views. Materialism, capitalism, efficiency, and effectiveness have become of interest and enthusiasm for life. The shift has changed society's view, i.e. the view of success and quality of education, in which education is measured from a rate of the absorption of graduates into labor market, therefore education is analyzed from the characteristics of an investment (capital-investment. A shift in meaning and responsibility of education encourages the education sector to create reformation through these following alternatives: creating new thoughts towards liberation and maturation, implementing education comprehensively and cooperating with all parties in partnership, and creating
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Dhika Suryananda
2012-09-01
Full Text Available Pertumbuhan ekonomi berdampak pada meningkatnya kebutuhan energi, sehingga menuntut peningkatan efisiensi dari power plant sebagai salah satu produsen energi. Pada saat ini power plant yang memiliki efisiensi paling tinggi adalah combined cycle power plant. Pada sistem combined cycle tersebut terdapat komponen Heat Recovery Steam Generator (HRSG yang berfungsi untuk meningkatkan efisiensi dari power plant dengan cara menggunakan sisa panas dari gas buang (exhaust gas turbine dan digunakan untuk memproduksi uap (steam untuk proses selanjutnya. Penelitian ini dilakukan menggunakan metode numerik (CFD dengan software FLUENT 6.3.26. Pemodelan yang dilakukan pada penelitian ini adalah 3 dimensi, aliran steady, turbulence model yang dipakai Relizable k-ε model dengan reaksi pembakarannya menggunakan spesies transport. Mixture materials yang digunakan merupakan methane-air. Data yang digunakan dalam penelitian ini menggunakan data yang di ambil di PT. GRESIK GASES and POWER INDONESIA.. Hasil yang didapatkan pada simulasi ini adalah bentuk bodi seperti enlargement, contraction, dan elbow memiliki pengaruh yang sangat besar terhadap distribusi temperatur, terkanan, dan kecepatan pada HRSG. Error dari hasil simulasi numerik dan referensi CCR sebagai berikut pada secondary superheater sebesar 8 %, pada primary superheater sebesar 6%, pada evaporator sebesar 0.00008% dan yang terakhir pada economizer sebesar 92 % . Penyebab perbedaan antara numerik dengan data CCR adalah kurang akuratnya proses simulasi dan simplifikasi dari jajaran heat exchanger terutama pada bagian economizer.
Desain dan Uji Kinerja Fungsional Sistem Penggerak dan Kendali ROVERGARD
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Moh Fikri Pomalingo
2017-04-01
Full Text Available Abstract The high population rate has an impact on increasing of land function change from agricultural land become housing and commercial building. As a result, it is difficult to get land for planting in the urban area. Therefore, this research is aimed to design equipment that can be used for planting in the narrow land using vertical gardening. This paper will report about design and functional testing of drive and control system on ROVERGARD. Drive system is based on water pump with additional gear train and chainsprocket mechanism. Control system use was on open loop type based on timer. The performance test of drive system was focused on electrical energy consumption and rotational speed of the system that was measured by multifunctional mini ammeter and tachometer. The control system was tested during 4 days, to evaluate their performances between set point and actual timing while filling water tank and rotate the system at maximal load condition. Electrical power consumption was 208 W at average rotational speed 2703 rpm. Increasing load caused an increase of energy consumption but made the drive rotation decline. The position control performance had on position error around 50 cm. Consequently, setting time on timer must be adjusted. Abstrak Laju pertumbuhan penduduk yang tinggi, mengakibatkan tingginya alih fungsi lahan pertanian menjadi bangunan perumahan dan komersial. Masalah ini mengakibatkan sulitnya mencari lahan pertanian di daerah padat penduduk khususnya perkotaan. Oleh karena itu perlu dirancang sebuah alat yang dapat digunakan untuk bercocok tanam di lahan sempit. Tujuan dari penelitian ini adalah mendesain dan menguji sistem penggerak dan kendali pada ROVERGARD. Sistem penggerak berasal dari pompa air yang dimodifikasi. Sedangkan sistem kendali menggunakan tipe open loop berbasis waktu dimana timer sebagai komponen utamanya. Pengujian kinerja penggerak difokuskan pada konsumsi listrik dan rpm yang diukur menggunakan
Park, G. I.; Wallace, J.; Wu, X.; Moin, P.
2010-11-01
Using a recent DNS of a flat-plate boundary layer, statistics of turbulence in transition at Reθ= 500 where spots merge (distributions of the mean velocity, rms velocity and vorticity fluctuations, Reynolds shear stress, kinetic energy production and dissipation rates and enstrophy) have been compared to these statistics for the developed boundary layer turbulence at Reθ= 1850. When the distributions in the transitional region, determined in narrow planes 0.03 Reθ wide, exclude regions and times when the flow is not turbulent, they closely resemble those in the developed turbulent state at the higher Reynolds number, especially in the buffer and sublayers. The skin friction coefficient, determined in this conditional manner in the transitional flow is, of course, much larger than that obtained by including both turbulent and non-turbulent information there, and is consistent with a value obtained by extrapolating from the developed turbulent region. We are attempting to perform this data analysis even further upstream in the transitioning flow at Reθ= 300 where the turbulent spots are individuated. These results add further evidence to support the view that the structure of a developed turbulent boundary layer is little different from its structure in its embryonic form in turbulent spots. *CTR 2010 Summer Program research.
Forest - added Turbulence: A parametric study on Turbulence intensity in and around forests
International Nuclear Information System (INIS)
Pedersen, Henrik Sundgaard; Langreder, Wiebke
2007-01-01
The scope of the investigation is to take on-site measured wind data from a number of sites inside and close to forests. From the collected on-site data the ambient turbulence intensity is calculated and analysed depending on the distance to the forest and height above the forest. From this forest turbulence intensity database it is possible to get an overview of the general behaviour of the turbulence above and down stream from the forest. The database currently consists of 65 measurements points from around the globe, and it will be continually updated as relevant sites are made available. Using the database a number of questions can be answered. How does the ambient turbulence intensity decay with height? What does the turbulence profile look like according to wind speed? Is it the general situation that high wind speeds are creating movement in the canopy tops, resulting in higher turbulence? How does the ambient turbulence intensity decay at different height as a function of distance to the forest? From the forest turbulence database it can be seen that in general, the majority of the turbulence intensity created by the forest is visible within a radius of 5 times the forest height in vertical and 500 meters downstream from the forest edge in horizontal direction. Outside these boundaries the ambient turbulence intensity is rapidly approaching normal values
KONTEKS DAN KONSTRUKSI SOSIAL MENGENAI KEMATIAN ELEKTIF ( EUTHANASIA ∗
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Helly Prajitno Soetjipto
2015-09-01
konteks sosial dan konstruksi sosial kematian. Euthanasia didiskusikan di dalam suatu kerangka pikir yang mencoba memberi perhatian kepada hal-hal yang kontekstual dan interpretatif fenomena sosial suatu proses kematian dan kejadian kematian
DIAGNOSIS DAN PENATALAKSANAAru LIMFOMA ORtsITA
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Ardizal Rahman
2014-12-01
Full Text Available Limfoma orbita merujuk pada limfoma yang terjadi di konjungtiva, kelenjar lakrimal, palpebradan otot-otot ekstraokular. Limfoma primer non-Hodgkin (NHL dari orbita dapat ditemukanpada hanya 1o/o dari semua limforna non-Hodgkin. Anaiisis mutasi somatik pada regiovariabel (V dari immunoglobulin (ig dan segmen gen rantai berat (H telah menunjukkanperan dari stimulasi antigen kronik pada patogenesis limfoma /nucosa-associated lymphoidflssue (MALT. Patogen mikroba seperti Helicobacter pylaridan Chlamydia pneumonia dapaimendasari proses inflamasi dan pada akhirnya memicu akuisisi MALT juga memainkanperan penting dalam tranformasi maligna dan ekspansi klonal lanjutan limfoma. Penentuanstadium kanker sangat penting karena akan menentukan terapi apa yang akan diberikan dankemungkinan remisi dan prognosisnya. Berdasarkan sistem stadium Ann-Arbor, limfoma yangterbatas di orbita disebut sebagai stadium l, keterlibatan struktur sekitar (sinus paranasal,tonsil, dan hidung menjadikannya stadium ll. Stadium lll adalah penyakit nodal abdominaldibawah diafragma dan stadium lV merujuk pada keterlibatan yang tersebar dari satu ataulebih lokasi ekstranodal (hepar, sum-sum tulang atau sistem saraf pusat. Mayoritas pasiendatang dengan keluhan massa konjungtiva berwarna pink (91%, diikuti hiperemis konjungtiva(32%, propiosis (27%, massa palpebra atau orbita (19"fi, penurunan visus dan ptosis (6%,dan diplopia(2%. Bilateralitas terjadi pada 10% hingga 15% kasus dimana 80 % terjadisecarasimultan sedangkan 20% merupakan kondisi yang berurutan. Penilaian lanjut untuk stagingyang akurat dan perencanaan terapitermasuk anamnesis yang lengkap dan pemeriksaan fisik,pemeriksaan laboratorium rutin, elektroforesis protein sei-um, LDH serum, Fr-mikroglobulin,rontgen thoraks, CT scan thoraks, abdornen, dan pelvis, dan biopsisum-sum tulang. Diagnosapositif harus berdasarkan pada perneriksaan histologik dari sampeltumor yang memadai yangdiperoleh dengan biopsiorbita. Beberapa kriteria
The Statistical Mechanics of Ideal MHD Turbulence
Shebalin, John V.
2003-01-01
Turbulence is a universal, nonlinear phenomenon found in all energetic fluid and plasma motion. In particular. understanding magneto hydrodynamic (MHD) turbulence and incorporating its effects in the computation and prediction of the flow of ionized gases in space, for example, are great challenges that must be met if such computations and predictions are to be meaningful. Although a general solution to the "problem of turbulence" does not exist in closed form, numerical integrations allow us to explore the phase space of solutions for both ideal and dissipative flows. For homogeneous, incompressible turbulence, Fourier methods are appropriate, and phase space is defined by the Fourier coefficients of the physical fields. In the case of ideal MHD flows, a fairly robust statistical mechanics has been developed, in which the symmetry and ergodic properties of phase space is understood. A discussion of these properties will illuminate our principal discovery: Coherent structure and randomness co-exist in ideal MHD turbulence. For dissipative flows, as opposed to ideal flows, progress beyond the dimensional analysis of Kolmogorov has been difficult. Here, some possible future directions that draw on the ideal results will also be discussed. Our conclusion will be that while ideal turbulence is now well understood, real turbulence still presents great challenges.
Cascade of circulations in fluid turbulence.
Eyink, Gregory L
2006-12-01
Kelvin's theorem on conservation of circulations is an essential ingredient of Taylor's theory of turbulent energy dissipation by the process of vortex-line stretching. In previous work, we have proposed a nonlinear mechanism for the breakdown of Kelvin's theorem in ideal turbulence at infinite Reynolds number. We develop here a detailed physical theory of this cascade of circulations. Our analysis is based upon an effective equation for large-scale coarse-grained velocity, which contains a turbulent-induced vortex force that can violate Kelvin's theorem. We show that singularities of sufficient strength, which are observed to exist in turbulent flow, can lead to nonvanishing dissipation of circulation for an arbitrarily small coarse-graining length in the effective equations. This result is an analog for circulation of Onsager's theorem on energy dissipation for singular Euler solutions. The physical mechanism of the breakdown of Kelvin's theorem is diffusion of lines of large-scale vorticity out of the advected loop. This phenomenon can be viewed as a classical analog of the Josephson-Anderson phase-slip phenomenon in superfluids due to quantized vortex lines. We show that the circulation cascade is local in scale and use this locality to develop concrete expressions for the turbulent vortex force by a multiscale gradient expansion. We discuss implications for Taylor's theory of turbulent dissipation and we point out some related cascade phenomena, in particular for magnetic flux in magnetohydrodynamic turbulence.
Numerical simulation of premixed turbulent methane combustion
International Nuclear Information System (INIS)
Bell, John B.; Day, Marcus S.; Grcar, Joseph F.
2001-01-01
In this paper we study the behavior of a premixed turbulent methane flame in three dimensions using numerical simulation. The simulations are performed using an adaptive time-dependent low Mach number combustion algorithm based on a second-order projection formulation that conserves both species mass and total enthalpy. The species and enthalpy equations are treated using an operator-split approach that incorporates stiff integration techniques for modeling detailed chemical kinetics. The methodology also incorporates a mixture model for differential diffusion. For the simulations presented here, methane chemistry and transport are modeled using the DRM-19 (19-species, 84-reaction) mechanism derived from the GRIMech-1.2 mechanism along with its associated thermodynamics and transport databases. We consider a lean flame with equivalence ratio 0.8 for two different levels of turbulent intensity. For each case we examine the basic structure of the flame including turbulent flame speed and flame surface area. The results indicate that flame wrinkling is the dominant factor leading to the increased turbulent flame speed. Joint probability distributions are computed to establish a correlation between heat release and curvature. We also investigate the effect of turbulent flame interaction on the flame chemistry. We identify specific flame intermediates that are sensitive to turbulence and explore various correlations between these species and local flame curvature. We identify different mechanisms by which turbulence modulates the chemistry of the flame
Generation of compressible modes in MHD turbulence
Energy Technology Data Exchange (ETDEWEB)
Cho, Jungyeon [Chungnam National Univ., Daejeon (Korea); Lazarian, A. [Univ. of Wisconsin, Madison, WI (United States)
2005-05-01
Astrophysical turbulence is magnetohydrodynamic (MHD) in nature. We discuss fundamental properties of MHD turbulence and in particular the generation of compressible MHD waves by Alfvenic turbulence and show that this process is inefficient. This allows us to study the evolution of different types of MHD perturbations separately. We describe how to separate MHD fluctuations into three distinct families: Alfven, slow, and fast modes. We find that the degree of suppression of slow and fast modes production by Alfvenic turbulence depends on the strength of the mean field. We review the scaling relations of the modes in strong MHD turbulence. We show that Alfven modes in compressible regime exhibit scalings and anisotropy similar to those in incompressible regime. Slow modes passively mimic Alfven modes. However, fast modes exhibit isotropy and a scaling similar to that of acoustic turbulence both in high and low {beta} plasmas. We show that our findings entail important consequences for star formation theories, cosmic ray propagation, dust dynamics, and gamma ray bursts. We anticipate many more applications of the new insight to MHD turbulence and expect more revisions of the existing paradigms of astrophysical processes as the field matures. (orig.)
Turbulence-chemistry interactions in reacting flows
Energy Technology Data Exchange (ETDEWEB)
Barlow, R.S.; Carter, C.D. [Sandia National Laboratories, Livermore, CA (United States)
1993-12-01
Interactions between turbulence and chemistry in nonpremixed flames are investigated through multiscalar measurements. Simultaneous point measurements of major species, NO, OH, temperature, and mixture fraction are obtained by combining spontaneous Raman scattering, Rayleigh scattering, and laser-induced fluorescence (LIF). NO and OH fluorescence signals are converted to quantitative concentrations by applying shot-to-shot corrections for local variations of the Boltzmann fraction and collisional quenching rate. These measurements of instantaneous thermochemical states in turbulent flames provide insights into the fundamental nature of turbulence-chemistry interactions. The measurements also constitute a unique data base for evaluation and refinement of turbulent combustion models. Experimental work during the past year has focused on three areas: (1) investigation of the effects of differential molecular diffusion in turbulent combustion: (2) experiments on the effects of Halon CF{sub 3}Br, a fire retardant, on the structure of turbulent flames of CH{sub 4} and CO/H{sub 2}/N{sub 2}; and (3) experiments on NO formation in turbulent hydrogen jet flames.
International Nuclear Information System (INIS)
Sullivan, J.P.; Houze, R.N.; Buenger, D.E.; Theofanous, T.G.
1981-01-01
Hot film Anemometry and Laser Doppler Velocimetry have been employed in this work to study the turbulence characteristics of Bubbly and Stratified two-phase flows, respectively. Extensive consistency checks were made to establish the reliability and hence the utility of these experimental techniques for the measurement of turbulence in two-phase flows. Buoyancy-driven turbulence in vertical bubbly flows has been identified experimentally and correlated in terms of a shear velocity superposition approach. This approach provides a criterion for the demarcation of the buoyancy-driven turbulence region from the wall shear-generated turbulence region. Our data confirm the roughly isotropic behavior expected for buoyancy-driven turbulence. Upgrading of our experimental system will permit investigations of the wall-shear dominated regime (i.e., isotropy, superposition approach, etc.). The stratified flow data demonstrate clearly that the maximum in the mean velocity profile does not coincide with the zero shear plane, indicating the existence of a negative eddy viscosity region. Previous studies do not take into account this difference and thus they yield incorrect friction factor data in addition to certain puzzling behavior in the upper wall region. The conditioned turbulence data in the wavy region indicate interesting trends and that an appropriate normalization of intensities must take into account the shear velocity at the interfacial (wavy) region
Turbulent Heat Transfer in Curved Pipe Flow
Kang, Changwoo; Yang, Kyung-Soo
2013-11-01
In the present investigation, turbulent heat transfer in fully-developed curved pipe flow with axially uniform wall heat flux has been numerically studied. The Reynolds numbers under consideration are Reτ = 210 (DNS) and 1,000 (LES) based on the mean friction velocity and the pipe radius, and the Prandtl number (Pr) is 0.71. For Reτ = 210 , the pipe curvature (κ) was fixed as 1/18.2, whereas three cases of κ (0.01, 0.05, 0.1) were computed in the case of Reτ = 1,000. The mean velocity, turbulent intensities and heat transfer rates obtained from the present calculations are in good agreement with the previous numerical and experimental results. To elucidate the secondary flow structures due to the pipe curvature, the mean quantities and rms fluctuations of the flow and temperature fields are presented on the pipe cross-sections, and compared with those of the straight pipe flow. To study turbulence structures and their influence on turbulent heat transfer, turbulence statistics including but not limited to skewness and flatness of velocity fluctuations, cross-correlation coefficients, an Octant analysis, and turbulence budgets are presented and discussed. Based on our results, we attempt to clarify the effects of Reynolds number and the pipe curvature on turbulent heat transfer. This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (2010-0008457).
TRANSFORMASI ORGANISASIONAL DAN MSDM: HAMBATAN DAN IMPLIKASINYA PADA REKRUTMEN DAN SELEKSI
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Licen Indahwati Darsono
2002-01-01
Full Text Available Rapid change of environment is an external force that causes the organization to transform. Fundamentally, the main purpose of the transformation is to change the organizational structure to be more flexible and competitive with fewer hierarchial levels, managers, and employees. The transformation needs to be radical, causing resistance from the organization's members. Their resistance can cause the transformation to fail, therefore organization must find ways to lessen this resistance. First, organization must learn about the diversity of its members' cultures and values. Second, organization must build its own organizational culture which can support the success of the transformation, by communicating it with the members of the organization. To support organizational culture building efforts, it needs changes in human resources practices, especially recruitment and selection. Abstract in Bahasa Indonesia : Perubahan yang cepat dalam lingkungan merupakan kekuatan eksternal yang mengakibatkan transformasi dalam sebuah organisasi. Pada dasarnya, tujuan utama dari transformasi tersebut adalah merubah struktur organisasi agar menjadi lebih fleksibel dan mampu bersaing, dengan tingkat structural yang sedikit, serta jumlah manajer dan karyawan yang lebih kecil. Transformasi tersebut harus menyeluruh, dan hal ini dapat menyebabkan resistensi dari para anggota organisasi yang memperhambat perubahan tersebut. Resistensi itu bisa menyebabkan perubahan tersebut batal, oleh karena itu organisasi harus mencari jalan untuk mengurangi hambatan-hambatan tersebut. Pertama, organisasi harus belajar keanekaragaman dari budaya dan nilai anggotanya. Kedua, organisasi harus mengembangkan budaya organisasi sendiri melalui komunikasi yang baik dengan anggotanya. Untuk mendukung usaha mengembangkan budaya organisasi, harus ada perubaban pada kebijakan sumber daya manusia, terutama dalam rekrutmen dan seleksi karyawan. Kata kunci: transformasi, resistensi, budaya
Perbandingan Akurasi Pengukuran Suhu Dan Kelembaban Antara Sensor DHT11 Dan DHT22
Saptadi, Arief Hendra
2014-01-01
Suhu dan kelembaban merupakan dua objek pengukuran yang acapkali terdapat di dalam sistem akuisisi data. Terdapat banyak piranti sensor yang berfungsi untuk mengukur dua objek tersebut dan akurasi merupakan salah satu parameter yang dapat digunakan untuk memilihnya. DHT11 dan DHT22 adalah sensor seri DHT dari Aosong Electronics yang dapat melakukan pengukuran suhu dan kelembaban secara serempak dengan keluaran digital. Informasi tentang akurasi terdapat di dalam lembar data keduanya. Kendati ...
Pertumbuhan dan Mutu Fisik Bibit Jabon (Anthocephalus Cadamba Miq.) di Polibag dan Politub
Junaedi, Ahmad
2010-01-01
Informasi pertumbuhan dan mutu fisik bibit jabon (Anthocephalus cadamba Miq.) di wadah bibit dengan volume yang berbeda diperlukan sebagai bagian yang akan diperhitungkan dalam pemilihan wadah bibit yang akan digunakan. Penelitian ini dilakukan untuk mengetahui pertumbuhan dan mutu fisik bibit jabon yang disapih pada wadah bibit polibag (volume 300 cm3) dan politub (volume 60 cm3). Tahapan penelitian meliputi : pembibitan serta pengamatan pertumbuhan dan penilaian mutu fisik bibit jabon yang ...
Aminah, Siti; Parmadi, Parmadi
2018-01-01
Penelitian ini bertujuan untuk menganalisis perkembangan Belanja irigasi dan jaringan serta perkembangan output GDP sektor pertanian Kota Jambi selama periode tahun 2005-2015 dan menganalisis pengaruh belanja irigasi dan jaringan terhadap GDP Output sektor pertanian dan pertumbuhan ekonomi Kota Jambi. Hasil penelitian menunjukkan Selama periode penelitian tahun 2005-2015 dengan rata-rata pertumbuhan 61,98%, nilai rata-rata PDRB harga berlaku Kota Jambi sebesar 157.601,68 dalam juta rupi...
Price setting in turbulent times
DEFF Research Database (Denmark)
Ólafsson, Tjörvi; Pétursdóttir, Ásgerdur; Vignisdóttir, Karen Á.
This price setting survey among Icelandic firms aims to make two contributions to the literature. First, it studies price setting in an advanced economy within a more turbulent macroeconomic environment than has previously been done. The results indicate that price adjustments are to a larger...... extent driven by exchange rate fluctuations than in most other advanced countries. The median Icelandic firm reviews its prices every four months and changes them every six months. The main sources of price rigidity and the most commonly used price setting methods are the same as in most other countries....... A second contribution to the literature is our analysis of the nexus between price setting and exchange rate movements, a topic that has attracted surprisingly limited attention in this survey-based literature. A novel aspect of our approach is to base our analysis on a categorisation of firms...
Magnetohydrodynamic Turbulence and the Geodynamo
Shebalin, John V.
2014-01-01
The ARES Directorate at JSC has researched the physical processes that create planetary magnetic fields through dynamo action since 2007. The "dynamo problem" has existed since 1600, when William Gilbert, physician to Queen Elizabeth I, recognized that the Earth was a giant magnet. In 1919, Joseph Larmor proposed that solar (and by implication, planetary) magnetism was due to magnetohydrodynamics (MHD), but full acceptance did not occur until Glatzmaier and Roberts solved the MHD equations numerically and simulated a geomagnetic reversal in 1995. JSC research produced a unique theoretical model in 2012 that provided a novel explanation of these physical observations and computational results as an essential manifestation of broken ergodicity in MHD turbulence. Research is ongoing, and future work is aimed at understanding quantitative details of magnetic dipole alignment in the Earth as well as in Mercury, Jupiter and its moon Ganymede, Saturn, Uranus, Neptune, and the Sun and other stars.
Pebble Accretion in Turbulent Protoplanetary Disks
Xu, Ziyan; Bai, Xue-Ning; Murray-Clay, Ruth A.
2017-09-01
It has been realized in recent years that the accretion of pebble-sized dust particles onto planetary cores is an important mode of core growth, which enables the formation of giant planets at large distances and assists planet formation in general. The pebble accretion theory is built upon the orbit theory of dust particles in a laminar protoplanetary disk (PPD). For sufficiently large core mass (in the “Hill regime”), essentially all particles of appropriate sizes entering the Hill sphere can be captured. However, the outer regions of PPDs are expected to be weakly turbulent due to the magnetorotational instability (MRI), where turbulent stirring of particle orbits may affect the efficiency of pebble accretion. We conduct shearing-box simulations of pebble accretion with different levels of MRI turbulence (strongly turbulent assuming ideal magnetohydrodynamics, weakly turbulent in the presence of ambipolar diffusion, and laminar) and different core masses to test the efficiency of pebble accretion at a microphysical level. We find that accretion remains efficient for marginally coupled particles (dimensionless stopping time {τ }s˜ 0.1{--}1) even in the presence of strong MRI turbulence. Though more dust particles are brought toward the core by the turbulence, this effect is largely canceled by a reduction in accretion probability. As a result, the overall effect of turbulence on the accretion rate is mainly reflected in the changes in the thickness of the dust layer. On the other hand, we find that the efficiency of pebble accretion for strongly coupled particles (down to {τ }s˜ 0.01) can be modestly reduced by strong turbulence for low-mass cores.
Energy Technology Data Exchange (ETDEWEB)
Mondin, H; Lavigne, P; Semeria, R [Commissariat a l' Energie Atomique, Grenoble (France). Centre d' Etudes Nucleaires
1964-07-01
oscillation, the conditions of burnout are compared with those obtained under steady conditions. The burn-out flux following uniform 'stopped' heating has been studied in a channel containing still water. The flux shows a maximum as a function of unsaturation. The influence of the geometry and the nature of the metal was investigated. 4 - Output Oscillations: Using a low pressure (8 atm) loop, the influence of various parameters on the periods of output oscillations in a boiling channel on the thresholds at which they appear, was studied. Some new aspects of this complex phenomena were observed and are reported. (authors) [French] On indique les principaux resultats obtenus a Grenoble depuis quatre ans dans le domaine des mecanismes de l'ebullition et des phenomenes connexes dans les reacteurs nucleaires. 1 - OBSERVATION DE L'EBULLITION: Par photographie et cinematographie ultrarapide (8000 images par seconde maximum) on a observe l'ebullition en vase ou en canal jusqu'a 140 kg/cm{sup 2}. On a denombre les populations de germes (sites) generateurs de bulles et obtenu une correlation donnant leur nombre par unite de surface en fonction du flux thermique et de la pression. Le diametre des bulles se detachant de la paroi a ete etudie jusqu'a 140 kg/cm{sup 2}. On a mis en evidence trois types de bulles: - Les bulles en equilibre dont le diametre suit la formule de Fritz et Ende, - Les bulles d'ebullition dont le diametre diminue rapidement avec la pression (1/100 mm a 140 kg/cm{sup 2}), - Les coalescences apparaissant en liquide sature au-dessus de 15 W/cm{sup 2} et dont la proportion est independante de la pression. Par visualisation en strioscopie on observe les mouvements du film thermique associes a l'amorcage des germes, au depart et a la condensation des bulles; les mecanismes responsables de l'excellent transfert de chaleur ont pu ainsi etre precises. 2 - PERTES DE PRESSION EN ECOULEMENT DIPHASE: On a etabli un modele de variation continue du taux de vide dans un canal
Wacana Penjarahan Dan Kekerasan Simbolik Terhadap Petani
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Agus Sudibyo
2002-01-01
Full Text Available Perlawanan kaum petani sudah lama terjadi dalam konteks sejarah hubungan antara si kaya dan si miskin dan antara kaum petani dan negara. Persoralannya selalu bahwa negara, aparat keamanan dan pemilik modal telah mengambil alih secara paksa surplus ekonomi dari petani. Mereka bekerja sama dalam aksi penyerobotan tanah petani, pendirian perkebunan-perkebunan dan dalam menghadapi gerakan protes petani. Negara bukan hanya menghadapi gerakan perlawanan petani dengan represi-represi fisik. Secara sistematis negara juga melakukan propaganda dengan menciptakan gambaran-gambaran yang unfavourable tentang petani pelaku penjarahan dalam berbagai representasi wacana. Dalam batas tertentu, media massa justru memperkuat kecenderungan ini dengan menonjolkan dimensi kekerasan, pemberontakan dan anarkisme dalam mewacanakan aksi-aksi penjarahan petani.
Motivasi, Kebiasaan, dan Keamanan Penggunaan Internet
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Zinggara Hidayat
2017-01-01
Full Text Available Abstract: This study investigates motivation, habits, and security of internet use by high schools and universities students in Jakarta, Bogor, Depok, Tangerang, and Bekasi. This descriptive and quantitative reasearch uses survey method. The findings of the study show that the strongest motivation is to show self existence, entertainment, and academic purposes. At some points, the habit of using the internet also makes the students face some risks such as verbal and nonverbal abuses, bullying, pornoghrapy, account hacking, and the risk of interaction with unknown parties. Abstrak: Penelitian ini menyelidiki motivasi, kebiasaan, dan keamanan penggunaan internet di antara siswa sekolah menengah atas dan universitas di Jakarta, Bogor, Depok, Tangerang, dan Bekasi. Penelitian deskriptif kuantitatif ini menggunakan metode survei. Hasil penelitian menunjukkan bahwa motivasi paling kuat adalah untuk memperlihatkan eksistensi diri, pencarian hiburan, dan penyelesaian tugas akademis. Kebiasaan penggunaan internet oleh pelajar dan mahasiswa menghadapi beberapa risiko, seperti kekerasan verbal dan nonverbal,
SOSIAL MEDIA DAN PERUBAHAN INDEKS PRESTASI MAHASISWA
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Risnah Risnah
2015-12-01
Tujuan dari penelitian ini adalah mengetahui jumlah mahasiswa semester II, IV, dan VI Jurusan Keperawatan yang menggunakan internet secara aktif dan karak-teristiknya, membandingkan hasil belajar mahasiswa semester II-III, IV-V, dan VI-VII Jurusan Keperawatan, dan mengetahui pengaruh sosial media (facebook dan twitter terhadap perubahan indeks prestasi mahasiswa, dengan jumlah res-ponden sebanyak 150 orang. Penelitian ini adalah deskriptif dengan desain pene-litian kausal. Pengumpulan data dengan menggunakan instrumen berupa kuesio-ner, dengan jumlah responden sebanyak 150 orang. Adapun hasil penelitian me-nunjukkan bahwa indeks prestasi mahasiswa dengan penggunaan sosial media umumnya responden menyatakan sosial media tidak mempengaruhi indeks prestasi. Dari hasil analisis uji statistik diperoleh terdapat pengaruh antara sosial media (facebook dan twitter dengan indeks prestasi. Dengan begitu, penggunaan sosial media harus digunakan sebagaimana mestinya, agar mahasiswa/i yang ak-tif pengunaan sosial media tidak mempengaruhi indeks prestasinya.
Large eddy simulations of an airfoil in turbulent inflow
DEFF Research Database (Denmark)
Gilling, Lasse; Sørensen, Niels N.
2008-01-01
Wind turbines operate in the turbulent boundary layer of the atmosphere and due to the rotational sampling effect the blades experience a high level of turbulence [1]. In this project the effect of turbulence is investigated by large eddy simulations of the turbulent flow past a NACA 0015 airfoil...
Directory of Open Access Journals (Sweden)
Zainal Arifin
2017-05-01
Abstrak: Perdebatan pluralisme agama masih mengemuka dalam konteks masyarakat majemuk di Nusantara. Bahkan, tidak jarang menimbulkan konflik dan perang pemikiran. Menarik melihat perspektif kiai dan santri Muhammadiyah dan NU terhadap isu pluralisme melalui praktik pendidikan di Ulama Tarjih Muhammadiyah (PUTM Yogyakarta dan Pondok Pesantren Aswaja Nusantara Yogyakarta yang dianggap representatif karena membawa muatan konsep, ide dan paradigma dari Muhammadiyah dan NU. Penelitian ini bersifat kualitatif, data diperoleh dari wawancara dan studi kepustakaan dengan saling memberikan verifikasi, koreksi dan pelengkap. Hasil penelitian ini, PUTM dan Pesantren Aswaja Nusantara memiliki konsep yang sama dalam memegang teguh akidah, yakni sikap eksklusif dan menolak pluralisme secara teologis namun menerimanya secara sosiologis. Sehingga, paradigma dari dua lembaga tersebut merepresentasikan dari paradigma Muhammadiyah dan NU dalam merespon fenomena pluralisme agama dan budaya.
VAKSIN DENGUE DAN PERKEMBANGANNYA SAAT INI DAN DI MASA MENDATANG
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Triwibowo Ambar Garjito
2012-09-01
Full Text Available Dengue virus merupakan salah satu virus anggota dari famili Flaviviridae yang sejak tahun 1956 telah dikenal dapat menimbulkan demam dengue maupun demam berdarah dengue (DBD. Penyakit yang ditularkan oleh nyamuk Aedes aegypti ini diperkirakan telah menjangkiti pada selatar 50-100 juta manusia dengan 500.000 kasus di antaranya dalam manifestasi yang ganas yang dikenal sebagai dengue haemorrhagic fever dan dengue shock syndrome dan 25.000 di antaranya berakibat fatal (meninggal. Saat ini pengembangan vaksin merupakan salah satu solusi yang diharapkan dapat menekan penyebaran penyakit tersebut. E (envelope merupakan salah satu bagian dari protein struktural virus yang sangat penting dalam pengembangan vaksin, yaitu sebagai badan yang memproduksi antibodi netralisasi untuk protein. Non-struktural protein l juga telah diketahui sebagai salah satu komponen penting dalam pengembangan vaksin oleh karena kemampuannya untuk dapat diekspresi pada permukaan sel yang diinfeksi yang dapat menjadi target untuk immune cytolisis. Ada dua pendekatan yang digunakan dalam memproduksi suatu vaksin dengue, yaitu: a. Vaksin hidup yang telah dilemahkan (live attenuated vaccine: b. Vaksin hasil rekayasa (engineered vaccine. Penelitian terhadap vaksin DENV baik rekombinan maupun non-rekombinan yang didasarkan pada uji virus telah dilakukan secara terus-menerus baik pada monyet dan manusia. Sampai saat ini telah dikembangkan sejumlah kandidat vaksin DENV yang berdasar pada tetravalent virus dengue, yaitu a. vaksin konvensional, b. vaksin dengue rekombinan berdasar pada flavivirus, c. vaksin intertypic chimeric, d. vaksin chimerivac, e. vaksin dengue rekombinan menggunakan vector non-ftavivirus dan f. vector adenovirus. Namun demikian, sampai sekarang belum ada vaksin yang siap digunakan untuk menangkal infeksi ke empat serotype virus dengue, sehingga masih diharapkan untuk pengembangan virus lebih lanjut. Kata kunci: Aedes aegypti, dengue virus, vaksin dengue.
Directory of Open Access Journals (Sweden)
Aron Pirade
2014-04-01
menempati urutan tertinggi. Wilayah Asia Selatan dan Asia Timur-Selatan (juga disebut Asia Tenggara adalah wilayah dengan prevalensi Gonore dan Klamidia terbesar. Prevalensi Gonore di tahun 1995 dan 1999 yaitu 29.11 dan 27.2 juta penduduk wilayah Asia Selatan dan Asia Tenggara. Klamidia, di tahun 1995 dan tahun 1999 yaitu 40.48 dan 42.89 juta penduduk wilayah Asia Selatan dan Asia Tenggara. Di Indonesia sendiri, pada 11 area penelitian menunjukkan bahwa prevalensi Gonore dalam wilayah Indonesia menunjukkan rata-rata prosentasenya 20%-40% dari keseluruhan STI pada wanita beresiko tinggi terkena STI. Sedangkan infeksi oleh Klamidia prosentasenya 15%- 45% dari keseluruhan STI pada wanita beresiko tinggi terkena penyakit kelamin. Prosentase Gonore dan Klamidia di Kota Manado rata-rata 15-30%. Tingginya prevalensi infeksi Gonore dan Klamidia di Asia Tenggara, ternyata diikuti juga dengan tingginya perkembangan infeksi Gonore dan Klamidia di Indonesia dan Kota Manado.
Turbulent energy losses during orchard heating
Energy Technology Data Exchange (ETDEWEB)
Bland, W.L.
1979-01-01
Two rapid-response drag anemometers and low time constant thermocouples, all at 4 m above a heated orchard floor, sampled wind component in the vertical direction and temperature at 30 Hz. The turbulent heat flux calculated revealed not more than 10% of the heat lost from the orchard was via turbulent transort. The observations failed to support previous estimates that at least a third of the energy applied was lost through turbulent transport. Underestimation of heat loss due to mean flow and a newly revealed flux due to spatial variations in the mean flow may explain the unaccounted for loss.
Spectral line profiles in weakly turbulent plasmas
International Nuclear Information System (INIS)
Capes, H.; Voslamber, D.
1976-07-01
The unified theory of line broadening by electron perturbers is generalized to include the case of a weakly turbulent plasma. The collision operator in the line shape expression is shown to be the sum of two terms, both containing effects arising from the non-equilibrium nature of the plasma. One of the two terms represents the influence of individual atom-particle interactions occuring via the nonequilibrium dielectric plasma medium. The other term is due to the interaction of the atom with the turbulent waves. Both terms contain damping and diffusion effects arising from the plasma turbulence
Turbulent transport in low-beta plasmas
DEFF Research Database (Denmark)
Nielsen, A.H.; Pécseli, H.L.; Juul Rasmussen, J.
1996-01-01
Low-frequency electrostatic fluctuations are studied experimentally in a low-P plasma, with particular attention to their importance for the anomalous plasma transport across magnetic field lines. The presence of large coherent structures in a turbulent background at the edge of the plasma column...... is demonstrated by a statistical analysis. The importance of these structures for the turbulent transport is investigated. The study is extended by a multichannel conditional analysis to illustrate detailed properties and parameter dependences of the turbulent transport. (C) 1996 American Institute of Physics....
Modification of tokamak edge turbulence using feedback
International Nuclear Information System (INIS)
Richards, B.; Uckan, T.; Wootton, A.J.; Carreras, B.A.; Bengtson, R.D.; Hurwitz, P.; Li, G.X.; Lin, H.; Rowan, W.L.; Tsui, H.Y.W.; Sen, A.K.; Uglum, J.
1994-01-01
Using active feedback, the turbulent fluctuation levels have been reduced by as much as a factor of 2 in the edge of the Texas Experimental Tokamak (TEXT) [K. W. Gentle, Nucl. Fusion Technol. 1, 479 (1981)]. A probe system was used to drive a suppressor wave in the TEXT limiter shadow. A decrease in the local turbulence-induced particle flux has been seen, but a global change in the particle transport at the present time has not been observed. By changing the phase shift and gain of the feedback network, the amplitude of the turbulence was increased by a factor of 10
An informal conceptual introduction to turbulence
Tsinober, Arkady
2009-01-01
This book is a second completely revised edition of ""An Informal Introduction to Turbulence"". The main emphasis is on conceptual and problematic aspects, physical phenomena, observations, misconceptions and unresolved issues rather than on conventional formalistic aspects, models, etc. Apart from the obvious fundamental importance of turbulent flows such an emphasis is a consequence of the view that without corresponding progress in fundamental aspects there is little chance for progress in any applications such as drag reduction, mixing, control and modeling of turbulence. More generally th
Turbulent momentum transport due to neoclassical flows
International Nuclear Information System (INIS)
Lee, Jungpyo; Barnes, Michael; Parra, Felix I; Belli, Emily; Candy, Jeff
2015-01-01
Intrinsic toroidal rotation in a tokamak can be driven by turbulent momentum transport due to neoclassical flow effects breaking a symmetry of turbulence. In this paper we categorize the contributions due to neoclassical effects to the turbulent momentum transport, and evaluate each contribution using gyrokinetic simulations. We find that the relative importance of each contribution changes with collisionality. For low collisionality, the dominant contributions come from neoclassical particle and parallel flows. For moderate collisionality, there are non-negligible contributions due to neoclassical poloidal electric field and poloidal gradients of density and temperature, which are not important for low collisionality. (paper)
Turbulence and Solar p-Mode Oscillations
Bi, S. L.; Xu, H. Y.
The discrepancy between observed and theoretical mode frequencies can be used to examine the reliability of the standard solar model as a faithful representation of solar real situation. With the help of an improved time-dependent convective model that takes into account contribution of the full spatial and temporal turbulent energy spectrum, we study the influence of turbulent pressure on structure and solar p-mode frequencies. For the radial modes we find that the Reynolds stress produces signification modifications in structure and p-mode spectrum. Compared with an adiabatic approximation, the discrepancy is largely removed by the turbulent correction.
Saturation of ion-acoustic turbulence
International Nuclear Information System (INIS)
Bychenkov, V.Yu.; Gradov, O.M.
1985-01-01
The time evolution of ion-acoustic turbulence is investigated taking into consideration both the scattering of electrons and the induced scattering of waves by the ions. The growth rate of the ion-acoustic turbulence is studied as the function of the wave number, including the long-wave ion sound excitations. It is shown that the relaxation of the ion-acoustic turbulence leads to the quasistationary noise distributions, which are the products of distributions according to the wave number and to the angle. The spectra conform to the stationary theory. (D.Gy.)
Wind Turbine Power Curves Incorporating Turbulence Intensity
DEFF Research Database (Denmark)
Sørensen, Emil Hedevang Lohse
2014-01-01
. The model and method are parsimonious in the sense that only a single function (the zero-turbulence power curve) and a single auxiliary parameter (the equivalent turbulence factor) are needed to predict the mean power at any desired turbulence intensity. The method requires only ten minute statistics......The performance of a wind turbine in terms of power production (the power curve) is important to the wind energy industry. The current IEC-61400-12-1 standard for power curve evaluation recognizes only the mean wind speed at hub height and the air density as relevant to the power production...
Turbulence near the wall in tokamaks
International Nuclear Information System (INIS)
Nedospasov, A.V.
1989-01-01
Causes of plasma turbulence in the shadow of poloidal limiter of tokamak are discussed. Current to limiter along the magnetic field plays the determining role. In this case the plasma on the external surrounding of torr is unstable relatively to channeled perturbations. Conditions of strong and weak recycling in limiter are considered. It is shown that in case of strong recycling, the amplitude and scale of turbulence pulsations and turbulent temperature conductivity of the plasma can be determined by low temperature of electrons near the limiter surface
Synchronization of two coupled turbulent fires
Takagi, Kazushi; Gotoda, Hiroshi; Miyano, Takaya; Murayama, Shogo; Tokuda, Isao T.
2018-04-01
We numerically study the scale-free nature of a buoyancy-induced turbulent fire and synchronization of two coupled turbulent fires. A scale-free structure is detected in weighted networks between vortices, while its lifetime obeys a clear power law, indicating intermittent appearances, disappearances, and reappearances of the scale-free property. A significant decrease in the distance between the two fire sources gives rise to a synchronized state in the near field dominated by the unstable motion of large-scale of transverse vortex rings. The synchronized state vanishes in the far field forming well-developed turbulent plumes, regardless of the distance between the two fire sources.
Turbulent energy generated by accelerations and shocks
International Nuclear Information System (INIS)
Mikaelian, K.O.
1986-01-01
The turbulent energy generated at the interface between two fluids undergoing a constant acceleration or a shock is calculated. Assuming linear density profiles in the mixed region we find E/sub turbulent//E/sub directed/ = 2.3A 2 % (constant acceleration) and 9.3A 2 % (shock), where A is the Atwood number. Diffusion models predict somewhat less turbulent energy and a density profile with a tail extending into the lower density fluid. Eddy sizes are approximately 27% (constant acceleration) and 17% (shock) of the mixing depth into the heavier fluid. 6 refs., 3 figs
NCEP ATP III dan Framingham score
Hasan, Refli; Fahila, Reny
2016-01-01
Laporan ini merupakan Program Pendidikan Kolesterol National yang diperbaharui yaitu pedoman klinis untuk melakukan pengujian kolesterol dan manajemen. ATP III dibuat berdasarkan bukti dan laporan ekstensif yang akan menjadi referensi dan rekomendasi ilmiah. Laporan ATP III dapat dijadikan pedoman untuk pemberian terapi penurun kolesterol yang intensif dalam praktek. Pedoman ini hanya sebagai informasi , tidak dapat mempengaruhi secara mutlak dalam penilaian klinis dokter yang akhirnya menent...
Using Indirect Turbulence Measurements for Real-Time Parameter Estimation in Turbulent Air
Martos, Borja; Morelli, Eugene A.
2012-01-01
The use of indirect turbulence measurements for real-time estimation of parameters in a linear longitudinal dynamics model in atmospheric turbulence was studied. It is shown that measuring the atmospheric turbulence makes it possible to treat the turbulence as a measured explanatory variable in the parameter estimation problem. Commercial off-the-shelf sensors were researched and evaluated, then compared to air data booms. Sources of colored noise in the explanatory variables resulting from typical turbulence measurement techniques were identified and studied. A major source of colored noise in the explanatory variables was identified as frequency dependent upwash and time delay. The resulting upwash and time delay corrections were analyzed and compared to previous time shift dynamic modeling research. Simulation data as well as flight test data in atmospheric turbulence were used to verify the time delay behavior. Recommendations are given for follow on flight research and instrumentation.
DESAIN, TATA LETAK, DAN KONSTRUKSI TAMBAK
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Akhmad Mustafa
2008-12-01
Full Text Available Komoditas yang umum dibudidayakan di tambak Indonesia adalah udang dan ikan bandeng yang menjadi komoditas unggulan untuk dikembangkan. Salah satu faktor penting yang sangat menentukan keberhasilan usaha budidaya tambak adalah rekayasa tambak yang mencakup disain, tata letak, dan konstruksi tambak. Secara umum, desain petakan tambak merupakan perencanaan bentuk tambak yang meliputi: ukuran panjang dan lebar petakan, kedalaman, ukuran pematang, ukuran berm, dan ukuran saluran keliling, serta ukuran dan letak pintu air. Tata letak suatu unit tambak harus memenuhi tujuan seperti: menjamin kelancaran mobilitas operasional sehari-hari, menjamin kelancaran dan keamanan pasok air, serta pembuangannya, dapat menekan biaya konstruksi tanpa mengurangi fungsi teknis dari unit tambak yang dibangun dan mempertahankan kelestarian lingkungan. Konstruksi tambak yang menggambarkan proses pengerjaan tambak harus disesuaikan dengan desain dan tata letak yang telah ada. Rekayasa tambak diarahkan pada kemampuan untuk menciptakan kondisi yang sesuai dengan keadaan alami yang dituntut oleh organisme akuatik yang dibudidayakan sehingga produktivitas tambak meningkat, efisien secara ekonomis, dan berkelanjutan.
KONTEKTUALISASI DAN (KEMUNGKINAN KONSEKUENSINYA BAGI PSIKOLOGI
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Prof. Supratiknya
2015-09-01
jaran di perguruan tinggi seperti kita kenal sekarang (selanjutnya disebut psikologi, lahir di Jerman pada penghujung abad ke‐19. Selanjutnya psikologi berkembang pesat di Amerika Utara khususnya Amerika Serikat dan negara‐negara lain di Eropa yang lebih dulu mengalami industrialisasi khususnya di Eropa Barat. 1 Alhasil, paling tidak sampai dasawarsa 1980‐an perkembangan dan persebaran psikologi di tingkat global ditandai oleh ketimpangan di antara apa yang oleh Moghaddam (1987 disebut tiga dunia tempat psikologi dikembangkan dan dipraktekkan, disimak antara lain berdasarkan besarnya produksi pengetahuan psikologis yang disebarluaskan melalui penyelenggaraan pendidikan tinggi psikologi maupun lewat publikasi ilmiah berupa baik berkala maupun buku rujukan dan buku teks.
Momentum and scalar transport at the turbulent/non-turbulent interface of a jet
DEFF Research Database (Denmark)
Westerweel, J.; Fukushima, C.; Pedersen, Jakob Martin
2009-01-01
and well-defined bounding interface between the turbulent and non-turbulent regions of flow. The jet carries a fluorescent dye measured with planar laser-induced fluorescence (LIF), and the surface discontinuity in the scalar concentration is identified as the fluctuating turbulent jet interface. Thence...... velocity and mean scalar and a tendency towards a singularity in mean vorticity. These actual or asymptotic discontinuities are consistent with the conditional mean momentum and scalar transport equations integrated across the interface. Measurements of the fluxes of turbulent kinetic energy and enstrophy...
Turbulence modulation induced by bubble swarm in oscillating-grid turbulence
International Nuclear Information System (INIS)
Morikawa, Koichi; Urano, Shigeyuki; Saito, Takayuki
2007-01-01
In the present study, liquid-phase turbulence modulation induced by a bubble swarm ascending in arbitrary turbulence was experimentally investigated. Liquid-phase homogeneous isotropic turbulence was formed using an oscillating grid in a cylindrical acrylic vessel of 149 mm in inner diameter. A bubble swarm consisting of 19 bubbles of 2.8 mm in equivalent diameter was examined; the bubble size and launching time were completely controlled using a bubble launching device through audio speakers. This bubble launching device was able to repeatedly control the bubble swarm arbitrarily and precisely. The bubble swarm was launched at a frequency of 4 Hz. The liquid phase motion was measured via two LDA (Laser Doppler Anemometer) probes. The turbulence intensity, spatial correlation and integral scale were calculated from LDA data obtained by the two spatially-separate-point measurement. When the bubble swarm was added, the turbulence intensity dramatically changed. The original isotropic turbulence was modulated to the anisotropic turbulence by the mutual interference between the bubble swarm and ambient isotropic turbulence. The integral scales were calculated from the spatial correlation function. The effects of the bubble swarm on the integral scales showed the tendencies similar to those on turbulence intensity. (author)
TASAWUF DAN TANTANGAN PERUBAHAN SOSIAL
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Yusno Abdullah Otta
2010-12-01
Full Text Available Abstract: Sufism in the eras of globalization and information often faces considerable challenges. The function and role of religion in modern life have in some aspects diminished, including sufism because it is claimed to have played no or less role in resolving problems nor stimulating social change. As one of Islamic traditions, sufism makes ihsan as its essential teaching. By this concept, sufism encourages humans to pray to God wholeheartedly. Sufism is now required to show its own existence and function by making fundamental contribution for modern life, an era which differ socio-culturally from the one when sufism firstly emerged. Sufism thus needs to adapt itself to the changes in the era of information and globalization so that it will remain relevant and suitable for human progress. Sufism needs to release itself from its exclusivism and to avoid being trapped in its own logic, namely speculative-trancendentalism Abstrak: Tasawuf di era globalisasi dan informasi seperti saat ini tengah menghadapi tantangan yang sangat berat. Kehidupan modern sudah sampai pada taraf tidak lagi mempercayai fungsi dan peran agama, termasuk di dalamnya tasawuf, sebagai ‘sesuatu’ yang dapat memberikan solusi bagi perubahan sosial. Sebagai manifestasi paripurna dari ajaran Islam, tasawuf berintikan pada konsep Ihsān yang mengajarkan untuk beribadah kepada Sang Pencipta secara ikhlas. Untuk menunjukkan eksistensinya, tasawuf dituntut peran aktifnya secara konstruktif-solutif terhadap berbagai kebutuhan manusia modern yang amat berbeda dengan setting maupun struktur masyarakat pada saat tasawuf “dilahirkan” pada zamannya. Tasawuf dituntut untuk memerlukan “baju” baru di era informasi yang kerap berubah ini, agar tetap realible dan suitable dengan kemajuan zaman. Hal itu dapat dilakukan dengan berusaha “keluar” dari eksklusifismenya dengan meminjam tradisi filsafat analitik pasca positivisme dan tradisi eksistensialis serta dinamika filsafat
Analisis Kinerja EIGRP dan OSPF pada Topologi Ring dan Mesh
Directory of Open Access Journals (Sweden)
DWI ARYANTA
2014-01-01
Full Text Available ABSTRAK EIGRP (Enhanced Interior Gateway Routing Protocol dan OSPF (Open Shortest Path Fisrt adalah routing protokol yang banyak digunakan pada suatu jaringan komputer. EIGRP hanya dapat digunakan pada perangkat Merk CISCO, sedangkan OSPF dapat digunakan pada semua merk jaringan. Pada penelitian ini dibandingkan delay dan rute dari kedua routing protokol yang diimplementasikan pada topologi Ring dan Mesh. Cisco Packet Tracer 5.3 digunakan untuk mensimulasikan kedua routing protokol ini. Skenario pertama adalah perancangan jaringan kemudian dilakukan pengujian waktu delay 100 kali dalam 5 kasus. Skenario kedua dilakukan pengujian trace route untuk mengetahui jalur yang dilewati paket data lalu memutus link utama. Pada skenario kedua juga dilakukan perbandingan nilai metric dan cost hasil simulasi dengan perhitungan rumus. Skenario ketiga dilakukan pengujian waktu konvergensi untuk setiap routing protokol pada setiap topologi. Hasilnya EIGRP lebih cepat 386 µs daripada OSPF untuk topologi Ring sedangkan OSPF lebih cepat 453 µs daripada EIGRP untuk topologi Mesh. Hasil trace route menunjukan rute yang dipilih oleh routing protokol yaitu nilai metric dan cost yang terkecil. Waktu konvergensi rata-rata topologi Ring pada EIGRP sebesar 12,75 detik dan 34,5 detik pada OSPF sedangkan topologi Mesh di EIGRP sebesar 13 detik dan 35,25 detik di OSPF. Kata Kunci: EIGRP, OSPF, Packet Tracer 5.3, Ring, Mesh, Konvergensi ABSTRACT EIGRP (Enhanced Interior Gateway Routing Protocol and OSPF (Open Shortest Path Fisrt is the routing protocol that is widely used in a computer network. EIGRP can only be used on devices Brand CISCO, while OSPF can be used on all brands of network. In this study comparison of both the delay and the routing protocol implemented on Ring and Mesh topology. Cisco Packet Tracer 5.3 is used to simulate both the routing protocol. The first scenario is the design of the network and then do the test of time delay 100 times in 5 cases. The
Analisis Kinerja EIGRP dan OSPF pada Topologi Ring dan Mesh
Directory of Open Access Journals (Sweden)
DWI ARYANTA
2016-02-01
Full Text Available ABSTRAK EIGRP (Enhanced Interior Gateway Routing Protocol dan OSPF (Open Shortest Path Fisrt adalah routing protokol yang banyak digunakan pada suatu jaringan komputer. EIGRP hanya dapat digunakan pada perangkat Merk CISCO, sedangkan OSPF dapat digunakan pada semua merk jaringan. Pada penelitian ini dibandingkan delay dan rute dari kedua routing protokol yang diimplementasikan pada topologi Ring dan Mesh. Cisco Packet Tracer 5.3 digunakan untuk mensimulasikan kedua routing protokol ini. Skenario pertama adalah perancangan jaringan kemudian dilakukan pengujian waktu delay 100 kali dalam 5 kasus. Skenario kedua dilakukan pengujian trace route untuk mengetahui jalur yang dilewati paket data lalu memutus link utama. Pada skenario kedua juga dilakukan perbandingan nilai metric dan cost hasil simulasi dengan perhitungan rumus. Skenario ketiga dilakukan pengujian waktu konvergensi untuk setiap routing protokol pada setiap topologi. Hasilnya EIGRP lebih cepat 386 µs daripada OSPF untuk topologi Ring sedangkan OSPF lebih cepat 453 µs daripada EIGRP untuk topologi Mesh. Hasil trace route menunjukan rute yang dipilih oleh routing protokol yaitu nilai metric dan cost yang terkecil. Waktu konvergensi rata-rata topologi Ring pada EIGRP sebesar 12,75 detik dan 34,5 detik pada OSPF sedangkan topologi Mesh di EIGRP sebesar 13 detik dan 35,25 detik di OSPF. Kata Kunci : EIGRP, OSPF, Packet Tracer 5.3, Ring, Mesh, Konvergensi ABSTRACT EIGRP (Enhanced Interior Gateway Routing Protocol and OSPF (Open Shortest Path Fisrt is the routing protocol that is widely used in a computer network. EIGRP can only be used on devices Brand CISCO, while OSPF can be used on all brands of network. In this study comparison of both the delay and the routing protocol implemented on Ring and Mesh topology. Cisco Packet Tracer 5.3 is used to simulate both the routing protocol. The first scenario is the design of the network and then do the test of time delay 100 times in 5 cases. The
Laguerre Gaussian beam multiplexing through turbulence
CSIR Research Space (South Africa)
Trichili, A
2014-08-17
Full Text Available We analyze the effect of atmospheric turbulence on the propagation of multiplexed Laguerre Gaussian modes. We present a method to multiplex Laguerre Gaussian modes using digital holograms and decompose the resulting field after encountering a...
ENERGY DISSIPATION PROCESSES IN SOLAR WIND TURBULENCE
Energy Technology Data Exchange (ETDEWEB)
Wang, Y.; Wei, F. S.; Feng, X. S.; Sun, T. R.; Zuo, P. B. [SIGMA Weather Group, State Key Laboratory for Space Weather, National Space Science Center, Chinese Academy of Sciences, Beijing 100190 (China); Xu, X. J. [Space Science Institute, Macau University of Science and Technology, Macao (China); Zhang, J., E-mail: yw@spaceweather.ac.cn [School of Physics, Astronomy and Computational Sciences, George Mason University, 4400 University Drive, MSN 3F3, Fairfax, Virginia 22030 (United States)
2015-12-15
Turbulence is a chaotic flow regime filled by irregular flows. The dissipation of turbulence is a fundamental problem in the realm of physics. Theoretically, dissipation ultimately cannot be achieved without collisions, and so how turbulent kinetic energy is dissipated in the nearly collisionless solar wind is a challenging problem. Wave particle interactions and magnetic reconnection (MR) are two possible dissipation mechanisms, but which mechanism dominates is still a controversial topic. Here we analyze the dissipation region scaling around a solar wind MR region. We find that the MR region shows unique multifractal scaling in the dissipation range, while the ambient solar wind turbulence reveals a monofractal dissipation process for most of the time. These results provide the first observational evidences for intermittent multifractal dissipation region scaling around a MR site, and they also have significant implications for the fundamental energy dissipation process.
Instantaneous aerosol dynamics in a turbulent flow
Zhou, Kun
2012-01-01
Dibutyl phthalate aerosol particles evolution dynamics in a turbulent mixing layer is simulated by means of direct numerical simulation for the flow field and the direct quadrature method of moments for the aerosol evolution. Most par
Vortices and turbulence at very low temperatures
Schneider, Wilhelm; Sergeev, Yuri
2009-01-01
Recent investigations have highlighted the similarities between turbulence in cryogenic fluids at temperatures close to absolute zero. This book contains lectures on various theoretical and experimental aspects of the problem.
Thermalized solutions, statistical mechanics and turbulence
Indian Academy of Sciences (India)
2015-02-20
Feb 20, 2015 ... In this study, we examine the intriguing connection between turbulence and equilibrium statistical mechanics. There are several recent works which emphasize this connection. Thus in the last ... Current Issue : Vol. 90, Issue 6.
Computational fluid dynamics investigation of turbulent separated ...
African Journals Online (AJOL)
user
Turbulent mixing is largely suppressed by the proximity of a wall boundary and ... the uncertainty between the experimental and CFD values falls within ± 3.8% of f .... Numerical, Experimental, and Theoretical Aspects, Vieweg, Berlin, 1989, pp.
Coherent Structures in Numerically Simulated Plasma Turbulence
DEFF Research Database (Denmark)
Kofoed-Hansen, O.; Pécseli, H.L.; Trulsen, J.
1989-01-01
Low level electrostatic ion acoustic turbulence generated by the ion-ion beam instability was investigated numerically. The fluctuations in potential were investigated by a conditional statistical analysis revealing propagating coherent structures having the form of negative potential wells which...
A dynamics investigation into edge plasma turbulence
International Nuclear Information System (INIS)
Thomsen, H.
2002-08-01
The present experimental work investigates plasma turbulence in the edge region of magnetized high-temperature plasmas. A main topic is the turbulent dynamics parallel to the magnetic field, where hitherto only a small data basis existed, especially for very long scale lengths in the order of ten of meters. A second point of special interest is the coupling of the dynamics parallel and perpendicular to the magnetic field. This anisotropic turbulent dynamics is investigated by two different approaches. Firstly, spatially and temporally high-resolution measurements of fluctuating plasma parameters are investigated by means of two-point correlation analysis. Secondly, the propagation of signals externally imposed into the turbulent plasma background is studied. For both approaches, Langmuir probe arrays were utilized for diagnostic purposes. (orig.)
Computational fluid dynamics incompressible turbulent flows
Kajishima, Takeo
2017-01-01
This textbook presents numerical solution techniques for incompressible turbulent flows that occur in a variety of scientific and engineering settings including aerodynamics of ground-based vehicles and low-speed aircraft, fluid flows in energy systems, atmospheric flows, and biological flows. This book encompasses fluid mechanics, partial differential equations, numerical methods, and turbulence models, and emphasizes the foundation on how the governing partial differential equations for incompressible fluid flow can be solved numerically in an accurate and efficient manner. Extensive discussions on incompressible flow solvers and turbulence modeling are also offered. This text is an ideal instructional resource and reference for students, research scientists, and professional engineers interested in analyzing fluid flows using numerical simulations for fundamental research and industrial applications. • Introduces CFD techniques for incompressible flow and turbulence with a comprehensive approach; • Enr...
Efficient Turbulence Modeling for CFD Wake Simulations
DEFF Research Database (Denmark)
van der Laan, Paul
Wind turbine wakes can cause 10-20% annual energy losses in wind farms, and wake turbulence can decrease the lifetime of wind turbine blades. One way of estimating these effects is the use of computational fluid dynamics (CFD) to simulate wind turbines wakes in the atmospheric boundary layer. Since...... this flow is in the high Reynolds number regime, it is mainly dictated by turbulence. As a result, the turbulence modeling in CFD dominates the wake characteristics, especially in Reynolds-averaged Navier-Stokes (RANS). The present work is dedicated to study and develop RANS-based turbulence models...... verified with a grid dependency study. With respect to the standard k-ε EVM, the k-ε- fp EVM compares better with measurements of the velocity deficit, especially in the near wake, which translates to improved power deficits of the first wind turbines in a row. When the CFD metholody is applied to a large...
Energetics of turbulent transport processes in tokamaks
International Nuclear Information System (INIS)
Haas, F.A.; Thyagaraja, A.
1987-01-01
The effect of electromagnetic turbulence on electrons and ions under Tokamak conditions is considered using a kinetic description. Taking the magnetic fluctuation spectrum as given, the density fluctuation spectrum is self-consistently calculated taking account of quasi-neutrality. The calculation is valid for arbitrary collisionality and appropriate to low frequencies typical of experiment. In addition to the usual enhancement of the radial electron energy transport, it is found that the turbulent fluctuations can heat the plasma at rates comparable to ordinary ohmic heating under well-defined conditions. Interestingly, electromagnetic turbulence appears to imply only an insignificant correction to the toroidal resistance of the plasma as estimated from Spitzer resistivity. The scalings of anomalous transport, fluctuations and heating with temperature and plasma volume are investigated. The assumption that the magnetic fluctuation spectrum of the turbulence is invariant under a wide range of conditions is shown to result in interesting consequences for JET-like plasmas. (author)
Near wall turbulence: An experimental view
Stanislas, Michel
2017-10-01
The present paper draws upon the experience of the author to illustrate the potential of advanced optical metrology for understanding near-wall-turbulence physics. First the canonical flat plate boundary layer problem is addressed, initially very near to the wall and then in the outer region when the Reynolds number is high enough to generate an outer turbulence peak. The coherent structure organization is examined in detail with the help of stereoscopic particle image velocimetry (PIV). Then the case of a turbulent boundary layer subjected to a mild adverse pressure gradient is considered. The results obtained show the great potential of a joint experimental-numerical approach. The conclusion is that the insight provided by today's optical metrology opens the way for significant improvements in turbulence modeling in upcoming years.
Theory of incremental turbulent transport in tokamaks
International Nuclear Information System (INIS)
Similon, P.L.
1991-01-01
The goal of this research is to understand how the various aspect of turbulent transport operate in tokamaks, in the presence of low frequency fluctuations such as drift waves or trapped electron modes
TIDAL TURBULENCE SPECTRA FROM A COMPLIANT MOORING
Energy Technology Data Exchange (ETDEWEB)
Thomson, Jim; Kilcher, Levi; Richmond, Marshall C.; Talbert, Joe; deKlerk, Alex; Polagye, Brian; Guerra, Maricarmen; Cienfuegos, Rodrigo
2013-06-13
A compliant mooring to collect high frequency turbulence data at a tidal energy site is evaluated in a series of short demon- stration deployments. The Tidal Turbulence Mooring (TTM) improves upon recent bottom-mounted approaches by suspend- ing Acoustic Doppler Velocimeters (ADVs) at mid-water depths (which are more relevant to tidal turbines). The ADV turbulence data are superior to Acoustic Doppler Current Profiler (ADCP) data, but are subject to motion contamination when suspended on a mooring in strong currents. In this demonstration, passive stabilization is shown to be sufficient for acquiring bulk statistics of the turbulence, without motion correction. With motion cor- rection (post-processing), data quality is further improved; the relative merits of direct and spectral motion correction are dis- cussed.
High Altitude Clear Air Turbulence Project
National Oceanic and Atmospheric Administration, Department of Commerce — The Air Force Flight Dynamics Laboratory conducted the High Altitude Clear Air Turbulence Project in the mid 1960s with the intention of better understanding air...
Non-equilibrium turbulence scalings in turbulent planar jets
Cafiero, Gioacchino; Vassilicos, John Christos; Turbulence, Mixing; Flow Control Group Team
2017-11-01
A revised version of the Townsend George theory, as proposed by Dairay et al. 2015, is applied to the study of turbulent planar jets (Cafiero and Vassilicos 2017). Requiring the self-similarity of only few quantities along with the non-equilibrium dissipation scaling law (Vassilicos 2015), it implies new mean flow and jet width scalings. In particular, the ratio of characteristic cross-stream to centreline streamwise velocities decays as the -1/3 power of streamwise distance in the region where the non-equilibrium dissipation scaling holds. In the definition of Cɛ both in Dairay et al. 2015 and in Cafiero and Vassilicos 2017 the local Reynolds number is based on the local flow width rather than on the integral lengthscale. We verify that the ratio of the integral lengthscale to the flow width is constant, thus enabling the use of the integral flow width in place of the integral lengthscale for defining Cɛ. The importance of this result is twofold: firstly it further strengthens the scalings obtained in the works of Dairay et al. 2015 and Cafiero and Vassilicos 2017; secondly the flow width is immediately accessible by any mean flow measurement, whereas the estimation of the integral lengthscale often requires an additional hypothesis. ERC Advanced Grant 320560.
KEJAHATAN PORNOGRAFI Upaya Pencegahan dan Penanggulangannya di Kabupaten Ponorogo
Directory of Open Access Journals (Sweden)
Irma Rumtianing Uswatul Hanifah
2013-12-01
Full Text Available Pemerintah telah mengeluarkan undang-undang No 44 Tahun 2008 tentang pornografi. Tujuan dari undang-undang tersebut salah satunya mewujudkan dan memelihara tatanan kehidupan masyarakat yang beretika, berkepribadian luhur, menjungjung tinggi nilai-nilai Ketuhanan Yang Maha Esa, serta menghormati harkat dan martabat kemanusiaan. Dalam perkembangannya, materi pornografi mengalami pertumbuhan dan penyebaran yang pesat seiring dengan perkembangan dan kemajuan teknologi informasi dan komunikasi. Peredaran dan penyebaran film porno kini semakin pesat karena ditopang dengan kecanggihan sarana informasi dan komunikasi salah satunya media internet yang bisa diakses oleh masyarakat pada setiap saat. Tulisan berikut akan mengkaji bagaimana upaya dan trategi yang dilakukan oleh Pemerintah Kabupaten Ponorogo dalam mencegah dan menanggulangi kejahatan pornografi di Kabupaten Ponorogo, apa hambatan dan bagaimana solusi dalam pencegahan serta penanggulangan kejahatan pornografi di Kabupaten Ponorogo serta bagaimana formulasi kebijakan untuk pencegahan dan penanggulangan kejahatan pornografi di Kabupaten Ponorogo. Kata kunci: Pornografi, Polres, KP3A
[Turbulence and spatio-temporal chaos
International Nuclear Information System (INIS)
1990-01-01
This report discusses Saffman-Taylor instability; cylinder wake; Levy walk and turbulent channel flow; bubble motion and bubble streams; spinal turbulent and wetting; collective behavior of a coupled map system with a conserved quantity; stability of temporally periodic states; generic nonergodic behavior in continuous systems; characterization of unstable periodic orbits; in low-dimensional chaotic attractors and repellers; and Ginzburg-Landau theory for oil-water-surfactant mixture
Transport due to ion pressure gradient turbulence
International Nuclear Information System (INIS)
Connor, J.W.
1986-01-01
Turbulent transport due to the ion pressure gradient (or temperature drift) instability is thought to be significant when etasub(i)=d(ln Tsub(i))/d(ln n)>1. The invariance properties of the governing equations under scale transformations are used to discuss the characteristics of this turbulence. This approach not only clarifies the relationships between earlier treatments but also, in certain limits, completely determines the scaling properties of the fluctuations and the consequent thermal transport. (author)
Chemical Reactions in Turbulent Mixing Flows
1992-07-01
Chemically-Reacting, Gas-Phase Turbulent Jets (Gilbrech 1991), that explored Reynolds number effects on turbulent flame length and the influence of...and asymptotes to a constant value beyond the flame tip. The main result of the work is that the flame length , as estimated from the temperature...8217. Specifically, the normalized flame length Lf/d* displays a linear dependence on the stoichiometric mixture ratio 0, with a slope that decreases from Re "• 1.0
Navier-Stokes equations and turbulence
Foias, C; Manley, Oscar; Rosa, Ricardo M S; Temam, R
2001-01-01
This book presents the mathematical theory of turbulence to engineers and physicists, and the physical theory of turbulence to mathematicians. The mathematical technicalities are kept to a minimum within the book, enabling the language to be at a level understood by a broad audience. Each chapter is accompanied by appendices giving full details of the mathematical proofs and subtleties. This unique presentation should ensure a volume of interest to mathematicians, engineers, and physicists.
Is there a statistical mechanics of turbulence?
International Nuclear Information System (INIS)
Kraichnan, R.H.; Chen, S.Y.
1988-09-01
The statistical-mechanical treatment of turbulence is made questionable by strong nonlinearity and strong disequilibrium that result in the creation of ordered structures imbedded in disorder. Model systems are described which may provide some hope that a compact, yet faithful, statistical description of turbulence nevertheless is possible. Some essential dynamic features of the models are captured by low-order statistical approximations despite strongly non-Gaussian behavior. 31 refs., 5 figs
Transfer anisotropy effect in a turbulent plasma
International Nuclear Information System (INIS)
Bychenkov, V.Yu.; Gradov, O.M.; Silin, V.P.
1982-01-01
A theory is developed of transfer phenomena with pronounced ion-sound turbulence. A transfer anisotropy effect is observed which is due to the temperature gradient. The corresponding fluxes across the effective force vector generating the turbulence are found to be considerably greater than the longitudinal fluxes in a plasma with a comparatively low degree of nonisothermality. In a strongly nonisothermal plasma the suppression of transverse fluxes occurs, corresponding to the growth of thermal insulation of the current-carrying plasma filaments
Turbulence of high-beta plasma
International Nuclear Information System (INIS)
Khvesyuk, V.I.; Chirkov, A.Y.
1999-01-01
Principals of numerical modelling of turbulence in high-beta plasma (β > 0.1) are discussed. Creation of transport model for axial symmetric nonuniform confining magnetic field is considered. Numerical model of plasma turbulence in FRC is presented. The physical and mathematical models are formulated from nonuniform axial symmetric high-beta plasma. It is shown that influence of waves arise under this plasma conditions lead to chaotic motion of charged particles across magnetic field. (author)
Progress in modeling hypersonic turbulent boundary layers
Zeman, Otto
1993-01-01
A good knowledge of the turbulence structure, wall heat transfer, and friction in turbulent boundary layers (TBL) at high speeds is required for the design of hypersonic air breathing airplanes and reentry space vehicles. This work reports on recent progress in the modeling of high speed TBL flows. The specific research goal described here is the development of a second order closure model for zero pressure gradient TBL's for the range of Mach numbers up to hypersonic speeds with arbitrary wall cooling requirements.
Composite asymptotic expansions and scaling wall turbulence.
Panton, Ronald L
2007-03-15
In this article, the assumptions and reasoning that yield composite asymptotic expansions for wall turbulence are discussed. Particular attention is paid to the scaling quantities that are used to render the variables non-dimensional and of order one. An asymptotic expansion is proposed for the streamwise Reynolds stress that accounts for the active and inactive turbulence by using different scalings. The idea is tested with the data from the channel flows and appears to have merit.
Generation of Synthetic Turbulence in Arbitrary Domains
DEFF Research Database (Denmark)
Gilling, Lasse; Nielsen, Søren R.K.; Sørensen, Niels
2009-01-01
A new method for generating synthetic turbulence is presented. The method is intended for generating a turbulent velocity field with a fine spatial resolution but only covering a small moving part of the rotor area of a wind turbine. For this application the Mann and Sandia methods cannot be used......-spectra a realization of a velocity field is determined by factorization and Fourier transform as in the Sandia method....
Direct numerical simulation of turbulent reacting flows
Energy Technology Data Exchange (ETDEWEB)
Chen, J.H. [Sandia National Laboratories, Livermore, CA (United States)
1993-12-01
The development of turbulent combustion models that reflect some of the most important characteristics of turbulent reacting flows requires knowledge about the behavior of key quantities in well defined combustion regimes. In turbulent flames, the coupling between the turbulence and the chemistry is so strong in certain regimes that is is very difficult to isolate the role played by one individual phenomenon. Direct numerical simulation (DNS) is an extremely useful tool to study in detail the turbulence-chemistry interactions in certain well defined regimes. Globally, non-premixed flames are controlled by two limiting cases: the fast chemistry limit, where the turbulent fluctuations. In between these two limits, finite-rate chemical effects are important and the turbulence interacts strongly with the chemical processes. This regime is important because industrial burners operate in regimes in which, locally the flame undergoes extinction, or is at least in some nonequilibrium condition. Furthermore, these nonequilibrium conditions strongly influence the production of pollutants. To quantify the finite-rate chemistry effect, direct numerical simulations are performed to study the interaction between an initially laminar non-premixed flame and a three-dimensional field of homogeneous isotropic decaying turbulence. Emphasis is placed on the dynamics of extinction and on transient effects on the fine scale mixing process. Differential molecular diffusion among species is also examined with this approach, both for nonreacting and reacting situations. To address the problem of large-scale mixing and to examine the effects of mean shear, efforts are underway to perform large eddy simulations of round three-dimensional jets.
Redistribution of energetic particles by background turbulence
International Nuclear Information System (INIS)
Hauff, T.; Jenko, F.
2007-01-01
The quest to understand the turbulent transport of particles, momentum and energy in magnetized plasmas remains a key challenge in fusion research. A basic issue being .still relatively poorly understood is the turbulent ExB advection of charged test particles with large gyroradii. Especially the interaction of alpha particles or impurities with the background turbulence is of great interest. In order to understand the dependence of the particle diffusivity on the interaction mechanisms between FLR effects and the special structure of a certain type of turbulence, direct numerical simulations are done in artificially created two dimensional turbulent electrostatic fields, assuming a constant magnetic field. Finite gyroradius effects are introduced using the gyrokinetic approximation which means that the gyrating particle is simply replaced by a charged ring. Starting from an idealized isotropic potential with Gaussian autocorrelation function, numerous test particle simulations are done varying both the gyroradius and the Kubo number of the potential. It is found that for Kubo numbers larger than about unity, the particle diffusivity is almost independent of the gyroradius as long as the latter does not exceed the correlation length of the electrostatic potential, whereas for small Kubo numbers the diffusivity is monotonically reduced. The underlying physical mechanisms of this behavior are identified and an analytic approach is developed which favorably agrees with the simulation results. The investigations are extended by introducing anisotropic structures like streamers and zonal flows into the artificial potential, leading to quantitative modulations of the gyroradius dependence of the diffusion coefficient. Analytic models are used to explain these various effects. After having developed a general overview on the behavior in simplified artificial potentials, test particle simulations in realistic turbulence created by the gyrokinetic turbulence code GENE are
Radial propagation of turbulence in tokamaks
International Nuclear Information System (INIS)
Garbet, X.; Laurent, L.; Samain, A.
1993-12-01
It is shown in this paper that a turbulence propagation can be due to toroidal or non linear mode coupling. An analytical analysis indicates that the toroidal coupling acts through a convection while the non linear effects induce a diffusion. Numerical simulations suggest that the toroidal propagation is usually the fastest process, except perhaps in some highly turbulent regimes. The consequence is the possibility of non local effects on the fluctuation level and the associated transport. (authors). 7 figs., 19 refs