Pre-operational forecasting of sea level height for the Río de la Plata

This paper presents the implementation and calibration of a pre-operational numerical model for the Río de la Plata river. This model is capable of predicting sea level variations in the Río de la Plata, and therefore constitutes a numerical tool of great value for the fluvial–maritime navigation and regional environmental management. A two-dimensional model (MOHID) with nested domains was used to simulate the hydrodynamics. This model was forced with a meso-scale atmospheric model (WRF) and a global tidal model (FES2004). The results obtained include astronomic and meteorological sea level variations in the Río de la Plata. Comparisons of modeled water levels with data have shown very good qualitative and quantitative agreement. The pre-operational test presented in this paper, a 4-day hydrodynamic forecast, was conducted in approximately 18 h.     

A 3D hydrodynamic numerical model of the Río de la Plata and Montevideo’s coastal zone

The 3D hydrodynamic numerical model MOHID was applied in the Río de la Plata and Montevideo coastal zone in order to represent the main dynamics and to study its complex circulation pattern. The hydrodynamic model was calibrated and validated considering the following main forces: fresh water flow, astronomical and meteorological tides in the oceanic boundary, and wind acting on the water surface. A series of water levels measured at six coastal stations and vertical profiles of current velocity measured at four different locations in the estuarine zone of the Río de la Plata were used for calibrating and validating the hydrodynamic model. The calibration process was carried out in two steps. First the astronomical waves propagation was calibrated comparing harmonic constants of observed and computed sea surface elevation data. Next, both the astronomical and meteorological wave propagation was calibrated. Direct comparison of scatter plot and root-mean square errors of model results and field data were used when evaluating the calibration quality. The calibrated model shows good agreement with the measured water surface level in the entire domain with mean error values being minor than 20% of the measured data and correlation factors higher than 0.74. Also, the intensity and velocity direction observed in the currents data are well represented by the model in both bottom and surface levels with errors similar to 30% of the currents data components. Using the 3D calibrated model the bottom and surface residual circulation for a four month period of time was analyzed.     

Residual currents and corridor of flow in the Rio de la Plata

The Rio de la Plata is a large and shallow water body that discharges onto the Atlantic Ocean. The main driving forces for the river flow are the bathymetry, tides, the outflow from the Paraná and Uruguay rivers and the winds. A numerical model covering the entire river was set up with the objective of increasing our understanding of the hydrographical features and morphological dynamics in the Estuary. The simulations revealed a counter-clockwise residual circulation in the Samborombón Bay and an eastward net flow near the Uruguayan coast. The residual flow is forced by both the tides and the bathymetry. The residence time for the entire river ranges from 40 to 80 days. However, residence times above 120 days was found in the Samborombón Bay. Three corridors of flow have been identified.     

Hydrodynamic numerical simulation at the mouths of the Parana and Uruguay rivers and the upper Rio de la Plata estuary: A realistic boundary condition

A hydrodynamic numerical study at the mouths of the Paraná and Uruguay rivers and the upper Río de la Plata is presented in this paper. Water Quality Mapping numerical model was implemented and realistic and very simple boundary conditions were specially developed for this complex estuarial system. A set of numerical experiments were carried out using different constant discharges for the Paraná and Uruguay rivers but unrealistic currents were generated. In order to obtain more realistic results, a set of numerical simulations were carried out imposing water level timeseries at the open boundaries. M₂, S₂, K₁ and O₁ harmonic constants were used to generate water levels at Zárate (Paraná river), Nueva Palmira (Uruguay river) and the eastern boundary of the domain (La Plata–Colonia). A mean water level equal to zero was set between La Plata and Colonia. Positive mean water levels (0.3–0.4 m) were imposed at Zárate and Nueva Palmira to simulate the hydraulic slope of both rivers and, consequently, to generate realistic and unsteady discharges. These boundary conditions, built by means of the addition of a mean water level and the astronomical tide, significantly improve the simulated currents at the northernmost region of the RDP estuary.     

A coupled wave–current–sediment transport model for an estuarine system: Application to the Río de la Plata and Montevideo Bay

Modelling the hydrodynamics and fine-sediment dynamics in estuarine environments is important for coastal engineering design and environmental assessment. This paper presents the application of a coupled wave–current–sediment transport model to a complex estuarine system with high spatial resolution in a harbour area. The case study was the Río de la Plata, with a focus on the Montevideo Bay area. We used a bidimensional depth-averaged approach, and the sediment transport modelling focused on fine cohesive sediments. The model considers realistic forcings, allows for the simulation of complex geometries such as those present in harbour basins and is capable of providing long-term environmental simulations (on the order of several years) within reasonable computational times. The model results are in good agreement with the measured data and satisfactorily represent the main features of the flow and sediment dynamics of the Río de la Plata. The effect of the internal coupling on the hydrodynamic results is analysed, and the computational times with various coupling alternatives are discussed.The dynamics of fine sediment in Montevideo Bay were analysed based on the model results. The current-induced bottom shear stress results are relevant for representing the permanent suspended sediment concentrations, whereas the wave-induced bottom shear stress is fundamental for reproducing the main resuspension events during storm conditions. The suspended fine-sediment dynamics in the estuary are strongly controlled by the sediment exchange between the bed and water column, whereas inside Montevideo Bay, the dynamics are controlled mainly by advection of sediment originating from the nearby coastal area.     

Environmental flows for the Yangtze Estuary based on salinity objectives

Environmental flows based on the salinity objectives for China’s Yangtze Estuary were quantified to assess the impacts of changing freshwater inflow on the estuarine ecosystem. The salinity objectives for three benthos habitats in the Yangtze Estuary were studied to determine their requirements during the most critical period of the year. The temporal variation in the natural monthly river discharge represented the temporal variation of the ecological objectives used to maintain natural flow regimes. A numerical model, coupled a hydrodynamic processes model with a salinity model and validated using field data of tidal height, current velocity, and salinity at different stations, was developed to simulate the spatial distribution of salinity as a function of the variation in freshwater inflows. The prediction results of the proposed model agreed well with the field data. Considering the salinity objectives for the different habitats, the environmental flow requirements for the Yangtze Estuary were determined. Annual environmental flows should be 9.63 × 10¹¹, 6.32 × 10¹¹, and 4.70 × 10¹¹ m³ for the high, medium, and minimum objectives, which are equivalent to 104%, 68%, and 50% of the annual river discharge, respectively. The periods from September to November should be considered as the critical seasons to maintain the minimum environmental flows in the Yangtze Estuary.     

Industrielle Systemforschung

Zusammenfassung Der Begriff "Automatismus" wird begründet und der Beitrag der Informationstheorie und Kybernetik zur Verwirklichung des industriellen Automatismus diskutiert.

---

Summary The concept of "automatism" is established and the contribution of information theory and cybernetics towards the realization of industrial automatism is discussed.

---

Résumé Le concept d' "automatisme" est établí et la contribution de la théorie de l'information et la cybernetique à la réalization de l'automatisme industriel est discuté.

---

---

Berichtet am Internationalen Kongreß für Automatik: Madrid, 13.–18. Oktober 1958. Siehe auch [1].     

Solitary fluid transients in rectangular ducts with transverse magnetic fields,II

Summary This paper treats a fluid hammer wave which is propagating into a fully devloped MHD duct flow. The wave is produced by suddenly closing a valve at some cross section of a rectangular duct with a uniform, transverse, applied magnetic field, with perfectly conducting walls parallel to the field and with either insulating or perfectly conducting walls perpendicular to the field. The Mach and magnetic Reynolds numbers are assumed to be small, while the Hartmann number is assumed to be large. The jump in velocity and pressure across the wave decreases exponentially in time. The fully developed flow ahead of the wave is undisturbed, and solutions for the velocity and pressure between the valve and the wave are presented.

---

Résumé Cet article traite de l'onde de choc produite par la fermeture subite d'une vanne et qui se propage dans un fluide conducteur d'électricité s'écoulant dans une conduite de section rectangulaire à laquelle est appliquée un champ magnétique transversal et homogène. Deux parois de la conduite sont parfaitement conductrices et parallèles au champ magnétique, les deux autres étant parfaitement conductrices ou isolantes. On admet que le nombre de Mach et le nombre magnétique de Reynolds sont petits et que le nombre de Hartmann est grand. Les changements de la vitesse et de la pression à travers l'onde diminuent exponentiellement à temps. L'écoulement à la tête de l'onde n'est pas perturbée. Des solutions pour la vitesse et la pression entre la vanne et l'onde sont presentées.

     

Etude de la chute de pression singulière dans les élargissements brusques en écoulement monophasique turbulent

Résumé On étude théoriquement et expérimentalement les effets de frottement pariétal et de distribution de vitesse moyenne et fluctuante sur le coefficient de chute de pression singulière dans un élargissement brusque en écoulement monophasique turbulent. Les résultats expérimentaux ont permis d'une part de tester la limite de validité de cette approche, et d'autre part de mieux preciser l'organisation de l'écoulement pariétal au voisinage de l'élargissement.

---

The theoretical and experimental study deals with the effects of wall shear stress and distribution of mean and fluctuating velocity on the coefficient of singular pressure loss in a sudden enlargement for a turbulent single phase flow. The experimental results allowed to verify the limit of validity of the present model, and specify the wall flow organization near the abrupt enlargement.

     

A numerical model of density currents in estuaries of Siberian rivers

A numerical model for studying the dynamic mixing of sea and river waters in estuary areas is proposed. The model is based on two-dimensional longitudinal vertical stratified fluid mechanics equations and an equation of salt transport. The model is used to simulate local density currents in the estuaries of branched deltas of Siberian rivers. The results of numerical experiments are given. The flow dynamic structure and the salinity profile are compared with observational data.     

A kinematical study of Kirchhoff-Rayleigh flow

Summary A method of calculating the separated flow of a viscous fluid is proposed, which allows to split up properly the boundary condition problem from the viscous phenomena. The theory is developed for the flow past a plate and yields wakes of finite extension having an underpressure which depends directly on the amount of vorticity diffusion and dissipation occurring in the fluid. Application of the method to real flows shows good agreement between the calculated and the measured velocity distributions in front of the plate and in the wake.

---

Résumé Une méthode de calcul de l'écoulement décollé d'un fluide visqueux est proposée qui permet de séparer clairement le problème aux limites des phénomènes visqueux. La théorie est développée pour l'écoulement autour d'une plaque et donne des sillages de longueur finie ayant une dépression de culot directement dépendante de l'intensité de la diffusion et dissipation de la vorticité se produisant dans le fluide. L'application de la méthode à des écoulements réels montre une bonne concordance entre les répartitions de vitesse calculées et mesurées sur le devant de la plaque et dans le sillage.

     

Flow past a sphere straddling the interface of a two-phase system

An explicit solution is found for flow past a sphere with perfect slip in a two phase flow of two immiscible viscous fluids. The interface remains flat and an expression is found for the drag on the sphere.

---

Résumé Une solution de l'équation de Stokes est présentée pour une sphère entièrement immergée, la surface de séparation de deux fluides non mélangeables se situant á la hauteur du centre de cette sphère. Pour la surface de cette dernière la condition d'immobilité est remplacée par une condition de tension de cisaillement nulle.

     

Radiative magnetogasdynamic Couette flow with variable parameters

Couette flow of an electrically conducting compressible fluid with uniform magnetic field applied transversely between flat walls of arbitrary electrical conductivity, radiative emissivity and temperature is analysed. The equations of steady flow are formulated with the introduction of temperature dependent coefficients of viscosity and thermal and electrical conductivity, together with absorption coefficient in addition dependent upon the density. Profiles of velocity, induced magnetic field, radiative flux and temperature are derived numerically under a one-dimensional modelling. The parameter dependence, expressed as a power law, is found to have a marked effect upon the velocity and magnetic field but to be of little import for the thermal profiles. Similar influence is found for the effect of wall electrical conductivity and emissivity. On the other hand, changes in the strength of the fluid thermal conductivity significantly affect the temperature profile in the presence of electromagnetic interaction.

---

Résumé Pour un fluide conducteur, rayonnant et compressible sous l'influence d'un champ magnétique constant et transverse l'écoulement de Couette entre deux surfaces planes conductrices et rayonnantes avec des températures arbitraires est analysé. On formule les équations d'un écoulement permanent quand la viscosité, la conductibilité thermique et la conductibilité électrique dépendent de la température et le coffficient d'absorption de la densité. On calcule la vitesse, le champ magnétique induit, le rayonnement et la température pour des écoulements qui ne sont fonction que de la cordonnée transverse.La vitesse et le champ magnétique dépendent de façon significative de ce paramètre, mais pas la température ni le rayonnement. On obtient des résultats similaires pour la conductibilité électrique et l'emissivité de rayonnement des surfaces planes. D'autre part quand la conductiblité électrique du fluide n'est pas nulle, une variation de la conductibilité thermique modifie la température d'une manière significative.

     

A second order boundary layer solution for separated flow past a bluff body

In this investigation second order boundary layer solutions are obtained for subsonic, plane flow over a circular cylinder with a wake. The outer flow due to displacement thickness is obtained by extending a first order solution, which includes wake effects. This enables realistic solutions for the displacement effect to be calculated as well as for the curvature effect. It is shown that as the first order separation point is approached the magnitudes of the second order velocity components become large and the surface shear becomes large and negative. There is also a significant upstream shift in the position of the separation point.

---

Résumé Dans ce travail, on obtient des solutions du second ordre des équations de la couche limite pour un écoulement subsonique plan autour d'un cylindre circulaire avec un sillage. On obtient l'écoulement extérieur dû à l'épaisseur de déplacement en étendant une solution du premier ordre qui comprend les effets du sillage. Ceci permet de calculer des solutions réalistes pour l'effet de déplacement ainsi que pour l'effet de courbure. On montre que les composantes de la vitesse du second ordre de même que la tension tangentielle deviennent très grandes et cette dernière négative au voisinage du point de décollement du premier ordre. Il y a aussi un déplacement significatif vers l'amont de la position du point de décollement.

     

On the equations of fully fluidized granular materials

Equations for fully fluidized granular materials are proposed and are solved in a simple case. In fully fluidized granular materials, the granular particles slip or collide with each other and energy is dissipated. In describing the energy dissipation process characteristic to granular materials, a measure of random motion of granular particles is introduced as a new internal variable. We derive the constitutive equations by using a simple kinematical model of the collision of particles. The set of equations for fully fluidized granular materials obtained has properties similar to the equations that describe turbulence. For reasonable assumptions, these equations predict the results of Bagnold, namely that the shear and normal stress depend upon the square of the velocity gradient. In case of steady one-dimensional gravity flow the calculated flow profiles resemble experimental ones.

---

Résumé Des équations pour des matériaux granulés entièrement fluides sont proposées et résolues dans un cas simple. Par le frottement et les collisions des particules entre elles, de l'énergie est dissipée. Pour décrire l'énergie de dissipation, on introduit une mesure du mouvement aléatoire des particules comme nouvelle variable intense. Un module cinématique simple de la collision des particules permet d'établir les équations. Ces équations ont des propriétés semblables aux équations de la turbulence. Sous des hypothèses raisonnables, elles prédisent les résultats de Bagnold, à savoir que l'abrasion et la tension normale dépendent du gradient de la vitesse. Pour un flux de granité stable, les profils de flux calculés ressemblent à ceux obtenus expérimentalement.

     

Gravity flow of coarse cohesionless granular materials in conical hoppers

This paper is concerned with the flow of cohesionless granular materials in conical hoppers. The granules are considered to be coarse such that the effects of interstitial fluid can be neglected. Two analytical approaches based upon the method of integral relations are presented. In the first the detailed variations of shear and normal stresses over the cross-section of the hopper are considered. The second is a very simple analysis which makes use of a mean normal stress averaged over the cross-section. The two analyses yield predictions for the flow rate which are almost identical. After the inclusion of an empirical correction factor to account for non-uniform exit velocity profiles and bulk density reductions near the outlet, the flow rate predictions and their variations with internal and wall friction angles and with hopper wall slope are found to agree well with experimental measurements.

---

Résumé Cet article traite de l'écoulement de matières granuleuses sans cohésion dans des trémies coniques. On admet que les granules sont assez gros pour que les effets dûs au fluide intersistiel restent négligeables. 2 méthodes d'approche analytiques basées sur la méthode des relations intégrales sont présentées. La première considère en détail la distribution des contraintes normales et de cisaillement sur la section de la trémie. La seconde méthode est une simple analyse basée sur la moyenne des contraintes normales sur cette section. Les 2 analyses fournissent des prédictions presque identiques sur le taux d'écoulement. En introduisant un facteur de correction empirique pour tenir compte de la non-uniformité de profils de vitesses d'écoulement ainsi que de la réduction de densité à la sortie, l'analyse fournit des taux d'écoulement et leurs variations avec la friction interne, les angles de friction aux parois et l'inclinaison des parois de la trémie. Les résultants obtenus sont en accord avec des mesures expérimentales.

---

---

On leave at the Department of Applied Mathematics and Theoretical Physics, University of Cambridge.     

Analyse numerique des ecoulements quasi-Newtoniens dont la viscosite obeit a la loi puissance ou la loi de carreau

Summary We prove abstract error estimates for the approximation of the velocity and the pressure by a mixed FEM of quasi-Newtonian flows whose viscosity obeys the power law or the Carreau law. These estimates are optimal in some cases. They can be applied to most finite elements used for the solution of Stokes's problem.

---

Analyse numerique des ecoulements quasi-Newtoniens dont la viscosite obeit a la loi puissance ou la loi de carreau

Résumé On prouve des estimations d'erreur abstraites pour l'approximation de la vitesse et la pression par une MEF mixtes d'écoulements quasi-Newtoniens dont la viscosité obéit à la loi puissance ou la loi de Carreau. Ces estimations sont optimales dans certains cas. Elles peuvent être appliquées à la plupart des éléments finis utilisés pour la résolution du problème de Stokes.

     

A hybrid method for calculating vector fields subject to inhomogeneous boundary conditions

Summary A method for calculating vector fields is proposed, which associates the potential method and the finite difference or finite element method. The first is used for satisfying the boundary conditions whereas the second fulfils the local conditions of the vector field considered. In this way, maximum accuracy can be obtained, in most cases, with minimum computation time. An example of flow in a turbine cascade is presented, which demonstrates the efficiency of the method.

---

Résumé Une méthode de calcul des champs de vecteurs est proposée qui associe la méthode des potentiels à la méthode des différences ou des éléments finis. La première est utilisée pour satisfaire les conditions aux limites alors que la seconde sert à tenir compte des conditions locales du champ vectoriel considéré. Cette façon de faire permet d'obtenir, dans la plupart des cas, une précision maximum avec un temps de calcul minimum. Un exemple d'écoulement au travers d'un aubage de turbine est présenté, qui démontre l'efficacité du procédé.

     

Disappearance of criticality in thermal ignition for a simple reactive viscous flow

Conditions for the disappearance of criticality for reactive plane-Poiseuille flow are obtained by means of a perturbation series in the viscous heating parameter; an approximation to the Arrhenius reaction-rate term proposed in this journal by Bazley and Wake is used.

---

Résumé On cherche les conditions pour la disparition de la limite critique pour l'écoulement Poiseuille de réactif entre deux plans en utilisant une série de perturbation de termes d'un paramètre que représente les effets thermiques de la viscosité; nous employons une approximation proposée dans ce journal par Bazley et Wake qui simplifie le terme d'Arrhenius dans l'équation de la balance de chaleur.

     

On the expansion wave problem in a long pipe with wall friction

The method of matched asymptotic expansions is used to study the flow out of a long tube or pipeline caused by a sudden rupture. The flow in the tube generated by the expansion wave propagating into the tube from the break point is shown to be modified substantially by the presence of wall friction. This depends primarily on the fact that, when there is wall friction, the velocity derivative along the tube becomes singular at the broken end exit for all times, as long as the flow is critical at the exit.

---

Résumé Le débit provenant d'un long tube ou d'un pipeline, suite à une rupture subite, a été étudié en employant la méthode des raccordements asymptotiques. On démontre que l'écoulement à l'intérieur du tube, généré par l'onde de détente qui se propage dans le tube à partir du point de rupture, subit une modification importante due au frottement pariétal. Ceci résulte principalement du fait qu'en cas de frottement pariétal, la dérive de vitesse le long du tube, à n'importe quel moment, devient singulière au point de rupture à condition que le débit soit critique à la sortie.