Abstract. We construct a new first order central-upwind numerical method for solving systems of hyperbolic equations in conservative form. It applies in multidimensional structured and unstructured meshes. The proposed method is an... more
Abstract. We construct a new first order central-upwind numerical method for solving systems of hyperbolic equations in conservative form. It applies in multidimensional structured and unstructured meshes. The proposed method is an extension of the UFORCE method developed by Stecca, Siviglia and Toro,[25] in which the upwind bias for the modification of the staggered mesh is evaluated taking into account the smallest and largest wave of the entire Riemann fan. The proposed first-order method is shown to be identical ...
Hydropower operations result in sharp water level and temperature fluctuations downstream the river section where water is released intermittently according to the pattern of hydropower generation. It has been widely recognized that these... more
Hydropower operations result in sharp water level and temperature fluctuations downstream the river section where water is released intermittently according to the pattern of hydropower generation. It has been widely recognized that these peaking flows cause severe degradation of the affected river reaches, but their biological effects and hydraulic behaviour have been studied mainly referring to the main channel. Field evidence (Sawyer et al., 2009, Loheide & Lundqvist, 2009) demonstrate that surface water level oscillations ...
ABSTRACT The morphodynamics of channelized river reaches is characterized by both steady and migrating bars. Steady bars are typically forced by planform non-uniformities, like localized discontinuities in channel curvature and/or width,... more
ABSTRACT The morphodynamics of channelized river reaches is characterized by both steady and migrating bars. Steady bars are typically forced by planform non-uniformities, like localized discontinuities in channel curvature and/or width, or the presence of a bifurcation. On the contrary migrating bars result from an inherent free instability mechanism of the flow - erodible bed system and freely develop in straight channels. Several analytical theories have been developed to separately predict asymptotic properties of both steady and migrating bars in straight reaches, based on perturbation solution of the governing morphodynamic equations. As also indicated by experimental evidence, instantaneous bed configurations result from a dynamic interaction between steady (forced) and migrating (free) bars. However, available theories for bars in straight channels separately focus on the two types of bars and their mutual interaction is an unsettled issue yet. The goal of the present study is to improve the present understanding of the interaction between steady and migrating bars in straight channels. To this purpose we employ an integrated approach whereby different sets of numerical runs are planned according to the outcomes of existing analytical theories for steady and migrating bars. The newly developed 2D fully coupled numerical model solves in the same time step both hydrodynamics and morphodynamics. The model works on unstructured grids, uses a centred finite volume numerical method extended to second order via a TVD approach and is well-balanced. Results provide a comprehensive picture of the interaction dynamics. The fundamental wavelength difference between steady and migrating bars allows to detect the dominant bar type under different morphodynamic conditions. Namely the development of steady bars under both sub- and super-resonant conditions is correctly reproduced, and the asymptotic trend in bed evolution is assessed. Outcomes from morphodynamic modelling is tested against field data on the temporal bar dynamics of a morphologically regulated reach of the Rhine River in Switzerland.
ABSTRACT In this paper we develop numerical fluxes of the centred type for one-step schemes in conservative form for solving general systems of conservation laws in two space dimensions on unstructured meshes. The proposed flux is an... more
ABSTRACT In this paper we develop numerical fluxes of the centred type for one-step schemes in conservative form for solving general systems of conservation laws in two space dimensions on unstructured meshes. The proposed flux is an extension of the multi-...
A three-parameter corresponding states model is proposed for the prediction of speed of sound surfaces of pure fluids and mixtures belonging to a homogeneous family of fluids as the halogenated alkanes. A preliminary conformality study is... more
A three-parameter corresponding states model is proposed for the prediction of speed of sound surfaces of pure fluids and mixtures belonging to a homogeneous family of fluids as the halogenated alkanes. A preliminary conformality study is developed confirming the high potentiality of the corresponding states methods when applied within a property-dependent framework. A procedure that separately models the ideal-gas part
A three-parameter corresponding states (CS) model is proposed here for the prediction of the saturated liquid density of pure fluids pertaining to the two conformal families of halogenated alkanes and hydrofluoroethers (HFE), most of... more
A three-parameter corresponding states (CS) model is proposed here for the prediction of the saturated liquid density of pure fluids pertaining to the two conformal families of halogenated alkanes and hydrofluoroethers (HFE), most of which are either already used or proposed for use as refrigerants.Two fluids from each family were chosen for their acentric factor value and the availability of dedicated saturated liquid density equations and at first, on the basis of the three-parameter CS model by Teja et al., the saturated liquid density of a given fluid was obtained in reduced variables. Assuming experimental saturated liquid density data for several components of each of the two families of fluids, an improvement was then introduced, substituting the acentric factor with a new constant scaling factor. As a final result, the proposed liquid model has a predictive nature.The prediction accuracy reached by this new method is similar to that of the dedicated equations, where available, for all the fluids in a family. The result is particularly satisfactory for application requirements in refrigeration.
Historical models with gE-EoS mixing rules, which combine a cubic equation of state (EoS) requiring only the three parameters Tc, Pc and ω as individual inputs with a gE model for the liquid phase, are only applied to the saturation... more
Historical models with gE-EoS mixing rules, which combine a cubic equation of state (EoS) requiring only the three parameters Tc, Pc and ω as individual inputs with a gE model for the liquid phase, are only applied to the saturation surfaces. A limitation of this rule is basically the number of parameters of the one-fluid EoS considered, which cannot exceed
A three parameters density model based on Corresponding States (CS) technique is proposed as a means of predicting the density of pure fluids and their mixtures on the entire PρT (PρTx) surface. The studied fluids belong to two conformal... more
A three parameters density model based on Corresponding States (CS) technique is proposed as a means of predicting the density of pure fluids and their mixtures on the entire PρT (PρTx) surface. The studied fluids belong to two conformal families of the new refrigerant fluids generation: the halogenated alkanes (HA) and the hydrofluoroethers (HFE). The new model is based on an original scaling factor parameter that is determined only on a saturated liquid density experimental value. Using two accurate dedicated equations of state (EoS) as references, the same structure of the Teja CS model is maintained, substituting the classical acentric factor with the new defined scaling parameter. Through this model, the density of the refrigerant fluids considered can be calculated on the whole surface with an accuracy level similar to that of the dedicated equations. The model is validated against experimental data for HFC refrigerants including fluoropropanes, fluorobutanes and fluoroethers. A comparison is also proposed with available density models regarded of high accuracy level.
In this work an original improvement of the Corresponding States technique is developed and a new model, based on a three parameters CS format, is proposed to predict the enthalpy and the entropy of the new generation halogenated alkanes... more
In this work an original improvement of the Corresponding States technique is developed and a new model, based on a three parameters CS format, is proposed to predict the enthalpy and the entropy of the new generation halogenated alkanes fluids together with some alkanes. Limiting the analysis of the selected fluids to a specific thermodynamic property behaviour, an appropriate conformality
