Comparative study of pressure-correction and Godunov-type schemes on unsteady compressible cases

International audienceTwo pressure-correction algorithms are studied and compared to an approximate Godunov scheme on unsteady compressible cases. The first pressure-correction algorithm sequentially solves the equations for momentum, mass and enthalpy, with sub-iterations which ensure conservativity. The algorithm also conserves the total enthalpy along a streamline, in a steady flow. The second pressure-correction algorithm sequentially solves the equations for mass, momentum and energy without sub-iteration. This scheme is conservative and ensures the discrete positivity of the density. Total enthalpy is conserved along a streamline, in a steady flow. It is numerically verified that both pressure-correction algorithms converge towards the exact solution of Riemann problems, including shock waves, rarefaction waves and contact discontinuities. To achieve this, conservativity is compulsory. The two pressure-correction algorithms and the approximate Godunov scheme are finally compared on cases with heat source terms: all schemes converge towards the same solution as the mesh is refined

Dike-break induced flows: a simplified model

A simplified model for the prediction of the steady-state outflow through a breach in an inland dike is presented. It consists in the application of the mass and momentum conservation principles to a macroscopic control volume. A proper definition of the shape of the control volume enables to take into account the main characteristics of the flow and thus to compensate for the extreme simplification of the space discretisation of the model. At the breach, a relation derived from the shallow-water equations is used to determine the directions of the flow. Developments have been guided by numerical simulations and results have been compared to experimental data. Both the precision and the application domain of the simplified model are found satisfactory

Flow at an Ogee Crest Axis for a Wide Range of Head Ratios: Theoretical Model

peer reviewedThe discharge coefficient of an ogee crest is a function of the ratio of the effective head to the design head. The purpose of the present study is to derive a theoretical model of this relation, which does not depend on empirical coefficients and whose predictions over a wide range of head ratios are accurate enough for practical use. The developments consider unsubmerged ogee crests without approach flow or lateral contraction effects, heads large enough to enable surface tensions to be neglected, and heads small enough to avoid flow separation. The method is based on potential flow theory, depth integration in a curvilinear reference frame, and critical flow theory. The characteristics of the crest shape are defined by the trajectory of a free jet passing over the crest at the design head. The dimensionless equations show that the position of the critical section is not at the apex of the crest. Nevertheless, they also suggest an approximate equation at the apex of the crest from which the discharge coefficient is derived, together with the local water depth, velocity, and pressure distribution. The results compare well with experimental data for head ratios between 0 and 5, which validates the underlying assumptions of the theoretical model.11. Sustainable cities and communitie

A Data Mining Analysis Applied to a Straightening Process Database

peer reviewedThe complexity of modern manufacturing processes in a highly competitive environment forces the manufacturers to invest massively in automation and monitoring systems. The large data flows from these new installations are sources of valuable and hidden knowledge that is so far hardly used. Data mining methods through integrated data analysis tools give a solution to this situation, allowing easy retrieval of knowledge starting from a data base. This is also a unique opportunity to learn faster about the process and to detect hidden and complex relationships between parameters involved. Within this framework we have decided to apply this data analysis method to the straightening process in shipbuilding. We refer to Caprace et al. (2007) for additional illustrations. In shipbuilding, the assembly of elements by welding involves temperature gradients within the ma- terial. These cause deformations which sometimes have to be reduced to obtain an acceptable surface flatness. The straightening process to eliminate these distortions for esthetical or functional reasons is labour intensive. Estimating the straightening impact on the production workload is interesting in the context of production simulation, cost assessment of ship hull, structure optimization, design for production, etc. To reach these objectives, the idea was to elaborate, through a data mining approach, a formula linking the straightening cost to the sections scantlings (plate thickness, dimension and inter-distance of longitudinal stiffeners, dimension and inter-distance of transversal frames) and to other section characteristics. This paper describes each stage of the methodology: data description, analysis of data quality, data exploration and finally choice of discriminatory attributes and the generation of the data-driven models.InterSHI

Code Saturne: A Finite Volume Code for the computation of turbulent incompressible flows - Industrial Applications

International audienceThis paper describes the finite volume method implemented in Code Saturne, Electricite de France general-purpose computational fluid dynamic code for laminar and turbulent flows in complex two and three- dimensional geometries. The code is used for industrial applications and research activities in several fields related to energy production (nuclear power thermal-hydraulics, gas and coal combustion, turbomachinery, heating, ventilation and air conditioning...). The set of equations considered consists of the Navier-Stokes equations for incompressible flows completed with equations for turbulence modelling (eddy-viscosity model and second moment closure) and for additional scalars (temperature, enthalpy, concentration of species, ...).The time-marching scheme is based on a prediction of velocity followed by a pressure correction step. Equations for turbulence and scalars are resolved separately afterwards. The discretization in space is based on the fully conservative, unstructured fi nite volume framework, with a fully colocated arrangement for all variables. Specic effort has been put into the computation of gradients at cell centres. Industrial applications illustrate important aspects of physical modelling such as turbulence (using Reynolds-Averaged Navier-Stokes equations or Large Eddy Simulation), combustion, conjugate heat transfer (coupled with the thermal code SYRTHES ) and fluid-particle coupling with a lagrangian approach. These examples also demonstrate the capability of the code to tackle a large variety of meshes and cell geometries, including hybrid meshes with arbitrary interfaces

Impacts of climate change on future flood damage on the river Meuse, with a distributed uncertainty analysis

peer reviewedFlood-risk assessments are an objective and quantitative basis for implementing harmonized flood mitigation policies at the basin scale. However, the generated results are subject to different sources of uncertainty arising from underlying assumptions, data availability and the random nature of the phenomenon. These sources of uncertainty are likely to bias conclusions because they are irregularly distributed in space. Therefore, this paper addresses the question of the influence of local features on the expected annual damage in different municipalities. Based on results generated in the frame of a transnational flood-risk-assessment project for the river Meuse (Western Europe) taking climate change into account, the paper presents an analysis of the relative contributions of different sources of uncertainty within one single administrative region (the Walloon region in Belgium, i.e. a river reach of approximately 150 km). The main sources of uncertainty are not only found to vary both from one municipality to the other and in time, but also to induce opposite effects on the computed damage. Nevertheless, practical conclusions for policy-makers can still be drawn

Depth-averaged flow modeling in curvilinear coordinates

A set of depth-averaged equations in curvilinear coordinates is presented. This extension of the standard shallow water equations to curved flows and to jet flows leads to a model which is very versatile. Its applicability and precision is assessed by the computation of a discharge coefficient and the nappe profiles for a sharp crested weir. Results confirm the relevance of the approach. Even if not taken into consideration in the set of equations presented here, a discussion shows that head losses could be included in the model so as to extend its application field to many civil and environmental engineering applications