Deterministic Partial Differential Equation Model for Dose Calculation in Electron Radiotherapy

Treatment with high energy ionizing radiation is one of the main methods in modern cancer therapy that is in clinical use. During the last decades, two main approaches to dose calculation were used, Monte Carlo simulations and semi-empirical models based on Fermi-Eyges theory. A third way to dose calculation has only recently attracted attention in the medical physics community. This approach is based on the deterministic kinetic equations of radiative transfer. Starting from these, we derive a macroscopic partial differential equation model for electron transport in tissue. This model involves an angular closure in the phase space. It is exact for the free-streaming and the isotropic regime. We solve it numerically by a newly developed HLLC scheme based on [BerCharDub], that exactly preserves key properties of the analytical solution on the discrete level. Several numerical results for test cases from the medical physics literature are presented.Comment: 20 pages, 7 figure

Ongoing research on advection schemes

Water Qualit

Comparison and Assessment of some Synthetic Jet Models

A synthetic jet is an oscillatory jet, with zero time-averaged mass-flux, used to manipulate boundary layer characteristics for flow control applications such as drag reduction, detachment delay, etc. The objective of this work is the comparison and assessment of some numerical models of synthetic jets, in the framework of compressible flows governed by Reynolds- averaged Navier-Stokes (RANS) equations. More specifically, we consider three geometrical models, ranging from a simple boundary condition, to the account of the jet slot and the computation of the flow in the underlying cavity. From numerical point of view, weak and strong oscillatory boundary conditions are tested. Moreover, a systematic grid and time-step refinement study is carried out. Finally, a comparison of the flows predicted with two turbulence closures (Spalart-Allmaras and Menter SST k − ω models) is achieved

FullSWOF_Paral: Comparison of two parallelization strategies (MPI and SKELGIS) on a software designed for hydrology applications

In this paper, we perform a comparison of two approaches for the parallelization of an existing, free software, FullSWOF 2D (http://www. univ-orleans.fr/mapmo/soft/FullSWOF/ that solves shallow water equations for applications in hydrology) based on a domain decomposition strategy. The first approach is based on the classical MPI library while the second approach uses Parallel Algorithmic Skeletons and more precisely a library named SkelGIS (Skeletons for Geographical Information Systems). The first results presented in this article show that the two approaches are similar in terms of performance and scalability. The two implementation strategies are however very different and we discuss the advantages of each one.Comment: 27 page

Simulating the aerodynamic characteristics of the Land Speed Record vehicle BLOODHOUND SSC

This paper describes the application of a parallel finite-volume compressible Navier–Stokes computational fluid dynamics solver to the complex aerodynamic problem of a land-based supersonic vehicle, BLOODHOUND SSC. This is a complex aerodynamic problem because of the supersonic rolling ground, the rotating wheels and the shock waves in close proximity to the ground. The computational fluid dynamics system is used to develop a mature vehicle design from the initial concept stage, and the major aerodynamic design changes are identified. The paper’s focus, however, is on the predicted aerodynamic behaviour of the finalised (frozen) design which is currently being manufactured. The paper presents a summary of the data bank of predicted aerodynamic behaviours that will be used as the benchmark for vehicle testing and computational fluid dynamics validation throughout 2015 and 2016 in an attempt to achieve a Land Speed Record of 1000 mile/h (approximately Mach 1.3). The computational fluid dynamics predictions indicate that the current design has a benign lift distribution across the whole Mach range of interest and a sufficiently low drag coefficient to achieve this objective. It also indicates that the fin is sized appropriately to achieve the static margin requirements for directional stability. The paper concludes by presenting the impact of feeding the detailed computational fluid dynamics predictions into the overall vehicle performance model together with recommendations for further computational fluid dynamics study

Interface Sharpening in Two-Phase Flows Based on Primitive Sub-Cell Reconstructions

The paper addresses a novel interface-capturing approach for two-phase flows governed by the five-equation diffuse interface model. To suppress the numerical diffusion of the interface, we introduce a primitive sub-cell reconstruction based on volume fractions in neighbouring cells. This reconstruction gives rise to a Riemann problem (CRP) with an additional contact discontinuity, so-called composite Riemann problem, which is stated on mixed cell faces. The CRP solution is used to calculate the numerical flux across cell faces of mixed cells with taking into account the interface reconstructed patterns. A hybrid HLLHLLC method is incorporated to approximate the solution of the CRP. The proposed approach is shown to effectively reduce the interface numerical diffusion without introducing spurious oscillations. Its performance and robustness is examined by 1D and 2D numerical tests

Coupling Local and Global Shape Optimization in Aerodynamic Design

Wing design in aerodynamics requires the definition of global geometrical characteristics, such as span, root/tip length ratio, angle of attack, twist angle, sweep angle, etc, as well as local geometrical features that determine the wing section. The objective of this study is to propose an efficient algorithm to achieve the optimization of both global and local shape parameters. We consider as testcase the drag minimization, under lift constraint, of the wing shape of a business aircraft in transonic regime, the flow being modeled by the compressible Euler equations. We show that a straightforward optimization of all parameters fails, due to multimodality of the optimization problem. Then, some alternative strategies are proposed. Among them, the use of virtual Nash games yields the best results, in terms of cost function value obtained as well as computational efficiency

Mesh adaptation strategies using wall functions and low-Reynolds models

International audienceThe scope of this paper is to determine an optimal mesh adaptation strategy to compute turbulent flows in presence of solid bodies using RANS models. To this end we propose to use additionally model specific wall functions when the low-Reynolds turbulence model is not sufficiently resolved. Such wall functions degenerate to the low-Reynolds turbulence model they mimic when the mesh size tends to 0. This significantly improves solutions on coarse initial grids and fasten computations toward the final solution

Verification and Validation of the k-kL Turbulence Model in FUN3D and CFL3D Codes

The implementation of the k-kL turbulence model using multiple computational uid dy- namics (CFD) codes is reported herein. The k-kL model is a two-equation turbulence model based on Abdol-Hamid's closure and Menter's modi cation to Rotta's two-equation model. Rotta shows that a reliable transport equation can be formed from the turbulent length scale L, and the turbulent kinetic energy k. Rotta's equation is well suited for term-by-term mod- eling and displays useful features compared to other two-equation models. An important di erence is that this formulation leads to the inclusion of higher-order velocity derivatives in the source terms of the scale equations. This can enhance the ability of the Reynolds- averaged Navier-Stokes (RANS) solvers to simulate unsteady ows. The present report documents the formulation of the model as implemented in the CFD codes Fun3D and CFL3D. Methodology, veri cation and validation examples are shown. Attached and sepa- rated ow cases are documented and compared with experimental data. The results show generally very good comparisons with canonical and experimental data, as well as matching results code-to-code. The results from this formulation are similar or better than results using the SST turbulence model