40,787 research outputs found
Considerazioni sulle differenze intercorrenti tra concessione di servizio pubblico e appalto di servizi
No full textA high-order discontinuous Galerkin method for natural convection problems
No full textDiscontinuous Galerkin (DG) methods have proved to be very well suited for the construction of robust high-order numerical schemes on unstructured and possibly non conforming grids for a wide variety of problems. In this paper we consider natural convection flow problems and present a high-order DG method for their numerical solution. The governing equations are the incompressible Navier-Stokes (INS) with the Boussinesq approximation to represent buoyancy effects and the energy equation to describe the temperature field. The method here presented is an extension to natural convection flows of a novel high-order DG method for the numerical solution of the INS quations, recently proposed in [1]. The distinguishing feature of this method is the formulation of the inviscid interface flux which is based on the solution of local Riemann problems associated with the artificial compressibility perturbation of the incompressible Euler equations. The discretization of the viscous term follows the well established DG scheme named BR2 [2, 3]. The method is fully implicit and the solution is advanced in time using either a first order backward Euler or a second order Runge-Kutta scheme. To assess the capabilities of the DG method developed in this paper we computed second-, third-and fourth-order space-accurate solutions of several benchmark problems on natural convection in two-dimensional cavities
High-order accurate p-multigrid discontinuous Galerkin solution of the Euler equations
No full textDiscontinuous Galerkin (DG) methods have proven to be perfectly suited for the construction of very highorder accurate numerical schemes on arbitrary unstructured and possibly nonconforming grids for a wide
variety of applications, but are rather demanding in terms of computational resources. In order to improve
the computational efficiency of this class of methods a p-multigrid solution strategy has been developed,
which is based on a semi-implicit Runge–Kutta smoother for high-order polynomial approximations and
the implicit Backward Euler smoother for piecewise constant approximations. The effectiveness of the
proposed approach is demonstrated by comparison with p-multigrid schemes employing purely explicit
smoothing operators for several 2D inviscid test cases
DG P-Multigrid. Efficient Solvers and Complex Applications
No full textThese lecture notes will focus on some efficiency-related topics relevant to an effective implementation of the p-multigrid technique, presented in the lecture notes “p-Multigrid For Discontinuous Galerkin Methods”, in a high-order DG method.
Actually, the underlying building blocks of the p-multigrid solver are those of an implicit DG code, named MIGALE, developed over the past years and more recently within the ADIGMA project. The code solves the Euler, Navier-Stokes and the coupled RANS and k-! turbulence model equations. The implicit implementation of the DG method is based on the exact linearization of residuals and on linearly implicit Runge-Kutta schemes for time integration. All the boundary conditions are also implemented implicitly.
Based on the framework of the implicit code, the matrix blocks of the semi-implicit p-multigrid solver are nothing but the matrix blocks of the implicit scheme local to the elements, i.e., the diagonal blocks. On the other hand, the backward Euler smoother employed at the lowest degree of the p-multigrid algorithm is exactly the same used by the implicit solver.
These notes summarize recent results of numerical investigation on how to improve the efficiency of our DG implementation, with special attention to benefits for the p-multigrid approach. For example, the polynomial approximations based on nodal collocation presented in the following should be particularly effective if coupled with the p-multigrid technique. The notes present also new advancements and results of closer investigations on efficiency of the implicit, high-order DG method, which are expected to be important for the p-multigrid and that will serve for assessing its efficiency.
The current capability of the implicit DG approach will be demonstrated by presenting some recent results of high-order turbulent flow computations of fairly complex test cases proposed within the ADIGMA project
Bitterness inheritance in apricot (P. armeniaca L.) seeds
No full textSeed bitterness, due to cyanogenic glucosides, has been reported in apricot as a recessive trait, being determined by a single gene. In this study, 21 F1 and 10 F2 populations from parents with either bitter or non-bitter ('sweet') phenotype were tested by seed tasting. Both the 'bitter' and the 'sweet' phenotypes were represented in populations from 'bitter x bitter' and 'sweet x sweet' crosses, as well as from self-pollination of either bitter- or sweet-seeded trees, providing evidence that more than one gene is involved in this trait. Ten populations showed segregation ratios inconsistent with a monofactorial inheritance of seed taste with the 'sweet' trait dominant over the 'bitter'. On the other hand, data from spectrophotometric assays indicate that seed cyanoglucoside content cannot be regarded as a quantitative trait. All the observed segregation ratios can be explained by an inheritance mechanism based on five, non-linked genes, involved in two distinct biochemical pathways. Three genes would control different steps in an 'additive' pathway (either the biosynthesis of cyanoglucosides, or their transport, or both) leading to accumulation of these metabolites in seeds: homozygosis of recessive alleles of at least one of them would result in the sweet phenotype. Two more genes would provide a cleaving activity, participating to cyanoglucoside catabolism; heterozygosis or homozygosis of dominant alleles at these loci would produce the 'sweet' phenotype, while homozygosis for recessive alleles of at least one of them would interrupt the catabolic pathway, leading to the 'bitter' trait, if associated with the anabolic function
An implicit high-order discontinuous Galerkin method for steady and unsteady incompressible flows
No full textThis paper presents the latest developments of a discontinuous Galerkin (DG) method for incompressible flows introduced in [Bassi F, Crivellini A, Di Pietro DA, Rebay S. An artificial compressibility flux for the discontinuous Galerkin solution of the incompressible Navier–Stokes equations. J Comput Phys 2006;218(2):794–815] for the steady Navier-Stokes equations and extended in [Bassi F., Crivellini A. A high-order discontinuous Galerkin method for natural convection problems. In: Wesseling P, Oñate E, Periaux J, editors. Electronic proceedings of the ECCOMAS CFD 2006 conference, Egmond aan Zee, The Netherlands, September 5–8; 2006. TU Delft] to
the coupled Navier–Stokes and energy equations governing natural convection flows. The method is fully implicit and applies to the governing equations in primitive variable form. Its distinguishing feature is the formulation of the inviscid interface flux, which is based on the solution of local Riemann problems associated with the artificial compressibility perturbation of the Euler equations. The tight coupling between pressure and velocity so introduced stabilizes the method and allows using equal-order approximation spaces for both pressure and velocity. Since, independently of the amount of artificial compressibility added, the interface flux reduces to the physical one for vanishing interface jumps, the resulting method is strongly consistent. In this paper, we present a review of the method together with two recently developed issues: (i) the high-order DG discretization of
the incompressible Euler equations; (ii) the high-order implicit time integration of unsteady flows. The accuracy and versatility of the method are demonstrated by a suite of computations of steady and unsteady, inviscid and viscous incompressible flows
Xanthophyll cycle pigments in wild type Arabidopsis and in aba mutants blocked in zeaxanthin epoxidation
No full textTBC and PML conditions for 2D and 3D BPM: a comparison
No full textAny implementation of the beam propagation method, when used to analyse open problems, requires a procedure allowing radiation to leave the computational window. In this paper we present the results of a case study on the effectiveness of the classical Hadley's Transparent Boundary Conditions (TBC) and the Perfectly Matched Layer (PML) to handle strong radiation at the boundaries. A polished fibre coupler will be studied both in 2D and in 3D configurations using, in the former case, a scalar method and, in the latter, a full vectorial approach. Numerical results show that simple TBC can be used in 2D simulations also when high radiation occurs but they easily fail in 3D structures. Therefore, in these cases, the more complicated PML conditions should be preferred
Amount of DNA complementary to ribosomal RNA in polyploid series of Scilla autumnalis L. and Urginea maritima (L.) Baker.
No full text- …
