1,720,966 research outputs found
High order semi-implicit schemes for viscous compressible flows in 3D
No full textIn this article we present a high order cell-centered numerical scheme in space and time for the solution of the compressible Navier-Stokes equations. To deal with multiscale phenomena induced by the different speeds of acoustic and material waves, we propose a semi-implicit time discretization which allows the CFL-stability condition to be independent of the fast sound speed, hence improving the efficiency of the solver. This is particularly well suited for applications in the low Mach regime with a rather small fluid velocity, where the governing equations tend to the incompressible model. The momentum equation is inserted into the energy equation yielding an elliptic equation on the pressure. The class of implicit-explicit (IMEX) time integrators is then used to ensure asymptotic preserving properties of the numerical method and to improve time accuracy. High order in space is achieved relying on implicit finite difference and explicit CWENO reconstruction operators, that ultimately lead to a fully quadrature-free scheme. To relax the severe parabolic restriction on the maximum admissible time step related to viscous contributions, a novel implicit discretization of the diffusive terms is designed. A variational approach based on the discontinuous Galerkin (DG) spatial discretization is devised in order to obtain a discrete cell-centered Laplace operator. High order corner gradients of the velocity field are employed in 3D to derive the Laplace discretization, and the resulting viscous system is proven to be symmetric and positive definite. As such, it can be conveniently solved at the aid of the conjugate gradient method. Numerical results confirm the accuracy and the robustness of the novel schemes in the challenging stiff limit of the governing equations characterized by low Mach numbers
An all Froude high order IMEX scheme for the shallow water equations on unstructured Voronoi meshes
No full textWe propose a novel numerical method for the solution of the shallow water equations in different regimes of the Froude number making use of general polygonal meshes. The fluxes of the governing equations are split such that advection and acoustic-gravity sub-systems are derived, hence separating slow and fast phenomena. This splitting allows the nonlinear convective fluxes to be discretized explicitly in time, while retaining an implicit time marching for the acoustic-gravity terms. Consequently, the novel schemes are particularly well suited in the low Froude limit of the model, since no numerical viscosity is added in the implicit solver. Besides, stability follows from a milder CFL condition which is based only on the advection speed and not on the celerity. High order time accuracy is achieved using the family of semi-implicit IMEX Runge-Kutta schemes, while high order in space is granted relying on two discretizations: (i) a cell-centered finite volume (FV) scheme for the nonlinear convective contribution on the polygonal cells; (ii) a staggered discontinuous Galerkin (DG) scheme for the solution of the linear system associated to the implicit discretization of the pressure sub-system. Therefore, three different meshes are used, namely a polygonal Voronoi mesh, a triangular subgrid and a staggered quadrilateral subgrid. The novel schemes are proved to be Asymptotic Preserving (AP), hence a consistent discretization of the limit model is retrieved for vanishing Froude numbers, which is given by the so-called “lake at rest” equations. Furthermore, the novel methods are well-balanced by construction, and this property is also demonstrated. Accuracy and robustness are then validated against a set of benchmark test cases with Froude numbers ranging in the interval Fr≈[10−6;5], hence showing that multiple time scales can be handled by the novel methods
High order Finite Difference/Discontinuous Galerkin schemes for the incompressible Navier-Stokes equations with implicit viscosity
No full textIn this work we propose a novel numerical method for the solution of the incompressible Navier-Stokes equations on Cartesian meshes in 3D. The semi-discrete scheme is based on an explicit discretization of the nonlinear convective flux tensor and an implicit treatment of the pressure gradient and viscous terms. In this way, the momentum equation is formally substituted into the divergence-free constraint, thus obtaining an elliptic equation on the pressure which eventually maintains at the discrete level the involution on the divergence of the velocity field imposed by the governing equations. This makes our method belonging to the class of so-called structure-preserving schemes. High order of accuracy in space is achieved using an efficient CWENO reconstruction operator that is exploited to devise a conservative finite difference scheme for the convective terms. Implicit central finite differences are used to remove the numerical dissipation in the pressure gradient discretization. To avoid the severe time step limitation induced by the viscous eigenvalues related to the parabolic terms in the governing equations, we propose to devise an implicit local discontinuous Galerkin (DG) solver. The resulting viscous sub-system is symmetric and positive definite, therefore it can be efficiently solved at the aid of a matrix-free conjugate gradient method. High order in time is granted by a semi-implicit IMEX time stepping technique. Convergence rates up to third order of accuracy in space and time are proven, and a suite of academic benchmarks is shown in order to demonstrate the robustness and the validity of the novel schemes, especially in the context of high viscosity coefficients
An efficient second order all Mach finite volume solver for the compressible Navier–Stokes equations
No full textIn the numerical simulation of fluid dynamic problems there are situations in which acoustic waves are very fast compared to the average velocity of the fluid and conversely situations in which the fluid moves at high speed and shock waves may be present. Ideally, a numerical method should be able to treat these different regimes without strong limitations in terms of time step and without excessive related computational cost. Unfortunately, standard explicit in time schemes often adopted for hyperbolic problems are not suitable for these problems, hence remedies have to be studied. To this aim, the results presented in this article concern the development of a second order in time and space numerical method for the compressible Navier–Stokes equation which works for both high and low Mach numbers. In particular, when the Mach number goes to zero, one recovers a numerical method for the limit Navier–Stokes system which under some additional hypothesis degenerates to the incompressible Navier–Stokes equations, while in the case of high Mach numbers the method exhibits a shock capturing structure. The idea is based on partitioning the equations into a fast and a slow scale and by taking implicit the fast scale dynamic together with the viscous terms. The resulting numerical scheme is stable for time steps which are independent both from the speed of the pressure waves and from the diffusive terms characterizing the viscous forces and the heat flux. The only time step limitation is induced by the average speed of the flow. The work here presented extends the seminal ideas developed in Dimarco et al. (2017, 2018) for isentropic Euler equations and in Boscheri et al. (2020) for the full set of compressible Euler equations to the multidimensional Navier–Stokes system and permits efficient three dimensional simulations of all Mach problems. The discretization is constructed on Cartesian meshes and the method is second order accurate in space and time. Numerical results show the accuracy, the robustness and the effectiveness of the new proposed approach
Preconditioning of EFIE Matrices when Using Additive High-Order Singular Bases
No full textIntegral equations modeling complex electromagnetic structures are solved numerically using the method of moments and iterative solvers whenever the system matrix is large. Fast-solvers can be used if the system matrix is well conditioned, which only happens by using appropriate formulations, or by re-conditioning the system of equations with algebraic preconditioners. In the case of surface integral equations, well-established techniques exist if the expansion functions are low-order vector polynomials, for example RWG functions. This paper instead considers surface integral equations discretized by additive bases formed by high-order polynomials and singular functions, showing that the electric field integral equation (EFIE) can be successfully solved by using a special general-purpose algebraic preconditione
Social Life Cycle Assessment (S-LCA) implementation in manufacturing companies
No full textSocial Life Cycle Assessment (S-LCA) is a method used to assess both beneficial and detrimental social impacts of products or services throughout their entire life cycle, from raw material extraction to final disposal. The objective of the assessment is to explore strategies to improve the product’s overall social performance. S-LCA considers various social aspects, such as labor conditions, human rights, occupational health and safety (OHS), community engagement, and product accountability. Despite the growing interest in S-LCA, the literature about its implementation in manufacturing companies is fragmented, hindering the identification of key trends. This study aims to fill this gap through a literature review, providing a structured overview of the existing research outcomes and future research directions. To achieve this goal, we followed the steps of the Systematic Literature Review (SLR) approach, conducting the search and selection of relevant studies through the Scopus database, obtaining 150 articles regarding case studies of S-LCA implementation in manufacturing companies. Then, we carried out a descriptive analysis, followed by a scientometric analysis; these include the analysis of journal sources, authors, citations, keywords, and geographic distribution to assess their influences in the domain of S-LCA. The examined case studies reveal a growing focus on S-LCA in the manufacturing industry. A significant observation is the emphasis on “workers,” who are the most examined stakeholders across the various studies. OHS emerged as the predominant subcategory of impact, appearing in majority of the studies that focused on workers. By employing various analysis techniques, this review offers a novel contribution to analyze the existing literature on S-LCA within the manufacturing sector, highlighting the major factors of interest in case studies and future research directions. Future research could focus on the characterization and in-depth analysis of case studies, exploring specific areas of the manufacturing sector in more detail
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
- …
