8 research outputs found
From Mesh to Meshless : a Generalized Meshless Formulation Based on Riemann Solvers for Computational Fluid Dynamics
Programa Oficial de Doutoramento en Enxeñaría Civil . 5011V01[Abstract]
From mesh to meshless: A generalized meshless formulation based on Riemann
solvers for Computational Fluid Dynamics
This thesis deals with the development of high accuracy meshless methods for the simulation
of compressible and incompressible flows. Meshless methods were conceived to
overcome the constraints that mesh topology impose on traditional mesh-based numerical
methods. Despite the fact that meshless methods have achieved a relative success
in some particular applications, the truth is that mesh-based methods are still the
preferred choice to compute flows that demand high-accuracy. Instead of assuming
that meshless and mesh-based methods are groups of methods that follow independent
development paths, in this thesis it is proposed to increase the accuracy of meshless
methods by taking guidance of some successful techniques adopted in the mesh-based
community.
The starting point for the development is inspired by the SPH-ALE scheme proposed
by Vila. Especially, the flexibility of the ALE framework and the introduction
of Riemann solvers are essential elements adopted. High accuracy is obtained by using
the Moving Least Squares (MLS) technique. MLS serves multiple tasks in the implemented
scheme: high order reconstruction of Riemann states, more accurate viscous
flux evaluation and the replacement of the limited kernel approximation by MLS approximation
with polynomial degree consistency by design. The stabilization of the
scheme for compressible flows with discontinuities is based on a posteriori stabilization
technique (MOOD) that introduces a great improvement compared with the traditional
a priori flux limiters.
The MLSPH-ALE scheme is the first proposed meshless formulation that uses high
order consistent MLS approximation in a versatile ALE framework. In addition, the
procedure to obtain the semi-discrete formulation keeps track of a boundary term,
which eases the implementation of the boundary conditions.
Another important contribution is related with the general concept of the MLSPHALE
formulation. The MLSPH-ALE scheme is proved to be a global meshless formulation
that under some particular settings provides the same semi-discrete equations
that other meshless formulations published.
The MLSPH-ALE scheme has been tested for the computation of turbulent flows.
The low dissipation inherent to the Riemann solver is compatible with the implicit LES turbulent model. The proposed formulation is able to capture the energy cascade in
the subsonic regime where traditional SPH formulations are reported to fail.[Resumen]
Desde métodos con malla a métodos sin malla: Una formulación sin malla
generalizada basada en solvers de Riemann para Dinámica de Fluidos
Computacional
Esta tesis aborda el desarrollo de métodos sin malla de alta precisión para la simulación
de flujos compresibles e incompresibles. Los métodos sin malla fueron creados
para superar las restricciones que la conectividad de la malla impone a los métodos
tradicionales. A pesar de haber alcanzado un ´éxito relativo en algunas aplicaciones, la
realidad es que los métodos con malla siguen siendo la opción preferida para el cálculo
de flujos que demandan alta precisión. En vez de asumir que métodos sin malla y con
malla son grupos de métodos que siguen caminos de desarrollo independientes, en esta
tesis se propone incrementar la precisión de los métodos sin malla tomando como guía
algunas de las técnicas más exitosas empleadas en la comunidad de los métodos con
malla.
El punto de partida para el desarrollo se inspira en el esquema SPH-ALE propuesto
por Vila. De manera especial, la flexibilidad del marco de referencia ALE y la introducción
de los solvers de Riemann son elementos esenciales adoptados. La alta precisión
se obtiene con la técnica de Mínimos Cuadrados Móviles (MLS). MLS sirve múltiples
funciones en la implementación del esquema: alto orden de reconstrucción de los estados
de Riemann, evaluaciones más precisas de los flujos viscosos y reemplazo de la
aproximación limitada tipo kernel por una aproximación MLS con un grado de consistencia
polinómica arbitraria. La estabilización del esquema para flujos compresibles
con discontinuidades se basa en una técnica de estabilización a posteriori (MOOD) que
introduce una importante mejora con respecto a los tradicionales limitadores de flujo
a priori.
El esquema MLSPH-ALE es la primera formulación sin malla propuesta que utiliza
la aproximación MLS de alto orden en un marco de referencia ALE. Además, el procedimiento
dado para obtener la forma semi-discreta realiza el seguimiento de un término
en la frontera del dominio que facilita la implementación discreta de las condiciones de
contorno.
Otra importante contribución está relacionada con el concepto general de la formulación MLSPH-ALE. Se ha demostrado que el esquema MLSPH-ALE es una formulación sin malla global que con ciertas configuraciones particulares es capaz de proporcionar
las mismas formas semi-discretas que otras formulaciones publicadas.
El método MLSPH-ALE ha sido puesto a prueba frente al cálculo de flujos turbulentos.
La baja disipación inherente a los solver de Riemann hace que el esquema sea
apto para modelar la turbulencia en un contexto de modelos implícitos LES. La formulación propuesta es capaz de capturar la cascada de energía en el rango de régimen
subsónico donde los métodos tradicionales presentan fallos.[Resumo]
Desde métodos con malla a métodos sen malla: Unha formulación sen malla
xeneralizada baseada en solvers de Riemann para Dinámica de Fluidos
Computacional.
Esta tese trata sobre o desenvolvemento de métodos sen malla de alta precisión para a
simulación de fluxos compresibles e incompresibles. Os métodos sen malla foron creados
para superar as restricións que a conectividade da malla impón sobre os métodos
tradicionais. A pesar de ter acadado un éxito relativo nalgunhas aplicacións, a realidade
é que os métodos con malla seguen sendo a opción preferente para o cálculo de
fluxos que demandan alta precisión. No canto de asumir que os métodos sen malla
e con malla son grupos que seguen camiños de desenvolvemento independentes, nesta
tese proponse incrementar a precisión dos métodos sen malla tomando como guía
algunha das técnicas de máis éxito empregadas na comunidade dos métodos con malla.
O punto de partida para o desenvolvemento inspírase no esquema SPH-ALE proposto
por Vila. A flexibilidade do marco de referencia ALE e a introducción dos solvers
de Riemann son os elementos esenciais utilizados nesta tese. A alta precisión acádase
coa técnica de Mínimos Cadrados Móbiles (MLS). MLS serve para múltiples tarefas
na implementación do esquema: acadar alto orde de reconstrución nos estados de Riemann,
avaliacións máis precisas dos fluxos viscosos e troco da aproximación limitada
tipo kernel por unha aproximación MLS con grado de consistencia polinómica arbitraria.
A estabilización do esquema para fluxos compresibles con descontinuidades baséase
nunha técnica de estabilización a posteriori (MOOD) que introduce unha importante
mellora con respecto a os tradicionais limitadores de fluxo a priori.
O esquema MLSPH-ALE ´e a primeira formulación sen malla proposta que emprega
a técnica de aproximación MLS con alta consistencia nun marco de referencia ALE.
Ademais, o procedemento seguido para obter a forma semi-discreta realiza o seguimento
dun termo na fronteira que facilita a implementación das condicións de contorno.
Outra importante contribución relacionase co concepto xeral da formulación MLSPHALE
proposta. Demostrase que o esquema MLSPH-ALE é unha formulación sen malla
global que con certas configuración particulares rende as mesmas formas semi-discretas
que outras formulacións publicadas.
O método MLSPH-ALE foi posto a proba fronte o cálculo de fluxos turbulentos. A
baixa disipación implícita aportada polo solver de Riemann fai que o esquema sexa apto
para acometer o modelado da turbulencia cos modelos implícitos LES. A formulación
proposta captura a cascada de enerxía no rango de réxime subsónico, onde os métodos
tradicionais SPH presentan deficiencias.This work has been partially supported by the Ministerio de Ciencia, Innovación
y Universidades (RTI2018-093366-B-100) of the Spanish Government and by the Consellería de Educación e Ordenación Universitaria of the Xunta de Galicia, cofinanced
with FEDER funds and the Universidade da Coruña
An Arbitrary Lagrangian-Eulerian SPH-MLS Method for the Computation of Compressible Viscous Flows
Financiado para publicación en acceso aberto: Universidade da Coruña/CISUG[Abstract] In this work we present a high-accurate discretization to solve the compressible Navier-Stokes equations using an Arbitrary Lagrangian-Eulerian meshless method (SPH-MLS), which can be seen as a general formulation that includes some well-known meshfree methods as a particular case. The formulation is based on the use of Moving Least Squares (MLS) approximants as weight functions on a Galerkin formulation and to accurate discretize the convective and viscous fluxes. This formulation also verifies the discrete partition of unity and reproduces the zero-gradient condition for constant functions. Convective fluxes are discretized using Riemann solvers. In order to obtain high accuracy MLS is also used for the high-order reconstruction of the Riemann states. The accuracy and performance of the proposed method is demonstrated by solving different steady and unsteady benchmark problems.This work has been partially supported by Ministerio de Ciencia, Innovación y Universidades of the Spanish Government (grant #RTI2018-093366-B-I00) and by the Consellería de Educación e Ordenación Universitaria of the Xunta de Galicia (grant# ED431C 2018/41), cofinanced with FEDER funds of the European Union. Luis Ramírez also acknowledges the funding provided by the Xunta de Galicia through the program Axudas para a mellora, creación, recoñecemento e estruturación de agrupacións estratéxicas do Sistema universitario de Galicia (reference # ED431E 2018/11)Xunta de Galicia; ED431C 2018/41Xunta de Galicia; ED431E 2018/1
SPH-ALE Scheme for Weakly Compressible Viscous Flow with a Posteriori Stabilization
[Abstract] A highly accurate SPH method with a new stabilization paradigm has been introduced by the authors in a recent paper aimed to solve Euler equations for ideal gases. We present here the extension of the method to viscous incompressible flow. Incompressibility is tackled assuming a weakly compressible approach. The method adopts the SPH-ALE framework and improves accuracy by taking high-order variable reconstruction of the Riemann states at the midpoints between interacting particles. The moving least squares technique is used to estimate the derivatives required for the Taylor approximations for convective fluxes, and also provides the derivatives needed to discretize the viscous flux terms. Stability is preserved by implementing the a posteriori Multi-dimensional Optimal Order Detection (MOOD) method procedure thus avoiding the utilization of any slope/flux limiter or artificial viscosity. The capabilities of the method are illustrated by solving one- and two-dimensional Riemann problems and benchmark cases. The proposed methodology shows improvements in accuracy in the Riemann problems and does not require any parameter calibration. In addition, the method is extended to the solution of viscous flow and results are validated with the analytical Taylor–Green, Couette and Poiseuille flows, and lid-driven cavity test cases.This research was funded by Ministerio de Ciencia, Innovación y Universidades of the Spanish Government Grant #RTI2018-093366-B-I00, by the Consellería de Educación e Ordenación Universitaria of the Xunta de Galicia (grant#ED431C 2018/41)Xunta de Galicia; ED431C 2018/4
MLS-SPH-ALE: A Review of Meshless-FV Methods and a Unifying Formulation for Particle Discretizations
Open Access funding provided thanks to the CRUE-CSIC agreement with Springer Nature.[Abstract:] Mesh-based and particle methods were conceived as two different discretization strategies to solve partial differential equations. In the last two decades computational methods have diversified and a myriad of hybrid formulations that combine elements of these two approaches have been developed to solve Computational fluid dynamics problems. In this work we present a review about the meshless-FV family of methods, an analysis is carried out showing that the MLS-SPH-ALE method can be considered as a general formulation from which a set of particle-based methods can be recovered. Moreover, we show the relations between the MLS-SPH-ALE method and the finite volume method. The MLS-SPH-ALE method is a versatile particle-based method that was developed to circumvent the consistency issues of particle methods caused by the use of the kernel approximation. The MLS-SPH-ALE method is developed from the differential equation in ALE form using the partition unity property which is automatically fulfilled by the Moving Least Squares approximation.The authors gratefully acknowledge the support provided by the [Grant PID2021-125447OB-I00] funded by MCIN/AEI/ 10.13039/501100011033 and by “ERDF A way of making Europe”, and the funds by [Grant TED2021–129805B-I00] funded by MCIN/AEI/ 10.13039/501100011033 and by the “European Union NextGenerationEU/PRTR”. They also acknowledge the funding provided by the Xunta de Galicia (Grant #ED431C 2022/06). J. Fernández-Fidalgo acknowledges the support provided by “Ayudas para la recualificación del sistema universitario español para 2021–2023. Modalidad Margarita Salas RSU.UDC.MS20" by the Ministerio de Universidades of the Spanish Government and European Union through the NextGenerationEU funds.Xunta de Galicia; ED431C 2022/0
Evolutionary Analyses of Entire Genomes Do Not Support the Association of mtDNA Mutations with Ras/MAPK Pathway Syndromes
BACKGROUND: There are several known autosomal genes responsible for Ras/MAPK pathway syndromes, including Noonan syndrome (NS) and related disorders (such as LEOPARD, neurofibromatosis type 1), although mutations of these genes do not explain all cases. Due to the important role played by the mitochondrion in the energetic metabolism of cardiac muscle, it was recently proposed that variation in the mitochondrial DNA (mtDNA) genome could be a risk factor in the Noonan phenotype and in hypertrophic cardiomyopathy (HCM), which is a common clinical feature in Ras/MAPK pathway syndromes. In order to test these hypotheses, we sequenced entire mtDNA genomes in the largest series of patients suffering from Ras/MAPK pathway syndromes analyzed to date (n = 45), most of them classified as NS patients (n = 42). METHODS/PRINCIPAL FINDINGS: The results indicate that the observed mtDNA lineages were mostly of European ancestry, reproducing in a nutshell the expected haplogroup (hg) patterns of a typical Iberian dataset (including hgs H, T, J, and U). Three new branches of the mtDNA phylogeny (H1j1, U5b1e, and L2a5) are described for the first time, but none of these are likely to be related to NS or Ras/MAPK pathway syndromes when observed under an evolutionary perspective. Patterns of variation in tRNA and protein genes, as well as redundant, private and heteroplasmic variants, in the mtDNA genomes of patients were as expected when compared with the patterns inferred from a worldwide mtDNA phylogeny based on more than 8700 entire genomes. Moreover, most of the mtDNA variants found in patients had already been reported in healthy individuals and constitute common polymorphisms in human population groups. CONCLUSIONS/SIGNIFICANCE: As a whole, the observed mtDNA genome variation in the NS patients was difficult to reconcile with previous findings that indicated a pathogenic role of mtDNA variants in NS
Experimental evaluation of the critical local wall shear stress around cylindrical probes fouled by diesel exhaust gases
The problem of fouling in the heat exchangers of exhaust systems has yet to be resolved. This results in enormous costs for engine manufacturers due to the required over-sizing during design and due to unscheduled maintenance needs. This article presents an experimental layout developed for measuring fouling in diesel engine exhaust gas systems. This facility was based on a circular cylindrical cross-flow device, with one straight and smooth stainless steel probe positioned transverse to the flow of exhaust gases. The probe can be cooled from the inside with water and fouled on the outside as a result of particle deposition from exhaust gases. The tests were conducted under constant engine operating conditions. Therefore, the asymptotic depth of the fouling layer could be measured at different angular positions at the end of each test. The critical wall shear stress rate is proposed as the controlling mechanism of the local removal process that leads to different fouling depths around each probe. This is in contrast to the critical velocity concept, which cannot be applied at a local scale due to its formulation. The experimental results, although subject to the usual uncertainties of fouling processes, seem to support this idea