29 research outputs found
Prediction of energy dissipation in violent sloshing flows simulated by Smoothed Particle Hydrodynamics
Prediction of energy dissipation in violent sloshing flows simulated by Smoothed Particle Hydrodynamic
Towards a Mini-App for Smoothed Particle Hydrodynamics at Exascale
The smoothed particle hydrodynamics (SPH) technique is a purely Lagrangian
method, used in numerical simulations of fluids in astrophysics and
computational fluid dynamics, among many other fields. SPH simulations with
detailed physics represent computationally-demanding calculations. The
parallelization of SPH codes is not trivial due to the absence of a structured
grid. Additionally, the performance of the SPH codes can be, in general,
adversely impacted by several factors, such as multiple time-stepping,
long-range interactions, and/or boundary conditions. This work presents
insights into the current performance and functionalities of three SPH codes:
SPHYNX, ChaNGa, and SPH-flow. These codes are the starting point of an
interdisciplinary co-design project, SPH-EXA, for the development of an
Exascale-ready SPH mini-app. To gain such insights, a rotating square patch
test was implemented as a common test simulation for the three SPH codes and
analyzed on two modern HPC systems. Furthermore, to stress the differences with
the codes stemming from the astrophysics community (SPHYNX and ChaNGa), an
additional test case, the Evrard collapse, has also been carried out. This work
extrapolates the common basic SPH features in the three codes for the purpose
of consolidating them into a pure-SPH, Exascale-ready, optimized, mini-app.
Moreover, the outcome of this serves as direct feedback to the parent codes, to
improve their performance and overall scalability.Comment: 18 pages, 4 figures, 5 tables, 2018 IEEE International Conference on
Cluster Computing proceedings for WRAp1
Smoothed Particle Hydrodynamics for Navier-Stokes Fluid Flow Application
The aim of this publication is to introduce the particle based computational fluid dynamics (CFD) method smoothed particle hydrodynamics (SPH) and introduce an applicable and valid SPH implementation for practical cases. For this purpose, current research approaches are combined regarding performance and numerical stability. The principles of the method, the mathematical basics and the discretization of the Navier-Stokes equations are clarified. Furthermore, the implementation of method-specific boundary conditions, wall, inlet and outlet, as well as several correction procedures and a surface tension setup into the present code framework are described. The advantages and validity of the method are shown based on different cases. The free surface fluid behavior of a dam break is compared to experimental data of the time dependent water level of selected positions. A Karman vortex street is validated by its Strouhal number for different Reynolds numbers. The frequency of an oscillating drop is analysed and compared to the analytical solution. The SPH is utilized for pipe flows influenced by a backward facing step and shows an expected qualitative flow field
SPH-EXA: Enhancing the Scalability of SPH codes Via an Exascale-Ready SPH Mini-App
Numerical simulations of fluids in astrophysics and computational fluid
dynamics (CFD) are among the most computationally-demanding calculations, in
terms of sustained floating-point operations per second, or FLOP/s. It is
expected that these numerical simulations will significantly benefit from the
future Exascale computing infrastructures, that will perform 10^18 FLOP/s. The
performance of the SPH codes is, in general, adversely impacted by several
factors, such as multiple time-stepping, long-range interactions, and/or
boundary conditions. In this work an extensive study of three SPH
implementations SPHYNX, ChaNGa, and XXX is performed, to gain insights and to
expose any limitations and characteristics of the codes. These codes are the
starting point of an interdisciplinary co-design project, SPH-EXA, for the
development of an Exascale-ready SPH mini-app. We implemented a rotating square
patch as a joint test simulation for the three SPH codes and analyzed their
performance on a modern HPC system, Piz Daint. The performance profiling and
scalability analysis conducted on the three parent codes allowed to expose
their performance issues, such as load imbalance, both in MPI and OpenMP.
Two-level load balancing has been successfully applied to SPHYNX to overcome
its load imbalance. The performance analysis shapes and drives the design of
the SPH-EXA mini-app towards the use of efficient parallelization methods,
fault-tolerance mechanisms, and load balancing approaches.Comment: arXiv admin note: substantial text overlap with arXiv:1809.0801
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
The suction effect during freak wave slamming on a fixed platform deck: Smoothed particle hydrodynamics simulation and experimental study
During the process of wave slamming on a structure with sharp corners, the wave receding after wave impingement can induce strong negative pressure (relative to the atmospheric pressure) at the bottom of the structure, which is called the suction effect. From the practical point of view, the suction force induced by the negative pressure, coinciding with the gravity force, pulls the structure down and hence increases the risk of structural damage. In this work, the smoothed particle hydrodynamics (SPH) method, more specifically the δ+SPH model, is adopted to simulate the freak wave slamming on a fixed platform with the consideration of the suction effect, i.e., negative pressure, which is a challenging issue because it can cause the so-called tensile instability in SPH simulations. The key to overcome the numerical issue is to use a numerical technique named tensile instability control (TIC). Comparative studies using SPH models with and without TIC will show the importance of this technique in capturing the negative pressure. It is also found that using a two-phase simulation that takes the air phase into account is essential for an SPH model to accurately predict the impact pressure during the initial slamming stage. The freak wave impacts with different water depths are studied. All the multiphase SPH results are validated by our experimental data. The wave kinematics/dynamics and wave impact features in the wave-structure interacting process are discussed, and the mechanism of the suction effect characterized by the negative pressure is carefully analyzed
Structural response and optimization of airtight blast door under gas explosion load
Airtight blast door, as one of the key components of a rescue device or a ventilating device in underground coal mine, which can not only guarantee the normal operation ventilation system, but also can prevent the propagation of shock wave and invasion of toxic gases. Therefore, high structural stability and safety is fundamental when designing a door. An airtight blast door was developed and optimized based on static analysis and topological optimization, and dynamic response analysis of the optimized airtight blast door subjected to gas explosion load was conducted using a novel approach proposed in this paper-the FEM-SPH contact algorithm. Results showed that the main component weight of this kind of door is 27.4 % smaller than the original one without reducing the blast and impact behavior, the maximum displacement and stress of the optimization door obtained by FEM-SPH contact algorithm (dynamic response) are much larger than those using static mechanical analysis. The FEM-SPH contact algorithm and typical optimization method as well as the example presented in this paper are helpful for the original design and optimization of other products. Some conducive suggestions were recommended based on the simulation results
Numerical Investigation of 2-D Wave Making Characteristics of a Submerged Hydrofoil
In this study, 2-D wave making characteristics of a submerged hydrofoil has been investigated in a
numerical fashion. Experimental data available for different depths of submergence and flow velocities
have been compared to the results obtained by a commercial RANS CFD code and an in-house SPH
code. The capabilities of the numerical approaches in terms of capturing the free surface deformation
have been assessed. At high Froude numbers, the induced wave profiles have been observed to exhibit
an unsteady nature by both numerical methods. The pressure contours obtained from the numerical
analysis have also been compared with each other. It has been seen that the agreement between the
results of the well-established RANS method and recently progressing SPH technique is encouraging for
further development
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
Numerical modelling of landslide behaviour
Landslides exhibit complicated and destructive behaviour with disastrous consequences. A landslide event is preceded by slope failure, which is governed by laws of soil mechanics. Once initiated, landslides often propagate downslope at rapid rates, exhibiting fluid-like behaviour. Landslide propagation is therefore frequently characterised by laws of fluid dynamics. Numerical models are vital for an improved understanding of these catastrophic events. Existing models are incapable of adequately simulating the dynamics of both initiation and propagation. Smoothed Particle Hydrodynamics (SPH) is a meshless method that is able to capture large displacements and rapid velocities, and it has been frequently applied to simulate landslide propagation. However, SPH is susceptible to numerical instabilities, that are particularly detrimental with regards to simulations of soil. These must be eliminated for SPH to be an ideal tool for general landslide modelling. The majority of approaches at removing the numerical instabilities from SPH are not universal -- some are applicable for small displacements problems only, while others require the tuning of artificial model parameters. In this research, a novel numerical model is developed capable of accurately simulating landslide behaviour -- including initiation and propagation. The numerical model -- Stress-Particle SPH -- removes instabilities in a way that does not require artificial parameter tuning. The method is an extension of SPH, and involves calculating velocities and stresses on two separate sets of particles -- nodes and stress-points. Previous literature suggests that the addition of stress-points have the potential to effectively stabilise SPH. Despite this, their implementation within SPH is relatively unexplored, and stress-points have only been applied to a limited range of problems. In this research, Stress-Particle SPH is extended for applicability to landslide behaviour, allowing the numerically stable simulation of high displacement problems with Stress-Particle SPH for the first time. The developments presented in this research offer the potential for SPH to tackle a broad range of problems beyond its current capabilities