Multi-level adaptive particle refinement method with large refinement scale ratio and new free-surface detection algorithm for complex fluid-structure interaction problems

Fluid-Structure Interaction (FSI) is a crucial problem in ocean engineering. The smoothed particle hydrodynamics (SPH) method has been employed recently for FSI problems in light of its Lagrangian nature and its advantage in handling multi-physics problems. The efficiency of SPH can be greatly improved with the Adaptive Particle Refinement (APR) method, which refines particles in the regions of interest while deploying coarse particles in the left areas. In this study, the APR method is further improved by developing several new algorithms. Firstly, a new particle refinement strategy with the refinement scale ratio of 4 is employed for multi-level resolutions, and this dramatically decreases the computational costs compared to the standard APR method. Secondly, the regularized transition sub-zone is deployed to render an isotropic particle distribution, which makes the solutions between the refinement zone and the non-refinement zone smoother and consequently results in a more accurate prediction. Thirdly, for complex FSI problems with free surface, a new free-surface detection method based on the Voronoi diagram is proposed, and the performance is validated in comparison to the conventional method. The improved APR method is then applied to a set of challenging FSI cases. Numerical simulations demonstrate that the results from the refinement with scale ratio 4 are consistent with other studies and experimental data, and also agree well with those employing the refinement scale ratio 2. A significant reduction in the computational time is observed for all the considered cases. Overall, the improved APR method with a large refinement scale ratio and the new free-surface detection strategy shows great potential in simulating complex FSI problems efficiently and accurately.Comment: 47 pages, 26 figures, accepted to be published by Journal of Computational Physic

A coupled SPH-DEM model for fluid-structure interaction problems with free-surface flow and structural failure

An integrated particle model is developed to study fluid-structure interaction (FSI) problems with fracture in the structure induced by the free surface flow of the fluid. In this model, the Smoothed Particle Hydrodynamics (SPH) based on the kernel approximation and particle approximation is used to model the fluid domain in accordance with Navier-Stokes equations and the Discrete Element Method (DEM) with a parallel bond model is used to represent the real solid structure through a hexagonal packing of bonded particles. Validation tests have been carried out for the DEM model of the structure with deformation and fracture failure, the SPH model of the fluid and the coupled SPH-DEM model of FSI without fracture, all showing very good agreement with analytical solutions and/or published experimental and numerical results. The simulation results of FSI with fracture indicate that the SPH-DEM model developed is capable of capturing the entire FSI process from structural deformation to structural failure and eventually to post-failure deformable body movement

A DEM approach for simulating flexible beam elements with the Project Chrono core module in DualSPHysics

This work presents a novel approach for simulating elastic beam elements in DualSPHysics leveraging functions made available by the coupling with the Project Chrono library. Such numerical frameworks, belonging to the Meshfree Particle Methods family, stand out for several features, like complex multiphase phenomena, moving boundaries, and high deformations which are handled with relative ease and reasonable numerical stability and reliability. Based on a co-rotating rigid element structure and lumped elasticity, a cogent mathematical formulation, relying on the Euler–Bernoulli beam theory for the structural discretization, is presented and applied to simulating two-dimensional flexible beams with the discrete elements method (DEM) formulation. Three test cases are presented to validate the smoothed particle hydrodynamics-based (SPH) structure model in both accuracy and stability, starting from an equilibrium test, to the dynamic response, and closing with a fluid–structure interaction simulation. This work proves that the developed theory can be used within a Lagrangian framework, using the features provided by a DEM solver, overtaking the initial limitations, and hence applying the results of static theories to complex dynamic problems.Xunta de Galicia | Ref. ED431C 2021/44Xunta de Galicia | Ref. ED481A-2021/337Ministerio de Ciencia, Innovación y Universidades | Ref. IJCI-2017-32592Agencia Estatal de Investigación | Ref. PID2020-113245RB-I0

Computational Modelling of Fluid-Solid Interaction Problems by Coupling Smoothed Particles Hydrodynamics and the Discrete Element Method

Discrete Element Method (DEM) and Smoothed Particles Hydrodynamics (SPH) are integrated to investigate the macroscopic dynamics of fluid-solid interaction (FSI) problems. This coupled model is originated from two different meshless methods without mesh generation, which can handle fluid-particle-structure interactions with structural deformation/failure. With SPH the fluid phase is represented by a set of SPH particle elements moving in accordance with the Navier-Stokes equations. The solid phase consists of single or multiple solid particle(s) phase and deformable structure(s) phase which are represented by DEM particle elements using a linear contact model and a linear parallel contact model to account for the interaction between particle elements, respectively. To couple the fluid phase and solid particle phase, a local volume fraction and a weighted average algorithm are proposed to reformulate the governing equations and the interaction forces. The structure phase is coupled with the fluid phase by incorporating the structure’s DEM particle elements in SPH algorithm. The interaction forces between the solid particles and the structure phases are computed using the linear contact model in DEM. The proposed model is capable of simulating simultaneously fluid-structure interaction, particleparticle interaction and fluid-particle interaction, with good agreement between complicated hybrid numerical methods and experimental results being achieved. Finally, two engineering problems in injection moulding and 3D printing process are carried out to demonstrate the capability of the integrated particle model for simulating fluid-solid interaction problems with the occurrence of structural failure

Hydrodynamic contact/impact modeling and application to ocean engineering problems

Fluid-structure interaction (FSI) is a very interesting and challenging multi-disciplinary field involving interaction of a movable or deformable structure with an internal or surrounding fluid flow. FSI has several practical engineering applications such as the determination of the hydrodynamic forces on a structure or the dynamics of motion of bodies on the water-free surface. A requirement for the solution of these class of contact and impact FSI problems need accurate model development and predictive assessment especially when complex structures are involved. Analysis of FSI problems is often difficult and therefore experimental investigations (or empirical laws) are performed by conducting experiments in a physical wave basin. These experiments though impendent with the real world scenario often are time-consuming and expensive. Importantly, it may not be economically viable to conduct parametric studies using experiments. Alternatively, numerical models when developed with similar capabilities will complement the experiments very well because of the lower costs and the ability to study phenomena that are not completely feasible in a physical laboratory. This dissertation systematically examines the contact and impact fluid-structure interaction numerical modeling procedure applied to various practical multi-physics ocean engineering problems. The significant component of contact and impact FSI problems addressed in this research is divided into three categories. First, the experimental and numerical investigations for a rigid-body contact and impact (drop tests) is presented, and followed by numerical simulation and analysis of low and high-filled multi-physics sloshing phenomena in the LNG tank including air compressibility effect. Second, the performance of a finite-element method and a smoothed particle hydrodynamic method is evaluated by using a consistent numerical platform for the simulation of contact and impact of a fluid interacting with a flexible body. Finally, numerical simulation and analysis of a complex-body contact and impact (a fully pressurized surface effect ship (SES) bow finger seal motions) is investigated

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 Hp-Adaptive Finite Element Procedure For Fluid-Structure Interaction In Fully Eulerian Framework

This thesis attempts to implement a fully automatic hp-adaptive finite element procedure for fluid-structure interaction (FSI) problems in two dimensions. This work hypotesizes the efficacy of Fully Eulerian framework of FSI in hp-adaptivity on an a posteriori error estimator and adaptation for minimization of error in energy norm. Automatic mesh adaptation over triangular elements is handled by red-green-blue (RGB) refinement method. An effective mesh adaptivity to avoid excessive growth of unknowns is also addressed. Since the hp-method uses high order polynomials as approximation functions, the resulting system matrices are less sparse leading to the notion of FSI computation with parallelism. The parallel hp-adaptive computation is assessed with the conventional uniform and h refinement on a number of benchmark test cases. Subsequently, the efficacy of the fully Eulerian framework is compared to the well known Arbitrary Lagrangian Framework( ALE) for two different material models, namely, the St. Venant Kirchoff and the Neo-Hookean models. It was found that the fully Eulerian framework provides accurate FSI predictions for large deformation without need of frequent remeshing. The hp-adaptive method was also found to be a viable approach in obtaining accurate solutions without much compromise in computer memory and time. Furthermore, the integration of parallelism is successful in reducing the computation time by up to two orders of magnitude relative to the serial solver. For the comparisons between the ALE and the fully Eulerian frameworks, the computed solutions in all test cases are observed to be in agreement with each other

Development of an incompressible smoothed particle hydrodynamics method for electrohydrodynamics of immiscible fluids and rigid particles

An incompressible smoothed particle hydrodynamics method for modeling immiscible and isothermal flow of two- and three-phase Newtonian fluids and solid particles subject to an external electric field has been developed. Continuum surface force method is used to calculate the surface tension forces on fluid-fluid interfaces. The materials are assumed to be either perfect or leaky dielectrics. Solid particles are modeled using viscous penalty method coupled with rigidity constraints. The equations are discretized using corrected derivatives and artificial particle displacement is used to ensure homogeneous particle distribution. The projection method is used to advance the governing equations of the flow and electric field in time. The components of the scheme are tested in three stages of two- and three-phase hydrodynamics, multiphase electrohydrodynamics and fluid-structure/solid interaction. The results of each stage is compared to experimental and numerical data available in literature and their validity is established. The combination of the individual elements of the numerical method is used to simulate the motion of rigid particles submerged in Newtonian fluids subject to an external electric field. The behavior of the particles are found to be in agreement with experimental and numerical observations found in the literature. This shows the applicability of the proposed incompressible smoothed particle hydrodynamics scheme in simulating such complex and relatively unexplored phenomena

Kinetische Methoden zur numerischen Simulation von nichtlinearen Strömungen mit freien Oberflächen im Bau- und Umweltingenieurwesen

This thesis focuses on the numerical simulation of non-linear free surface flow problems. Different simulation kernels based on the Lattice Boltzmann method (LBM) have been developed or extended, implemented, and, after validation, applied to a number of applications in civil and environmental engineering. The LB model solves viscous and turbulent flows, essentially representing similar physics as Navier-Stokes or reduced shallow water models, but with specific solver advantages concerning data locality and parallel computing. The first part of this thesis deals with numerical simulations on high-performance GPU (graphics processing unit) hardware. Validations and applications of a reduced LB model for solving the shallow water equations are presented. The resulting GPU kernel has shown to be applicable to state-of-the-art benchmark problems, dealing with wave propagation and wave run-up. Subsequently, the GPU implementation of a 3D numerical wave tank for the simulation of various applications in civil engineering is presented. The second main target of this thesis is to develop and apply a novel model based on an enhanced representation and advection of the phase interface for the simulation of more complex and demanding free surface flow problems. A volume-of-fluid (VOF) approach in combination with a piecewise linear interface reconstruction (PLIC) has been coupled with the LBM. The resulting hybrid model has been successfully validated against various benchmark experiments. Even a breaking wave during shoaling on a slope, which is a demanding test case for VOF solvers, was successfully simulated. Apart from the model development and validation itself, a coupling to a rigid body engine for the simulation of FSI problems has been established. Finally, several techniques for the coupling to a potential flow solver are discussed and validated, in order to generate realistic wave profiles and for the efficient simulation of wave run-up and wave breaking.Die vorliegende Dissertation behandelt die numerische Simulation von nichtlinearen Strömungen mit freien Oberflächen. Dazu werden verschiedene Simulationskerne auf Basis der Gitter-Boltzmann-Methode (LBM) entwickelt, implementiert und nach ihrer Validierung auf zahlreiche Aufgabenstellungen im Bau- und Umweltingenieurwesen angewendet. Die LB-Methode wird verwendet, um viskose und turbulente Strömungen numerisch zu simulieren und bietet im Vergleich zu konventionellen Lösern deutliche Vorteile bezüglich Datenlokalität und parallelem Rechnen. Der erste Teil der Arbeit beschäftigt sich mit der Simulation von Strömungsproblemen auf High-Performance-GPU (Graphics Processing Unit) Hardware. Einleitend wird die Validierung und Anwendung eines LB-Modells für Flachwassergleichungen dargestellt. Im Anschluss wird eine GPU-Implementierung eines dreidimensionalen numerischen Wellenkanals für die Simulation turbulenter Wehrströmungen, Dammbruchszenarien, des Wellenschlages auf Pfahlbauwerke und anderer Anwendungen im Bauingenieurwesen präsentiert. Das zweite Ziel dieser Arbeit ist die Entwicklung und Anwendung eines neuartigen Modells für die Simulation von komplexeren Problemen mit freier Oberfläche unter Zuhilfenahme einer erweiterten Repräsentation der Phasengrenzfläche. Ein Volume-of-Fluid (VOF) Ansatz auf der Grundlage einer abschnittsweise linearen Interface-Rekonstruktion (PLIC) wird an die LBM gekoppelt. Das resultierende hybride Modell wird anhand verschiedener Benchmarks erfolgreich validiert. Im Anschluss wird eine Kopplung an einen Starrkörper-Löser realisiert, welche die Simulation von Problemstellungen aus dem Bereich der Fluid-Struktur-Interaktion ermöglicht. Abschließend werden Techniken zur Kopplung des hybriden Lösers an einen numerischen Wellenkanal auf Basis der Potentialströmungstheorie diskutiert und validiert, die die Erzeugung realistischer Wellenprofile und die effiziente Simulation von Wellenauflauf sowie Wellenbrechen ermöglichen