Posibilidades de un método numérico lagrangiano para dinámica de fluidos en ingeniería civil

El campo de la Ingeniería Civil fue de los primeros en utilizar el método de elementos finitos (Finite Element Method, FEM) para aplicaciones prácticas. El cálculo de estructuras complejas se realiza a menudo y cada día con más asiduidad por este método. Sin embargo, el uso de los elementos finitos no se limita a este campo, y puede ser de gran utilidad dentro del electromagnetismo, la propagación de ondas, flujo en medio poroso, problemas de convección-difusión e incluso dinámica de fluidos. En particular, el método de elementos finitos sin malla (Meshless Finite Element Method, MFEM), una variante del FEM, se ha empezado a utilizar principalmente para modelizar el movimiento de fluidos. El programa Dam, desarrollado en CIMNE durante los últimos años, en colaboración con CIMEC, usa el MFEM aplicado a las ecuaciones de la dinámica de fluidos en formulación lagrangiana, y aparece como un intento de resolver algunos de los problemas asociados a otras formulaciones. Como característica novedosa, el programa calcula una nueva malla a cada nuevo paso de tiempo de cálculo. La ventaja de la formulación lagrangiana es que no aparecen en las ecuaciones los términos convectivos, responsables de muchos y tradicionales problemas en la resolución numérica cuando se aplica la formulación euleriana. Por otro lado, el remallado a cada paso de tiempo permite abordar problemas de grandes deformaciones de forma natural, con un leve gasto de tiempo en el mallado, especialmente rentable en los casos 3D. El hecho de desconocer si los resultados que el programa Dam proporciona se ajustan a la realidad ha desencadenado la realización de esta tesina, cuyo objeto es hacer un estudio de su aplicabilidad en el mundo de la Ingeniería Civil, es decir, una valoración objetiva de sus posibilidades como herramienta real de cálculo para el ingeniero. Para una mejor comprensión de lo que representan a nivel práctico tanto la formulación lagrangiana como el remallado, así como los elementos finitos sin malla, se presenta con cierto detalle el algoritmo de cálculo y el de mallado,. A continuación se analizan los resultados de Dam sobre determinados problemas, contrastándolos con otros resultados analíticos o experimentales a esos mismos problemas. El estudio del campo de velocidades revela una gran semejanza entre los resultados de Dam y los analíticos de la teoría lineal en los casos de olas estudiados, y el estudio del campo de presiones en el caso hidrostático coincide exactamente con la ley analítica de presiones hidrostáticas, que es lineal con la profundidad. Al intentar contrastar los resultados de presiones en casos con gran presencia de presión dinámica es difícil encontrar expresiones analíticas que den buenos resultados, y por eso se ha preferido comparar a Dam con resultados experimentales obtenidos en canal de ensayos (CIEM, UPC) mediante sensores de presión. La comparación revela un buen ajuste en las presiones, pero también que se requiere un cierto tratamiento especializado de los datos en su interpretación. Se presenta también un conjunto de ejemplos variados mostrando los diversos problemas y casos que el programa Dam puede abordar, con condiciones de contorno diversas y simulando situaciones habituales en Ingeniería Civil. Finalmente se dedica un capítulo a la propia aplicación del programa a un caso concreto de la Ingeniería Civil: el estudio de la incidencia de una ola sobre un dique vertical. Este capítulo se ha realizado con el objeto de evidenciar las facilidades que Dam ofrece si realmente decide utilizarse. Todo ello permite afirmar que Dam tiene una verdadera utilidad para el ingeniero civil, dada su adaptabilidad y sus buenos resultados, pero aún es necesario un cierto desarrollo y perfeccionamiento del programa para conseguir la total fiabilidad

A particle finite element method for fluid-related problems in civil engineering

The work presented in this Thesis is a set of developments focused on the Particle Finite Element Method (PFEM) and its applicability in several fields in Civil Engineering. The PFEM had already been proven to be a powerful tool for the free surface flows with large deformation and domain separation, but the application to actual engineering problems requires many more advances. The interaction between the fluid and many solids contacting with each other, the erosion of soils and the transport of small particles are some of these advances, which are main topics addressed in this document. Apart from them, other developments related with the fluid solution are included, which are intended to get deeper than ever before in the practical use of PFEM.El treball que es presenta en aquesta Tesi és un conjunt de desenvolupaments centrats en el Particle Finite Element Method (PFEM) i en la seva aplicació a diversos camps de l'enginyeria civil. El PFEM ja havia demostrat ser una eina potent pels fluxes amb superfície lliure amb grans deformacions i separació de dominis, però l'aplicació a problemes d'enginyeria reals requereix molts més avenços. La interacció entre el fluid i molts sòlids que contacten els uns amb els altres, l'erosió de sòls i el transport de partícules petites són alguns d'aquests avenços, que són els principals temes tractats en aquesta Tesi. Apart d'aquests, s'inclouen altres desenvolupaments relacionats amb la solució del fluid, que miren d'arribar més profunditat que mai abans en l'ús pràctic del PFEM i la seva implementació. Primer es presenta el PFEM, es descriuen els desenvolupaments de l'autor millorant la solució de la dinàmica de fluids i altres capacitats simples que s'hi han afegit. Després, tres capítols principals es centren en a) l'algoritme d'interacció fluid-estructura amb contacte b) l'erosió de sòls c) el transport de partícules. A continuació altres aplicacions del mètode s'expliquen, així com una llista dels projectes d'investigació amb els quals aquesta tesi ha tingut vincle.Postprint (published version

PFEM application in fluid structure interaction problems

In the current paper the Particle Finite Element Method (PFEM), an innovative numerical method for solving a wide spectrum of problems involving the interaction of fluid and structures, is briefly presented. Many examples of the use of the PFEM with GiD support are shown. GiD framework provides a useful pre and post processor for the specific features of the method. Its advantages and shortcomings are pointed out in the present work.Peer ReviewedPostprint (published version

Pressure measurement in 2D sloshing simulations with SPH

Sloshing for low filling level resonant pitch motion is studied experimentally and numerically using SPH. Special attention is paid to the pressure fields on the tanks. Comparisons are made with experimental data and with Particle Finite Element Method (PFEM) calculations.Postprint (published version

Particle-structure interaction using cad-based boundary descriptions and isogeometric B-REP analysis (IBRA)

The procedure and the properties with the use of NURBS-described CAD models in particle-structure interaction are presented within this contribution. This implies the needed entities of those models and the description of trimmed multipatches to discretize analysis suitable numerical models. Finally, the properties will be shown with some test cases in comparison to analytical benchmarks and simulations with FEM as boundary description

A modular, partitioned, discrete element framework for industrial grain distribution systems with rotation machinery

The final publication is available at Springer via http://dx.doi.org/10.1007/s40571-015-0089-9A modular discrete element framework is presented for large-scale simulations of industrial grain-handling systems. Our framework enables us to simulate a markedly larger number of particles than previous studies, thereby allowing for efficient and more realistic process simulations. This is achieved by partitioning the particle dynamics into distinct regimes based on their contact interactions, and integrating them using different time-steps, while exchanging phase-space data between them. The framework is illustrated using numerical experiments based on fertilizer spreader applications. The model predictions show very good qualitative and quantitative agreement with available experimental data. Valuable insights are developed regarding the role of lift vs drag forces on the particle trajectories in-flight, and on the role of geometric discretization errors for surface meshing in governing the emergent behavior of a system of particles.Postprint (author's final draft

Shockwaves in spillways with the particle finite element method

The final publication is available at Springer via http://dx.doi.org/10.1007/s40571-019-00252-1.Changes in direction and cross section in supercritical hydraulic channels generate shockwaves which result in an increase in flow depth with regard to that for uniform regime. These disturbances are propagated downstream and need to be considered in the design of the chute walls. In dam spillways, where flow rates are often high, this phenomenon can have significant implications for the cost and complexity of the solution. It has been traditionally analysed by means of reduced-scale experimental tests, as it has a clear three-dimensional character and therefore cannot be approached with two-dimensional numerical models. In this work, the ability of the particle finite element method (PFEM) to reproduce this phenomenon is analysed. PFEM has been successfully applied in previous works to problems involving high irregularities in free surface. First, simple test cases available in the technical bibliography were selected to be reproduced with PFEM. Subsequently, the method was applied in two spillways of real dams. The results show that PFEM is capable of capturing the shockwave fronts generated both in the contractions and in the expansions that occur behind the spillway piers. This suggests that the method may be useful as a complement to laboratory test campaigns for the design and hydraulic analysis of dam spillways with complex geometries.Peer ReviewedPostprint (author's final draft

An accurate nonlocal bonded discrete element method for nonlinear analysis of solids: application to concrete fracture tests

The final publication is available at Springer via http://dx.doi.org/10.1007/s40571-019-00278-5.We present a numerical procedure for elastic and nonlinear analysis (including fracture situations) of solid materials and structures using the discrete element method. It can be applied to strongly cohesive frictional materials such as concrete and rocks. The method consists on defining nonlocal constitutive equations at the contact interfaces between discrete particles using the information provided by the stress tensor over the neighbor particles. The method can be used with different yield surfaces, and in the paper, it is applied to the analysis of fracture of concrete samples. Good comparison with experimental results is obtained.Peer ReviewedPostprint (author's final draft

Design and validation of rockfall protection systems by numerical modeling with discrete elements

Rockfall protection systems are installed in order to preserve civil infrastructures against landslides and falling rocks. For the evaluation of these systems,one of the main problems is the difficulty to develop laboratory tests, since landslides and falling rocks are unpredictable events that involve the movement of large masses of material over several meters or evenkil-ometers. For this reason, the use of numerical methods, which allows reproducing full-scale situations without the need of laboratory devices or sliding materials, has become more popular. The study presented in this document shows theapplication of the Discrete Element Method (DEM) for the analysis of the behavior of one of the most popular rockfall protection systems, flexible metallic fences.Postprint (published version

Possibilities of the particle finite element method in computational mechanics

We present some developments in the formulation of the Particle Finite Element Method (PFEM) for analysis of complex coupled problems in fluid and solid mechanics accounting for fluid-structure interaction and coupled thermal effects. The PFEM uses an updated Lagrangian description to model the motion of nodes (particles) in both the fluid and the structure domains. Nodes are viewed as material points which can freely move and even separate from the main analysis domain representing, for instance, the effect of water drops. A mesh connects the nodes defining the discretized domain where the governing equations are solved as in the standard FEM. The necessary stabilization for dealing with the incompressibility of the fluid is introduced via the finite calculus (FIC) method. An incremental iterative scheme for the solution of the non linear transient coupled fluid-structure problem is described. Extensions of the PFEM to allow for frictional contact conditions at fluid-solid and solid-solid interfaces via mesh generation are described. A simple algorithm to treat erosion in the fluid bed is presented. Examples of application of the PFEM to solve a number of coupled problems such as the effect of large wave on structures, the large motions of floating and submerged bodies, bed erosion situations and melting and dripping of polymers under the effect of fire are given.Preprin