Structure-Seabed Interactions in Marine Environments

The phenomenon of soil–structure interactions in marine environments has attracted great attention from coastal geotechnical engineers in recent years. One of the reasons for the growing interest is the rapid development of marine resources (such as in the oil and gas industry, marine renewable energy, and fish farming industry) as well as the damage to marine infrastructure that has occurred in the last two decades. To assist practical engineers in the design and planning of coastal geotechnical projects, a better understanding of the mechanisms of soil–structure interactions in marine environments is desired. This Special Issue reports the recent advances in the problems of structure–seabed interactions in marine environment and provides practical engineers and researchers with information on recent developments in this field

Coastal Geohazard and Offshore Geotechnics

With rapid developments being made in the exploration of marine resources, coastal geohazard and offshore geotechnics have attracted a great deal of attention from coastal geotechnical engineers, with significant progress being made in recent years. Due to the complicated nature of marine environmnets, there are numerous natural marine geohazard preset throughout the world’s marine areas, e.g., the South China Sea. In addition, damage to offshore infrastructure (e.g., monopiles, bridge piers, etc.) and their supporting installations (pipelines, power transmission cables, etc.) has occurred in the last decades. A better understanding of the fundamental mechanisms and soil behavior of the seabed in marine environments will help engineers in the design and planning processes of coastal geotechnical engineering projects. The purpose of this book is to present the recent advances made in the field of coastal geohazards and offshore geotechnics. The book will provide researchers with information reagrding the recent developments in the field, and possible future developments. The book is composed of eighteen papers, covering three main themes: (1) the mechanisms of fluid–seabed interactions and the instability associated with seabeds when they are under dynamic loading (papers 1–5); (2) evaluation of the stability of marine infrastructure, including pipelines (papers 6–8), piled foundation and bridge piers (papers 9–12), submarine tunnels (paper 13), and other supported foundations (paper 14); and (3) coastal geohazards, including submarine landslides and slope stability (papers 15–16) and other geohazard issues (papers 17–18). The editors hope that this book will functoin as a guide for researchers, scientists, and scholars, as well as practitioners of coastal and offshore engineering

Study of large deformation geomechanical problems with the Material Point Method

The numerical simulation of real geomechanical problems often entails an high level of complexity; indeed they are often characterized by large deformations, soil-structure interaction and solid-fluid interaction. Moreover, the constitutive behavior of soil is highly non-linear. Landslides, dam failure, pile installation, and undrground excavation are typical examples of large deformation problems in which the interaction between solid a fluid phase as well as the contact between bodies are essential. This thesis addresses the challenging issue of the numerical simulation of large deformation problems in geomechanics. The standard lagrangian finite element methods are not well suited to treat extremely large deformations because of severe difficulties related with mesh distortions. The need to overcome their drawbacks urged researchers to devote considerable effort to the development of more advanced computational techniques such as meshless methods and mesh based particle methods. In this study, the Material Point Method (MPM), which is a mesh based particle method, is exploited to simulate large deformation problems in geomechanics. The MPM simulates large displacements with Lagrangian material points (MP) moving through a fixed mesh. The MP discretize the continuum body and carry all the information such as mass, velocity, acceleration, material properties, stress and strains, as well as external loads. The mesh discretizes the domain where the body move through; it is used to solve the equations of motion, but it does not store any permanent information. In undrained and drained conditions the presence of water can be simulated in a simplified way using the one-phase formulation. However, in many cases the relative movement of the water respect to the soil skeleton must be taken into account, thus requiring the use of the two-phase formulation. The contact between bodies is simulated with an algorithm specifically developed for the MPM at the beginning of the century. This algorithm was originally formulated for the frictional contact. It extension to the adhesive contact is considered in this thesis, which is well suited to simulate soil-structure interaction in case of cohesive materials. In this thesis typical geomechanical problems such as the collapse of a submerged slope and the simulation of cone penetration testing are considered. Numerical results are successfully compared with experimental data thus confirming the capability of the MPM to simulate complex phenomena

SOLID-SHELL FINITE ELEMENT MODELS FOR EXPLICIT SIMULATIONS OF CRACK PROPAGATION IN THIN STRUCTURES

Crack propagation in thin shell structures due to cutting is conveniently simulated using explicit finite element approaches, in view of the high nonlinearity of the problem. Solidshell elements are usually preferred for the discretization in the presence of complex material behavior and degradation phenomena such as delamination, since they allow for a correct representation of the thickness geometry. However, in solid-shell elements the small thickness leads to a very high maximum eigenfrequency, which imply very small stable time-steps. A new selective mass scaling technique is proposed to increase the time-step size without affecting accuracy. New ”directional” cohesive interface elements are used in conjunction with selective mass scaling to account for the interaction with a sharp blade in cutting processes of thin ductile shells

A CUDA-based implementation of an improved SPH method on GPU

We present a CUDA-based parallel implementation on GPU architecture of a modified version of the Smoothed Particle Hydrodynamics (SPH) method. This modified formulation exploits a strategy based on the Taylor series expansion, which simultaneously improves the approximation of a function and its derivatives with respect to the standard formulation. The improvement in accuracy comes at the cost of an additional computational effort. The computational demand becomes increasingly crucial as problem size increases but can be addressed by employing fast summations in a parallel computational scheme. The experimental analysis showed that our parallel implementation significantly reduces the runtime, with speed-ups of up to 90,when compared to the CPU-based implementation

Modellierung und Analyse von Wellen-Bauwerk-Boden Interaktion für monolithische Wellenbrecher

Monolithic breakwaters are preferred to other types of structures in terms of economical and environmental aspects. Nevertheless, they are more vulnerable to foundation failures, especially to stepwise failures. Due to the highly complex processes involved in wave-structure-foundation interaction, no reliable model yet exists for this failure mechanism. Therefore, a semi-coupled CFD-CSD model system and a simplified model are developed in OpenFOAM to describe wave-structure-foundation interaction for monolithic breakwaters, and particularly stepwise failures. The CFD model is an extension of the incompressible multiphase Eulerian solver of OpenFOAM by introducing different seepage laws and a simplified fluid compressibility model. The CFD model is successful in reproducing breaking wave impact including effect of entrapped air. A new CSD model is developed to solve the fully dynamic, coupled Biot equations with a new approach taking advantage of the PISO algorithm to resolve pore fluid velocity-pressure coupling. Soil-structure interaction is introduced via a frictional contact model and for soil behaviour, a multi-surface plasticity model is implemented. The model is validated against analytical models and physical tests. The model succeeds to reproduce wave-induced residual pore pressure buildup and soil densification followed by pore pressure dissipation. A one-way coupling of both models is achieved by transforming the CFD model output into input for the CSD model. The semi-coupled model system is applied successfully to reproduce selected results of a caisson breakwater subject to breaking wave impact in the Large Wave Flume (GWK). The model system is applied to expand the range of conditions tested in GWK for response of the soil foundation. A new load eccentricity concept, is proposed to classify response of the foundation in four load eccentricity regimes. Load eccentricity carries all significant information related to wave loads (horizontal and uplift) and to properties of the structure (mass and geometry). Using this concept, recommendations are drawn for design of monolithic breakwaters, and a new simplified nonlinear 3-DOF model is developed with elastoplastic springs. Model parameters are calibrated using results from the CFD-CSD model for different sand relative densities and different load eccentricities. The simplified model can simulate the stepwise failure (sliding, settlement and tilt) as well as the overall failure (overturning).Caisson-Wellenbrecher werden aufgrund ökonomischer und Umweltaspekte bevorzugt. Jedoch sind sie empfindlicher gegen das Versagen des Baugrundes insbesondere gegen schrittweises Versagen. Aufgrund der Komplexität der Wellen-Bauwerk-Boden Interaktion liegt noch kein verlässliches Modell für diesen Versagensmechanismus vor. Deswegen werden ein semi-gekoppeltes CFD-CSD Modellsystem und ein vereinfachtes Modell in OpenFOAM entwickelt. Das CFD-Modell stellt eine durch Sickerströmungsgesetze und ein vereinfachtes Modell der Fluidkompressibilität erweiterte Version des mehrphasigen Strömingslösers von OpenFOAM dar. Das CFD-Modell wurde erfolgreich eingesetzt, um Druckschlagbelastungen durch brechende Wellen mit Lufteinschlüssen zu reproduzieren. Ein neues CSD-Modell wurde für die Lösung der voll dynamischen, gekoppelten Biot-Gleichungen mit einem neuen Ansatz entwickelt. Dabei wird der PISO-Algorithmus genutzt, um die Kopplung von Geschwindigkeit und Druck des Porenfluids zu lösen. Die Bauwerk-Boden Interaktion wird über ein Reibungs-Kontaktmodell eingeführt und für die Plastizität des Bodens ein Mehrflächenmodell implementiert. Die Validierung des CSD-Modells erfolgte durch analytische Modelle und Laborversuche. Mit dem Modell ist es gelungen, den Porenwasserdruckaufbau, die Bodenverdichtung und die Dissipation des Porenwasserdruckes zu reproduzieren. Es wurde eine Einweg-Kopplung der Modelle implementiert, in dem der Output des CFD-Modells als Input für das CSD-Modell aufbereitet wird. Mit dem validierten semi-gekoppelten Modellsystem ist es gelungen die Experimente im Großen Wellenkanal (GWK) zu reproduzieren. Darüber hinaus wurde das Modellsystem eingesetzt, um die getesteten Bedingungen zu erweitern. Ein neues Lastexzentrizitätskonzept wurde eingeführt, um die Gründungsverhaltens in vier Regime zu klassifizieren. Die Lastexzentrizität fasst alle relevanten Informationen der Wellenbelastung (Horizontal und Auftrieb) und der Bauwerkseigenschaften (Masse und Geometrie) zusammen. Unter Anwendung dieses Konzepts werden Empfehlungen für die Bemessung monolithisches Wellenbrechers ausgesprochen. Darüber hinaus wurde ein vereinfachtes nichtlineares 3-DOF Modell mit elasto-plastischen Federn entwickelt. Die Modellparameter wurden für unterschiedliche relative Dichte des Bodens und Lastexzentrizität kalibriert. Das vereinfachte Modell kann das schrittweise Versagen (Gleiten, Setzung und Kippen) sowie das Gesamtversagen (Umkippen) simulieren

Mécanique des roches, phénomènes de rupture avec la prise en compte des fissures existantes et l’écoulement du fluide interne à travers les fissures : thèse de doctorat

This thesis deals with the problem of localized failure in rocks, which occurs often in civil engineering practice like in dam failure, foundation collapse, stability of excavations, slopes and tunnels, landslides and rock falls. The risk of localized failure should be better understood in order to be prevented. The localized failure in rocks is usually characterized by a sudden and brittle failure without warning in a sense of larger and visible deformations prior to failure. This happens also under the strong influence of material heterogeneities, pre-existing cracks and other defects. The three novel numerical models, incorporating the localized failure mechanisms, heterogeneity of rock and pre-existing cracks and other defects, are presented in this thesis. First model deals with 2D plane strain two-phase rock composite, where stronger phase represents the intact rock and weaker phase initial defects. Second model represents the extension of the previous model towards the 3D space, where full set of 3D failure mechanisms is considered. Heterogeneous properties are taken here through the random distribution and Gauss statistical variation of material properties. The latter model is also used for the analysis of intact rock core specimens geometrical shape deviations influencing the uniaxial compressive strength. Third model is a 2D, dealing with volumetric fluid-structure interaction and localized failure under the influence of fluid flow through the porous rock medium. The discrete beam lattice approach is chosen for general framework for three models, where Voronoi cells represent the rock grains kept together by Timoshenko beams as cohesive links. The enhanced kinematics characterized for embedded discontinuity approach is added upon standard kinematics of cohesive links. This serves for the macrocrack propagation in all failure modes and their combinations, between the rock grains. The fracture process zone formation followed by micro-cracks coalescence, preceding the localized failure, is considered as well. Fluid flow is governed by a Darcy law, while coupling conditions obey Biot’s theory of poroplasticity. The results of the numerical models were verified by the benchmarks available from literature in 2D case. The 3D model was validated against the experimental results conducted on 90 rock specimens, where even slight geometrical deviations of specimens are considered. Presentation of these models, as well as their implementation aspects are given in full detail. Embedded discontinuity concept and the local nature of enhancements required to capture the displacement discontinuities leads to the very efficient approach with static condensation of enhanced degrees of freedom and technique that can be efficiently incorporated into finite element code architecture.Ova doktorska disertacija bavi se problemom lokaliziranog sloma u stijenama koji se često pojavljuje u različitima zadaćama u inženjerskoj praksi kod otkazivanja nosivosti brana, sloma temelja, stabilnosti iskopa, klizišta i tunela ili stijenskih odrona. Bolje razumijevanje ovog fenomena je nužno zbog prevencije rizika od lokaliziranog sloma. Lokalizirani slom u stijenama karakteriziran je iznenadnim i krtim slomom bez upozorenja u obliku velikih i vidljivih deformacija, a uvjetovan je materijalnim heterogenostima, postojećim pukotinama i oslabljenjima. U ovome radu prezentirana su tri nova numerička modela koja uključuju mehanizme lokaliziranog sloma, materijalnu heterogenost stijene s postojećim pukotinama i drugim oslabljenjima. Prvi je 2D model za analizu ravninskog stanja deformacija dvofazne kompozitne stijene, kod koje čvršća faza predstavlja intaktnu stijenu, a slabija faza početne nepravilnosti (oslabljenja) u stijeni. Drugi model predstavlja proširenje opisanog 2D modela u 3D područje, gdje su uključeni 3D mehanizmi sloma. Heterogenost je uzeta u obzir pomoću slučajne raspodjele i Gaussove statističke varijacije materijalnih karakteristika. Ovaj model je upotrijebljen u analizi utjecaja geometrijskih nepravilnosti oblika stijenskih uzoraka na jednoosnu tlačnu čvrstoću. Treći numerički model je dvodimenzionalni, a bavi se volumenskom interakcijom tekućine i konstrukcije i lokaliziranim slomom pod utjecajem protoka tekućine kroz poroznu stijensku sredinu. Osnova sva tri numerička modela je pristup zasnovan na diskretnoj rešetkastoj mreži greda u kojem su Voronoi ćelije kao diskretne čestice stijene međusobno povezane kohezivnim vezama modeliranima pomoću Timoshenkovih greda. Poboljšana kinematika, karakteristična za metodu konačnih elemenata s ugrađenim diskontinuitetima, dodana je standardnoj kinematici kohezivnih veza što omogućuje nastanak i širenje makropukotina između mineralnih zrna stijene u svim mehanizmima sloma i njihovim kombinacijama. Proces nastanka mikropukotina koji prethodi lokaliziranom slomu stijene je također uzet u obzir u modelu. Protok tekućine definiran je Darcijevim zakonom dok je volumenska interakcija tekućine i stijene zasnovana na Biotovoj teoriji poroplastičnosti. Rezultati razvijenih numeričkih 2D modela su verificirani na primjerima iz literature. Validacija 3D modela provedena je usporedbom s eksperimentalnim rezultatima dobivenima ispitivanjem 90 stijenskih uzoraka, gdje su razmatrane i geometrijske nepravilnosti stijenskih uzoraka. U ovoj doktorskoj disertaciji detaljno su prezentirani svi razvijeni numerički modeli, kao i njihova matematička i numerička implementacija. Pristup s ugrađenim diskontinuitetima i lokalnim poboljšanjima za simulaciju diskontinuiteta u polja pomaka te statičkom kondenzacijom dodatnih stupnjeva slobode je na vrlo efikasan način ugrađen u program za analizu konstrukcija metodom konačnih elemenata.Cette thèse aborde le problème de la rupture localisée dans les roches, qui charcterise un grand nombre d’applications dans le domaine du génie civil, tels que la rupture du barrage, effondrement desfondations, la stabilité des excavations ou les tunnels, les glissements de terrain et éboulements. Le risque de rupture localisée devrait être mieux apprehendé pour mieux l’évitér. La rupture localisée dans les roches est généralement caractérisé par une une rupture soudaine et quasi-fragile sans avertissement dans un sens de plus grandes déformations et visibles avant l’échec. Cela se produit également sous l’influence des hétérogénéités matériels, influencé par des fissures existantes et d’autres défauts initaux. Les trois nouveaux modèles numériques, intégrant les mécanismes de rupture localisées, l’hétérogénéité de la roche et de fissures existantes et d’autres défauts, sont présentés dans cette thèse. Premier modèle propose une représentation 2D de roche composite à deux phases, où la phase solide représente la roche intacte et les plus faibles en phase défauts initiaux. Deuxième modèle représente l’extension du modèle précédent vers l’espace 3D, où un ensemble complet de mécanismes de défaillance 3D est considéré. Propriétés hétérogènes sont prises ici par la distribution aléatoire en accord avec la variation statistique Gaussienne des propriétés des matériaux. Ce dernier modèle est également utilisé pour l’analyse de la roche intacte spécimens écarts de forme géométriques qui influencent la résistance à la compression uniaxiale. Troisième modèle est un modèle 2D, traitant interaction volumétrique entre fluide et structure et la rupture localisée sous l’influence de l’écoulement du fluide à travers le milieu de la roche poreuse. L’approche de lattice discret est choisi pour construire le cadre général pour trois modèles, où les cellules de Voronoi représentent les grains de roche gardés ensemble par Timoshenko poutres que des liens de cohésion. La cinématique améliorées caractérisées pour l’approche intégrée de discontinuité est ajouté sur la cinématique standard de liens cohérents. Cela sert pour la propagation de la fissure macro dans tous les modes de défaillance et de leurs combinaisons, entre les grains de la roche. La formation de la zone de processus de rupture suivie par des micro-fissures coalescence, précédant la rupture localisée, est considéré comme bien. Écoulement de fluide est régie par une loi de Darcy, tandis que les conditions de couplage obéissent à la théorie de Biot de poroélasticité. Les résultats des modèles numériques ont été vérifiées par les repères de la littérature dans le cas 2D. Le modèle 3D a été validé contre les résultats expérimentaux effectués 12 sur 90 échantillons de roches, où de légères déviations géométriques de spécimens sont considérés. Présentation de ces modèles, ainsi que leurs aspects de mise en oeuvre sont présentés en détail. Notion de discontinuité intrinsèque et le caractère local des améliorations nécessaires pour capturer les discontinuités de déplacement conduit à l’approche très efficace avec condensation statique des degrés améliorés de liberté et de technique qui peut être efficacement intégrés dans architecture standarde d’un logiciel élément finis

New Advances in Marine Engineering Geology

The ocean is the cradle of life and is rich in natural resources. With the worldwide boom in exploration and application of ocean resources, a dramatically increasing amount of coastal engineering and offshore engineering facilities have been constructed in the last few decades. The rapid development of human economic activities and the global climate change have significant impacts on the marine environment, resulting in frequent geological disasters. Under this circumstance, there is an urgent demand for a platform for scientists and engineers to share their state-of-art research outcomes in the field of Marine Engineering Geology. This book is a collection of a series of articles from the 2nd International Symposium of Marine Engineering Geology (ISMEG 2019), presenting some of the recent efforts made towards marine engineering geology and geotechnics, including theoretical advances, laboratory and field testing, design methods, and the potential for further development of these disciplines

Fully Coupled Thermo-Hydro-Mechanical Modeling of Discontinuities in Porous Media Incorporating High Aspect Ratio Interface Elements

The process of evolving discontinuities (in the form of fractures, cracks or fissures) in porous media is a very complex problem and possesses several challenges. This research proposal aims to progress the current understanding in this area by developing a fully coupled thermo-hydromechanical (THM) approach. The discontinuity will be modeled by using the mesh fragmentation technique (MFT), which consists of introducing finite elements with high aspect ratio between the standard (bulk) elements of the mesh. This new methodology has been successfully employed in concrete structures and soils, but by only assuming the mechanical problem. In this dissertation, the mass and heat flows are also incorporated in the formulation by considering THM processes. The MFT has been implemented in the in house CODE_BRIGHT finite element program, which was originally developed to solve coupled THM problems in continuous porous media. In this context, numerical simulations were performed in order to achieve a better understanding of discontinuities under complex conditions, mimicking desiccation tests in soils and energy production in rock reservoirs. The results have shown that the technique is very promising to model the formation and propagation of discontinuities in geo-engineering problems