Accurate and Real-Time Granular Flow Modeling of Robot-Terrain Interactions

An important challenge in robotics is understanding the interactions between robots and deformable terrains that consist of granular material. Granular flows and their interactions with rigid bodies still pose several open questions. A promising direction for accurate, yet efficient, modeling is using continuum methods. Also, a new direction for real-time physics modeling is the use of geometric machine learning. This research advances continuum and machine learning methods for modeling rigid body-driven granular flows, for application to space robotics (where the effect of gravity is an important factor) as well as terrestrial industrial machines. For accurate and efficient design applications, this research develops a continuum method comprising a modern constitutive model, nonlocal granular fluidity (NGF), and a state-of-the-art numerical solver, material point method (MPM). We design a numerical approach, within a hyperelasticity framework, to implement the dynamical form of the viscoplastic NGF constitutive model in three-dimensional MPM. This approach is thermodynamically consistent, and the dynamical form includes the nonlocal effect of flow cessation. This is verified by both quantitative measurements and qualitative visualization of our excavation and wheel experiments. Furthermore, this research explores the gravity sensitivity of continuum numerical solvers. It explains why MPM is an appropriate continuum solver to model granular flows under different gravity. For real-time control applications, this research considers the development of a subspace machine learning simulation approach. To generate training datasets, we utilize our high-fidelity MPM-NGF method. Principal component analysis (PCA) is used to reduce the dimensionality of data. This research shows that the first few principal components of our high-dimensional data keep almost the entire variance in data. A graph network simulator (GNS) is trained to learn the underlying subspace dynamics. The learned GNS is then able to predict particle positions and interaction forces with good accuracy. More importantly, PCA significantly enhances the time and memory efficiency of GNS in both training and rollout. This enables GNS to be trained using a single desktop Graphics Processing Unit (GPU) with moderate Video-RAM. This also makes the GNS real-time on large-scale 3D physics configurations (and 700x faster than our MPM-NGF)

Infrastructure Design, Signalling and Security in Railway

Railway transportation has become one of the main technological advances of our society. Since the first railway used to carry coal from a mine in Shropshire (England, 1600), a lot of efforts have been made to improve this transportation concept. One of its milestones was the invention and development of the steam locomotive, but commercial rail travels became practical two hundred years later. From these first attempts, railway infrastructures, signalling and security have evolved and become more complex than those performed in its earlier stages. This book will provide readers a comprehensive technical guide, covering these topics and presenting a brief overview of selected railway systems in the world. The objective of the book is to serve as a valuable reference for students, educators, scientists, faculty members, researchers, and engineers

Numerical modelling of deformation and recrystallisation mechanics in ice and ice-air aggregates

Ice sheets and glaciers flow under their own weight and their flow of ice is a major contributor to both global sea-level and climate changes. The macroscopic flow of ice is affected by the properties of the microstructure, which is formed by a small aggregate of individual ice crystals. The deformation of ice is accompanied by recrystallisation, a term which describes mechanisms causing re-orientations of the crystalline lattice, the formation of new crystals or the migration of their boundaries. The ice crystal is marked by a significant viscoplastic anisotropy, which causes a distinctly higher resistance to flow, if the crystalline lattice is unfavourably oriented. With deformation, the ice grains align and develop a crystallographic-preferred orientation within the ice-aggregate, which induces a macroscopic anisotropy. A knowledge of the micro-dynamic deformation and recrystallisation mechanisms and how they affect the properties of the ice aggregate is a key to understand ice sheet dynamics. The objective of this thesis to investigate the deformation and recrystallisation mechanisms in ice and the involved changes in the microstructures of ice- and ice-air aggregates. This is done by means of two-dimensional numerical simulations using the modelling platform Elle, which optimised for modelling interacting micro-dynamic processes. The simulations couple a numerical model for viscoplastic deformation of anisotropic polycrystalline aggregates to implementations of recrystallisation mechanisms in Elle. In particular, an explicit numerical approach to consider secondary phases such as air inclusions in the numerical setup is developed, implemented and used in this thesis for the first time. Additionally, the new approach allows grain-size-reducing mechanisms, which allows the achievement of stable-state microstructures with deformation. In each scientific publication presented in the thesis, qualitative comparisons to natural polar ice accompany the numerical simulations. The results of this thesis show that the deformation and microstructures of ice are generally more heterogeneous than previously thought. Strain localisation is common in ice and related to viscoplastic anisotropy and intensified by the presence of air inclusions. Probably, strain localisation is occurring over a range of scales and has implications for the large-scale flow of ice. The thesis further demonstrates that deformation-induced recrystallisation mechanisms are common in ice and discusses their relation to strain localisation. In particular, the study points out the importance of the dissection of grains by migrating grain boundaries as an additional grain-size-reducing process in polar ice, which was not studied previously. This thesis confirms that the activation of deformation and recrystallisation mechanisms is a function of the deformation conditions such as strain rate, temperature and likely the load of impurities and dust particles. The steady-state numerical-microstructures reflect the prescribed deformation conditions, but appear largely independent from the initial microstructures. These results of this study indicate a high rate of change in crystallographic-preferred orientation and other microstructural properties. Furthermore, the thesis confirms that the development of crystallographic-preferred orientation is a function of strain rather than time or stress.Eisschilde und Gletscher fließen unter ihrem eigenen Gewicht und ihr Fluss hat einen großen Einfluss sowohl auf globale Meeresspiegel- als auch Klimaveränderungen. Das makroskopische Fließverhalten von Eis wird von den Eigenschaften der Mikrostruktur, die sich aus kleinen Gefügen von einzelnen Eiskristallen zusammensetzt, beeinflusst. Die Deformation des Eises geht mit Rekristallisation einher, ein Begriff, der Mechanismen beschreibt, die eine Neuorientierung des Kristallgitters, das Entstehen neuer Kristalle oder die Bewegung der Kristallgrenzen verursachen. Der Eiskristall ist durch eine deutliche mechanische Anisotropie gekennzeichnet, was einen deutlich höhren Widerstand gegen Deformation bedeutet, wenn das Kristallgitter ungünstig orientiert ist. Mit der Deformation richten sich Eiskristalle innhalb des Gefüges entlang einer kristallographisch bevorzugten Richtung aus, was auch makroskopisch eine Anisotropie erzeugt. Kenntnisse über die mikrodynamischen Deformations- und Rekristallisationsmechanismen und deren Einlfuss auf die Eigenschaften der Eismikrostruktur sind grundlegend für ein verbessertes Verständnis der Eisschilddynamik. Das Anliegen dieser Arbeit ist eine Untersuchung der Deformations- und Rekristallisationsmechanismen in Eis und der damit einhergehenden mikrostrukturellen Veränderung in reinem Eis und Eis mit Lufteinschlüssen. Dafür sieht die Arbeit zweidimensionale numerische Simulationen mit Hilfe der Modellierplattform Elle, die für die Modellierung von interagierenden mikrodynamischen Prozessen optimiert ist, vor. Die Simulationen koppeln ein numerisches Modell für viskoplastische Deformation unter Beachtung der Kristallanisotropie mit Implementierungen von Rekristallisations-mechanismen in Elle. Insbesondere beschäftigt sich die Arbeit erstmalig mit der Entwicklung, Implementierung und Anwednung eines numerischen Ansatzes, der weitere Phasen wie Lufteinschlüsse einbezieht. Zusätzlich erlaubt der neue Ansatz korngrößenverkleindernde Prozesse, wodurch die simulierten Mikrostrukturen mit Deformation einen Gleichgewichtszustand erreichen können. Jede wissenschaftliche Veröffentlichung in dieser Arbeit, nimmt außerdem qualitative Vergleiche von natürlichem polarem Eis mit numerischen Simulationen vor. Die Ergebnisse dieser Arbeit zeigen generell eine höhere Heterogenität in Eisdeformation und Mikrostruktur als bislang angenommen. Verformungslokalisation ist verbreitet in Eis, steht in Verbindung mit der Kristallanisotropie und wird durch Lufteinschlüsse verstärkt. Wahrscheinlich kann eine Verformungslokalisation über verschiedene Größenordnungen auftreten und hat eine Bedeutung für das großmaßstäbliche Eisfließen. Desweiteren zeigt die Arbeit, dass deformationsinduzierte Rekristallisationsmechanismen in Eis verbreitet sind und diskutiert deren Verhältnis zur Verformungslokalisation. Insbesondere zeigt die Arbeit, dass die Zerteilung von Körnern durch Korngrenzmigration ein wichtiger, jedoch bislang nicht untersuchter, korngrößenverkleindernder Prozess in polarem Eis ist. Die Arbeit bestätigt außerdem, dass die Aktivierung von Deformations- und Rekristallisationsmechanismen von Deformationsbedingungen wie Verformungsrate, Temperatur und wahrscheinlich dem Anteil von Verunreinigungen abhängt. Im Gleichgewichtszustand spiegeln die simulierten Mikrostrukturen die vorgegebenen Deformationsbedingungen wider, aber sind größtenteils unabhängig von der Ausgangsmikrostruktur. Diese Ergebnisse deuten darauf hin, dass die Rate der mikrostrukturellen Änderungen in beispielsweise kristallographisch bevorzugten Richtungen oder Korngrößen in Eis hoch ist. Außerdem bestätigt die Arbeit, dass die Entwicklung einer kristallographisch bevorzugten Richtung von der aufgebauten Verformung abhängt, nicht aber vom Zeit oder Spannungszustand

Computational Modelling of Concrete and Concrete Structures

Computational Modelling of Concrete and Concrete Structures contains the contributions to the EURO-C 2022 conference (Vienna, Austria, 23-26 May 2022). The papers review and discuss research advancements and assess the applicability and robustness of methods and models for the analysis and design of concrete, fibre-reinforced and prestressed concrete structures, as well as masonry structures. Recent developments include methods of machine learning, novel discretisation methods, probabilistic models, and consideration of a growing number of micro-structural aspects in multi-scale and multi-physics settings. In addition, trends towards the material scale with new fibres and 3D printable concretes, and life-cycle oriented models for ageing and durability of existing and new concrete infrastructure are clearly visible. Overall computational robustness of numerical predictions and mathematical rigour have further increased, accompanied by careful model validation based on respective experimental programmes. The book will serve as an important reference for both academics and professionals, stimulating new research directions in the field of computational modelling of concrete and its application to the analysis of concrete structures. EURO-C 2022 is the eighth edition of the EURO-C conference series after Innsbruck 1994, Bad Gastein 1998, St. Johann im Pongau 2003, Mayrhofen 2006, Schladming 2010, St. Anton am Arlberg 2014, and Bad Hofgastein 2018. The overarching focus of the conferences is on computational methods and numerical models for the analysis of concrete and concrete structures

A new mixed model based on the enhanced-Refined Zigzag Theory for the analysis of thick multilayered composite plates

The Refined Zigzag Theory (RZT) has been widely used in the numerical analysis of multilayered and sandwich plates in the last decay. It has been demonstrated its high accuracy in predicting global quantities, such as maximum displacement, frequencies and buckling loads, and local quantities such as through-the-thickness distribution of displacements and in-plane stresses [1,2]. Moreover, the C0 continuity conditions make this theory appealing to finite element formulations [3]. The standard RZT, due to the derivation of the zigzag functions, cannot be used to investigate the structural behaviour of angle-ply laminated plates. This drawback has been recently solved by introducing a new set of generalized zigzag functions that allow the coupling effect between the local contribution of the zigzag displacements [4]. The newly developed theory has been named enhanced Refined Zigzag Theory (en- RZT) and has been demonstrated to be very accurate in the prediction of displacements, frequencies, buckling loads and stresses. The predictive capabilities of standard RZT for transverse shear stress distributions can be improved using the Reissner’s Mixed Variational Theorem (RMVT). In the mixed RZT, named RZT(m) [5], the assumed transverse shear stresses are derived from the integration of local three-dimensional equilibrium equations. Following the variational statement described by Auricchio and Sacco [6], the purpose of this work is to implement a mixed variational formulation for the en-RZT, in order to improve the accuracy of the predicted transverse stress distributions. The assumed kinematic field is cubic for the in-plane displacements and parabolic for the transverse one. Using an appropriate procedure enforcing the transverse shear stresses null on both the top and bottom surface, a new set of enhanced piecewise cubic zigzag functions are obtained. The transverse normal stress is assumed as a smeared cubic function along the laminate thickness. The assumed transverse shear stresses profile is derived from the integration of local three-dimensional equilibrium equations. The variational functional is the sum of three contributions: (1) one related to the membrane-bending deformation with a full displacement formulation, (2) the Hellinger-Reissner functional for the transverse normal and shear terms and (3) a penalty functional adopted to enforce the compatibility between the strains coming from the displacement field and new “strain” independent variables. The entire formulation is developed and the governing equations are derived for cases with existing analytical solutions. Finally, to assess the proposed model’s predictive capabilities, results are compared with an exact three-dimensional solution, when available, or high-fidelity finite elements 3D models. References: [1] Tessler A, Di Sciuva M, Gherlone M. Refined Zigzag Theory for Laminated Composite and Sandwich Plates. NASA/TP- 2009-215561 2009:1–53. [2] Iurlaro L, Gherlone M, Di Sciuva M, Tessler A. Assessment of the Refined Zigzag Theory for bending, vibration, and buckling of sandwich plates: a comparative study of different theories. Composite Structures 2013;106:777–92. https://doi.org/10.1016/j.compstruct.2013.07.019. [3] Di Sciuva M, Gherlone M, Iurlaro L, Tessler A. A class of higher-order C0 composite and sandwich beam elements based on the Refined Zigzag Theory. Composite Structures 2015;132:784–803. https://doi.org/10.1016/j.compstruct.2015.06.071. [4] Sorrenti M, Di Sciuva M. An enhancement of the warping shear functions of Refined Zigzag Theory. Journal of Applied Mechanics 2021;88:7. https://doi.org/10.1115/1.4050908. [5] Iurlaro L, Gherlone M, Di Sciuva M, Tessler A. A Multi-scale Refined Zigzag Theory for Multilayered Composite and Sandwich Plates with Improved Transverse Shear Stresses, Ibiza, Spain: 2013. [6] Auricchio F, Sacco E. Refined First-Order Shear Deformation Theory Models for Composite Laminates. J Appl Mech 2003;70:381–90. https://doi.org/10.1115/1.1572901