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• 3D simulation of Vajont disaster. Part 2: Multi-failure scenarios

  A. Franci, M. Cremonesi, U. Perego, E. Oñate, G. Crosta

  Engineering Geology (2020). Vol. 279, 105856

  
  

  Abstract

  Prediction of multi-hazard slope stability events requires an informed and judicious choice of the possible scenarios. An incorrect definition of landslide conditions in terms of expected failure volume, material behavior, or boundary conditions can lead to inaccurate predictions and, in turn, to wrong engineering and risk management decisions. Reduced-scale experiments carried out two years before the Vajont disaster were carried out with a material not representative of the actual rockslide behavior and failed in not considering the simultaneous failure of the whole landslide body. Based on these inappropriate assumptions, the physical models led to wrong estimates of the safety operational level for the Vajont reservoir. This work uses the Particle Finite Element Method (PFEM) to analyze the implications of the wrong hypotheses considered in the pre-event experiments, simulating numerically the Vajont disaster for different sliding volumes and material properties. The use of the PFEM for the accurate assessment of the consequences of landslides impinging in water reservoirs has been already validated in a companion paper. In this work, we demonstrate the capabilities of a robust and reliable numerical modeling approach for the simulation of different scenarios, assessing what could have been a safe operational reservoir level in the case of a landslide generated impulse wave. The three-dimensional analyses were run with a high mesh resolution and demonstrate the suitability and robustness of the PFEM model for large-scale landslide and multi-hazard events simulation.

  Abstract
  Prediction of multi-hazard slope stability events requires an informed and judicious choice of the possible scenarios. An incorrect definition of landslide conditions in terms [...]

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• 3D simulation of Vajont disaster. Part 1: Numerical formulation and validation

  A. Franci, M. Cremonesi, U. Perego, G. Crosta, E. Oñate

  Engineering Geology (2020). Vol. 279, 105854, 2020

  
  

  Abstract

  This work presents a numerical method for the simulation of landslides generated impulse waves and its application to the historical Vajont case study. The computational tool is based on the Particle Finite Element Method (PFEM), a Lagrangian strategy that combines the finite element solution of the governing equations with an efficient remeshing strategy to deal with large deformation problems. After presenting the numerical formulation, different landslide impulse wave problems with Froude number ranging from 0.5 to 2.8, are analyzed to validate the proposed methodology. The computational method is shown to be able to reproduce accurately the landslide runout, the momentum transfer between the sliding material and the impounded water, and the consequent wave propagation observed in experimental physical models. Then, the PFEM model is applied to the numerical simulation of the Vajont disaster, which is analyzed with a fully-resolved three-dimensional model. The numerical results are discussed and compared to the post-event observations and the numerical results of other computational methods. The results in terms of landslide velocity and runout, geometry of the deposit, maximum water runup, dam overtopping wave, and water discharge in the downstream valley are in good agreement with observations and reconstructions. The calibration and validation performed for this study form the basis for the PFEM analyses presented in a companion paper finalized to simulate different scenarios of the Vajont rockslide considered in the experimental tests done a year before the disaster.

  Abstract
  This work presents a numerical method for the simulation of landslides generated impulse waves and its application to the historical Vajont case study. The computational tool [...]

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• A State of the Art Review of the Particle Finite Element Method (PFEM)

  M. Cremonesi, A. Franci, S. Idelsohn, E. Oñate

  Archives of Computational Methods in Engineering (2020). Vol. 27, pp. 1709–1735, 2020

  
  

  Abstract

  The particle finite element method (PFEM) is a powerful and robust numerical tool for the simulation of multi-physics problems in evolving domains. The PFEM exploits the Lagrangian framework to automatically identify and follow interfaces between different materials (e.g. fluid–fluid, fluid–solid or free surfaces). The method solves the governing equations with the standard finite element method and overcomes mesh distortion issues using a fast and efficient remeshing procedure. The flexibility and robustness of the method together with its capability for dealing with large topological variations of the computational domains, explain its success for solving a wide range of industrial and engineering problems. This paper provides an extended overview of the theory and applications of the method, giving the tools required to understand the PFEM from its basic ideas to the more advanced applications. Moreover, this work aims to confirm the flexibility and robustness of the PFEM for a broad range of engineering applications. Furthermore, presenting the advantages and disadvantages of the method, this overview can be the starting point for improvements of PFEM technology and for widening its application fields.

  Abstract
  The particle finite element method (PFEM) is a powerful and robust numerical tool for the simulation of multi-physics problems in evolving domains. The PFEM exploits the Lagrangian [...]

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• Modelling 3D metal cutting problems with the particle finite element method

  J. Puigbó, . J.M.Rodríguez, E. Oñate

  Computational Mechanics (2020). Vol. 66, pp. 603–624, 2020

  
  

  Abstract

  This work presents the development of the Particle Finite Element Method (PFEM) for the modelling of 3D solid mechanics problems under cutting conditions. The study and analysis of numerical models reproducing the cut of a material is a matter of interest in several areas; namely, the improvement of the material properties, the optimization of the process and tool geometries and the prediction of unexpected failures. The analysis of bi-dimensional (2D) models is the most common approach for different reasons. Just focusing on the simulation point of view, it is the simplest procedure, the cheapest in terms of computational cost and sometimes the only feasible numerical solution. However, many industrial machining processes, such as cutting, blanking, milling and drilling have not a possible simplification to 2D models. Actually even a simple turning processes for non-orthogonal cuts can not be simplified to 2D. This work present an upgrade of the PFEM techniques in order to deal with the 3D machining problems. We present recent improvements in the finite element formulation, the meshing re-connections and the contact detection. By applying these developments the PFEM has the capability for modelling a wide range of practical machining processes. In this paper the capacity of the formulation and the accuracy of the results are analyzed and validated with some representative examples.

  Abstract
  This work presents the development of the Particle Finite Element Method (PFEM) for the modelling of 3D solid mechanics problems under cutting conditions. The study and analysis [...]

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• Innovative mathematical and numerical models for studying the deformation of shells during industrial forming processes with the Finite Element Method

  V. Mataix Ferrándiz, E. Oñate, R. Rossi

  Monograph CIMNE (2020). M190

  
  

  Abstract

  This document contains the result resulting from the work in the doctoral thesis Innovative mathematical and numerical models for studying the deformation of shells during industrial forming processes with the Finite Element Method. The objective of this thesis is to contribute to the development of finite element methods for the analysis of the stamping processes, an area of problems with a very clear industrial application. Indeed these kinds of problems involve multiple disciplines and require the understanding of different mechanical problems, being the most relevant disciplines the continuous mechanics, the plasticity, contact problems, among others, depending of the problematic of study.

  Abstract
  This document contains the result resulting from the work in the doctoral thesis Innovative mathematical and numerical models for studying the deformation of shells during [...]

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• Evaluation of the performance of ballasted railway structures subjected to high-speed train loads by the Discrete Element Method

  . s:, J. Irazábal, F. Salazar, E. Oñate, J. Irazábal González

  J. Irazábal's Conference proceedings (2019). 1

  
  

  Abstract

  Conventional and high-speed train lines are being constructed all over the world with the objective of improving the mobility of both people and goods. Most of these infrastructures are built with railway ballast, a granular material whose main functions are resisting train loads and facing climate actions. The growth in popularity of railway infrastructures has led to an increasing interest in the development of numerical models to evaluate their performance and improve their maintenance. To this respect, the Discrete Element Method (DEM) is an approach that considers the discontinuous nature of granular materials, such as railway ballast. Moreover, it can also be used to compute the behaviour of continuum materials, such as rails and bearing plates, applying the so-called bonded DEM. The code used is developed within DEMPack, a specific software tool for modelling physical problems using the DEM. After evaluating the different geometrical alternatives for representing railway ballast and considering the high amount of material involved in the full-scale tests (more than 130,000 particles) the calculations were carried out using the most efficient option, spheres with rolling friction. This geometrical simplification is not suitable for small-scale tests, however, previous analysis showed that it is accurate enough for reproducing the macroscopic behaviour of the ballast layer. The numerical results correctly capture the effect of changing several parameters such as ballast compaction, inter-particle friction or grain size. It can be concluded that the DEM increases the possibilities for analysing innovative solutions aiming to improve ballasted tracks design, maintenance and performance, since real case-scenarios can be studied with enough accuracy and feasible time.

  Abstract
  Conventional and high-speed train lines are being constructed all over the world with the objective of improving the mobility of both people and goods. Most of these infrastructures [...]

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• Towards the Virtual Wind Tunnel for civil engineering applications

  R. Zorrilla, E. Oñate, R. Rossi

  Monograph CIMNE (2020). M189

  
  

  Abstract

  This monograph develops a numerical tool (the Virtual Wind Tunnel, VWT) for the reso-lution of problems involving fluid flow around structures. Due to the limitations that traditional methods may have in this context, the VWT is based on the use of fixed mesh technologies (CutFEM-type) combined with an implicit representation of the embedded bodies. One of the main contributions of the monograph is the use of such fixed mesh methods to solve lightweight thin-walled structures problems. Hence, two embedded formulations capable of representing the flow around bodies with and without internal volume are proposed. The first one results in a simpler implementation and lower computational effort but can only represent a slip behavior of the wall. The second one gets rid of such limitation by including a Nitsche imposition of the Navier-slip condition, thus allowing modelling any wall behavior as a wall law would do. The applicability range of the VWT includes the fluid–structure i nteraction problem (FSI). To that purpose an improvement for the boundary condition imposition of the FM-ALE algorithm mesh motion problem is also proposed. Moreover, the implementation, which has been conceived to be easily extended to any other coupled problem, is also treated. The validation of the technologies within the VWT includes multiple theoretical test cases as well as feasible industrial applications. Among these, the FSI analysis of a 4-point tent during a strong wind episode deserves to be highlighted as it showcases the achievement of the initial objective of the monograph.

  Abstract
  This monograph develops a numerical tool (the Virtual Wind Tunnel, VWT) for the reso-lution of problems involving fluid flow around structures. Due to the limitations that [...]

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• Detailed simulation of viral propagation in the built environment (preprint)

  R. Lohner, H. Antil, S. Idelsohn, E. Oñate

  Computational Mechanics (2020). 10.1007/s00466-020-01881-7

  
  

  Abstract

  A summary is given of the mechanical characteristics of virus contaminants and the transmission via droplets and aerosols. The ordinary and partial differential equations describing the physics of these processes with high fidelity are presented, as well as appropriate numerical schemes to solve them. Several examples taken from recent evaluations of the built environment are shown, as well as the optimal placement of sensors.

  Abstract
  A summary is given of the mechanical characteristics of virus contaminants and the transmission via droplets and aerosols. The ordinary and partial differential equations [...]

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• An embedded Finite Element framework for the resolution of strongly coupled Fluid–Structure Interaction problems. Application to volumetric and membrane-like structures

  R. Zorrilla, R. Rossi, R. Wüchner, E. Oñate

  Computer Methods in Applied Mechanics and Engineering (2020). Volume 368, pp. 113179

  
  

  Abstract

  This work presents a Fluid–Structure Interaction framework for the robust and efficient simulation of strongly coupled problems involving arbitrary large displacements and rotations. We focus on the application of the proposed tool to lightweight membrane-like structures. Nonetheless, all the techniques we present in this work can be applied to both volumetric and volumeless bodies. To achieve this, we rely on the use of embedded mesh methods in the fluid solver to conveniently handle the extremely large deflections and eventual topology changes of the structure. The coupling between the embedded fluid and mechanical solvers is based on an interface residual black-box strategy. We validate our proposal by solving reference benchmarking examples that consider both volumetric and volumeless geometries. Whenever it is possible, we also compare the embedded solution with the one obtained with our reference body fitted solver. Finally we present a real-life application of the presented embedded Fluid–Structure Interaction solver.

  Abstract
  This work presents a Fluid–Structure Interaction framework for the robust and efficient simulation of strongly coupled problems involving arbitrary large displacements [...]

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• Análisis numérico del proceso de filtración en presas de escollera

  C. Tapia, E. Oñate, A. LARESE

  (2009). Research Report, IT-591

  
  

  Abstract

  Las presas de materiales sueltos funcionan como presas de gravedad, el peso propio de los materiales que la componen aportan la resistencia necesaria para soportar el empuje horizontal y la flexión que producen las aguas en el trasdós. El inconveniente principal de éstas presas está en el sobrevertido. Si se produce una avenida y el agua vierte sobre la presa, ésta se comporta de manera inestable y puede colapsarse y desmoronarse. Se sabe que este fenómeno del sobrevertido es una de las principales razones por las que colapsan este tipo de presas, pero se trata de un fenómeno poco conocido y poco desarrollado. Por ello existe un interés cada vez mayor en el estudio del comportamiento de las presas de materiales sueltos cuando se lleva a cabo el llenado, y el sobrevertido de agua sobre el talud aguas abajo. Este estudio está limitado por la ausencia de un método de cálculo, por lo que es esencial llegar a constituir un método numérico que modelice el comportamiento físico de estos procesos en dichas presas.

  Abstract
  Las presas de materiales sueltos funcionan como presas de gravedad, el peso propio de los materiales que la componen aportan la resistencia necesaria para soportar el empuje [...]

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