On December 21st 2020, Alejandro Cornejo has successfully defended his PhD Thesis entitled “A fully Lagrangian formulation for fluid-structure interaction between free surface flows and multifracturing solids and structures”.
The thesis has been developed in the framework of the PhD Programme in Structural Analysis of the Technical University of Catalonia (UPC · Barcelona Tech). The thesis supervisors have been the UPC professors Eugenio Oñate and Francisco Zarate. Due to the COVID-19 restrictions, the thesis defense took place in the online mode. The thesis obtained a qualification of Excellent Cum Laude.
The PhD Exam Committee was formed by Professors Miguel Cervera (Chair), from UPC · Barcelona Tech; Umberto Perego, from Politecnico di Milano (Italy); and Antonia Larese, from Università degli Studi di Padova (Italy).
From left to right: Prof. Eugenio Oñate, PhD Alejandro Cornejo and Dr. Francisco Zárate
From left to right: Prof. Eugenio Oñate, Prof. Miguel Cervera, PhD Alejandro Cornejo and Dr. Francisco Zárate
The objective of this thesis is to develop an advanced numerical method capable of simulating multi-fracture processes in materials and structures. The new numerical methodology is meant to cover the maximum spectrum of engineering applications possible. For this purpose, a coupled formulation of the Finite Element Method (FEM) and the Discrete Element Method (DEM) is used. An isotropic damage constitutive model is employed to simulate the initial degradation of the material. Once the strength of the material has been completely exhausted, the damaged finite elements are removed from the mesh and a set of discrete elements are generated at the corresponding mesh nodes. In order to ensure mass conservation, the frictional forces between the discrete elements prevent the indentation between the cracking planes.
The thesis also studies how the proposed FEM-DEM technique together with the smoothing of stresses based on the super-convergent patch is able to obtain reasonably mesh-independent results. This favours the inclusion of an adaptive remeshing technique that will refine the mesh where it is required (according to the Hessian of a nodal indicator of interest) thus improving the discretization quality of the cracks obtained and optimizing the simulation cost.
The FEM-DEM formulation has been coupled to the Particle Finite Element Method (PFEM) approach for solving fluid-structure interaction problems typical of natural disasters involving complex free-surface water flows such as floods and tsunamis. The applicability of the resulting strongly coupled formulation has been shown in the analysis of many cases of free surface fluid flows impacting with fracturing solids and structures such as walls and dikes, among others.