An a priori error analysis of a type III thermoelastic problem with two porosities

In this work, we study, from the numerical point of view, a type III thermoelastic model with double porosity. The thermomechanical problem is written as a linear system composed of hyperbolic partial differential equations for the displacements and the two porosities, and a parabolic partial differential equation for the thermal displacement. An existence and uniqueness result is recalled. Then, we perform its a priori error numerical analysis approximating the resulting variational problem by using the finite element method and the implicit Euler scheme. The linear convergence of the algorithm is derived under suitable additional regularity conditions. Finally, some numerical simulations are shown to demonstrate the accuracy of the approximations and the dependence of the solution on a coupling coefficient.Ministerio de Ciencia, Innovación y Universidades | Ref. PGC2018‐096696‐B‐I00Ministerio de Economía y Competitividad | Ref. MTM2016‐74934‐

Thermo-mechanical parametric analysis of packed-bed thermocline energy storage tanks

© 2016. This version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/A packed-bed thermocline tank represents a proved cheaper thermal energy storage for concentrated solar power plants compared with the commonly-built two-tank system. However, its implementation has been stopped mainly due to the vessel’s thermal ratcheting concern, which would compromise its structural integrity. In order to have a better understanding of the commercial viability of thermocline approach, regarding energetic effectiveness and structural reliability, a new numerical simulation platform has been developed. The model dynamically solves and couples all the significant components of the subsystem, being able to evaluate its thermal and mechanical response over plant normal operation. The filler material is considered as a cohesionless bulk solid with thermal expansion. For the stresses on the tank wall the general thermoelastic theory is used. First, the numerical model is validated with the Solar One thermocline case, and then a parametric analysis is carried out by settling this storage technology in two real plants with a temperature rise of 100 °C and 275 °C. The numerical results show a better storage performance together with the lowest temperature difference, but both options achieve suitable structural factors of safety with a proper design.Peer ReviewedPostprint (author's final draft

Quantifying thermally driven fracture geometry during CO₂ storage

textThe desired lifetime for CO₂ injection for sequestration is several decades at a high injection rate (up to 10 bbl/min or 2,400 tons/day per injector). Government regulations and geomechanical design constraints may impose a limit on the injection rate such that, for example, the bottomhole pressure remains less than 90% of the hydraulic fracture pressure. Despite injecting below the critical fracture pressure, fractures can nevertheless initiate and propagate due to a thermoelastic stress reduction caused by cool CO₂ encountering hot reservoir rock. Here we develop a numerical model to calculate whether mechanical and thermal equilibrium between the injected CO₂ and the reservoir evolves, such that fracture growth ceases. When such a condition exists, the model predicts the corresponding fracture geometry and time to reach that state. The critical pressure for fracture propagation depends on the thermoelastic stress, a function of rock properties and the temperature difference between the injected fluid and the reservoir (ΔT). Fractures will propagate as long as the thermoelastic stress and the fluid pressure at the fracture tip exceed a threshold; we calculate the extent of a fracture such that the tip pressure falls below the thermoelastically modified fracture propagation pressure. Fracture growth is strongly dependent upon the formation permeability, the level of injection pressure above fracture propagation pressure, and ΔT.Petroleum and Geosystems Engineerin

Thermoelastic Modelling of Additive Manufacturing by Selective Laser Melting

Additive manufacturing represents a powerful tool for the production of lightweight and optimised aerospace components capable of enabling an overall mass reduction of the system they are embedded in and, consequently, minimising fuel consumption and pollutant emissions. In particular, combining additive methods with titanium alloys is an attractive solution for saving weight while ensuring structural integrity due to their outstanding specific mechanical properties. The problems associated with the manufacturing of titanium by traditional processes, namely the waste of raw material in relation to the material actually utilised, can be solved by the adoption of additive methods, in particular Selective Laser Melting. Active Space Technologies has been investigating additive­titanium solutions in the scope of the ADVANSS project whose aim was the research, development and manufacturing of a support structure, the Large Lens Mounting. However, the considerable heat exchanges between the substrate, the powder bed, the melt pool and the surrounding environment involved in the process are responsible for inducing large stress concentrations that may cause part failure. The main objective of this work is the development of a thermoelastic model capable of replicating the phenomena occurring during Selective Laser Melting, including material melting and subsequent cooling, with good flexibility in parameter variation. By predicting thermal stresses induced during manufacturing, it is possible to establish a set of process parameters capable of mitigating part imperfections. A series of complementary goals have been proposed as well: carrying out parametric studies to predict stresses induced by a specific set of parameters for a single layer, and later of a whole component, with n layers; building a hierarchy of parameters according to their ability to minimise stresses; and enriching Active Space Technologies expertise in additive manufacturing technologies. The prospect is that the knowledge acquired with this project contributes to the development of a similar model that would optimise the fabrication process of the Large Lens Mounting.O fabrico aditivo representa uma ferramenta poderosa na produção de componentes aeroespaciais leves e otimizados capazes de reduzir a massa do sistema onde estão inseridos e, consequentemente, o consumo de combustível e das emissões de poluentes. Em particular, a combinação de métodos aditivos e ligas de titânio é uma solução atraente para minimizar o peso ao mesmo tempo que confere integridade estrutural ao produto graças às suas excelentes propriedades mecânicas específicas. Os problemas associados ao fabrico de titânio por processos tradicionais, nomeadamente o elevado desperdício de matéria­prima em relação ao material efetivamente aproveitado, podem ser resolvidos através da adoção de métodos aditivos, em particular da Fusão Seletiva a Laser. A Active Space Technologies começou a investigar soluções de titânio em conjunto com técnicas de fabrico aditivo no âmbito do projeto ADVANSS, cujo intuito era a investigação, desenvolvimento e fabrico de uma estrutura de suporte, o Large Lens Mounting. No entanto, as consideráveis trocas de calor entre o substrato, a cama de pó, a poça de material fundido e o ambiente circundante envolvidas no processo são responsáveis por induzir grandes concentrações de tensões que podem resultar em falhas na peça. O objetivo principal deste trabalho é o desenvolvimento de um modelo termoelástico capaz de replicar os fenómenos presentes durante a Fusão Seletiva a Laser, incluindo a fusão do material e o posterior arrefecimento, com boa flexibilidade na variação dos parâmetros. Ao prever as tensões térmicas induzidas durante o processo de fabrico é possível estabelecer um conjunto de parâmetros de processamento capazes de mitigar as imperfeições das peças. Um conjunto de objetivos complementares também foi proposto: a realização de estudos paramétricos para prever tensões induzidas por um conjunto específico de parâmetros para uma única camada e, posteriormente, para um componente inteiro, com n camadas; a construção de uma hierarquia de parâmetros de acordo com sua capacidade de minimizar tensões e o enriquecimento das competências da Active Space Technologies no que diz respeito a tecnologias de manufatura aditiva. A perspectiva é que o conhecimento adquirido com este projeto contribua para o desenvolvimento de um modelo semelhante para otimizar o processo de fabricação do Large Lens Mounting

A nontraditional method for reducing thermoelastic stresses of variable thickness rotating discs

Funding Open access funding provided by The Science, Technology & Innovation Funding Authority (STDF) in cooperation with The Egyptian Knowledge Bank (EKB). This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.Peer reviewedPublisher PD

Computational thermomechanics of crystalline rock, Part I: A combined multi-phase-field/crystal plasticity approach for single crystal simulations

Rock salt is one of the major materials used for nuclear waste geological disposal. The desired characteristics of rock salt, i.e., high thermal conductivity, low permeability, and self-healing are highly related to its crystalline microstructure. Conventionally, this microstructural effect is often incorporated phenomenologically in macroscopic damage models. Nevertheless, the thermo-mechanical behavior of a crystalline material is dictated by the nature of crystal lattice and micromechanics (i.e., the slip-system). This paper presents a model proposed to examine these fundamental mechanisms at the grain scale level. We employ a crystal plasticity framework in which single-crystal halite is modeled as a face-centered cubic (FCC) structure with the secondary atoms in its octahedral holes, where a pair of Na and Cl ions forms the bond basis. Utilizing the crystal plasticity framework, we capture the existence of an elastic region in the stress space and the sequence of slip system activation of single-crystal halite under different temperature ranges. To capture the anisotropic nature of the intragranular fracture, we couple a crystal plasticity model with a multi-phase-field formulation that does not require high-order terms for the phase field. Numerical examples demonstrate that the proposed model is able to capture the anisotropy of inelastic and damage behavior under various loading rates and temperature conditions

Doctor of Philosophy

dissertationEnhanced Geothermal Systems (EGS) have the potential to tap vast amounts of energy. In order to improve EGS functionality, in depth experimental and computational studies of the heat transfer and fracture mechanics of bench top geothermal rock analogs were performed. These experiments contribute to the understanding of hydraulic and thermal fracturing as well as the effects of different heat transfer modes that can be used for heat mining. The work was conducted as follows: 1.Heat transfer rates in a hot dry rock analog containing a circular hole were quantified experimentally and computationally for single-phase fluid flow, and for water vaporization resulting from pore pressure reduction. 2.An experimental examination of hydraulic and thermal fracturing in plane strain was conducted to validate theoretical results and study the fracture morphologies. 3.Thermal fracturing of cement paste, acrylic, and granite was examined experimentally and computationally to understand the role of flaw orientation on resultant fracture geometry in a wellbore. Proof of concept experiments were performed to evaluate the heat mining potential of a new and innovative way to operate an Enhanced Geothermal System. By injecting water into hot dry rock, allowing it to thermally equilibrate and then dropping the pressure, steam can be produced at a large rate of heat transfer from the rock. This process has a distinct advantage of only needing one well to function. It was found that the steam generation has around 10 times higher heat transfer rates than that of low Peclet number, single phase flow, characteristic of conditions found in the reservoir away from the wellbore and preferential flow pathways. Experimental work was performed to evaluate the fracture morphology from hydraulic and thermal fractures. One of the purposes of this work was to validate the concept of creating thermal fractures that have faces perpendicular to the maximum horizontal earth stress. The bench top experimental analog was created to study thermal fracturing by uniaxially loading the specimen, thus creating conditions with only one principal stress which is perpendicular to the axis of the hole. Thermal fractures were created and observed with faces that are perpendicular to the maximum principal stress in 3-dimensional specimens for the first time since they were theorized in the 1970s. Finally a finite difference thermoelastic code with a linear elastic fracture mechanics assessment was created in order to evaluate the effect of various types of heat transfer on the thermal stresses and fracture nucleation potential. It was concluded that the circumferential fractures that were created experimentally in acrylic occurred from flaws that are at least four times larger in that orientation from drilling. In order to create thermal fractures in geologic reservoirs that are perpendicular to the maximum horizontal principal stress, half an order of magnitude larger flaws or preexisting fractures would have to exist in that orientation than features parallel to the maximum horizontal principal stress

A stabilized finite element formulation for monolithic thermo-hydro-mechanical simulations at finite strain

An adaptively stabilized monolithic finite element model is proposed to simulate the fully coupled thermo-hydro-mechanical behavior of porous media undergoing large deformation. We first formulate a finite-deformation thermo-hydro-mechanics field theory for non-isothermal porous media. Projection-based stabilization procedure is derived to eliminate spurious pore pressure and temperature modes due to the lack of the two-fold inf-sup condition of the equal-order finite element. To avoid volumetric locking due to the incompressibility of solid skeleton, we introduce a modified assumed deformation gradient in the formulation for non-isothermal porous solids. Finally, numerical examples are given to demonstrate the versatility and efficiency of this thermo-hydro-mechanical model