Numerical analysis of coupled thermo-hydraulic problems in geotechnical engineering

© 2016 Elsevier Ltd.Ground source energy systems, such as open-loop systems, have been widely employed in recent years due to their economic and environmental benefits compared to conventional heating and cooling systems. Numerical modelling of such geothermal system requires solving a coupled thermo-hydraulic problem characterised by a convection-dominated heat transfer which can be challenging for the Galerkin finite element method (GFEM). This paper first presents the coupled thermo-hydraulic governing formulation as well as the coupled thermo-hydraulic boundary condition, which can be implemented into a finite element software. Subsequently, the stability condition of the adopted time marching scheme for coupled thermo-hydraulic analysis is established analytically. The behaviour of highly convective problems is then investigated via a series of analyses where convective heat transfer along a soil bar is simulated, with recommendations on the choice of an adequate discretisation with different boundary conditions being provided to avoid oscillatory solutions. Finally, the conclusions from the analytical and numerical studies are applied to the simulation of a boundary value problem involving an open-loop system, with the results showing good agreement with an approximate solution. The main objective of this paper is to demonstrate that the GFEM is capable of dealing with highly convective geotechnical problems

An alternative coupled thermo-hydro-mechanical finite element formulation for fully saturated soils

Accounting for interaction of the soil’s constituents due to temperature change in the design of geo-thermal infrastructure requires numerical algorithms capable of reproducing the coupled thermo-hydro-mechanical (THM) behaviour of soils. This paper proposes a fully coupled and robust THM formulation for fully saturated soils, developed and implemented into a bespoke finite element code. The flexibility of the proposed formulation allows the effect of some coupling components, which are often ignored in existing formulations, to be examined. It is further demonstrated that the proposed formulation recovers accurately thermally induced excess pore water pressures observed in undrained heating tests

A coupled thermo-hydro-mechanical finite element formulation of one-dimensional beam elements for three-dimensional analysis

Finite element (FE) analysis in geotechnical engineering often involves entities which can be represented as one-dimensional elements in three-dimensions (e.g. structural components, drains, heat exchanger pipes). Although structural components require an FE formulation accounting only for their mechanical behaviour, for the latter two examples, a coupled approach is necessary. This paper presents the first complete coupled thermo-hydro-mechanical FE formulation for one-dimensional beam elements for three-dimensional analysis. The possibility of deactivating each of the systems enables simulation of both coupled and uncoupled behaviour, and hence a range of engineering problems. The performance of these elements is demonstrated through various numerical simulations

Predictive modelling of thermo-active tunnels in London Clay

Thermo-active structures are underground facilities which enable the exchange of thermal energy between the ground and the overlying buildings, thus providing renewable means of space heating and cooling. Although this technology is becoming increasingly popular, the behaviour of geotechnical structures under additional thermal loading is still not fully understood. This paper focuses on the use of underground tunnels as thermo-active structures and explains their behaviour through a series of finite element analyses based on an existing case study of isothermal tunnels in London Clay. The bespoke finite element codeI CFEP is adopted which is capable of simulating the fully coupled thermo-hydro-mechanical behaviour of porous materials. The complex coupled interactions between the tunnel and the surrounding soil are explored bycomparing results from selected types of coupledand uncoupled simulations. It is demonstratedthat: (1) the thermally-induceddeformation of the tunnel and the ground are more critical design aspects than the thermally-induced forces in the tunnel lining, and (2) the modelling approach in terms of the type of analysis, as well as the assumed permeability of the tunnel lining, have a significant effect on the computed tunnel response and,hence, must be chosen carefull

Finite element modelling of heat transfer in ground source energy systems with heat exchanger pipes

Ground source energy systems (GSES) utilise low enthalpy geothermal energy and have been recognised as an efficient means of providing low carbon space heating and cooling. This study focuses on GSES where the exchange of heat between the ground and the building is achieved by circulating a fluid through heat exchanger pipes. Although numerical analysis is a powerful tool for exploring the performance of such systems, simulating the highly advective flows inside the heat exchanger pipes can be problematic. This paper presents an efficient approach for modelling these systems using the finite element method (FEM). The pipes are discretised with line elements and the conductive-advective heat flux along them is solved using the Petrov-Galerkin FEM instead of the conventional Galerkin FEM. Following extensive numerical studies, a modelling approach for simulating heat exchanger pipes, which employs line elements and a special material with enhanced thermal properties, is developed. The modelling approach is then adopted in three-dimensional simulations of two thermal response tests, with an excellent match between the computed and measured temperatures being obtained

Examining Infants’ Individuation of Others by Sociomoral Disposition

Early on infants seem to represent social actions of others from a moral perspective, evaluating others’ dispositions as “mean” or “nice.” The current research examined whether or not 11-month-old infants represent these sociomoral dispositions as deep and identity-determining properties using an object individuation task. Infants were shown two identical looking characters emerging sequentially from behind a screen and engaging in two different sociomoral actions. By using a looking-time paradigm the results show an interaction effect between the baseline and test trials, showing that infants seem to represent two different characters involved in the event, disregarding their same external appearance. This effect was mainly apparent when infants witnessed a negative event first in test trials. Experiments 2 and 3 control for alternative explanations. In Experiment 2 infants failed to individuate two characters when they are shown two identical looking puppets. In Experiment 3 infants fail to represent two characters when social information was taken away from the show. We discuss the possibility that by the end of the first year of life infants might represent sociomoral dispositions as diagnostic of individual identity

Five-year follow-up of participants diagnosed with chronic airflow obstruction in a South African Burden of Obstructive Lung Disease (BOLD) survey

Background. A community-based prevalence survey performed in two suburbs in Cape Town, South Africa (SA), in 2005, using the international Burden of Obstructive Lung Disease (BOLD) method, confirmed a prevalence of chronic airflow obstruction (CAO) in 23.1% of adults aged >40 years. Objectives. To study the clinical course and prognosis over 5 years of patients with CAO identified in the 2005 survey. Methods. Patients with CAO in 2005 were invited to participate. Standard BOLD and modified questionnaires were completed. Spirometry was performed using spirometers of the same make as in 2005. Results. Of 196 eligible participants from BOLD 2005, 45 (23.0%) had died, 8 from respiratory causes, 10 from cardiovascular causes and 6 from other known causes, while in 21 cases the cause of death was not known. On multivariate analysis, only age and Global initiative for Obstructive Lung Disease (GOLD) stage 4 disease at baseline were significantly associated with death. Of the 151 survivors, 11 (5.6% of the original cohort) were unavailable and 33 (16.8%) declined or had medical exclusions. One hundred and seven survivors were enrolled in the follow-up study (54.6%, median age 63.1 years, 45.8% males). Post-bronchodilator spirometry performed in 106 participants failed to confirm CAO, defined as a forced expiratory volume in 1 second (FEV1)/forced vital capacity (FVC) ratio of <0.7, in 16 participants (15.1%), but CAO was present in 90. The median decline in FEV1 was 28.9 mL/year (interquartile range –54.8 - 0.0) and was similar between GOLD stages. The median total decline in FVC was 75 mL, and was significantly greater in GOLD stage 1 (–350 mL) than in stages 2 or 3 (–80 mL and +140 mL, respectively; p<0.01). Fifty-eight participants with CAO in 2005 (64.4%) remained in the same GOLD stage, while 21 (23.3%) deteriorated and 11 (12.2%) improved by ≥1 stage. Only one-third were receiving any treatment for chronic obstructive pulmonary disease (COPD). Conclusions. The prevalence, morbidity and mortality of CAO and COPD in SA are high and the level of appropriate treatment is very low, pointing to underdiagnosis and inadequate provision of and access to effective treatments and preventive strategies for this priority chronic non-communicable disease.info:eu-repo/semantics/publishedVersio