Page 89 - Analysis and Design of Energy Geostructures

Energy geostructures 59

Associated with the previous principles are the energy conservation equation, the
mass conservation equation and the momentum conservation equations. In some (sim-
ple) situations, the energy, mass and momentum conservation equations can be indi-
vidually solved to address thermal problems involving heat transfer, hydraulic problems
involving mass transfer and mechanical problems involving deformation. In general,
however, the coupled solution of more than one among the energy, mass and
momentum conservation equations may be required for a rigorous treatment of heat
transfer, mass transfer and deformation. The reason for this is that heat transfer, mass
transfer and deformation are coupled phenomena (i.e. the dependent variables govern-
ing them can influence each other to a more or less pronounced extent) and result in
couplings in the material behaviour as well.

2.7.3 Modelling approaches serving the analysis and design
of energy geostructures
The coupled analysis of heat transfer, mass transfer and deformation and the resulting
thermohydromechanical behaviour of materials have been addressed in detail, for
example, by Lewis and Schrefler (1987) and Lewis et al. (1996), and relies on a so-
called thermohydromechanical modelling approach. While the referenced approach
may be considered to be the most accurate for addressing the considered phenomena
in the scope of energy geostructures, separate yet coupled analyses of heat transfer and
mass transfer as well as of deformation and heat transfer phenomena can be employed.
This modelling approach may be particularly effective when the use of a single conser-
vation equation to address the relevant variable governing heat transfer, mass transfer
or deformation prevents the analysis of the considered phenomena, and the simulta-
neous solution of the energy, mass and momentum conservation equations is impracti-
cal. In this context thermohydraulic modelling may be employed to address essential
aspects of heat and mass transfers, while thermomechanical modelling may be
employed to address deformation and heat transfer. These possibilities should be
accounted for the analysis and design of energy geostructures.

2.7.4 Problems of interest

In the analysis and design of energy geostructures, two classes of problems may conve-
niently be distinguished: (1) problems related to heat and mass transfers (and deforma-
tion) that occur in the pipes embedded within energy geostructures or in the
underground built environments potentially adjacent to such structures (e.g. metro
tunnels and railway stations); and (2) problems related to heat and mass transfers, and
deformations that characterise the geomaterials constituting energy geostructures
and the surrounding ground. Despite relying on the same governing equations, the
phenomena involved in the former class of problems are typically addressed from