The interaction factor method for energy pile groups

Prior to this study, no simplified yet rational methods were available for estimating the vertical displacements of energy pile groups subjected to thermal loads. Observing such a challenge, the goal of this study has been threefold: (i) to extend the interaction factor concept from the framework of conventional pile groups to that of energy pile groups, (ii) to present charts for the analysis of the displacement interaction between two identical energy piles over a broad range of design conditions, and (iii) to propose, apply and validate the interaction factor method for the displacement analysis of energy pile groups

Energy and geotechnical behaviour of energy piles for different design solutions

Energy piles are heat capacity systems that have been increasingly exploited to provide both supplies of energy and structural support to civil structures. The energy and geotechnical behaviours of such foundations, which are governed by their response to thermo-mechanical loads, is currently not fully understood, especially considering the different design solutions for ground-coupled heat exchangers. This paper summarises the results of numerical sensitivity analyses that were performed to investigate the thermo-mechanical response of a full-scale energy pile for different (i) pipe configurations, (ii) foundation aspect ratios, (iii) mass flow rates of the fluid circulating in the pipes and (iv) fluid mixture compositions. This study outlines the impacts of the different solutions on the energy and geotechnical behaviour of the energy piles along with important forethoughts that engineers might consider in the design of such foundations. It was observed that the pipe configuration strongly influenced both the energy and the geotechnical performance of the energy piles. The foundation aspect ratio also played an important role in this context. The mass flow rate of the fluid circulating in the pipes remarkably influenced only the energy performance of the foundation. Usual mixtures of a water-antifreeze liquid circulating in the pipes did not markedly affect both the energy and the geotechnical performance of the pile

The key role of interband transitions in hot-electron-modulated TiN films

Titanium nitride (TiN) is an emerging new material in the field of plasmonics, both for its linear and nonlinear optical properties. Similarly to noble metals, like, e.g., gold (Au), the giant third-order optical nonlinearity of TiN following excitation with fs-laser pulses has been attributed to the generation of hot electrons. Here we provide a numerical study of the Fermi smearing mechanism associated with photogenerated hot carriers and subsequent interband transitions modulation in TiN films. A detailed comparison with Au films is also provided, and saturation effects of the permittivity modulation for increasing pump fluence are discussed

Unfolding the Origin of the Ultrafast Optical Response of Titanium Nitride

Ultrafast plasmonics is driving growing interest for the search of novel plasmonic materials, overcoming the main limitations of noble metals. In this framework, titanium nitride (TiN) is brought in the spotlight for its refractory properties combined with an extremely fast electron-lattice cooling time (<100 fs) compared to gold (approximate to 1 ps). Despite the results reported in literature, a clear-cut explanation of the origin of the ultrafast and giant optical response of TiN-based materials upon excitation with femtosecond laser pulses is still missing. To address this issue, an original model is introduced, capable of unfolding the modulation of TiN optical properties on a broad bandwidth, starting from the variations of electronic and lattice temperatures following ultrafast photoexcitation. The numerical analysis is validated on ultrafast pump-probe spectroscopy experiments on a simple structure, a TiN film on glass. This approach enables a complete disentanglement of the interband and intraband contributions to the permittivity modulation. Moreover, it is also shown that, varying the synthesis conditions of the TiN film, not only the static, but also the dynamical optical response can be efficiently tuned. These findings pave the way for a breakthrough in the field: the design of TiN-based ultrafast nanodevices for all-optical modulation of light

Design and testing of ultrafast plasmonic lens nanoemitters

Nanoscale electron pulses are increasingly in demand, including as probes of nanoscale ultrafast dynamics and for emerging light source and lithography applications. Using electromagnetic simulations, we show that gold plasmonic lenses as multiphoton photoemitters provide unique advantages, including emission from an atomically at surface, nanoscale pulse diameter regardless of laser spot size, and femtosecond-scale response time. We then present fabrication of prototypes with sub-nm roughness via e-beam lithography, as well as electro-optical characterization using cathodoluminescence spectromicroscopy. Finally, we introduce a DC photogun at LBNL built for testing ultrafast photoemitters. We discuss measurement considerations for ultrafast nanoemitters and predict that we can extract tens of pA photocurrent from a single plasmonic lens using a Ti:Sa oscillator. Altogether, this lays the groundwork to develop and test a broad class of plasmon-enhanced ultrafast nanoemitters

The role of ground conditions on the heat exchange potential of energy walls

Geotechnical structures are being increasingly employed, in Europe as all around the world, to exchange heat with the ground and supply thermal energy for heating and cooling of buildings and de-icing of infrastructure. Most current practical applications are related to energy piles, but embedded retaining walls are now also being adopted. However, analysis and design methods for these new dual use foundations and ground heat exchangers are currently lacking, making it hard to provide estimates of energy availability without recourse to full numerical simulation. This paper helps to fill this gap by using coupled thermo-hydro finite element analysis to develop charts of energy capacity that could be applied at the outline design stage for energy walls. In particular, the influence of ground properties (hydraulic and thermal conductivities), and ground conditions, (groundwater temperature and flow velocity) are investigated with the results showing that the hydrogeological conditions and the temperature difference between the ground source and application temperature are especially important in determining the performance of the energy wall

Thermo-mechanical schemes for energy piles

Currently, schemes based on seminal empirical knowledge about energy piles subjected to mechanical and thermal loads are available to describe the response of such foundations. However, schemes based on theoretical principles may more closely reflect the predictions made for the analysis and design of energy piles. Looking at such challenge, this paper presents thermo-mechanical schemes based on thermo-elasticity theory to address the response of single energy piles to mechanical and thermal loads. The proposed schemes highlight a number of key aspects associated with the modelling of energy pile response to loading and may be considered in analysis and design. © Springer Nature Switzerland AG 2019

Thermo-mechanical performance of energy pile groups

Employing geostructures as structural supports and geomaterials as reservoirs for the extraction and storage of heat represent effective means to meet human activity needs since ancient times. This doctoral thesis focuses on the thermo-mechanical behaviour and performance of an innovative, multifunctional technology that couples the aforementioned roles for the structural support and energy supply of any type of built environment, i.e., energy piles. The multifunctional role of energy piles involves mechanical and thermal loads applied to such geostructures. These loads pose unprecedented challenges to engineers because they cause variations in the temperature, stress, deformation and displacement in the subsurface that need to be considered during analysis and design. Prior to this work, a substantial amount of research had been made available to address the thermo-mechanical performance of single energy piles. Design guidance has also been proposed to advise in the geotechnical and structural design of such geostructures. However, energy pile foundations do not consist of a single energy pile but of a group of energy piles. In this framework, (i) limited knowledge, if available, was present to address the thermo-mechanical behaviour and performance of energy pile groups subjected to thermal and mechanical loads; (ii) no simplified models and methods were accessible to perform the analysis and design of energy pile groups against the action of such loads; and (iii) no comprehensive framework for the effect of thermal (and mechanical) loads on the performance and the related design of both single and groups of energy piles was avail-able. To address such challenges, this doctoral research was performed to (i) investigate the thermo-mechanical behaviour and performance of energy pile groups over typical time-scales of practical applications via the first available in situ tests and coupled numerical analyses of such geostructures; (ii) provide the only simplified analytical models and methods for predicting the vertical deformation of energy pile groups subjected to thermal and mechanical loads; and (iii) propose a comprehensive framework for the effect of thermal and mechanical loads on the performance and related performance-based design (e.g., geotechnical and structural) of single and groups of energy piles. The results presented in this thesis suggest the conclusion that (a) the thermo-mechanical behaviour and performance of energy pile groups are critically different from those of single energy piles; (b) thermal loads, applied alone or in conjunction to mechanical loads, represent a serviceability and not an ultimate limit state problem; and (c) no energy pile analysis and design can be considered complete without addressing the behaviour of piles as both isolated elements and in a group