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Abstract The Green’s function of a bimaterial infinite domain with a plane interface is applied to thermal analysis of a spherical underground heat storage tank. The heat transfer from a spherical source is derived from the integral of the Green’s function over the spherical domain. Because the thermal conductivity of the tank is generally different from soil, the Eshelby’s equivalent inclusion method (EIM) is used to simulate the thermal conductivity mismatch of the tank from the soil. For simplicity, the ground with an approximately uniform temperature on the surface is simulated by a bimaterial infinite domain, which is perfectly conductive above the ground. The heat conduction in the ground is investigated for two scenarios: First, a steady-state uniform heat flux from surface into the ground is considered, and the heat flux is disturbed by the existence of the tank due to the conductivity mismatch. A prescribed temperature gradient, or an eigen-temperature gradient, is introduced to investigate the local temperature field in the neighborhood of the tank. Second, when a temperature difference exists between the water in the tank and soil, the heat transfer between the tank and soil depends on the tank size, conductivity, and temperature difference, which provide a guideline for heat exchange design for the tank size. The modeling framework can be extended to two-dimensional cases, periodic, or transient heat transfer problems for geothermal well operations. The corresponding Green’s functions are provided for those applications. 

Abstract The paper extends the recent work (JAM, 88, 061002, 2021) of the Eshelby's tensors for polynomial eigenstrains from a two dimensional (2D) to three dimensional (3D) domain, which provides the solution to the elastic field with continuously distributed eigenstrain on a polyhedral inclusion approximated by the Taylor series of polynomials. Similarly, the polynomial eigenstrain is expanded at the centroid of the polyhedral inclusion with uniform, linear and quadratic order terms, which provides tailorable accuracy of the elastic solutions of polyhedral inhomogeneity by using Eshelby's equivalent inclusion method. However, for both 2D and 3D cases, the stress distribution in the inhomogeneity exhibits a certain discrepancy from the finite element results at the neighborhood of the vertices due to the singularity of Eshelby's tensors, which makes it inaccurate to use the Taylor series of polynomials at the centroid to catch the eigenstrain at the vertices. This paper formulates the domain discretization with tetrahedral elements to accurately solve for eigenstrain distribution and predict the stress field. With the eigenstrain determined at each node, the elastic field can be predicted with the closed-form domain integral of Green's function. The parametric analysis shows the performance difference between the polynomial eigenstrain by the Taylor expansion at the centroid and the 𝐶0 continuous eigenstrain by particle discretization. Because the stress singularity is evaluated by the analytical form of the Eshelby's tensor, the elastic analysis is robust, stable and efficient. 

Broadband terahertz (THz) wave emission from flowing liquid targets has been demonstrated under short optical pulse excitation. Observations have been reported by using liquid THz sources, including optimal angle of incidence, preference of subpicosecond pulse excitation, and strong sideway emission. Compared with solid targets, the fluidity of liquid allows each laser pulse to interact with a fresh area, which makes it possible to use a table-top laser with a high repetition rate for excitation. Liquids with a comparable material density to solids make them promising candidates for the study of high-density plasma and bright THz sources. In this paper, we review recent progress, challenges, and opportunities of THz emission from liquids. This topic may offer new possibilities in the exploration of THz liquid photonics and may play an indispensable role in the study of laser-liquid interaction.

 

Matters are generally classified within four states: solid, liquid, gas, and plasma. Three of the four states of matter (solid, gas, and plasma) have been used for THz wave generation with short laser pulse excitation for decades, including the recent vigorous development of THz photonics in gases (air plasma). However, the demonstration of THz generation from liquids was conspicuously absent. It is well known that water, the most common liquid, is a strong absorber in the far infrared range. Therefore, liquid water has historically been sworn off as a source for THz radiation. Recently, broadband THz wave generation from a flowing liquid target has been experimentally demonstrated through laser-induced microplasma. The liquid target as the THz source presents unique properties. Specifically, liquids have the comparable material density to that of solids, meaning that laser pulses over a certain area will interact with three orders more molecules than an equivalent cross-section of gases. In contrast with solid targets, the fluidity of liquid allows every laser pulse to interact with a fresh area on the target, meaning that material damage or degradation is not an issue with the high-repetition rate intense laser pulses. These make liquids very promising candidates for the investigation of high-energy-density plasma, as well as the possibility of being the next generation of THz sources.