Buried Source Research Articles

Interpreting the direction of the gravity gradient tensor eigenvectors: The main tidal force and its relation to the curvature parameters of the equipotential surface

Rotating the gravity gradient tensor about a vertical axis by an appropriate angle allows one to express its components as functions of the curvatures of the equipotential surface. The description permits the identification of the gravity gradient tensor as the Newtonian tidal tensor and part of the tidal potential. The identification improves the understanding and interpretation of gravity gradient data. With the use of the plunge of the eigenvector associated with the largest eigenvalue or plunge of the main tidal force, it is possible to estimate the location and depth of buried gravity sources; this is illustrated in model data and applied to FALCON airborne gravity gradiometer data from the Canning Basin, Australia.

Axisymmetric analysis of a thermoelastic isotropic half-space under buried sources in displacement and temperature potentials

ABSTRACTAnalytical and numerical investigations have been made to determine the solution of a thermoelastic isotropic half-space under buried mechanical load and heat flux based on Biot’s coupled thermoelasticity. Using a scalar potential function, the coupled governing equations have been uncoupled and a sixth order partial differential equation that governs the potential function is received. Applying the Hankel transform to suppress the radial variable, a sixth order ordinary differential equation with respect to depth is received. Solving that equation and utilizing the boundary and continuity conditions, the potential function is derived and displacements, temperature, and stress components are derived in the transformed domain in two regions. Applying the inverse Hankel transform, responses are derived in the physical domain as line integrals. The line integrals are calculated numerically through Mathematica software. Numerical results are depicted graphically for different cases of vertical load and heat flux. Effects of elastic and thermal properties as well as the depth of buried loads and frequency of excitation are investigated. Numerical evaluation shows that the agreement between the results of this study for surface excitation and the results reported in the literature is excellent.

An analytical solution for the transient response of a semi-infinite elastic medium with a buried arbitrary cylindrical line source

This study develops an analytical solution for the transient response of a semi-infinite medium subjected to an arbitrary cylindrical line source buried at a certain depth by using the Laplace transform and Cagniard's method. The analytical solution is presented in a simple closed form and each term represents a transient physical wave. During the solution procedure, the arbitrary source pulse is first decomposed into a compressional wave (P) and a tangential wave (S), and then analytical solutions in the Laplace domain for the P and S pulse sources are derived. By applying Cagniard's inverse Laplace transform method and the convolution theorem, analytical solutions in the time domain are obtained. Finally, the analytical solution for arbitrary source pulse can be expressed as the superposition of the solutions for the P and S pulse sources. Numerical examples are provided to illustrate some interesting features of the cylindrical P and S wave propagation in a semi-infinite media with a free surface. A head wave can be observed in a certain area of the semi-infinite media due to the S pulse, which is not found in the P pulse problem.

The thermal regime around buried submarine high-voltage cables

The expansion of offshore renewable energy infrastructure and the need for trans-continental shelf power transmission require the use of submarine High Voltage (HV) cables. These cables have maximum operating surface temperatures of up to 70°C and are typically buried 1–2 m beneath the seabed, within the wide range of substrates found on the continental shelf. However, the heat flow pattern and potential effects on the sedimentary environments around such anomalously high heat sources in the near surface sediments are poorly understood. We present temperature measurements from a 2D laboratory experiment representing a buried submarine HV cable, and identify the thermal regimes generated within typical unconsolidated shelf sediments—coarse silt, fine sand and very coarse sand. We used a large (2 × 2.5 m) tank filled with water-saturated spherical glass beads (ballotini) and instrumented with a buried heat source and 120 thermocouples, to measure the time-dependent 2D temperature distributions. The observed and corresponding Finite Element Method (FEM) simulations of the steady state heat flow regimes, and normalised radial temperature distributions were assessed. Our results show that the heat transfer and thus temperature fields generated from submarine HV cables buried within a range of sediments are highly variable. Coarse silts are shown to be purely conductive, producing temperature increases of >10°C up to 40 cm from the source of 60°C above ambient; fine sands demonstrate a transition from conductive to convective heat transfer between c. 20°C and 36°C above ambient, with >10°C heat increases occurring over a metre from the source of 55°C above ambient; and very coarse sands exhibit dominantly convective heat transfer even at very low (c. 7°C) operating temperatures and reaching temperatures of up to 18°C above ambient at a metre from the source at surface temperatures of only 18°C. These findings are important for the surrounding near surface environments experiencing such high temperatures and may have significant implications for chemical and physical processes operating at the grain and sub-grain scale; biological activity at both micro-faunal and macro-faunal levels; and indeed the operational performance of the cables themselves, as convective heat transport would increase cable current ratings, something neglected in existing standards.

Interpreting the direction of the gravity gradient tensor eigenvectors: Their relation to curvature parameters of the gravity field

Rotating the gravity gradient tensor about a vertical axis by an appropriate angle allows one to express its components as functions of the curvatures of the equipotential surface. The description permits the identification of the gravity gradient tensor as the Newtonian tidal tensor and part of the tidal potential. The identification improves the understanding and interpretation of gravity gradient data. With the use of the plunge of the eigenvector associated with the largest eigenvalue or plunge of the main tidal force, it is possible to estimate the location and depth of buried gravity sources; this is developed in model data and applied to FALCON airborne gravity gradiometer data from the Canning Basin, Australia.

Tension‐saturated and unsaturated flows from line sources in subsurface irrigation: Riesenkampf's and Philip's solutions revisited

AbstractRiesenkampf's (1938), R‐38 (referred to here as R‐38), analytical solution for steady 2‐D flow from a buried line source in a homogeneous Green‐Ampt soil, with a wetting plume bounded by a free surface (capillary fringe), is compared with Philip's (1969), (P‐69), one for genuinely unsaturated wetting of Gardner's infinite‐extension soil. Conformal mappings are used in R‐38, from which we derived the flow net, pore‐water isobars, isochrones, fields of Darcian velocity and resultant force acting on saturated porous skeleton, fine geometry (shape and size) of the constant‐head contour encompassing a mole‐emitter or leaky‐pipe, as well as the dependence of the total discharge per unit pipe length on uniform pressure in the pipe, capillarity of the soil, radius of the pipe, and saturated hydraulic conductivity. An ovalic “water table” isobar, encompassing P‐69 source, is compared with one of R‐38 for a fixed discharge and saturated conductivity but adjusted sorptive numbers. The Whisler and Bouwer (1970) relation between the static height of capillary rise and sorptive number is shown to give a good match between R‐38 and P‐69 isobars. This allows to use R‐38 in the source vicinity and P‐69 in the far‐field zone. Computer algebra (Mathematica) routines are used for visualization of the known and extended R‐38 and P‐69 solutions.

Seismic response of reduced micropolar elastic half-space

This paper explores reduced micropolar theory to simulate ground motion during an earthquake. In this theory, rotational motions are kinematically independent of translational motions. Analytical expressions for ground displacement and rotational motions due to a buried seismic source are presented in this paper. This theory requires two additional material constants which characterise the microstructure of the medium compared with linear elastic theory. Ground motions are simulated for an earthquake of magnitude (M w) 5.0. The sensitivity of ground motion to these new material constants is reported. It is observed that rotations are sensitive to microstructure of the medium. A comparison with recorded rotations of the M w 5.2 Izu peninsula, Japan event is also presented in this article.

Plant Root Templated Irrigation

AbstractA new method is explored for subsurface irrigation where the plant root structure is used as the subsurface water distribution system. Plants are severed at the stem and the stem stump is attached to a pressurized water source such that water may permeate into surrounding soil through the existing buried root system. This pressurized root system serves as a well‐ distributed buried irrigation water source to the other nearby growing plants taking up water. The feasibility of using an existing root structure in this manner to supply water at rates necessary to satisfy other growing plants was determined by conducting laboratory water hydraulic conductance studies. Laboratory growth studies were used to directly test the proposed root templated irrigation (RTI) approach. Modelling simulations were also utilized to extend laboratory findings to other scenarios and compare expected water use efficiency benefits associated with this proposed irrigation method with surface irrigation (SI) and subsurface drip irrigation (SDI) practices. Irrigation study measurements showed that RTI provides more efficient water use as compared to SI. Modelling calculations were in qualitative agreement with the experimental studies, indicating that RTI yields improvement in root water uptake over the SI and also SDI unless SDI source spacing is narrow. Copyright © 2016 John Wiley & Sons, Ltd.

The horizontal boundary and top depth estimates of buried source using gravity data and their applications

A new method of the horizontal location of boundaries and the estimates of top depth of gravity anomaly sources is presented to meet the need of the quick interpretation of potential field data. On the basis of the theory of Tilt angle and Tilt-depth, we derive new Tilt-depth method for gravity anomaly from the forward formula of the upright dyke model, namely Tilt-depth2. This method combines the second order of horizontal and vertical gradient of gravity data. It not only indicates the horizontal locations of boundaries according to the 0° contour line, but also estimates the top depths of buried sources calculated from the horizontal distances from 45° and 90° contour line to 0° contour line. In the synthetic model tests, 2D and 3D combined designed model is used to show effectiveness of the Tilt-depth2, where the results are more in accordance with the true parameters. In a case study of Nanmeitou ore deposit in China, the geological bodies' boundaries are well identified and the depth estimates of the focus area are relatively consistent with the drilling data, which can provide effective reference for subsequent drilling target selection.

In-situ characterisation of a buried 137Cs source in the frame of nuclear forensics

An approach is demonstrated, through simulations using MCNP, to characterise buried radioactive sources, in terms of their depth, radioactivity and location of their edges in the case of a volumetric one. The approach involves scanning of the sources with a collimated HPGe detector, positioned vertically and at an angle. The sought parameters to characterise the sources considered, were accurately reproduced. The approach was verified experimentally for 137Cs cuboid and point buried sources. The parameters of interest were determined to within 22 % of the actual values.

Extended precise integration method for axisymmetric thermo‐elastic problem in transversely isotropic material

SummaryThis paper presents a numerical solution for the analysis of the axisymmetric thermo‐elastic problem in transversely isotropic material due to a buried heat source by means of extended precise integral method. By virtue of the Laplace–Hankel transform applied into the basic governing equations, an ordinary differential matrix equation is achieved, which describes the relationship between the generalized stresses and displacements in transformed domain. An extended precise integration method is introduced to solve the aforementioned matrix equation, and the actual solution in the physical domain is acquired by inverting the Laplace–Hankel transform. Numerical examples are carried out to demonstrate the accuracy of the proposed method and elucidate the influence of the character of transverse isotropy, the anisotropy of linear expansion coefficient, the anisotropy of thermal diffusivity, and medium's stratification on the thermo‐elastic response. Copyright © 2015 John Wiley & Sons, Ltd.

Dynamic Impedance Functions for Arbitrary-Shaped Rigid Foundation Embedded in Anisotropic Multilayered Soil

AbstractThis paper presents a hybrid numerical method for the evaluation of dynamic impedance of rigid foundation embedded in anisotropic multilayered soil. The proposed approach includes two main parts: (a) the solution of wave propagation in anisotropic multilayered soil in the frequency wave-number domain; (b) the evaluation of Green’s functions for a buried source lying in the anisotropic multilayered soil in the frequency spatial domain. The derivation of part (a) is based on the precise integration method (PIM) and the mixed variable formulation (MVF) of wave motion equations, which ensure accuracy of the solution and make it convenient to deal with the assembly of layers for multilayered soil. Part (b) can be preceded by applying the inverse Fourier transformation directly. Finally, the flexible volume method is used to obtain the impedance of foundation embedded in anisotropic multilayered soil. A comparison of the numerical results with those available in the literature validates the effectivenes...

Axisymmetric thermal consolidation of multilayered porous thermoelastic media due to a heat source

SummaryThis paper presents an analytical layer element solution to axisymmetric thermal consolidation of multilayered porous thermoelastic media containing a deep buried heat source. By applying the Laplace–Hankel transform to the state variables involved in the basic governing equations of porous thermoelasticity, the analytical layer elements that describe the relationship between the transformed generalized stresses and displacements of a finite layer and a half‐space are derived. The global stiffness matrix equation is obtained by assembling the interrelated layer elements, and the real solutions in the physical domain are achieved by numerical inversion of the Laplace–Hankel transform after obtaining the solutions in the transformed domain. Finally, numerical calculations are performed to demonstrate the accuracy of this method and to investigate the influence of heat source's types, layering, and the porous thermoelastic material parameters on thermal consolidation behavior. Copyright © 2015 John Wiley & Sons, Ltd.

Seismic ground motion in micropolar elastic half-space

In this article, analytic expressions for the frequency wave number spectra are derived for the displacement and rotational components at the ground surface of a micropolar elastic half-space. The ground motion is caused by buried sources described in terms of unit impulsive force and micro-moments. Closed-form analytic expressions for both plane strain and anti-plane strain conditions are established. In the sequel, Green’s functions for reduced micro polar half-space where the couple stresses are zero and the stress tensor is nonsymmetric are also presented. Numerical results are presented for anti-plane strain case. The derived expressions can be used to simulate rotational and displacement components of ground motion during earthquakes.

Determination of block rotations and the Curie Point Depths of magnetic sources along the NW–SE-trending Sülüklü–Cihanbeyli-Gölören and Şereflikoçhisar-Aksaray Fault Zones, Central Anatolia, Turkey

The Şereflikoçhisar-Aksaray Fault (SAF) and Sülüklü–Cihanbeyli–Gölören Fault (SCGF) zones are located at the eastern and the western margins of the Salt Lake Basin-SLB (Tuzgölü Basin), central Anatolia, Turkey. These fault zones display intense magnetic anomalies along their trends and the positive amplitudes of these anomalies may reach up to 650 nT. In this paper, the body magnetisation directions are estimated from the selected five different magnetic anomalies with positive and negative peaks along these fault zones. Results of calculations indicated that local clockwise rotations are in the range of 34°E and 70°E. These magnetic anomalies were mainly created by the buried intrusive rocks. Locations of buried causative sources along the fault zones were determined from the analytic signal transformation of magnetic anomaly data. Curie Point Depths (CPDs) are also estimated from the aeromagnetic data to determine the thermal structure of the study area and they are correlated with the SAF and SCGF zones. It was found that the depth of magnetic crust varies from 11 to 22 km, consistent with the tectonic fault zones in the study area. The average value was determined as 16.7 km. These depths were correlated with the deep seismic reflection data and depths obtained from two windows in the seismic section, GTRS-87-801 are consistent with the CPDs. Shallow CPDs of magnetic sources are located along the SAF and SCGF to the east and west of the Lake Tuzgölü (Salt Lake) and it may be suggested that magnetic sources are probably located at the upper part of the crust.

HIGH-LYING OH ABSORPTION, [C II] DEFICITS, AND EXTREMELFIR/MH2RATIOS IN GALAXIES

Herschel/PACS observations of 29 local (Ultra-)Luminous Infrared Galaxies, including both starburst and AGN-dominated sources as diagnosed in the mid-infrared/optical, show that the equivalent width of the absorbing OH 65 um Pi_{3/2} J=9/2-7/2 line (W_{eq}(OH65)) with lower level energy E_{low}~300 K, is anticorrelated with the [C ii]158 um line to far-infrared luminosity ratio, and correlated with the far-infrared luminosity per unit gas mass and with the 60-to-100 um far-infrared color. While all sources are in the active L_{IR}/M_{H2}>50 Lsun/Msun mode as derived from previous CO line studies, the OH65 absorption shows a bimodal distribution with a discontinuity at L_{FIR}/M_{H2}~100 Lsun/Msun. In the most buried sources, OH65 probes material partially responsible for the silicate 9.7 um absorption. Combined with observations of the OH 71 um Pi_{1/2} J=7/2-5/2 doublet (E_{low}~415 K), radiative transfer models characterized by the equivalent dust temperature, Tdust, and the continuum optical depth at 100 um, tau_{100}, indicate that strong [C ii]158 um deficits are associated with far-IR thick (tau_{100}>~0.7, N_{H}>~10^{24} cm^{-2}), warm (Tdust>~60 K) structures where the OH 65 um absorption is produced, most likely in circumnuclear disks/tori/cocoons. With their high L_{FIR}/M_{H2} ratios and columns, the presence of these structures is expected to give rise to strong [C ii] deficits. W_{eq}(OH65) probes the fraction of infrared luminosity arising from these compact/warm environments, which is >~30-50% in sources with high W_{eq}({OH65}). Sources with high W_{eq}({OH65}) have surface densities of both L_{IR} and M_{H2} higher than inferred from the half-light (CO or UV/optical) radius, tracing coherent structures that represent the most buried/active stage of (circum)nuclear starburst-AGN co-evolution.

Characteristics of the horizontal component of Rayleigh waves in multimode analysis of surface waves

In surface-wave analysis, S-wave velocity estimations can be improved by the use of higher modes of the surface waves. The vertical component of P-SV waves is commonly used to estimate multimode Rayleigh waves, although Rayleigh waves are also included in horizontal components of P-SV waves. To demonstrate the advantages of using the horizontal components of multimode Rayleigh waves, we investigated the characteristics of the horizontal and vertical components of Rayleigh waves. We conducted numerical modeling and field data analyses rather than a theoretical study for both components of Rayleigh waves. As a result of a simulation study, we found that the estimated higher modes have larger relative amplitudes in the vertical and horizontal components as the source depth increases. In particular, higher-order modes were observed in the horizontal component data for an explosive source located at a greater depth. Similar phenomena were observed in the field data acquired by using a dynamite source at 15-m depth. Sensitivity analyses of dispersion curves to S-wave velocity changes revealed that dispersion curves additionally estimated from the horizontal components can potentially improve S-wave velocity estimations. These results revealed that when the explosive source was buried at a greater depth, the horizontal components can complement Rayleigh waves estimated from the vertical components. Therefore, the combined use of the horizontal component data with the vertical component data would contribute to improving S-wave velocity estimations, especially in the case of buried explosive source signal.

Analysis of axisymmetric thermo-elastic problem in multilayered material with anisotropic thermal diffusivity

An analytical solution is derived for the axisymmetric thermo-elastic problem of multilayered material with anisotropic thermal diffusivity due to a buried heat source. By applying the Laplace–Hankel transform to the state variables involved in the basic governing equations, the analytical layer-element which describes the relationship between the transformed generalized stresses and displacements is obtained. Considering the continuity conditions between adjacent layers and the boundary conditions, the global stiffness matrix for a multilayered system is assembled and solved in the transformed domain. The actual solutions of the problem in the physical domain are acquired by inverting the Laplace–Hankel transform. Finally, some numerical examples are given to demonstrate the accuracy of the proposed method and to illustrate the influences of the heat source’s types and the anisotropy of thermal diffusivity on the thermo-elastic response.

Novel 4<italic>F</italic><sup>2</sup> Buried-Source-Line STT MRAM Cell With Vertical GAA Transistor as Select Device

Spin transfer torque (STT) magnetic random access memories (MRAMs) have recently emerged as one of the strongest contenders for universal memory technology. They have entire range of features, i.e., high speed, nonvolatility, high density, and low power, which make them cynosure to every memory designer's notion. Researchers are working ardently to use STT MRAMs under continuously increasing scaling challenges. To accommodate a larger amount of embedded memory, the cell size must be reduced. Therefore, the designs target to attain an optimistic figure of 4F <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> (F being the feature size) array density, which is the maximum achievable two-dimensional (2-D) density. With this objective in mind, a novel 4F <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> buried-source-line (SL) STT MRAM cell structure with a vertical gate all around (GAA) cylindrical buried source NMOS transistor is proposed. The magnetic tunnel junction (MTJ) multilayer structure is stacked above the select device with both occupying the same 2-D area. The diameters of perpendicular MTJ and vertical silicon nanowire are equal (i.e., F). Device simulations have been carried out on TCAD for buried source vertical GAA device structure. Furthermore, these TCAD results are used to calibrate the BSIM CG model for cylindrical GAA transistors. The proposed STT MRAM cell is then analyzed using calibrated Verilog-A models for perpendicular anisotropy MTJ and vertical GAA NMOS transistor (BSIM CG). The performance analysis in terms of read stability, write margins, and power dissipation for the proposed cell is also presented.

Study on Combined Operation of Ground Source Heat Pump and Ice Storage System

In the present work, an operational air-conditioning system combined with buried pipe ground source heat pump and ice storage (ABI) was designed according to the loading characteristic of one office building. Additionally, the system running process and working mode together with the operational strategy on both designing day and non-designing day were discussed in this paper. To satisfy the cooling demand as well as cut down the operational cost, operating modes on different occasions must be planned reasonably to better control the system while running.