Buried Cylinder Research Articles

Location and imaging of two‐dimensional pipes buried in a lossy half earth

AbstractSeveral dielectric as well as conducting pipes buried in the lossy half ground are reconstructed from the scattered fields measured along the air–earth interface. The iterative inversion method using the hybrid optimization algorithm combining the genetic and Levenberg–Marquardt algorithms is used in finding the positions, sizes, and medium parameters, such as the permittivities and conductivities, of the buried pipe cylinders, as well as those of the background lossy half ground. Ill posedness of the inversion caused by the errors in the measured scattered fields is regularized by filtering out the evanescent modes of the scattered fields. © 2001 John Wiley & Sons, Inc. Microwave Opt Technol Lett 31: 140–143, 2001.

Novel diffraction tomographic algorithm for imaging two-dimensional targets buried under a lossy Earth

A novel diffraction tomographic algorithm has been proposed to detect two-dimensional (2D) dielectric cylinders buried under a lossy Earth. In this algorithm, the air-Earth interface has been taken into account and the exact treatment of Sommerfeld-like integrals has been considered. Using the algorithm, all locations, shapes, and dielectric properties of buried cylinders can be accurately reconstructed under the low-contrast condition. For high-contrast targets, this algorithm can also be used to determine their locations and approximate their dielectric properties. Due to the use of fast Fourier transforms to implement the problem, this algorithm is very fast and quite tolerant to the error of measurement data. Numerical examples are given to show the validity of the algorithm.

Neural detection of pipe signatures in ground penetrating radar images

A processing chain for the analysis of the data recorded by a ground penetrating radar (GPR) is presented. In particular, the detection and localization of pipes is implemented by exploiting the a priori knowledge that a buried cylinder gives rise to a hyperbolic signature in GPR images. The image interpretation is performed by a suitably trained simple neural detector after some preprocessing steps aiming toward the enhancement of the buried objects' signatures. The algorithm has been tested on actual GPR images and compared with the information extracted by a trained human operator, and the agreement is extremely satisfying. Moreover, the possibilities and advantages to exploiting some sort of spatial diversity by combining the analysis of data simultaneously recorded by different antennas are presented and discussed.

Geometric and dielectric characterization of buried cylinders by using simple time‐domain electromagnetic data and neural networks

An analysis of the performances of the neural-network approach for the geometric and dielectric characterization of buried cylinders is carried out. The neural-network process data are obtained from the time-domain formulation of the electromagnetic scattering problem. This analysis is based on the use of simplified models which allow the analytical calculations of the solutions. The question of what data need to be extracted from the transient scattered field in order to make the characterization process work correctly is addressed, and the results obtained are shown. © 2000 John Wiley & Sons, Inc. Microwave Opt Technol Lett 24: 24–31, 2000.

Geometric and dielectric characterization of buried cylinders by using simple time-domain electromagnetic data and neural networks

Geometric and dielectric characterization of buried cylinders by using simple time-domain electromagnetic data and neural networks

Polarization effects in the scattering of electromagnetic waves by an object beneath a random rough surface

We put forward exact numerical calculations that show the Mueller matrix elements and the near field for a cylinder beneath a two-dimensional randomly rough surface. Different cases have been addressed in order to investigate the dependence of the perturbation introduced by the buried object on several parameters as size, position, and optical constants of the buried cylinder. The numerical illustrations are focused on surface profiles, optical constants, and ensemble averages that can be directly compared with practical implementations.

A study of the photothermal signal produced by a series of subsurface cylinders in opaque materials

We present a theoretical and experimental study of the photothermal signal produced by a series of buried cylinders in an optically opaque sample. The models are valid for any value of the thermal properties of the cylinder and sample (the extreme cases treated are isolating and conducting cylinders), and the modulated excitation can be extended (plane wave generation) or punctual (spherical wave generation). The model results are compared with measurements performed on calibrated samples using two photothermal techniques: “mirage” deflection and infrared radiometry. Semiquantitative agreement between theory and experiment is found showing that this methodology can be used as a tool for the nondestructive evaluation of close subsurface cylinders, which represents a further step to the photothermal study of some materials of interest as the fiber-reinforced composites.

Scattering of light and other electromagnetic waves from a body buried beneath a highly rough random surface

It is shown that the presence of an arbitrary body buried near a dielectric highly rough random surface produces a remarkable enhanced backscattering peak in the angular distribution of mean scattered intensity. This is in contrast with the distribution that the dielectric rough surface yields in the absence of the body. In order for the peak to appear, the surface must be very rough and the contrast between the dielectric constants of the body and the medium in which it is immersed must be 2 at least. We illustrate the results with a two-dimensional (2-D) calculation of a cylinder in front of a 2-D rough profile immersed in a dielectric medium. Different cases have been addressed in order to investigate the dependence of the backscattering enhancement on several physical parameters such as the width of the incident beam; the size, position, and optical constant of the buried cylinder; and the surface correlation function, as well as the difficult task of performing averages that resemble the ideal ensemble averaging of the rough surface in this system.

Photothermal study of subsurface cylindrical structures. I. Theory

A study of the photothermal signal generated by subsurface cylindrical structures is presented in two parts: theoretical modelization (Part I), and experimental measurements on calibrated samples (Part II). In this first part we develop a theoretical study of the scattering of planar and spherical thermal waves by a buried single infinite cylinder, parallel to the sample surface, as a function of its size and depth, and the thermal characteristics (thermal conductivity and diffusivity) of both the sample and cylinder. Temperature field solutions to the heat conduction equation are explored in two ways: by means of the Green’s function method and by a series expansion. We discuss the limits and accuracy provided by both types of calculations, and we compare the resulting temperature field for extended and pointlike illumination. Our study shows that photothermal methods allow one to locate and characterize the geometrical and thermal properties of the buried cylinder.

Photothermal study of subsurface cylindrical structures. II. Experimental results

We present an extensive experimental study of the photothermal signal produced by subsurface cylinders immersed in opaque solids. The results provided by three different modulated photothermal techniques (thermoreflectance, infrared radiometry, and mirage) for a variety of sample and cylinder thermal properties show very good agreement with the theoretical models presented in Part I of this work. A single subsurface cylinder can be quantitatively characterized by means of photothermal measurements (i.e., the determination of its size, depth, orientation, and thermal properties). We also present experimental data on a series of buried cylinders parallel to the surface that show multiple-scattering effects on the incident thermal wave.

The source of explosive eruptions of Sakurajima volcano, Japan

To understand the nature of explosive eruptions, in particular the role played by exsolution of magmatic gases, we studied the seismic waveforms produced by two such eruptions of Sakurajima volcano on October 30 and November 14,1986. An explosion begins when a mixture of magmatic gases and fragmented magma flows upward through a narrow vertical channel to the surface. The source region is a reservoir of gas‐rich magma, where the pressure drops as gases flow out. The form of low‐frequency seismic waves can be explained by a source that consists of two components. One component is a single force directed downward that represents the reaction to ejection of gas and magma. The other, more important component is a moment tensor that represents expansion or contraction of rock around a source. The first motion of seismic waves produced by an explosion is directed away from the volcano. Tilt and strain measurements show that the initial motion directed outward is soon followed by subsidence around the volcano. The eigenvectors of the seismic moment tensor are either nearly horizontal or vertical. The ratio of horizontal to vertical eigenvalues was 1.8:1 for the October 30 explosion. This suggests the geometry of the explosive source can be approximated as a buried vertical cylinder. The volume of contraction, 2×l03 m3, can be produced by a pressure change of 0.3 MPa over a cylinder with a radius of 160 m and a height of 300 m. We propose that an explosive eruption occurs after a small shallow source of high pressure forms within a vertical conduit, possibly exsolution of magmatic gases. Eventually, the small source bursts and pushes open a pathway to the surface, providing an upward escape for trapped gases. It is this burst that causes the initial outwardly directed motion at the surface. A deeper reservoir of gas‐rich magma is then subjected to a lower confining pressure and also bursts, causing the explosion.

Steady infiltration in unsaturated soil from a buried circular cylinder: The separate contributions from top and bottom halves

Waechter and Philip (1985) obtained the asymptotic expansion of the mean infiltration rate for large s from a buried circular cylinder using a scattering analog. Here s(= αl/2) is defined as the ratio of the characteristic length l of the water supply surface (in fact, its radius) to the sorptive length 2α−1 of the soil and a satisfies the relationship K(ψ) = K(0) eαψ, where K is the hydraulic conductivity, and ψ is the moisture potential. This exact solution cannot be used directly to obtain the separate contributions to the mean infiltration rate from the top and the bottom halves of the cylinder; our analysis is based on a new class of special functions derived from the modified Bessel equation with a forcing term. In this paper, we obtain the separate asymptotics for the two halves for large s to make a comparison with the results of the trench problem (Waechter and Mandal, 1993). The asymptotic expansions for top and bottom halves are (2/π)(0.69553s−2/3) and (2/π)(1+0.30066s−2/3), respectively, whereas for a semicircular trench, the mean infiltration rate is given by (2/π)(1+0.30066s−2/3).

Stefan problem around a refrigerated buried cylinder: identification of principal parameters and development of a simple prediction method

The aim of this paper is to study the principal parameters influencing the thermal behaviour of the ground around refrigerated shallow buried pipes. Thermal behaviour is obtained using a numerical model of the two-dimensional Stefan problem. A finite-element enthalpy numerical method is used to solve the Stefan problem for different thermal boundary conditions, thermophysical properties and geometry. Thus the principle parameters influencing the thermal behaviour of the ground around the pipes are identified. A practical method is proposed. This method, applied to a specific refrigerated gas pipe, shows how the behaviour of the freezing/thawing interface during a period of time can be determined with precision.

Shape and depth solutions from gravity data using correlation factors between successive least‐squares residuals

The gravity anomaly expression produced by most geologic structures can be represented by a continuous function in both shape (shape factor) and depth variables with an amplitude coefficient related to the mass. Correlation factors between successive least‐squares residual gravity anomalies from a buried vertical cylinder, horizontal cylinder, and sphere are used to determine the shape and depth of the buried geologic structure. For each shape factor value, the depth is determined automatically from the correlation value. The computed depths are plotted against the shape factor representing a continuous correlation curve. The solution for the shape and depth of the buried structure is read at the common intersection of correlation curves. This method can be applied to a Bouguer anomaly profile consisting of a residual component caused by local structure and a regional component. This is a powerful technique for automatically separating the Bouguer data into residual and regional polynomial components. This method is tested on theoretical examples and a field example. In both cases, the results obtained are in good agreement with drilling results.

Numerical integral equation solution for scattering from a one-dimensional penetrable fluid interface and a buried rigid cylinder

Ocean bottom scattering problems involve contributions from both the roughness of the seafloor and inhomogeneities within the sediment or buried objects. Here, a numerical procedure has been developed to find an exact solution for scattering from an infinitely long rigid cylinder buried beneath a one-dimensional rough interface. In this model, the water–sediment interface is a penetrable fluid boundary with the conditions that pressure and vertical particle velocity are continuous. The cylinder surface is rigid, i.e., the vertical particle velocity on the boundary is zero. A boundary integral approach is used: the pressure field and its normal derivative on the rough surface, and the pressure field on the cylinder surface, are determined, then used to find the far-field scattered field. This method was previously used for a pressure-release boundary condition [E. I. Thorsos, J. Acoust. Soc. Am. 83, 78–92 (1988)] and the penetrable boundary [E. I. Thorsos, J. Acoust. Soc. Am. 90, 2232(A) (1991)]. It is now developed for the combination of a penetrable boundary and a rigid cylinder to validate possible approximation methods. As a benefit of this formalism, the shape of the buried object may be readily varied to model elliptical and perhaps other cylinder cross sections.

Geometrically nonlinear analysis of buried cylinders : Moore, I D; Booker, J R Proc 3rd International Symposium on Numerical Models in Geomechanics (NUMOG III), Niagara Falls, 8–11 May 1989P716–723. Publ London: Elsevier Applied Science, 1989

Geometrically nonlinear analysis of buried cylinders : Moore, I D; Booker, J R Proc 3rd International Symposium on Numerical Models in Geomechanics (NUMOG III), Niagara Falls, 8–11 May 1989P716–723. Publ London: Elsevier Applied Science, 1989

Coupled saturated‐unsaturated quasilinearized steady state flows from buried and surface cavities

The coupled saturated‐unsaturated flow that results from water‐filled cavities in soils is studied, under the assumption of quasilinearization for the unsaturated flow, using a combined boundary element‐finite element method. Buried two‐dimensional circular cylindrical cavities and two‐dimensional semicircular cavities are examined in detail. The effect of the size of the cavity and the soil type on the flux from the cavity and the size of the saturated zone and effectively wetted region is illustrated. Comparisons with previous analytical and numerical results, in which the depth of water in the cavity was neglected, are also made. These comparisons indicate the severe errors that are introduced into the calculation of the flux and the flow field when the depth of water is neglected. In particular, it is shown that the percentage error in the flux from a buried circular cylinder with water depth neglected increases from 20% to 220% as the dimensionless cavity size s increases from 0.1 to 1, and that the saturated zone extends to a depth of approximately 7.9 times the cavity radius for s = 1.

Matric Potential of Clay Loam Soils on Arid Rangelands in Southern New Mexico

The matric potential of soil water is presented for 6 clay loam sites on floodplains of arid rangelands. Gypsum resistance blocks impregnated with plaster of paris were placed at 6 soil depths to 122 cm. At 4 locations, blocks were placed inside and outside a buried sheet metal cylinder so that estimates could be obtained of matric potential due to precipitation and due to precipitation plus run-in. The average annual precipitation during the approximate 20-year study period was 242 mm, slightly above the long-time average. Haplargids dominated by tobosa [Hilaria mutica (Buckl.)Benth.] had a greater probability of the matric potential greater than or equal to -1.5 MPa (wet soil) than the Calciorthids dominated by burrograss (Scleropogon brevifolius Phil.). The probability of matric potential greater than or equal to -1.5 MPa (wet soil) was as great or greater in winter as during the summer growing season. The factors affecting matric potential were amount and nature of precipitation, amount of run-in water, soil and vegetation type, position on the landscape, and microrelief.

Responses of buried cylinders to surface loads : Moore, I D J Geotech Engng Div ASCEV113, N7, July 1987, P758–773

Responses of buried cylinders to surface loads : Moore, I D J Geotech Engng Div ASCEV113, N7, July 1987, P758–773

Responses of buried cylinders to surface loads : Moore, I D J Geotech Engng Div ASCEV113, N7, July 1987, P758–773

Responses of buried cylinders to surface loads : Moore, I D J Geotech Engng Div ASCEV113, N7, July 1987, P758–773