Radar signature of a 2.5-D tunnel

Geophysics ◽  
1993 ◽  
Vol 58 (11) ◽  
pp. 1573-1587 ◽  
Author(s):  
Mark L. Moran ◽  
Roy J. Greenfield
Keyword(s):  
Fourier Transform ◽  
Green’S Function ◽  
Green's Function ◽  
Electric Dipole ◽  
Short Pulse ◽  
Three Dimensional ◽  
Acute Angle ◽  
Peak Power Output ◽  
Early Arrival ◽  
Low Amplitude

The effects of an infinitely long cylindrical void on short‐pulse cross‐borehole radar waveforms are modeled and analyzed. Pulsed electromagnetic sensing system (PEMSS) data are of particular interest. The PEMSS system developed by the Southwest Research Institute uses a vertically oriented electric dipole that emits a short electromagnetic pulse with peak power output centered around 30 MHz, which gives wavelengths of roughly 1.5 cavity diameters. The transmitter and receiver are typically located in boreholes separated by approximately 30 m. The model is based on field solutions for a vertically oriented point‐source electric dipole. A three‐dimensional (3-D) analytical frequency domain derivation of the Green’s function is found using a spatial Fourier transform over the cylinder axis. The resulting wavenumber integral is evaluated by a numerical integration over wavenumber. Time‐domain waveforms are produced by applying a Fourier transform to a 7-80 MHz band of frequencies in the Green’s function spectrum. Model results agree well with PEMSS field data sets. Further modeling examines the effects on waveforms for a wide variety of cases in which the raypath is not orthogonal to the tunnel axis, including the effect of tunnel dip. An air‐filled tunnel with a radius greater than 1.0 m produces a low amplitude shadow zone along its entire length. A low amplitude early arrival is observed in simulations with air‐filled tunnels in which the source to receiver path forms an acute angle larger than 45 degrees with the tunnel axis. This arrival is interpreted as propagation through the tunnel. When this angle is smaller than 45 degree the tunnel is effectively an opaque object and only the energy diffracted around the cylindrical void is observed. Waveform behavior gradually transitions from propagation through the tunnel in the vicinity of 45 degrees.

Theory of Electron Diffraction by Crystals

1967 ◽  
Vol 22 (4) ◽  
pp. 422-431 ◽  
Author(s):  
Kyozaburo Kambe
Keyword(s):  
Integral Equation ◽  
Electron Diffraction ◽  
General Theory ◽  
Green’S Function ◽  
Green's Function ◽  
Scattering Problem ◽  
Three Dimensional ◽  
Two Dimensions ◽  
The Third ◽  
Third Dimension

A general theory of electron diffraction by crystals is developed. The crystals are assumed to be infinitely extended in two dimensions and finite in the third dimension. For the scattering problem by this structure two-dimensionally expanded forms of GREEN’S function and integral equation are at first derived, and combined in single three-dimensional forms. EWALD’S method is applied to sum up the series for GREEN’S function.

Formulation of Three-Dimensional Green’s Function and its Application to Fatigue Life Evaluation of Pressurizer

2006 ◽  
Vol 324-325 ◽  
pp. 387-390
Author(s):  
Yoon Suk Chang ◽  
Shin Beom Choi ◽  
Jae Boong Choi ◽  
Young Jin Kim ◽  
Myung Jo Jhung ◽  
...  
Keyword(s):  
Finite Element ◽  
Fatigue Life ◽  
Green’S Function ◽  
Green's Function ◽  
Three Dimensional ◽  
Stress Transfer ◽  
Life Assessment ◽  
Element Analysis ◽  
Fatigue Evaluation ◽  
Effective Assessment

Major nuclear components have been designed by conservative codes to prevent unanticipated fatigue failure. However, more realistic and effective assessment is necessary in proof of continued operation beyond the design life. In the present paper, three-dimensional stress and fatigue evaluation is carried out for pressurizer employing complex full geometry itself instead of conventional discrete subcomponents. For this purpose, temperature and mechanical stress transfer Green’s functions are derived from finite element analyses and applied to critical locations of pressurizer. In accordance with comparison of resulting stresses obtained from the Green’s function and detailed finite element analysis, suitability of the specific Green’s function is investigated. Finally, prototype of fatigue life assessment results is provided along with relevant ongoing activities.

Green’s function–based surrogate model for windfields using limited samples

2017 ◽  
Vol 42 (3) ◽  
pp. 164-176 ◽  
Author(s):  
Joshua Paul Marshall ◽  
Joseph David Richardson ◽  
Carlos Jose Montalvo
Keyword(s):  
Green’S Function ◽  
Wind Velocity ◽  
Green's Function ◽  
Surrogate Model ◽  
Dimensional Space ◽  
Three Dimensional ◽  
Fast Method ◽  
Three Dimensional Model ◽  
Wind Velocities ◽  
Wind Measurements

There exists many applications for which wind-velocity is desired over a three-dimensional space. The vector field associated with these wind velocities is known as a “windfield” or “velocity-windfield.” The present work provides a fast method to characterize windfields. The approach uses the free-space Green’s function for potential theory as an inexpensive surrogate model in lieu of either complicated physics-based models or other types of surrogate models, both of which require volumetric discretizations for the three-dimensional case. Using the gradient of the third Green’s identity, the wind-velocity in the interior of a domain is entirely characterized by a surface discretization while still providing a three-dimensional model. The unknown densities on the surface are determined from enforcement of the interior form of the identity at arbitrary points coinciding with wind measurements taken by unmanned aerial vehicles. Numerical results support the feasibility of the method.

scholarly journals THE MOTIONS OF A MOORED SHIP IN A HARBOR BASIN

1982 ◽  
Vol 1 (18) ◽  
pp. 165 ◽  
Author(s):  
T. Sawaragi ◽  
M. Kubo
Keyword(s):  
Green’S Function ◽  
Green's Function ◽  
Close Agreement ◽  
Three Dimensional ◽  
Ship Motion ◽  
Experimental Results ◽  
New Methods

In harbors affected by ocean swells,cargo handlings are often interrupted and irooring lines are broken as a result of severe ship motionsl). In order to decrease such accidents, the noored ship notions in a harbor basin must be studied. In this paper the ship notions in the harbor basin are investigated by using three dimensional Green's function and close agreement between theoretical and experimental results can be found. New methods to reduce noored ship motion are also proposed. The efficiency of these methods is verified theoretically and experimentally.

Sign in / Sign up

Export Citation Format

Share Document