A CALIBRATED MODEL SEISMIC SYSTEM

Geophysics ◽  
1972 ◽  
Vol 37 (3) ◽  
pp. 445-455 ◽  
Author(s):  
C. N. G. Dampney ◽  
B. B. Mohanty ◽  
G. F. West

Simple electronic circuitry and axially polarized ceramic transducers are employed to generate and detect elastic waves in a two‐dimensional analog model. The absence of reverberation and the basic simplicity. of construction underlie the advantages of this system. If the form of the fundamental wavelet in the model itself, as modified by the linear filtering effects of the remainder of the system, can be found, then calibration is achieved. This permits direct comparison of theoretical and experimental seismograms for a given model if its impulse response is known. A technique is developed for calibration and verified by comparing Lamb’s theoretical and experimental seismograms for elastic wave propagation over the edge of a half plate. This comparison also allows a critical examination of the basic assumptions inherent in a model seismic system.

Geophysics ◽  
1987 ◽  
Vol 52 (6) ◽  
pp. 765-771 ◽  
Author(s):  
B. Kummer ◽  
A. Behle ◽  
F. Dorau

We have constructed a hybrid scheme for elastic‐wave propagation in two‐dimensional laterally inhomogeneous media. The algorithm is based on a combination of finite‐difference techniques and the boundary integral equation method. It involves a dedicated application of each of the two methods to specific domains of the model structure; finite‐difference techniques are applied to calculate a set of boundary values (wave field and stress field) in the vicinity of the heterogeneous domain. The continuation of the near‐field response is then calculated by means of the boundary integral equation method. In a numerical example, the hybrid method has been applied to calculate a plane‐wave response for an elastic lens embedded in a homogeneous environment. The example shows that the hybrid scheme enables more efficient modeling, with the same accuracy, than with pure finite‐difference calculations.


Author(s):  
И.Б. Петров

Существует значительное количество прикладных задач, для решения которых применяется математическое моделирование динамических процессов в деформируемых средах. К таким задачам относят моделирование распространения упругих волн в геологических средах, в том числе с учетом ледовых образований, их рассеяния на зонах трещиноватости. Актуальность этих постановок обусловлена важностью решения обратных задач сейсмической разведки, обработки данных сейсмической разведки с целью уточнения запасов углеводородов и определения расположения углеводородов и других полезных ископаемых. Поэтому приобретает важность разработка высокоточных численных методов, позволяющих моделировать упругие волны в деформируемых средах. Одним из этих методов является сеточно-характеристический численный метод, примененный в данной работе. Этот численный метод применяется для решения прямых задач, то есть для расчета распространения упругих волн при известных параметрах рассматриваемой среды. А для решения обратной задачи по восстановлению параметров геологической среды по данным сейсмической разведки можно применять нейронные сети, для обучения которых можно использовать многократное решение прямых задач сеточно-характеристическим методом. В данной работе приведены примеры решения разнообразных прямых задач по распространению упругих волн в неоднородных геологических средах, в том числе в зоне Арктики, а также представлена постановка задачи по обучению нейронных сетей и графики, показывающие эффективность их обучения с использованием двух различных подходов. Many problems can be solved with the simulation of dynamic processes in deformable media. They are the simulation of elastic wave propagation in rocks including ice formations, and wave scattering on rock-fracture zones. Such studies are important for solving inverse problems of seismic exploration and seismic data processing to get a better estimation of hydrocarbon reserves, locate hydrocarbons and other minerals. Therefore, it is necessary to develop high-precision numerical methods used to simulate elastic waves in deformable media. One of such methods is the grid-characteristic approach used in this work. It is suitable for solving direct problems, i.e., to analyze the propagation of elastic waves in a medium with known properties. Neural networks can be applied to solve the inverse problem: reconstructing the geology from seismic survey data. Multiple solving of direct problems by the gridcharacteristic approach is used for network training. This paper contains some examples of solving a range of direct problems on the elastic wave propagation in heterogeneous rocks, also in the Arctic zone, and the problem statement for training neural networks and graphs is proposed to demonstrate the efficiency of training with two approaches.


Author(s):  
Bernhard R. Tittmann

Elastic wave propagation in porous media will be introduced by a discussion of scattering to show the use of broad frequency band pulses in relating the attenuation, velocity and backscattering to information on porosity. Examples will be given for microporosity in castings and powder metal components. This will be followed by a discussion of the influence of volatiles within the pores on the absorption of elastic waves in porous ceramics and rocks. Implications of these findings will be given for ultrasonic device applications and for the interpretation of the lunar seismic experiments carried out as part of the Apollo missions to the moon.


2015 ◽  
Vol 20 (1) ◽  
pp. 159-170 ◽  
Author(s):  
M. Rucka ◽  
B. Zima

Abstract This study deals with experimental and numerical investigations of elastic wave propagation in steel bars partially embedded in mortar. The bars with different bonding lengths were tested. Two types of damage were considered: damage of the steel bar and damage of the mortar. Longitudinal waves were excited by a piezoelectric actuator and a vibrometer was used to non-contact measurements of velocity signals. Numerical calculations were performed using the finite elements method. As a result, this paper discusses the possibility of condition assessment in bars embedded in mortar by means of elastic waves.


1967 ◽  
Vol 34 (3) ◽  
pp. 725-734 ◽  
Author(s):  
L. D. Bertholf

Numerical solutions of the exact equations for axisymmetric wave propagation are obtained with continuous and discontinuous loadings at the impact end of an elastic bar. The solution for a step change in stress agrees with experimental data near the end of the bar and exhibits a region that agrees with the one-dimensional strain approximation. The solution for an applied harmonic displacement closely approaches the Pochhammer-Chree solution at distances removed from the point of application. Reflections from free and rigid-lubricated ends are studied. The solutions after reflection are compared with the elementary one-dimensional stress approximation.


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