Application of fourier transformation and frequency domain to prepare a dynamic test model to determine dynamic properties of buried structure and surrounding soil

Abstract eng:
When a structure is under a dynamic force such as ground motion acceleration, in addition to the static terms, dynamic terms such as damping and inertia would become activated too. In an underground structure, such as energy transporting pipeline network like gas, sewage, underground tanks and tunnels, in addition to the weight and stiffness force, other dynamic forces such as inertia force and damping force have a great role against earthquake forces. The basic parameters are, the amount of dynamic stiffness or Impedance function, damping ratio and a part of soil mass named added mass that contributes with the structure’s dynamic activities .The way to determine the added mass and its effect is quite complex. At this paper, Fourier Transformation has been applied to the governmental equations. The transformation has been applied to the forces, displacements, time dependent dynamic stiffness, Then, the form of the equations have been changed by transforming to the frequency and mixed domain .Finally, by representing a dynamic experimental model, the unknown previous parameters have been found. The suggested Numerical and Formulation method at this paper are based on distributing the basic dynamics of structures, mechanical vibrations and random vibration theory. Finally, It has been shown that the amount of instigation frequency is a very important parameter and has a great effect on the dynamic properties.

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