Nazari Rasoul - Department of Civil Engineering, Shahid Bahonar University, Kerman, Iran
Mohammad Kangazian - Department of Civil Engineering, Shahid Bahonar University, Kerman, Iran
Amid Hadi - Department of Civil Engineering, Jami institute of Technology, Isfahan, Iran
Milad Babadi Soultanzadeh - Department of Mechanical Engineering, Islamic Azad University, Khomeini Shahr Branch

Unsteady flow is the result of turbulence (valve shut, pump deactivation, etc.) in the steady flow. A sudden change in the velocity of fluid, flowing inside the tube, brings about an abrupt change in pressure and water hammer occurs as the result. Because of internal fluid-structure interaction inside the pipe, this phenomenon effects on the pipe system. During water hammer phenomenon, considerable dynamic forces are exerted on the pipe. If these forces cause deformation of the structure, Fluid-structure interaction occurs. Thus, the present research intended to investigate the pip dynamic behaviour in frequency domain. In time models proposed for solving water hammer equations in pipe structure, because of using interpolation a great deal of time was required for transmission of hydraulic parameters to structure equations and vice versa. Therefore, by simplicity of water hammer differential equation in frequency domain, the problem was solved in this domain. The comparison made between the achieved results of this research and those obtained by other researchers confirmed the accuracy and efficiency of this method

Unsteady Flow, Fluid-Structure interaction, Water Hammer, Frequency Domain