M Mohammadi - Department of Engineering, Khuzestan Provinc e Gas Company, National Iranian Gas Company,
A.A Nekounam - Department of Measurement and Gas Distribution, Khuzestan Province Gas Company, National Iranian Gas Company,
M Amiri - Department Engineering, College of Mechanical Engineering, Ahvaz Branch, Islamic Azad University, Ahvaz, Iran,

The fluid-conveying pipe is a fundamental dynamical problem in the field of fluid– structure interactions. In recent years considerable attentionhas been given to the lateral vibrations of pipescontaining by a moving fluid. In this paper, the vibration analysis of composite natural gas pipelinein the thermal and humidity environment isstudied. By applying the Hamilton’s principle, the equation of motion is derived for the pipe with theeffects of both linear and non-linear stresstemperature cases. The differential quadrature method (DQM) has been utilized in computing theresults for the pipe conveying fluid. Sample resultsare presented for several cases with varying values of the system parameter. Results are demonstratedfor the dependence of natural frequencies on the flow velocity as well as temperature change and humidity percent. The influence of temperature change on the critical flow velocity at whichbuckling instability occurs is investigated. It is concluded that the effect of temperature change onthe instability of conveyed fluid pipe is significant.

Composite pipes; Fluid-induced vibration; Thermal load; Humidity percentage effect