Journal of Applied Sciences1812-56541812-5662Asian Network for Scientific Information10.3923/jas.2014.2054.2060I. Al-HashimyZahidH. Al-KayiemHussainHasanF.MohmmeddA.O.1220141418Vibration characteristics of pipe conveying fluid with sudden enlargement-sudden contraction were studied in this study. The problem was modeled mathematically and simulated numerically. The governing equations of motion for a pipe conveying fluid were derived using beam theory and the mathematical model was solved using transfer matrix method in MATLAB-R2012 environment. The simulation was carried out by Mechanical APDL in ANSYS 14. Two types of fluids; namely, water and oil were used to demonstrate the effect of density on the natural frequencies and their corresponding mode shapes. The support type selected for this investigation is flexible support. The small and large diameters of the investigated pipe were 12.7 and 25.4 mm, made of copper. The external force was assumed to apply at mid length of the large diameter. A good agreement between the mathematical solution and the numerical simulation was achieved. In all cases, it was found that the natural frequencies with any fluid flow were lower than the case of pipe without fluid flow. The study can be extended for further cases of pipe geometries and for two phases fluid flows.]]>Al-Yaari, M. and B. Abu-Sharkh,2011Blevins, R.D.,1979Douglas, J.F., J.M. Gasiorek and J.A. Swaffield,1981Durst, F. and T. Loy,1985Hammoudi, R.U.,2007Lilkova-Markova, S.V. and D.S. Lolov,2004Lolov, D.S. and S.V. Lilkova-Markova,2006Mahdi, A.A.,2001Pittard, M.T.,2003Reddy, J.N. and C.M. Wang,2004Saleh, B.M.,1978