Abstract: Free vibration variational equation of a camped pipe conveying fluid (liquid-solid coupled problem) is derived, based on variational principle. The natural frequency formula of a camped pipe conveying fluid are obtained by used of direct method. The influence of flowing velocity on natural frequency of a camped pipe conveying fluid is discussed. The limit velocity of liquid in the camped pipe conveying fluid is obtained.

Key words: Direct method camped pipe conveying fluid, Limit velocity of liquid, Liquid-solid coupled problem, Variational principle