Vibration Analysis Of Cracked Pipe Conveying Fluid

As one of the important structure forms, pipelines are commonly used in many projectfields e.g. chemical, oil and gas transportation, et al. Nowadays, with the vigorous exploitation ofmarine oil and gas resources, submarine pipelines as the most important way to gather andtransport offshore hydrate link the upstream and downstream of exploitation, known as the lifelineof marine oil and gas field project, However, the harsh marine environment makes submarinepipes inevitably produce dent, crack and other damage. The accumulation and expansion ofdamage would seriously reduce the resisting capacity of the structures against the disaster, evenresulting in collapse. This would cause not only the huge economic losses to the state, but alsoserious pollution of the marine environment, which destructs the local ecological balance andresults in adverse social impacts. Thus, the safe operation and prolongation of the service lifeurgently motivate the research on the structural vibration analysis, health diagnosis and safeassessment for submarine pipelines. In this paper, a theoretical study on the vibrationcharacteristics of crack pipes is carried out. The main contents include:(1) Based on linear fracture mechanics and strain energy release principle, the matrix of localflexibility for crack pipes were deduced.(2) The effect of the open crack and a moving mass on the dynamic behavior of a cantileverpipe conveying fluid with a tip mass are investigated，The cantilever pipe is modeled by theEuler-Bernoulli beam theory. The equation of motion is derived by using Lagrange’s equation andanalyzed by numerical method. The crack section is represented by a local flexibility matrixconnecting two undamaged pipe segments. That is, the crack is modeled as a rotational spring.This matrix defines the relationship between the displacements and forces across the crack section.The influences of the crack severity ratio, the position ratio of the crack, the moving mass and it’svelocity, the velocity of fluid, the tip-mass and it’s moment of inertia and the coupling of thesefactors on the vibration mode, the frequency ratio, and the tip displacement of a cantilever pipe aredepicted.(3) The effect of the open crack and a moving mass on the dynamic behavior of a simplysupported pipe conveying fluid are investigated，The simply supported pipe is modeled by theEuler-Bernoulli beam theory. The equation of motion is derived by using Lagrange’s equation andanalyzed by numerical method. The crack section is represented by a local flexibility matrixconnecting two undamaged pipe segments. That is, the crack is modeled as a rotational spring.This matrix defines the relationship between the displacements and forces across the crack section.The influences of the crack severity ratio, the position ratio of the crack, the moving mass and itsvelocity, the velocity of fluid, and the coupling of these factors on the vibration mode, thefrequency ratio, and the mid-span displacement of a simply supported pipe are depicted.