Dynamics of a long tubular cantilever conveying fluid downwards, which then flows upwards around the cantilever as a confined annular flow

Dynamic stability of a stepped drillstring conveying drilling fluid

“…The correctness of the finite element method and the numerical model is verified by comparing the present results with those given by Dai et al (2013) and Paidoussis et al (2008).…”

“…3). This result can be compared to that given by Paidoussis et al (2008) Figure 4 illustrates the first four complex frequencies of this DP-DC system varying with the flow rate U i1 , and indicates that the system is in the stable state for U i1 110 m/s. With an increase in U i1 , Re(ω) and Im(ω) all decrease gradually, and stability of the DP-DC system deteriorates.…”

“…(2.1) and the model of the drillstring-like system of Paidoussis et al (2008) are mainly in two aspects: 1) except for the friction damping C f and density ρ f , all the physical parameters are different between the DP part and DC part; 2) WOB that is an important factor in the stability of the drillstring is included and the drill bit is constrained by a movable hinge. So, the present model and parameters are more closely related to a real system.…”

“…Later, Zhang and Miska (2005) reduced the drillstring to a uniform tubular beam, and used the model of fluid-conveying pipe to simulate the dynamic stability of the drillstring system in response to its own weight, WOB and drilling fluid flowing inside and outside the string. In 2008, Paidoussis et al (2008) revised the expression of the frictional viscous force in the normal direction due to the external flow used in the previous studies (Luu, 1983), and discussed the effect of flow velocity on the stability of the drillstring-like system with a floating drill bit by using Galerkin-Fourier method. Meanwhile, Qian et al (2008) studied dynamics of the drill-string-like system in the counterflush drilling process where the drilling fluid flowed downwards to the bottom through the annular region and returned upwards to the ground in the drillstring.…”

Stochastic dynamics of a drill-string with uncertain weight-on-hook

“…where g is the gravity acceleration, M f is the fluid mass per unit length, A i and A 0 are the cross-sectional areas corresponding to the inner and outer diameters of the column, D is the diameter, U 0 is the flow speed outside the column, C f is a fluid viscous damping coefficient and p i is the pressure inside the column (see Paidoussis et al (2008) and Ritto et al (2009) for details). The concentrated force at the bit is written as…”