Three-dimensional nonlinear responses to impact loads on free-span pipeline: Torsional coupling and load steps
- Colorado School of Mines, Golden, CO (United States). Dept. of Engineering
- Tsinghua Univ., Beijing (China)
For a heavy object falling on a free-span pipeline, this study assesses three-dimensional (3-D) pipe-span responses with the torsional ({theta}x-) coupling of a pipeline through the biaxial (y) bending responses. The static pipe-span equilibrium is achieved with its self-weight and buoyancy and the external torsional moment induced by the cross-flow (y-directional) current on the sagged pipe span. Load steps taken for 2 different sequences of applying static loads induced different pipe deformations, and the pipe twists in entirely different pattern. The two types of impact loads are applied in the vertical (z-) direction to excite the pipe span in its static equilibrium: (1) triangular impulse loading and (2) ramp loading. Boundary condition of the span supports is ``fixed-fixed`` at both ends in both displacement and rotation. 3-D coupled axial (x-), bending (y- and z-) and torsional ({theta}x-) responses, both state and dynamic, to the z-directional impact loadings, are modeled and analyzed by a nonlinear FEM method for a 16-in pipeline. The 3-D responses are compared with 2-D responses. The comparison shows significant torsional vibrations caused by the cross-flow current, especially for longer spans. The torsional ({theta}x-) coupling is very sensitive to the time-step size in achieving numerical stability and accuracy, particularly for the ramp loading and for a shorter span. For very large impact loads, the response frequencies differ from the fundamental frequencies of the span, exhibiting beatings and strong bending-to-axial and to-twist couplings. Also, the eigenvalues for the linear system are not necessarily the resonance frequencies for these nonlinear coupled responses.
- OSTI ID:
- 237919
- Report Number(s):
- CONF-950604-; ISBN 1-880653-18-4; TRN: IM9625%%244
- Resource Relation:
- Conference: 5. international conference on offshore and polar engineering, The Hague (Netherlands), 11-15 Jun 1995; Other Information: PBD: 1995; Related Information: Is Part Of Proceedings of the fifth (1995) international offshore and polar engineering conference. Volume 2; Chung, J.S. [ed.] [Colorado School of Mines, Golden, CO (United States)]; Sayed, M. [ed.] [National Research Council Canada, Ottawa, Ontario (Canada)]; Gresnigt, A.M. [ed.] [Delft Univ. of Technology (Netherlands)]; PB: 580 p.
- Country of Publication:
- United States
- Language:
- English
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