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ABSTRACT Deep-ocean mining R&D took a direct approach to the development of deep-ocean systems and technology at the 6,000-m ocean depth with an equivalently long pipe, bypassing the offshore industry's step-by-step approach to going deeper from a short pipe. Such a fresh approach โ with some risk โ led this R&D to its success. Some of the experiences (among those published) from the deep-ocean tests and research with a long pipe deployed from a ship provided benefit and confidence to the offshore industry's endeavor of going deeper. When going deeper with a longer pipe, the varying surface-to-oceanfloor physical environmental properties play a larger role in the coupled ship-pipe-equipment dynamics and behavior, thrust power and integrated ship-pipe control. While now going to deeper water with a longer pipe, some technical issues appear to have been overlooked. Some of the associated critical issues and design/operational parameters as the industry goes from deep to still deeper with shorter pipe and associated longer pipes are discussed. INTRODUCTION In the past 40 years the offshore petroleum industry has taken a stepby- step approach to its technology and system development and operation from deep to deeper water: a lower-risk approach. It has been guessing and identifying and learning many unknowns while going deeper and deeper with a longer riser or pipe. In meeting the new challenges, it has been coming up with innovative engineering concepts and solutions for design, installation and operations, although taking much longer time. For the deep-ocean mining R&D at the 6,000-m ocean depth in the 1970s, the development teams of the advanced commercial deep-ocean mining systems and technology had to take the approach of starting the technology and system development directly from the deep ocean depth. Cost and time were the key factors.
- Asia (0.46)
- North America > United States (0.46)
Three-Dimensional Coupled Responses of a Vertical Deep-Ocean Pipe:Part I. Excitation At Pipe Ends And External Torsion
Chung, Jin S. (Department of Engineering, Colorado School of Mines) | Cheng, Bao-rong (Tsinghua University) | Huttelmaier, H.P. (Department of Engineering, Colorado School of Mines)
ABSTRACT: For the simulation of three-dimensional (3-D), nonlinear, coupled axial, bending and torsional responses of a very long pipe system, a new nonlinear FEM code is developed, and a 4,000-ft-longvertical ocean-mining pipe is analyzed. The pipe top is pinned to a ship, while the bottom end of the pipe is connected to equipment on the seafloor. The pipe system is subject to a vertically varying current in establishing the static (initial) equilibrium configuration. For dynamic analysis, the pipe is excited by periodic horizontal, as well as vertical, ship motions at the pipe top and the periodic vertical motion of the equipment on the seafloor. It is also subject to the internal slurry flow and the external hydrodynamic forces. For torsional coupling, a consistent mass-matrix formulation is used. The external flow-induced torsional moment induces the biaxial bending in response to the ocean current and causes appreciable pipe twist. Excitation with concurrent axial and horizontal motions reduces the mean pipe deflections from the static equilibrium. Resonance frequencies for the present nonlinear coupled responses are different from those of the linear vibrations. Varying axial forces and bending moments change the natural frequencies of vibrations of a pipe column. The excitation frequency dominates the pipe vibration frequency, except for the torsional vibration. The biaxial bending (y-) and torsional vibrations are most sensitive to the time-step size. Part II presents the case of the free pipe bottom, which shows some response characteristics different from Part I. INTRODUCTION The importance of the axial stress for design was first pointed out by Chung and Whitney (1981), for which only uncoupled axial stress was investigated for deep-ocean manganese nodule mining with an 18,000-ft vertical pipe. The present paper points out the necessity of the three-dimensional (3-D) modeling coupled with the torsional deformation for the pipe design.
- North America > United States (0.94)
- Asia (0.68)
Three-Dimensional Coupled Responses of a Vertical Deep-Ocean Pipe:Part II. Excitation At Pipe Top And External Torsion
Chung, Jin S. (Department of Engineering, Colorado School of Mines) | Cheng, Bao-rong (Tsinghua University) | Huttelmaier, H.P. (Department of Engineering, Colorado School of Mines)
ABSTRACT: Three-dimensional (3-D), nonlinear, coupled, axial, bending and torsional responses of an 18,000-ftpipe system are studied with the new nonlinear finite element method (FEM) code presented in Part I with an example of the recovery of manganese nodules in the Pacific Ocean. For this Part II, the pipe top is pinned to a ship in waves, and its bottom end is attached with equipment (e.g., buffer) and is free and independent of the self-propelled seafloor nodule miner. The pipe system is subject to a vertically varying, current flow when establishing the static equilibrium configuration. For dynamic analysis, the pipe top is excited by periodic large-amplitude horizontal, as well as vertical, motions, the internal slurry flow, and the external hydrodynamic forces. For torsional coupling, a consistent mass-matrix formulation is used. The external torsional moments induce biaxial bending deflection and vibration in response to a unidirectional ocean current and cause a large pipe twist. The axial-to-torsion and axial-to-bending couplings are found to be strong. Response periods to large-amplitude excitations vary from the top to bottom of the pipe. The upward internal slurry flow reduces the axial stress and increases the horizontal displacements. Numerical stability of the solution is sensitive to the specific sequence of load steps, large flowinduced torsional moment, excitation frequencies, and excessive axial excitation amplitudes. INTRODUCTION In the "70s and "80s (Chung, 1985; Chung and Tsurusaki, 1994), some international consortia of private corporations conducted extensive research and developed manganese nodule recovery technologies and mining systems for test operations in the 10,000-18,000-ยฃ1 ocean floor. One of the more advanced technologies are reviewed in Chung and Tsurusaki (1994). The importance of axial stress as a design parameter was first pointed out by Chung and Whitney (1981 a), for which only an uncoupled axial stress was investigated for an 18,000-ยฃ1 vertical pipe.
- North America > United States (0.69)
- Asia (0.46)
ABSTRACT: In view of increasing applications of the discrete element method (OEM) to pipe and cable dynamics in the offshore environment, explicit stiffness and mass coefficients are derived which allow a direct calculation of the eigenvalues for OEM systems. Relevant OEM derivations are presented which include axial, bending and torsional effects as well as stress stiffening. Eigenvalues are computed by the FEM, OEM and exact solution and are compared for a 1905 m vertical pipe system in the ocean. The comparisons are made for two typic3.J boundary conditions:fixed at top of the pipe and free at its bottom and fixed at both top and bottom of the pipe. Accurate OEM prediction of eigenvalues for each mode of motion is a first step in further applications of OEM to an ocean pipe system. INTRODUCTION In recent publications (Mustoe, Huttelmaier and Chung, 1992a, 1 992b) the discrete element method (OEM) was introduced for the analysis of flexible deep ocean pipes, subjected to (i) dynamic excitations induced by ship motion and (ii) hydrodynamic damping forces. This analysis allowed to include coupled effects due to axial and bending vibrations. The DEM represents a powerfull procedure when applied for dynamic analyses as an explicit scheme. The method allows to trace the full dynamic response through time histories. This has a drawback, however, that basic dynamic properties such as fundamental frequencies cannot be determined directly, and have to be derived indirectly from response curves. Associated mode shapes cannot be determined at all. In this paper a numerical method based on energy principles is described. This allows for a direct derivation of explicit coefficient matrices for a discrete element pipe system. Element stiffness and mass matrices are presented which can be used within a standard assembly procedure.
- North America > United States (0.47)
- Asia (0.29)
Abstract Unlike the usual drill pipe, a long, ocean mining pipe with the equipment attached to its free bottom end would experience significant static as well as dynamic stretching in addition to the extension due to the pipe and equipment weight. The dynamic stretching/contracting oscillation is initially caused by the oscillation of the pipe top end hanging from the mining ship in a seaway. The bottom end oscillation can be amplified near resonance several times of the top end oscillation amplitude, which can become unique design and operation problems of the subsea mining system _equipment. A direct solution approach has been applied to solve the differential equation for vertical displacement, accounting for the added mass and damping of the bottom end equipment. The solution is obtained through numerical iteration for an 18,000-ft long pipe with the bottom equipment, which is handled from a 300,000-ton mining ship. Itshows significantly large pipe stretching near the resonance. The same trend of stretching is measured by the at-sea test with the Glomar Explorer mining operation. Near resonance, the bottom end motion is out of phase with the top end motion, thus increasing the net pipe stretching. The pipe response characteristics can be significantly altered by the pipe weight distribution, wall thickness, and length. These extensive transfer functions, spectral analysis results and parametric analyses for the operational sea states near the mining site in the Northeast Pacific Ocean can provide a basis for the requirements of deployment and retrieval operations of the bottom mining equipments, heave compensator, load on the equipment, pump pressure heads, and transient nodule lift flows. Since the resonant frequency would be within the commonly encountered wave frequency range, the stretching oscillation can impose stringent requirements on the design and operation of the equipment hardware at the bottom end. the analysis method also applies to the OTEC cold water pipe, and to the re-entry operation of deepsea drilling Introduction A long vertical pipe (e.g. deepsea drill pipe) held at the top at the ship's moonpool (Fig. 1) would experience static as well as dynamic stretching. Such dynamic stretching/contracting oscillation is initially caused by the axial or heaving motion of the pipe top due to the floating platform or ship. The vertical pipe oscillation at the bottom end can amplify significantly near the resonant frequency. The subsequent, large-amplitude oscillation can significantly influence the design and operation requirements of the ocean mining system equipment. The first analytical formulation and analysis of this problem were carried out by Greenfield and Lubinski in 1967 [1] to determine the stroke of the bumper sub at the bottom end of a deepsea drill pipe in a vertical configuration which was greater than the top end amplitude.
- Materials > Metals & Mining (1.00)
- Energy > Oil & Gas > Upstream (1.00)