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Keywords: frequency
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Proceedings Papers

Paper presented at the The First ISOPE European Offshore Mechanics Symposium, August 20–22, 1990
Paper Number: ISOPE-E-90-021
... vortex shedding problems. STATFJORD-A VIBRATIONS At Statfjord A the vibration was an overall vibration of the tie, see figure 1. Calculations of the natural frequency of the individual panel sections of the main chord showed that it was close to the recorded frequency and to the vortex shedding...
Proceedings Papers

Paper presented at the The First ISOPE European Offshore Mechanics Symposium, August 20–22, 1990
Paper Number: ISOPE-E-90-016
... of maxima (envelope statistics) can be estimated subsequently, leading to probabilistic fatigue life evaluations. approximation assumption equation significant wave height reference natural frequency coefficient probability distribution cumulant separability approximation simulation result...
Proceedings Papers

Paper presented at the The First ISOPE European Offshore Mechanics Symposium, August 20–22, 1990
Paper Number: ISOPE-E-90-056
... on the frequency content of the planar ship motion. For purely oscillatory motion, the drag coefficient decreased as the frequency of motion increased. The reduction in the drag coefficient may be related to the amplitude modulation of the flow-induced vibrations of the cable which are magnified during unsteady...
Proceedings Papers

Paper presented at the The First ISOPE European Offshore Mechanics Symposium, August 20–22, 1990
Paper Number: ISOPE-E-90-006
... ABSTRACT The results of experimental measurements of the slowly varying surge motion of a soft moored rectangular barge in the bi-frequency domain are compared to numerical predictions based on a Volterra model and linear diffraction theory. Theoretical calculations were made using...
Proceedings Papers

Paper presented at the The First ISOPE European Offshore Mechanics Symposium, August 20–22, 1990
Paper Number: ISOPE-E-90-026
... ABSTRACT The mooring line dynamics is modelled using the finite element method, and its non-Gaussian response property is investigated using the time domain method. By comparison to the time domain (TD) approach, the application of the hybrid time-frequency domain (HTFD) fatigue analysis...
Proceedings Papers

Paper presented at the The First ISOPE European Offshore Mechanics Symposium, August 20–22, 1990
Paper Number: ISOPE-E-90-031
... to be conservative at wave excitation close to the system natural frequencies. A non-linear analysis was undertaken to confirm this hypothesis. The introduction of representative damping through viscous drag forces was expected to reduce the conservatism. The results from a non-linear time history analysis...
Proceedings Papers

Paper presented at the The First ISOPE European Offshore Mechanics Symposium, August 20–22, 1990
Paper Number: ISOPE-E-90-007
... in the frequency domain to give the Quadratic Transfer Functions. 1. INTRODUCTION Semi submersibles are designed such that their natural freiquencies are well below the frequencies which have significant 'wave energy. However, model tests (Lundgren and Berg, 1982), and full scale measurements (MacLeod, 1986...
Proceedings Papers

Paper presented at the The First ISOPE European Offshore Mechanics Symposium, August 20–22, 1990
Paper Number: ISOPE-E-90-027
... is appropriate if the stress spectrum has a single peak which may be observed under certain conditions e.g. a) when the wave frequency and the natural frequency of the structure lie within close proximity of each other or b) assumption of a quasi-static response of the structure neglecting the effect...
Proceedings Papers

Paper presented at the The First ISOPE European Offshore Mechanics Symposium, August 20–22, 1990
Paper Number: ISOPE-E-90-032
... ABSTRACT The high frequency vibration of the tendons of tension leg platforms (TLPs) with slender columns and pontoons is investigated in this paper. The equations for the two-dimensional rigid body motion of a TLP in heave, surge and pitch are solved in the time domain using a Runge-Kutta...
Proceedings Papers

Paper presented at the The First ISOPE European Offshore Mechanics Symposium, August 20–22, 1990
Paper Number: ISOPE-E-90-059
... waters. In such cases, the well-documented dynamic tension amplification (Triantafyllou et al, 1985) attains its maximum value within the wave frequency range. This is entirely due to the action of the nonlinear drag force, Which, by preventing the mooring line from lateral motion, forces it to respond...
Proceedings Papers

Paper presented at the The First ISOPE European Offshore Mechanics Symposium, August 20–22, 1990
Paper Number: ISOPE-E-90-018
... offshore structure beam sea mooring system calculation frequency structural analysis response analysis storage barge coefficient hydrodynamic analysis upstream oil & gas regular wave artificial intelligence rubber fender equation motion analysis morison equation PIOLeedmgs...
Proceedings Papers

Paper presented at the The First ISOPE European Offshore Mechanics Symposium, August 20–22, 1990
Paper Number: ISOPE-E-90-003
... ABSTRACT A common model for short crested seas is considered in view of wave measurements from the Norwegian continental Shelf. The directional spectrum is given as a product of a frequency spectrum and a frequency dependent spreading function. The spreading function is assumed to attain...
Proceedings Papers

Paper presented at the The First ISOPE European Offshore Mechanics Symposium, August 20–22, 1990
Paper Number: ISOPE-E-90-048
... of interaction, has to be envisaged. In this paper main parameters of concern for risk of pipe damage from dragging ship anchors are discussed, in particular the ones which give a significant contribution to the assessment of the frequency of pipe-anchor interaction and of the pipe damage. 1. INTRODUCTION...
Proceedings Papers

Paper presented at the The First ISOPE European Offshore Mechanics Symposium, August 20–22, 1990
Paper Number: ISOPE-E-90-004
... ABSTRACT It is demonstrated how information about the undisturbed wave at all frequencies of interest can be retrieved by constrained deconvolution of the outputs of several sensors with different known linear response characteristics, placed on or around a floating structure. A model...
Proceedings Papers

Paper presented at the The First ISOPE European Offshore Mechanics Symposium, August 20–22, 1990
Paper Number: ISOPE-E-90-039
... there are two basic approaches. The first is called "direct", where stresses and strains in a structure are determined on the basis of definition of external loads. pile foundation upstream oil & gas evaluation foundation subsea system dynamic identification fundamental frequency topside mass...
Proceedings Papers

Paper presented at the The First ISOPE European Offshore Mechanics Symposium, August 20–22, 1990
Paper Number: ISOPE-E-90-044
... of the suspended lengths of pipeline (Ref.1,2,3,4,5). It is important for the fatigue life evaluation of a span to take into account the restoring force of the adjacent pipe section interacting with the soil, which contributes to increase the natural frequencies and consequently to reduce the occurrence...
Proceedings Papers

Paper presented at the The First ISOPE European Offshore Mechanics Symposium, August 20–22, 1990
Paper Number: ISOPE-E-90-014
... ABSTRACT Sample calculations illustrate uncertainties in predicting second-order wave forces and low-frequency motions of a large moored structure. The results, for a "deep-draught floater" in regular and irregular waves, demonstrate sensitivity to numerical modelling procedures...
Proceedings Papers

Paper presented at the The First ISOPE European Offshore Mechanics Symposium, August 20–22, 1990
Paper Number: ISOPE-E-90-010
... sea. This is because of the behavior of the oscillatory flow at low Keulegan-Carpenter (Kc) numbers. For waves of small amplitudes with high frequencies, which generally occur everyday in the North-Sea, the 15m diameter member will have Kc numbers less than or equal to 2. At low Kc numbers...
Proceedings Papers

Paper presented at the The First ISOPE European Offshore Mechanics Symposium, August 20–22, 1990
Paper Number: ISOPE-E-90-005
... to second-order effect, there are variations both in excitation forces and the damping models. Normally, the second-order (low-frequency) motions are assumed to be uncoupled from the first-order motion this assumption is not generally valid, and that may be the reason why, for supply vessels moored...
Proceedings Papers

Paper presented at the The First ISOPE European Offshore Mechanics Symposium, August 20–22, 1990
Paper Number: ISOPE-E-90-045
... to the flat plate simulating the sea bed. Furthermore, the axial stiffness of restraints could be adjusted, to simulate different pipe-soil interactions at the free-span shoulders. static condition application gap ratio modal plane onset frequency displacement houston offshore pipeline...

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