Frequency domain response of a parametrically excited riser under random wave forces

2014 ◽  
Vol 333 (2) ◽  
pp. 485-498 ◽  
Author(s):  
Song Lei ◽  
Wen-Shou Zhang ◽  
Jia-Hao Lin ◽  
Qian-Jin Yue ◽  
D. Kennedy ◽  
...  
Keyword(s):  
Frequency Domain ◽  
Random Wave ◽  
Wave Forces ◽  
Parametrically Excited ◽  
Frequency Domain Response

Seismic Analysis of a Double-Hinged Articulated Offshore Tower

2008 ◽  
Author(s):  
Syed Danish Hasan ◽  
Nazrul Islam ◽  
Khalid Moin
Keyword(s):  
Seismic Analysis ◽  
Offshore Structures ◽  
Random Wave ◽  
Wave Forces ◽  
Offshore Structure ◽  
Concentrated Mass ◽  
Energy Principle ◽  
Rotational Angle ◽  
Sea Bed ◽  
Time Histories

The response of offshore structures under seismic excitation in deep water conditions is an extremely complex phenomenon. Under such harsh environmental conditions, special offshore structures called articulated structures are feasible owing to reduced structural weight. Whereas, conventional offshore structure requires huge physical dimensions to meet the desired strength and stability criteria, therefore, are uneconomical. Articulated offshore towers are among the compliant offshore structures. These structures consist of a ballast chamber near the bottom hinge and a buoyancy chamber just below the mean sea level, imparting controlled movement against the environmental loads (wave, currents, and wind/earthquake). The present study deals with the seismic compliance of a double-hinged articulated offshore tower to three real earthquakes by solving the governing equations of motion in time domain using Newmark’s-β technique. For this purpose Elcentro 1940, Taft 1952 and Northridge 1994 earthquake time histories are considered. The tower is modeled as an upright flexible pendulum supported to the sea-bed by a mass-less rotational spring of zero stiffness while the top of it rigidly supports a deck in the air (a concentrated mass above water level). The computation of seismic and hydrodynamic loads are performed by dividing the tower into finite elements with masses lumped at the nodes. The earthquake response is carried out by random vibration analysis, in which, seismic excitations are assumed to be a broadband stationary process. Effects of horizontal ground motions are considered in the present study. Monte Carlo simulation technique is used to model long crested random wave forces. Effect of sea-bed shaking on hydrodynamic modeling is considered. The dynamic equation of motion is formulated using Lagrangian approach, which is based on energy principle. Nonlinearities due to variable submergence and buoyancy, added mass associated with the geometrical non-linearities of the system are considered. The results are expressed in the form of time-histories and PSDFs of deck displacement, rotational angle, base and hinge shear, and the bending moment. The outcome of the response establishes that seismic sea environment is an important design consideration for successful performance of hinges, particularly, if these structures are situated in seismically active zones of the world’s ocean.

Time and frequency domain wave forces on offshore structures

1988 ◽  
Vol 10 (1) ◽  
pp. 43-46 ◽  
Author(s):  
Ove T. Gudmestad ◽  
George A. Poumbouras
Keyword(s):  
Frequency Domain ◽  
Offshore Structures ◽  
Wave Forces

scholarly journals Time and Frequency Domain Response of HTS Resonators for Use as NMR Transmit Coils

2019 ◽  
Vol 29 (5) ◽  
pp. 1-5
Author(s):  
Ghoncheh Amouzandeh ◽  
Vijaykumar Ramaswamy ◽  
Nicolas Freytag ◽  
Arthur S. Edison ◽  
Lawrence A Hornak ◽  
...  
Keyword(s):  
Frequency Domain ◽  
Frequency Domain Response

scholarly journals Analytical and Numerical Analysis of the Dynamics of a Moonpool Platform–Wave Energy Buoy (MP–WEB)

Energies ◽  
2019 ◽  
Vol 12 (21) ◽  
pp. 4083
Author(s):  
Kong ◽  
Liu ◽  
Su ◽  
Ao ◽  
Chen ◽  
...  
Keyword(s):  
Frequency Domain ◽  
Wave Energy ◽  
Time Domain ◽  
Impulse Response Function ◽  
Radiation Force ◽  
Resonance Phenomenon ◽  
Hydrodynamic Performance ◽  
Wave Forces ◽  
Diffraction Radiation ◽  
The Time Domain

In this work the hydrodynamic performance of a novel wave energy converter configuration was analytically and numerically studied by combining a moonpool and a wave energy buoy, called the moonpool platform–wave energy buoy (MP–WEB). A potential flow, semi-analytical approach was adopted to assess the total (incident, diffraction, radiation) wave forces acting on the device, and the wave capture and energy efficiency performance of this configuration was assessed, both in the time and frequency domain. The performance of the two configurations, single float and double float, were analyzed and compared in terms of diffraction force, added mass radiation force, motion, and power in the frequency domain. Using an impulse response function-based (IRF) method, the frequency domain results were converted in the time domain. The same parameters in the time domain were derived and the main results were confirmed. Wave energy conversion efficiency was significantly increased due to the resonance phenomenon inside the moonpool.

scholarly journals The influence of level ice on the frequency domain response of floaters

2017 ◽  
Vol 143 ◽  
pp. 112-125 ◽  
Author(s):  
Chris Keijdener ◽  
João Manuel de Oliveira Barbosa ◽  
Andrei V. Metrikine
Keyword(s):  
Frequency Domain ◽  
Level Ice ◽  
Frequency Domain Response
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