Vibration control for the offshore platforms with delayed control under irregular wave forces

A wideband multiple extended tuned mass dampers (METMD) system has been developed for reducing the multiple resonant responses of the platforms to all kinds of loads, such as earthquake, typhoon, tsunami and big ice load. This system is composed of several subsystems, each of which consists of one set of extended tuned mass damper (ETMD) unit covering a specific frequency bandwidth, and its average frequency is tuned to one of the first resonant frequencies of the platform. The offshore platform is simplified to a single degree-of-freedom (DOF) system to which a METMD subsystem (composed of m ETMDs) is attached and constitutes m+1 DOFs system. The total mass ratio of the METMD subsystem to the platform is 14% and the frequency ratio of the exciting frequency to the platform’s natural frequency varies in [0.5, 1.5]. The theory analysis shows that: 1) the platform has the better vibration control effect when the non-dimensional frequency bandwidth Ω, which is defined as the ratio of the frequency range to the controlled (target) platforms natural frequency, is in [0.35, 0.6]; 2) the damping coefficient ξ of ETMD systems is in [0.05, 0.15] and 3) the number of the ETMDs is 5 when Ω = 0.45 and ξ = 0.1. The FEM simulation shows that the METMD has a better vibration control effect on the mega-platforms’ vibration control under the random ocean wave load.

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Irregular Wave Forces Acting on a Submerged Sphere

Coastal Engineering in Japan ◽

10.1080/05785634.1987.11924468 ◽

1987 ◽

Vol 30 (1) ◽

pp. 117-130 ◽

Cited By ~ 2

Author(s):

Koichiro Iwata ◽

Norimi Mizutani ◽

Shinzo Kasai

Keyword(s):

Wave Forces ◽

Irregular Wave ◽

Submerged Sphere

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An experimental study of irregular wave forces on multiple quasi-ellipse caissons

Journal of Marine Science and Application ◽

10.1007/s11804-014-1256-8 ◽

2014 ◽

Vol 13 (3) ◽

pp. 265-273

Author(s):

Xiaozhong Ren ◽

Peng Zhang ◽

Yuxiang Ma ◽

Yufan Meng

Keyword(s):

Experimental Study ◽

Wave Forces ◽

Irregular Wave

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Effect of Seabed Slope on Offshore Pile Lateral Behaviour Under Wave Force

29th International Conference on Ocean, Offshore and Arctic Engineering: Volume 1 ◽

10.1115/omae2010-21164 ◽

2010 ◽

Author(s):

Sathyanarayanan Dhandapani ◽

Muthukkumaran Kasinathan

Keyword(s):

Finite Element ◽

Vertical Direction ◽

Pile Group ◽

Element Model ◽

Wave Force ◽

Wave Forces ◽

Extreme Conditions ◽

Offshore Platforms ◽

Wave Loads ◽

Offshore Structure

Fixed offshore platforms supported by pile foundations are required to resist dynamic lateral loading due to wave forces. The response of a jacket offshore tower is affected by the flexibility and nonlinear behavior of the supporting piles. In this study, a typical fixed offshore platform is chosen, and dynamic wave analysis is performed on it. Analysis has been performed for normal environmental conditions and extreme conditions. For the foundation, the deflections and reactions at regular intervals along the vertical direction from the seabed have been found out from the dynamic analysis, and the results have been compared for normal and extreme conditions. The aim of this study is to investigate the effects of the combined lateral and vertical loads on pile group foundation of a fixed offshore structure and the effects of seabed slope on the pile responses. To provide a more accurate and effective design for offshore pile foundation systems under axial structural loads and lateral wave loads, a finite element model which is modelled in FLAC3D is employed herein to determine the soil structure interaction under similar loading conditions. Three dimensional modelling and the analyses are done using FLAC3D — a finite element package.

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