TITLE:
Theoretical Analysis of Mechanical Vibration for Offshore Platform Structures
AUTHORS:
Saeed A. Asiri, Yousuf Z. AL-Zahrani
KEYWORDS:
Vibrations Attenuation; Periodic Structures; Offshore Platforms; Periodic Legs
JOURNAL NAME:
World Journal of Mechanics,
Vol.4 No.1,
January
20,
2014
ABSTRACT: A new class of support structures, called Periodic
Structures, is introduced in this paper as a viable means for isolating the
vibration transmitted from the sea waves to offshore platform structures
through its legs. A passive approach to reduce transmitted vibration generated
by waves is presented. The approach utilizes the property of periodic structural
components that create stop and pass bands. The stop band regions can be
tailored to correspond to regions of the frequency spectra that contain
harmonics of the wave frequency, attenuating the response in those regions. A
periodic structural component is comprised of a repeating array of cells, which
are themselves an assembly of elements. The elements may have differing
material properties as well as geometric variations. For the purpose of this
research, only geometric and material variations are considered and each cell
is assumed to be identical. A periodic leg is designed in order to reduce
transmitted vibration of sea waves. The effectiveness of the periodicity on the
vibration levels of platform will be demonstrated theoretically. The theory
governing the operation of this class of periodic structures is introduced
using the transfer matrix method. The unique filtering characteristics of
periodic structures are demonstrated as functions of their design parameters
for structures with geometrical and material discontinuities, and
determine the propagation factor by using the spectral finite element analysis
and the effectiveness of design on the leg structure by changing the ratio of
step length and area interface between the materials is demonstrated in order
to find the propagation factor and frequency response.