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.
Highlights
Offshore construction is the installation of structures and pipelines in a marine environment for the production and transmission of oil and gas.Construction in the offshore environment is a dangerous activity and where possibly the construction is modular in nature with the individual modules being assembled on shore and using a Crane Barge to lift the modules into place
The aim will be minimized these vibrations on offshore platforms caused by the impact of the sea wave transmission to the offshore platforms through the platform’s leg structure; we try to make a good solution to provide a better isolation of mechanical vibration by using the periodic structure technique [1]
This dissertation has presented the fundamentals governing the operation of a new class of structures for the legs of offshore platform structure which are exposed to the sea waves
Summary
Offshore construction is the installation of structures and pipelines in a marine environment for the production and transmission of oil and gas (see Figure 1). The oil and gas exploration platforms are the best example of offshore structures that can be placed in water depths of 2 kilometers or more. These structures may be made of steel, reinforced concrete or a combination of both. One of the major sources of such mechanical vibrations on offshore platforms is the impact of sea waves on to the platform’s legs. The aim will be minimized these vibrations on offshore platforms caused by the impact of the sea wave transmission to the offshore platforms through the platform’s leg structure; we try to make a good solution to provide a better isolation of mechanical vibration by using the periodic structure technique [1]
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