Aspects of Articulated Column Design Including Rigid Body and Elastic Vibration

Hill, Alan B (1988) Aspects of Articulated Column Design Including Rigid Body and Elastic Vibration. MSc(R) thesis, University of Glasgow.

Abstract

The work contained in this thesis mainly relates to aspects of the dynamic behaviour of articulated column production platforms. However, the work can be applied in a more general sense to certain other compliant structures which share some of the dynamic characteristics of articulated columns. After an introductory chapter on the characteristics and uses of articulated columns, some time is devoted to the examination of fundamental aspects which will have an important bearing on the feasibility of the articulated column concept. Such features as the amount of buoyancy required in terms of payload and static heel considerations, space utilisation within the structure, installation procedure and human awareness to motion responses are, discussed. Data are provided which are intended to give general guidance to designers and also establish the inter-dependence of certain parameters. Chapters 4 and 5, are concerned with the rigid body motion response in the time domain. Computer programs have been developed to solve the equations of motion on a time incremental basis, using the modified Morison equation as the forcing function. Once developed, the programs have been applied to examine certain of the non-linear behaviour characteristics of articulated columns in regular waves. Chapter 5 is devoted to examining those aspects of dynamic instability which are readily examined in a time series analysis. Instability mechanisms examined are those due to regular waves and wave groups. Experimental results have been obtained and comparisons with theory are made. The slenderness of the construction of articulated columns gives rise to elastic vibration characteristics which may result in undesirable resonant vibrations. Chapter 6 is concerned with an examination of this aspect, in terms of free vibration analysis, and of those parameters which have the greatest influence on vibration. The finite element method has been used for the free vibration analysis. In Chapter 7, the development of programs to examine the full vibration analysis of articulated columns, in the time domain, is described. The programs have been used to examine, in the time domain, certain of those parameters which were examined in the free vibration analysis presented in Chapter 6. Some experimental results for a very flexible structure are presented and the programs have been adapted to simulate the model construction and test conditions. These results give credibility to the use of a full vibration analysis in the time domain and comparisons of observed non-linear behaviour and predicted non-linear behaviour are made. The non-linear behaviour of articulated columns is shown to play a major part in concept feasibility as are elastic vibration characteristics. However, the concept comprising a lower column of relatively straightforward structural section is shown to be feasible in water depths up to 300 metres. Thereafter, greater flexural rigidity is required.

• Item Type: Thesis (MSc(R))
• Qualification Level: Masters
• Keywords: Naval engineering
• Date of Award: 1988
• Depositing User: Enlighten Team
• Unique ID: glathesis:1988-77639
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 14 Jan 2020 11:53
• Last Modified: 14 Jan 2020 11:53
• URI: https://theses.gla.ac.uk/id/eprint/77639