The paper reports the analytical part of a development project into the design and fatigue performance of composite umbilicals, carried out under Work Package 2 of the "Umbilical - The Future" joint industry funded project A computer model of an electrohydraulical, symrnetrical umbilical subjected to various axial loads and bent around sheaves of different diameters has been developed This model entitled Gneg2 calculates the relative sliding between the cores and stresses due to the effects of bending, axial load and friction


Over recent years, umbilicals have been increasingly used in many off-shore applications worldwide for subsea control, chemical Injection etc The failure of these components in a remote subsea installation can be extremely expensive both in lost production and rectification

Unfortunately, insufficient knowledge of the complex behaviour of umbilicals has often led to defective design, manufacture, installation and operation A report from the Engineering Research Centre, dated July 1990, revealed a significant number of problems associated with unbilicals [3] It was concluded that some form of planned R&D was necessary if the industry was to improve umbilical reliability

From 1985 to 1992 BP Norway Ltd, ABB Norsk Kabel and EFT, which is a part of the SINTEF Group. Norway, ran a project in order to achieve a better understanding of the behaviour of umbilicals and to try to reveal factors having a great influence on the life of umbilials

It was decided, as a start, to concentrate on electrical umbilicals, both unarmoured and armoured, and to try to determine the stresses and the fatigue life of an axially loaded umbilical running back and forth over a sheave If this problem could be solved it was expected that more complex umbilicals and other types of bending problems could be included in later phases

The theory developed, which was implemented in a computer program entitled Grieg was able to describe and calculate the internal movements and forces in all-electric umbilicals [l] and [2] However, there was a need to extend ths theory to the more common umbilical configurations containing both electrical cores and hydraulic hoses

In 1993, when the R&D programme "Umbilicals - The Future" started, it was decided to continue the research work within a Work Package 2, called "Umbilical Modelling and Design" All results and expenence gained in the former project was made available to the new project This paper is the first of two papers which give a summary of work, description and results from both these projects

The problems were attacked both analytically and experimentally simultaneously as the analysis required knowledge of parameters which have not previously been studied or quantified

The analytical work, which will be presented in this paper, was based on several assumptions Some of these could be tested directly, others could only be tested indirectly by observing which assumptions and parameter values gave correspondence between calculation and test results

Flgure 1 Investigated umbilicals (Available in full paper)

Figure 1 shows the Investigated umbil~calsd unng the first project [I]

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