ABSTRACT

The paper reports the experimental part of a development project on the design and fatigue performance of composite umbilicals, carried out under Work Package 2 of the "Umbilicals - The Future" joint industry funded project A series of tests have been carried out to improve the understanding of the internal behaviour of an umbilical, to verify the theoretical analysis and to gather physical data necessary for the development of an analytical theory for calculating internal stresses in an umbilical being bent over a sheave

INTRODUCTION

An analytical theory has been developed to describe the behaviour of a syrnmetrical electro-hydraulic umbilical and its internal electrical, mechanical and hydraulic components when it is forcibly bent around a sheave wheel This theory, which has been implemented in a computer program entitled Gneg2, is reported in Part 1 of this paper [l] The work has been carried out under Work Package 2 Umbilical Modelling and Design of the "Umbilical - The Future" joint industry funded project which was commenced in 1993

This paper describes a supporting programme of experimental work which was undertaken to provide essential input data for the Gneg2 program, and also to validate some key aspects of the theoretical analysis

OBJECTIVES AND TYPES OF TESTING

A number of experimental tests have been carried out in parallel with the development of the analytical theory described in Part 1

The man objectives for the experimental work were

  1. To improve the understanding of the internal behaviour of an umbilical as it is loaded and bent over a sheave

  2. To perform tests to verify and if necessary, modify the theoretical analysis as it was developed

  3. To gather necessary physical data that is used as inputs to the theoretical model Tests to improve the understanding of the internal behaviour of an umbilical and to verify analytical calculations include

    • Measurement of the stiffness of hydraulic hoses under bending as well as in transverse, axial and shear loading

    • Bend stiffness tests to measure the force required to bend the umbilical over a sheave with different axial loads on the umbilical

    • Measurements to determine the strain in a core of an umbilical as it moves on a sheave for comparison with the results given by the analytical theory

STIFFNESS OF HYDRAULIC HOSES

Umbilicals often contain hydraulic hoses, which are usually so flexible that they will seldom be exposed to high stresses due to bending of the umbilical The behaviour of the hoses will, however, affect the pressure and the frictional forces between the other elements in the umbilical It is therefore necessary to know the stiffness characteristic of the hydraulic hoses in order to take the deflection under load Into consideration

Test specimens

Four different hoses were tested, two with outer diameters of 20 and 30 mm (called Poly20 and Poly30) and two with outer diameters of 23 and 36 mm (called ABB23 and ABB36) The hoses had the following data

Table 1 Data of tested hoses (Available in full paper)

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