Abstract

Nowadays, in order to be competitive on the market, it is fundamental to design optimized devices. This is especially true in the Offshore sector where the product's weight has a material influence on all operations. Reducing this parameter implies a significant decrease in the project's cost. This paper proposes the study of the kinematic rotation of a prototype machine required to lay down an umbilical system, needed to provide the vital supply (electricity and fiber optic) from platforms or topside vessel to subsea oil and gas furniture. In the studied case, the Client asked to have a cable that partially floats once it reaches the sea water showing incredible benefits such as the possibility to be replaced and small umbilical deflections due to a catenary effect reduction. Due to this singular request, the proposed prototype machine - characterized by the rotation of an articulated parallelogram, activated by two main pistons - ensures safety operation and integrity of the laid umbilical. During the piston design phase, some limitations of current DNV standards (when dealing with offshore technologies) have been highlighted. To investigate this peculiar phenomenon several results obtained by different numerical approaches are proposed. The present machine could be even applied in the renewable energy field, for connecting wind turbines in the wind farm's hub and then to carry the produced energy on shore. This analysis results in a 15﹪ machine weight reduction with respect to the initial design. Such simulation provided a practical design tool for the offshore market.

Introduction

When an ocean communication cable is laying, considerable care is usually exercised to ensure safety operation and the integrity of the product. One form of apparatus for laying cables is an arrangement mounted on and supported by a floating vessel such as a barge. Such an apparatus is adapted for laying cables in both shallow and deep-sea environment and in one embodiment has a guide means positioned in order to permit a cable to pass over an edge of the vessel and means arranged to support the cable during this operation [1]. Other installation aspects related to flexible risers and offshore umbilical systems can be found in the paper by Johnston [2].

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