Apparatus with strake elements and methods for installing strake elements

Abstract

There is disclosed an apparatus comprising a plurality of strake elements, each strake element adapted to cover an arc-angle about a circumference of a structural element; and a mechanism adapted to attach the strake elements to each other to cover at least a portion of the circumference of the structural element.

Description

CROSS-REFERENCE TO RELATED APPLICATION [0001] The present application claims the benefit of the filing date of U.S. Provisional patent application Ser. No. 60 / 684,034, filed on May 24, 2005, the disclosure of which is incorporated herein by reference.FIELD OF INVENTION [0002] There is disclosed an apparatus with strake elements and methods for installing strake elements. BACKGROUND [0003] Production of oil and gas from offshore fields has created many unique engineering challenges. One of these challenges is dealing with effects of currents on marine elements. Such marine elements may be employed in a variety of applications, including, e.g., subsea pipelines; drilling, production, import and export risers; tendons for tension leg platforms; legs for traditional fixed and for compliant platforms; other mooring elements for deepwater platforms; and, the hull structure for spar type structures. These currents may cause vortexes to shed from the sides of the marine elements, inducing v...

AI Technical Summary

Benefits of technology

[0022] Improvements and advantages of the invention include one or more of the following: an improved strake element manufacturing system and method, an improved strake element installin

Problems solved by technology

Production of oil and gas from offshore fields has created many unique engineering challenges.

One of these challenges is dealing with effects of currents on marine elements.

These currents may cause vortexes to shed from the sides of the marine elements, inducing vibrations that can lead to the failure of the marine elements or their supports.

These vibrations may be caused by oscillating dynamic forces on the surface which can cause substantial vibrations of the structure, especially if the forcing frequency is at or near a structural natural frequency.

The vibrations may be larger in the transverse (to flow) direction; however, in-line vibrations can also cause stresses which may be sometimes larger than those in the transverse direction.

If the frequency of this harmonic load is near the resonant frequency of the structure, large vibrations transverse to the current can occur.

These vibrations can, depending on the stiffness and the strength of the structure and any welds, lead to unacceptably short fatigue lives.

In fact, stresses caused by high current conditions in marine environments have been known to cause structures such as risers to break apart and fall to the ocean floor.

For instance, a riser pipe that is vibrating due to vortex shedding will disrupt the flow of water around it more than a stationary riser.

This may result in more energy transfer from the current to the riser, and hence more drag.

Likewise, elongated structures with excessive VIV and drag forces that extend far above the ground can be difficult, expensive and dangerous to install VIV and / or drag reduction devices.

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