Dean Leroy Henning

Ultrashort fairings for suppressing vortex-induced-vibration

An ultrashort fairing is disclosed for suppressing vortex-induced vibration in substantially cylindrical marine elements. The ultrashort falling has a leading edge substantially defined by the circular profile of the marine element for a distance following at least about 270 degrees thereabout and a pair of shaped sides departing from the circular profile of the marine riser and converging at a trailing edge. The ultrashort fairing has dimensions of thickness and chord length such that the chord to thickness ratio is between about 1.20 and 1.10.

The Effects of Mixing Helical Strakes and Fairings on Marine Tubulars and Arrays

Most deepwater tubulars experiencing high currents frequently require vortex-induced vibration (VIV) suppression to maintain an acceptable fatigue life. Helical strakes and fairings are the most popular types of VIV suppression devices in use today.It is quite common to use only one type of device (helical strakes or fairings) on a single tubular and, in fact, to use a single device type on an entire tubular array. The use of both styles of suppression devices on a single tubular has grown in popularity, but mixing them within an array is a relatively new concept. It is sometimes desirable to use one suppression device on one tubular and another suppression device on an adjacent or tandem tubular.This paper utilizes results from two different types of VIV experiments. The first consists of a long tubular at high Reynolds numbers with VIV suppression on the outer end where current speeds are the highest. The use of only fairings, only strakes, or a mixture of the two devices is examined.The second VIV experiment examines the use of helical strakes on one tubular and fairings on a tandem tubular. Results are compared to experiments with either helical strakes on both tubulars or fairings on both tubulars. This paper is intended to provide some direction, and in many cases assurance, for mixing helical strakes and fairings on deepwater tubulars.Copyright

Practical Design Considerations for Managing Marine Growth on VIV Suppression Devices

Most deepwater tubulars experiencing high currents frequently require vortex-induced vibration (VIV) suppression to maintain an acceptable fatigue life. Helical strakes and fairings are the most popular VIV suppression devices in use today.Marine growth can significantly affect the VIV of a bare riser, often within just a few weeks or months after riser installation. Marine growth can have a strong influence on the performance of helical strakes and fairings on deepwater tubulars. This influence affects both suppression effectiveness as well as the drag forces on the helical strakes and fairings. Unfortunately, many VIV analyses and suppression designs fail to account for the effects of marine growth at all, even on a bare riser.This paper utilizes results from both high and low Reynolds number VIV test programs to provide some design considerations for managing marine growth for VIV suppression devices.Copyright

S-Lay Installation of Riser Fairings for the Independence Hub

One of the challenges of insuring adequate fatigue life of marine risers due to vortex-induced vibrations (“VIV”) is the installation of VIV suppression devices in a cost effective manner. In the past, short fairings for production risers have been restricted to J-lay or Reel-Lay installations, where the fairings are installed either before or during pipelay, or retrofit installations where the fairings are installed underwater, using specially designed tooling and Remotely-Operated Vehicles, after the riser has already been installed. Both of these options can be expensive by either restricting the vessels that can install the risers (in the case of J-lay installation) or through expensive rental of ROV and associated equipment for retrofit installation. S-lay installation of fairings is particularly challenging due to the shape of the fairings and the need to install thrust collars to keep the fairings in their axial position once they are installed. Additional complexity is added by the requirement that the fairings be able to withstand mud forces from the temporary placement of the riser on the seabed. These challenges were addressed for the Independence Hub project, which required fairings for both adequate fatigue life due to VIV and for thermal heat transfer considerations. An S-lay testing machine was developed for testing fairings experiencing roller loads up to 115 kips. In addition, wave tank tests were performed to insure that the fairings would stay in proper position during S-lay while experiencing wave forces. Upon successful test results, the S-lay fairings were installed on the Spiderman East, Spiderman West, Jubilee East, Jubilee West, and Merganser flowline risers for the Independence Hub project. These flowline installations are the deepest so far in the world. This required close collaboration by all personnel involved to meet the challenges of insuring success for this type of installation. This paper discusses the methodology used to produce successful S-lay fairing installations for the Independence Hub risers. Presented are test results from the roller and wave tank tests, and a discussion on how the final design was derived. Finally, field experiences from the offshore installations are discussed. This paper should be of interest to engineers involved in the design and installation of deepwater risers.Copyright