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Deepstar Experimental VIV Program

Lake Tests
(Nov 2003, Spring 2004)
Lake Seneca, New York




Click here to view video footage from Seneca in November 2003 (62 mb)
Offshore Tests
(Summer 2004)
Gulf stream current


Motivating questions

  • Does lock-in occur at high mode number in uniform flows or sheared flow?
  • How is the boundary between single and multi-mode behavior affected by mode number, shear, and damping?
  • What is the relative contribution of in-line and cross-flow response to up-crossing frequency, stress amplitude, and fatigue damage rate?
  • How much fairing coverage is required to prevent significant VIV?
  • Can we measure hydrodynamic damping during VIV?
  • How does mean Cd vary with A/D and the number of participating modes.



  • Deciding on experimental program

    The desire for ease of mechanical handling together with a long fatigue life ultimately lead to the selection of a fiberglass coil tubing pipe for the testing program. The type of instrumentation was selected to be a network of triaxial accelerometers. This was decided after an investigation into various state-of-the-art technologies and whether they can be easily implemented.




    Offshore Tests - The Gulf Stream Test: Overview (Miami II)

    The Gulf Stream test was conducted in October 2006. The main objectives of the Gulf
    Stream test were the following:
    • Collect vortex-induced vibration response data on densely instrumented cylinder
    responding at high mode numbers.
    • Test full and partial coverage configurations for triple-helical strakes and fairings.
    • Estimate drag coefficients for bare pipe and pipe covered with strakes and
    fairings.

    The Gulf Stream test was conducted on the Research Vessel F. G. Walton Smith out of
    the University of Miami using a composite pipe of length 500.4 feet and an outer
    diameter 1.43 inches. The length and diameter of the pipe were chosen such that high
    mode numbers were possible; where high mode numbers are defined as modes greater
    than approximately 10th mode. The experiments were conducted by towing the pipe from
    the boat. A railroad wheel, weighing 805 pounds in air and 725 pounds in water, was
    attached at the bottom end of the pipe to provide tension. The pipe simulated a pinnedpinned
    tensioned beam. The pipe’s dynamic response was tension dominated with the
    bending stiffness of the pipe having negligible effect. Universal joints were used at both
    ends of the pipe to create the pinned connection.
    The pipe was instrumented with fiber optic strain gauges to monitor the vibrations.
    Additional instrumentation included a tiltmeter to measure the pipe top end angle of
    inclination, a load cell to measure the tension at the top end and two mechanical current
    meters located near the top and bottom ends. A pressure transducer was also installed on
    the railroad wheel in order to measure its depth. An Acoustic Doppler Current Profiler
    (ADCP) was used to measure the magnitude and direction of the incident flow profile.


    The properties of the pipe tested during the 2006 Gulf Stream test are listed below.

    Inner Diameter 0.98 in. (0.0249 m)
    Outer Diameter 1.43 in. (0.0363 m)
    EI 1.483e3 lb ft2 (613 N m2)
    EA 7.468e5 lb (3.322e6 N)
    Weight in Seawater 0.1325 lb/ft (0.1972 kg/m)
    Weight in air 0.511 lb/ft (0.760 kg/m)
    Density of pipe material 86.39 lb/ft3 (1383 kg/m3)
    Effective mean tension 725 lb (3225 N, wet weight of railroad wheel)
    Material Glass fiber epoxy composite
    Length 500.4 ft (152.524 m)
    Manufactured by FiberSpar Inc.

    Insensys Fiber Optic System:

    Fiber optic strain gauges were used to measure the vibrations in the pipe. Eight separate
    fibers were embedded into the pipe during its manufacturing process at a radius of 0.685
    inches from the center.


    Each fiber contained 35 strain gauges. Two fibers were located in each of the four
    quadrants of the pipe. The two fibers had strain gauges located every 14 feet; though the
    strain gauges from the two fibers were off-set from each other to allow measurement
    every 7 feet along the pipe. An Insensys Fiber Optic System (FSI unit) was used to record
    the data. The system was limited to a sampling rate of 2000 Hz divided by the number of
    strain gauges being sampled in the fiber.

    Strake Experiments

    The strakes were a triple helix design made of polyethylene, with a pitch of 17.5 times
    the diameter of the pipe. This represents a typical design for strakes in the industry. The
    properties of the strakes are listed below. The strakes had a slit down the side that
    allowed them to be snapped over the outside of the pipe. The strakes were then secured to
    the pipe using tie wraps. The strakes were manufactured by AMS International.

    Material Polyethylene
    Length 26.075 in. (0.662 m)
    Shell OD 1.49 in. (0.038 m)
    Shell ID 1.32 in. (0.034 m)
    Strake Height 0.375 in. (0.0095 m, 25% of shell OD)
    Wall thickness 0.09 in. (0.002 m)
    Pitch 17.5 times the diameter
    Weight 0.11 lb/ft ±10% (0.164 kg/m, large variation)

     

    Published Paper based on Gulf Stream Test Data

    1. Jaiswal, V. and Vandiver, J.K., 2007, "VIV Response Prediction for Long Risers with
      Variable Damping", Proceedings of OMAE2007, OMAE2007-29353
    2. Jhingran, V. and Vandiver, J.K., 2007, "Incorporating the Higher Harmonics in VIV
      Fatigue Predictions", Proceedings of OMAE2007, OMAE2007-29352
    3. Marcollo, H., Chaurasia H. and Vandiver J. K., “Phenomena Observed in VIV Bare
      Riser Field Tests”, Proceedings of OMAE2007, OMAE2007-29562
    4. Swithenbank, S. and Vandiver, J.K., 2007, "Identifying the Power-in Region for
      Vortex-Induced Vibration on Long Flexible Cylinders", Proceedings of OMAE2007,
      OMAE2007- 29156



    Lake Tests

    The lake tests use all the equipment developed and put together by the team at MIT and its subcontractor SSI (Scientific Solutions Inc.). Additionally, DEEPSTAR have subcontracted BMT-SMS from San Diego to supply a data acquisition system which reads from a network of accelerometers. Each accelerometer is made to sample simultaneously, the information is held in memory and then sent to the surface packet by packet.

    Click here for the full details of pipe properties.

    The lake tests consist of two main configurations:

    Uniform flow towing tests:




    Linear shear flow pendulum tests:



    In November 2003, the MIT team went to Lake Seneca and conducted some preliminary shake-down proof tests. Click here to view video footage from these tests (62 mb). Below are some photographs:

    Lake Seneca Navy Facility:




    Design and deployment of stable bottom weights:

                    (With bottom current meter attached)



    Mechanical handling techniques with crane developed:

                              (Pipe laying on deck in 100 foot sections)                                  (Crane lifting pipe in to place)



    Vigorous VIV observed:
    Video: VIV footage 1 (25 mb)
    Video: VIV footage 2 (25 mb)
    Video: Seneca footage (62mb)