Dean L. Henning

Drilling Riser Fairing Tests at Prototype Reynolds Numbers

Tow tests have been performed on flexible circular cylinders, with and without short weathervaning fairings, towed in a basin at critical and supercritical Reynolds numbers. The tests were conducted in the David Taylor Model Basin and the Rotating Arm Facility, at the Carderock Division, Naval Surface Warfare Center, in West Bethesda, Maryland. Measurements were made of both the drag and acceleration (due to vortex-induced vibration) of the cylinder. A 5-9/16-inch diameter PVC pipe was used to achieve Reynolds numbers ranging from about 7×105 to 1.5×106 , in uniform flow, for straight tow tests with the pipe experiencing first mode bending vortex-induced vibration. Fiberglass pipes with a 2.5 inch diameter were used to achieve high mode number vortex-induced vibration, in sheared flow, at Reynolds numbers as high as about 3.75×105 . The test results illustrate the importance of conducting tests at prototype Reynolds numbers for drilling riser as well as the importance of conducting tests in sheared flows and at higher mode numbers to fully understand the performance of a suppression device.Copyright

Damping Characteristics of Fairings for Suppressing Vortex-Induced Vibrations

Vortex-induced vibration (VIV) tests have been performed on long, flexible pipes with fairings in sheared flows in a circular towing tank at prototype Reynolds numbers for production risers [1]. It is discovered that there existed strong attenuation of the vibration responses for the test configuration with fairings placed in the strong current zone, compared to the pipe configuration without any fairings. Wave attenuation is typical when waves travel in systems with dissipation. Strong attenuation is an indication of large damping. Additional pluck tests of pipes with fairings in still water were conducted to determine damping in the system in a quantitative manner. The results, though scattered, provide evidence on the level of damping that could exist in structures with fairings. Furthermore, analytical models based on a Green’s function solution and mode superposition method for a taut string were also used to complement experimental data. A range of damping values was considered to find the damping value for which the level of attenuation matched that of the experiments. It is found that this damping value is close to that from the tests.Copyright

Blade Henning Devices for VIV Suppression of Offshore Tubulars

This paper discusses a new type of vortex-induced vibration (VIV) suppression devices, the blade Henning device, named after one of the primary inventors, Dean Henning. It consists of four blades, 90-degree apart, on a circular shaped sleeve. Tests of these devices on a flexible cylinder in uniform flows have been conducted. The results indicate that the amount of suppression required with this type of apparatus to effectively mitigate VIV is significantly reduced.Copyright

High Reynolds Number Flow Tests of Flexible Cylinders With Helical Strakes

Tow tests have been performed on flexible circular cylinders, with and without short helical strakes, towed in a basin at critical and supercritical Reynolds numbers. The tests were conducted at the Naval Surface Warfare Center’s David Taylor Model Basin in Carderock, Maryland. Measurements were made of both the drag and acceleration (due to vortex-induced vibration) of the cylinder. A 3-1/2 inch diameter ABS pipe was used to achieve Reynolds numbers ranging from about 2×105 to 5×105 , and a 5-9/16-inch diameter PVC pipe was used to achieve Reynolds numbers ranging from about 7×105 to 1.5×106 . Tests were also conducted with aluminum inserts (strong-backs), made to fit just inside the test cylinders, in order to obtain stationary (rigid) cylinder drag measurements for comparison purposes. The test results for cylinders fitted with triple-start helical strakes are presented in this paper.Copyright

Vortex-Induced Vibration Tests of Two Faired Cylinders in Tandem at Prototype Reynolds Numbers

This paper presents and discusses vortex-induced vibration (VIV) test results for two faired flexible cylinders in tandem at three spacings (5, 10, and 20 cylinder diameters), which were subjected to uniform flows. It starts with a description of the test facility, test setup, data acquisition, and data processing. It then presents and discusses the VIV responses and motion of both cylinders. Conclusions on the fairing performance are drawn at the end of this paper.Copyright

Vortex Induced Vibration Tests of Smooth and Rough Flexible Cylinders at High Reynolds Numbers

Vortex-induced vibration (VIV) tests have been performed on long, flexible pipes with various levels of roughness, in sheared flows in a circular towing tank at high Reynolds numbers. The test pipes, made of fiberglass composite, were mounted horizontally beneath a rotating arm that has a span of 129 ft, and a width of 25 ft. As the towing bridge rotates, it drives the cylinder in a circular path in still water. The sheared flows experienced by the cylinder excite its VIV motion. The Reynolds numbers for the tests reported herein ranged from 152,000 to 339,000 at the high-speed end of the pipe. Two surface roughness levels were tested: one comprised of the exterior surface of a filament wound fiberglass pipe; and one with carpet glued to the exterior of the pipe. The VIV responses of the test cylinders, represented by displacement time traces, spectrum, and motion trajectories, are presented in this paper. Effects of the surface roughness and Reynolds numbers on the VIV responses are discussed. The response behavior of the cylinders varied from single-mode dominance to multi-mode responses, in addition to certain traveling wave activities. These results should be of interest to researchers and engineers in the area of vortex-induced vibrations.© 2005 ASME

Vortex-Induced Vibration Current Tank Tests of Two Equal Diameter Cylinders Offset From Tandem

Two equal diameter ABS cylinders, offset from tandem, were subjected to uniform and sheared flows in a current tank at subcritical Reynolds numbers. Both tubes were filled with a saltwater solution to produce a specific gravity of 1.38. An accelerometer in each cylinder was used to measure the vortex-induced vibration response, which primarily varied between the third and seventh transverse bending modes. The cylinders were spaced at 3 to 20 diameters in the in-line direction and at 0, 0.5, and 1.0 diameter in the offset direction. Test results indicate that a downstream cylinder, for a pure tandem (no offset) configuration, experiences less vibration than the upstream cylinder when the upstream cylinder rms displacement is larger than about 0.35D. Offsets of 0.5 and 1.0 times the outside diameter produce lower vibration of the downstream cylinder relative to that of the upstream cylinder.© 2004 ASME

Advances in Designing for Riser Impacts Resulting From VIV

Well bay configurations often attempt to place risers as close as possible without incurring interference. Often avoiding interference is not possible, or resulting spacings are impractical and uneconomical. Alternatively, attempts have been made to quantify the results of impacts incurred by risers in service. Collision tests and numerical analyses have been conducted on pipe-on-pipe collisions to help establish such design guidelines. Collected test data have been scanned to establish the design algorithms for strength assessments and fatigue damage predictions of riser systems. This paper illustrates the methodologies and procedures to obtain the desired information from the test results.Copyright