Experimental Investigation on the Suppression Device of VIV of a Flexible Riser

2014 ◽  
Author(s):  
Yun Gao ◽  
Shixiao Fu ◽  
Leijian Song ◽  
Tao Peng ◽  
Runpei Lei
Keyword(s):  
Fatigue Damage ◽  
Experimental Results ◽  
Experimental Investigations ◽  
Flexible Riser ◽  
Excited Mode ◽  
Response Characteristics ◽  
Helical Strakes ◽  
Uniform Current ◽  
Viv Suppression ◽  
Synchronization Regime

Experimental investigations were conducted on a flexible riser with and without helical strakes. A uniform current was obtained by towing a riser model in a tank, and the vortex-induced vibration (VIV) suppression of strakes with different heights and pitches was studied. The results of the bare riser show that the characteristics of the synchronization of the VIV for a flexible riser have many orders, and the excited mode jumps from one to another abruptly. During the high order synchronization regime, the VIV response decreases with the increased order of the synchronization. The experimental results also indicate that the response characteristics of a bare riser can be quite distinct from those of a riser with helical strakes, and the suppression performance depends on the geometry of the helical strakes. The fatigue damage in the CF direction is of the same order as that in the IL direction for the bare riser. However, for the riser fitted with helical strakes, the fatigue damage in the CF direction is much smaller than that in the IL direction. The experimental results also confirmed that strake height has a greater influence on the VIV response than the strake pitch, and the drag exerted on the riser increases with strake pitch and height.

Evaluation of Fairing Performance by Three-Dimensional Tests Using a Flexible Riser Model

2015 ◽  
Author(s):  
Kjetil Skaugset ◽  
Rolf Baarholm ◽  
Halvor Lie ◽  
Henning Braaten
Keyword(s):  
Three Dimensional ◽  
Real Life ◽  
Hydrodynamic Performance ◽  
Small Scale ◽  
Attractive Alternative ◽  
Flexible Riser ◽  
Full Coverage ◽  
Helical Strakes ◽  
Viv Suppression ◽  
Further Development

Due to its low drag and suppression effectiveness, fairings are considered to be an attractive alternative to helical strakes for mitigation of riser Vortex Induced Vibrations (VIV). The Norwegian Deepwater Programme has conducted a project with the objective to develop and qualify effective low drag fairing concepts with respect to VIV and galloping. Furthermore, emphasis is put on easy handling and installation. By use of 2D small scale tests in a towing tank and in a large cavitation tunnel, a total of 10 different fairing designs have been evaluated and screened in terms of hydrodynamic performance [1]. Three fairing design candidates were promoted for further development. This paper describe the work and findings when studying the effectiveness of promoted fairings on a 3D flexible riser model with respect to galloping and VIV. Three different fairing profiles have been studied in the present model tests. The tests were carried out in the sub-critical Reynolds number regime with Rn up to about 53000. Four different fairing coverages were tested for each design: full coverage, 60 % coverage, 40 % coverage and full coverage of the lower half of riser. Differences in performance have been noticed for the fairing profiles, and the findings have laid the ground for further development of the most promising candidates for real life applications. Further, it is concluded that the combination of 2D and 3D tests, as well as combination of small scale and prototype scale tests, has been an efficient strategy in development of VIV suppression devices.

Suppressing Vortex-Induced Vibrations of Long Flexible Riser by Multiple Control Rods

2010 ◽  
Author(s):  
Hao Wu ◽  
Dapeng Sun ◽  
Lin Lu ◽  
Bin Teng ◽  
Jianqiao Zhang ◽  
...  
Keyword(s):  
Passive Control ◽  
Control Method ◽  
Slenderness Ratio ◽  
Experimental Investigations ◽  
Flexible Riser ◽  
Multiple Control ◽  
Control Rod ◽  
Response Characteristics ◽  
Pitch Distance ◽  
Control Rods

Experimental investigations on a passive control method for suppressing VIV of long flexible riser are presented in this work. A riser model with L/D (slenderness ratio) of 1750 was horizontally installed on a carriage and uniform current was simulated by towing the riser using the carriage in a wave tank, which leads to the Reynolds numbers ranging from 103 to 104. Four slender control rods with diameter d = 0.25D were placed parallel to the riser at uniform angle (i.e. at 90° intervals around the riser circumference). Different pitch distances l/D = 0.813, 1 and 1.188 were considered in this work, where l is the center-to-center distance between control rod and riser model. Strain along the riser and tension were measured by Fiber Bragg Grating and tensionmeter, respectively. The experimental results indicate that the response characteristics of a riser model with multiple control rods are quite distinct from that of a bare riser. Multiple control rods can suppress VIV response significantly, and their performance is mainly dependent on the pitch distance. It is found that the spatial maximum standard deviation of strain decreases about 84% due to the existence of control rods. The optimal pitch distance is found to be l/D ≤ 1. Moreover, spectrum analysis shows that the dominate frequency increases linearly with the increasing of flow velocity, for both the bare riser and the riser with control rods, while the frequency band of the suppressed riser becomes broader compared with the bare riser. It is also observed that the tension of the riser is slightly increased due to the presence of four rods, but not sensitive to the pitch distance.

Experimental Study on Flexible Bare Pipe Arrays Undergoing Vortex-Induced Vibrations

2018 ◽  
Author(s):  
Y. Liu ◽  
C. Shi ◽  
Z. Liu ◽  
J. Wang ◽  
X. Bao
Keyword(s):  
Fatigue Damage ◽  
Dynamic Responses ◽  
Array Configuration ◽  
Damage Rate ◽  
Flexible Pipes ◽  
Vortex Induced Vibrations ◽  
Helical Strakes ◽  
Preliminary Study ◽  
Single Pipe ◽  
Center Distance

Vortex-induced vibration (VIV) excited by current is a major contributor to the fatigue accumulation of marine risers. For deepwater operations, several risers are often arranged together in an array configuration. In this study, a set of four identical flexible pipes of a rectangular arrangement were tested in a water tunnel. By comparing the dynamic responses of a pipe in an array with that of a single isolated pipe, the effects of the current speed and the center-to-center distance between the up-stream and downstream pipes on their dynamic responses were investigated. Fatigue damages accumulated on each pipe in an array was calculated and a factor, termed “fatigue damage amplification factor”, was defined as a ratio between the fatigue damage rate of pipe in an array and the fatigue damage rate of a single pipe at a same current condition. The results showed that for bare pipes (i.e., without helical strakes), the downstream pipes in an array configuration may have larger dynamic responses and fatigue damage rates than those of a single pipe; and, it is not always conservative to assume that the fatigue damage rate estimated for a single pipe can be used to represent the fatigue damage rates of pipes in an array. This preliminary study provided some meaningful results for the design, analysis and operation of marine riser arrays.

The effect of yaw angle on VIV suppression for an inclined flexible cylinder fitted with helical strakes

2017 ◽  
Vol 67 ◽  
pp. 263-276 ◽  
Author(s):  
Wanhai Xu ◽  
Yingsen Luan ◽  
Qinghua Han ◽  
Chunning Ji ◽  
Ankang Cheng
Keyword(s):  
Flexible Cylinder ◽  
Helical Strakes ◽  
Viv Suppression ◽  
Yaw Angle

scholarly journals Boundary Layers on Rough Compressor Blades

1972 ◽  
Author(s):  
K. Bammert ◽  
R. Milsch
Keyword(s):  
Boundary Layer ◽  
Friction Coefficient ◽  
Boundary Layers ◽  
Axial Flow ◽  
Experimental Results ◽  
Experimental Investigations ◽  
Compressor Blades ◽  
Turbulent Transition ◽  
Good Reproduction ◽  
Compressor Efficiency

Blades of axial flow compressors are often roughened by corrosion or erosion. There is only scant information about the influence of this roughening on the boundary layers of the blades and thereby on the compressor efficiency. To obtain detailed information for calculating the efficiency drop due to the roughness, experimental investigations with an enlarged cascade have been executed. The results enabled to develop new formulas for a modified friction coefficient in the laminar region and for the laminar-turbulent transition and the separation points of the boundary layer. Thus, together with the Truckenbrodt theory, it was possible, to get a good reproduction of the experimental results.

Practical Design Considerations for Managing Marine Growth on VIV Suppression Devices

2015 ◽  
Author(s):  
Don W. Allen ◽  
Li Lee ◽  
Dean Henning ◽  
Stergios Liapis
Keyword(s):  
Reynolds Number ◽  
Fatigue Life ◽  
Strong Influence ◽  
Low Reynolds Number ◽  
Vortex Induced Vibration ◽  
Design Considerations ◽  
Drag Forces ◽  
Practical Design ◽  
Helical Strakes ◽  
Viv Suppression

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.

An Approach to Include Observed VIV Likelihood in Drilling Riser Fatigue Analyses

2009 ◽  
Author(s):  
Michael A. Tognarelli ◽  
Rene D. Gabbai ◽  
Mike Campbell
Keyword(s):  
Fatigue Damage ◽  
Field Measurements ◽  
Scaling Analysis ◽  
Current Profile ◽  
Vortex Induced Vibration ◽  
Probability Of Occurrence ◽  
Industry Standard ◽  
Annual Probability ◽  
Analysis Computer ◽  
Viv Suppression

Field measurements of the response of a number of drilling risers indicate that vortex-induced vibration (VIV) occurs significantly less often than predicted by the industry-standard fatigue analysis computer program SHEAR7 V4.4. Several comparisons to model tests and field data, including one published by BP and 2H in 2007 [1], demonstrate that this analysis program is generally quite conservative, given that VIV occurs. Furthermore, this conservatism does not take into account those situations in which VIV fatigue is predicted but none is observed in the field, which adds yet another layer of “hidden” conservatism to design analyses. In an effort to address this and reduce conservatism to a more appropriate level, the probability of occurrence of vortex-induced vibration (VIV) is examined using full-scale measured data. The data has been collected over the past several years from five drilling risers without VIV suppression devices. These risers are on rigs under contract to BP at high-current-susceptible sites worldwide. Collectively, the data correspond to 9,600 10-minute field measurements, equivalent to 0.18 years of continuous monitoring. The riser response is obtained from motion loggers placed at selected positions along the riser as described in [1]. Each logger measures 3D accelerations and 2D angular rates. Through-depth currents are measured via Acoustic Doppler Current Profilers (ADCP). By comparison of measurements to computer predictions based on the observed current profile, a relationship is developed between the intensity of the fatigue damage predicted and the probability that VIV is observed in the field. Subsequently, an approach is proposed for scaling analysis predictions to reflect the relative likelihood of VIV. The database of measured and SHEAR7 maximum predicted fatigue damage rates is statistically characterized to determine how it may be used to determine factors of safety (FOS) for VIV design. A worked example for a deepwater drilling riser in the GoM is used to show how the FOS methodology can be applied in the case of multiple design currents each with a different annual probability of occurrence.

Experimental Investigations of the Machinability of Titanium Alloy TC4 with Different Hydrogen Contents

2011 ◽  
Vol 418-420 ◽  
pp. 1307-1311
Author(s):  
Jun Hu ◽  
Yong Jie Bao ◽  
Hang Gao ◽  
Ke Xin Wang
Keyword(s):  
Surface Roughness ◽  
Titanium Alloy ◽  
Cutting Force ◽  
Hydrogen Content ◽  
Experimental Results ◽  
Cutting Conditions ◽  
Experimental Investigations ◽  
Cutting Condition ◽  
The Given

The experiments were carried out in the paper to investigate the effect of adding hydrogen in titanium alloy TC4 on its machinability. The hydrogen contents selected were 0, 0.25%, 0.49%, 0.63%, 0.89% and 1.32%, respectively. Experiments with varing hydrogen contents and cutting conditions concurrently. Experimental results showed that the cutting force of the titanium alloy can be obviously reduced and the surface roughness can be improved by adding appropriate hydrogen in the material. In the given cutting condition, the titanium alloy TC4 with 0.49% hydrogen content showed better machinability.

scholarly journals Modeling Study on Stiffness Characteristics of Hydraulic Cylinder under Multi-Factors

2017 ◽  
Vol 63 (7-8) ◽  
pp. 447 ◽  
Author(s):  
Hao Feng ◽  
Qungui Du ◽  
Yuxian Huang ◽  
Yongbin Chi
Keyword(s):  
Mechanical System ◽  
Volume Expansion ◽  
Hydraulic Cylinder ◽  
Experimental Results ◽  
Axial Deformation ◽  
Response Characteristics ◽  
Stiffness Model ◽  
Hydraulic Cylinders ◽  
Stiffness Characteristics ◽  
Cylinder Barrel

For a complex mechanical system driven by hydraulic cylinders, the dynamic response characteristics of the mechanical system are significantly affected by the stiffness characteristics of hydraulic cylinders. This paper comprehensively studies the impacts of various factors on the stiffness characteristics of the hydraulic cylinders, including the oil bulk modulus, the air content in the hydraulic oil, the axial deformation of the piston rod, the volume expansion of the cylinder barrel, the volume expansion of the metal pipes and the flexible hoses, and the deformation of the hydraulic cylinder sealing. By combining the theoretical analysis and the experimental results, the level of each impacting factor was quantified, and the stiffness model of the hydraulic cylinder was established. Finally, comparative analysis of the stiffness was conducted by taking the experimental hydraulic cylinder as an example; it was verified that the calculated results of the proposed hydraulic cylinder stiffness model approximated the experimental results. Compared with stiffness models presented in current literature, the average accuracy was improved by more than 15 %.

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