scholarly journals The Identification of Power-In Region in Vortex-Induced Vibration of Flexible Cylinders

2014 ◽  
Author(s):  
Zhibiao Rao ◽  
Themistocles L. Resvanis ◽  
J. Kim Vandiver
Keyword(s):  
Fiber Optic ◽  
Lessons Learned ◽  
Recent Model ◽  
Strain Gauges ◽  
Flexible Cylinder ◽  
Vortex Induced Vibration ◽  
Sheared Flow ◽  
Primary Power ◽  
Novel Method ◽  
Secondary Power

This paper proposes a novel method to identify the power-in regions of long flexible cylinders subjected to vortex-induced vibration (VIV). It also attempts to address a practical problem: “Will a secondary power-in region appear after the primary power-in region is covered with suppression devices?” The source of data is a recent model test on a 38 meter long flexible cylinder, densely instrumented with fiber optic strain gauges and accelerometers. For pipes with partial coverage of suppression devices in uniform flow, the bare region would be expected to be a power-in region and the section with suppression devices is expected to be a power-out region. Experimental data from these types of tests are used to benchmark the proposed power-in zone identification method. The method is then used to identify the power-in zones on a bare cylinder in a sheared flow. This paper also explores the occurrence of secondary power-in regions that may exist, when suppression devices are placed in the primary power-in zone. Secondary power-in regions were observed. Lessons learned from the power-in region identification in sheared flows will be a useful tool for designer/engineers choosing where to place suppression devices.

Spatial Variation of Drag on Long Cylinders in Sheared Flow

2008 ◽  
Author(s):  
Vikas Jhingran ◽  
Vivek Jaiswal ◽  
J. Kim Vandiver
Keyword(s):  
Drag Coefficient ◽  
Fiber Optic ◽  
Local Variation ◽  
Strain Gauges ◽  
Prediction Formula ◽  
Flexible Pipe ◽  
Drag Coefficients ◽  
Sheared Flow ◽  
Source Regions ◽  
Long Cylinder

A method is described for measuring the local drag coefficient on a long cylinder which exhibits vortex-induced vibration (VIV). Results are shown from a field experiment in which a long flexible pipe was instrumented with two-hundred and eighty fiber optic strain gauges. The measured local drag coefficients are compared to a commonly used drag coefficient prediction formula. The formula is shown to be useful as a tool for predicting the average drag coefficients for the whole cylinder but is not able to accurately capture local variation in CD. The local CD measurements also reveal the location of VIV source regions.

scholarly journals Modeling Low Intensity Fires: Lessons Learned from 2012 RxCADRE

Atmosphere ◽  
2021 ◽  
Vol 12 (2) ◽  
pp. 139
Author(s):  
Rodman R. Linn ◽  
Judith L. Winterkamp ◽  
James H. Furman ◽  
Brett Williams ◽  
J. Kevin Hiers ◽  
...  
Keyword(s):  
Prescribed Fire ◽  
Fire Spread ◽  
Lessons Learned ◽  
Field Sampling ◽  
Wind Fields ◽  
Low Intensity ◽  
Novel Method ◽  
Wind Input ◽  
Variable Wind ◽  
Local Variability

Coupled fire-atmosphere models are increasingly being used to study low-intensity fires, such as those that are used in prescribed fire applications. Thus, the need arises to evaluate these models for their ability to accurately represent fire spread in marginal burning conditions. In this study, wind and fuel data collected during the Prescribed Fire Combustion and Atmospheric Dynamics Research Experiments (RxCADRE) fire campaign were used to generate initial and boundary conditions for coupled fire-atmosphere simulations. We present a novel method to obtain fuels representation at the model grid scale using a combination of imagery, machine learning, and field sampling. Several methods to generate wind input conditions for the model from eight different anemometer measurements are explored. We find a strong sensitivity of fire outcomes to wind inputs. This result highlights the critical need to include variable wind fields as inputs in modeling marginal fire conditions. This work highlights the complexities of comparing physics-based model results against observations, which are more acute in marginal burning conditions, where stronger sensitivities to local variability in wind and fuels drive fire outcomes.

scholarly journals VIV Excitation Competition Between Bare and Buoyant Segments of Flexible Cylinders

2013 ◽  
Author(s):  
Zhibiao Rao ◽  
J. Kim Vandiver ◽  
Vikas Jhingran
Keyword(s):  
Model Test ◽  
Practical Problem ◽  
Excitation Frequency ◽  
Ocean Basin ◽  
Recent Model ◽  
Total Amplitude ◽  
Vortex Induced Vibration ◽  
Pipe Model ◽  
Exploration And Production ◽  
Different Diameters

This paper addresses a practical problem: “Under which coverage of buoyancy modules, would the Vortex Induced Vibration (VIV) excitation on buoyant segments dominate the response?” This paper explores the excitation competition between bare and buoyant segments of a 38 meter long model riser. The source of data is a recent model test, conducted by SHELL Exploration and Production at the MARINTEK Ocean Basin in Trondheim Norway. A pipe model with five buoyancy configurations was tested. The results of these tests show that (1) the excitation on the bare and buoyant regions could be identified by frequency, because the bare and buoyant regions are associated with two different frequencies due to the different diameters; (2) a new phenomenon was observed; A third frequency in the spectrum is found not to be a multiple of the frequency associated with either bare or buoyancy regions, but the sum of the frequency associated with bare region and twice of the frequency associated with buoyancy region; (3) the contribution of the response at this third frequency to the total amplitude is small; (4) the power dissipated by damping at each excitation frequency is the metric used to determine the winner of excitation competition. For most buoyancy configurations, the excitation on buoyancy regions dominates the VIV response; (5) a formula is proposed to predict the winner of the excitation competition between bare and buoyant segments for a given buoyancy coverage.

Lessons Learned From Freespans at Pipeline Watercourse Crossings

2020 ◽  
Author(s):  
Gerry Ferris
Keyword(s):  
Static Load ◽  
Water Velocity ◽  
Lessons Learned ◽  
Vortex Induced Vibration ◽  
Water Loading ◽  
Relevant Question ◽  
The Past ◽  
Load Limit ◽  
Pipeline Failure

Abstract Over the past 10 years inspections (site visits, boat based surveys or diver surveys) have been completed at nearly 20,000 pipeline watercourse crossings for 20 different pipeline owners. During the last 10 years there have been 721 unique locations where an exposed pipeline was found and at 213 of these locations a freespan was encountered. Only one of the freespans resulted in the failure (loss of product) of the pipeline. This record illustrates what is now become widely accepted, that pipeline exposure does not necessarily lead to pipeline failure. The record adds to this, pipeline freespan does not necessarily lead to failure. This highlights that the relevant question for “water loading caused pipeline failure” is: Does the combination of freespan length and water velocity exceed a combination that would lead to vortex induced vibration or the exceedance of the static load limit of the pipe?

scholarly journals ANALYSIS OF THE ACCURACY OF FIBRE-OPTIC STRAIN GAUGES

2013 ◽  
Vol 53 (6) ◽  
pp. 872-877
Author(s):  
Dita Jiroutová ◽  
Miroslav Vokáč
Keyword(s):  
Fiber Optic ◽  
Strain Gauges ◽  
Relative Deformation ◽  
Fibre Optic ◽  
Reinforced Concrete Structure ◽  
Structure Monitoring ◽  
Fiber Optic Technology ◽  
Long Term Monitoring ◽  
Term Monitoring

In recent years, the field of structure monitoring has been making increasing use of systems based on fiber-optic technologies. Fiber-optic technology offers many advantages, including higher quality measurements, greater reliability, easier installation and maintenance, insensitivity to the environment (mainly to the electromagnetic field), corrosion resistance, safety in explosive and flammable environments, the possibility of long-term monitoring and lower cost per lifetime. We have used SOFO fibre-optic strain gauges to perform measurements to check the overall relative deformation of a real reinforced concrete structure. Long-term monitoring of the structure revealed that the measurement readings obtained from these fibre-optic strain gauges differed from each other. Greater attention was therefore paid to the calibration of the fibre-optic strain gauges, and to determining their measurement accuracy. The experimental results show that it is necessary to calibrate SOFO strain gauges before they are used, and to determine their calibration constant.

Vortex-Induced Vibration and Drag Coefficients of Long Cables Subjected to Sheared Flows

1986 ◽  
Vol 108 (1) ◽  
pp. 77-83 ◽  
Author(s):  
Y.-H. Kim ◽  
J. K. Vandiver ◽  
R. Holler
Keyword(s):  
Field Experiments ◽  
Broad Band ◽  
Single Mode ◽  
Response Spectra ◽  
Flow Speed ◽  
Current Profile ◽  
Vortex Induced Vibration ◽  
Sheared Flow ◽  
Typical Experiment ◽  
Lock In

The vortex-induced vibration response of long cables subjected to vertically sheared flow was investigated in two field experiments. In a typical experiment, a weight was hung over the side of the research vessel by a cable that was instrumented with accelerometers. A typical experiment measured the acceleration response of the cable, the current profile, the tension, and angle of inclination at the top of the cable. Total drag force was computed from the tension and angle measurements. Two braided Kevlar cables were tested at various lengths from 100 to 9,050 ft. As a result of these experiments, several important conclusions can be drawn: (i) the wave propagation along the length of the cable was damped, and therefore, under most conditions the cable behaved like an infinite string; (ii) response spectra were quite broad-band, with center frequencies determined by the flow speed in the region of the accelerometer; (iii) single mode lock-in was not observed for long cables in the sheared current profile; (iv) the average drag coefficient of long cables subjected to sheared flow was considerably lower than observed on short cables in uniform flows; (v) the r.m.s. response was higher in regions of higher current speed. A new dimensionless parameter is proposed that incorporates the properties of the cable as well as the sheared flow. This parameter is useful in establishing the likelihood that lock-in may occur, as well as in estimating the number of modes likely to respond.

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