Fatigue Damage From High Mode Number Vortex-Induced Vibration

2006 ◽  
Author(s):  
J. Kim Vandiver ◽  
Susan B. Swithenbank ◽  
Vivek Jaiswal ◽  
Vikas Jhingran
Keyword(s):  
Fatigue Damage ◽  
Field Experiments ◽  
Higher Harmonics ◽  
Vortex Induced Vibration ◽  
Third Harmonic ◽  
The Third ◽  
Damage Rate ◽  
Surface Vessels ◽  
Vortex Shedding Frequency ◽  
First Time

This paper presents results from two field experiments using long flexible cylinders, suspended vertically from surface vessels. The experiments were designed to investigate vortex-induced vibration (VIV) at higher than tenth mode in uniform and sheared flows. The results of both experiments revealed significant vibration energy at the expected Strouhal frequency (referred to in this paper as the fundamental frequency) and also at two and three times the Strouhal frequency. Although higher harmonics have been reported before, this was the first time that the contribution to fatigue damage, resulting from the third harmonic, could be estimated with some certainty. This was enabled by the direct measurement of closely spaced strain gauges in one of the experiments. In some circumstances the largest RMS stress and fatigue damage due to VIV are caused by these higher harmonics. The total fatigue damage rate including the third harmonic is shown to be up to forty times greater than the damage rate due to the vibration at the fundamental vortex-shedding frequency alone. This dramatic increase in damage rate due to the third harmonic appears to be associated with a narrow range of reduced velocities in regions of the pipe associated with significant flow-induced excitation.

scholarly journals On the Significance of the Higher-Order Stress in Riser Vortex-Induced Vibrations Responses

2018 ◽  
Vol 141 (1) ◽  
Author(s):  
Jie Wu ◽  
Decao Yin ◽  
Halvor Lie ◽  
Carl M. Larsen ◽  
Rolf J. Baarholm ◽  
...  
Keyword(s):  
Fatigue Damage ◽  
Flexible Pipe ◽  
Third Order ◽  
Higher Harmonics ◽  
The Third ◽  
Flexible Pipes ◽  
Vortex Induced Vibrations ◽  
Vortex Shedding Frequency ◽  
Order Stress ◽  
The Impact

Vortex-induced vibrations (VIV) can lead to fast accumulation of fatigue damage and increased drag loads for slender marine structures. VIV responses mainly occur at the vortex shedding frequency, while higher harmonics can also be excited. Recent VIV model tests with flexible pipes have shown that higher harmonics in the crossflow (CF) direction can contribute to the fatigue damage significantly due to its higher frequency. Rigid cylinder experiments show that the CF third-order harmonics are more pronounced when the motion orbit is close to a “figure 8” shape and the cylinder is moving against the flow at its largest CF motion. However, there is still lack of understanding of when and where higher harmonics occur for a flexible pipe. Therefore, significant uncertainty remains on how to account for fatigue damage due to higher harmonics in VIV prediction. In the present paper, representative VIV data from various riser model test campaigns are carefully studied and analyzed. The key parameters that influence the magnitude of the third-order harmonic stress are found to be the bending stiffness, the reduced velocity, and the orbit stability. The experimental data are analyzed in order to assess the impact of each parameter on the third-order harmonic stress. A preliminary empirical response model to estimate the maximum CF third-order harmonic stress based on these identified structural and hydrodynamic parameters has been proposed. The results of this study will contribute to reduce the uncertainty and unnecessary conservatism in VIV prediction.

On the Vortex-Induced Vibration Response of a Model Riser and Location of Sensors for Fatigue Damage Prediction

2010 ◽  
Author(s):  
C. Shi ◽  
L. Manuel ◽  
M. A. Tognarelli ◽  
T. Botros
Keyword(s):  
Fatigue Damage ◽  
Traveling Waves ◽  
Wavelet Transforms ◽  
Cross Flow ◽  
Waveform Analysis ◽  
Flexible Cylinder ◽  
Vortex Induced Vibration ◽  
Damage Prediction ◽  
Time Frequency ◽  
Damage Rate

This study is concerned with vortex-induced vibration (VIV) of deepwater marine risers. Riser response measurements from model tests on a densely instrumented long, flexible riser in uniform and sheared currents offer an almost ideal set-up for our work. Our objectives are two-fold: (i) we use the measured data to describe complexities inherent in riser motions accompanying VIV; and (ii) we discuss how such data sets (and even less spatially dense monitoring) can be used effectively in predicting fatigue damage rates which is of critical interest for deepwater risers. First, we use mathematical tools including Hilbert and wavelet transforms to estimate instantaneous amplitudes and phases of cross-flow (CF) and in-line (IL) displacements for the model riser as well as scalograms to understand time-frequency characteristics of the response; this work confirms that the motion of a long flexible cylinder is far more complex than that of a rigid cylinder, and that non-stationary characteristics, higher harmonics, and traveling waves are evident in the riser response. Second, a well-established empirical procedure, which we refer to as Weighted Waveform Analysis (WWA), is employed to estimate the fatigue damage rate at various locations along the length of the riser from strain measurements at only eight sensors. By iterating over numerous different combinations of these eight strain sensors as inputs (from among all the twenty-four available locations on the riser), optimal locations for the eight sensors on the riser are identified by cross-validation, whereby predicted strains and fatigue damage rates at locations of instrumented sensors are compared with strains and fatigue damage rates based on actual recorded measurements there. We find that, if properly placed, as few as eight sensors can provide reasonably accurate estimates of the fatigue damage rate over the entire riser length. Finally, we demonstrate how more accurate fatigue damage prediction can result when non-stationary response characteristics are considered and a modified WWA method (that more effectively accounts for traveling waves than the WWA method alone does) is employed.

Vortex-Induced Vibration Characteristics of an Elastic Square Cylinder on Fixed Supports

2004 ◽  
Vol 127 (2) ◽  
pp. 241-249 ◽  
Author(s):  
Z. J. Wang ◽  
Y. Zhou
Keyword(s):  
Circular Cylinder ◽  
Vortex Shedding ◽  
Flow Separation ◽  
Natural Frequencies ◽  
Separation Point ◽  
Square Cylinder ◽  
Vortex Induced Vibration ◽  
The Third ◽  
Vortex Shedding Frequency ◽  
Shedding Frequency

The vortex-induced structural vibration of an elastic square cylinder, on fixed supports at both ends, in a uniform cross flow was measured using fiber-optic Bragg grating sensors. The measurements are compared to those obtained for an elastic circular cylinder of the same hydraulic diameter in an effort to understand the effect of the nature (fixed or oscillating) of the flow separation point on the vortex-induced vibration. It is found that a violent vibration occurs at the third-mode resonance when the vortex-shedding frequency coincides with the third-mode natural frequency of the fluid-structure system, irrespective of the cross-sectional geometry of the cylinder. This is in distinct contrast to previous reports of flexibly supported rigid cylinders, where the first-mode vibration dominates, thus giving little information on the vibration of other modes. The resonance behavior is neither affected by the incidence angle (α) of the free stream, nor by the nature of the flow separation point. However, the vibration amplitude of the square cylinder is about twice that of the circular cylinder even though the flexural rigidity of the former is larger. This is ascribed to a difference in the nature of the flow separation point between the two types of structures. The characteristics of the effective modal damping ratios, defined as the sum of structural and fluid damping ratios, and the system natural frequencies are also investigated. The damping ratios and the system natural frequencies vary little with the reduced velocity at α=0deg, but appreciable at α⩾15deg; they further experience a sharp variation, dictated by the vortex-shedding frequency, near resonance.

Alternative Empirical Procedures for Fatigue Damage Rate Estimation of Instrumented Risers Undergoing Vortex-Induced Vibration

2010 ◽  
Author(s):  
C. Shi ◽  
L. Manuel ◽  
M. A. Tognarelli
Keyword(s):  
Fatigue Damage ◽  
Waveform Analysis ◽  
Phase Reconstruction ◽  
Empirical Methods ◽  
Empirical Estimation ◽  
Flexible Cylinder ◽  
Vortex Induced Vibration ◽  
Damage Rate ◽  
Data Loggers ◽  
Proper Orthogonal

Vortex-induced vibration (VIV) is a topic of great importance in fatigue damage assessment and life prediction for marine risers. In order to gain insight into riser motions and estimated fatigue damage due to VIV, data loggers such as strain sensors and/or accelerometers are sometimes installed on risers to monitor their motion in different current velocity conditions. Accurate reconstruction of the riser response and empirical estimation of fatigue damage rates over the entire riser length using measurements from a limited number of sensors is important for efficient utilization of the costly measurements recorded. In this study, different empirical methods are employed to analyze the VIV response of a long flexible cylinder subjected to uniform and sheared current profiles. The methods include weighted waveform analysis (WWA), proper orthogonal decomposition (POD), modal phase reconstruction (MPR), a modified WWA procedure, and a hybrid method which combines MPR and the modified WWA method. Fatigue damage rates estimated using these different empirical methods are compared and cross-validated against measurements. Formulations for each method are briefly presented and discussed with examples. Results show that all the empirical methods, despite different underlying assumptions in each of them, can be employed to estimate fatigue damage rates quite well from limited strain measurements.

Calculation of Vortex-Induced Resonance on a Thermo Well

2014 ◽  
Vol 635-637 ◽  
pp. 447-450
Author(s):  
Ming Lei ◽  
Jian Gang Ge
Keyword(s):  
Natural Gas ◽  
Fatigue Damage ◽  
Vortex Shedding ◽  
Vortex Induced Vibration ◽  
Vortex Shedding Frequency ◽  
Shedding Frequency

When vortex-induced resonance happens, the amplitude is big enough to affect the comfort and safety of the structure using, also it can cause fatigue damage to the structure. Being in the tube full of flowing natural gas, the thermo well may vibrate and be damaged. In this paper, based on the theory of vortex-induced vibration, by using ANSYS (FEA software), the author will test and verify whether the vortex-induced resonance will occur on the thermo well according to one example. Keywords: vortex-induced vibration; thermo well; vortex shedding frequency

scholarly journals Ultrafast Third-Order Nonlinear Optical Response Excited by fs Laser Pulses at 1550 nm in GaN Crystals

Materials ◽  
2021 ◽  
Vol 14 (12) ◽  
pp. 3194
Author(s):  
Adrian Petris ◽  
Petronela Gheorghe ◽  
Tudor Braniste ◽  
Ion Tiginyanu
Keyword(s):  
Harmonic Generation ◽  
Nonlinear Optical ◽  
Laser Pulses ◽  
Third Harmonic Generation ◽  
High Repetition Rate ◽  
Third Order ◽  
Third Harmonic ◽  
The Third ◽  
High Repetition ◽  
Gan Crystal

The ultrafast third-order optical nonlinearity of c-plane GaN crystal, excited by ultrashort (fs) high-repetition-rate laser pulses at 1550 nm, wavelength important for optical communications, is investigated for the first time by optical third-harmonic generation in non-phase-matching conditions. As the thermo-optic effect that can arise in the sample by cumulative thermal effects induced by high-repetition-rate laser pulses cannot be responsible for the third-harmonic generation, the ultrafast nonlinear optical effect of solely electronic origin is the only one involved in this process. The third-order nonlinear optical susceptibility of GaN crystal responsible for the third-harmonic generation process, an important indicative parameter for the potential use of this material in ultrafast photonic functionalities, is determined.

Early Permian fossil vertebrate footprints and their stratigraphic setting in megacyclic sequence II red beds, Prim Point, Prince Edward Island

1989 ◽  
Vol 26 (3) ◽  
pp. 591-605 ◽  
Author(s):  
David J. Mossman ◽  
Craig H. Place
Keyword(s):  
Central Europe ◽  
Prince Edward Island ◽  
River Sediments ◽  
Early Permian ◽  
Red Beds ◽  
Sparse Vegetation ◽  
The Third ◽  
Fossil Vertebrate ◽  
Crevasse Splay ◽  
First Time

Vertebrate trace fossils are reported for the first time from red beds near the top of megacyclic sequence II at Prim Point in southwestern Prince Edward Island. They occur as casts of tetrapod trackways. The ichnocoenose also includes a rich invertebrate ichnofauna. The trackmakers thrived in an area of sparse vegetation and occupied out-of-channel river sediments, most likely crevasse-splay deposits.Amphisauropus latus, represented by three trackways, has been previously reported from Germany, Poland, and Czechoslovakia. It is here interpreted as the track of a cotylosaur. It occurs together with the track of Gilmoreichnus kablikae, which is either a captorhinomorph or possibly a juvenile pelycosaur. These facilitate the assignment of a late Early Permian (late Autunian) age to the strata. The third set of footprints, those of a small herbivorous pelycosaur, compare most closely with Ichniotherium willsi, known hitherto from the Keele beds (latest Stephanian) of the English Midlands.This ichnocoenose occurs in a plate-tectonically rafted segment of crust stratigraphically equivalent to the same association of ichnofauna in the English Midlands and central Europe. The community occupied piedmont-valley-flat red beds within the molasse facies of Variscan uplands.

Acrolein Reduces Biomass and Seed Production of Potamogeton pectinatus in Irrigation Channels

2004 ◽  
Vol 18 (3) ◽  
pp. 605-610 ◽  
Author(s):  
Diego J. Bentivegna ◽  
Osvaldo A. Fernández ◽  
María A. Burgos
Keyword(s):  
Plant Growth ◽  
Field Experiments ◽  
Plant Biomass ◽  
Treatment Plant ◽  
Irrigation District ◽  
Potamogeton Pectinatus ◽  
Individual Plant ◽  
Plant Weight ◽  
The Third ◽  
Irrigation Channels

Chemical weed control with acrolein has been shown to be a lower cost method for reducing submerged plant biomass of sago pondweed in the irrigation district of the Lower Valley of Rio Colorado, Argentina (39°10′S–62°05′W). However, no experimental data exist on the effects of the herbicide on plant growth and its survival structures. Field experiments were conducted during 3 yr to evaluate the effect of acrolein on growth and biomass of sago pondweed and on the source of underground propagules (i.e., rhizomes, tubers, and seeds). Plant biomass samples were collected in irrigation channels before and after several herbicide treatments. The underground propagule bank was evaluated at the end of the third year. Within each treatment, plant biomass was significantly reduced by 40 to 60% in all three study years. Rapid new plant growth occurred after each application; however, it was less vigorous after repeated treatments. At the end of the third year at 3,000 m downstream from the application point, plant biomass at both channels ranged from 34 to 3% of control values. Individual plant weight and height were affected by acrolein treatments, flowering was poor, and seeds did not reach maturity. After 3 yr, acrolein did not reduce the number of tubers. However, they were significantly smaller and lighter. Rhizomes fresh weight decreased by 92%, and seed numbers decreased by 79%. After 3 yr of applications, operational functioning of the channels could be maintained with fewer treatments and lower concentrations of acrolein.

Oilseed rape

1984 ◽  
Vol 13 (3) ◽  
pp. 118-124 ◽  
Author(s):  
D. H. Scarisbrick ◽  
R. W. Daniels
Keyword(s):  
Oilseed Rape ◽  
Financial Incentives ◽  
Field Experiments ◽  
Full Potential ◽  
World Production ◽  
Wheat Field ◽  
The Third ◽  
Important Crop ◽  
The Uk

Oilseed rape is currently the third most important crop in the UK after barley and wheat. Field experiments show that despite the already attractive yields the full potential of the crop has not yet been achieved. However, its future is uncertain in that the area devoted to it within the EEC—representing one-fifth of world production—is strongly influenced by the financial incentives offered. It is suggested that within the Community output should be limited to 3.3m tonnes p.a. for the next five years.

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