Experimental Investigation on the Hydrodynamic Responses and Coefficients of Straked Flexible Pipe in Oscillatory Flow

2018 ◽  
Author(s):  
Haojie Ren ◽  
Jingyun Cheng ◽  
Mengmeng Zhang ◽  
Peimin Cao ◽  
Shixiao Fu
Keyword(s):  
Oscillatory Flow ◽  
Least Square Method ◽  
Ocean Basin ◽  
Least Square ◽  
Flexible Pipe ◽  
Drag Coefficients ◽  
Vortex Induced Vibrations ◽  
Helical Strakes ◽  
Riser Design ◽  
Inverse Analysis Method

The helical strakes are now widely being used in offshore riser design for the suppression of vortex induced vibrations (VIV). The purpose of this paper is to investigate the responses and suppression effectiveness of a straked pipe in a more real working conditions of the risers which will endure a kind of “oscillatory flow” due to the relative motions between the fluid around and the risers induced by the top platform motions. Experiments are performed on a flexible straked pipe with pitch length/height of 15D/0.25D in ocean basin. The pipes are forced to harmonically oscillate in various combinations of amplitude and period with Keulegan-Carpenter (KC) number varying between 5 and 165, and maximum reduced velocities from 4 to 12. Responses in both in direction are firstly investigated. Inverse analysis method and the Least Square method are adopted to identify drag coefficients and added mass coefficients. The results show that strakes can reduce the higher frequency responses in both CF and IL direction. Suppression efficiencies of the strakes and are not ideal as expected in oscillatory flow. Moreover, the hydrodynamic coefficients change dramatically under the small KC number and stabilize under the large KC number. The drag coefficients obviously magnify at KC ∼ 20.

scholarly journals Numerical evaluation of the modulus of longitudinal elasticity in structural round timber elements of the Eucalyptus genus

2011 ◽  
Vol 31 (5) ◽  
pp. 1007-1014 ◽  
Author(s):  
André L. Christoforo ◽  
Túlio H. Panzera ◽  
Fabiano B. Batista ◽  
Paulo H. R. Borges ◽  
Francisco A. R. Lahr
Keyword(s):  
Inverse Analysis ◽  
Numerical Evaluation ◽  
Least Square Method ◽  
Least Square ◽  
Analysis Method ◽  
The Finite Element Method ◽  
Eucalyptus Citriodora ◽  
Inverse Analysis Method ◽  
Round Timber

Currently, the standards that deal with the determination of the properties of rigidity and strength for structural round timber elements do not take in consideration in their calculations and mathematical models the influence of the existing irregularities in the geometry of these elements. This study has as objective to determine the effective value of the modulus of longitudinal elasticity for structural round timber pieces of the Eucalyptus citriodora genus by a technique of optimization allied to the Inverse Analysis Method, to the Finite Element Method and the Least Square Method.

On the Torsional Friction of Freely Rotating Short Fairing

2014 ◽  
Author(s):  
Halvor Lie ◽  
Decao Yin ◽  
Stergios Liapis
Keyword(s):  
Numerical Models ◽  
Damping Ratio ◽  
Ocean Basin ◽  
Suitable Model ◽  
Flexible Pipe ◽  
Friction Coefficients ◽  
Spectra Analysis ◽  
Vortex Induced Vibrations ◽  
Decay Tests ◽  
Uniform Currents

Vortex-induced vibrations (VIV) model tests were carried out by Shell on a 38 m flexible pipe at the MARINTEK Ocean Basin in March 2011, Trondheim. As part of the model test campaign, the pipe with short fairings under two different torsional friction conditions between riser and fairings was tested in uniform currents. Test with ‘high’ friction show small responses, tests with ‘low’ friction show distinct large responses, even though, the spectra analysis shows that the responses seem to be dominated by vortex induced forces. Decay tests were carried out on a riser section with fairings to further investigate the torsional friction effect. Friction coefficients were calculated by ‘Coulomb damping model’, which is proved to be a suitable model for fairing-riser friction. The friction coefficients could be directly used to determine the damping ratio and implemented in numerical models. Such decay tests are especially useful to design, manufacture and install fairings in order to achieve a proper friction level and avoid unstable responses such as galloping.

Hydrodynamic Coefficients of a Flexible Pipe With Staggered Buoyancy Elements and Strakes Under VIV Conditions

2017 ◽  
Author(s):  
Shixiao Fu ◽  
Halvor Lie ◽  
Jie Wu ◽  
Rolf Baarholm
Keyword(s):  
Inverse Analysis ◽  
Natural Frequencies ◽  
Forced Oscillation ◽  
Hydrodynamic Force ◽  
Added Mass ◽  
Ocean Basin ◽  
Hydrodynamic Coefficients ◽  
Analysis Method ◽  
Flexible Pipe ◽  
Inverse Analysis Method

A 38m long flexible pipe with staggered buoyancy modules and strakes has been tested in the ocean basin of SINTEF Ocean (former Marintek) for VIV investigation of a lazy wave riser. In this paper the inverse analysis method was presented and applied into the investigation of the hydrodynamic force coefficients along this tested flexible pipe with the measured responses as inputs. The feasibility of the inverse analysis method is firstly validated by numerical simulations. The distributions of the added mass and excitation coefficients along the flexible pipe with staggered buoyancy modules and strakes are then investigated. The identified coefficients are validated by check of the natural frequencies and responses of the model, and are finally compared against those from the forced oscillation tests.

scholarly journals Experimental Investigation on Vortex-Induced Vibration of a Flexible Pipe under Higher Mode in an Oscillatory Flow

2020 ◽  
Vol 8 (6) ◽  
pp. 408 ◽  
Author(s):  
Haojie Ren ◽  
Mengmeng Zhang ◽  
Jingyun Cheng ◽  
Peimin Cao ◽  
Yuwang Xu ◽  
...  
Keyword(s):  
Oscillatory Flow ◽  
Cross Flow ◽  
Dominant Frequency ◽  
Ocean Basin ◽  
Dominant Mode ◽  
Flexible Pipe ◽  
Vortex Induced Vibration ◽  
Displacement Reconstruction ◽  
Vessel Motion ◽  
Lock In

Different from the previous studies of the vortex-induced vibration (VIV) dominated by first mode of flexible pipe in an oscillatory flow, the features of a higher mode dominated are experimentally investigated in the ocean basin. The flexible pipe is forced to harmonically oscillate with different combinations of a period and amplitude. The design dominant mode consists of first and second modes under the maximum reduced velocity (VR) of approximately 5.5 with a KC number ranging from 22 to 165. The VIV responses between only the excited first mode and the excited higher mode are compared and studied using displacement reconstruction and wavelet transform methods. The discrepancies of spatial and temporal response between smaller and larger KC numbers (KC = 56 and 121) are first observed. The strong alternate mode dominance and lock-in phenomena occur in the case of larger KC numbers, while they cannot be observed in the case of smaller KC numbers under higher modes. The VIV dominant frequency in the in-line (IL) direction is found to be always triple the oscillatory flow frequency and not twice that in the cross flow (CF) direction. The dominant frequency in the CF direction can be predicted by the Strouhal law, and the Strouhal number is approximately 0.18 under VR = 5.5, which is not affected by the excited mode. Moreover, differences of response motion trajectory are also revealed in this paper. The present work improves the basic understanding of vessel motion induced VIV and provides helpful references for developing prediction methods of VIV in an oscillatory flow.

Vortex-induced vibration of flexible pipe fitted with helical strakes in oscillatory flow

2019 ◽  
Vol 189 ◽  
pp. 106274 ◽  
Author(s):  
Haojie Ren ◽  
Yuwang Xu ◽  
Jingyun Cheng ◽  
Peimin Cao ◽  
Mengmeng Zhang ◽  
...  
Keyword(s):  
Oscillatory Flow ◽  
Flexible Pipe ◽  
Vortex Induced Vibration ◽  
Helical Strakes

Distribution of drag coefficients along a flexible pipe with helical strakes in uniform flow

2019 ◽  
Vol 184 ◽  
pp. 216-226 ◽  
Author(s):  
Haojie Ren ◽  
Yuwang Xu ◽  
Mengmeng Zhang ◽  
Shixiao Fu ◽  
Yanxin Meng ◽  
...  
Keyword(s):  
Uniform Flow ◽  
Flexible Pipe ◽  
Drag Coefficients ◽  
Helical Strakes

Direct Assessment of Effective Renal Plasma Flow from Renoscintigraphy with a Gamma Camera and an On-Line Computer

1981 ◽  
Vol 20 (06) ◽  
pp. 274-278
Author(s):  
J. Liniecki ◽  
J. Bialobrzeski ◽  
Ewa Mlodkowska ◽  
M. J. Surma
Keyword(s):  
Count Rate ◽  
Renal Plasma Flow ◽  
Early Period ◽  
Least Square Method ◽  
Least Square ◽  
Uptake Coefficient ◽  
Positive Linear Correlation ◽  
On Line ◽  
Best Fit ◽  
Plasma Activity

A concept of a kidney uptake coefficient (UC) of 131I-o-hippurate was developed by analogy from the corresponding kidney clearance of blood plasma in the early period after injection of the hippurate. The UC for each kidney was defined as the count-rate over its ROI at a time shorter than the peak in the renoscintigraphic curve divided by the integral of the count-rate curve over the "blood"-ROI. A procedure for normalization of both curves against each other was also developed. The total kidney clearance of the hippurate was determined from the function of plasma activity concentration vs. time after a single injection; the determinations were made at 5, 10, 15, 20, 30, 45, 60, 75 and 90 min after intravenous administration of 131I-o-hippurate and the best-fit curve was obtained by means of the least-square method. When the UC was related to the absolute value of the clearance a positive linear correlation was found (r = 0.922, ρ > 0.99). Using this regression equation the clearance could be estimated in reverse from the uptake coefficient calculated solely on the basis of the renoscintigraphic curves without blood sampling. The errors of the estimate are compatible with the requirement of a fast appraisal of renal function for purposes of clinical diagknosis.

PENGARUH KNOWLEDGE MANAGEMENT, KOMPETENSI, MOTIVASI TERHADAP KINERJA KARYAWAN

2015 ◽  
Vol 5 (2) ◽  
pp. 1
Author(s):  
Miftahol Arifin
Keyword(s):  
Knowledge Management ◽  
Linear Regression ◽  
Significant Influence ◽  
Employee Performance ◽  
Least Square Method ◽  
Least Square ◽  
Analysis Tool ◽  
Ordinary Least Square ◽  
Competence Motivation ◽  
Performance Analyze

The purpose of this research is to analyze the influence of knowledge management on employee performance, analyze the effect of competence on employee performance, analyze the influence of motivation on employee performance). In this study, samples taken are structural employees PT.centris Kingdom Taxi Yogyakarta. The analysis tool in this study using multiple linear regression with Ordinary Least Square method (OLS). The conclusion of this study showed that the variables of knowledge management has a significant influence on employee performance, competence variables have an influence on employee performance, motivation variables have an influence on employee performance, The analysis showed that the variables of knowledge management, competence, motivation on employee performance.Keywords: knowledge management, competence, motivation, employee performance.

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