scholarly journals Vortex-Induced-Vibration of Jack-Ups With Cylindrical Legs in Regular Waves

2019 ◽  
Author(s):  
Sudheesh Ramadasan ◽  
Longbin Tao ◽  
Arun Kr Dev
Keyword(s):  
Oscillatory Flow ◽  
Damping Ratio ◽  
Cross Flow ◽  
Radius Of Gyration ◽  
Regular Waves ◽  
Conservation Of Energy ◽  
Vortex Induced Vibration ◽  
Current Mass ◽  
Rectangular Configuration ◽  
Jack Up

Abstract A simple mathematical model is developed based on the single-degree-of-freedom analogy and principle of conservation of energy evaluating various modes of Vortex-Induced-Vibration (VIV) of a jack-up with cylindrical legs in regular waves. Similar to uniform current, mass ratio, damping ratio and mode factor are found to be the important parameters controlling the cross-flow VIV and radius of gyration also for the yaw VIV. Criteria for the initiation of the mentioned VIV modes are developed for the cases of a single 2D cylinder experiencing planar oscillatory flow, four rigidly coupled 2D cylinders in rectangular configuration experiencing planar oscillatory flow and jack-up experiencing regular waves. The newly developed VIV model is validated by a set of experiments conducted in a wind, wave and current flume. The importance of mass damping parameter is further demonstrated in suppressing VIV in regular waves. The mathematical method will equip engineers to consider the effect of VIV due to regular waves in jack-up designs.

Structural Simplification of Jack-Up Rig and Its Dynamic Responses in Regular Waves

1988 ◽  
Vol 32 (02) ◽  
pp. 134-153
Author(s):  
Jong-Shyong Wu ◽  
Cuann-Yeu Chang
Keyword(s):  
Virtual Work ◽  
Damping Ratio ◽  
Equations Of Motion ◽  
Dynamic Responses ◽  
Jacobi Method ◽  
Mode Shapes ◽  
Regular Waves ◽  
Static Condensation ◽  
Rigid Joints ◽  
Jack Up

This paper is composed of two main parts: simplification of leg structure of the jack-up rig, and dynamic analysis of the entire rig due to excitation of regular waves. First, the legs of spatial beamlike lattice with rigid joints are replaced by the equivalent beams through application of the theory of static condensation and the principle of virtual work. Then the equations of motion of the entire rig are derived based on the simplified mathematical model, and the natural frequencies and mode shapes are sought by the Jacobi method. Finally, the dynamic behavior of the hinged rig and fixed rig operating in four kinds of water depths (and hence effective leg lengths) and wave heights is studied by means of the mode superposition technique. The phase angles between responses of the legs and the influence on responses of support conditions at the seabed, wave attack angle, and damping ratio are the key points of the investigation.

Experimental Evaluation of Pure In-Line Vortex Induced Vibration (VIVx) of Low Mass-Damping Ratio Cylinder

2016 ◽  
Author(s):  
Mohammad Mobasher Amini ◽  
Antonio Carlos Fernandes
Keyword(s):  
Reynolds Number ◽  
Circular Cylinder ◽  
Damping Ratio ◽  
Cross Flow ◽  
Current Channel ◽  
Number Range ◽  
Vortex Induced Vibration ◽  
Numerical Studies ◽  
Lower Amplitude ◽  
Low Mass

Numerous experimental and numerical studies have been carried out to better understand and to improve prediction of cylinder VIV (vortex Induced Vibration) phenomenon. The behavior of cylinder due to in-line vibration (VIVx) has been neglected in the earlier studies because of its lower amplitude in comparison with cross flow vibration (VIVy). However, some researchers have studied VIVx in 2DOF along with VIVy. Recent investigations show that response amplitude of structure caused by VIVx is large enough to bring it to consideration. This study focuses on understanding the origin and prediction of VIVx amplitude exclusively in 1DOF and subcritical flow regime. The experiments were performed in current channel on bare circular cylinder with low mass-damping ratio in Reynolds number range Re = 10000 ∼ 45000.

Numerical Investigation of Vortex-Induced Vibration of a Circular Cylinder Close to a Plane Boundary Subject to Oscillatory Flow

2016 ◽  
Author(s):  
Adnan Munir ◽  
Ming Zhao ◽  
Helen Wu
Keyword(s):  
Circular Cylinder ◽  
Oscillatory Flow ◽  
Numerical Study ◽  
Cross Flow ◽  
Navier Stokes ◽  
Plane Boundary ◽  
Vortex Induced Vibration ◽  
Gap Ratio ◽  
Wide Range ◽  
Close Proximity

This paper presents a numerical study of flow around an elastically mounted circular cylinder in close proximity to a plane boundary vibrating in the transverse and inline directions in an oscillatory flow. The Reynolds-Averaged Navier-Stokes (RANS) equations and the SST k-ω turbulent equations are solved using the Arbitrary Langrangian-Eulerian (ALE) scheme and Petrov-Galerkin Finite Element Method for simulating the flow. The equation of motion is solved using the fourth-order Runge-Kutta method to find the displacements of the cylinder in the transverse and inline directions. The numerical model is validated against the previous results of vortex-induced vibration of an isolated circular cylinder in both cross-flow and inline directions. The flow model is further extended to study the vortex-induced vibration of a cylinder near a plane boundary with a very small gap ratio (e/D) of 0.01, with D and e being the diameter and the gap between the cylinder and the plane boundary, respectively. Simulations are carried out for two Keulegan-Carpenter (KC) numbers of 5 and 10 and a wide range of reduced velocities. It is observed that both the KC number and the reduced velocity affect the vibration of the cylinder significantly.

Vortex-Induced Vibration of a Flexible Cylinder Experiencing Oscillatory Flow With Different Aspect Ratios

2019 ◽  
Author(s):  
Di Deng ◽  
Lei Wu ◽  
Decheng Wan
Keyword(s):  
Oscillatory Flow ◽  
Flow Direction ◽  
Decomposition Analysis ◽  
Cross Flow ◽  
Offshore Platforms ◽  
Analysis Method ◽  
Flexible Cylinder ◽  
Vortex Induced Vibration ◽  
Aspect Ratios ◽  
Oil Exploitation

Abstract In deep sea oil exploitation, offshore platforms will move periodically in the water under the combined effects of waves, currents and winds. The relatively oscillatory flow is generated between the riser connected to the platform and the water. Vortex-induced Vibration (VIV) features of a single cylinder in the oscillatory flow are more complicated than that in the uniform flow. In this paper, numerical investigations on VIV of a flexible cylinder with different aspect ratios exposed to the oscillatory flow are carried out by the in-house CFD solver viv-FOAM-SJTU, which is developed based on the open source toolbox OpenFOAM. The flexible cylinder is forced to oscillate harmonically in the in-line direction in the still water and is allowed to freely vibrate in the cross-flow direction. Firstly, comparisons on referred experiments and simulations are conducted to verify the validity of the solver. Then, the modal decomposition analysis method and the Fast Fourier Transform (FFT) method are used to obtain the dominant vibration modes and frequencies of the cylinder in the following simulations.

Features of Vortex-Induced Vibration in Oscillatory Flow

2013 ◽  
Vol 136 (1) ◽  
Author(s):  
Shixiao Fu ◽  
Jungao Wang ◽  
Rolf Baarholm ◽  
Jie Wu ◽  
C. M. Larsen
Keyword(s):  
Wavelet Transformation ◽  
Oscillatory Flow ◽  
Cross Flow ◽  
Ocean Basin ◽  
Mode Transition ◽  
Time Sharing ◽  
Flexible Cylinder ◽  
Vortex Induced Vibration ◽  
Flow Features ◽  
Lock In

Vortex-induced vibration (VIV) in oscillatory flow is experimentally investigated in the ocean basin. The test flexible cylinder was forced to harmonically oscillate in various combinations of amplitude and period with Keulegan-Carpenter (KC) number between 26 and 178 in three different maximum reduced velocities, URmax=4, URmax=6.5, and URmax=7.9 separately. VIV responses at cross-flow (CF) direction are investigated using modal decomposition and wavelet transformation. The results show that VIV in oscillatory flow is quite different from that in steady flow; features, such as intermittent VIV, hysteresis, amplitude modulation, and mode transition (time sharing) are observed. Moreover, a VIV developing process including “building-up,” “lock-in,” and “dying-out” in oscillatory flow, is further proposed and analyzed.

Numerical Investigation of Vortex-Induced Vibration (VIV) of a Circular Cylinder in Oscillatory Flow

2011 ◽  
Author(s):  
Ming Zhao ◽  
Liang Cheng ◽  
Tongming Zhou
Keyword(s):  
Circular Cylinder ◽  
Oscillatory Flow ◽  
Stokes Equations ◽  
Flow Direction ◽  
Cross Flow ◽  
Frequency Component ◽  
Degree Of Freedom ◽  
Navier Stokes ◽  
Navier Stokes Equations ◽  
Vortex Induced Vibration

Vortex-induced vibration (VIV) of a circular cylinder in oscillatory flow is investigated numerically in this study. The incompressible Reynolds-Averaged Navier-Stokes equations governing fluid flow around a circular cylinder are solved using Arbitrary Langrangian-Eulerian (ALE) scheme and Petrov-Galerkin finite element method. The equation of motion is solved for the displacements of the cylinder both in the inline and cross-flow directions. The numerical model is firstly validated against the experimental results of one-degree-of-freedom VIV in cross-flow direction. It is found that both VIV frequency and amplitude vary with reduced velocity for a fixed KC number. In most of the simulated cases the vibration comprises of multiple frequencies of different amplitudes. Each frequency component is multiple times of the frequency of the oscillatory flow. Two-degree-of-freedom VIV is investigated with the same parameters used in the one-degree-of-freedom case. By examining the XY-trajectory of the vibration, it if found that the vibration follows different trajectory for different KC numbers or reduced velocities.

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 Vibrations of a Cylinder at Subcritical Reynolds Number

2011 ◽  
Author(s):  
Yoann Jus ◽  
Elisabeth Longatte ◽  
Jean-Camille Chassaing ◽  
Pierre Sagaut
Keyword(s):  
Reynolds Number ◽  
Numerical Simulations ◽  
Numerical Study ◽  
Damping Ratio ◽  
Experimental Studies ◽  
Cross Flow ◽  
Physical Analysis ◽  
Arbitrary Lagrangian Eulerian ◽  
Vortex Induced Vibrations ◽  
Low Mass

The present work focusses on the numerical study of Vortex-Induced Vibrations (VIV) of an elastically mounted cylinder in a cross flow at moderate Reynolds numbers. Low mass-damping experimental studies show that the dynamic behavior of the cylinder exhibits a three-branch response model, depending on the range of the reduced velocity. However, few numerical simulations deal with accurate computations of the VIV amplitudes at the lock-in upper branch of the bifurcation diagram. In this work, the dynamic response of the cylinder is investigated by means of three-dimensional Large Eddy Simulation (LES). An Arbitrary Lagrangian Eulerian framework is employed to account for fluid solid interface boundary motion and grid deformation. Numerous numerical simulations are performed at a Reynolds number of 3900 for both no damping and low-mass damping ratio and various reduced velocities. A detailed physical analysis is conducted to show how the present methodology is able to capture the different VIV responses.

scholarly journals On Damping and Fluidelastic Instability in a Tube Bundle Subjected to Two-Phase Cross-Flow

2007 ◽  
Author(s):  
Joaquin E. Moran ◽  
David S. Weaver
Keyword(s):  
Flow Regime ◽  
Void Fraction ◽  
Tube Bundle ◽  
Damping Ratio ◽  
Pressure Fluctuations ◽  
Cross Flow ◽  
Phase Changes ◽  
Working Fluid ◽  
Two Phase ◽  
Fluidelastic Instability

An experimental study was conducted to investigate damping and fluidelastic instability in tube arrays subjected to two-phase cross-flow. The purpose of this research was to improve our understanding of these phenomena and how they are affected by void fraction and flow regime. The working fluid used was Freon 11, which better models steam-water than air-water mixtures in terms of vapour-liquid mass ratio as well as permitting phase changes due to pressure fluctuations. The damping measurements were obtained by “plucking” the monitored tube from outside the test section using electromagnets. An exponential function was fitted to the tube decay trace, producing consistent damping measurements and minimizing the effect of frequency shifting due to fluid added mass fluctuations. The void fraction was measured using a gamma densitometer, introducing an improvement over the Homogeneous Equilibrium Model (HEM) in terms of density and velocity predictions. It was found that the Capillary number, when combined with the two-phase damping ratio (interfacial damping), shows a well defined behaviour depending on the flow regime. This observation can be used to develop a better methodology to normalize damping results. The fluidelastic results agree with previously presented data when analyzed using the HEM and the half-power bandwidth method. The interfacial velocity is suggested for fluidelastic studies due to its capability for collapsing the fluidelastic data. The interfacial damping was introduced as a tool to include the effects of flow regime into the stability maps.

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