Time Domain Simulation of Vortex-Induced Vibrations Based on Phase-Coupled Oscillator Synchronization

2015 ◽  
Author(s):  
Mats J. Thorsen ◽  
Svein Sævik ◽  
Carl M. Larsen
Keyword(s):  
Vortex Shedding ◽  
Time Domain ◽  
Hydrodynamic Force ◽  
Circular Cross Section ◽  
Cross Flow ◽  
Force Model ◽  
Time Domain Simulation ◽  
Local Flow ◽  
Hydrodynamic Damping ◽  
Vortex Induced Vibrations

Since 2012, there has been ongoing development of a simplified hydrodynamic force model at the Norwegian University of Science and Technology which enables time domain simulation of vortex-induced vibrations (VIV). Time domain simulation has a number of advantages compared to frequency domain. More specifically, having a time domain formulation of the hydrodynamic force which is efficient and reliable, will allow designers to include any relevant non-linear effects in their simulations, thereby increasing the level of realism and confidence in the results. The present model computes the dynamic cross-flow and in-line fluid force on a circular cross-section based on the incoming local flow velocity and the motion of the cylinder section. The most important difference between this and other existing models is the way synchronization between the vortex shedding and cylinder motion is taken into account. In contrast to the traditional VIV prediction tools, the vortex shedding frequency is in this model free to vary within a specified range, and changes according to the instantaneous phase difference between the cylinder velocity and the vortex shedding process itself. Hence, the oscillating lift and drag forces continuously update their frequencies, trying to lock on to the frequency of vibration. Combined with a simple hydrodynamic damping model and a constant added mass, it has previously been shown that highly realistic results can be obtained. In this paper, the theoretical background is reviewed, and the capabilities of the model are tested against new cases. These are: i) High mode VIV of tension-dominated riser in sheared flow, and ii) Low mode VIV of a pipeline with high bending stiffness. Both cross-flow and in-line vibrations are considered, and comparison with experimental observations is given. Based on the results, strengths and weaknesses of the model is discussed, and an outline of future developments is given.

Simulating High Mode Vortex Induced Vibration of Riser in Linear Sheared Current Using an Empirical Time Domain Model

2020 ◽  
Author(s):  
Sang Woo Kim ◽  
Svein Sævik ◽  
Jie Wu
Keyword(s):  
Frequency Domain ◽  
Vortex Shedding ◽  
Time Domain ◽  
Structural Model ◽  
Cross Flow ◽  
Domain Model ◽  
Vortex Induced Vibrations ◽  
The One ◽  
The Time Domain ◽  
Empirical Coefficients

Abstract This paper addresses the performance evaluation of an empirical time domain Vortex Induced Vibrations (VIV) model which has been developed for several years at NTNU. Unlike the frequency domain which is the existing VIV analysis method, the time domain model introduces new vortex shedding force terms to the well known Morison equation. The extra load terms are based on the relative velocity, a synchronization model and additional empirical coefficients that describe the hydrodynamic forces due to cross-flow (CF) and In-line (IL) vortex shedding. These hydrodynamic coefficients have been tuned to fit experimental data and by considering the results from the one of existing frequency domain VIV programs, VIVANA, which is widely used for industrial design. The feature of the time domain model is that it enables to include the structural non-linearity, such as variable tension, and time-varying flow. The robustness of the new model’s features has been validated by comparing the test results in previous researches. However, the riser used in experiments has a relatively small length/diameter (L/D) ratio. It implies that there is a need for more validation to make it applicable to real riser design. In this study, the time domain VIV model is applied to perform correlation studies against the Hanøytangen experiment data for the case of linear sheared current at a large L/D ratio. The main comparison has been made with respect to the maximum fatigue damage and dominating frequency for each test condition. The results show the time domain model showed reasonable accuracy with respect to the experimental and VIVANA. The discrepancy with regard to experiment results needs to be further studied with a non-linear structural model.

In-Line and Cross-Flow Interaction of a Flexible Beam Subjected to Vortex Induced Vibrations

2014 ◽  
Author(s):  
Jie Wu ◽  
Halvor Lie ◽  
Carl M. Larsen ◽  
Stergios Liapis
Keyword(s):  
Phase Angle ◽  
Hydrodynamic Force ◽  
Travelling Waves ◽  
Cross Flow ◽  
Travelling Wave ◽  
Flexible Beam ◽  
Force Coefficients ◽  
Hydrodynamic Damping ◽  
Vortex Induced Vibrations ◽  
Response Modes

It has long been known that in-line (IL) response will influence cross-flow (CF) vortex shedding forces and vice versa. However, empirical codes for prediction of vortex induced vibrations (VIV) of slender marine structures have so far been limited to handle CF or IL response separately without taking into account the interaction between the two response modes. The motion phase angle between IL and CF displacement is a key parameter to be included in the empirical codes in order to model such interaction. The present study uses the data from Shell’s High mode VIV experiments that were performed at the MARINTEK Offshore Basin in March 2011. This extensive test program provides a rich dataset for measuring the motion phase angle and hydrodynamic force coefficients under different flow conditions. It is found that the energy transfer from the fluid to the pipe is related to counter-clockwise trajectories inside the excitation region; while clockwise trajectories are associated with hydrodynamic damping forces. The influence of the travelling wave behavior on motion phase angle and hydrodynamic force coefficients are also studied. It was found that the spatial variation of the motion phase angle of the beam is different when travelling waves dominate the response.

scholarly journals Vortex-induced vibrations of a long flexible cylinder in shear flow

2011 ◽  
Vol 677 ◽  
pp. 342-382 ◽  
Author(s):  
REMI BOURGUET ◽  
GEORGE E. KARNIADAKIS ◽  
MICHAEL S. TRIANTAFYLLOU
Keyword(s):  
Shear Flow ◽  
Vortex Shedding ◽  
Cross Flow ◽  
Maximum Velocity ◽  
Travelling Wave ◽  
Transition To Turbulence ◽  
Wave Component ◽  
Flexible Cylinder ◽  
Vortex Induced Vibrations ◽  
Lock In

We investigate the in-line and cross-flow vortex-induced vibrations of a long cylindrical tensioned beam, with length to diameter ratio L/D = 200, placed within a linearly sheared oncoming flow, using three-dimensional direct numerical simulation. The study is conducted at three Reynolds numbers, from 110 to 1100 based on maximum velocity, so as to include the transition to turbulence in the wake. The selected tension and bending stiffness lead to high-wavenumber vibrations, similar to those encountered in long ocean structures. The resulting vortex-induced vibrations consist of a mixture of standing and travelling wave patterns in both the in-line and cross-flow directions; the travelling wave component is preferentially oriented from high to low velocity regions. The in-line and cross-flow vibrations have a frequency ratio approximately equal to 2. Lock-in, the phenomenon of self-excited vibrations accompanied by synchronization between the vortex shedding and cross-flow vibration frequencies, occurs in the high-velocity region, extending across 30% or more of the beam length. The occurrence of lock-in disrupts the spanwise regularity of the cellular patterns observed in the wake of stationary cylinders in shear flow. The wake exhibits an oblique vortex shedding pattern, inclined in the direction of the travelling wave component of the cylinder vibrations. Vortex splittings occur between spanwise cells of constant vortex shedding frequency. The flow excites the cylinder under the lock-in condition with a preferential in-line versus cross-flow motion phase difference corresponding to counter-clockwise, figure-eight orbits; but it damps cylinder vibrations in the non-lock-in region. Both mono-frequency and multi-frequency responses may be excited. In the case of multi-frequency response and within the lock-in region, the wake can lock in to different frequencies at various spanwise locations; however, lock-in is a locally mono-frequency event, and hence the flow supplies energy to the structure mainly at the local lock-in frequency.

On Vessel Motion Induced Vortex-Induced Vibrations of a Steel Lazy Wave Riser

2021 ◽  
Author(s):  
Decao Yin
Keyword(s):  
Vortex Shedding ◽  
Time Domain ◽  
Oscillatory Flow ◽  
Domain Model ◽  
Time Varying ◽  
Structure Interaction ◽  
Response Characteristics ◽  
Vortex Induced Vibrations ◽  
The Time Domain ◽  
Vessel Motion

Abstract Deepwater steel lazy wave risers (SLWR) subject to vessel motion will be exposed to time-varying oscillatory flow, vortices could be generated and the cyclic vortex shedding force causes the structure vibrate, such fluid-structure interaction is called vortex-induced vibrations (VIV). To investigate VIV on a riser with non-linear structures under vessel motion and oscillatory flows, time domain approaches are needed. In this study, a time-domain approach is used to simulate a full-scale SLWR. Two cases with simplified riser top motions are simulated numerically. By using default input parameters to the time domain approach, the key oscillatory flow induced VIV response characteristics such as response frequency, curvature and displacements are examined and discussed. More accurate VIV prediction could be achieved by using realistic hydrodynamic inputs into the time domain model.

Forced Vibration Tests for In-Line Vortex-Induced Vibration to Assess Partially Strake-Covered Pipeline Spans

2020 ◽  
Vol 143 (3) ◽  
Author(s):  
Jie Wu ◽  
Decao Yin ◽  
Elizabeth Passano ◽  
Halvor Lie ◽  
Ralf Peek ◽  
...  
Keyword(s):  
Forced Vibration ◽  
Hydrodynamic Force ◽  
Cross Flow ◽  
Added Mass ◽  
Vortex Induced Vibrations ◽  
Helical Strakes ◽  
Vibration Tests ◽  
Flow Vortex ◽  
Hydrodynamic Data ◽  
Mass Functions

Abstract Helical strakes can suppress vortex-induced vibrations (VIVs) in pipelines spans and risers. Pure in-line (IL) VIV is more of a concern for pipelines than for risers. To make it possible to assess the effectiveness of partial strake coverage for this case, an important gap in the hydrodynamic data for strakes is filled by the reported IL forced-vibration tests. Therein, a strake-covered rigid cylinder undergoes harmonic purely IL motion while subject to a uniform “flow” created by towing the test rig along SINTEF Ocean's towing tank. These tests cover a range of frequencies, and amplitudes of the harmonic motion to generate added-mass and excitation functions are derived from the in-phase and 90 deg out-of-phase components of the hydrodynamic force on the pipe, respectively. Using these excitation- and added-mass functions in VIVANA together with those from experiments on bare pipe by Aronsen (2007 “An Experimental Investigation of In-Line and Combined In-Line and Cross-Flow Vortex Induced Vibrations,” Ph.D. thesis, Norwegian University of Science and Technology, Trondheim, Norway.), the IL VIV response of partially strake-covered pipeline spans is calculated. It is found that as little as 10% strake coverage at the optimal location effectively suppresses pure IL VIV.

Towards a Time-Domain Finite Element Analysis of Vortex Induced Vibrations

2011 ◽  
Author(s):  
Philippe Mainc¸on ◽  
Carl M. Larsen
Keyword(s):  
Frequency Domain ◽  
Time Domain ◽  
Laguerre Polynomials ◽  
Cross Flow ◽  
Domain Model ◽  
Time Step ◽  
Element Analysis ◽  
Vortex Induced Vibrations ◽  
Frequency Components ◽  
Chaotic Nature

Slender structures immersed in a cross flow can experience vibrations induced by vortex shedding (VIV), which cause fatigue damage and other problems. Engineering VIV models tend to operate in the frequency domain. A time domain model would allow to capture effects beyond the scope of today’s frequency domain empirical codes: interaction between in-line and cross-flow vibrations, higher order frequency components, structural non-linearities, simultaneous actions from other loads like waves and forced motions at boundaries. There is also the potential to capture the chaotic nature of VIV. Such a model was formulated in the present work: for each cross section and at each time step, the recent velocity history is described as a combination of Laguerre polynomials. The coefficients of that combination are used to enter an interpolation function to predict the instantaneous force, allowing to step the dynamic analysis. An offshore riser was modeled in this way: Some analyses provided an unusually fine level of realism, while in other analyses, the riser fell into an unphysical pattern of vibration. It is concluded that the concept is very promising, yet that more work is needed to understand trajectory stability and related issues, in order to further progress towards an engineering tool.

scholarly journals Virtual Spring–Damping System for Flow-Induced Motion Experiments

2015 ◽  
Vol 137 (6) ◽  
Author(s):  
Hai Sun ◽  
Eun Soo Kim ◽  
Marinos P. Bernitsas ◽  
Michael M. Bernitsas
Keyword(s):  
First Generation ◽  
Closed Loop ◽  
Hydrodynamic Force ◽  
Circular Cross Section ◽  
Data Generation ◽  
University Of Michigan ◽  
Hydrokinetic Energy ◽  
Vortex Induced Vibrations ◽  
Induced Motion ◽  
The University

Flow-induced motion (FIM) experiments of a single circular cylinder or multiple cylinders in an array involve several configuration and hydrodynamic parameters, such as diameter, mass, damping, stiffness, spacing, Reynolds number, and flow regime, and deviation from circular cross section. Due to the importance of the FIM both in suppression for structural robustness and in enhancement for hydrokinetic energy conversion, systematic experiments are being conducted since the early 1960s and several more decades of experimentation are required. Change of springs and dampers is time consuming and requires frequent recalibration. Emulating springs and dampers with a controller makes parameter change efficient and accurate. There are two approaches to this problem: The first involves the hydrodynamic force in the closed-loop and is easier to implement. The second called virtual damping and spring (Vck) does not involve the hydrodynamic force in the closed-loop but requires an elaborate system identification (SI) process. Vck was developed in the Marine Renewable Energy Laboratory (MRELab) of the University of Michigan for the first time in 2009 and resulted in extensive data generation. In this paper, the second generation of Vck is developed and validated by comparison of the FIM experiments between a Vck emulated oscillator and an oscillator with physical springs and dampers. The main findings are: (a) the Vck system developed keeps the hydrodynamic force out of the control-loop and, thus, does not bias the FIM, (b) The controller-induced lag is minimal and significantly reduced compared to the first generation of Vck built in the MRELab due to use of an Arduino embedded board to control a servomotor instead of Labview, (c) The SI process revealed a static, third-order, nonlinear viscous model but no need for dynamic terms with memory, and (d) The agreement between real and virtual springs and dampers is excellent in FIM including vortex-induced vibrations (VIVs) and galloping measurements over the entire range of spring constants and velocities tested (16,000 < Re < 140,000).

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