A simplified method for time domain simulation of cross-flow 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.

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

Journal of Offshore Mechanics and Arctic Engineering ◽

10.1115/1.4048660 ◽

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.

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

Volume 1: Offshore Technology ◽

10.1115/omae2020-18271 ◽

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.

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Improved In-Line Vortex-Induced Vibrations Prediction for Combined In-Line and Cross-Flow Vortex-Induced Vibrations Responses

Journal of Offshore Mechanics and Arctic Engineering ◽

10.1115/1.4038350 ◽

2017 ◽

Vol 140 (3) ◽

Cited By ~ 1

Author(s):

Decao Yin ◽

Elizabeth Passano ◽

Carl M. Larsen

Keyword(s):

Cross Flow ◽

Hydrodynamic Coefficients ◽

Marine Structures ◽

Flexible Pipe ◽

Flexible Beams ◽

Forced Motion ◽

Pipe Model ◽

Vortex Induced Vibrations ◽

Flow Vortex ◽

Semi Empirical

Slender marine structures are subjected to ocean currents, which can cause vortex-induced vibrations (VIV). Accumulated damage due to VIV can shorten the fatigue life of marine structures, so it needs to be considered in the design and operation phase. Semi-empirical VIV prediction tools are based on hydrodynamic coefficients. The hydrodynamic coefficients can either be calculated from experiments on flexible beams by using inverse analysis or theoretical methods, or obtained from forced motion experiments on a circular cylinder. Most of the forced motion experiments apply harmonic motions in either in-line (IL) or crossflow (CF) direction. Combined IL and CF forced motion experiments are also reported. However, measured motions from flexible pipe VIV tests contain higher order harmonic components, which have not yet been extensively studied. This paper presents results from conventional forced motion VIV experiments, but using measured motions taken from a flexible pipe undergoing VIV. The IL excitation coefficients were used by semi-empirical VIV prediction software vivana to perform combined IL and CF VIV calculation. The key IL results are compared with Norwegian Deepwater Programme (NDP) flexible pipe model test results. By using present IL excitation coefficients, the prediction of IL responses for combined IL and CF VIV responses is improved.

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Phasing mechanisms between the in-line and cross-flow vortex-induced vibrations of a long tensioned beam in shear flow

Computers & Structures ◽

10.1016/j.compstruc.2013.01.002 ◽

2013 ◽

Vol 122 ◽

pp. 155-163 ◽

Cited By ~ 13

Author(s):

Rémi Bourguet ◽

George Em Karniadakis ◽

Michael S. Triantafyllou

Keyword(s):

Shear Flow ◽

Cross Flow ◽

Vortex Induced Vibrations ◽

Flow Vortex

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Interaction of In-Line and Cross-Flow Vortex Induced Vibrations in Risers

21st International Conference on Offshore Mechanics and Arctic Engineering, Volume 1 ◽

10.1115/omae2002-28303 ◽

2002 ◽

Cited By ~ 1

Author(s):

Erik Asp Hansen ◽

Mads Bryndum ◽

Stefan Mayer

Keyword(s):

Cross Flow ◽

Recent Model ◽

Experimental Investigations ◽

Numerical Tests ◽

Vortex Induced Vibrations ◽

Model Set ◽

Line Cross ◽

Set Up ◽

The Individual ◽

Flow Vortex

VIV in pipeline and risers has been studied through numerous experimental investigations using simplified model set-up, consisting of spring mounted rigid cylinders. Models have been constructed to allow in-line, cross-flow, or both in-line and cross-flow motions. Comparison of the model results shows overall agreement, although distinct differences exist between the individual model test series. Different explanation models have been established to try to improve the consistency, however, seldom definitive conclusions have been reached. The present paper presents the use of CFD to document the importance of the interaction of in-line and cross-flow motions on VIV response. 2D numerical tests have been performed using NS3 (DHI-CFD code) for a model undergoing in-line, cross-flow, combined in-line and cross-flow, and cross-flow in combination with forced in-line motions. The paper compares the results with some recent model tests and quantifies the significance of interaction.

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