Time domain model for calculation of pure in-line vortex-induced vibrations

Ulveseter, Jan Vidar; Sævik, Svein; Larsen, Carl M.

doi:10.1016/j.jfluidstructs.2016.10.013

Cited by 16 publications

(4 citation statements)

References 23 publications

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“…As a suggestion for future work, the original model by Thorsen et al (2017) should be modified to include forcing term(s) for simultaneous cross-flow and in-line VIV (and potentially also pure in-line vibrations (Ulveseter et al, 2017)). The proposed stochastic synchronization might be applied in a similar form as in this paper, to provide realistic randomness in the combined cross-flow and in-line response.…”

Section: Resultsmentioning

confidence: 99%

Stochastic modelling of cross-flow vortex-induced vibrations

et al. 2017

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Semi-empirical models are commonly used to predict vortex-induced vibrations (VIV). Empirical parameters are often based on forced harmonic motion tests of short rigid cylinders in one degree of freedom, which is a significant simplification of the three dimensional VIV experienced by flexible cylinders. Still, the models may provide satisfactory estimates of the response of slender marine structures exposed to current. At least in terms of root mean square (r.m.s.) of displacements and strains, dominating frequency and dominating mode. However, VIV of long slender beams, especially in sheared current, show large response variability in time and space, which appears to be of a random nature. Semi-empirical models that predict steady-state VIV are hence unable to reflect the non-stationary response observed in experiments, even though the time and space averaged result might be well represented.In this work, a previously published semi-empirical time domain model for cross-flow vortex-induced vibrations is modified to describe the stochastic nature of the response of long slender beams subjected to stationary current. The mean non-dimensional frequency of the synchronization model (previously constant) is taken to be a simplified Gaussian process, where standard deviation and spectral frequencies are input. The stochastic synchronization model allows the response to jump between different eigenfrequencies and corresponding modes, and still predict mean and r.m.s. values close to the deterministic model. Its performance is verified through simulation of an experiment with a long riser in sheared flow. The response sensitivity of standard deviation and spectral frequencies is investigated. It indicates that for a proper choice of empirical coefficients, the chaotic response of the riser can be quite realistically simulated in terms of frequency variation and, to some extent, amplitude modulation.

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Section: Resultsmentioning

confidence: 99%

Stochastic modelling of cross-flow vortex-induced vibrations

et al. 2017

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“…is is probably due to significantly larger response amplitudes than what is observed in the in-line direction [9]. However, in later years, in-line vibrations and the combination of cross-flow and in-line VIV have become a larger focus area [9][10][11][12]. e top of the riser is connected with the platform which has motions (surge and heave) in ocean waves.…”

Section: Introductionmentioning

confidence: 93%

Numerical and Experimental Research on the Effect of Platform Heave Motion on Vortex‐Induced Vibration of Deep Sea Top‐Tensioned Riser

Zhang

Zeng

Tang

et al. 2021

Shock and Vibration

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The prediction and control of vortex-induced vibration (VIV) is one of the key problems for riser design. The effect of platform heave motion on VIV of deep sea top-tensioned riser (TTR) is presented by means of numerical simulation and experiment in this research. First, the heave motion was modeled as a parametric excitation, and the governing equation of VIV of riser considering the parametric excitation was established. Then, the dynamic response of TTR was calculated numerically by the finite difference method based on the Van der Pol wake-oscillator model. Finally, a validation experiment was carried out at the towing tank of Tianjin university. The results show that the VIV response at the bottom of riser is significantly increased due to the platform heave motion, especially in the situation of low current velocity. The larger amplitude and the higher frequency of the platform heave motion with the greater influence are generated on VIV of TTR. In particular, the value of 0.5 times, 1 time, or other multiples of the platform heave frequency will be included in the vibration frequency component of TTR when the platform heave amplitude is large and the frequency is high.

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“…Pure in-line vibrations are not modelled here, since all the following case studies are outside of this regime. However, it is to be noted that a similar synchronization model as stated above has successfully been used for pure in-line vibrations [23,24].…”

Section: In-line Synchronizationmentioning

confidence: 99%

Time domain simulation of riser VIV in current and irregular waves

et al. 2018

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A semi-empirical time domain force model for combined cross-flow and in-line vortex-induced vibrations (VIV) is proposed, based on a series of earlier publications. The new feature is a term which represents the effect of vortex shedding in the flow direction, referred to as the in-line vortex shedding load. The latter is added to Morison's equation and a cross-flow vortex shedding force. The fundamental idea of how to model the effect of vortex shedding is the same as in previous works. An algorithm for synchronization is applied between the vortex shedding loading terms themselves and the structural response, which excites vibrations for a pre-determined frequency interval. The originality of the present study is rather how the VIV-terms are integrated as part of Morison's equation, which is there to provide a description of inertia and drag forces. All the loading terms combined enables simultaneous simulation of VIV and other response phenomena, such as wave induced motion and static drag displacement.The performance of the time domain model is verified against measurements of a vertical riser subjected to two different external flow cases. The first one is simply steady uniform current whereas the second flow case combines the latter with irregular waves. To simulate the experiments, a linear finite element model of the riser is made, and the proposed hydrodynamic force model is applied to the translation degrees of freedom along the structure. It is to be noted that the same empirical coefficients are used to simulate both experiments. In uniform flow, the results are good. Dominating frequency and vibration amplitude agree well in both cross-flow and in-line directions. The simulated time series show more regular/less tendency of amplitude modulations than the experiments, but the overall agreement is still acceptable for engineering purposes. For the second flow case, where the riser was towed in irregular waves, the model provides a highly realistic representation of the riser motion. Both when the total response (containing wave and VIV frequencies) and the filtered signal (including only VIV frequencies) are analysed, the predictions follow the measurements closely. From before, the cross-flow part of the VIV model has been tested in oscillating flow and regular waves, and the performance of the former was experimentally proven. It is hence concluded that the proposed prediction tool is applicable to a variety of non-stationary flow conditions, implying that the synchronization model captures parts of the underlying physics, despite its simple form.

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Time domain model for calculation of pure in-line vortex-induced vibrations

Cited by 16 publications

References 23 publications

Stochastic modelling of cross-flow vortex-induced vibrations

Stochastic modelling of cross-flow vortex-induced vibrations

Numerical and Experimental Research on the Effect of Platform Heave Motion on Vortex‐Induced Vibration of Deep Sea Top‐Tensioned Riser

Time domain simulation of riser VIV in current and irregular waves

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