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

2017 ◽  
Vol 68 ◽  
pp. 158-173 ◽  
Author(s):  
J.V. Ulveseter ◽  
S. Sævik ◽  
C.M. Larsen
Keyword(s):  
Time Domain ◽  
Domain Model ◽  
Line Vortex ◽  
Vortex Induced Vibrations

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.

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.

Vortex Induced Vibrations of Pipelines With Non-Linear Seabed Contact Properties

2016 ◽  
Author(s):  
Jan V. Ulveseter ◽  
Svein Sævik ◽  
Carl M. Larsen
Keyword(s):  
Frequency Domain ◽  
Linear Model ◽  
Time Domain ◽  
Structural Model ◽  
Life Time ◽  
Domain Model ◽  
Linear Interaction ◽  
Vortex Induced Vibrations ◽  
Non Linear ◽  
Soil Damping

A promising time domain model for calculation of cross-flow vortex induced vibrations (VIV) is under development at the Norwegian University of Science and Technology. Time domain, as oppose to frequency domain, makes it possible to include non-linearities in the structural model. Pipelines that rest on an irregular seabed will experience free spans. In these areas VIV is a concern with respect to the fatigue life. In this paper, a time domain model for calculation of VIV on free spanning pipelines is proposed. The model has non-linear interaction properties consisting of discrete soil dampers and soil springs turning on or off depending on the pipeline response. The non-linear model is compared to two linear models with linear stiffness and damping properties. One linear model is based on the promising time domain VIV model, while the other one is based on RIFLEX and VIVANA, which calculates VIV in frequency domain. Through four case studies the effect of seabed geometry, current velocity and varying soil damping and soil stiffness is investigated for a specific pipeline. The results show that there is good agreement between the results produced by VIVANA and the linear model. The non-linear model predicts smaller stresses at the pipe shoulders, which is positive for the life time estimations. Soil damping does not influence the response significantly.

Vortex-Induced Vibrations on Flexible Cylindrical Structures Coupled With Non-Linear Oscillators

2009 ◽  
Author(s):  
Guilherme F. Rosetti ◽  
Kazuo Nishimoto ◽  
Jaap de Wilde
Keyword(s):  
Time Domain ◽  
Lift Coefficient ◽  
Domain Model ◽  
Scale Model ◽  
Small Scale ◽  
Current Profile ◽  
Flexible Cylinder ◽  
Vortex Induced Vibrations ◽  
Offshore Industry ◽  
New Time

The recent escalade of the oil prices encourages the search and exploration of new oil fields. This represents a challenge to engineers, due to more difficult conditions of operation in harsh environments and deeper reservoirs. The offshore industry faces, in the edge of technology with new necessities and limiting conditions imposed by the environment, an increase in the cost of production. It is, therefore, of vital importance to have the equipments operating at the most optimized conditions in order to reduce these costs. VIV software developed in the frequency domain was successful in designing risers and pipelines using large safety factors and making conservative assumptions. These tools only predict single-mode vibrations. In this perspective, the present paper describes the results obtained from a new time-domain code developed to assess the vortex-induced vibrations of a long flexible cylinder. A time-domain analysis was chosen because this suits the problem well, since it is able to predict and calculate different modes of vibrations. In the model, a cylinder is divided into elements that can be exposed to an arbitrary current profile. Each of these elements is free to oscillate parallel and transversely to the flow, and is coupled to a pair of van der Pol’s wake oscillators. This simulates the vortex shedding and, therefore, the fluctuating nature of drag and lift coefficient during the occurrence of VIV. The governing equations are solved by 4th-Order Runge-Kutta schemes in time domain. The new time-domain model is compared with small scale model test data from benchmarking.

Frequency and Time Domain Analysis of Vortex Induced Vibrations for Free Span Pipelines

2002 ◽  
Author(s):  
Carl M. Larsen ◽  
Kamran Koushan ◽  
Elizabeth Passano
Keyword(s):  
Time Domain ◽  
Structural Model ◽  
Linear Time ◽  
Time Domain Analysis ◽  
Linear Response Theory ◽  
Domain Model ◽  
Vortex Induced Vibrations ◽  
Non Linear ◽  
New Strategy ◽  
Stress Prediction

The present paper will discuss various models for calculation of vortex induced vibrations (VIV) of free span pipelines, and present a new strategy for such analyses. Applications of traditional models are presented and their limitations discussed. The new approach is based on the combination of an empirical linear frequency domain model, and a non-linear time domain structural model. The first step is to carry out the VIV analysis according to linear response theory, and next introduce the calculated hydrodynamic forces to the non-linear structural model. The benefit from using the non-linear model is to describe stresses at the shoulders more accurately, which is important since fatigue damage in many cases will be largest in this area. The conclusion is that the interaction between pipe and seafloor is crucial for accurate stress prediction, and that a non-linear time domain model will give the most accurate result.

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.

Time and Frequency Domain Analysis of Catenary Risers Subjected to Vortex Induced Vibrations

2006 ◽  
Author(s):  
Carl M. Larsen ◽  
Elizabeth Passano
Keyword(s):  
Frequency Domain ◽  
Linear Model ◽  
Time Domain ◽  
Structural Model ◽  
Linear Time ◽  
Domain Analysis ◽  
Domain Model ◽  
Vortex Induced Vibrations ◽  
Non Linear ◽  
Bending Stresses

Catenary risers in deep waters will experience conditions with insignificant wave forces in combination with strong current. The response will in such cases be dominated by vortex induced vibrations (VIV). Dynamic bending stresses will vary along the riser, but a large peak will almost always be seen near the touch down point. This peak is caused by the restrictions on riser displacements from the presence of the seafloor, and the local bending stresses will be influenced by stiffness and damping propertoes of the bottom. Analysis models based on finite elements will represent the interaction between riser and seafloor by discrete springs, which for the linear case will remain constant independent of the displacements. This type of model may give a significant over-prediction of bending stresses at the touch down point since a linear spring will give tensile forces instead of being released and allowing the pipe to lift off from the bottom. A non-linear time domain model will, however, account for changes by releasing springs if tension occurs and adding in new springs if free nodes obtain temporary contact with the bottom. The results will hence become far more realistic. Traditional empirical models for VIV prediction are based on a frequency domain dynamic analysis with constant stiffness. There is hence an obvious need for improvements when dealing with catenary risers. This paper will describe a new approach that is based on combined use of an empirical linear frequency domain model for VIV, and a non-linear model for time domain analysis. The first step is to carry out the VIV analysis according to linear response theory, and next introduce the calculated hydrodynamic forces to the non-linear structural model. The benefit from using the non-linear model is that stresses in the touch down area are described more accurately. A case study is also reported. Bottom stiffness and friction are varied, and results are compared to a simple model with a hinge at the touch down point. The conclusion is that the interaction between riser and seafloor is crucial for accurate stress prediction, and that a non-linear time domain model will give the most accurate result.

scholarly journals Prediction of deepwater riser VIV with an improved time domain model including non-linear structural behavior

2021 ◽  
Vol 236 ◽  
pp. 109508
Author(s):  
Sang Woo Kim ◽  
Svein Sævik ◽  
Jie Wu ◽  
Bernt Johan Leira
Keyword(s):  
Time Domain ◽  
Domain Model ◽  
Structural Behavior ◽  
Non Linear ◽  
Deepwater Riser
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