An Analytical/Computational Approach in Assessing Vortex-Induced Vibration of a Variable Tension Riser

2010 ◽  
Vol 132 (3) ◽  
Author(s):  
Per M. Josefsson ◽  
Charles Dalton
Keyword(s):  
Fluid Flow ◽  
Flow Field ◽  
Natural Frequency ◽  
Vortex Shedding ◽  
Beam Equation ◽  
Vortex Induced Vibration ◽  
Forcing Function ◽  
Strip Theory ◽  
Constant Tension ◽  
Variable Tension

The transverse vibratory response of a long, slender vertical top tension riser, subject to an ocean current, is studied. The problem is treated as a coupled fluid flow/vibration problem, which is solved numerically. The fluid flow part is represented by the 2D Navier–Stokes equations, with large-eddy simulation turbulence modeling and strip theory, which are solved numerically to obtain the flow field and determine the vortex-shedding behavior in the flow. The approach flow is a shear flow ranging in Reynolds number from 8000 to 10,000. Given the flow field and vortex-shedding behavior, the transverse fluid forcing function can be determined at a given instant, which becomes the input to the Euler–Bernoulli beam equation to calculate the displacement of the riser, using a technique that involves the Wentzel–Kramers–Brillouin (WKB) method and modal decomposition. The boundary conditions for the fluid flow equations are updated each time step as the cylinder moves. The natural frequency of the riser is tension dominated, not bending-stiffness dominated. With the decrease in tension with increasing depth, the natural frequency is affected. Therefore, the solution will be influenced by the depth-dependent tension. This study has indicated some interesting features regarding the vortex-induced vibration of a variable-tension riser. The vibrational response is greater for a variable-tension riser than for a constant-tension riser, when the variable-tension riser is assumed to have the same top tension as the constant-tension riser. Thus, this is one reason why it is important to take into account the variable tension when estimating fatigue failures of marine risers.

Vortex-Induced Vibration of a Variable Tension Riser

2007 ◽  
Author(s):  
Per M. Josefsson ◽  
Charles Dalton
Keyword(s):  
Fluid Flow ◽  
Flow Field ◽  
Natural Frequency ◽  
Vortex Shedding ◽  
Beam Equation ◽  
Time Step ◽  
Forcing Function ◽  
Strip Theory ◽  
Constant Tension ◽  
Variable Tension

The transverse vibratory response of a long, slender vertical top-tension riser, subject to an ocean current, is studied. The problem is treated as a coupled fluid-flow/vibration problem which is solved numerically. The fluid flow part is represented by the 2-D Navier-Stokes equations, with LES and strip theory, which are solved numerically to obtain the flow field and determine the vortex-shedding behavior in the flow. The approach flow is a shear flow ranging in Reynolds number from 8000 to 10,000. Given the flow field and vortex-shedding behavior, the transverse fluid forcing function can be determined at a given instant, which becomes the input to the Euler-Bernoulli beam equation to calculate the displacement of the riser, using a technique that involves the WKB method and modal decomposition. The boundary conditions for the fluid-flow equations are updated each time step as the cylinder moves. The natural frequency of the riser is tension-dominated, not bending stiffness-dominated. With the decrease in tension with increasing depth, the natural frequency is affected. Therefore, the solution will be influenced by the depth-dependent tension. This study has indicated some interesting features regarding the VIV of a variable-tension riser. The vibrational response is greater for a variable-tension riser than for a constant-tension riser, when the variable-tension riser is assumed to have the same top tension as the constant-tension riser. Therefore, it is important to take into account the variable tension when estimating fatigue failures of marine risers.

Experimental Analysis of Vortex Induced Vibration in the Bladeless Small Wind Turbine

2019 ◽  
Author(s):  
Micha Premkumar Thomai ◽  
Lasoodawanki Kharsati ◽  
Nakandhrakumar Rama Samy ◽  
Seralathan Sivamani ◽  
Hariram Venkatesan
Keyword(s):  
Energy Conversion ◽  
Wind Turbine ◽  
Natural Frequency ◽  
Cross Section ◽  
Vortex Shedding ◽  
Rectangular Cross Section ◽  
The Body ◽  
Test Facility ◽  
Vortex Induced Vibration ◽  
Small Wind Turbine

Abstract Vortex-induced vibration is one of the predominant fundamental concepts for forced oscillation which attracts considerable practical engineering application for energy conversion. In this work, an oscillation of a mast arising as a result of wind force is utilized for energy conversion. The paradigm for energy conversion from vortex-induced vibration in the mast is the bladeless wind turbine. It consists of a rigid mass known as a mast, fixed in the spring of stiffness (k) and allowed to oscillate along the direction of the flow. In this work, four different types of mast have been fabricated and tested. The first is uniform tapered hollow conical mast (MAST1), the cross-section of the second is uniform tapered plus symbol (MAST2), the third is uniform tapered inversed plus symbol (MAST3) and the fourth is uniform tapered simple rectangular cross-section (MAST4). All the masts were fabricated using fiber carbon. The experiments were conducted in a versatile small wind turbine testing facility of Hindustan Institute of Technology and Science, Chennai. This test facility contained an open jet wind tunnel with variable frequency drive and other measuring instruments. The vibration sensor was located in the mast where it experienced a large oscillation in a free stream. In this experiment, an increase in wind velocity led to a terrible change in the amplitude of vibration. A vigorous oscillation was experienced in this mast at this critical frequency, when the natural frequency of the mast was synchronized with the frequency of the vortex shedding and the frequency of the oscillation of the mast. The total force in this oscillation was a summation of the body force due to the mass of the mast and vorticity force that is mainly which was the result of the shedding of the vortices. In this work, extensive studies have been carried out for Reynolds number ranging from 2.5 × 105 to 5.0 × 105. The mast length to diameter ratio of 13 was exposed to various speeds of wind and response was measured. The occurrence of the maximum oscillation in a simple rectangular mast was seen where vortex shedding due to the bluff body was large for constant mass and spring stiffness. The frequency of the oscillation at maximum amplitude of the rectangular cross-section mast was equal to the natural frequency, due to vortices shedding at critical velocity. This demonstrated the appropriateness of the simple rectangular cross-section for harnessing the low rated wind energy and its suitability for renewable energy conversion in the small bladeless wind turbine.

A Numerical Simulation of Vortex Induced Vibration on a Elastically Supported Circular Rigid Cylinder at Moderate Reynolds Numbers

2008 ◽  
Author(s):  
Jean-Franc¸ois Sigrist ◽  
Cyrille Allery ◽  
Claudine Beghein
Keyword(s):  
Numerical Simulation ◽  
Fluid Flow ◽  
Circular Cylinder ◽  
Finite Volume ◽  
Vortex Shedding ◽  
Numerical Study ◽  
Reynolds Numbers ◽  
Forced Oscillations ◽  
Vortex Induced Vibration ◽  
Elastically Supported

The present paper is the sequel of a previously published study which is concerned with the numerical simulation of vortex-induced-vibration (VIV) on an elastically supported rigid circular cylinder in a fluid cross-flow (A. Placzek, J.F. Sigrist, A. Hamdouni; Numerical Simulation of Vortex Shedding Past a Circular Cylinder at Low Reynolds Number with Finite Volume Technique. Part I: Forced Oscillations, Part II: Flow Induced Vibrations; Pressure Vessel and Piping, San Antonio, 22–26 July 2007). Such a problem has been thoroughly studied over the past years, both from the experimental and numerical points of view, because of its theoretical and practical interest in the understanding on flow-induced vibration problems. In this context, the present paper aims at exposing a numerical study based on a fully coupled fluid-structure simulation. The numerical technique is based on a finite volume discretisation of the fluid flow equations together with i) a re-meshing algorithm to account for the cylinder motion ii) a projection subroutine to compute the forces induced by the fluid on the cylinder and iii) a coupling procedure to describe the energy exchanges between the fluid flow and solid motion. The study is restricted to moderate Reynolds numbers (Re∼2.000–10.000) and is performed with an industrial CFD code. Numerical results are compared with existing literature on the subject, both in terms of cylinder amplitude motion and fluid vortex shedding modes. Ongoing numerical studies with different numerical techniques, such as ROM (Reduced Order Models)-based methods, will complete the approach and will be published in next PVP conference. These numerical simulations are proposed for code validation purposes prior to industrial applications in tube bundle configuration.

Vortex Induced Vibration of a Rotating Blade

2017 ◽  
Author(s):  
Lokanna Hoskoti ◽  
Ajay Misra ◽  
Mahesh Manchakattil Sucheendran
Keyword(s):  
Vortex Shedding ◽  
Coupling Parameter ◽  
Coupled System ◽  
Beam Equation ◽  
Vortex Induced Vibration ◽  
Coupled Equations ◽  
Rotating Blade ◽  
Response Equation ◽  
The Stability ◽  
Lock In

The vortex-induced vibration (VIV) of a rotating blade is studied in this paper. Euler-Bernoulli beam equation and the nonlinear oscillator satisfying Van der Pol equation are used to model the rotating blade and vortex shedding, respectively. While the fluctuating lift due to vortex shedding acts on the blade and the blade is coupled with fluid through a linear inertial coupling, resulting in a fluid-structure interaction problem. The coupled equations are discretized by using modes which satisfy the Eigenvalue problem. The work attempts to understand the instabilities associated with the frequency lock-in phenomenon. The method of multiscale is used to obtain the frequency response equation and frequency bifurcation diagrams of the coupled system. They are obtained for the primary (1:1) resonance for different values of the coupling parameter. The stability of the solution is presented by examining the nature of the Eigenvalues of the Jacobian matrix.

scholarly journals Prediction of Wind Velocity to Raise Vortex-Induced Vibration through a Road-Rail Bridge with Truss-Shaped Girder

2018 ◽  
Vol 2018 ◽  
pp. 1-10 ◽  
Author(s):  
Seungtaek Oh ◽  
Sung-il Seo ◽  
Hoyeop Lee ◽  
Hak-Eun Lee
Keyword(s):  
Wind Tunnel ◽  
Natural Frequency ◽  
Wind Velocity ◽  
Vortex Shedding ◽  
Natural Frequencies ◽  
Wind Tunnel Test ◽  
Resonance Phenomenon ◽  
Vortex Induced Vibration ◽  
Vortex Shedding Frequency ◽  
Shedding Frequency

Vortex-induced vibration (VIV) of bridges, related to fluid-structure interaction and maintenance of bridge monitoring system, causes fatigue and serviceability problems due to aerodynamic instability at low wind velocity. Extensive studies on VIV have been performed by directly measuring the vortex shedding frequency and the wind velocity for indicating the largest girder displacement. However, previous studies have not investigated a prediction of wind velocity to raise VIV with a various natural frequency of the structure because most cases have been focused on the estimation of the wind velocity and peeling-off frequency by the mounting structure at the fixed position. In this paper, the method for predicting wind velocity to raise VIV is suggested with various natural frequencies on a road-rail bridge with truss-shaped girder. For this purpose, 12 cases of dynamic wind tunnel test with different natural frequencies are performed by the resonance phenomenon. As a result, it is reasonable to predict wind velocity to raise VIV with maximum RMS displacement due to dynamic wind tunnel tests. Furthermore, it is found that the natural frequency can be used instead of the vortex shedding frequency in order to predict the wind velocity on the dynamic wind tunnel test. Finally, curve fitting is performed to predict the wind velocity of the actual bridge. The result is shown that predicting the wind velocity at which VIV occurs can be appropriately estimated at arbitrary natural frequencies of the dynamic wind tunnel test due to the feature of Strouhal number determined by the shape of the cross section.

Optimal control of a broadband vortex-induced vibration energy harvester

2019 ◽  
Vol 31 (1) ◽  
pp. 137-151
Author(s):  
E Azadi Yazdi
Keyword(s):  
Optimal Control ◽  
Natural Frequency ◽  
Vortex Shedding ◽  
Energy Harvester ◽  
Control Technique ◽  
Vibration Energy ◽  
Vibration Energy Harvester ◽  
Vortex Induced Vibration ◽  
Vortex Shedding Frequency ◽  
Shedding Frequency

A vortex-induced vibration energy harvester consists of a relatively long cylinder mounted on a flexible structure. In a flow field, the periodically shedding vortices induce transverse vibrations in the cylinder that is converted to electricity by means of piezoelectric generators. In most vortex-induced vibration harvesters, the output power is considerable only in a narrow band around the wind speed where the vortex shedding frequency matches the natural frequency of the structure. To overcome this limitation, a tuned mass mechanism is employed in the proposed vortex-induced vibration energy harvester that can change the natural frequency of the turbine to match the vortex shedding frequency in a broad band of wind speeds. The tuned mass mechanism should work in close cooperation with the piezoelectric generators to maximize the electric power of the turbine. To this end, a nonlinear piezoaeroelastic model of the system is derived, and a model predictive control technique is formulated to find the optimal control inputs for the tuned mass actuator and the piezoelectric generators. Results of numeric simulations confirmed that the tuned mass mechanism not only increases the velocity band over which the turbine is effective but also increases the peak power output of the turbine by 294%.

Fluid flow over and through a regular bundle of rigid fibres

2016 ◽  
Vol 792 ◽  
pp. 5-35 ◽  
Author(s):  
Giuseppe A. Zampogna ◽  
Alessandro Bottaro
Keyword(s):  
Porous Medium ◽  
Fluid Flow ◽  
Flow Field ◽  
Stokes Equations ◽  
Transversely Isotropic ◽  
Navier Stokes ◽  
Leading Order ◽  
Macroscopic Scale ◽  
Navier Stokes Equations ◽  
Homogenized Model

The interaction between a fluid flow and a transversely isotropic porous medium is described. A homogenized model is used to treat the flow field in the porous region, and different interface conditions, needed to match solutions at the boundary between the pure fluid and the porous regions, are evaluated. Two problems in different flow regimes (laminar and turbulent) are considered to validate the system, which includes inertia in the leading-order equations for the permeability tensor through a Oseen approximation. The components of the permeability, which characterize microscopically the porous medium and determine the flow field at the macroscopic scale, are reasonably well estimated by the theory, both in the laminar and the turbulent case. This is demonstrated by comparing the model’s results to both experimental measurements and direct numerical simulations of the Navier–Stokes equations which resolve the flow also through the pores of the medium.

Fluid Flow Field in the Annulus of Boiling Water (BWR) Nuclear Reactors Under Normal and Accident Conditions

2009 ◽  
Author(s):  
Raju Ananth ◽  
Karen Fujikawa ◽  
Jay Gillis
Keyword(s):  
Fluid Flow ◽  
Velocity Field ◽  
Flow Field ◽  
Pressure Vessel ◽  
Theoretical Study ◽  
Nuclear Reactors ◽  
Boiling Water ◽  
Flow Conditions ◽  
Accident Conditions ◽  
Reactor Pressure

This paper presents a theoretical study of the velocity field in the annulus formed between the Reactor Pressure Vessel (RPV) and the shroud of a Boiling Water Reactor (BWR) under normal and accident flow conditions. Simplified geometry and an ideal irrotational flow are assumed to solve the problem using velocity potentials.

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