Effects of natural frequency ratio on vortex-induced vibration of a cylindrical structure

2015 ◽  
Vol 110 ◽  
pp. 62-76 ◽  
Author(s):  
Xiangxi Han ◽  
Wei Lin ◽  
Youhong Tang ◽  
Chengbi Zhao ◽  
Karl Sammut
Keyword(s):  
Natural Frequency ◽  
Frequency Ratio ◽  
Vortex Induced Vibration ◽  
Cylindrical Structure

scholarly journals Influence of Frequency Ratio on the Hydroelastic Response of a Cylinder with Degrees of Freedom under Vortex Induced Vibration

2019 ◽  
Vol 8 (9S3) ◽  
pp. 307-312
Keyword(s):  
Natural Frequency ◽  
Frequency Ratio ◽  
Degrees Of Freedom ◽  
Structural Parameters ◽  
Lift Coefficient ◽  
Cross Flow ◽  
Vortex Induced Vibration ◽  
Ocean Environment ◽  
Hydroelastic Response ◽  
Lock In

Vortex induced vibration of cylindrical structures is an extensively researched topic. Most of the studies have concentrated on the response of the cylinder in the cross flow (CF) direction. In a realistic ocean environment, structures such as drilling and marine risers are more or less free to vibrate both in CF and in line (IL) directions. It has also been observed that the IL vibrations have significant influence on the CF response. Interaction between the responses in inline and cross flow directions has still been not fully understood. This paper addresses the same through a simplified numerical method for understanding the interaction between these two responses using two dimensional computational fluid dynamics (CFD) simulations. Here analyzes two cases have been considered; where in the cylinder is modeled with two different values of ratio of natural frequency of the cylinder in the IL direction to that in the CF direction. The trends of variation of hydrodynamic and structural parameters have been analyzed to comprehend the effect of directional natural frequency ratio on the cylinder response and hydrodynamic force coefficients. The shedding pattern has also been studied in this paper. An increase by 18% in the value of the lift coefficient and 38 % of that in the drag coefficient has been observed when the frequency ratio is increased from 1 to 2. The results show that the cylinder with frequency ratio 2 is more prone to lock in vibration. This phenomenon may be related to the shifting of shedding pattern from 2S to P + S mode when the frequency ratio is 2.

Axial Load on the Submarine Pipeline Suspended Law of Vortex Induced Vibration

2011 ◽  
Vol 94-96 ◽  
pp. 1511-1514
Author(s):  
Yi Fei Yan
Keyword(s):  
Natural Frequency ◽  
Axial Force ◽  
Scientific Basis ◽  
Oil Field ◽  
Span Length ◽  
Submarine Pipeline ◽  
Vortex Induced Vibration ◽  
Vibration Effect ◽  
Pipeline Vibration ◽  
The Impact

The study is about submarine pipeline. Considering the impact of different axial force, The reduced velocity is introduced as the pipeline vibration effect of vortex trail releasing. The vibration parameters of the span pipeline are analyzed and vibration control formula is built. The natural span length of the submarine pipeline is calculated according to the DNV-OS-F101 rule. The natural frequency of the span pipeline and the allowable span length are solved. The case study of submarine pipeline in Chengdao oil field is made and the variation law of natural frequency of span pipeline is got. The stream reduced velocity decreases as the axial force increase. The theory analysis of the vortex induced vibration can provide the scientific basis for the safety design of offshore submarine pipeline.

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.

Managing Vortex Induced Vibration in Well Jumper Systems

2008 ◽  
Author(s):  
Kenneth Bhalla ◽  
Lixin Gong
Keyword(s):  
Natural Frequency ◽  
Natural Frequencies ◽  
Cross Flow ◽  
Mitigation Measures ◽  
Mode Shapes ◽  
Bottom Current ◽  
Vortex Induced Vibration ◽  
Flow Response ◽  
Out Of Plane ◽  
Lock In

The purpose of this paper is to present a method that has been developed to identify if vortex induced vibration (VIV) occurs in well jumper systems. Moreover, a method has been developed to determine when VIV mitigation measures such as strakes are required. The method involves determining the in-plane and out-of-plane natural frequencies and mode shapes. The natural frequencies are then used, in conjunction with the maximum bottom current expected at a given location to determine if suppression is required. The natural frequency of a jumper system is a function of many variables, e.g. span length, leg height, pipe diameter and thickness, buoyancy placement, buoyancy uplift, buoyancy OD, insulation thickness, and contents of the jumper. The suppression requirement is based upon calculating a lower bound lock-in current speed based upon an assumed velocity bandwidth centered about the lock-in current. The out-of-plane VIV cross-flow response is produced by a current in the plane of the jumper; whereas the in-plane VIV cross-flow response is produced by the out-of-plane current. Typically, the out-of-plane natural frequency is smaller than the in-plane natural frequency. Jumpers with small spans have higher natural frequencies; thus small span jumpers may require no suppression or suppression on the vertical legs. Whereas, larger span jumpers may require no suppression, suppression on the vertical legs or suppression on all the legs. The span of jumper systems (i.e. production, water injection, gas lift/injection ...) may vary in one given field; it has become apparent that not all jumper systems require suppression. This technique has allowed us to recognize when certain legs of a given jumper system may require suppression, thus leading to a jumper design whose safety is not compromised while in the production mode, as well as minimizing downtime and identifying potential savings from probable fatigue failures.

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.

Dynamic models for the contact analysis of a tensioned beam with a moving oscillator

2013 ◽  
Vol 228 (4) ◽  
pp. 676-689
Author(s):  
Kyuho Lee ◽  
Jintai Chung
Keyword(s):  
Natural Frequency ◽  
Nonlinear Model ◽  
Frequency Ratio ◽  
Dynamic Models ◽  
Equations Of Motion ◽  
Contact Analysis ◽  
Contact Forces ◽  
Accurate Analysis ◽  
Moving Oscillator ◽  
Velocity Decrease

Several dynamic models are proposed for the contact analysis of a tensioned beam with a moving oscillator. Depending on whether the strain and stress used to derive the equations of motion are nonlinear, four models are established to analyze the beam deflections and the contact force between the beam and moving oscillator. We find that the differences in the contact forces and deflections computed with the models become large as the beam tension and moving velocity decrease and the natural frequency ratio of the oscillator to the beam increases. The nonlinear model derived with nonlinear strain and stress is desirable for an accurate analysis.

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