scholarly journals Effect of the relative differences in the natural frequencies of parallel cable-stayed bridges during interactive vortex-induced vibration

2017 ◽  
Vol 171 ◽  
pp. 330-341 ◽  
Author(s):  
Jin Park ◽  
Ho-Kyung Kim
Keyword(s):  
Natural Frequencies ◽  
Vortex Induced Vibration ◽  
Relative Differences ◽  
Cable Stayed Bridges

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.

Research on Dynamic Characteristics for Large Span Cable-Stayed Suspension Bridges with CFRP Cables

2013 ◽  
Vol 683 ◽  
pp. 845-850
Author(s):  
Rong Gui Liu ◽  
Guo Ying Feng ◽  
Bei Chen
Keyword(s):  
Dynamic Characteristics ◽  
Natural Vibration ◽  
Natural Frequencies ◽  
Suspension Bridge ◽  
Suspension Bridges ◽  
Bridge Structure ◽  
Reinforced Plastics ◽  
New Type ◽  
Carbon Fibre Reinforced Plastics ◽  
Cable Stayed Bridges

Cable-stayed suspension bridge with Carbon Fibre Reinforced Plastics(CFRP) cables is a new type of bridge structure. To study the dynamic characteristics for this kind of bridges, and its differences from cable-stayed bridges of the same span level, finite element dynamic modle of a Cable-stayed suspension bridge with main span of 1488 meters is established and a series of calculations is done. The results show that, natural frequencies of cable-stayed suspension bridges with CFRP cables are relatively small, integral frequencies are stepped and discontinuous; Its modes are centralized and the natural vibration modes show a lot of coupling; The natural frequencies of this kind of bridges are smaller than cable-stayed bridges of the same span level, the entire stiffness decreased.

scholarly journals On the determination of natural frequencies and mode shapes of cable-stayed bridges

2001 ◽  
Vol 25 (12) ◽  
pp. 1099-1115 ◽  
Author(s):  
F.T.K. Au ◽  
Y.S. Cheng ◽  
Y.K. Cheung ◽  
D.Y. Zheng
Keyword(s):  
Natural Frequencies ◽  
Mode Shapes ◽  
Cable Stayed Bridges

Vortex-Induced Vibration Characteristics of an Elastic Square Cylinder on Fixed Supports

2004 ◽  
Vol 127 (2) ◽  
pp. 241-249 ◽  
Author(s):  
Z. J. Wang ◽  
Y. Zhou
Keyword(s):  
Circular Cylinder ◽  
Vortex Shedding ◽  
Flow Separation ◽  
Natural Frequencies ◽  
Separation Point ◽  
Square Cylinder ◽  
Vortex Induced Vibration ◽  
The Third ◽  
Vortex Shedding Frequency ◽  
Shedding Frequency

The vortex-induced structural vibration of an elastic square cylinder, on fixed supports at both ends, in a uniform cross flow was measured using fiber-optic Bragg grating sensors. The measurements are compared to those obtained for an elastic circular cylinder of the same hydraulic diameter in an effort to understand the effect of the nature (fixed or oscillating) of the flow separation point on the vortex-induced vibration. It is found that a violent vibration occurs at the third-mode resonance when the vortex-shedding frequency coincides with the third-mode natural frequency of the fluid-structure system, irrespective of the cross-sectional geometry of the cylinder. This is in distinct contrast to previous reports of flexibly supported rigid cylinders, where the first-mode vibration dominates, thus giving little information on the vibration of other modes. The resonance behavior is neither affected by the incidence angle (α) of the free stream, nor by the nature of the flow separation point. However, the vibration amplitude of the square cylinder is about twice that of the circular cylinder even though the flexural rigidity of the former is larger. This is ascribed to a difference in the nature of the flow separation point between the two types of structures. The characteristics of the effective modal damping ratios, defined as the sum of structural and fluid damping ratios, and the system natural frequencies are also investigated. The damping ratios and the system natural frequencies vary little with the reduced velocity at α=0deg, but appreciable at α⩾15deg; they further experience a sharp variation, dictated by the vortex-shedding frequency, near resonance.

Interference Between Risers

2007 ◽  
Author(s):  
Ricardo Franciss ◽  
Andre´ Fujarra
Keyword(s):  
Degrees Of Freedom ◽  
Natural Frequencies ◽  
Maximum Amplitude ◽  
Elastic Base ◽  
Drag Coefficients ◽  
Vortex Induced Vibration ◽  
Two Degrees Of Freedom ◽  
Towing Tank ◽  
Lift And Drag ◽  
Made In

This article shows the results of the tests of interference between rigid risers, in relation of Vortex Induced Vibration (VIV), made in the Institute de Pesquisas Tecnolo´gicas do Estado de Sa˜o Paulo (IPT), Brazil. It was tested several conditions with different arrangements with two cylinders in tandem and side by side positions, with different distances between them. The models were installed in an elastic base with two degrees of freedom for each cylinder. The stiffness and the natural frequencies were calibrated to have the maximum amplitude of VIV within the possible range of velocities in the IPT towing tank. The final lift and drag coefficients were measured, for one cylinder with and without strakes and for two cylinders. All these data are used in Riser Analyses giving more real results in relation of VIV analysis, clashing and interference between risers.

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