Damping Characteristics of Fairings for Suppressing Vortex-Induced Vibrations

2004 ◽  
Author(s):  
Li Lee ◽  
Don W. Allen ◽  
Dean L. Henning ◽  
Doug McMullen
Keyword(s):  
Wave Attenuation ◽  
Analytical Models ◽  
Superposition Method ◽  
Test Configuration ◽  
Function Solution ◽  
Mode Superposition Method ◽  
Flexible Pipes ◽  
Vortex Induced Vibrations ◽  
Vibration Responses ◽  
Quantitative Manner

Vortex-induced vibration (VIV) tests have been performed on long, flexible pipes with fairings in sheared flows in a circular towing tank at prototype Reynolds numbers for production risers [1]. It is discovered that there existed strong attenuation of the vibration responses for the test configuration with fairings placed in the strong current zone, compared to the pipe configuration without any fairings. Wave attenuation is typical when waves travel in systems with dissipation. Strong attenuation is an indication of large damping. Additional pluck tests of pipes with fairings in still water were conducted to determine damping in the system in a quantitative manner. The results, though scattered, provide evidence on the level of damping that could exist in structures with fairings. Furthermore, analytical models based on a Green’s function solution and mode superposition method for a taut string were also used to complement experimental data. A range of damping values was considered to find the damping value for which the level of attenuation matched that of the experiments. It is found that this damping value is close to that from the tests.

scholarly journals Transient Response of Bridge Piers to Structure Separation under Near-Fault Vertical Earthquake

2021 ◽  
Vol 11 (9) ◽  
pp. 4068
Author(s):  
Wenjun An ◽  
Guquan Song
Keyword(s):  
Large Scale ◽  
Bending Moment ◽  
Relative Displacement ◽  
Superposition Method ◽  
Longitudinal Displacement ◽  
Transient Wave ◽  
Vibration Period ◽  
Vertical Excitation ◽  
Mode Superposition Method ◽  
Main Girder

Given the possible separation problem caused by the double-span continuous beam bridge under the action of the vertical earthquake, considering the wave effect, the transient wave characteristic function method and the indirect mode superposition method are used to solve the response theory of the bridge structure during the earthquake. Through the example analysis, the pier bending moment changes under different vertical excitation periods and excitation amplitudes are calculated. Calculations prove that: (1) When the seismic excitation period is close to the vertical natural vibration period of the bridge, the main girder and the bridge pier may be separated; (2) When the pier has a high height, the separation has a more significant impact on the longitudinal displacement of the bridge, but the maximum relative displacement caused by the separation is random; (3) Large-scale vertical excitation will increase the number of partitions of the structure, and at the same time increase the vertical collision force between the main girder and the pier, but the effect on the longitudinal displacement of the form is uncertain; (4) When V/H exceeds a specific value, the pier will not only be damaged by bending, but will also be damaged by axial compression.

scholarly journals Structural and Acoustic Responses of a Submerged Stiffened Conical Shell

2014 ◽  
Vol 2014 ◽  
pp. 1-14 ◽  
Author(s):  
Meixia Chen ◽  
Cong Zhang ◽  
Xiangfan Tao ◽  
Naiqi Deng
Keyword(s):  
Conical Shell ◽  
Element Model ◽  
Analytical Models ◽  
Superposition Method ◽  
Far Field ◽  
Fluid Loading ◽  
Low Frequencies ◽  
Structural Responses ◽  
The Individual ◽  
Field Sound

This paper studies the vibrational behavior and far-field sound radiation of a submerged stiffened conical shell at low frequencies. The solution for the dynamic response of the conical shell is presented in the form of a power series. A smeared approach is used to model the ring stiffeners. Fluid loading is taken into account by dividing the conical shell into narrow strips which are considered to be local cylindrical shells. The far-field sound pressure is solved by the Element Radiation Superposition Method. Excitations in two directions are considered to simulate the loading on the surface of the conical shell. These excitations are applied along the generator and normal to the surface of the conical shell. The contributions from the individual circumferential modes on the structural responses of the conical shell are studied. The effects of the external fluid loading and stiffeners are discussed. The results from the analytical models are validated by numerical results from a fully coupled finite element/boundary element model.

Experimental Study on Flexible Bare Pipe Arrays Undergoing Vortex-Induced Vibrations

2018 ◽  
Author(s):  
Y. Liu ◽  
C. Shi ◽  
Z. Liu ◽  
J. Wang ◽  
X. Bao
Keyword(s):  
Fatigue Damage ◽  
Dynamic Responses ◽  
Array Configuration ◽  
Damage Rate ◽  
Flexible Pipes ◽  
Vortex Induced Vibrations ◽  
Helical Strakes ◽  
Preliminary Study ◽  
Single Pipe ◽  
Center Distance

Vortex-induced vibration (VIV) excited by current is a major contributor to the fatigue accumulation of marine risers. For deepwater operations, several risers are often arranged together in an array configuration. In this study, a set of four identical flexible pipes of a rectangular arrangement were tested in a water tunnel. By comparing the dynamic responses of a pipe in an array with that of a single isolated pipe, the effects of the current speed and the center-to-center distance between the up-stream and downstream pipes on their dynamic responses were investigated. Fatigue damages accumulated on each pipe in an array was calculated and a factor, termed “fatigue damage amplification factor”, was defined as a ratio between the fatigue damage rate of pipe in an array and the fatigue damage rate of a single pipe at a same current condition. The results showed that for bare pipes (i.e., without helical strakes), the downstream pipes in an array configuration may have larger dynamic responses and fatigue damage rates than those of a single pipe; and, it is not always conservative to assume that the fatigue damage rate estimated for a single pipe can be used to represent the fatigue damage rates of pipes in an array. This preliminary study provided some meaningful results for the design, analysis and operation of marine riser arrays.

scholarly journals Identification of Acoustic-Vibratory System by Acoustic Measurement

1996 ◽  
Vol 3 (1) ◽  
pp. 27-37
Author(s):  
Takuzo Iwatsubo ◽  
Shozo Kawamura ◽  
Masahito Kamada
Keyword(s):  
Inverse Analysis ◽  
Coefficient Matrix ◽  
Superposition Method ◽  
Vibration Modes ◽  
Identification Problems ◽  
Mathematical Property ◽  
Vibratory System ◽  
Stochastic Error ◽  
Mode Superposition Method ◽  
Ill Conditioning

A new method for reducing ill-conditioning in a class of identification problems is proposed. The key point of the method is that the identified vibration of the sound source is expressed as a superposition of vibration modes. The mathematical property of the coefficient matrix, the practical error expanding ratio, and the stochastic error expanding ratio are investigated in a numerical example. The mode-superposition method is shown to be an effective tool for acoustic-vibratory inverse analysis.

scholarly journals Dynamic Impact Factor Determination of an Existing Pre-stressed Concrete I-Girder Bridge Using Vehicle-Bridge Interaction Modelling

2021 ◽  
Vol 10 (3) ◽  
pp. 163-176
Author(s):  
Shuvrodeb Adhikary ◽  
Shohel Rana ◽  
Jerin Tasnim ◽  
Nazrul Islam
Keyword(s):  
Impact Factor ◽  
Dynamic Model ◽  
Superposition Method ◽  
Dynamic Impact ◽  
Mode Superposition Method ◽  
Road Roughness ◽  
Girder Bridge ◽  
Dynamic Impact Factor ◽  
Interaction Problem

The dynamic Impact Factor (IM) of a bridge is influenced by many factors, including Vehicle-Bridge Interaction (VBI), vehicle speed and road roughness. This paper represents the dynamic effects of moving vehicles and the determination of IM of an existing Pre-stressed concrete I-girder bridge utilizing VBI modeling. Evaluation of the IM is expected to provide valuable information for condition assessment and management of the existing bridge. The interaction problem between the vehicle and the bridge includes a dynamic model for the bridge structure subsystem, a dynamic model for the vehicle subsystem, interaction constraints, road roughness modelling and numerical solution techniques for the dynamic systems. The Half-car model is utilized for modelling of the vehicle dynamics and the bridge dynamic model is idealized according to Finite Element Method (FEM). Then FEM along with the mode superposition method are utilized for determining the Equation of Motion (EOM) for the bridge subsystem. D’Alembert’s principle is used for developing EOM for the vehicle subsystem. The interaction between vehicle vibration and bridge vibration is established through the contact forces between the wheels and the bridge by employing the compatibility relationship between the contact points and by applying the static equilibrium condition. Lastly, Newmark’s-β method is used for solving the coupled mathematical model of the vehicle and bridge interaction problem to determine the responses of the two sub-systems. The whole procedure is then performed for different vehicle speeds and various bridge deck surface roughness conditions to determine the dynamic impact on the existing I-girder bridge named Teesta Bridge located in Bangladesh.

Investigation into the linear velocity response of cantilever beam embedded with impact damper

2019 ◽  
Vol 25 (7) ◽  
pp. 1365-1378 ◽  
Author(s):  
Yiqing Yang ◽  
Xi Wang
Keyword(s):  
Cantilever Beam ◽  
Continuous System ◽  
Linear Velocity ◽  
Superposition Method ◽  
Momentum Exchange ◽  
Impact Damper ◽  
Mode Superposition Method ◽  
Velocity Response ◽  
The Impact ◽  
Nonlinear Velocity

The impact damper causes momentum exchange between the primary structure and impact mass, and achieves vibration attenuation through repeated collisions. A cantilever beam embedded with the impact damper is modeled in the form of a continuous system, and the equations of motion are formulated based on the mode superposition method. The mechanism of the impact damper is investigated, and linear velocity response is achieved by a proper selection of a mass ratio of 8.4%, clearance within 0.30 mm, and excitation force ranged from 3.2 N to 5.5 N. The reverse collision has higher damping than co-directional collision, based on which a new criterion of response regimes is proposed for the design of the impact damper. The velocity responses of the damped cantilever beam under sinusoidal and impulse excitation are simulated and verified via the sinusoidal sweep experiments. The velocity amplitudes of the damped cantilever beam are linearly decreased when the clearance is increased within 0.30 mm. Finally, linear and nonlinear velocity responses of the damped cantilever beam are discussed. It is found that the nonlinear velocity response reaches larger damping, but that a strongly modulated response exists.

scholarly journals Wave absorption control in the new designed photonic metamaterials with artificial opal

2018 ◽  
Vol 178 ◽  
pp. 04004 ◽  
Author(s):  
Daniela Ionescu ◽  
Gabriela Apreotesei
Keyword(s):  
Magnetic Field ◽  
Ferromagnetic Resonance ◽  
Wave Attenuation ◽  
Control Process ◽  
Inclusion Size ◽  
Test Configuration ◽  
Wave Absorption ◽  
Artificial Opal ◽  
Spatial Dimensions ◽  
Microwave Electronic

Photonic metamaterials consisting of artificial opal with magnetic inclusions were considered, used in controllable microwave electronic devices. The analyzed structures consist of matrices of SiO2 nanospheres (diameter 200 - 400 nm) with included clusters of ferrite spinels (MnxCo0.6-xZn0.4Fe2O4, NixCo0.6-xZn0.4Fe2O4, LaxCo0.6-xZn0.4Fe2O4, NdxCo0.6-xZn0.4Fe2O4) in interspherical nanospacing (4 ÷ 7% concentration). The ellipsoidal clusters are polycrystalline, with spatial dimensions of 20 – 30 nm and grains of 5 – 12 nm. A controlled wave absorption was obtained in these high inductivity structures. Evolution of the wave attenuation coefficient, α[dB/m], in function of the applied magnetic field and particle inclusion size, for different content of the magnetic ions in the ferrite inclusion, have been determined at frequencies around the samples ferromagnetic resonance, by structural simulation. The test configuration was: sample inside the rectangular waveguide, mode TE10, in the frequency range 24 ÷ 40 GHz. The polarizing magnetic field for the ferrites was tested in the range of 0 ÷ 20 kOe and minimized by modifying the structure. The metamaterial design optimization was realized, controllable by different parameters at structure level. The ferromagnetic resonance influence on the control process was pointed out and also the particular results and effects which can be induced by the resonant behavior.

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