Papers by Keyword: Flow-Induced Vibration

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Authors: Wei Wei, Hao Ren
Abstract: The best is to read these instructions and follow the outline of this text. The physical and numerical models were combined to analyze flow-induced vibration response of Qingshuihe River underwater horizontal gate in this paper; the pressures acting on the gate were divided into two parts: the fluctuating pressure of flow on the stationary gate and the hydrodynamic pressure caused by the gate vibration, which is additional pressure induced by disturbed flow. The temporal-spatial correlation of fluctuating pressures obtained by model experiments between different nodes was analyzed. In the study the coherence function is defined in frequency domain with consideration of different levels of correlation for different frequency components, and the nodal load of the fluctuating pressure could be obtained. A new distribution of additional mass with considering radial vibration of the gate is adopted as equivalent hydrodynamic pressure. Based on random vibration theory, the flow-induced vibration response of the gate was obtained. The results provide the reliable reference evidence for structural dynamic design of the gate and show that the hydrodynamic stability of the gate can meet the requirement. On the other hand, it is shown that this method is reasonable and feasible.
Authors: Dong Seok Oh, Young Ho Lee, Chang Hwan Shin, Tae Hyun Chun, Hyung Kyu Kim, Kye Bock Lee
Abstract: A new device for measuring an acceleration in a fuel rod has been developed. The primary purpose is to apply it to the experiments for a nuclear fuel fretting, which is caused by a fuel rod and grid interaction due to a flow-induced vibration of the rods. A bi-axial accelerationdetecting device of a cylindrical shape for an insertion into a cladding tube is designed. Two unimorph piezoelectric accelerometers of small size and for special use in a high temperature condition were attached to the housing’s inner wall of the mounting device, which were oriented perpendicularly with each other to accommodate the acceleration signal during a fretting. Verification is carried out by a displacement and a frequency response analysis. The verification results of the bi-axial acceleration-detecting device showed a good response for the amplitude and bi-directional trace. This paper mainly presents the detailed design of the bi-axial accelerationdetecting device which is developed by using the design optimization of a cylindrical type and applying it to the lower and upper plugs to sustain the device in the tube wall. The verification is carried out by a displacement analysis and a frequency response analysis. An elaboration of the development procedure, calibration method and results are also given in this paper.
Authors: Wan Fu Zhang, Jian Gang Yang, Hao Cao, Rui Guo, Dan Sun
Abstract: This paper sets up a dynamic analysis model for cylinder-seal system. A new identification method for fluid-induced force and stiffness coefficients in eccentric seal is presented. The study shows that the system stability decreases with increasing cross-coupled stiffness in a certain range. Beyond this range, the system will be destabilized. Influences of rotating speed, inlet pressure, eccentricity and clearance on fluid-induced force were tested in the rig. It was found that a large tangential fluid-induced force was produced in the direction perpendicular to the eccentric displacement of rotor. The difference between the tangential and radial fluid-induced force became larger and larger with the increasing rotating speeds. Under the action of the seal force, the logarithmic decrement descended with increasing rotating speeds, and the stability of the system decreased. These effects became more and more serious for higher inlet pressure and tighter clearance.
Authors: Kang Hee Lee, Heung Seok Kang, Kyung Ho Yoon, Kee Nam Song
Abstract: A 5x5 partial fuel assembly was used for a comparative design evaluation test of a newly developed spacer grid from a mechanical/hydraulic vibration aspect. Axial flow pattern along this rod bundle in the test was very complex due to the intermediate spacers and the mixing vane; Understanding of this flow field of a dynamic pressure is a preliminary step for a theoretical analysis of a vibratory behavior of a partial fuel assembly. Since a fluctuating pressure induced by the randomly-varying flow turbulence cannot be accurately predicted by an analysis alone, it has to be measured directly on the surface over the rod or in an accessible vicinity of the bundle. In this study, the fluctuating pressure acting on a partial fuel assembly with a spacer grid and a mixing vane was measured. The measured PSD showed different spectral features from the results of the literatures and had a series of periodic pulsations with sidebands over the specific frequency ranges; it is believed that the periodic components in the PSD have to do with the design of the spacer grid and the mixing vane. And, the exciting force function for the theoretical analysis of a partial fuel assembly with spacers and a mixing vane was estimated as a possible PSD form.
Authors: Chen Quan Hua, Hua Wei Pan, Yan Feng Geng, Lan Chang Xing
Abstract: Flow-induced vibration occurs widely in flow pipelines, and pipeline vibration signals have various frequency characteristics corresponding to different flow regimes. Therefore, an novel noninvasive approach to flow regime identification for wet gas flow in a horizontal pipeline is presented in this paper. The vibration signals were collected by a transducer installed on external wall of pipeline. Empirical mode decomposition (EMD) was used to decompose the vibration signal into different intrinsic mode functions (IMFs), and then the kurtosis of each IMF component for each experimental data was calculated. Finally, the IMF kurtosis feature vector was input to the support vector machine (SVM) to identify three typical flow regimes for wet gas flow including stratified/stratified wavy flow, annular/annular mist flow and slug flow in a horizontal pipeline 50 mm in diameter. The experimental results show that the proposed approach can identify flow regimes effectively, and the identification rate is 80.6%.
Authors: Norio Arai, Kota Fujimura, Yoko Takakura
Abstract: When a bluff body is located in a uniform flow, the flow is separated and vortices are formed. Consequently, the vortices cause “flow-induced vibrations”. Especially, if the Strouhal number and the frequency of the body oscillation coincide with the natural frequency, the lock-in regime will occur and we could find the large damages on it. Therefore, it is profitable, in engineering problems, to clarify this phenomenon and to suppress the vibration, in which the effect of elastic walls on the suppression is focused. Then, the aims of this article are to clarify the oscillatory characteristics of the elastic body and the flowfield around the body by numerical simulations, in which a square pillar with elastic walls is set in a uniform flow. Two dimensional incompressible flows are solved by the continuity equation, Navier-Stokes equation and the Poisson equation which are derived by taking divergence of Navier-Stokes equation. Results show that a small deformation of elastic walls has a large influence on the body motion. In particular, the effect is very distinct at the back.
Authors: Li Hong Zhang, Tian Yun Liu, Qing Bin Li, Xiao Ning Lyu
Abstract: The flow-induced micro-vibration in Shuifu County Town near Xiangjia Dam is studied in this paper. First the characteristics of the micro-vibration are investigated based on the in situ measurement, and then the dynamic property of the still basin which is thought to be the vibration source is analyzed with the effect of fluid-structure interaction (FSI) considered. Finally, the reason of the micro-vibration in Shuifu county town is discussed and several possible engineering suggestions for vibration reduction are also proposed.
Authors: Xin Wang, Shao Ze Luo
Abstract: In order to study the flow-induced vibration of the spillway tunnel working gate of one reservoir, hydraulic model test with scale 1:20 was conducted to obtain the dynamic pressure characteristics on the working gate. Experiment modal analysis method was employed to identify the structure dynamic characteristics through the 1:10 working gate mode test. The 3D FEM model of the gate was built to simulate the vibration response of the structure. The research showed the low order modal frequencies of the working gate were not fully breaking away from the high energy zone of the dynamic water, which would induce severe vibration. The vibration response of the gate became the biggest when it was operating at 0.5 partial opening.
Authors: Seop Hur, S.H. Nam, Dai Bum Cha, Seung Hwan Seong, Won Man Park, Jung Taek Kim, Jae Young Nam, Sang J. Lee
Authors: Y.C. Su, Pei Qi Ge, K. Yan
Abstract: The characteristic of flow-induced vibration and heat transfer of a cylinder with elastic supporting in two-dimensional fluid flow was numerically investigated by Workbench and CFX software. The numerical results show that, in the same conditions, the greater elastic support stiffness of the cylinder is ,the greater the value and range of fluid speed where the vortex-induced vibration of a circular occurs; With the same elastic support stiffness, the frequency and amplitude of flow-induced cylinder vibrating along transverse direction are much greater than that of in in-line direction(longitudinal direction), and the value and range of fluid speed where the vortex-induced vibration along longitudinal direction of a cylinder occurs is much smaller than that of along transverse direction. When the max vibration velocity of cylinder is much less than the flow speed, the flow-induced cylinder vibration can not reach the effect of heat transfer enhancement.
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