Dynamic Characteristics of a Submerged, Flexible Cylinder Vibrating in Finite Water Depths

1992 ◽  
Vol 36 (02) ◽  
pp. 154-167
Author(s):  
A. Ergin ◽  
W. G. Price ◽  
R. Randall ◽  
P. Temarel
Keyword(s):  
Free Surface ◽  
Resonance Frequency ◽  
Water Depth ◽  
Dynamic Characteristics ◽  
Mode Shapes ◽  
Flexible Cylinder ◽  
Rigid Boundary ◽  
Fluid Structure ◽  
Resonance Frequencies ◽  
Theoretical Predictions

This paper presents experimental data and theoretical predictions of the dynamic characteristics (natural and resonance frequencies, mode shapes) of a flexible cylinder vibrating in air and at fixed positions below a free surface in water of finite depth. The flat-ended, thin cylindrical shell of overall length 1284 mm, external radius 180 mm, thickness 3 mm is made of mild steel. In the experiments, the shell was tethered (i) at 0.21, 0.23, and 0.68 m depths below the free surface in water of depth 1.6 m and (ii) at 0.25, 1.5, and 3.5 m depths in 4 m of water. The resonance frequency data recorded provide measures of the influences of free surface, cylinder position, rigid boundary, water depth, etc. occurring in the fluid-structure interaction process. The theoretical predictions are derived from a three-dimensional hydroelastic mathematical model which, through the calculations of the generalized fluid loadings, accounts for the influence of free surface and rigid boundaries, position of submerged cylinder, neutral buoyancy or, as in the present case, with tethers and buoyancy effects. An extensive comparison of results is included. The experimental restrictions of water depth, cylinder position, etc. and the fluid-structure interactions are assessed and illustrated through the calculated resonance frequency values.

Modal Test of Scaled-Down Reactor Internals in SMART Considering the Fluid-Structure Interaction

2011 ◽  
Author(s):  
Seungho Lim ◽  
Kyungrok Ha ◽  
Kyoung-Su Park ◽  
No-Cheol Park ◽  
Young-Pil Park ◽  
...  
Keyword(s):  
Dynamic Characteristics ◽  
Seismic Analysis ◽  
Fluid Structure Interaction ◽  
Mass Effect ◽  
Mode Shapes ◽  
Structural Dynamic ◽  
Fluid Structure ◽  
Structure Interaction ◽  
Standard Design ◽  
Reactor Internals

The System-integrated Modular Advanced ReacTor (SMART) is a small modular integral-type reactor for the seawater desalination and small-scaled power generation under development in Korea. Although the SMART is innovative reactor with a sensible mixture of the proven technology and advanced design features aimed at enhanced safety, there is no valid prototype which can specify the structural dynamic characteristics of reactor internals. Thus, extensive research for the technology verification and standard design approval are in progress. One of them is to perform the dynamic characteristics identification of reactor internals. Especially, it is focused on the added mass effect caused by the fluid-structure interaction because the reactor internals is submerged in the reactor coolant. The extracted dynamic characteristics such as the natural frequencies and the vibratory mode shapes can be used as the basis on further dynamic analysis, for example, seismic analysis and a postulated pipe break analysis.

Influence of Supports and Water Depths on Dynamic Characteristics of Aqueduct Structure

2011 ◽  
Vol 243-249 ◽  
pp. 4592-4595
Author(s):  
Xin Li Bai ◽  
Hai Li Su ◽  
Qian Pan
Keyword(s):  
Water Depth ◽  
Dynamic Characteristics ◽  
Mode Shape ◽  
Mode Shapes ◽  
Element Analysis ◽  
Characteristics Analysis ◽  
Simple Support ◽  
North Water ◽  
Completely Simple ◽  
Water Depths

In this paper, dynamic characteristics analysis is carried out for a large aqueduct of South-to-North Water Transfer Project using large finite element analysis software. Two kinds of connection supports are considered, namely elastic support and completely simple support. Six kinds of water depths are calculated by additional mass method: empty aqueduct, 1/4 water depth, 1/2 water depth, 3/4 water depth, designed water depth, full water depth. Results show that basin type rubber support strengthens the constraint to aqueduct, and strengthens the connection of aqueduct to pier, and also increases the system stiffness, therefore the natural frequency is higher than that of completely simple support; The influence of water to dynamic characteristics of the aqueduct is quite obvious, so water effect must be considered in computation; Water has no influence on the principal mode shapes of the aqueduct structure, i.e. the dry mode shape and the wet mode shape are similar in appearance.

On Wave Diffraction of a Two-Dimensional Moonpool in a Two-Layer Fluid in Finite Water Depth

2018 ◽  
Author(s):  
Xingyu Song ◽  
Xin Xu ◽  
Xinshu Zhang ◽  
Yunxiang You
Keyword(s):  
Free Surface ◽  
Resonance Frequency ◽  
Internal Wave ◽  
Wave Mode ◽  
Resonance Frequencies ◽  
Exciting Forces ◽  
Wave Exciting Forces ◽  
Free Surface Wave ◽  
Piston Mode ◽  
Wave Elevations

This paper studies the wave diffraction of a two-dimensional moonpool in a two-layer fluid in finite water depth by using a domain decomposition scheme and an eigenfunction matching method. The formulae of the wave exciting forces, the free surface and internal wave elevations at zero-frequency are derived. Numerical convergence has been assessed by repeating the computations for increasing values of the truncation orders. The present model has been validated by comparing a limiting case with a single-layer fluid case and the comparisons are in general satisfactory. Although the wave exciting forces and free surface wave elevations around resonance frequency are overestimated, the piston mode resonance frequency is well predicted. Two typical configurations with different moonpool widths are selected for computations in both free surface and internal wave modes. It is found that, the wave exciting forces, free surface and internal wave elevations in internal wave mode are much smaller than those in free surface wave mode. In addition, the wave exciting forces in internal wave mode attenuate to zero quickly as incident wave frequency increases. For moonpool with small width, only piston mode resonance can be observed. The piston mode resonance frequencies identified in free surface and internal wave modes are the same. The characteristics of piston mode resonance can also be observed in the horizontal and vertical wave exciting forces. Around the piston mode resonance frequency, the wave exciting forces reach their local maximums. It is revealed that, as moonpool width increases, the piston mode resonance frequency decreases. Meanwhile, it shows that more asymmetric and symmetric sloshing mode resonances appear alternately and occur at higher frequencies than the piston mode resonance. Moreover, the predicted sloshing mode resonance frequencies are compared with those estimated by a simple approximate formula.

Dynamic Characteristics Analysis of a Large Aqueduct

2011 ◽  
Vol 255-260 ◽  
pp. 1130-1133
Author(s):  
Bing Bai ◽  
Yu He Li ◽  
Xiao Shan Deng
Keyword(s):  
Seismic Design ◽  
Water Depth ◽  
Dynamic Characteristics ◽  
Natural Frequencies ◽  
Mode Shapes ◽  
Element Analysis ◽  
Characteristics Analysis ◽  
Practical Engineering ◽  
North Water ◽  
Dynamic Characteristics Analysis

By use of large finite element analysis software, dynamic characteristics analysis is carried out for an aqueduct in South-to-North Water Transfer Project. Westergaard method and Housner method are used respectively to simulate the water. The natural frequencies and mode shapes (wet) of the aqueduct structure are calculated under two kinds of water depths (designed water depth, half water depth). The results show that the influence of the water on the dynamic characteristics of the aqueduct is obvious. Natural frequencies decrease with the increases of the water depth. The distinction between the two methods was analyzed: Housner method is closer to the practical engineering because both the pulsation effect and the convection effect of the water are considered. The results and conclusions can be referenced for seismic design of large aqueduct.

scholarly journals Buckling and Vibration of Carbon Nanotubes Embedded in Polyethylene Polymers

2011 ◽  
Vol 148-149 ◽  
pp. 1016-1020
Author(s):  
Dai Shi ◽  
Quan Wang
Keyword(s):  
Carbon Nanotubes ◽  
Carbon Nanotube ◽  
Resonance Frequency ◽  
Molecular Mechanics ◽  
Dynamic Characteristics ◽  
Van Der Waals ◽  
High Strength ◽  
Van Der Waals Forces ◽  
Buckling Instability ◽  
Resonance Frequencies

The discovery of buckling instability and vibration of polyethylene/ carbon nanotube matrices is reported by molecular mechanics simulations. The research is aimed to acquire a high strength design of PE-CNT matrix with proper PE/CNT ratio as well as discovering the dynamic characteristics of the PE-CNT composites. The buckling strains and the resonance frequencies are found to decrease with an increase in the number of polyethylene chains in the polyethylene/carbon nanotube matrices. Van der Waals forces are collected to explain the relation of the PE chains to the buckling strain and the resonance frequency of the composites.

scholarly journals Study on dynamic characteristics of leaf spring system in vibration screen

2021 ◽  
pp. 146134842110229
Author(s):  
Jiacheng Zhou ◽  
Chao Hu ◽  
Ziqiu Wang ◽  
Zhengfa Ren ◽  
Xiaoyu Wang ◽  
...  
Keyword(s):  
Dynamic Characteristics ◽  
Vertical Direction ◽  
Maximum Amplitude ◽  
Exciting Force ◽  
Mode Shapes ◽  
Leaf Spring ◽  
Amplification Factors ◽  
Simulation And Experiment ◽  
Exciting Forces ◽  
Spring System

By studying dynamic characteristics of the leaf spring system, a new elastic component is designed to reduce the working load and to a certain extent to ensure the linearity as well as increase the amplitude in the vertical and horizontal directions in vibration screen. The modal parameters, amplitudes, and amplification factors of the leaf spring system are studied by simulation and experiment. The modal results show that the leaf spring system vibrates in horizontal and vertical directions in first and second mode shapes, respectively. It is conducive to loosening and moving the particles on the vibration screen. In addition, it is found that the maximum amplitude and amplification factor in the horizontal direction appear at 300 r/min (5 Hz) while those in the vertical direction appear at 480 r/min (8 Hz), which are higher than those in the disc spring system. Moreover, the amplitude of the leaf spring system increases proportionally with the increase of exciting force while the amplification factors are basically the same under different exciting forces, indicating the good linearity of the leaf spring system. Furthermore, the minimum exciting force occurs in the leaf spring system under the same amplitude by comparing the exciting force among different elastic components. The above works can provide guidance for the industrial production in vibration screen.

Split beam method for determining mode shapes of cantilever beams under multiple loading conditions

2021 ◽  
pp. 107754632110276
Author(s):  
Jun-Jie Li ◽  
Shuo-Feng Chiu ◽  
Sheng D Chao
Keyword(s):  
Operation Mode ◽  
Point Contact ◽  
Mode Shapes ◽  
Cantilever Beams ◽  
Loading Conditions ◽  
Mechanical Responses ◽  
Relative Contribution ◽  
Resonance Frequencies ◽  
Beam Method ◽  
Multiple Loading

We have developed a general method, dubbed the split beam method, to solve Euler–Bernoulli equations for cantilever beams under multiple loading conditions. This kind of problem is, in general, a difficult inhomogeneous eigenvalue problem. The new idea is to split the original beam into two (or more) effective beams, each of which corresponds to one specific load and bears its own Young’s modulus. The mode shape of the original beam can be obtained by linearly superposing those of the effective beams. We apply the split beam method to simulating mechanical responses of an atomic force microscope probe in the “dynamical” operation mode, under which there are a stabilizing force at the positioner and a point-contact force at the tip. Compared with traditional analytical or numerical methods, the split beam method uses only a few number of basis functions from each effective beam, so a very fast convergence rate is observed in solving both the resonance frequencies and the mode shapes at the same time. Moreover, by examining the superposition coefficients, the split beam method provides a physical insight into the relative contribution of an individual load on the beam.

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