• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 2007.11a
• /
• pp.7-12
• /
• 2007

Previously study on structural design of the main wing of the twenty-seat class WIG (Wing in Ground Effect) craft. In the final design, three spars construction was selected for safety in the critical flight load, and the Carbon-Epoxy material was selected for lightness and structural stability. In this study, the forced vibration analysis was performed on the composite main wing structure of the twenty-seat class WIG craft with two-stroke pusher type reciprocating engine. The vibration analysis based on the finite element method was performed using a commercial FEM code, MSC/NASTRAN. Excitations for the frequency response analysis were assumed as the Y-mode (lateral mode), the Z-mode (vertical mode) and the $M_{xyz}$-mode (twisted mode) which are typical main vibration modes of engine. And excitations for the transient response analysis were assumed as the X-mode (longitudinal mode) with the oscillating propeller thrust which occurs in operation.

• Journal of Biosystems Engineering
• /
• v.12 no.4
• /
• pp.9-15
• /
• 1987

The vibrational characteristics of a radial-ply (155SR13 4PR) and a biased-ply tire (6.15-134PR) were investigated for examining the effects of tires with different structure on the ride characteristics of the vehicle. The natural frequencies at the tread band, mode shapes, and damping factors of two tires at the state of plane vibration were determined experimentally. The test work was performed at four levels of the inflation pressure, ranging from 171.7 kPa to 245.2 kPa, and three levels of the vertical load, deviating by 10% from the standard load designated by the Department of Transportation of the United States of America. The following results were drawn by the analysis of the test results: 1. The first-order natural frequencies of the radial-ply and the biased-ply tires at the tread band were 112 Hz and 159 Hz, respectively, at the state o f the free vibration when the inflation pressure of 196.2 kPa was applied. It was known that the biased-ply tire has higher resonant frequency than the radial-ply tire and the natural frequencies of the both tires move to the high frequency range as t he inflation pressure is increased. 2. The vibration modes of both tires were quite different. No big difference in mode shapes was examined as the inflation pressure was increased. But the natural frequencies of two tires were changed. For the radial-ply tire, no difference in mode shape was found whether the vertical load was applied or not. But a significant difference in mode shape was examined for the biased-ply tire. 3. Any difference was not found in damping factor as the different inflation pressures were applied. 4. When no vertical load was applied, damping factors of the radial-ply and biased-ply tire at the state of the natural vibration ranged from 2.6 to 5.9%, and from 4.1 to 7.8%, respectively. It was estimated that the radial-ply tire would have better cushioning than the biased-ply tire since the vertical spring rate of the radial-ply tire was much less than that of the biased-ply tire, even though the damping effect of the radial-ply tire was smaller than that of the biased-ply tire.

• The Transactions of The Korean Institute of Electrical Engineers
• /
• v.66 no.12
• /
• pp.1852-1865
• /
• 2017

The vibration of the structures with restrained motion has long been observed in various engineering fields. When the motion of vibrating structure is restrained due to the adjacent objects, the frequencies and the mode shapes of the structure change and its vibration characteristics becomes unpredictable, in general. Although the importance of the study on this type of vibration model increases in many engineering areas, most studies conducted so far are limited to the theoretical study on dynamic responses of the structure with stops, including some experimental works. Specially, the study on the nonlinear phenomena due to the impact between the structure and the stops have been mainly performed theoretically. In the paper, both numerical analyses and experiments are conducted to study the chaotic vibration characteristics of the nonlinear motion and the dynamic response of a cantilevered beam which has restrained motion at the free end by the stops. Results are presented for various magnetic forces and gaps between the beam and stops. The conclusions are as follows : Firstly, Numerical simulation results have a good agreement with experimental ones. Secondly, the effect of higher modes of beams are increased with increasing magnitude of exciting force, and displacement and velocity curves become more complicated shapes. Thirdly, nonlinear characteristics tend to appear greatly with increasing magnitude of exciting force, and fractal dimension is increased.

• Smart Structures and Systems
• /
• v.13 no.2
• /
• pp.281-303
• /
• 2014

In order to suppress the wind-induced vibrations of the Canton Tower, a pair of active mass driver (AMD) systems has been installed on the top of the main structure. The structural principal directions in which the bending modes of the structure are uncoupled are proposed and verified based on the orthogonal projection approach. For the vibration control design in the principal X direction, the simplified model of the structure is developed based on the finite element model and modified according to the field measurements under wind excitations. The AMD system driven by permanent magnet synchronous linear motors are adopted. The dynamical models of the AMD subsystems are determined according to the open-loop test results by using nonlinear least square fitting method. The continuous variable gain feedback (VGF) control strategy is adopted to make the AMD system adaptive to the variation in the intensity of wind excitations. Finally, the field tests of free vibration control are carried out. The field test results of AMD control show that the damping ratio of the first vibration mode increases up to 11 times of the original value without control.

• Wind and Structures
• /
• v.38 no.3
• /
• pp.215-229
• /
• 2024

Guyed mast structures exhibit characteristics such as high flexibility, low mass, small damping ratio, and large aspect ratio, leading to a complex wind-induced vibration response mechanism. This study analyzed the time- and frequency-domain characteristics of the wind-induced response of a guyed mast structure using measured acceleration response data obtained from the Shenzhen Meteorological Gradient Tower (SZMGT). Firstly, 734 sets of 1-hour acceleration samples measured from 0:00 October 1, 2021, to 0:00 November 1, 2021, were selected to study the vibration shapes of the mast and the characteristics of the generalized extreme value (GEV) distribution. Secondly, six sets of typical samples with different vibration intensities were further selected to explore the Gaussian property and modal parameter characteristics of the mast. Finally, the modal parameters of the SZMGT are identified and the identification results are verified by finite element analysis. The findings revealed that the guyed mast vibration shape exhibits remarkable diversity, which increases nonlinearly along the height in most cases and reaches a maximum at the top of the tower. Moreover, the GEV distribution characteristics of the 734 sets of samples are closer to the Weibull distribution. The probability distribution of the structural wind vibration response under strong wind is in good agreement with the Gaussian distribution. The structural response of the mast under wind loading exhibits multiple modes. As the structural response escalates, the first three orders of modal energy in the tower display a gradual increase in proportion.

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 2005.06a
• /
• pp.653-656
• /
• 2005

This paper introduces design, fabrication and experiment process of a novel scanner for the high speed AFM(Atomic Force Microscope). A proper design modification is proposed through analyses on the dynamic characteristics of the existing linear motion stages using a dynamic analysis program, Recurdyn. Since the scanning speed of each direction is allowed to be different, the linear motion stage for the high-speed scanner of AFM can be so designed to have different resonance frequencies for the modes with one dominant displacement in the desired directions. One way to achieve this objective is to use one-direction flexure mechanism for each direction and to mount one stage for fast motion on the other stage for slow motion. This unsymmetrical configuration separates the frequencies of the two vibration modes with one dominant displacement in each desired direction, hence, the coupling between the motions in the two directions. In addition, a pair of actuators is used for each axis to decrease the cross talks in the two motions and gives a force large enough to actuate the slow motion stage, which carries the fast motion stage. After these design modifications, a novel scanner with scanning speed higher than 10 Hz can be achieved to realize undistorted images in the high speed AFM.

• Journal of Ocean Engineering and Technology
• /
• v.8 no.1
• /
• pp.144-153
• /
• 1994

An algorithm to locate and estimate severity of damage in jacket-type offshore structures for which modal responses are availabit' for very few vibrational modes is presented. First, a theory of damage locaization and severity estimation(which yields information on the location and severity of damage directly from changes in mode shapes) is formulated. Next, the feasibility the damage detection algorithm is demonstrated by using a numerical example of an offshore jacket platform for which only three vibration modes are measured. Form the material presented here, two major results are observed. First, all damage locations in the offshore jacket platform are correctly predicted. Next, predicted damage is relatively correctly estimated.

• Journal of the Earthquake Engineering Society of Korea
• /
• v.7 no.1
• /
• pp.65-72
• /
• 2003

The objective of this study is to estimate the frequency characteristics of group walking loads based on the information of measured responses. At first, dynamic properties such as natural frequencies and modes are obtained from input/output relation for building structures by heel drop test. Second, a method to estimate group walking loads by the transfer functions from measured responses to group walking loads is proposed. The method turned out to estimate the group walking loads accurately. Higher modes could be important in estimating the amplitude of group walking loads with the information of single walking load.

• Advances in aircraft and spacecraft science
• /
• v.6 no.6
• /
• pp.515-528
• /
• 2019

The structural vibrations of a flat plate induced by fluctuating wall pressures within wall-bounded transonic jet flow downstream of a high-aspect ratio rectangular nozzle are simulated. The wall pressures are calculated using Hybrid RANS/LES CFD, where LES models the large-scale turbulence in the shear layers downstream of the nozzle. The structural vibrations are computed using modes from a finite element model and a time-domain forced response calculation methodology. At low flow speeds, the convecting turbulence in the shear layers loads the plate in a manner similar to that of turbulent boundary layer flow. However, at high nozzle pressure ratio discharge conditions the flow over the panel becomes transonic, and the shear layer turbulence scatters from shock cells just downstream of the nozzle, generating backward traveling low frequency surface pressure loads that also drive the plate. The structural mode shapes and subsonic and transonic surface pressure fields are transformed to wavenumber space to better understand the nature of the loading distributions and individual modal responses. Modes with wavenumber distributions which align well with those of the pressure field respond strongly. Negative wavenumber loading components are clearly visible in the transforms of the supersonic flow wall pressures near the nozzle, indicating backward propagating pressure fields. In those cases the modal joint acceptances include significant contributions from negative wavenumber terms.

• Bulletin of the Society of Naval Architects of Korea
• /
• v.23 no.1
• /
• pp.23-32
• /
• 1986

By virtue of an application of the receptance method, simplified formulae to calculate natural frequencies of stiffened plates having a resiliently mounted or concentrated mass are obtained. Some numerical results are compared with those based on Lagrange's equation of motion and with experimental results. For the problem formulation the stiffened plate is reduced to an equivalent orthotropic plate, a resiliently mounted mass to a spring-mass system, and mode shapes of the plate are assumed with comparison functions consisting of Euler beam functions. The proposed formulae give results in good conformity to both numerical results based on Lagrange's equation of motion and experimental results for in-phase modes of the coupled system. For out-of-phase modes the conformity is assured only in case that the natural frequency of the attached system is less than a half of that the stiffened plate. It is also found that a resiliently mounted mass having its own natural frequency of about two or more times that of the stiffened plate can be reduced to a concentrated mass with assurance of a few percent error in the frequency.