• Wind and Structures
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• v.13 no.4
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• pp.363-374
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• 2010

Appropriate scaling methods for wind tunnel modelling of building internal pressures induced through a dominant opening were investigated. In particular, model cavity volume distortion and geometric scaling of the opening details were studied. It was found that while model volume distortion may be used to scale down buildings for wind tunnel studies on internal pressure, the implementation of the added volume must be done with care so as not to create two cavity resonance systems. Incorrect scaling of opening details was also found to generate incorrect internal pressure characteristics. Furthermore, the effective air slug or jet was found to be longer when the opening was near a floor or sidewall as evidenced by somewhat lower Helmholtz frequencies. It is also shown that tangential flow excitation of Helmholtz resonance for off-centre openings in normal flow is also possible.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2008.04a
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• pp.212-217
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• 2008

Acoustic noises generated during motor operation in mechanical system are from electromagnetic, mechanical, aerodynamic, and electrical sources. For identification of mechanical noise origins, misalignment, unbalance, fan shape, resonance, and vibration modes have been extensively considered to describe noise behavior. An experiment-based approach as well as a mathematical approach needs to be adopted for a realistic study into noise and vibration of the motor, because motor noise characteristics differ from type to type due to various noise sources. In this paper, a brushless DC motor for air-conditioner fan is analyzed by finite element method to identify noise source, and the analysis results are verified by experiments, and sensitivity analysis is performed by design of experiments.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.19 no.9
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• pp.863-869
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• 2009

Acoustic noises generated during motor operation in mechanical system are from electromagnetic, mechanical, aerodynamic and electrical sources. For identification of mechanical noise origins, misalignment, unbalance, fan shape, resonance, and vibration modes have been extensively considered to describe noise behavior. An experiment-based approach as well as a mathematical approach needs to be adopted for a realistic study into noise and vibration of the motor, because motor noise characteristics differ from type to type due to various noise sources. This paper analyzes noise characteristics of a brushless DC motor for air-conditioner fan, and proves that the test motor noise originates from acoustic modes of airspace in the motor. The motor noise sensitivity analysis by design of experiments reveals that the noise characteristics are closely related to switching frequency and frame thickness.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.10 s.181
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• pp.2413-2419
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• 2000

Harmonic resonances in a continuous rotating shaft with distributed mass are discussed. The restoring force of the shaft has geometric stiffening nonlinearity due to the extension of the shaft centerline. The effect of a distributed lateral force, such as the gravity, is assumed. The possibility of the occurrences of harmonic resonances, the shapes of resonance curves, and internal resonance phenomena are investigated.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.30 no.2 s.245
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• pp.171-178
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• 2006

Experimental and theoretical study of the non-planar response motions of a circular cantilever beam subject to base harmonic excitation has been presented in this paper work. Theoretical research is conducted using two non-linear coupled integral-differential equations of motion. These equations contain cubic linearities due do curvature term and inertial term. A combination of the Galerkin procedure and the method of multiple scales are used to construct a first-order uniform expansion for the case of one-to-one resonance. The results show that the non-linear geometric terms are very important for the low-frequency modes of the first and second mode. The non-linear inertia terms are also important for the high-frequency modes. We present the quantitative and qualitative results for non-planar motions of the dynamic behavior.

• Proceedings of the KSME Conference
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• 2008.11a
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• pp.1767-1772
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• 2008

A microcantilever is a well-known MEMS structure for sensing bio-chemical molecules. When bio-chemical molecules are adsorbed on the microcantilever's surface, resonance frequency shift is generated. There are two issues in this phenomena. The first one is which one between mass change and surface stress change effects is more dominant on the resonance frequency shift. The second one is what will be the performance change when the boundary condition is changed from cantilevers to double clamped beams. We have studied the effect of surface stress change and compared it with that of mass change by using FEM analysis. Furthermore, for microstructures having different boundary conditions, we have studied Q-factor, which determines the detection limit of micro/nano mechanical sensors.

• Journal of Aerospace System Engineering
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• v.13 no.5
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• pp.9-15
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• 2019

In this paper, dynamic analysis of a nonlinear active vibration absorber is conducted with a time delay acceleration feedback to suppress the vibration of a nonlinear single degree of freedom primary system. The primary system consisting of linear and nonlinear cubic springs, mass, and damper is subjected to the multi-harmonic hard excitation with a parametric excitation. It is proposed to reduce the vibration of the primary system and the absorber by using a lead zirconate titanate (PZT) stack actuator in series with a spring in the absorber which configures as an active vibration absorber. The method of multiple scales (MMS) is used to obtain the approximate solution of the system under the internal resonance, subharmonic, superharmonic, and principal parametric resonance conditions simultaneously. Frequency and time responses of the system are investigated considering a delay in the feedback for the various parameters of the absorber configuration and controlling force.

• Interaction and multiscale mechanics
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• v.3 no.2
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• pp.111-121
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• 2010

Dynamic analysis of nano/micro bio-sensors based on a multiscale atomistic/continuum theory is introduced. We use a generalized atomistic finite element method (GAFEM) to analyze a bio-sensor which has $3{\times}N_a{\times}N_p$ degrees of freedom, where $N_p$ is the number of representative unit cells and $N_a$ is the number of atoms per unit cell. The stiffness matrix is derived from interatomic potential between pairs of atoms. This work contains two studies: (1) the resonance analysis of nano bio-sensors with different amount of target analyte and (2) the dependence of resonance frequency on finite element mesh. We also examine the Courant-Friedrichs-Lewy (CFL) condition based on the highest resonance frequency. The CFL condition is the criterion for the time step used in the dynamic analysis by GAFEM. Our studies can be utilized to predict the performance of micro/nano bio-sensors from atomistic perspective.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.45 no.4
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• pp.328-341
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• 2017

In the control actuator system of a launch vehicle based on thrust vectoring, the interaction between electro-mechanical position servo and inertial load are combined with the dynamic characteristics of the flexible vehicle support to generate synthetic resonance. This occurred resonance is fed back to the attitude control system and can influence stability of launch vehicle. In this study, we proposed a simulation model to analyze synthetic resonance of electro-mechanical actuation system for thrust vector control and explained the results of simulation and test using dynamic force feedback control which improves dynamic characteristics of servo actuation system by reducing synthetic resonance.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.21 no.7
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• pp.21-27
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• 2022

This study was conducted to evaluate the structural stability of a CNC automatic lathe structure and avoid resonance. The analysis conditions were analyzed by applying the weight of the upper assembly. From the structural analysis, the stress and deformation were low, and the safety factor was high. From the dynamic characteristic analysis, it was determined that resonance does not occur because the natural frequency is outside the driving range. The error between the dynamic characteristic analysis and vibration test results is very low; thus, the reliability of the analysis results can be secured.