• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.48 no.3
• /
• pp.167-174
• /
• 2020

A study of flow characteristics of supersonic fluidic oscillators with shared feedback channel inside was carried out. Unsteady CFD analysis were performed and the numerical results were validated by comparison with the experimental ones observed for the same operation conditions. It was found that the mass flow between individual oscillators through the shared feedback channel directly influenced on the oscillating flow mechanism inside the oscillator, and finally on the synchronization of the jet oscillations. It was also observed that the oscillator with shared feedback channel provided higher pressure loss as well as higher oscillation frequency as compared to the single oscillator of the same geometric shape.

• Computational Structural Engineering
• /
• v.7 no.4
• /
• pp.151-158
• /
• 1994

The free vibrations of thermally buckled, simply supported, symmetrically laminated, rectangular, and quasi-isotropic plates are investigated. The nonlinear postbuckling analysis is performed by the finite element method based on the first order shear deformable plate theory with the use of von Karman type nonlinear strains and the Duhamel-Newman type constitutive law. The postbuckling solutions are used to obtain free vibration responses of buckled plates. Several numerical examples for quasi-isotropic laminated plates are considered. The effects of width-to-thickness ratios and aspect ratios on the free vibration characteristics of buckled plates are investigated.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 1996.10a
• /
• pp.37-42
• /
• 1996

기계의 진동.소음은 환경요인과 함께, 기계의 정밀도 향상 및 고장진단과 관련, 기계공학의 중요분야이다. 특히, 전동기(motor)는 많은 기계의 동력원으로서 진동.소음의 1차적 원인을 제공하고 있어, 자체적으로도 저감되어야 함은 물론이며, 감속기등 전동기와 연결되어 사용되는 기계의 진동.소음 발생의 직접적인 원인을 제공하므로 전동기의 진동, 소음 특성은 보다 명확히 밝혀져야 한다. 전동기는 내부에 회전자와 고정자가 있는 회전 기계이면서, 전자기력에 의해 구동되는 전기기계이다. 따라서 축정렬불량(misalignment), 불평형(unbalance)등 기계적 요인과 함께, 고정자와 회전자 사이에 존재하는 공극(air-gap)에서 발생하는 전자기적 요인을 해석함으로써 전동기의 진동.소음의 원인을 밝혀볼 수 있다. 각 전동기에 따라 진동.소음의 크기 및 주파수 성분은 달라질 수 밖에 없으며, 특정 부위에 이상이 있는 경우, 전동기의 진동, 소음특성은 크게 달라지므로, 전동기의 진동, 소음에 관한 연구는 실험적 현상을 기초로 해야한다. 이에 본 연구에서는 전동기이 진동.소음을 규명하기 위해, 부하장치를 가진 전동기 구동 실험장치를 구성하여, 전동기 구동에 따른 진동.소음 신호를 획득, 분석함으로써 전동기에서 발생하는 진동,소음의 원인을 추정하였다.

• Aerospace Engineering and Technology
• /
• v.6 no.1
• /
• pp.35-44
• /
• 2007

In this study was made the flutter analysis for the export model of Firefly(Bandi-ho), the small canard aircraft. Stiffness model based on internal load generation finite element model was generated. Mass model based on the weight DB for weight control was generated. Aerodynamic model based on Doublet Lattice Method was generated. Preliminary flutter analysis was made. Based on it, major vibration modes are identified and experimentally obtained via the ground vibration test. The obtained normal mode frequencies were used to correlate the finite element model. Flutter analysis was made again and major flutter mechanisms were summarized. The most important flutter root was identified as a coupled root between rigid body roll mode and anti-symmetric wing pitching mode.

• The Journal of the Acoustical Society of Korea
• /
• v.42 no.2
• /
• pp.83-93
• /
• 2023

Trapezoidal corrugated plates are often treated as orthotropic plates to simplify the modelling of the corrugation. However, this simplification is not valid at high frequencies in which the localized vibration within the parts of corrugation takes place. In this study, the vibrational and acoustical characteristics of corrugated plates are investigated up to high frequencies by means of the wavenumber domain numerical approach. Based on the findings from this numerical analysis, an approximate method to predict vibro-acoustic characteristics of corrugated plates is proposed. This approximate model consists of four equivalent plates which can represent global and local behaviours of corrugated plates. The radiation efficiency of corrugated plates is predicted from the approximate model and validated through the comparison with those of the numerical method.

• Proceedings of the Acoustical Society of Korea Conference
• /
• spring
• /
• pp.301-306
• /
• 2004

자동차의 경음기는 보행자나 다른 차량에게 경고를 보내기 위해 필요한 장치로 너무 작은 소리를 내는 경우에는 경고를 전달할 수 없는 문제점이 생기고, 너무 큰 소리를 내는 경우에는 소음피해를 주게 된다. 경음기의 소리 크기 뿐만 아니라 음색 또한 무시할 수 없는 중요한 인자라 할 수 있는데 이것은 경고음에 대한 사람의 반응에 영향을 줄 뿐만 아니라 자동차에 대한 고객들의 감성적인 평가에 영향을 미치기 때문이다. 본 연구에서는 자동차용 디스크 타입 경음기의 특징을 이해하기 위해 진동 및 음향특성에 관한 실험을 수행하였고, 이를 기반으로 전자기적, 기계적인 힘의 상호관계를 바탕으로 FEM, BEM 등의 방법으로 해석하였으며, 경음기의 소음 진동 특성을 시뮬레이션하였다. 이를 바탕으로 경음기의 형상 인자와 경음기의 소음 특성간의 관계를 해석하여 진동판과 방사판의 형상에 따른 주파수 특성관계를 도출하였다.

• Journal of the Earthquake Engineering Society of Korea
• /
• v.10 no.5 s.51
• /
• pp.63-71
• /
• 2006

In seismic response analysis of building structures, the input ground accelerations have considerable effect on the nonlinear response characteristics of structures. The characteristics of soil and the locality of the site where those ground motions were recorded affect on the contents of earthquake waves. Therefore, it is difficult to select appropriate input ground motions for seismic response analysis. This study describes a generation of artificial earthquake wave compatible with seismic design spectrum, and also evaluates the nonlinear response spectra by the simulated earthquake motions. The artificial earthquake wave are generated according to the previously recorded earthquake waves in past earthquake events. The artificial wave have identical phase angles to the recorded earthquake wave, and their overall response spectra are compatible with seismic design spectrum with 5% critical viscous damping. Each simulated earthquake wave has a identical phase angles to the original recorded ground acceleration, and match to design spectra in the range of period from 0.02 to 10.0 seconds. The seismic response analysis is performed to examine the nonlinear response characteristics of SDOF system subjected to the simulated earthquake waves. It was concluded that the artificial earthquake waves simulated in this paper are applicable as input ground motions for a seismic response analysis of building structures.

• Computational Structural Engineering
• /
• v.5 no.4
• /
• pp.93-102
• /
• 1992

The design of reactor internals requires the accurate vibration characteristics of each component for subsequent dynamic structural response analyses. For Korean standard nuclear power plant some modifications on the Control Element Assembly shroud from the reference design have been made, Since the shroud is complex in geometry having an array of vertical round tubes and webs in a square grid pattern, and being tied down by preloaded tie rods into position, it is planned to perform a vibration measurement program consisting of both experimental and analytical modal studies upon that component. The shroud modal testing was performed on the low frequency global survey to measure the first several modes. The analysis using the finite element model was also performed for the as-tested conditions. The natural frequencies and mode shapes from both test and analysis have been acquired and compared to be in good agreement. It is concluded that finite element model generated is good enough to be used in the design for the dynamic response analysis under various loading conditions.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.38 no.8
• /
• pp.798-805
• /
• 2010

Whole composite structure small class (150kg) satellite, STSAT-3, was initially developed in Korea. The structure does have aluminum frames that support the structure, and it is composed of only composite sandwich panels. A number of electronic boxes and mechanical apparatus will be shielded within the compartments built up by the composite panels. This study focused on the random vibration responses of the satellite. For this objective, vibration tests and analyses have been successfully performed with respect to STM (structure and thermal model) of the satellite. Additionally, through the experiment and theoretical analyses, the both results' accuracy was verified by comparison each other.

• Composites Research
• /
• v.33 no.6
• /
• pp.377-382
• /
• 2020

The free vibration characteristics of corrugated laminated composite plates with axial stiffeners is investigated using the Rayleigh-Ritz method. The plate is stiffened by beams with open cross-section area. The equivalent homogenization model is used for the corrugated laminated composite plates. This homogenization model is treated a corrugated plate as an orthotropic plate that has different material properties in two perpendicular directions. The motion of equivalent plate is represented on the basis of the first order shear deformation theory (FSDT) to account for the effect of rotary inertia and transverse shear deformation. Stiffeners are considered as discrete elements to predict the local vibration mode to be generated by the presence of stiffeners. To validate the proposed analytical approach, natural frequencies and vibration mode shapes from the analytical method are compared with those from the FEA by ANSYS.