• Transactions of the Korean Society for Noise and Vibration Engineering
• /
• v.16 no.6 s.111
• /
• pp.658-664
• /
• 2006

Shock vibrations are usually experienced in vehicles excited by impulsive input, such as bumps. The frequency weighting functions of the current standards in ISO 2631 and BS 6841 are to help objectively predict the amount of discomfort of stationary vibration. This experimental study was designed to develop frequency weighting shape for shock vibration having various fundamental frequencies from 0.5 to 16Hz. The specks were produced from the response of single. degree-of-freedom model to a half-sine force input. Fifteen subjects used the magnitude estimation method to judge the discomfort of vertical shock vibration generated on the rigid seat mounted on the simulator. The magnitudes of the shocks, expressed in terms of both peak-to-peak value and un-weighted vibration dose values (VDVs) , were correlated with magnitude estimates of the discomfort. The frequency weighting shapes from the correlation were developed and investigated having nonlinearity due to the magnitude of the shock.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2004.11a
• /
• pp.407-412
• /
• 2004

본 연구에서는 PMN-PT bimorph actuator를 이용하여 초소형 광디스크 드라이브용 광픽업 구동기를 제작하였다. 최근에 휴대용 기기에서의 고용량 정보 저장기기에 대한 필요성이 대두됨에 따라 착탈식이 가능한 수 기가급 초소형 광디스크 드라이브가 개발중에 있다. PMN-PT는 약 1.5kV/cm 이하의 전기장에서는 PZT같은 압전 소자와 마찬가지로 입력 전압에 대한 변형률이 선형성을 나타내는데, 사용된 PMN-PT는 PZT의 약 3배 가까운 압전 상수값을 나타내었다. 보 끝단에 외부 힘이 작용할 때 PMN-PT bimorph 구동기가 낼 수 있는 수직 방향의 힘과 변위에 대해서 일반적인 적층 형태로 이론적인 해석을 수행 하였다. 그리고 이 bimorph로 구동될 Cymbal 형태의 변위 확대 기구의 변위에 대한 이론적인 모델을 제시하고, 이를 이용하여 2개의 bimorph로 2축을 동시에 구동하는 픽업 구동기를 제작하였다. 3개의 제작된 prototype으로 실험을 수행하여 예상 변위량과 잘 일치함을 보였다. 또한, 상용 해석 프로그램인 Matlab과 Ansys를 이용하여 Cymbal 확대 기구의 여러 파라미터에 따른 구동 성능의 민감도를 확인해 보았다.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2004.11a
• /
• pp.269-274
• /
• 2004

The aims of this study were to Investigate the floor impact noise isolation performance of floating floor with isolation materials and propose the improvement direction of floor impact noise measurement method and evaluation classes using impact ball. Reduction of light-weight impact sound pressure level can be achieved by the finishing materials, such as vinyl finishing material and wooden flooring with isolation materials. Floor impact noise Isolation material which satisfy the properties of the floor impact noise isolation materials cause resonance in the low frequency band and worsen heavy-weight impact sound pressure level. Heavy-weight impact sound level can be reduced by using noise reduction flooring, ceiling and increase of slab thickness. Strong impact force in low frequency bang below 63Hz of bang machine is not similar to human impact source and causes some problem in evaluating heavy-weight impact noise but heavy-weight impact noise measurement and evolution using impact ball which is very similar to human impact is more reliable than bang machine. Correction value on the background noise and sensitivity of residents should be considered on the floor impact noise evaluation classes.

• Journal of Environmental Health Sciences
• /
• v.50 no.2
• /
• pp.81-82
• /
• 2024

Urban air mobility (UAM) is emerging as an innovative transportation solution for cities. However, the potential noise impact on urban life must be carefully examined. Continuous exposure to UAM noise, with its unique frequency characteristics and temporal variability, may adversely affect citizens' health by causing sleep disorders, cardiovascular disease, and cognitive impairmenet, particularly in children. NASA has formed a UAM Noise Working Group to study this issue comprehensively. In Korea, the Seoul Metropolitan Government's UAM demonstration project is expected to accelerate related research and development. Scientific analysis, including noise measurement, prediction modeling, and health impact assessment, must be prioritized. Measures to minimize noise should be established based on this evidence, such as optimizing flight modes, developing noise reduction technologies, and establishing new noise management standards. Transparency and social consensus are crucial throughout this process. Expert review and open communication with civil society are necessary to address related concerns. Sharing demonstration project results and providing opportunities to experience UAM noise through digital twin simulations can help address public concerns and build social consensus. Proactively and scientifically tackling noise issues is essential for the sustainable development and successful integration of UAM into daily life.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.39 no.4
• /
• pp.437-445
• /
• 2015

A design method for a perforated panel is suggested to reduce the level of incident noise without obstructing the flow of incoming fluid. The key idea was to insert an array of 1/4 wavelength tubes around the holes of the perforate panel. First, various case studies were performed for a unit model with only one hole. In order to avoid any increase in the panel thickness, the unit model was vertically divided into three layers, and only the middle layer was used as the design domain. The number and array of 1/4 wavelength tubes connected to the hole were optimized to obtain the widest effective frequency range in the transmission loss curve as possible. Then, the optimally designed unit model was converted to a periodic array in the perforated panel to achieve the design goals. Even if the target frequency and the target transmission loss were set to 1000 Hz and 10 dB, respectively, the suggested design method for the a perforated panel could achieve noise reduction for various target values.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.13 no.3
• /
• pp.967-976
• /
• 2012

This study presents a model to minimize vibration and noise of powertrain mount on a compact car which has the application of Stop & Go performance, in order to reduce CO2 and achieve better fuel-efficiency in accordance with the environmental regulations in automotive industries. In the first step, we analyze the powertrain mount system of the automobile "A" and present variables about rubber stiffness applied on powertrain mount using the Taguchi method. In the next step, we verify the optimization of vibration and noise which meet Stop & Go performance using the AHP(Analytic Hierarchy Process) method on the proto products for each variable. Using this validation system on the initial stage of the powertrain mount design, it is expected that we can grasp vibration and noise problems caused by engine movements and control them effectively without engineering know-how about powertrain mount rubber stiffness.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2012.04a
• /
• pp.348-353
• /
• 2012

This paper presents the HRTF based experimental approach to figure out why the human auditory perception on the interior noise source including the directional tonal components does not well match with the dominant features extracted from recorded acoustic signals in terms of psycho-acoustics. Since the general objective evaluation models for tonalness among various sound attributes are a function of width, frequency, excessive level of tonal components respectively, the directional tonal components cannot be properly evaluated without considering the effects of head-related transfer function on the binaural auditory perception. Thus, the directivity of source is additionally considered to prevent the erroneous conclusions from the same sound source in the process of source identification. The signal synthesis technique is used to solve a little difficulty in measuring all of desired acoustic signals for jury evaluation. The sound attributes of synthetic acoustics signals are analyzed to roughly predict the results of jury evaluation in advance by using sound quality factors such as loudness, sharpness, roughness, fluctuation strength and tonality. The jury evaluation is carefully conducted based on the recommended guideline suggested by N. Ottoet al. Each sound is respectively evaluated by selecting a value between -2 and 2 in intervals of 0.2 point. Through above procedure, based on the results of jury evaluation, it is confirmed that serious problems can be caused in the process of analyzing the dominant sound attributes in terms of psycho-acoustics according to the type of a microphone and a playback system.

• Journal of Aerospace System Engineering
• /
• v.11 no.1
• /
• pp.28-34
• /
• 2017

Elastomeric o-ring performance and structure when subjected to a foreign object is studied using finite element analysis (FEA). Elastomeric o-rings have been studied using 2D analysis for a long time. Contact pressure is an important factor in o-ring design. When contact pressure is lower than applied pressure, leaking, vibration, and noise can occur; resulting in decreased output. In this study, we compared 2D and 3D analyses of elastomeric o-rings. Similar results were shown for 2D and 3D contact pressure. However, when an o-ring encounters foreign object matter, 3D analysis is required because contact pressure in every direction needs to be considered. We determined the influence of foreign matter on o-ring performance and structure by analyzing 10 cases with different clearances in a 3D model. Therefore, an o-ring encountering foreign object matter must be analyzed in 3D with the result included in the o-ring design.

• The Journal of the Acoustical Society of Korea
• /
• v.36 no.5
• /
• pp.314-320
• /
• 2017

A pressure relief valve is generally used to prevent piping systems from being broken due to high pressure gas flows. However, the sudden pressure drop caused by the pressure relief valve produces high acoustic energy which propagates in the form of compressible acoustic waves in the pipe and sometimes causes severe vibration of the pipe structure, thereby resulting in its failure. In this study, internal aerodynamic noise due to valve flow is estimated for a simple contraction-expansion pipe by combining the LES (Large-Eddy Simulation) technique with the wavenumber-frequency analysis, which allows the decomposition of fluctuating pressure into incompressible hydrodynamic pressure and compressible acoustic pressure. In order to increase the convergence, the steady Reynolds-Averaged Navier-Stokes equations are numerically solved. And then, for the unsteady flow analysis with high accuracy, the unsteady LES is performed with the steady result as the initial value. The wavenumber-frequency analysis is finally performed using the unsteady flow simulation results. The wavenumber-frequency analysis is shown to separate the compressible pressure fluctuation in the flow field from the incompressible one. This result can provide the accurate information for the source causing so-called acoustic-induced-vibration of a piping system.

• The Journal of the Acoustical Society of Korea
• /
• v.21 no.4
• /
• pp.339-438
• /
• 2002

This paper presents a method to simulate noise propagation by a computer for outdoor environment. Sound propagated in 3 dimensional space generates reflected waves whenever it hits boundary surfaces. If a receiver is away from a sound source, it receives multiple sound waves which are reflected from various boundary surfaces in space. The algorithm being developed in this paper is based on a ray sound theory. If we get 3 dimensional geometry input as well as sound sources, we can compute sound effects all over the boundary surfaces. In this paper, we present two approaches to compute sound: the first approach, called forward tracing, traces sounds forwards from sound sources. while the second approach, called geometry based computation, computes possible propagation routes between sources and receivers. We compare two approaches and suggest the geometry based sound computation for outdoor simulation. Also this approach is very efficient in the sense we can save computational time compared to the forward sound tracing. Sound due to impulse-response is governed by physical environments. When a sound source waveform and numerically computed impulse in time is convoluted, the result generates a synthetic sound. This technique can be easily generalized to synthesize realistic stereo sounds for virtual reality, while the simulation result is visualized using VRML.