• Journal of the KSME
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• v.51 no.6
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• pp.54-58
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• 2011

자동차용 풍동은 대부분 난류강도를 최대한 낮게 하여 시험의 재현성과 반복성을 극대화하도록 하였다. 그러나 최근 들어 뚜렷한 두 가지 흐름이 일고 있는데 지면재현과 실도로에서 경험하는 난류 강도를 풍동에서 재현하고자 하는 움직임이다. 이 글에서는 이러한 움직임의 이유와 방향에 대해 짚어보고자 한다.

• Bulletin of Korea Environmental Preservation Association
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• s.408
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• pp.9-11
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• 2013

우리의 생활공간에서 실내공기, 소음, 전자파 등 생활공해로 인한 피해는 시시각각으로 일어나고 있다. 그 동안 깨끗하고 쾌적한 실내환경과 정온한 생활환경 속에서 모든 국민이 건강하게 생활할 수 있도록 다양한 생활환경관리 정책을 추진해 왔다. 하지만, 정부의 노력만으로는 한계가 있다. 국민이 편안한 생활환경의 창출을 위해서는 그 구성원의 자발적인 노력과 참여가 필요하다.

• The Journal of the Acoustical Society of Korea
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• v.39 no.2
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• pp.77-86
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• 2020

In this study, the Eulerian/Lagrangian one-way coupling method is proposed to predict flow noise due to Blade-Tip Vortex Cavitation (BTVC). The proposed method consists of four sequential steps: flow field simulation using Computational Fluid Dynamics (CFD) techniques, reconstruction of wing-tip vortex using vortex model, generation of BTVC using bubble dynamics model and acoustic wave prediction using the acoustic analogy. Because the CFD prediction of tip vortex structure generally suffers from severe under-prediction of its strength along the steamwise direction due to the intrinsic numerical damping of CFD schemes and excessive turbulence intensity, the wing-tip vortex along the freestream direction is regenerated by using the vortex modeling. Then, the bubble dynamics model based on the Rayleigh-Plesset equation was employed to simulate the generation and variation of BTVC. Finally, the flow noise due to BTVC is predicted by modeling each of spherical bubbles as a monople source whose strength is proportional to the rate of time-variation of bubble volume. The validity of the proposed numerical methods is confirmed by comparing the predicted results with the measured data.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.40 no.3
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• pp.201-208
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• 2012

In this paper, a series of experiment is performed for a scaled hovering rotor in a semi-anechoic chamber and the results are compared to the noise spectra predicted by using Lowson's loading noise equation and FW-H equation. It was founded that the sound directivity pattern for both experiments and predictions are similar in their trend. Meanwhile the FW-H equation showed better agreement with experiments in the near-field noise spectra, but at the far-field the Lowson's equation performed better. The discrete noise are known to be proportional to the loading on the blades, which can be controlled by collective pitch angle of the blades. It was founded that the predicted spectra with FW-H equation come close to the measured noise spectra in low collective pitch, but in high collective pitch angles the Lowson's equation be more reliable.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.16 no.11 s.116
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• pp.1115-1123
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• 2006

Nuclear fuel rods are exposed to axial flow in a reactor, and flow-induced-vibration due to the flow usually causes damage in the fuel rods. Thus a prior knowledge about dynamic behavior of a fuel rod exposed to the flow condition should be provided. This paper shows that dynamic characteristics of a nuclear fuel rod depend on axial flow velocity. Assuming small lateral displacement, the effects of uniform axial flow are investigated. The analytic results show that axial flow generally reduces fuel rod stiffness and raises its damping in normal condition. Also, the critical axial velocities which make the fuel rod behavior unstable were found. That is, solving generalized eigenvalue equation of the fuel rod dynamic system, the eigenvalues with positive real part are detected. Based on the simulation results, on the other hand, it turns out that the ordinary axial flow in nuclear reactors does not affect to stability of a nuclear fuel rod even in the conservative condition.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2007.11a
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• pp.465-470
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• 2007

In this paper, a two-way tuned liquid mass damper(TLMD) using a tuned liquid column damper(TLCD) and a rubber-bearing-type tuned mass damper(TMD) was manufactured for controlling two-way direction acceleration responses of a high-rise building structure. The proposed controlling device behaves as a tuned liquid column damper in one direction and as a tuned mass damper in the other direction. In this study, Performance evaluation of the downscaled model is conducted. The results show that the two-way controllability is behaved independently each other and realscale TLMD applicable to the high-rise building can be designed.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2007.11a
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• pp.415-420
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• 2007

The objective of this study analyzes the influence of shimmy & shake phenomena due to tire design parameters which are RFV(radial force variation), DB(dynamic balance), RRO(radial run out) and air pressure. These parameters are inspection items for Q.C. after tires are manufactured. In order to analyze these parameters on this study, vehicle driving tests were achieved. The test modes are two type which are constant speed and coast-down driving. On this tests the dynamic characteristics of shimmy & shake are measured by the 3-axises accelerometers at the various positions that are knuckle(left & right), rack pinion, seat and steering wheel. In according to analyzed results, the longitudinal vibration of knuckle parts affects the lateral vibration of rack pinion and this vibration affects the lateral vibration of steering wheel that is the shimmy phenomena. Also the over and under DB by comparison with normal DB and the increment of RRO affect the occurrence of shimmy & shake phenomena.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.40 no.5
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• pp.489-495
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• 2016

This study focuses on a detailed ball-bearing model for spur gears. The nonlinear ball-bearing stiffness with radial clearance is derived and calculated. The bearing stiffness is used to the 3-degree-of-freedom (DOF) spur gear system model. The mode characteristics of the gear system model are analyzed and verified by performing finite-element analysis (FEA). From the results, the bearing stiffness on the radial clearance was more sensitive under low-load conditions compared to high-load conditions. The bearing stiffness significantly affected the gear dynamics in the low-frequency region, while the mesh stiffness affected the high natural frequency.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.15 no.3 s.96
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• pp.259-265
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• 2005

A two-degree-of-freedom out-of-plane model with contact stiffness is presented to describe dynamical interaction between the pad and disc of a disc brake system. It is assumed that the out-of-plane motion of the system depends on the friction force acting along the in-plane direction. Dynamic friction coefficient is modelled as a function of both in-plane relative velocity and out-of-plane normal force. When the friction coefficient depends only on the relative velocity, the contact stiffness has the role of negative stiffness. The results of stability analysis show that the stiffness of both pad and disc is equally important. Complex eigen value analysis is conducted for the case that the friction coefficient is also dependent on the normal force. The results further verify the importance of the stiffness. It has also been found that increasing the gradient of friction coefficient with respect to the normal force makes the system more unstable.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2008.04a
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• pp.432-441
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• 2008

In this study, the control performance of a Tuned Liquid Mass Damper(TLMD) manufactured to reduce the orthogonal bi-directional responses of building structures was experimentally evaluated. the TLMD using only one control device reduce bi-directional responses of building structures by making the TLMD behave as TMD and TLCD to the strong and weak axial direction of building structures. first, the control performance was evaluated by forcing sinusoidal waves to a test model that the TLMD is installed on the scale-downed building structure. Second, the real-time hybrid shaking table test was performed to evaluate the performance of the vibration control system made up of numerical part as a scale-downed building structural model and a physical experimental part as a TLMD. the superiority of bi-directional vibration control performance of the manufactured TLMD was verified by comparing the uncontrolled and controlled results of these tests.