• 한국소음진동공학회논문집
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• 제14권8호
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• pp.668-674
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• 2004

The possibility of global noise reduction by the sound power control through selection of distribution and impedance of absorptive materials is discussed. It is necessary to investigate the relation between the global sound energy in the field and the total sound power radiated by sources. In the previous work,$^{(1.2)}$ the authors presented a useful design method to change boundary condition that can be useful to reduce noise in acoustically small enclosures. Changing boundary condition Is related to not only enclosure’s geometrical shape but also acoustical treatment on walls for example, attaching of impedance patches (ex: absorptive material). In many practical situations, we often meet situation to change acoustical treatment on walls. The possibility of total acoustic potential energy(globa1 noise) reduction by acoustic source power control is examined in an acoustically small cavity Using acoustic energy balance equation, the relation between global noise control performance and absorptive material’s arrangement/impedance is deduced. Numerical simulation is performed to interpret its physical meaning in terms of absorbent’s distribution and impedance.

• 오토저널
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• 제14권1호
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• pp.25-37
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• 1992

Interior noise in a car is known to have an important influence on product acceptability. This noise is closely correlated with structural-acoustic vibration. When considering noise problem, the structural-acoustic relation of a vehicle cabin model needs to be identified. However, it is very difficult to get the modal parameters of this kind of cabin structure composed of thin plates: because it not only can be excited by the acoustic vibration of cavity, but also tends to have decoupling effects of one plate from another. In order to obtain modal parameters more precisely, various excitation techniques, i.e. impact, pure random, burst random, and swept sine testing are applied for the first step. In the case of the cabin model, impact and swept sine testing show good results. Next, the determination of the excitation point by trial- and-error and the accurate measurements of FRF's are performed with these methods. The modal parameter extraction is carried out for the final step. This paper proposes a new approach to find the modal parameters more reliably in the case of high decoupling effects. That is, the convergence of MIF and MCF in each panel, which provide some criteria for the validity of the obtained modal parameters, is observed. And from those results, the pretty accurate modal parameters can be determined. A comparative assessment between the modal testing and the FEM is also performed.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2004년도 추계학술대회논문집
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• pp.737-740
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• 2004

The interior noise reduction of construction equipment is concerned for improving the driver comfort in this study. From the baseline test, the exhaust noise gives a big contribution to the interior noise of construction equipment. And the detail noise contribution analysis of the exhaust system, the tail pipe, which is for ventilation an engine room hot air to outside, amplify the exhaust noise around operating engine RPM associated with tail pipe structural and cavity resonances. To remove the noise amplifying effects, the tail pipe has to be shorted its length. Even the noise can be attenuated the ventilation flux when using the redesigned tail pipe is reduced than the original one. Thus, a shape change of the tail pipe is additionally needed for increasing the ventilation flux and attenuating the exhaust noise using CFD technique. The CFD results of the tail pipe give a meaning full information what obstructs the ventilation flex in the current design and how changes the tail pipe.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2004년도 추계학술대회논문집
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• pp.916-919
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• 2004

The monopole theory has long been used to model air-pumped effect from the elastic cavities in car tire. This approach models the change of an air as a piston moving backward and forward on a spring and equates local air movements exactly with the volume changes of the system. Thus, the monopole theory has a restricted domain of applicability due to the usual assumption of a small amplitude acoustic wave equation and acoustic monopole theory. This paper describes an approach to predict the air-pumping noise of a car ave with CFD/Kirchhoff integral method. The type groove is simply modeled as piston-cavity-sliding door geometry and with the aid of CFD technique flow properties in the groove of rolling car tyre are acquired. And these unsteady flow data are used as a air-pumping source in the next Cm calculation of full tyre-road geometry. Acoustic far field is predicted from Kirchhoff integral method by using unsteady flow data in space and time, which is provided by the CFD calculation of full tyre-road domain. This approach can cover the non-linearity of acoustic monopole theory with the aid of using Non-linear governing equation in CFD calculation. The method proposed in this paper is applied to the prediction of air-pumping noise of modeled car tyre and the predicted results are qualitatively compared with the experimental data.

• 한국소음진동공학회논문집
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• 제25권10호
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• pp.692-699
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• 2015

Buffeting noise through a rear window in an automobile is investigated by using lattice Boltzmann method. The generation mechanism of the buffeting noise can be understood as the resonance mechanism in a Helmholtz resonator, which is driven by the convecting vortex in a shear-layer flow over the neck of the resonator. Two methods to suppress the buffeting noise are proposed, and their effects are quantitatively assessed. Opening front window reduces the observed buffeting tonal noise by 25 dB and the overall SPL by 4 dB, and the installation of a Helmholtz resonator acting as a dynamic damper reduces the tonal component that by 35 dB and the overall SPL by 10 dB.

• Earthquakes and Structures
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• 제24권4호
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• pp.247-258
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• 2023

Multiple pounding tuned rolling mass damper (MPTRMD) distributed in the cavity of voided slabs is proposed to passively control multi-story frame structures, which disperses the mass of the oscillator to multiple dampers so that the control device can be miniaturized without affecting the vibration control performance. The mechanism and the differential motion equations of the MPTRMD-controlled multi-degree-of-freedom system are derived based on the Lagrange principle. Afterward, this advanced RMD is applied to a simplified 20-floor steel frame to evaluate the seismic control performance in the numerical analysis. A four-storey frame structure equipped with MPTRMD is then taken for a shaking table test to verify its effectiveness of control performance. The pounding mechanism has been detailed studied numerically and experimentally as well. The numerical and experimental results show that the proposed damper is practically promising not only for its prominent control performance but also for its lightweight and space-saving. Additionally, the pounding mechanism influenced by the variable impact parameters exhibits a balance between the two effects of motional limitations and energy dissipation.

• 한국재료학회지
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• 제13권3호
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• pp.144-149
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• 2003

This study shows an experimental investigation of a reversible nano colloidal damper, which is statically loaded. The porous matrix is composed from silica gel (labyrinth or central-cavity architecture), coated by organo-silicones substances, in order to achieve a hydrophobic surface. Water is considered as associated lyophobic liquid. Reversible colloidal damper static test rig and the measuring technique of the static hysteresis are described. Influence of the pore and particle diameters, particle architecture and length of the grafted molecule upon the reversible colloidal damper hysteresis is investigated, for distinctive types and mixtures of porous matrices. Variation of the reversible colloidal damper dissipated energy and efficiency with temperature, pressure, is illustrated. As a result, he proposed nano damper is effective one, which can be replaced the conventional damper.

• 대한기계학회논문집
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• 제1권2호
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• pp.113-124
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• 1977

By spplying the ultrasomic wave to the solidifing liquid metal, grain sizes of the ingot are refined and the structures are homogenized. One of the reason is the enhancement of nucleation by ultrasonic vibration. According to the reports on this subject, the uncleating conditions are formed by the increse of melting point which is produced by the high pressure due to caviation. In this paper we study whether the caviations are the orgin of the nucleation and analized whether the nucleating conditions are formed by the increase of melting point or not and also compared the analytical result with the experim nt. We analized the pressure change induced by cllaphsing of cavity and the motion of cavith in oscillating pressure field. And we further analized the variation of melting point with pressure change.

• 소음진동
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• 제8권6호
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• pp.1113-1120
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• 1998

For an analysis of some Helmholtz resonators, it is likely to be more appropriate to consider acoustic field within cavity than just the 1-DOF analogous model. However, a design method that considers increased parameters than the lumped model. is not a trivial process due to the trade-off effect among the parameters. In this paper. the genetic algorithm. one of the optimization technique that rapidly converges to global fittest solution and robust convergence. is applied to the design process of Helmholtz resonators. Results show that the genetic algorithm can be successfully and efficiently used to find the resonant frequencies for both lumped model and distributed model.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2001년도 추계 학술대회논문집
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• pp.138-143
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• 2001

An experimental model to enhance the mixing of parallel supersonic-subsonic jet ($M_1$=1.78 and $M_2$=0.30) is simulated with a numerical technique by modeling the wall-mounted cavity to a boundary condition of oscillating pressure. The computed pilot pressure distributions along three representative cross sections show a good agreement with the equivalent experimental data. The irradiation of acoustic wave in the ultrasonic range causes the mixing augmentation of jet and wake due to the transfer of vibration energy between fluid particles.