• Transactions of the Korean Society of Automotive Engineers
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• v.10 no.3
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• pp.237-244
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• 2002

Analyzing acoustic-structural systems such as automobiles and aircraft, the FRF-based substructuring (FBS) method is one of the most powerful tools. In this paper, a general procedure for the parametric sensitivity analysis of vibro-acoustic problems has been presented using the multi-domain FRF-based substructuring formulation. For an acoustic-structural system sub-structured by multiple domains, the substructuring formulation gives the reaction farces on the interface boundaries. The design sensitivity formula is obtained from the direct differentiation of the reaction force expression with respect to the design vector. As a practical application, the proposed design sensitivity formula is applied to an engine mount system of passenger car. An objective of the problem is to identify the most effective engine mounts and bushes in minimizing the interior noise over the concerned rpm range. The comparison of the sensitivity results with those of the finite difference method shows excellent agreement. In addition, stiffness modifications of the mounts and bushes identified through the design sensitivity analysis lead to a successful decrease of the interior noise. This results show usefulness of the present method very well.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2004.05a
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• pp.282-287
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• 2004

Noise and vibrations in the pipe systems may be arisen from pumps. compressors, etc. The source mechanism is classified with the mechanical and hydraulic. Mechanical vibrations may be excited by the unbalance in rotating machinery. Hydraulic source may be generated in the turbulent flow. The vibro-acoustic behaviour of flexible, fluid-filled pipe system is a very complex and determined by two parameters: the frequency and the mass ratio of fluid and pipe wall. As the frequency increases, the mode number in the pipe increases. The mass ratio is close to one, the structure and the fluid are strongly coupled. In ease the diameter is very small to the length of pipe, the behaviour of pipe is same as a beam. The finite element formulation when the fluid and the structure are coupled is derived by using beam element. The Numerical results are compared with the package (Sysnoise) which is using the shell element.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2004.11a
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• pp.949-953
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• 2004

In this paper, Power Flow Boundary Element Method(PFBEM) is studied as the numerical method for the vibration and sound predictions of complex structures in medium-to-high frequency ranges. NASPFA, the sound analysis software based on PFBEM, is developed and is used for the vibro-acoustic analysis. And also the developed software is used for the prediction of interior and exterior sound fields of vibrating structures and for the analysis of the multi-domain problems. To verify the accuracy, NASPFA is applied to the prediction of the energy distribution in the simple structures, and its results are compared with exact PFA solutions. And various practical vehicle systems are modeled and the distributions of the acoustical energy density are successfully predicted.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2001.05a
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• pp.103-108
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• 2001

The structure of hard disk drive(HDD) is excited by dynamic motion of a disk-spindle motor, and it makes sound noise. Therefore, the cover and the base of HDD should be designed to reduce noise and vibration induced by spindle motor. The prediction technique of sound pressure level(SPL) of a given structural shape enables us to design a cover and a base with much less vibration and noise. In this paper, we measured the force of disk-spindle motor and predicted SPL from HDD by computational simulation. To get a SPL of HDD by computational simulation, modal analysis and forced vibration analysis were performed with ANSYS, and sound radiation was computed using SYSNOISE. The calculated results were compared with experimental results and a good agreement was obtained. With this computer simulation procedure and design of experiment(DOE), optimal thickness of noise barrier and damper was calculated.

• International Journal of Naval Architecture and Ocean Engineering
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• v.12 no.1
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• pp.343-353
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• 2020

Based on the Precise Transfer Matrix Method (PTMM), the dynamic model is constructed to observe the vibration behaviour of cylindrical shells with variable thickness by solving a set of first-order differential equations. The free vibration of stiffened cylindrical shells with variable thickness can be obtained to compare with the exact solution and FEM results. The reliability of the present method of free vibration is well proved. Furthermore, the effect of thickness on the vibration responses of the cylindrical shell is also discussed. The acoustic response of immersed cylindrical shells is analyzed by a Pluralized Wave Superposition Method (PWSM). The sound pressure coefficient can be gained by collocating points along the meridian line to satisfy the Neumann boundary condition. The mode convergence analysis of the cylindrical shell is carried out to guarantee calculation precision. Also, the reliability of the present method on sound radiation is verified by comparing with experimental results and numerical results.

• The Journal of the Acoustical Society of Korea
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• v.42 no.2
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• pp.83-93
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• 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 Korean Society for Noise and Vibration Engineering Conference
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• 2012.04a
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• pp.461-466
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• 2012

Customers want to have more convenient and comfortable vehicle. Motor-on-caliper EPB(Electrical Parking Brake) System is one of the new systems for customer's convenience. It is applied for Midsize vehicle for reducing weight/price compared to cable puller type EPB. In this paper we studied sound quality improvement of motor-on-caliper EPB system. We developed the sound quality index and suggested the interior sound quality target value. To meet the target value cascading target was also suggested. EPB motor vibration level & sound radiation level, vibro-acoustic transfer function level from EPB to interior was defined. To find out effective way of sound quality improvement and find cascading target, TPA(Transfer Path Analysis) was carried out.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2006.11a
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• pp.694-698
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• 2006

This paper presents an optimal design process using beads on a body panel to improve interior noise of a passenger vehicle. Except modification of structural members, it is difficult to find effective countermeasures that can work for the intermediate frequency range from 100 Hz to 300 Hz which lies between the booming and low medium frequency. In this study, it is a major goal to find additional counter-measures for this intermediate frequency range by performing optimal design of beads on body panels. The proposed method for design optimization consists of 4 sub-steps, that is, a) problem definition, b) cause analysis, c) countermeasure development and d) validation. The objective function is minimization of interior noise level. The major design variables are the geometrical shape of a bead and combination of beads on the critical panels. Sensitivity analysis and optimization are performed according to the predefined process for an optimal design. It is verified that the proposed design decreases the level of noise transfer function above 5 dB.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2000.11a
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• pp.731-736
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• 2000

The recently developed BEM-based NAH(nearfield acoustical holography) is a useful technique for identifying the sound source of vibrating objects. The acoustic parameters of a sound source can be reconstructed by using the vibro-acoustic transfer matrix, which is determined by means of BEM, and the sound pressure measured in the nearfield. Theoretically, one can come up with a very nice reconstructed result as the field plane gets near to the source surface. However, when a microphone is placed in the very close nearfield of the source surface, the scattering, reflection, or resonance in the gap between the source and the microphone can distort the acoustic field, and therefore, the measured field pressure would differ from the actual one in the absence of the microphone. In order to analyze this problem, the interference effect of the microphone is numerically calculated by using the nonsingular BEM that yields very small error in the nearfield. From this analysis, it is found that the prediction error of the field pressure decreases firstly and then increases as the microphone approaches the vibrating surface from the farfield to the close nearfield. It is noted that the microphone should be separated from the source surface by at least a diameter of the microphone for an error ratio less than 2% in the low frequency range less than about 2.7kHz. This means that if one wants to put a microphone in the very close nearfield. a microphone with small diameter should be used.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2007.11a
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• pp.1366-1370
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• 2007

Predicting the noise radiated from vibrating structures is important in the automotive, aerospace, construction equipment, and defense industries. In this paper, a numerical implementation of the boundary element method in solving the Helmholtz integral equation for radiated noise prediction is presented. To predict the noise emitted by vibrating structure, the developed code can use the results from a structure analysis performed by a multi-purpose structural finite element code like ANSYS and directly measured data by non-contact vibration sensor like Laser Doppler Vibrometer. To verify the accuracy of developed code, two kinds of verification are perfomed. Firstly, the computer code used the harmonic analysis results of ANSYS in simple model and try to match with SYSNOISE. After matching with simulation results, the code compared with the result from SYSNOISE which used the velocity data from the LDV measurement with different number of points. The performance of the developed code for vibro-acoustic noise prediction is presented using the experimental results of the non-contact sensor