• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2011.10a
• /
• pp.635-636
• /
• 2011

• Journal of Korean Society of Transportation
• /
• v.17 no.2
• /
• pp.163-178
• /
• 1999

Conventional shortest path searching a1gorithms are based on the partial searching method such as Dijsktra, Moore etc. The a1gorithms are effective to find a shortest path in mini-modal condition of a network. On the other hand, in multi-modal case they do not find a shortest path or calculate a shortest cost without network expansion. To copy with the problem, called Searching Area Problem (SAP), a global searching method is developed in this paper with Genetic Algorithm. From the results of two examples, we found that the a1gorithm is useful to solving SAP without network expansion.

• Journal of KSNVE
• /
• v.10 no.5
• /
• pp.843-848
• /
• 2000

BEA(Boundary Element Analysis) based on Kirchhoff-Helmholtz integral equation is widely used in the prediction of sound radiation problems of vibrating structures. Accurate estimation of sound pressure distribution by BEA can be [possible if and only if dynamic behavior of the relating structure was described correctly. Another plausible method of sound radiation phenomena could be the NAH(Nearfield Acoustic Holography) method. NAH also based on the identical governing equation with BEA could be one of the best acoustic imaging schemes but it has disadvantages of the complexity of measurement and of the need of large amount of measuring points. In this paper, modal expansion method is presented for taking accurate dynamic data of the structures efficiently. This method makes use of vibration principle an arbitrary dynamic behavior of the structure is described by the summation of that structures mode shapes which can be calculated by FEA easily and accurately. Sound pressure field from a vibration flat plate is calculated using the combination of vibration signal on that flat plate from experiment, and of the natural mode shapes form FEA. When sound pressure field from vibration signal is calculated the importance of the phase information was emphasized.

• Transactions of the Korean Society for Noise and Vibration Engineering
• /
• v.17 no.7 s.124
• /
• pp.596-604
• /
• 2007

This article investigates the effects of geometric configuration on the vibro-acoustic characteristics of in-plane vibration of a thick annular disc. Disc thickness and outer radius for a given inner radius are selected as independent variables having reasonable ranges. Variations in structural eigensolutions for radial modes are investigated using pre-developed analytical method. Based on these data, far-field sound pressure distributions due to the modal vibrations for a given geometry are also calculated using an analytical solution. Modal sound powers and radiation efficiencies are calculated from the far-field sound pressure distributions and vibratory velocity distributions on the radial surfaces. Based on the results explained above, the geometric configuration that minimizes modal sound radiations in a given frequency range is determined. Finally sound power and radiation efficiency spectra for a unit harmonic force from the selected geometric configuration are obtained from structural and acoustic modal data using the modal expansion technique. Multi-modal sound radiations of the optimized disc that are obtained using proposed analytical methods are confirmed with numerical results. Using the procedure introduced in this article, sound radiation due to in-plane modes within a specific frequency range can be minimized by the disc geometry modifications in a comprehensive and convenient manner.

• Transactions of the Korean Society for Noise and Vibration Engineering
• /
• v.14 no.11
• /
• pp.1083-1090
• /
• 2004

Two noise reduction systems are proposed in order to overcome the geometric restriction of the reactive muffler such as an expansion chamber. First, membrane is installed as a part of a duct wall and an air cavity is covered outside membrane. Second, membrane is installed inside a duct, which gives no volume change of the duct. Structural-acoustic coupling between membrane and fluid inside the cavity and duct causes rapid impedance mismatching and thereby reflected wave. Theoretical prediction is conducted by using modal expansion approach. The results are compared with the experimental results, which show better noise reduction performance than an expansion chamber.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2004.05a
• /
• pp.474-479
• /
• 2004

Two noise reduction systems are proposed in order to overcome the geometric restriction of the reactive muffler such as an expansion chamber. First, membrane is installed as a part of a duct wall and an air cavity is covered outside membrane. Second, membrane is installed inside a duct, which gives no volume change of the duct. Structural-acoustic coupling between membrane and fluid inside the cavity and duct causes rapid impedance mismatching and thereby reflected wave. Theoretical prediction is conducted by using modal expansion approach. The results are compared with the experimental results, which show better noise reduction performance than an expansion chamber.

• Nuclear Engineering and Technology
• /
• v.22 no.4
• /
• pp.371-379
• /
• 1990

The Xenon spatial oscillation may give rise to operational difficulties in a nuclear power plant. In this study, in order to investigate the Xenon instability for a PWR, the frequency-domain technique is adopted by using Generalized Nyquist Criterion, which is more general and suitable for the multi-input/multi-output system. Also linearized modal fluxes are obtained by a modal expansion. This model has been implemented to test the axial Xenon stability of YGN-1 unit against the changes in plant operating parameters ; power level, control rod position, and core average burnup. The results show that the increase of power level and the deeper insertion of control rod have the destabilizing effect, and that the burnup progress makes the core less stable. Also the results show that the overestimation due to modal interaction was found not to be significant.

• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
• /
• 2004.04a
• /
• pp.213-217
• /
• 2004

Laboratory scale study for an area of influence and flowing aspect of groundwater saturated zone was conducted for three sediment grains. On the AMG(Average Modal diameter Grains) 0.34, 1.38, 3.89mm diameter samples, the affected area of the aquifer were 15.2, 37.0, 30.0%/m2 each. Air flow for AMG 0.34mm diameter grain size provides indication of pattern of channelized air flow in saturated zone and expansion state in above saturated zone. For AMG of 1.38, 3.89mm diameter grains, air flow are pervasive air flow, forming a symmetrical cone of influence around the injection point. And also AMG 1.38, 3.89mm diameter samples show onset of collapse and approach to steady state in above saturated zone, respectively. In this study, optimal sites for in situ air sparging, may be grain diameters between about AMC 1.5～2.5mm diameter.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2002.11b
• /
• pp.498-504
• /
• 2002

Vibration beat phenomenon is theoretically investigated on a slightly asymmetric cylindrical shell, which is a simplified model of Korean bell. Mode pairs of the slightly asymmetric shell are obtained by receptance analysis and impulse response of the shell is derived using modal expansion and Laplace transform. Based on the impulse response model, beat mapping method is proposed to explain the reason that the beat of a bell vibration shows periodic distribution on the circumference. Beat characteristics of King Song-Dok Bell are explained in detail using the beat map and the measured modal data.

• Structural Engineering and Mechanics
• /
• v.46 no.3
• /
• pp.371-385
• /
• 2013

Vibration isolators and anti-vibration mounts are ideal, for example, in creating floating floors for gymnasiums, or performance spaces. However, it is well-known that there are great difficulties on isolating vibration transmission in structural steel components, especially steel floors. Besides, the selection of inertia blocks, which are usually used by engineers as an effective vibration control measure, is usually based on crude methods or the experience of the engineers. Thus, no simple method or indices have been available for assessing the effect of inertia blocks on vibration isolation or stability of vibratory systems. Thus, the aims of this research are to provide further background description using a FE model and present and implement a modal approach, that was validated experimentally, the latter assisting in providing improved understanding of the vibration transmission phenomenon in steel buildings excited by a velocity-source type of excitation. A better visualization of the mean-square velocity distribution in the frequency domain is presented using the concept of modal expansion. Finally, the variation of the mean-square velocity with frequency, whilst varying mass and/or stiffness of the coupled system, is presented.