Hyun-Gwon Kil

Vibrational energy flow models of finite orthotropic plates

In this paper energy flow models for the transverse vibration of finite orthotropic plates are developed. These models are expressed with time- and locally space-averaged far-field energy density, and show more general forms than the conventional EFA models for isotropic plates. To verify the accuracy of the developed models, numerical analyses are performed for finite rectangular plates vibrating at a single frequency, and the calculated results expressed with the energy and intensity levels are compared with those of classical models by changing the frequency and the damping.

Power flow model of flexural waves in finite orthotropic plates

In this paper, an approximate power flow model is developed for the analysis of the flexural waves in finite orthotropic plate transversely vibrating in the medium-to-high frequency ranges. The derived energy equation for the model is expressed with time- and locally space-averaged farfield wave energy density. It could be the more general form than that of the conventional power flow analysis model seen in the isotropic plate. With the derived model, dynamic characteristics varying with the direction can be expressed. To verify the validity and accuracy of the model, numerical analyses are performed for the case where a finite rectangular plate is excited by a harmonic point force, and the calculated results expressed with the energy levels are compared with classical modal solutions by changing the frequency and the damping loss factor of the plate. The dominant power transmission paths in the plate are also predicted from the distribution of the approximate intensity fields.

Power Flow Analysis of Vibration of a Plate Covered with a Damping Sheet

In this paper, the power flow analysis(PFA) has been used to analyze the vibration of a plate covered with a damping sheet. Experiments have been performed to measure the loss factor and frequency response functions of the plate covered with the damping sheet. The data for the loss factor has been used as the input data to predict the vibration of the coupled plates with PFA. The comparison between the experimental results and the predicted PFA results for the frequency response functions has been performed. It showed that PFA can be effectively used to predict structural vibration of a plate covered with a damping sheet in medium-to-high frequency range.

Vibro-acoustic Analysis of Adjoined Two Rooms Using 3-D Power Flow Finite Element Method

Power flow analysis(PFA) methods have shown many advantages in noise predictions and vibration analysis in medium-to-high frequency ranges. Applying the finite element technique to PFA has produced power flow finite element method(PFFEM) that can be effectively used for analysis of vibration of complicated structures. PFADS(power flow analysis design system) based on PFFEM as the vibration analysis program has been developed for vibration predictions and analysis of coupled structural systems. In this paper, to improve the function of vibro-acoustic coupled analysis in PFADS, the PFFEM has been extended for analysis of the interior noise problems in the vibro-acoustic fully coupled systems. The vibro-acoustic fully coupled PFFEM formulation based on energy coupled relations is extended to structural system model by using appropriate modifications to structural-structural, structural-acoustic and acoustic-acoustic joint matrices. It has been applied to prediction of the interior noise in two room model coupled with panels, and the PFFEM results are compared to those of statistical energy analysis(SEA).

Prediction of Vibrational Responses of Automotive Door System Using Energy Flow Analysis in Medium-to-high Frequencies

In this paper, the energy flow analysis(EFA) of the body-in-white door of a real automotive was performed using the energy flow finite element method(EFFEM) to effectively predict the vibrational responses of built-up structures in the medium to high frequency range. To increase the validity of EFA results, the structural hysteresis damping loss factor was measured by the experiment using the concept of statistical energy analysis(SEA). As the excitation frequency increases, the predicted results simulated with EFFEM generally agree with the experimental results.

Using a small-scale reverberation chamber to improve a ship's double sandwich panel noise attenuation performance

Regulations now require passenger ships to have low noise levels in accommodation spaces. Complex structural wall panels such as a double sandwich panels are often used to provide the required high noise attenuation. However, because of their complex structures, the prediction and improvement of the sound transmission loss (STL) of these panels often can not be achieved only with theoretical approaches. In this paper, an experimental approach using a small-scale reverberation chamber is applied to improve the STL of a double sandwich panel for installment in a ship. Firstly, a small-scale reverberation chamber is set up. For test chamber qualification, the STLs of a thin plate, a commercial ships sandwich panel and a high noise attenuation panel are measured and compared with those tested in a large-scale reverberation chamber and those calculated by the transfer matrix method (TMM). Secondly, the small-scale reverberation chamber is used to analyze the STL of a double sandwich panel in terms of the influences of the inside perforate plates and air gap thickness on attenuation. In order to improve the attenuation performance of the double sandwich panel, the STLs of test specimens with various materials between sandwich panels are measured and compared. Finally, the panel with the highest noise attenuation is proposed and verified using the large-scale reverberation chamber

Energy flow models for the out-of-plane vibration of horizontally curved beams

The purpose of this work is to develop energy flow models to predict the out-of-plane vibration of horizontally curved beams in the mid- and high-frequency range. The dispersion relations of waves are approximately separated into relations to the propagation of flexural waves and torsional waves generating the out-of-plane vibration of the horizontally curved beams with Kirchhoff-Love hypotheses. The energy flow models are based on the energy governing equations for the flexural waves and the torsional waves propagating in the curved beams. Those equations are driven to predict the time- and locally space-averaged energy density and intensity in the curved beams. Total values for the energy density and the intensity as well as contributions of each type of waves on those values are predicted. A verification of the energy flow models for the out-of-plane vibration of the horizontally curved beams is performed by comparing the energy flow solutions for the energy density and the intensity with analytical so...

Structural Integrity Analysis of Underwater Acoustic Sensors due to Underwater Explosion

ABSTRACT Underwater acoustic sensors are significantly damaged from underwater explosion. The damage that affects sensor should be evaluated for its smooth operations and safety. For satisfying these ob-jectives, it is necessary to obtain more accurate values of the pressure and the energy flux density by distance. This paper is divided into two part. First, to obtain more accurate value of the pressure and the energy flux density at each point, the simulation results and the reference values were compared. For fitting to the reference pressure and the reference energy flux density, the sizes of fluid and TNT model are corrected, and the comparison results show good agreements. Second, based on these results, the structural integrity of underwater sensor structure was analyzed when TNT located in 10 meters from underwater sensors structure. This simulation used the commercial software MSC/DYTRAN. * 1. 서 론 수중폭발이 발생하면 폭발물로부터 고온, 고압의 가스로부터 급격한 에너지가 유체로 전달된다. 이로 인해 구면파(spherical wave)의 형태로 충격파(shock wave)가 전파된다. 폭발로 인한 충격파가 임의의 몰수체에 전달되면, 충격으로 인해 상당한 피해를 입게 된다. 이를 대비하기 위해서 시뮬레이션을 통한 수중폭발에 대한 구조물의 구조건전성에 대한 정확한 해석이 필요하다

Analysis of Sound Transmission Characteristics of Multi-complex Panel for Noise Reduction in High Value-added Vessel Cabin

*Department of Naval Architecture and Ocean Engineering, Seoul National University, Seoul, Korea**Department of Mechanical Engineering, University of Suwon, Su won, Korea***Defense Acquisition Program Administration, Naval Ship Progr am, Department Combatant Ships Project Team, Seoul, Korea****Department of Naval Architecture and Ocean Engineering, Cho nnam National University, Yeosu, KoreaKEY WORDS: High value-added vessel 고부가가치선, Cabin 선실, Mini reverberant chamber 간이잔향실, Transmission loss 투과 손실, Multi-complex panel 복합패널ABSTRACT: Recently, as the importance of the interior noise in a ship cab in has risen, ship builders have becomeconcerned about the use of noise reduction panels to reduce cabin noise. The results of previous researches have been based on analytical and experimental meth ods using simple sandwich panels. However, panel structures are becoming more co mplex to improve the transmission loss. Thus, researches that a nalyze the transmission loss of a panel are reaching the limit of study. T his paper reports on research that was performed to determine t he sound transmission characteristics of multi-complex panels applicable to high valu e-added vessels. It presents comparisons between analytical met hods and experimental results by using a mini-reverberant chamber with components of sound attenuation panels, including the core and surface materi als. The sound transmission loss of multi-complex panels are also analyzed in terms of the influences of the inside perforate plates and air gap thickness on the attenuation. Finally, the multi-complex panel with the highest noise attenuation is proposed based on the analysis results and experimental results in mini-reverberant chamber, which wereverified using a real-si ze reverberant chamber.교신저자 송지훈: 전라남도 여수시 미평로 386, 061-659-7156, jhs@chonnam.ac.kr

Vibration Power Flow Analysis of Coupled Co-planar Orthotropic Plates

In this paper, the power flow analysis(PFA) method was developed to predict the vibrational responses of coupled co-planar orthotropic plates in frequencies ranging from medium to high. To cover the power transmission and reflection at the joint of the orthotropic plates, the wave transmission approach is applied with the assumption that all the incident waves are normal to the joint. Through numerical analyses, the power flow energy density and intensity fields of coupled co-planar orthotropic plates were compared with those of classical modal solutions by changing the frequency and internal loss factor, and they show good agreement in terms of the global decay and the attenuation patterns of the energy density.