Hyun-Wung Kwon

Effect of IciA protein on the expression of the nrd gene encoding ribonucleoside diphosphate reductase in E. coli.

Abstract The E. coli nrd operon contains the genes encoding the two subunits of ribonucleoside diphosphate reductase. We found that the IciA protein binds specifically to the AT-rich upstream region of nrd promoter. In vivo overexpression of IciA increases the expression of nrd gene by four- to five-fold, suggesting that IciA functions as a transcriptional activator for the nrd gene.

Energy flow boundary element method for vibration analysis of one and two dimension structures

In this paper, Energy Flow Boundary Element Method (EFBEM) was developed to predict the vibration behavior of one- and two-dimensional structures in the medium-to-high frequency ranges. Free Space Green functions used in the method were obtained from EFA energy equations. Direct and indirect EFBEMs were formulated for both one- and two-dimensional cases, and numerically applied to predict the energy density and intensity distributions of simple Euler-Bernoulli beams, single rectangular thin plates, and L-shaped thin plates vibrating in the medium-to-high frequency ranges. The results from these methods were compared with the EFA solutions to verify the EFBEM.

Transient Power Flow Analysis of Beam and Plate

PFA (power flow analysis) has been recognized as a useful method in vibration analysis of medium-to-high frequency ranges. Until now, PFA method has been developed for steady-state vibration problems. In this paper, PFA method has been expanded to transient problem. New energy governing equations are derived considering time dependent terms in beam and plate. Analytic solutions of those equations are found in simple beam and plate, and are verified by comparing with modal solutions.

Development of Received Acoustic Pressure Analysis Program of CHA using Beam Tracing Method

In order to predict acoustic pressure distributions by exterior incident wave at Cylindrical Hydrophone Array (CHA) sensor`s positions, acoustic pressure analysis is performed by using beam tracing method. Beam tracing method is well-known of reliable pressure analysis methods at high-frequency range. When an acoustic noise source is located at the center of rectangular room, acoustic pressure analysis is performed by using both beam tracing method and Power Flow Boundary Element Method (PFBEM). By comparing with results of beam tracing method and those of PFBEM, the accuracy of beam tracing method is verified. We develop the CHA pressure analysis program by verified beam tracing method. The developed software is composed of model input, sensor array creator, analysis option, solver and post-processor. We can choose a model option of 2D or 3D. The sensor array generator is connected to a sonar which is composed of center position, bottom, top and angle between sensors. We also can choose an analysis option such as analysis frequency, beam number, reflect number, etc. The solver module calculates the ray paths, acoustic pressure and result of generating beams. We apply the program to 2D and 3D CHA models, and their results are reliable.

Development of Acoustic Target Strength Analysis System for Submarine

【The acoustic target strength (TS) is one of the most important parameters for a submarines stealth design. Because modem submarines are larger than their predecessors, TS must be managed at each design stage in order to reduce it. To predict the TS of a submarine, TASTRAN R1 was developed based on a Kirchhoff approximation in a high-frequency range. This program can present TS values that include multi-bounce effect in the exterior and interior of the structure by combining geometric optics (GO) and physical optics (PO) methods, anechoic coating effect by using the reflection coefficient, and response time pattern for a detected target. In this paper, TS calculations for a submarine model with the above effects are simulated by using this developed program, and the TS results are discussed.】

Vibration and Noise Analysis for Rotary Compressor in Medium-to-high Frequency Ranges

Power flow analysis(PFA) is introduced for solving the noise and vibration analysis of system structures in medium-to-high frequency ranges. The vibration analysis software, R4 based on power flow finite element method(PFFEM) and the noise prediction software, R1 based on power flow boundary element method(PFBEM) are developed. In this paper, the coupled PFFE/PFBE method is used to investigate the vibration and radiated noise of the rotary compressor. PFFEM is employed to analyze the vibrational responses of the rotary compressor, and PFBEM is applied to analyze the radiation noise around rotary compressor. The vibrational energy of the structure is used as an acoustic intensity boundary condition of PFBEM. Numerical simulations are presented for the rotary compressor, and reliable results have been obtained.

Acoustic insulation performance of a honeycomb panel using a transfer matrix method

Honeycomb panels have good mechanical properties and are widely used in various industries because of their high strength-to-weight ratio. However, more research into their acoustic insulation is needed. In this study, a transfer matrix was derived for the acoustic insulation performance prediction of a honeycomb panel. To properly derive the transfer matrix for the model, it should be configured from the relationship between the pressure and particle velocity of the front and rear sections of the honeycomb panel. Each type (fluid, solid, etc.) consisting of a layer was analyzed by a continuous pressure and velocity condition. The numerical results were verified through experimental results using the intensity method. We confirmed that the two results (numerical and experimental result) were in good agreement within approximately 2 dB. Finally, the acoustic insulation performance was studied in relation to the honeycomb thickness, cell size, cell-wall thickness, and cell shape. We observed that smaller cell sizes and thicker cell walls improved the insulation performance. We confirmed that acoustic insulation performance of honeycomb panels can be improved by changing the cell design.

Development of acoustic target strength near-field equation for underwater vehicles

For modern weapon systems, the most important factor in survivability is detection capability. Acoustic target strength is a major parameter of the active sonar equation. The traditional target strength equation used to predict the re-radiated intensity for the far field is derived with a plane-wave assumption. In this study, a near-field target strength equation was derived without a plane-wave assumption for a polygonal plate. The target strength equation for polygonal plates, which is applicable to the near field, is provided by the Helmholtz–Kirchhoff formula that is used as the primary equation for solving the re-radiated pressure field. A generalized definition of the sonar cross section is suggested that is applicable to the near field. In comparison experiments for a cylinder, the target strength equation for polygonal plates in near field was executed to verify the validity and accuracy of the analysis. In addition, an underwater vehicle model was analyzed with the developed near-field equation to confirm various parameter effects such as distance and frequency.

Vibrational energy flow models for dilatational wave in elastic solids

The analysis of medium- to high-frequency vibrations of structures is of particular interest in various fields, including the aviation and ship-building industries. Energy flow analysis is well known to be effective for structural acoustics problems in the medium- to high-frequency range, with sufficient detail to include all significant information of the vibrational energy levels or global variation in vibrational energy densities. The aim of this article is to develop energy flow models for a dilatational wave in three-dimensional elastic solids. The energy governing equation derived for the model is expressed in terms of the time- and space-averaged energy density, which represents the global variation of the energy density quite well. Numerical analyses are performed to verify the validity and accuracy of the model for a cube-shaped structure vibrating at a single frequency, and the results of the analysis of energy density distributions from the energy flow analysis that is developed are compared to those obtained using NASTRAN. The energy flow models for the elastic solids, which are useful in the prediction of the vibrational response for a three-dimensional structural analysis at a medium-to-high frequency, are newly derived.

Turbulent-induced Noise of 2-dimensional Sonar Dome Shaped Structure

The latest research has shown that the turbulence-induced noise is important in total characteristics of flow noise. Also, turbulence-induced noise have a significant influence for performance of sonar dome. In this paper, Flow analysis is performed on vicinity of the sonar dome model using Large Eddy Simulation method. Also, direct method that extracts perturbational sound pressure, FW-H method without turbulence-induced noise and permeable FW-H method that is able to calculate turbulence- induced noise were compared in order to show turbulence effect.