• Journal of the Korean Society of Marine Environment & Safety
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• v.21 no.6
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• pp.737-743
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• 2015

This paper are mainly focusing on the facts influencing on RCS reductions, appling radar absorbing materials by using RCS contributions of elements and appling a metamaterials which is high-tech radar absorbing materials. RCS analysis results are given for a simplified ship model, with radar absorbing materials and metamaterials cause RCS reduction in terms of mean values.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.32 no.6
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• pp.64-71
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• 2004

The object of this study is to design the Radar Absorbing Structures (RAS) having sandwich structures in the X-band ($8.2{\sim}12.4GHz$) frequencies. Glass fabric/epoxy composites containing conductive carbon blacks and carbon fabric/epoxy composites were used for the face sheets. Polyurethane(PU) foams containing multi-walled carbon nanotube (MWNT) were used for the core. Their permittivities in the X-band were measured using the transmission line technique. The reflection loss characteristics for multi-layered sandwich structures were calculated using the theory of transmission and reflection in a multi-layered medium. Three kinds of specimens were fabricated and their reflection losses in the X-band were measured using the free space technique. Experimental results were in good agreements with simulated ones in 10dB absorbing bandwidth.

• The Journal of the Acoustical Society of Korea
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• v.41 no.4
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• pp.375-388
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• 2022

This paper deals with the process of obtaining sound transmission loss of a cylindrical silencer lined with multi-layered poroelastic sound absorbing materials. The Biot model and the Johnson-Champoux-Allard-Lafarge (JCAL) model were used to deal with waves propagating in multi-layered poroelastic materials. The boundary conditions required for analysis of the silencer were obtained and the numerical process of finding modes was explained. A numerical experiment was conducted on the 2-layered silencer using the modes and the transmission loss converged with the first 12 modes. Finally, the mode matching method proposed in this research was validated by being compared with the results calculated from Finite Element Method (FEM) about different kinds of sound absorbing materials.

• Journal of Korean Association for Spatial Structures
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• v.6 no.2 s.20
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• pp.131-136
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• 2006

It is important to evaluate energy absorption capacity of frames required during a design earthquake. An inelastic computer analysis based on mathematical modelling of energy absorbing frames and elements makes it possible to evaluate required energy absorption capacity. But such an analysis sometimes consumes much computation time particularly in case of complicated structural system. This paper presents a proposal to predict energy absorption of multi-bent steel frames by simple equivalent linear method.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.12 no.6
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• pp.1002-1008
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• 2001

The absorbing structure composed of multi-layered fiber reinforced composite materials was designed and microwave absorbing properties are investigated. On the basis of transmission line theory, the theoretical equations to predict the reflection loss and the appropriate composite material for each functional layer are suggested. The most significant result of this study is the successful design and fabrication of triple-layered composite laminates which has the superior microwave absorbing porperties (more than 10 dB in 4∼12 GHz range), without using the ferrite filler in the impedance transforming layer. In the two-layered composite laminate (absorber/substrate), however, the use of ferrite filler (about 40 wt %) in the absorbing layer is necessary to obtain the certain level of microwave absorbance. By combining the glass-fiber composite with ferrite filler and carbon-fiber composite substrate, the microwave absorbing properties more than 10 dB in 4∼12 GHz frequencies than be obtained.

• Journal of Drive and Control
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• v.11 no.1
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• pp.1-7
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• 2014

This paper presents a novel concept of wave energy converter for electric generation from the ocean wave energy. In this paper, a Multi-Point Absorbing Wave Energy Converter, shortened as MPAWEC by using Secondary Control Hydrostatic Transmission (SCHST) was proposed. The power take-off (PTO) system in the proposed MPAWEC includes multi heaving buoys to drive hydraulic pumps placed at different points. The application of SCHST in MPAWEC gives some advantages, such as longevity of hydraulic components; more energy is harvested; the variation of the pressure in the accumulator limited; therefore the accumulator volume is reduced and the output speed is more stable, etc. A PID controller was designed for speed control of the hydraulic motor. The simulation results indicated that the speed of the generator was ensured with the relative error as 0.67%; the efficiency of the proposed system was 71.4%.

• The Journal of the Acoustical Society of Korea
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• v.41 no.6
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• pp.723-729
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• 2022

In this study, the multi perforated plate is used to reduce the compressor noise in the low frequency band inside the refrigerator machine room. To predict the sound absorption results, the impedance of the sound absorption material is measured. Using the measured impedance results, it is confirmed that the results used for FEM analysis is almost similar to the experimental values. The sound-absorbing structure that can operate in the target frequency band inside the refrigerator machine room is designed by controlling the hole diameter and arrangement in the perforated plate. The effect of reducing noise in the low frequency band is confirmed by applying perforated plate-based sound absorbing structures to the machine room.

• Journal of Korean Tunnelling and Underground Space Association
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• v.19 no.1
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• pp.1-9
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• 2017

In this study, a test-bed system simulated a tunnel and concrete track is tested on cite and invested an allowed limit of multi-layered sound absorbing panel for reducing noise reflected on the concrete track in train tunnel considering the criteria and limitation on the theoretical back ground. The studied results are an effective evaluating system of the sound absorbing coefficient influenced fluid effects depending on the vehicle speed in the urban train tunnel and measuring not only structural behaviors of maximum displacement and acceleration of the panel but also dynamic characteristics of damping ratio and natural frequency.

• Journal of the Institute of Electronics Engineers of Korea TE
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• v.37 no.2
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• pp.91-95
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• 2000

A new damping composite materials with asphalt and EM absorber are studied for high advantage values. The composite Ni-Zn ferrite and dielectric PZT with a main material is well developed of EM absorbing, and is continuous maintained of origin character, damping absorbing. Experiments and calculation results are shown to act two points frequencies at 928MHz and from 2MHz to 4GHz below -l0dB The narrow band widths of ferrite change to broad band as insert of dielectric material, PZT good of EM wave absorbtion and broad band widths in multi layers with ferrite These are applied to develop of new material at new need frequencies.

• Journal of the Korean housing association
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• v.11 no.1
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• pp.171-181
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• 2000

The purpose of the resent research is to investigate the characteristics of sound insulation at the circular voided concrete slab in the multi-housing. In order to do this research, the method for field measurement of floor impact sound level was used following the Korea Standard F2810-1996. For the multi-housing, three kinds of circular voided concrete slabs are used to measure the characteristics of sound insulation.The results are as follows; 1.The main factor affecting the characteristics of sound insulation at the circular voided concrete slab in the multi-housing is sound-absorbing materials in the circular tube. 2. The main factor to effect the difference of sound pressure level is circular tube in the concrete slab. 3. The forms of circular tubes effect the characteristics of sound insulation at the circular tube. 4. Sound Pressure Level resulting from the piping direction of circular tubes in little different to octave band level.More study will be needed about the depth and distance of sound insulation materials, and the components of sound insulation materials for the multi-housing.