• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.41 no.10
• /
• pp.820-826
• /
• 2013

In this paper, a compact and wideband CLAS(Conformal Load bearing Antenna Structure) was studied using smart skin technique. In order to satisfy the electrical performance of the CLAS antenna, the proposed CLAS antenna is composed of conductive mesh, face-sheet, radiator, honeycomb, housing. Especially, radiator is composed of composite magneto-dielectric material and radiating element etched on the PCB (Printed Circuit Board). The radiating element is inserted into the composite magneto-dielectric material and has sloted Folded LP(Log Periodic) structure. By fabricated composite magneto-dielectric, the resonance frequency is decreased and the impedance matching characteristics is improved. We verified that the antenna has wideband characteristics and compact size using the antenna test results.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.37 no.6
• /
• pp.586-594
• /
• 2009

This paper is the study on random, sinusoidal and shock vibration responses for the STSAT-3(science and technology satellite-3) proto-model which is the first small size all-composite satellite in Korea. The structure system of the STSAT-3 forms box type structure by joining several hybrid sandwich panels comprised of honeycomb core and carbon fiber reinforced laminated composite skins on both side. Mode shape, stress, displacement and acceleration responses are obtained on both the frequency domain and time domain by means of a commercial FEA software MSC/NASTRAN. From these analysis results, failure, safety factor and design validity are assessed. These results can be successfully applicable as reference data when a new satellite is developed as well as giving out an excellent criteria in satellite vibration treatment design.

• Proceedings of the KSME Conference
• /
• 2007.05b
• /
• pp.1920-1925
• /
• 2007

A transformer is a device that changes the current and voltage by electricity induced between coil and core steel, and it is composed of metals and insulating materials. In the core of the transformer, the thermal load is generated by electric loss and the high temperature can make the break of insulating. So we must cool down the temperature of transformer by external radiators. According to cooling fan's usage, there are two cooling types, OA(Oil Natural Air Natural) and FA(Oil Natural Air Forced). For this study, we used Fluent 6.2 and analyzed the cooling characteristic of radiator. we calculated 1-fin of detail modeling that is similar to honeycomb structure and multi-fin(18-fin) calculation for OA and FA types. For the sensitivity study, we have different positions(side, under) of cooling fans for forced convection of FA type. The calculation results were compared with the measurement data which obtained from 135.45/69kV ultra transformer flowrate and temperature test. The aim of the study is to assess the Fluent code prediction on the radiator calculation and to use the data for optimizing transformer radiator design.

• Korean Journal of Materials Research
• /
• v.12 no.11
• /
• pp.856-859
• /
• 2002

To investigate effects of heat treatments including grain size control in substrate aluminum on nanopore arrays in anodic alumina template, aluminum was heat treated at $500^{\circ}C$ for 1h. The heat treated aluminum was anodized by two successive anodization processes in oxalic solution and the nanopore arrays in anodic alumina layer were studied using TEM and FE-SEM. The highly ordered porous alumina templates with 110 nm interpore distance and 40 nm pore diameter have been observed and the pore array of the anodic alumina has a uniform and closely-packed honeycomb structure. In the case of alumina template obtained from heat treated aluminum substrate, the well- ordered nanopore region in anodic alumina increased and became more homogeneous compared with that from non-heattreated one.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2016.02a
• /
• pp.410.1-410.1
• /
• 2016

Vanadium dioxide ($VO_2$) is a well-known material that exhibits a metal-semiconductor transition at 340 K, with drastic change of transmittance at NIR region. However, $VO_2$ based thermochromics accompany with low visible transmittance value and unfavorable color (brownish yellow). Herein, we demonstrate the adjustment of visible transmittance of $VO_2$ thin film by nanosphere template assisted patterning process using sol-gel method. 2-Dimenstional honeycomb shape was varied as function of diameter of nanosphere and coating conditions. The morphological geometry of the films was investigated by FE-SEM and AFM. Result shows that inversed shape of nanosphere was formed clearly and pattern width was altered according to the bead size. This structure creates the geometrical blank area from the position of nanosphere which improves the optical transmittance at the visible region. Moreover, such patterned $VO_2$ thin film not only maintains the optical switching efficiency, but also generate the gorgeous scattering effect which presumably support the glazing application.

• Transactions of the Korean Society for Noise and Vibration Engineering
• /
• v.20 no.8
• /
• pp.703-709
• /
• 2010

An analysis tool for predicting transmission loss in high speed trains based on combined use of the statistical energy analysis and the finite element methods has been proposed. The analysis utilizes a commercially available numerical solver VA ONE with imbedded NASTRAN module. The proposed analysis tool is first verified by comparing numerically predicted transmission loss of a light rail transport(LRT) structure with experimental results. The comparison shows that the numerically predicted transmission loss is similar to the experimental data. The analysis tool is then applied to the prediction of transmission loss in the high speed train(HST) currently under development. Various sub-structures such as the floor, side panel and ceiling have been numerically analyzed to predict their transmission losses. The results obtained here can be used as input data for predicting the interior noise level of the HST at design stage.

• Journal of the Korean Society for Railway
• /
• v.12 no.1
• /
• pp.110-114
• /
• 2009

This study is for the evaluation of compressive strength restoration of sandwich composite laminates with adhesively bonded scarf patches. It was used in this study that the sandwich composite laminate with an aluminum honeycomb core and CF1263 woven fabric carbon/epoxy faces was applied to the car body structure for Korean tiling train. In this study, it was damaged by low velocity impact and repaired using scarf repair method. Then, the compressive strength restoration of assessed by compressive after impact (CAI) test. From the test, it could be known that the compressive strength was restored up to 72% by only scarf repair method and 91% applied by an extra ply over the undamaged one.

• Korean Journal of Materials Research
• /
• v.12 no.6
• /
• pp.458-463
• /
• 2002

Carbon nanotubes were synthesized at various conditions using Ni-catalytic thermal chemical vapor deposition method and their characteristic properties were investigated by SEM, TEM and Raman spectroscopy. Carbon nanotubes were formed on very fine Ni-catalytic particles. The carbon nanotubes synthesized by thermal decomposition of acetylene at $700^{\circ}C$ had a coiled shape, while those synthesized at $850^{\circ}C$ showed a curved and Y-shape having a bamboo-like morphology. It was found that the carbon nanotube was also made on the fine Ni-catalytic particles formed on the surface of 100~400nm sized large ones after pretreatment with $NH_3$.ber composites show the high dielectric constant and large conduction loss which is increased with anisotropy of fiber arrangement. It is, therefore, proposed that the glass and carbon fiber composites can be used as the impedance transformer (surface layer) and microwave reflector, respectively. By inserting the foam core or honeycomb core (which can be treated as an air layer) between glass and carbon fiber composites, microwave absorption above 10 dB (90% absorbance) in 4-12 GHz can be obtained. The proposed fiber composites laminates with sandwitch structure have high potential as lightweight and high strength microwave absorbers.

• Journal of the Korean Society of Clothing and Textiles
• /
• v.3 no.2
• /
• pp.23-27
• /
• 1979

The normal transmission characteristics of curtain fabrics were measured by sound level meter. Transmission coefficient was calculated by difference of incidence SPL and transmission SPL. The relation between this value and factors relating to the structure of curtain fabrics were investigated. The results of experiment were shown follow; 1. Transmission coefficients(approximately over $95\%$) of sound in curtain fabrics differ from according to the frequency. It was lower in 500Hz frequency, on the other hand, higher in 400, 640. 1000Hz frequency. It had a tendency to frequency among the samples. 2. The greater cover factor of sample was, the smaller the transmission coefficient of sound was. It was not influenced by thickness. 3. Air permeability was increased as the transmission coefficient of sound were greater. (correl. ation coefficient=0.83) 4. In the case of special single cloth weave(special honeycomb weave), there sometimes took place that transmission SPL was greater than incidence SPL.

• Composites Research
• /
• v.15 no.5
• /
• pp.19-26
• /
• 2002

Real defects in composite structures were detected by using laser measuring system. Four types of real defects, that is, impact-induced delamination in a composite laminate, debond in a honeycomb structure, free-edge delamination in a composite laminate and debond in an adhesive joint, were made by applying several types of loads to the specimens. Laser measuring system such as ESPI and shearography technique were used to detect those defects. Thermal loading method, which can easily induce the surface deformation of specimen, was used to detect the defects. Experimental results show that the defects in composite structures could be easily detected by ESPI and shearography technique. Moreover, it shows that ESPI and shearography technique could be usefully applied to the detection of defects in various kinds of composite structures.