• Proceedings of the Acoustical Society of Korea Conference
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• autumn
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• pp.233-236
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• 2001

일반적으로 스피커를 동작시키게 되면, 스피커 보이스 코일에 열이 발생하게 되고, 열에 의한 보이스코일의 저항의 증가가 나타나게 되는데, 기존의 연구는 저음용 스피커(Woofer) 만을 대상으로 스피커의 음향특성 변화들에 관해 수행되었다. 그러나, 현대의 스피커는 A/V시스템분야의 발전에 따라 고음재생의 충실도가 강조되고 있는 경향이므로, 고음용 스피커(Tweeter)에 대한 열 발생의 영향을 조사하였다. 본 연구에서는 고음용 스피커의 입력전력에 따른 특성 변화를 조사하고, 입력전력의 증가로 인한 보이스코일(voice coil)의 저항 증가에 따른 고음용 스피커의 특성변화에 관해 실험하였다. 그리고, 스피커의 진동에 의한 펌프(pump) 역할을 이용하는 냉각용 구멍을 뚫어 스피커의 특성변화를 검토하였다. 실험대상으로는 직경 25mm의 돔(Dome)형 진동판을 가진 고음용 스피커와 이 스피커의 후면 중심부에 구멍을 뚫어 열 방출구가 형성된 3종의 시료를 대상으로 특성변화를 비교$\cdot$측정하였다. 여기에서, 사용된 시료는 국내 Y사의 판매용 고음용 스피커로 제품의 원 상태인, 구멍이 없는 것을 기준시료로 하고, 이와 동일한 제품들의 후면에 각각 직경 5mm, 10mm, 15mm의 구멍을 가공하여 비교시료로 하였다. 기준 및 비교시료의 스피커 특성을, 한국산업규격 KS C 6027의 측정법에 따라, 입력 1W 상태에서 기준시료의 사양을 측정하였고[1], 입력을 0.5W, 1W, 2W, 4W, 8W, 16W로 가하여, 시료별 입력증가에 따른 스피커의 주파수 응답특성, 임피던스(Impedance), 조화 왜(Harmonic Distortion)의 변화율 측정을 통해 스피커의 특성변화 정도를 검토하였다. 향후, 본 연구의 결과는 고음용 스피커의 특성 열화에 대한 예측 및 개선 방안을 제시하는 기본 자료로 활용이 가능할 것으로 사료된다.용하여 현금흐름예측을 할 수 있는 Model을 제시하였다. 특히 건설공사의 현금흐름 예측의 중요한 요소인 Cash-Out에 대하여, 공사비 구성요소인 자재, 노무, 중기, 외주, 경비등 각 Resource의 보할(Weights)을 실 공사원가에 따른 보할의 변화와 Resource들의 Time Lag를 적용 기존 연구자의 Model과 다른 Model을 제시하였다. 또한 기존 연구자들의 Model과 비교하여 편리성, 정확도 및 신뢰성이 높은 Model임도 증명하였다.세대까지도 발현수준이 유지될 것으로 판단된다. 이러한 연구결과는 계통으로 확립된 형질전환 동물에 부여된 새로운 유전형질은 지속적으로 후대로 유전될 수 있음을 제시한다.잖⨀瘀Ā퀇Āゑ잖⨀Ā퀇Ԁ￿™잖⨀䌀Ā퀇ĀꄏĀꀏꄏĀꀏ₱?⨀Ā Ԁ￿䂱?⨀ऀĀ耀Ā삱?⨀؀Ā Ā?⨀ጀĀ耀Ā?돀ꢘ?⨀硩?⨀ႎ?⨀?⨀넆돐쁖잖⨀쁖잖⨀／ࠐ?⨀焆덐瀆倆Āⶇ퍟ⶇ퍟ĀĀĀĀ磀鲕좗?⨀肤?⨀⁅Ⴅ?⨀쀃잖⨀䣙熸ጁ↏?⨀

• Explosives and Blasting
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• v.31 no.1
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• pp.55-63
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• 2013

With increasing needs in power, Singapore is requiring stronger power transmission. Singapore Transmission Cable Tunnel is underground tunnel for transmission system installation such as 400 kV cable. This Transmission Cable Tunnel is 35 km long in total. The North-South Transmission Cable Tunnel is 18.5 km long and there is a total of three (3) contracts; NS1, NS2 and NS3 in respect of the design and construction. The East-West Transmission Cable Tunnel is 16.5 km long, and also there is a total of three (3) contracts; EW1, EW2 and EW3. Among of them, SK E&C has been awarded and operating contract EW2 and NS2. In scope of works, each contract has 3 to 4 shafts which connect aboveground and underground high volt cable and those shafts are used as TBM launching shafts during construction. Transmission Cable Tunnel is undercrossing middle of Singapore and most of shafts are located in urban area. Thus, optimal blasting design satisfying high blasting efficiency as well as blasting vibration limit of Singapore is highly required. Blasting design for large shaft of Singapore Transmission Cable Tunnel follows blasting vibration limits in Singapore and reflects our blasting engineering skills. With Singapore Transmission Cable Tunnel Contract EW2, it is expected that our excellent blasting engineering and performance skills can be delivered to the world.

• Journal of the Earthquake Engineering Society of Korea
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• v.9 no.4 s.44
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• pp.19-28
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• 2005

Long span structures with low natural frequencies such as shopping malls, large offices, and assembly rooms may experience signification dynamic responses due to human activities. In many cases, the group activities are common thing in comparison with the single activity. The purpose of this study is to evaluate the responses of building structure subjected to group human loads using mode shapes. For this purpose, equations to estimate the magnitudes ol responses ol structure subjected to group walking loads are derived. And the correlation of loads is verified for identifying the relation of each human load composing of group human loads using two load cells. The method is proposed for evaluating the responses of structure subjected to group loads using mode shapes and correlation function related to each human loads. The effectiveness ol the proposed method is verified analytically using a simple beam and floor and experimentally on a footbridge measuring the structural response induced by group pedestrians for the case of synchronization or not. Results indicate that the amplitudes of group walking loads can be easily estimated if the mode shapes are available, and that the corresponding structural responses can be estimated easily by the simple response measurement using the proposed method.

• Journal of the Society of Naval Architects of Korea
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• v.29 no.1
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• pp.143-157
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• 1992

For the design of structural systems having the prescribed or optimum dynamic characteristics, some design changes of the initially designed system are required. In these cases, if the sensitivity analysis which can predict the changes of dynamic characteristics due to the changes of design variables is applied, the design changes can be carried out rationally and very efficiently. For many structural systems, it is well known that the analysis by the transfer matrix method(TMM) and the combined finite element-transfer matrix method(FETMM) is more efficient than the analysis by the finite element method. However, most known studies on the sensitivity analysis of structural systems premise using the finite element method. In this paper, the sensitivity analysis methods by the TMM and the FETMM are presented and some numerical investigations on the beam-column with elastically restrained ends and intermediate contraints and the stiffened plate having subsystems are carried out. The results of the numerical examples show good accuracy and computational efficiency of the presented methods, and show that the application of sensitivity analysis in the dynamic characteristic reanalysis give good results within the practically changeable range of design variables.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.1
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• pp.27-33
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• 2010

This paper focuses on the design of microspeakers with minimum flux leakage, for use in radiotelegraphy. The response surface methodology (RSM) is applied as the optimization technique for obtaining a large magnetic force and a small flux leakage on diaphragm. The object functions of this optimization are the magnetic force and the flux leakage along three factors; pole piece thickness, magnet grade and yoke thickness, which are determined by the design of the experiment. The magnetic force and the flux leakage are calculated for each condition and optimized by results evaluated with RSM. For a pole piece thickness of 0.9 mm, a magnet grade of N42H and a yoke thickness of 0.75 mm, the magnetic force is satisfied as initial model and flux leakage is decreased to 11.8% than initial model.

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
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• v.11 no.1
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• pp.12-17
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• 2018

This study describes the design and implementation of Antenna for Digital Satellite Communication. The Antenna unit for SHF band consists of Reflector, Septom Polarizer, Feed Horn and Support Frame etc. Thought analysis of space environment before production, the possibility of the malfunction of equipment minimized and we designed a reliable Antenna through simulation for vibration and thermal analysis generated during the launch, and compared pre-simulation of main performance results to test results about main performances of Antenna after production. After fabricating the antenna, the maximum gain of the antenna main beam is 36.5dBi, which satisfies the requirement of 35dBi or more, and it also satisfies the requirement of -20dB for return loss of less than -24dB. Also, the isolation of the transmission and reception of the antenna is -22.6dB or less, which satisfies the requirement of -20dB or less. The antenna for digital satellite communication described in this paper can be used in the satellite field of geostationary earth orbit and low earth orbit requiring high reliability in the future.

• Journal of Satellite, Information and Communications
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• v.1 no.2
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• pp.63-70
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• 2006

This paper presents the results of Ka band qualification model multiplexers for COMS Payload to be launched in 2008. These are the input and output multiplexers of the satellite transponder to use available frequency resources effectively and the diplexer of the satellite antenna to use the same reflector for both transmitting and receiving frequency bands, respectively. The input multiplexer with four frequency channels has four(4) independent channel filters which consist of an 8-pole elliptic band-pass filter for high frequency selectivity and a 2-pole equalizer for group delay equalization. For low insertion loss, mass and volume reduction, manifold type os employed for output multiplexer. E-plane T-junction is used for either splitting or combining a frequency band into two sub-bands. Asymmetric inductive irises are used to tune the receiving filter easily. The electrical performance and environmental test such as vibration test, mechanical shock test, thermal vacuum test and EMC test are performed and the results of all qualification model multiplexers are compliant to the requirement of each multiplexer. Followed by this qualification, the flight model equipment will be developed.

• Journal of Biomedical Engineering Research
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• v.28 no.5
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• pp.647-656
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• 2007

The purpose of this study was to analyze the effects of vibratory stimulus as somatosensory inputs on the postural control in human standing. To study these effects, the center of pressure(COP) was observed while subjects were standing on a stable and an unstable support with co-stimulated mechanical vibrations to flexor ankle muscles(tibialis anterior tendon, achilles tendon) and two plantar zones on both foot. The COP sway measurement was repeated twice in four conditions: (1) with visual cue and vibration, (2) without visual cue and vibration, (3) with visual cue and without vibration, (4) without visual cue and with vibration. The calculated parameters were the COP sway area and the distance, the median frequency and the spectral energy of COP sway in three intervals $0.1{\sim}0.3,\;0.3{\sim}1,\;1{\sim}3Hz$. The results showed that vibratory stimulus affect postural stability. The reduction rate of the COP sway with vibratory stimulus were higher on the unstable support because the effect of postural stability increases when afferent nervous flow is more activated by vibration on unstable support. If unclear visual or vibratory information is received, one type of information is compared with the other type of sensory information. Then the input balance between visual and vibratory information is corrected to maintain postural stability. These findings are important for the rehabilitation system of postural balance control and the use of vibratory information.

• Journal of the Korean Society for Railway
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• v.15 no.1
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• pp.62-70
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• 2012

Dynamic behaviors of line type bearings, spherical bearings and disk bearings which are being used for railway steel bridges are investigated, and that of the bridges is also analyzed. For the purpose, the vertical displacements of the three bearings including fixed and expansion type are measured and analyzed. Also, the deformation of the PTFE plate placed inside of spherical and disk bearings of expansion type is measured and its effect on the dynamic behavior of the bridges is discussed. The up-lift phenomenon at the bearings installed for the steel bridges is estimated. The vertical displacements at mid-span of the bridges are compared according to the bearing types. Finally, the 1st mode natural frequencies are estimated and the relationship to the vertical displacement is discussed.

• Journal of the Korean Vacuum Society
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• v.21 no.1
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• pp.36-40
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• 2012

We have developed the detection method of the resonance frequency of micro/nano mechanical resonator using optical method. The optical interferometery method enabled us to detect the displacement change of resonators within several nm scale. The micro mechanical resonator was produced by attaching a micro mechanical cantilever to a piezo ceramic. The mass of cantilever was increased by evaporating Au using electron beam evaporator and the mass variation was estimated by detecting the resonance frequency changes.