• Earthquakes and Structures
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• 제13권3호
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• pp.255-265
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• 2017

In this paper, an efficient shear deformation theory is developed for wave propagation analysis in a functionally graded beam. More particularly, porosities that may occur in Functionally Graded Materials (FGMs) during their manufacture are considered. The proposed shear deformation theory is efficient method because it permits us to show the effect of both bending and shear components and this is carried out by dividing the transverse displacement into the bending and shear parts. Material properties are assumed graded in the thickness direction according to a simple power law distribution in terms of the volume fractions of the constituents; but the rule of mixture is modified to describe and approximate material properties of the functionally graded beams with porosity phases. The governing equations of the wave propagation in the functionally graded beam are derived by employing the Hamilton's principle. The analytical dispersion relation of the functionally graded beam is obtained by solving an eigenvalue problem. The effects of the volume fraction distributions, the depth of beam, the number of wave and the porosity on wave propagation in functionally graded beam are discussed in details. It can be concluded that the present theory is not only accurate but also simple in predicting the wave propagation characteristics in the functionally graded beam.

• Architectural research
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• 제15권3호
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• pp.151-158
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• 2013

Offshore oil and gas process plants are exposed to hazardous accidents such as explosion and fire, so that the structural components should resist such accidental loads. Given the possibilities of thousands of different scenarios for the occurrence of an accidental hazard, the best way to predict a reasonable size of a specific accidental load would be the employment of a probabilistic approach. Having the fact that a specific procedure for probabilistic accidental hazard analysis has not yet been established especially for explosion and fire hazards, it is widely accepted that engineers usually take simple and conservative figures in assuming uncertainties inherent in the procedure, resulting either in underestimation or more likely in overestimation in the topside structural design for offshore plants. The variation in the results of a probabilistic approach is determined by the assumptions accepted in the procedures of explosion probability computation, explosion analysis, and structural analysis. A design overpressure load for a sample offshore plant is determined according to the proposed probabilistic approach in this study. CFD analysis results using a Flame Acceleration Simulator, FLACS_v9.1, are utilized to create an overpressure hazard curve. Moreover, the negative impulse and frequency contents of a blast wave are considerably influencing structural responses, but those are completely ignored in a widely used triangular form of blast wave. An idealistic blast wave profile deploying both negative and positive pulses is proposed in this study. A topside process module and piperack with blast wall are 3D FE modeled for structural analysis using LS-DYNA. Three different types of blast wave profiles are applied, two of typical triangular forms having different impulse and the proposed load profile. In conclusion, it is found that a typical triangular blast load leads to overestimation in structural design.

• 대한기계학회논문집B
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• 제25권10호
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• pp.1327-1336
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• 2001

The structural modes driven by the low wave-number components of smooth elastic wall pressure provide a relatively weak coupling between the flow and the wall motion. If the elastic thin plate has any resonant mode whose wave-number of resonance coincides with $\omega$/U$\sub$c/, the power will be transmitted to those modes of vibration by the flows. We examine the problem in which the elastic thin plate is subject to pressure fluctuations under turbulent boundary layer. Measurements are presented of the frequency spectra of the near- and far-field pressures and radiated sound contributed by the various wave modes of the thin elastic plate. Dispersion equation for wave motions of elastic plate is used to investigate the effect of bending waves of relatively low wave number on radiated sound. The low wave-number motion of elastic plate is observed to have much less influence on the low-frequency energy of wall pressure fluctuations than that of the rediated sound. High amplitude events of the wall pressure are observed to weakly couple with high-frequency energy of radiated sound for case of low tension applied to the plate. The sound source localization is applied to the measurement of radiated sound by using acoustic mirror system.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2003년도 하계학술대회 논문집 Vol.4 No.1
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• pp.50-53
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• 2003

CMP (chemical mechanical polishing) process remained to solve several problems in deep sub-micron integrated circuit manufacturing process. especially consumables (polishing pad, backing film, slurry, pad conditioner), one of the most important components in the CMP system is the slurry. Among the composition of slurries (buffer solution, bulk solution, abrasive particle, oxidizer, inhibitor, suspension, antifoaming agent, dispersion agent), the abrasive particles are important in determining polish rate and planarization ability of a CMP process. However, the cost of abrasives is still very high. So, in order to reduce the high COO (cost of ownership) and COC (cost of consumables) in this paper, we have collected the silica abrasive powders by filtering after subsequent CMP process for the purpose of abrasive particle recycling. And then, we have studied the possibility of recycle of reused silica abrasive through the analysis of particle size and hardness. Also, we annealed the collected abrasive powders to promote the mechanical strength of reduced abrasion force. Finally, we compared the CMP characteristics between self-developed KOH-based silica abrasive slurry and original slurry. As our experimental results, we obtained the comparable removal rate and good planarity with commercial products. Consequently, we can expect the saving of high cost slurry.

• 에너지공학
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• 제6권1호
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• pp.41-51
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• 1997

단일 드럼형 보일러를 갖는 발전 플랜트의 동특성 해석을 위한 프로세스 모델이 모듈 개념을 기반으로 묘사된다. 현재의 프로세스 모델은 플랜트 전체 구성 요소 및 고부하에서의 부하 변동을 포함하며 lumped parameter에 의해 물리적으로 접근된다. 플랜트 성분을 의미하는 모듈은 필수적으로 성분 특성을 잘 묘사하며 사용자에 의해 결정된 배열에 대해 압력점 방식에 의해 상호 연결된다. 프로세스 모델의 발전 플랜트 시스템에 대한 적용성 여부를 조사하기 위해 100MW발전 플랜트의 실제 운전 LOG-IC을 갖는 제어 시스템에 연결하여 3MW/min 부하 변동율로 75MW에서 95MW, 95MW에서 75MW조건에 대해 조사된다.

• 공업화학
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• 제10권6호
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• pp.809-813
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• 1999

D상 유화법을 적용하고 상도를 이용하여 유화메커니즘을 설명하였다. D상 유화작용은 등방성 계면활성제 용액의 형성과 함께 시작되며 계면활성제 용액에 octamethyl cyclotetrasiloxane(OMCS)의 분산으로 계면활성제중 오일(O/D) 겔 유화물의 형성에 의해 진행된다. 폴리올은 이 실험목적상 필수성분이다. 폴리올의 기능을 이해하기 위해 비이온 계면활성제/오일/물/폴리올계의 용액거동을 폴리옥시에틸렌올레일에테르/OMCS/프로필렌글리콜(PG)의 수용액인 3성분의 상도를 이용하여 조사하였다. 등방성 계면활성제상에서 오일의 용해도는 PG를 가함에 따라 증가하였다. D상 유화물은 OMCS의 농도가 70~90% 범위에서와 계면장력이 2.0~3.0 dyne/cm 범위에서만 형성되었으며, D상 유화물은 $10{\mu}m$ 정도 크기의 균일한 구상으로 O/W 형이었다.

• 한국의류학회지
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• 제12권2호
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• pp.225-235
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• 1988

The effects of surface free energy of substrates on the soiling and on the detergency of the oily soil were studied. The surface tension consisted of dispersion force and polar force components of substrate, oily soil and surfactant solutions were calculated by extended Fowkes' equation. From these values, work of adhesion($W_a$), work of detergency($W_D$), ana residual work of detergency($W_{D,R}$) were calculated. The correlations between these theoretical values of the works and detergency were discussed. MAA grafted PET film was used as substrate, triolein as oily soil and nonylphenol polyoxyethylene ether(NPE) having various mole numbers of oxyethylene adducts and dodecylbenzene sulfonate (DBS) as surfactants. Detergency was estimated by means of radioactive tracer method using $C^{14}-triolein$. The results showed that $W_a$ was decreased with the increase of surface free energy of substrate. In water, $W_D\;and\;W_{D,R}$ were decreased and detergency of tiolein was increased with the increase of surface free energy of substrate. In surfactant solutions, the lower the surface free energy of substrate and the lower oxyethylene adducts of NPE were the more effective on detergency. The detergency of DBS solution was the lowest in the case of ungrafted PET film, but even small increase in surface free energy by grafting showed much increase in detergency.

• 자원환경지질
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• 제26권1호
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• pp.97-106
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• 1993

In order to provide informations for the earth's deep interior and the earthquake mechanism, we have been operating the three components of Streckeisen Seismometers at Pohang Observatory, Korea, as a part of a long period seismic network (POSEIDON) in the northwestern Pacific now under construction. The recording system is specially designed to be able to obtain outputs of broad band and wide dynamic range; BRB (Broad Band), LP (Long Period), and VLP (Very Long Period) output. The triggered BRB and LP signals are digitized with the sampling intervals of 0.1 and 0.4 second, respectively. The lowpass filtered VLP output is digitized and recorded contineously with the sampling interval of 10 seconds. About 120 regional and teleseismic events have been successfully recorded for one and half year since late March, 1991. As a preliminary study, eight events of them are analyzed to determine Rayleigh wave dispersion curves in the period range of 20 to 300 seconds for the continental and oceanic paths. The curves are compared with the typical continental and oceanic ones to discuss the earth's deep interior.

• 대한의용생체공학회:의공학회지
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• 제16권4호
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• pp.525-532
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• 1995

이 연구는 다음 두가지 사실에 기초를 두고 있다. 첫째, 혈관의 맥동은 전통적으로 동양의 한방에서 오랫동안 인체진단을 위해 사용되어져 왔다는 것이고, 둘째는 신체조직에서 파동의 비선형전파특성이 의용진단에 유용한 정보를 준다는 것이다. 따라서, 혈관의 벽을 전파하는 맥동파의 비선형전파특성은 의용진단을 위하여 효과적으로 이용될 수 있다는 것을 예측할 수 있다. 본 논문에서는, 혈관을 따른 두 지점에서 변위파형을 초음파 도플러 신호에 대한 직교검파에 의해 구하고, 여기에 바이스펙트럼해석과 볼테라모델전개를 적용하여 두지점 사이의 비선형 전달함수를 추정하며, 이것이 의용진단에 적용가능한지 모의샘플에 대하여 고찰하는 것을 목적으로 한다.

• 한국전자파학회논문지
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• 제11권6호
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• pp.990-995
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• 2000

밀러미터 내역(30~300GHz)의 전파에 대한 관심이 증가하면서 저손실 특성을 갖는 Nonradiative Dielectric(NRD) 도파로에 대한 관심이 커지고 있다. NRD 도파로는 분산특성이나 유전체 내의 필드 분포 형태로 볼 때 양 측면의 전도체가 없는 유전체가 채워진 도파관과 유사하므로 도파관으로 구현되는 대부분의 소자들은 NRD도파로를 이용하여 구현할 수 있다. 기존의 gap-coupled NRD guide 대역통과 여파기의 설계에서는 갭(gap) 영역의 임피던스를 Variational Method를 이용하여 해석하였으나 본 논문에서는 갭 영역을 차단영역 도파관의 등가회로 모델로 대치하여 해석함으로써 설계과정을 간단히 하였다. 또 이러한 설계 방법을 미리미터 대역의 필터에 적용하기 전에 시험적으로 중심 주파수가 10GHz인 대역통과 필터(3-Pole, 0.1dB ripple, 2% bandwidth)를 설계, 제작하였다. 측정한 결과느느 HFSS (High Frequency Structure Simulator)로 시뮬레이션 한 결과와 제작의 오차범위 내에서 일치하였다.