• Structural Engineering and Mechanics
• /
• 제87권1호
• /
• pp.95-106
• /
• 2023

This paper investigates the dynamic response of a functionally graded material (FGM) coated half-plane excited by distributed time harmonic loading. Three types of typical distributed surface loads, including uniform load, Hertz load, and square-root singular load, are considered. The mass density and elastic modulus of the FGM coating are supposed to be described by the exponential function. The material damping is modelled by a linearly hysteretic damping which is expressed by a complex modulus in the time harmonic motion. Using Fourier integral transform technique and numerical integral method, the effects of the excitation frequency, gradient index, damping, and load type on the dynamic stresses and displacements are discussed.

• 한국정보통신학회:학술대회논문집
• /
• 한국정보통신학회 2022년도 추계학술대회
• /
• pp.536-538
• /
• 2022

Space-time line code (STLC)라는 새로운 다이버시티 기술의 발명 이후로, 오류율과 에르고딕 용량이 이론적으로 분석되었지만, 아웃티지 확률에 대한 연구가 수행되지 않았다. 본 논문에서는 STLC 시스템의 순시 신호 대 잡음비의 확률 밀도 함수를 도출하고, 아웃티지 확률의 닫힌-형식 표현을 수학적으로 유도하였다. 또한, 전산 실험을 통하여 분석 결과의 정확성을 검증하고, 시스템 설계 및 구현에 대한 통찰을 제시하였다.

• 산업경영시스템학회지
• /
• 제42권4호
• /
• pp.194-202
• /
• 2019

Reliability analysis of the components frequently starts with the data that manufacturer provides. If enough failure data are collected from the field operations, the reliability should be recomputed and updated on the basis of the field failure data. However, when the failure time record for a component contains only a few observations, all statistical methodologies are limited. In this case, where the failure records for multiple number of identical components are available, a valid alternative is combining all the data from each component into one data set with enough sample size and utilizing the useful information in the censored data. The ROK Navy has been operating multiple Patrol Killer Guided missiles (PKGs) for several years. The Korea Multi-Function Control Console (KMFCC) is one of key components in PKG combat system. The maintenance record for the KMFCC contains less than ten failure observations and a censored datum. This paper proposes a Bayesian approach with a Dirichlet mixture model to estimate failure time density for KMFCC. Trends test for each component record indicated that null hypothesis, that failure occurrence is renewal process, is not rejected. Since the KMFCCs have been functioning under different operating environment, the failure time distribution may be a composition of a number of unknown distributions, i.e. a mixture distribution, rather than a single distribution. The Dirichlet mixture model was coded as probabilistic programming in Python using PyMC3. Then Markov Chain Monte Carlo (MCMC) sampling technique employed in PyMC3 probabilistically estimated the parameters' posterior distribution through the Dirichlet mixture model. The simulation results revealed that the mixture models provide superior fits to the combined data set over single models.

• 전기전자학회논문지
• /
• 제28권1호
• /
• pp.38-45
• /
• 2024

간단한 자기장 감금이 레이저 유도 플라즈마의 전하 입자들에 미치는 영향이 논의 되었다. 자기장 영향에 대한 이전 연구들은 주로 플라즈마 방전 세기의 향상이나 수명시간 연장에 집중되었다. 이와 대조적으로, 본 개발은 과거에 거의 다뤄지지 않았던, 플라즈마 소멸에 대해 연구하였다. 이는 플라즈마를 활용한 기술개발에 혁신적인 도움이 될 것으로 기대한다. Nd:YAG 레이저(1064 nm, 6 ns)가 3가지 타입의 금속 물질(Al, Ti, STS)과 공기 중에 집광되었다. Nd₂Fe₁₄B 자석으로 0.4T 크기의 자기장을 만들었고, 이를 레이저 유도 플라즈마에 관통시켰다. 플라즈마 스펙트럼은 레이저 파워와 분광기의 딜레이 타임을 조정해 가면서 자기장 여부에 따른 수치가 측정되었다. O I(777.42 nm), Fe I (520.447 nm), Ti I (503.649 nm), Al I (396.147 nm) 스펙트럼 분석을 통해 자기장에 의한 플라즈마의 소멸이 특정 조건에 상관없이 항상 촉진됨을 독점적으로 발견하였다.

• 한국신재생에너지학회:학술대회논문집
• /
• 한국신재생에너지학회 2007년도 추계학술대회 논문집
• /
• pp.417-423
• /
• 2007

Oxy-gasification or oxygen-blown gasification, enables a clean and efficient use of coal and opens a promising way to CO2 capture. The coal gasification process of a slurry feed type, entrained-flow coal gasifier was numerically predicted in this paper. The purposes of this study are to develop an evaluation technique for design and performance optimization of coal gasifiers using a numerical simulation technique, and to confirm the validity of the model. By dividing the complicated coal gasification process into several simplified stages such as slurry evaporation, coal devolatilization, mixture fraction model and two-phase reactions coupled with turbulent flow and two-phase heat transfer, a comprehensive numerical model was constructed to simulate the coal gasification process. The influence of turbulence on the gas properties was taken into account by the PDF (Probability Density Function) model. A numerical simulation with the coal gasification model is performed on the Conoco-Philips type gasifier for IGCC plant. Gas temperature distribution and product gas composition are also presented. Numerical computations were performed to assess the effect of variation in oxygen to coal ratio and steam to coal ratio on reactive flow field. The concentration of major products, CO and H2 were calculated with varying oxygen to coal ratio (0.2-1.5) and steam to coal ratio(0.3-0.7). To verify the validity of predictions, predicted values of CO and H2 concentrations at the exit of the gasifier were compared with previous work of the same geometry and operating points. Predictions showed that the CO and H2 concentration increased gradually to its maximum value with increasing oxygen-coal and hydrogen-coal ratio and decreased. When the oxygen-coal ratio was between 0.8 and 1.2, and the steam-coal ratio was between 0.4 and 0.5, high values of CO and H2 were obtained. This study also deals with the comparison of CFD (Computational Flow Dynamics) and STATNJAN results which consider the objective gasifier as chemical equilibrium to know the effect of flow on objective gasifier compared to equilibrium. This study makes objective gasifier divided into a few ranges to study the evolution of the gasification locally. By this method, we can find that there are characteristics in the each scope divided.

• 수산해양기술연구
• /
• 제27권1호
• /
• pp.1-12
• /
• 1991

적분방식에 의한 어군량추정법을 실험적으로 검증하기 위하여, 실험수조에서 50 kHz와 200 kHz의 주파수를 대상으로 모의어군의 분포밀도와 초음파산란강도의 관계를 검토하고, 또 계량어군탐지기의 정도를 개선하기 위한 문제들에 대하여 고찰을 행한 결과를 요약하면 다음과 같다. 1. 어체의 모의표적으로 이용한 steel ball (직영 35mm)의 실측 echo 파형은 이론 echo 파형과 잘 일치하였다. 2. 5 종류의 주파수에 대하여 고등어 (체장 36cm)의 반사주파수특성을 조사한 결과, 측정주파수가 변화함에 따라 어체에 의한 echo 신호의 진폭과 파형이 크게 변동하고 있음을 알 수 있었다. 3. 송수파기의 음속 내에서 5개/m 상(3)와 30개/m 상(3)의 표적 군이 서로 상하로 존재할 때, 상부 표적군의 존재에 의해 하부 표적군의 echo level이 -0.43 dB 감쇠하는, 소위 그늘효과(shadowing effect)가 발생하였다. 4. 동지나해에서 정박 중에 탐지한 고밀도 어군의 echo신호와 그 어군직하의 해저에서 산란된 echo 신호를 상호 연관시켜 분석한 결과, 어군층내에서 발생한 어군감쇠와 다중산란효과가 해저 echo 신호의 변동에 큰 영향을 미치고 있음을 알 수 있었다. 5. 정치망의 원통에 인망한 정어리의 단위체적당에 대한 분포밀도가 36마리/m 상(3)였을 때, 해저기녹이 소실되는 어군감쇠현상과, 어군 echo 신호가 해저까지 신장되는 다중산란현상이 동시에 발생하였다. 6. 50kHz와 200kHz의 주파수에서 표적군의 평균체적산란강도(:dB)와 표적의 분포밀도($\rho$:개/m 상(3))의 간에 다음의 회귀직선식을 얻었다. 50kHz : =-46.2+13.7 Log($\rho$). 200kHz : =-43.9+13.4 Log($\rho$). 7. 표적의 분포밀도가 5, 10, 15, 20, 25, 30 개/m 상(3)였을 때, 적분방식에 의한 추정치는 50kHz에서 2.0, 8.1, 9.9, 14.1, 19.2, 26.7 개/m 상(3)이었고, 200kHz에서는 2.0, 8.0, 9.1, 15.0, 20.1, 24.1 개/m 상(3)이었으며, 단위체적당에 분포하는 표적의 수가 많을수록, 그 추정치의 정도가 높아지는 경향을 나타내었다. 또한, 양주파수에서 분포밀도의 추정치는 실제보다 약 30%정도 과소추정되었다.

• 한국초전도ㆍ저온공학회논문지
• /
• 제26권2호
• /
• pp.9-18
• /
• 2024

The current study deals with the possible interplay between superconductivity and spin density wave in two band model high temperature iron based superconductor (FeBSC) Ba_1-xNa_xFe₂As₂. The electron and hole bands in the presence of the inter-band interaction between the two bands is becoming a vital issue to deal with the high temperature physics of the iron-based superconductors. In this research work, a model Hamiltonian appropriate for the system under consideration has been developed and the temperature dependent Green's function technique has been employed to get the solution for the equations of motion constructed for the two band model high temperature FeBSC Ba_1-xNa_xFe₂As₂. By making use of the decoupling procedure, the equations of motion for the dependence of superconducting transition temperature (T_C) on spin density wave(SDW) order parameter (Δ_SDW) in the electron intra-band (Δ_sc(e)) , hole intra-band (Δ_sc(h)) and inter-band (Δ_sc(eh)) for Ba_1-xNa_xFe₂As₂ have been obtained. We have also obtained the expression for the dependence of spin density wave transition temperature(T_SDW) on Δ_SDW for Ba_1-xNa_xFe₂As₂. Using some plausible approximations and appropriate experimental values for the parameters in the obtained equations of motion, phase diagrams of T_C versus Δ_sc(e), Δ_sc(h) and Δ_sc(eh) are plotted. Furthermore, a phase diagram of T_SDW versus Δ_SDW is plotted for the material under consideration. Finally, using the above mentioned phase diagrams, the interplay between superconductivity and spin density wave in the two band model high temperature FeBSC Ba_1-xNa_xFe₂As₂ has been demonstrated to be a very distinct possibility. The agreement of the current finding with the experimental observations is quite commendable.

• 한국컴퓨터그래픽스학회논문지
• /
• 제17권3호
• /
• pp.1-7
• /
• 2011

최근에 GPU 기반의 볼륨 광선 투사법을 가속화하는 기법들이 많이 연구되고 있다. 하지만 이런 기법들은 CPU-GPU간 데이터 전송 시 병목 현상을 야기하고 계층구조를 표현하기 위한 추가적인 GPU 메모리 공간이 필요할 뿐만 아니라 불투명도 전이 함수가 변경되었을 때 실시간에 대응하지 못하는 문제점들이 발생할 수 있다. 본 논문에서는 이러한 문제점들을 해결하기 위해 GPU 기반의 효율적인 빈 공간 도약 기법을 제안한다. 브릭(brick) 안에 포함되는 복셀들의 최대 밀도 값을 하나의 정점에 저장하고 불투명도 전이 함수에 의하여 투명하다고 판별된 정점들을 기하 쉐이더에서 삭제한다. 이 정점들을 랜더링 시간에 기하 쉐이더의 입력 값으로 사용해 투명하지 않은 영역의 바운딩 박스를 만들어 광선이 효과적으로 진행하도록 한다. 생성된 정점들은 렌더링 중에 시점의 변화에 무관하게 사용할 수 있지만 불투명도 전이 함수가 변경되면 투명하지 않은 정점들을 다시 생성해야 한다. 이는 기하 쉐이더를 통해서 GPU 안에서 고속으로 생성되기 때문에 대화식 처리가 가능하다. 제안하는 방법은 기존 광선 투사법의 결과와 동일한 영상을 생성하며 렌더링 속도는 기존의 방법에 비해 최대 10배 이상 향상되었다.

• Nuclear Engineering and Technology
• /
• 제52권6호
• /
• pp.1297-1303
• /
• 2020

In this study, nuclear radiation shielding and rigidity parameters of Y (0.1-x)B0.6Bi1.8O3La2x glassy system were investigated in order to determine it's suitability for use as nuclear radiation shielding materials. Therefore, a group of bismuth borate glass samples with La₂O₃ additive were synthesized using the technique of melt quenching. According to the results, the increase of the La₂O₃ additive increases the density of the glass samples and the mass attenuation coefficient (μ_m) values, whereas the half-value layer (HVL) and mean free path (MFP) values decrease. The effective atomic number (Z_eff) is also enhanced with an increment of both mass removal cross section for neutron (Σ_R) and absorption neutron scattering cross section (σ_abs). In addition to the other parameters, rigidity parameter values were theoretically examined. The increase of La₂O₃ causes some other important magnitudes to increase. These are the average crosslink density, the number of bonds per unit volume, as well as the stretching force constant values of these glass samples. These results are in concordance with the increase of elastic moduli in terms of the Makishima-Mackenzie model. This model showed an increase in the rigidity of the glass samples as a function of La₂O₃.

• 한국전기전자재료학회논문지
• /
• 제23권5호
• /
• pp.413-417
• /
• 2010

Line to ground faults by deterioration of insulators has frequently occurred in power system, and the main cause is surface contamination of the insulators. The contamination of insulator is analyzed by monitoring the surface leakage current flowing them. The suspension insulator is monitored by installation of a zero-phase current sensor(ZCT), but the line-post insulator is impossible to apply the same method because of its large diameter structure. This paper proposed a detection method of surface leakage current for a line-post insulator, and it can easily be applied to new and/or built insulators. The leakage current is indirectly calculated from the potential difference between the metal electrode attached on the surface of insulator and the ground connector. To evaluate the performance of the proposed method, the leakage current is compared as a function of contamination condition controlled by the density of NaCl solution. The leakage current is proportioned to the density of NaCl solution, and the voltage detected by the electrode showed the same trend. From the experimental results, we designed and fabricated a monitoring device which is composed of a detection electrode, signal converter, microprocessor, and ZigBee, and its measurement range is $10{\mu}A{\sim}5mA$.