• Structural Engineering and Mechanics
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• 제43권2호
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• pp.199-209
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• 2012

Two carbon fiber composite laminates, $[0/90]_{2S}$ and $[0/+45/90/-45]_S$, were considered in this work to find out the perforation threshold energy to complete the perforation process and the corresponding maximum contact force. Explicit finite element commercial software, LS-DYNA, was used to predict these values. According to the simulation results, these two types of composite laminates were tested by using a vertical drop-weight testing machine. After testing, the damage condition of these specimens were observed and compared with the results from finite element analysis. The testing results indicate that the perforation threshold energy is 6 Joules for $[0/90]_{2S}$ and 7 Joules for $[0/+45/90/-45]_S$, which is in good agreement with the simulation results. Also, the maximum contact force at the case of perforation threshold energy is the lowest as compared to the maximum contact forces occurring at the impact energy that is larger or less than the perforation threshold energy.

• 한국통신학회논문지
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• 제31권3B호
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• pp.232-238
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• 2006

본 논문에서는 셀룰러 시스템에서 다양한 특성을 갖는 밀티미디어 서비스에 우선순위를 각각 부여하여 효율적으로 제어하여 핸드오버 서비스나 신규 서비스에 대한 블록킹 확률을 최소화하는 호 수락제어 기법을 제안하였다. 본 알고리즘은 비실시간 서비스들이 대역폭을 공유하는 Packing 방식, Queuing 방식, Power reallocation 방식의 호 수락 제어 방법에 관한 것으로 비실시간 서비스들의 트래픽 특성에 따라 공유 대역폭을 할당하고 남은 잉여 자원을 우선순위가 높은 실시간 서비스에게 제공하여 QoS를 보장하였다. 본 논문에서 성능판단 파라메타로는 블록킹 확률과 강제절단 확률을 설정하였고 다양한 형태의 멀티미디어 트래픽에 대해서 블록킹 확률과 강제절단 확률을 시뮬레이션을 통하여 각각 비교 분석하였다.

• Nuclear Engineering and Technology
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• 제54권3호
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• pp.860-866
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• 2022

An accurate prediction of the pressure drop along the flow paths is crucial in the design of advanced passive systems cooled by heavy liquid metal coolants. To date, a generic pressure drop correlation over spacer grids by Rehme has been applied extensively, which was obtained from substantial experimental data with multiple types of components. However, a few experimental studies have reported that the correlation may give large discrepancies. To provide a more reliable correlation for ring-type spacer grids, the current numerical study aims at figuring out the most critical factor among four hypothetical parameters, namely the flow area blockage ratio, number of fuel rods, type of fluid, and thickness of the spacer grid in the flow direction. Through a set of computational fluid dynamics simulations, we observed that the flow area blockage ratio dominantly influences the pressure loss characteristics, and thus its dependence should be more emphasized, whereas the other parameters have little impact. Hence, we suggest a new correlation for the drag coefficient as C_B = C_ν,m/ε^2.7, where C_ν,m is formulated by a nonlinear fit of simulation data such that C_ν,m = -11.33 ln(0.02 ln(Re_b)).

• Journal of the Korean Society for Industrial and Applied Mathematics
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• 제5권2호
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• pp.71-99
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• 2001

The model and analytical method for solving the problem of coupled fluid flow in the reservoir/well system is presented. The 3-D drainage area is composed of three connected media: the tubing, the annuli as a super conducting collector, and the reservoir itself. To couple these three types of fluid flows a non-overlapping Dirichlet-Neumann domain decomposition method is developed. The method allows us to apply an analytical hybrid simulator for accurate evaluation of the impact of main geometrical and hydrodynamic parameters of the 3-D system on the pressure drop along the horizontal well and its production index.

• 전자공학회논문지T
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• 제35T권2호
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• pp.6-12
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• 1998

박막의 SOI(Silicon-On-Insulator) 소자는 짧은 채널 효과(short channel effect), subthreshold slope의 개선, 이동도 향상, latch-up 제거 등 많은 이점을 제공한다. 반면에 이 소자는 current kink effect와 같이 정상적인 소자 동작에 있어 주요한 저해 요소인 floating body effect를 나타낸다. 본 논문에서는 이러한 문제를 해결하기 위해 T-형 게이트 구조를 갖는 SOI NMOSFET를 제안하였다. T-형 게이트 구조는 일부분의 게이트 산화막 두께를 다른 부분보다 30nm 만큼 크게 하여 TSUPREM-4로 시뮬레이션 하였으며, 이것을 2D MEDICI mesh를 구성하여 I-V 특성 시뮬레이션을 시행하였다. 부분적으로 게이트 산화층의 두께가 다르기 때문에 게이트 전계도 부분적으로 차이가 발생되어 충격 이온화 전류의 크기도 줄어든다. 충격 이온화 전류가 감소한다는 것은 current kink effect가 감소하는 것을 의미하며, 이것을 MEDICI 시뮬레이션을 통해 얻어진 충격 이온화 전류 곡선, I-V 특성 곡선과 정공 전류의 분포 형태를 이용하여 제안된 구조에서 current kink effect가 감소됨을 보였다.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2006년도 춘계학술대회 논문집
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• pp.405-406
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• 2006

Recently, the flat display modules such as plasma or TFT-LCD employ thin crystallized panels which are normally weak to high level transient mechanical energy inputs. As a result, anti-shock performance is one of the most important design specifications for TFT-LCD modules. However, most of large display module designs are generated based on engineers own experiences. Also, a large-scale analysis to evaluate complex material and structural behaviors is one of interesting topic in diverse engineering and scientific fields. The utilization of massively parallel processors has also been a recent trend of high performance computing. The objective of this paper is to introduce a parallel process system which consists of general purpose finite element analysis solver as well as parallelized PC cluster. The parallel processing system is constructed using thirty-two processing elements and the finite element program is developed by adopting hierarchical domain decomposition method. In order to verify the efficiency of the established system, an impact analysis on thin and complex sub-parts of flat display modules is performed. The evaluation results showed a good agreement with the corresponding reference solutions, and thus, the parallel process system seems to be a useful tool fur the complex structural analysis such as IT related products.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2008년도 춘계학술대회논문집
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• pp.559-564
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• 2008

A prediction of binary droplets collision is important in the formation of falling drops and the evolution of sprays. The droplet velocity, impact parameter and drop-size ratio have influence on the interaction of the droplets. By the effect of these parameter, the collision processes are generated with the complicated phenomena. The droplet collision can be classified into four interactions such as the bouncing, coalescence, reflexive separation and stretching separation. In this study, the two-phase flow of the droplet collision was simulated numerically by using the Level Set method. 2D axi-symmetric simulations on the head-on collisions in the coalescence and reflexive separation, and 3D simulation on the off-center collisions in the coalescence and stretching separation were performed. These numerical results showed good agreements with the experimental and analytical results. For tracking the identity of droplets after the collision, transport equation for the volume fraction of the each initial droplet were used. From this, the identities of droplets were analyzed on the collision of droplets having different size.

• 한국자동차공학회논문집
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• 제20권2호
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• pp.64-69
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• 2012

Head injury is one of the most common cause of deaths in car-to-pedestrian collisions. To reduce the severity of such injuries, many international safety committees have performed headform impact test for pedestrian protection. In this paper, an adult headform impactor model is developed based on the finite element (FE) method and validated through the numerical simulation. The skin material of headform impactor is known as polyvinyl chloride skin (PVC) and its material was assumed as viscoelastic. The viscoelastic parameters of headform skin are identified by a series of trial and error methods. The new developed FE adult headform impactor is verified by the drop test and FE JARI adult headform impactor provided by Madymo program.

• 대한조선학회지
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• 제27권2호
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• pp.87-95
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• 1990

본 논문에서는 충격시험에 의해 얻어진 구조물의 과도진동응답 신호로부터 구조물의 동특성치를 구하는 기존방법에 대하여 살펴보고 이들 기존 방법의 단점을 개선할 수 있는 방법으로 최대엔트로피방법(Maximum Entropy Method)과 최소자승 Prony법(Least Square Prony Method)를 도입하여 수치실험을 통한 성능시험을 수행하였다. 그리고 적용예로서 선박의 낙묘시험으로부터 얻은 시계열에 이들을 적용하여 그 결과 FFT법 결과와 비교하였다. 연구결과, 최대엔트로피방법은 구조물의 인접 고유진동수들이 가까이 있고 얻을 수 있는 동적응답 시계열의 data 길이가 짧을 때의 고유진동수 추정에 유용하나 감쇠비 산정에는 유용하지 못함이 밝혀졌다. 또한, 최소자승 Prony법은 과감쇠계의 고유진동수 및 감쇠비 추정에 유용하나 동적응답 시계열에 많은 잡음이 포함되어 있을 경우, 감쇠비 추정성능이 크게 저하되는 것으로 나타났다.

• 한국구조물진단유지관리공학회 논문집
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• 제26권5호
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• pp.49-56
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• 2022

본 연구에서는 능동소음제어(ANC, Active Noise Control) 기술을 이용하여 공동주택의 층간소음을 저감시키는 시뮬레이션 기반 연구를 수행하였다. ANC의 층간소음 저감 활용 가능성을 검토하기 위하여 층간소음시험시설에서 가속도계와 소음 수집용 마이크로폰을 설치하여 임팩트볼 낙하에 의한 소음진동을 측정하여 Fx-LMS 알고리즘 기반의 능동소음제어 시뮬레이션을 수행하였다. 이 과정에서 적응제어 수렴계수 등의 최적 시뮬레이션 조건을 도출한 후 가속도계와 스피커 수량을 변수로 하는 수치 시뮬레이션을 통해 소음저감효과를 분석하여 제한된 조건에서 층간소음을 저감시킬 수 있는 것을 확인하였다.