• 한국군사과학기술학회지
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• 제20권1호
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• pp.18-24
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• 2017

This paper is a part of developing a computer code that can be used to generate synthetic IR images by calculating the outgoing infrared signal from objects. To predict the reflected component that is a part of the outgoing IR signal, such as those components reflected from the target surface by the solar and sky irradiations, it is necessary to calculate the complicated BRDF values for considering the directional surface reflection characteristics. Since the calculation of reflectance using the BRDF requires a large amount of computation time due to the hemispherical integral term, it is frequently restricted in applying for a real-time prediction of IR signal. In this research, the simplified method for calculating IR reflected component has been proposed by replacing the integral terms into two parts, a directionally uniform component and a step function representing the specular component, to reduce computation time. The proposed method is proved to result in very fast calculation of the BRDF (up to 600 times faster calculations) for most of the surfaces with minimal loss of the accuracy.

• 한국항행학회논문지
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• 제18권5호
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• pp.468-475
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• 2014

추천시스템은 선호 데이터가 대형화, 컴퓨터 처리능력과 추천 알고리즘 등에 의해 실시간 추천이 어려워지고 있다. 이에 따라 추천시스템은 대형 선호데이터를 분산처리 하는 방법에 대한 연구가 활발히 진행되고 있다. 본 논문은 하둡 분산처리 플랫폼과 머하웃 기계학습 라이브러리를 이용하여, 선호데이터를 분산 처리하는 방법을 연구하였다. 추천 알고리즘은 아이템 협업필터링과 유사한 동시발생 행렬을 이용하였다. 동시발생 행렬은 하둡 클러스터의 여러 노드에서 분산처리를 할 수 있으며, 기본적으로 많은 계산량이 필요하지만, 분산처리과정에서 계산량을 줄일 수 있다. 또한, 본 논문은 동시발생 행렬처리의 분산 처리과정을 4 단계에서 3 단계로 단순화하였다. 결과로서, 맵리듀스 잡을 감소할 수 있으며, 동일한 추천 파일을 생성할 수 있었다. 또한, 하둡 의사 분산모드를 이용하여 데이터를 처리하였을 때 빠른 처리속도를 보였으며, 맵 출력 데이터가 감소되었다.

• Journal of Welding and Joining
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• 제22권6호
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• pp.25-29
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• 2004

Some industrial steel structures are composed by components linked by several welding joints to constitute an assembly. The main interest of assembly simulation is to evaluate the global distortion of welded structure. The general method, thermo-elasto-plastic analysis, leads to excessive model size and computation time. In this study, a simplified method called "Local and Global approach" was developed to break down this limit and to provide a accurate solution for distortion. Local and global approach is composed of 3 steps; 1) Local simulation of each welding joint on a dedicated mesh (usually very fine due to high thermal gradients), taking into account for the non linearity of the material properties and the moving heat source. 2) Transfer to the global model of the effects of the welding joints by projection of the plastic strain tensors. 3) Elastic simulation to determine final distortions in global model. The welding deformation test for mock-up structure was performed to verify this approach. The predicted welding distortion by this approach had a good agreement with experiment results.

• Mass Spectrometry Letters
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• 제6권3호
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• pp.59-64
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• 2015

Quadrupole ion trap mass analyzer with a simplified geometry, namely, the cylindrical ion trap (CIT), has been shown to be well-suited using in miniature mass spectrometry and even in mass spectrometer arrays. Computation of stability regions is of particular importance in designing and assembling an ion trap. However, solving CIT equations are rather more difficult and complex than QIT equations, so, analytical and matrix methods have been widely used to calculate the stability regions. In this article we present the results of numerical simulations of the physical properties and the fractional mass resolutions m/Δm of the confined ions in the first stability region was analyzed by the fifth order Runge-Kutta method (RKM5) at the optimum radius size for both ion traps. Because of similarity the both results, having determining the optimum radius, we can make much easier to design CIT. Also, the simulated results has been performed a high precision in the resolution of trapped ions at the optimum radius size.

• Structural Engineering and Mechanics
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• 제15권4호
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• pp.415-436
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• 2003

The combination of spatial latticed structures (hereafter SLS) and flexible cables, the cable-stayed spatial latticed structures (hereafter CSLS) can cross longer span. According to variation principle, a novel geometric nonlinear formulation for 3-D bar elements considering large displacement and infinitesimal rotation increments with second-order precision is developed. The cable nonlinearity is investigated and it is taken that the secant modulus method can be considered as an exact method for a cable member. The tower column with which the cables link is regarded as a special kind of beam element, and, a new simplified stiffness formulation is presented. The computational strategies for the nonlinear dynamic response of structures are given, and the ultimate load carrying capacities and seismic responses are analyzed numerically. It is noted that, compared with corresponding spatial latticed shells, the cable-stayed spatial latticed shells have more strength and more stiffness, and that the verical seismic responses of both CSLS and CLS are remarkably greater than the horizontal ones. In addition, the computation shows that the stiffness of tower column influences the performance of CSLS to a certain extent and the improvement of structural strength and stiffness of CSLS is relevant not only to cables but also to tower columns.

• 한국항공운항학회지
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• 제26권4호
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• pp.13-19
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• 2018

Master plan plans for new airports should estimate the approximate scale of the airside's moorings and terminals. The size of the pavilion can be determined by complex factors such as the operating hours of the operating company, the frequency of operation, and the aircraft class. Among them, the number of flights is calculated using the Horon-jeff equation because of the relationship between the number of flights and the time occupied by the mains. Since this estimation formula is a simplified formula, it is necessary to verify the appropriateness of the method of estimating the scale and to suggest improvement directions. Therefore, in this study, we propose a method of estimating the size of the western flags by investigating and analyzing the main airports of overseas airports to determine whether the application of the Horon-jeff formula is appropriate.

• International Journal of Naval Architecture and Ocean Engineering
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• 제3권4호
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• pp.274-285
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• 2011

The supercavitating vehicle is an underwater vehicle that is surrounded almost completely by a supercavity to reduce hydrodynamic drag substantially. Since the cruise speed of the vehicle is much higher than that of conventional submarines, the drag force is huge and a buckling may occur. The buckling phenomenon is analyzed in this study through static and dynamic approaches. Critical buckling load and pressure as well as buckling mode shapes are calculated using static buckling analysis and a stability map is obtained from dynamic buckling analysis. When the finite element method (FEM) is used for the buckling analysis, the solver requires a linear static solver and an eigenvalue solver. In this study, these two solvers are integrated and a consolidated buckling analysis module is constructed. Furthermore, Particle Swarm Optimization (PSO) algorithm is combined in the buckling analysis module to perform a design optimization computation of a simplified supercavitating vehicle. The simplified configuration includes cylindrical shell structure with three stiffeners. The target for the design optimization process is to minimize total weight while maintaining the given structure buckling-free.

• Computers and Concrete
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• 제30권4호
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• pp.277-287
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• 2022

Due to the scarcity of extortionate experimental data, fatigue failure of the reinforced concrete (RC) element might be achieved economically adopting nonlinear finite element (FE) analysis as an alternative approach. However, conventional implicit dynamic analysis is expensive, quasi-static method overlooks interaction effects and inertia, direct cyclic analysis computes stabilized responses. Apart from this, explicit dynamic analysis may provide a numerical operating system for factual long-term responses. The study explores the fatigue behavior based on a simplified explicit dynamic solution employing nonlinear time domain analysis. Among fourteen RC beams, one beam is selected to validate under static loading, one under fatigue with the experimental study and other twelve to check the detail fatigue behavior. The SWOT (Strength, Weakness, Opportunities, Threats) analysis has been carried out to pinpoint the detail scenario in the adoption of numerical approach as an alternative to the experimental study. Excellent agreement of FE and experimental results is seen. The 3D nonlinear RC beam model at service fatigue limits is truthful to be used as an expedient contrivance to envisage the precise fatigue behavior. The simplified analysis approach for RC beam under fatigue offers savings in computation to predict responses providing acceptable accuracy rather than the complicated laboratory investigation. At higher frequency, the flexural failure occurs a bit earlier gradually compared to the repeated loading case of lower frequency. The deflection increases by 6%-10% at the end of first cycle for beams with increasing frequency of cyclic loading. However, at the end of fatigue loading, greater deflection occur earlier for higher load range because of more rapid stiffness degradation. For higher frequency, a slight boost in concrete compressive strains at an initial stage of loading has been seen indicating somewhat stepper increment. Stiffness degradation in larger loading cycle at same duration escalates the upsurge of the rate of strain in case of higher frequency.

• International Journal of Fluid Machinery and Systems
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• 제9권1호
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• pp.66-74
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• 2016

Concerning the numerical simulation of high-speed water jet with intensive cavitation this paper presents a practical compressible mixture flow method by coupling a simplified estimation of bubble cavitation and a compressible mixture flow computation. The mean flow of two-phase mixture is calculated by URANS for compressible fluid. The intensity of cavitation in a local field is evaluated by the volume fraction of gas phase varying with the mean flow, and the effect of cavitation on the flow turbulence is considered by applying a density correction to the evaluation of eddy viscosity. High-speed submerged water jets issuing from a sheathed sharp-edge orifice nozzle are treated when the cavitation number, ${\sigma}=0.1$, and the computation result is compared with experimental data The result reveals that cavitation occurs initially at the entrance of orifice and bubble cloud develops gradually while flowing downstream along the shear layer. Developed bubble cloud breaks up and then sheds downstream periodically near the sheath exit. The pattern of cavitation cloud shedding evaluated by simulation agrees experimental one, and the possibility to capture the unsteadily shedding of cavitation clouds is demonstrated. The decay of core velocity in cavitating jet is delayed greatly compared to that in no-activation jet, and the effect of the nozzle sheath is demonstrated.

• 한국정보전자통신기술학회논문지
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• 제16권1호
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• pp.33-40
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• 2023

슈퍼 컴퓨팅 기술 및 하드웨어 기술의 발달로 수치 연산 방식 또한 고도화되고 있다. 그에 따라 이전 대비 향상된 기상 예측 또한 가능해진다. 본 논문에서는 SCAM(Single-Columns Atmospheric Model, CESM(Community Earth System Model)을 간소화 한 버전)에 포함되어 있으며 대기 연산을 수행하는 적운 모수화 코드, Unicon(A Unified Convection Scheme)의 성능을 향상하기 위하여 소스 코드 내의 선형대수 수치적 연산 부분에 고밀도 선형대수 연산을 위한 라이브러리인 LAPACK(Linear Algebra PACKage) BLAS(Basic Linear Algebra Subprograms)의 level1 함수를 적용할 것을 제안한다. 이를 분석하기 위하여 SCAM의 전체적인 실행 구조도를 제시하고 해당 실행환경에서 테스트를 진행하였다. 기존 소스 코드 대비 SCOPY 함수는 0.4053%, DSCAL 함수는 0.7812%, DDOT 함수는 0.0469%의 성능 향상을 이끌어 내었으며 이를 모두 적용한 결과 기존 소스 코드 대비 0.8537%의 성능 향상을 보였다. 이는 본 논문에서 제안한 고밀도 선형대수 연산을 위한 라이브러리인 LAPACK BLAS 적용 방법이 동일한 CPU 환경에서 추가적인 하드웨어의 개입 없이 성능을 향상시킬 수 있음을 의미한다.