• Journal of Communications and Networks
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• 제18권5호
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• pp.846-856
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• 2016

Wireless sensor networks (WSNs) are widely applied in monitoring and control of environment parameters. It is sometimes necessary to disseminate data through wireless links after they are deployed in order to adjust configuration parameters of sensors or distribute management commands and queries to sensors. Several approaches have been proposed recently for data dissemination in WSNs. However, none of these approaches achieves both high efficiency and low complexity simultaneously. To address this problem, cluster-tree based network architecture, which divides a WSN into hierarchies and clusters is proposed. Upon this architecture, data is delivered from base station to all sensors in clusters hierarchy by hierarchy. In each cluster, father broadcasts data to all his children with instantly decodable network coding (IDNC), and a novel scheme targeting to maximize total transmission gain (MTTG) is proposed. This scheme employs a new packet scheduling algorithm to select IDNC packets, which uses weight status feedback matrix (WSFM) directly. Analysis and simulation results indicate that the transmission efficiency approximate to the best existing approach maximum weight clique, but with much lower computational overhead. Hence, the energy efficiency achieves both in data transmission and processing.

• Structural Engineering and Mechanics
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• 제38권5호
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• pp.633-649
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• 2011

The paper presents a study aimed at understanding some characteristics of an interior explosion within a room with limited or no venting. The explosion may occur in ammunition storage or result from a terrorist action or from a warhead that had penetrated into this room. The study includes numerical simulations of the problem and analytical derivations. Different types of analysis (1-D, 2-D and 3-D analysis) were performed for a room with rigid walls and the results were analyzed. For the 3D problem the effect of the charge size and its location within the room was investigated and a new insight regarding the pressure distribution on the interior wall as function of these parameters has been gained. The numerical analyses were carried out using the Eulerian multi-material approach. Further, an approximate analytical formula to predict the residual internal pressure was developed. The formula is based on the conservation law of total energy and its implementation yields very good agreement with the results obtained numerically using the complete statement of the problem for a wide range of explosive weights and room sizes that is expressed through a non-dimensional parameter. This new formula is superior to existing literature recommendations and compares considerably better with the above numerical results.

• 한국가스학회지
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• 제28권2호
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• pp.66-75
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• 2024

본 연구에서는 말레이시아 고갈 유전에 대해 노달분석을 통한 CO₂ 주입성 분석 모델을 개발하였다. 유정시험이 수행된 평가정 현장 자료를 토대로 기본 모델을 구축하고 주입 압력, 주입관 크기, 저류층 압력, 저류층 투과도, 그리고 두께에 대하여 민감도 분석을 수행하였다. A 유전 평가정 산출시험 보고서를 토대로 생산 노달분석을 수행하여 투과도를 10md로 산출하였다. A 평가정 기본 입력자료를 활용하여 주입정 모델을 설정한 후, 기본 모델에 대하여 노달 분석 결과 운영 공저 압력 3000.74psia에서 CO₂ 주입량이 13.29MMscfd로 산출되었다. 민감도 분석 결과, 주입 압력, 저류층 두께, 투과도가 높아지거나 저류층 압력이 낮아지면 주입량이 대략 선형적으로 증가하였다. 또한, 단위 인치 당 주입량 분석을 통해 주입관 크기 2.548inch일 때 가장 효율적으로 주입할 수 있음을 도출할 수 있었다. 지층 파쇄압력을 알고 있다면 노달분석을 수행하여 운영 공저 압력과의 비교를 통해 주입 가능한 최대 저류층 압력과 주입 압력을 예측할 수 있을 것으로 생각된다.

• Journal of Theoretical and Applied Mechanics
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• 제3권1호
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• pp.66-80
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• 2002

The bilinear formulation proposed earlier by Peters and Izadpanah to develop finite elements in time to solve undamped linear systems, Is extended (and found to be readily amenable) to develop time finite elements to obtain transient responses of both linear and nonlinear, and damped and undamped systems. The formulation Is used in the h-, p- and hp-versions. The resulting linear and nonlinear algebraic equations are differentiated to obtain the first- and second-order sensitivities of the transient response with respect to various system parameters. The present developments were tested on a series of linear and nonlinear examples and were found to yield, when compared with results obtained using other methods, excellent results for both the transient response and Its sensitivity to system parameters. Mostly. the results were obtained using the Legendre polynomials as basis functions, though. in some cases other orthogonal polynomials namely. the Hermite. the Chebyshev, and integrated Legendre polynomials were also employed (but to no great advantage). A key advantage of the time finite element method, and the one often overlooked in its past applications, is the ease In which the sensitivity of the transient response with respect to various system parameters can be obtained. The results of sensitivity analysis can be used for approximate schemes for efficient solution of design optimization problems. Also. the results can be applied to gradient-based parameter identification schemes.

• Journal of the Korean Society for Industrial and Applied Mathematics
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• 제15권3호
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• pp.223-231
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• 2011

During spray coating, especially in an air plasma spray (APS), pores, cracks, and splat boundaries are developed and those factors exert influence on thermomechanical properties such as elastic modulus, thermal conductivity, and coefficient of thermal expansion. Moreover, the thermo mechanical properties are crucial elements to determine the thermoelastic characteristics, for instance, temperature distribution, displacements, and stresses. Two types of thermal barrier coating (TBC) model, the dense and porous microstructures, are taken into account for the analysis of microstructural characterizations. $TriplexPro^{TM}$-200 system was applied to prepare TBC samples, and the METECO 204 C-NS powder is adopted for the relatively porous microstructure and METECO 204 NS powder for the dense microstructure in the top coat of TBCs. Governing partial differential equations were derived based on the thermoelastic theory and approximate estimates for the thermoelastic characteristics were obtained using a finite volume method for the governing equations.

• Smart Structures and Systems
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• 제20권6호
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• pp.709-728
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• 2017

This disquisition proposes a nonlocal strain gradient beam theory for thermo-mechanical dynamic characteristics of embedded smart shear deformable curved piezoelectric nanobeams made of porous electro-elastic functionally graded materials by using an analytical method. Electro-elastic properties of embedded curved porous FG nanobeam are assumed to be temperature-dependent and vary through the thickness direction of beam according to the power-law which is modified to approximate material properties for even distributions of porosities. It is perceived that during manufacturing of functionally graded materials (FGMs) porosities and micro-voids can be occurred inside the material. Since variation of pores along the thickness direction influences the mechanical and physical properties, so in this study thermo-mechanical vibration analysis of curve FG piezoelectric nanobeam by considering the effect of these imperfections is performed. Nonlocal strain gradient elasticity theory is utilized to consider the size effects in which the stress for not only the nonlocal stress field but also the strain gradients stress field. The governing equations and related boundary condition of embedded smart curved porous FG nanobeam subjected to thermal and electric field are derived via the energy method based on Timoshenko beam theory. An analytical Navier solution procedure is utilized to achieve the natural frequencies of porous FG curved piezoelectric nanobeam resting on Winkler and Pasternak foundation. The results for simpler states are confirmed with known data in the literature. The effects of various parameters such as nonlocality parameter, electric voltage, coefficient of porosity, elastic foundation parameters, thermal effect, gradient index, strain gradient, elastic opening angle and slenderness ratio on the natural frequency of embedded curved FG porous piezoelectric nanobeam are successfully discussed. It is concluded that these parameters play important roles on the dynamic behavior of porous FG curved nanobeam. Presented numerical results can serve as benchmarks for future analyses of curve FG nanobeam with porosity phases.

• Nuclear Engineering and Technology
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• 제52권12호
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• pp.2733-2742
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• 2020

This paper presents an assessment of applicability of the multigroup cross sections generated with Monte Carlo tools to the fast reactor analysis based on transport calculations. 33-group cross section sets were generated for simple one- (1-D) and two-dimensional (2-D) sodium-cooled fast reactor problems using the SERPENT code and applied to deterministic steady-state and depletion calculations. Relative to the reference continuous-energy SERPENT results, with the transport corrected P₀ scattering cross section, the k-eff value was overestimated by 506 and 588 pcm for 1-D and 2-D problems, respectively, since anisotropic scattering is important in fast reactors. When the scattering order was increased to P₅, the 1-D and 2-D problem errors were increased to 577 and 643 pcm, respectively. A sensitivity and uncertainty analysis with the PERSENT code indicated that these large k-eff errors cannot be attributed to the statistical uncertainties of cross sections and they are likely due to the approximate anisotropic scattering matrices determined by scalar flux weighting. The anisotropic scattering cross sections were alternatively generated using the MC²-3 code and merged with the SERPENT cross sections. The mixed cross section set consistently reduced the errors in k-eff, assembly powers, and nuclide densities. For example, in the 2-D calculation with P3 scattering order, the k-eff error was reduced from 634 pcm to -223 pcm. The maximum error in assembly power was reduced from 2.8% to 0.8% and the RMS error was reduced from 1.4% to 0.4%. The maximum error in the nuclide densities at the end of 12-month depletion that occurred in ²³⁷Np was reduced from 3.4% to 1.5%. The errors of the other nuclides are also reduced consistently, for example, from 1.1% to 0.1% for ²³⁵U, from 2.2% to 0.7% for ²³⁸Pu, and from 1.6% to 0.2% for ²⁴¹Pu. These results indicate that the scalar flux weighted anisotropic scattering cross sections of SERPENT may not be adequate for application to fast reactors where anisotropic scattering is important.

• 한국산학기술학회논문지
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• 제19권4호
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• pp.683-688
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• 2018

최근 하이브리드 전기자동차의 보급 확대에 따라 전기에너지 수요가 증가하고 있다. 본 연구에서는 전기에너지 수요에 대응하기 위해 에너지 하베스팅 기술을 이용해 자가발전이 가능한 3가지 구조의 현가장치 적용 선형 발전 시스템을 ANSYS MAXWELL을 사용하여 전자기 시뮬레이션을 통해 각 구조의 발전 특성을 비교 분석 하였다. 다음으로 각 모델에 대해 상용 PIDO(Process Integration and Design Optimization)툴인 PIAnO(Process Integration, Automation and Optimization)을 사용하여 최적설계를 수행하였다. 3가지 설계변수를 선정하여 실험계획법 기법 중 직교 배열표(Orthogonal Array)를 이용해 도출한 18개의 실험 점에 대해 전자기 해석을 통해 완성한 실험계획법을 바탕으로 근사 모델을 생성하였으며 진화 알고리즘(Evolutionary Algorithm)을 이용한 최적 설계를 수행하였다. 마지막으로 초기 모델과 동일한 해석 조건을 사용해 최적 설계 결과 모델에 대한 전자기 시뮬레이션을 통해 최적설계 결과를 검증 하였다. 각 선형 발전기 모델에 대해 최적의 구조에 대한 발전 특성을 비교한 결과 8pole-8slot, 12pole-12slot, 16pole-16slot 구조에서 최대 발전량은 각각 366.5W, 466.7W, 579.7W로 slot, pole 조합 수가 많아질수록 발전량이 증가하는 결과를 확인하였다.

• 한국융합학회논문지
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• 제9권6호
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• pp.175-182
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• 2018

본 연구에서는 초음파 진동에너지가 융합된 커팅기용 공구 혼 제작에 대한 기초 연구 자료를 제작하고자 이론적방법과 유한요소해석을 병행하여 설계하였다. 고 성능의 초음파 절단을 진행하기 위해서는 횡진동이 아닌 종진동으로만 진동해야 하며, 기계적 진동에너지를 효율적으로 전달하기 위해 출력부에 최대진폭이 발생해야 한다. 따라서 공구 혼은 발진기의 가진 주파수와 공구 혼의 고유주파수가 동일하게 설계되어야만 한다. 공구 혼을 공진설계하기 위해서는 1차원 파동방정식을 이용한 이론적 접근법과, 유한요소 해석결과를 설계모델에 반영하는 방법이 있는데, 본 연구에서는 최초에 공구 혼의 대략적인 치수를 1차원 파동방정식을 통해 결정하고, 유한요소 해석 결과를 바탕으로 최적 모델을 선정하여 공구 혼의 최종 형상에 반영하였다. 이와 같은 내용을 실제 커팅용 공구 혼의 기초자료로 활용하고자 하며, 추후 제작 및 실험 데이터를 본 연구내용과 비교할 예정이다.

• 예술인문사회 융합 멀티미디어 논문지
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• 제7권3호
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• pp.383-391
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• 2017

영상 분할은 영상처리 분야에서 오랜 기간 많은 연구자들에 의해 연구되었으며 현재도 다양한 방법이 연구되어지고 있다. 영상 분할은 영상에 포함된 객체들을 분리하는 문제로, 특히 사람의 얼굴은 영상에 포함된 객체들 중 가장 중요한 객체로 다루어진다. 본 논문에서는 영상에 포함된 얼굴 경계선을 추출하는 방법을 제안한다. 이를 위해 먼저 비올라존스 방법을 사용해 영상에서 대략적인 얼굴 위치를 검출한다. 그러나 비올라존스 알고리즘에 의해 검출된 결과는 얼굴의 대략적인 위치이지 정확한 얼굴 영역이 아니다. 본 논문에서는 비올라존스 알고리즘의 결과로부터 좀 더 정확한 얼굴 영역을 추출하기 위해 적응적 스킨칼라 모델을 사용하고 스킨칼라 모델의 결과로 주어지는 스킨영역에 대해 수평, 수직 히스토그램을 분석하여 얼굴 영역을 추출한다. 마지막으로 추출된 얼굴 영역에 대해 스네이크 알고리즘을 적용해 최종 얼굴 경계선을 결정한다. 본 논문에서는 Williams등[7]에 의해 제안된 스네이크 알고리즘을 기반으로 얼굴 경계선 추출을 위해 변형된 스네이크 에너지 함수를 제안한다.