• 대한안전경영과학회지
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• 제7권5호
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• pp.155-174
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• 2005

Parametric life-cycle cost(LCC) models have been integrated with traditional design tools, and used in prior work to demonstrate the rapid solution of holistic, analytical tradeoffs between detailed design variations. During early designs stages there may be competing concepts with dramatic differences. Additionally, detailed information is scarce, and decisions must be models. for a diverse range of concepts, and the lack of detailed information make the integration make the integration of traditional LCC models impractical. This paper explores an approximate method for providing preliminary life-cycle cost. Learning algorithms trained using the known characteristics of existing products be approximated quickly during conceptual design without the overhead of defining new models. Artificial neural networks are trained to generalize on product attributes and life cycle cost date from pre-existing LCC studies. The Product attribute data to quickly obtain and LCC for a new and then an application is provided. In additions, the statistical method, called regression analysis, is suggested to predict the LCC. Tests have shown it is possible to predict the life cycle cost, and the comparison results between a learning LCC model and a regression analysis is also shown

• Structural Engineering and Mechanics
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• 제59권2호
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• pp.343-371
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• 2016

In this paper thermo-mechanical vibration analysis of a porous functionally graded (FG) Timoshenko beam in thermal environment with various boundary conditions are performed by employing a semi analytical differential transform method (DTM) and presenting a Navier type solution method for the first time. The temperature-dependent material properties of FG beam are supposed to vary through thickness direction of the constituents according to the power-law distribution which is modified to approximate the material properties with the porosity phases. Also the porous material properties vary through the thickness of the beam with even and uneven distribution. Two types of thermal loadings, namely, uniform and linear temperature rises through thickness direction are considered. Derivation of equations is based on the Timoshenko beam theory in order to consider the effect of both shear deformation and rotary inertia. Hamilton's principle is applied to obtain the governing differential equation of motion and boundary conditions. The detailed mathematical derivations are presented and numerical investigations are performed while the emphasis is placed on investigating the effect of several parameters such as porosity distributions, porosity volume fraction, thermal effect, boundary conditions and power-low exponent on the natural frequencies of the FG beams in detail. It is explicitly shown that the vibration behavior of porous FG beams is significantly influenced by these effects. Numerical results are presented to serve benchmarks for future analyses of FG beams with porosity phases.

• Earthquakes and Structures
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• 제23권4호
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• pp.363-371
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• 2022

Traditional metal dampers have disadvantages such as a higher yield point and inadequate adjustability. The experimental results show that the low yield point steel has superior energy dissipation hysteretic capacity and can be applied to seismic structures. To overcome these deficiencies, a novel compound metal damper comprising both low yield point steel plates and common steel plates is presented. The optimization objectives, including "maximum rigidity" and "full stress state", are proposed to obtain the optimal edge shape of a compound metal damper. The numerical results show that the optimized composite metal damper has the advantages such as full hysteresis curve, uniform stress distribution, more sufficient energy consumption, and it can adjust the yield strength of the damper according to the engineering requirements. In view of the mechanical characteristics of the compound metal damper, the equivalent model of eccentric cross bracing is established, and the approximate analytical solution of the yield strength and the yield displacement is proposed. A nonlinear simulation analysis is carried out for the overall aseismic capacity of three-layer-frame structures with a compound metal damper. It is verified that a compound metal damper has better energy dissipation capacity and superior seismic performance, especially for a damper with double-objective optimized shape.

• 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.

• 한국원자력학회:학술대회논문집
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• 한국원자력학회 1995년도 추계학술발표회논문집(2)
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• pp.707-712
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• 1995

Grain boundary diffusion plays significant role in the fission gas release, which is one of the crucial processes dominating nuclear fuel performance. Gaseous fission products such as Xe and Kr generated inside fuel pellet have to diffuse in the lattice and in the grain boundary before they reach open space in the fuel rod. In the mean time, the grains in the fuel pellet grow and shrink according to grain growth kinetics, especially at elevated temperature at which nuclear reactors are operating. Thus the boundary movement ascribed to the grain growth greatly influences the fission gas release rate by lengthening or shortening the lattice diffusion distance, which is the rate limiting step. Sweeping fission gases by the moving boundary contributes to the increment of the fission gas release as well. Lattice and grain boundary diffusion processes in the fission gas release can be studied by 'tracer diffusion' technique, by which grain boundary diffusion can be estimated and used directly for low burn-up fission gas release analysis. However, even for tracer diffusion analysis, taking both the intragranular grain growth and the diffusion processes simultaneously into consideration is not easy. Only a few models accounting for the both processes are available and mostly handle them numerically. Numerical solutions are limited in the practical use. Here in this paper, an approximate analytical solution of the lattice and stationary grain boundary diffusion in a polycrystalline solid is developed for the tracer diffusion techniques. This short closed-form solution is compared to available exact and numerical solutions and turns out to be acceptably accurate. It can be applied to the theoretical modeling and the experimental analysis, especially PIE (post irradiation examination), of low burn up fission. gas release.

• 한국정보통신학회:학술대회논문집
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• 한국정보통신학회 2012년도 춘계학술대회
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• pp.693-695
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• 2012

본 연구에서는 DGMOSFET의 항복전압에 대하여 고찰할 것이다. 이를 위하여 포아송방정식의 분석학적 해를 이용하였으며 Fulop의 항복전압 조건을 사용하였다. DGMOSFET는 게이트길이가 나노단위까지 사용가능한 소자로서 단채널효과를 감소시킬 수 있다는 장점이 있다. 그러나 단채널에서 나타나는 항복전압의 감소는 피할 수 없으므로 이에 대한 연구가 필요하다. 포아송방정식을 풀 때 사용하는 전하분포함수에 가우시안 함수를 적용함으로써 보다 실험값에 가깝게 해석하였으며 이때 이중게이트 MOSFET의 소자크기에 따라 항복전압의 변화를 관찰하였다. 본 연구의 전위모델에 대한 타당성은 이미 기존에 발표된 논문에서 입증하였으며 본 연구에서는 이 모델을 이용하여 항복전압을 분석할 것이다. DGMOSFET의 항복전압을 관찰한 결과, 채널길이가 감소할수록 그리고 도핑농도가 증가할수록 항복전압이 감소하는 것으로 나타났다. 또한 게이트산화막두께 및 채널두께에 따라서 항복전압의 변화가 관찰되었다.

• 한국정보통신학회논문지
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• 제17권2호
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• pp.372-377
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• 2013

DGMOSFET의 항복전압에 대하여 고찰하였으며 이를 위하여 포아송방정식의 분석학적 해 및 Fulop의 항복전압 조건을 사용하였다. DGMOSFET는 게이트단자의 전류제어능력 향상으로 단채널 효과를 감소시킬 수 있다는 장점이 있다. 그러나 단채널에서 나타나는 항복전압의 감소는 피할 수 없으므로 이에 대한 연구가 필요하다. 포아송방정식을 풀 때 사용하는 전하분포함수에 가우시안 함수를 적용함으로써 보다 실험값에 가깝게 해석하였으며 이때 이중게이트 MOSFET의 소자크기에 따라 항복전압의 변화를 관찰하였다. 본 연구의 전위모델에 대한 타당성은 이미 기존에 발표된 논문에서 입증하였으며 본 연구에서는 이 모델을 이용하여 항복전압을 분석할 것이다. DGMOSFET의 항복전압을 관찰한 결과, 채널길이가 감소할수록 그리고 도핑농도가 증가할수록 항복전압이 감소하는 것으로 나타났다. 또한 게이트산화막 두께 및 채널두께에 따라서 항복전압의 변화가 관찰되었다.

• 한국정보통신학회논문지
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• 제17권11호
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• pp.2621-2626
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• 2013

비대칭 이중게이트 MOSFET의 전위분포에 대하여 고찰하였으며 이를 위하여 포아송방정식의 해석학적 해를 구하였다. 대칭 DGMOSFET는 3단자 소자로서 상하단의 게이트단자가 상호 연결되어 있어 상하단 동일한 제어능력을 가지고 있으나 비대칭 DGMOSFET 소자는 4단자 소자로서 상하단 게이트단자의 전류제어능력을 각각 설정할 수 있다는 장점이 있다. 전위분포를 구할 때 포아송방정식을 이용하였으며 도핑분포함수에 가우시안 함수를 적용함으로써 보다 실험값에 근사하게 해석하였다. 비대칭 이중게이트 MOSFET의 게이트 단자전압 및 게이트 산화막 두께 그리고 채널도핑의 변화에 따라 전위분포의 변화를 관찰하였다. 비대칭 DGMOSFET의 전위분포를 관찰한 결과, 게이트단자 전압 및 게이트 산화막 두께 등에 따라 전위분포는 크게 변화하는 것을 알 수 있었다. 특히 게이트 산화막 두께가 증가하는 단자에서 전위분포의 변화가 더욱 크게 나타나고 있었으며 채널도핑이 증가하면 드레인 측보다 소스 측 전위분포가 크게 변화하는 것을 알 수 있었다.

• International Journal of Fluid Machinery and Systems
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• 제10권3호
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• pp.240-253
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• 2017

Latin hypercube sampling is widely used design-of-experiment technique to select design points for simulation which are then used to construct a surrogate model. The exploration/exploitation properties of surrogate models depend on the size and distribution of design points in the chosen design space. The present study aimed at evaluating the performance characteristics of various surrogate models depending on the Latin hypercube sampling (LHS) procedure (sample size and spatial distribution) for a diverse set of optimization problems. The analysis was carried out for two types of problems: (1) thermal-fluid design problems (optimizations of convergent-divergent micromixer coupled with pulsatile flow and boot-shaped ribs), and (2) analytical test functions (six-hump camel back, Branin-Hoo, Hartman 3, and Hartman 6 functions). The three surrogate models, namely, response surface approximation, Kriging, and radial basis neural networks were tested. The important findings are illustrated using Box-plots. The surrogate models were analyzed in terms of global exploration (accuracy over the domain space) and local exploitation (ease of finding the global optimum point). Radial basis neural networks showed the best overall performance in global exploration characteristics as well as tendency to find the approximate optimal solution for the majority of tested problems. To build a surrogate model, it is recommended to use an initial sample size equal to 15 times the number of design variables. The study will provide useful guidelines on the effect of initial sample size and distribution on surrogate construction and subsequent optimization using LHS sampling plan.

• 한국정보통신학회:학술대회논문집
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• 한국정보통신학회 2013년도 추계학술대회
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• pp.691-694
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• 2013

비대칭 이중게이트 MOSFET의 전위분포에 대하여 고찰하였으며 이를 위하여 포아송방정식의 해석학적 해를 구하였다. 대칭 DGMOSFET는 3단자 소자로서 상하단의 게이트단자가 상호 연결되어 있어 상하단 동일한 제어능력을 가지고 있으나 비대칭 DGMOSFET 소자는 4단자 소자로서 상하단 게이트단자의 전류제어능력을 각각 설정할 수 있다는 장점이 있다. 전위분포를 구할 때 포아송방정식을 이용하였으며 전하분포함수에 가우시안 함수를 적용함으로써 보다 실험값에 근사하게 해석하였다. 비대칭 이중게이트 MOSFET의 게이트 단자전압 및 게이트 산화막 두께 그리고 채널도핑의 변화에 따라 전위분포의 변화를 관찰하였다. 비대칭 DGMOSFET의 전위분포를 관찰한 결과, 게이트단자 전압 및 게이트 산화막 두께 등에 따라 전위분포는 크게 변화하는 것을 알 수 있었다. 특히 게이트 산화막 두께가 증가하는 단자에서 전위분포의 변화가 더욱 크게 나타나고 있었으며 채널도핑이 증가하면 드레인 측보다 소스 측 전위분포가 크게 변화하는 것을 알 수 있었다.