• Advanced Composite Materials
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• 제17권4호
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• pp.373-407
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• 2008

This paper will examine the possibilities of the virtual tests of composite structures by simulating mechanical behaviors by using supercomputing technologies, which have now become easily available and powerful but relatively inexpensive. We will describe mainly the applications of large-scale finite element analysis using the direct numerical simulation (DNS), which describes composite material properties considering individual constituent properties. DNS approach is based on the full microscopic concepts, which can provide detailed information about the local interaction between the constituents and micro-failure mechanisms by separate modeling of each constituent. Various composite materials such as metal matrix composites (MMCs), active fiber composites (AFCs), boron/epoxy cross-ply laminates and 3-D orthogonal woven composites are selected as verification examples of DNS. The effective elastic moduli and impact structural characteristics of the composites are determined using the DNS models. These DNS models can also give the global and local information about deformations and influences of high local in-plane and interlaminar stresses induced by transverse impact loading at a microscopic level inside the materials. Furthermore, the multi-scale models based on DNS concepts considering microscopic and macroscopic structures simultaneously are also developed and a numerical low-velocity impact simulation is performed using these multi-scale DNS models. Through these various applications of DNS models, it can be shown that the DNS approach can provide insights of various structural behaviors of composite structures.

• Ocean Systems Engineering
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• 제8권1호
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• pp.21-32
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• 2018

Due to the escalation in hydrocarbon consumption, the offshore industry is now looking for advanced technology to be employed for deep sea exploration. Riser system is an integral part of floating structure used for such oil and gas extraction from deep water offering a system of drill twines and production tubing to spread the exploration well towards the ocean bed. Thus, the marine risers need to be precisely employed. The incorporation of the strengthening material, fiber reinforced polymer (FRP) for deep and ultra-deep water riser has drawn extensive curiosity in offshore engineering as it might offer potential weight savings and improved durability. The design for FRP strengthening involves the local design for critical loads along with the global analysis under all possible nonlinearities and imposed loadings such as platform motion, gravity, buoyancy, wave force, hydrostatic pressure, current etc. for computing and evaluating critical situations. Finite element package, ABAQUS/AQUA is the competent tool to analyze the static and dynamic responses under the offshore hydrodynamic loads. The necessities in design and operating conditions are studied. The study includes describing the methodology, procedure of analysis and the local design of composite riser. The responses and fatigue damage characteristics of the risers are explored for the effects of FRP strengthening. A detail assessment on the technical expansion of strengthening riser has been outlined comprising the inquiry on its behavior. The enquiry exemplifies the strengthening of riser as very potential idea and suitable in marine structures to explore oil and gas in deep sea.

• Bulletin of the Korean Chemical Society
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• 제30권1호
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• pp.67-76
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• 2009

The development of a variety of methods like AM1, PM3, PM5 and DFT now allows the calculation of atomic and molecular properties with high precision as well as the treatment of large molecules with predictive power. In this paper, these methods have been used to calculate a number of quantum chemical descriptors (like Klopman atomic softness in terms of $E_n^{\ddag}\;and\;E_m^{\ddag}$, chemical hardness, global softness, electronegativity, chemical potential, electrophilicity index, heat of formation, total energy etc.) for 75 alkanes to predict their boiling point values. The 3D modeling, geometry optimization and semiempirical & DFT calculations of all the alkanes have been made with the help of CAChe software. The calculated quantum chemical descriptors have been correlated with observed boiling point by using multiple linear regression (MLR) analysis. The predicted values of boiling point are very close to the observed values. The values of correlation coefficient ($r^2$) and cross validation coefficient ($r_{cv}^2$) also indicates the generated QSPR models are valuable and the comparison of all the methods indicate that the DFT method is most reliable while the addition of Klopman atomic softness $E_n^{\ddag}$ in DFT method improves the result and provides best correlation.

• 한국CDE학회논문집
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• 제14권4호
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• pp.242-253
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• 2009

Nowadays, manufacturing industry has been making its effort not only for productivity elevation but also for cost reduction in order to survive in the global market which is more and more challenging. In this paper, the method for planning of digital manufacturing system is proposed and door trim assembly system is determined as the subject of our research. First of all, the process sequence is generated based on the product analysis. And, the static and dynamic relationships between system components are represented using IDEF0 and UML model. The working time is estimated through the regression analysis based on MODAPTS method. According to the system configuration strategy, initial concept system layout is implemented 3D virtual environment. The problems caused by bad working motions are detected and modified through the ergonomic analysis using RULA method. According to proposed procedure, digital door trim assembly system is implemented in DLEMIA.

• 대한조선학회논문집
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• 제34권1호
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• pp.93-101
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• 1997

본 연구에서는 전통적인 비선형 최적화 기법의 문제점을 극복하기 위하여 유전자알고리즘과 지식베이스의 통합을 통한 새로운 개념의 최적화 기법을 개발하였다. 여기에서는 제한조건이 있는 비선형 최적화 문제를 해결하기 위해 사용되는 전통적인 순차적 선형화 방법과 새로운 유전자 알고리즘의 장단점을 서로 보완한 하이브리드형 최적화 기법을 개발하였다. 여기에 지식베이스를 통한 최적화 지원 기법 및 최적화 모델의 자동생성 모듈을 개발하여 최적화 모텔의 성능을 한층 개선할 수 있었다. 개발된 최적화 기법의 검증을 위하여 수학적 비선형 모델을 이용한 여러가지 기법의 비교 검토를 수행하였다.

• International Journal of Naval Architecture and Ocean Engineering
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• 제5권1호
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• pp.101-115
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• 2013

This paper examines the application of structural reliability analysis to submarine pressure hulls to clarify the merits of probabilistic approach in respect thereof. Ultimate strength prediction methods which take the inelastic behavior of ring-stiffened cylindrical shells and hemi-spherical shells into account are reviewed. The modeling uncertainties in terms of bias and coefficient of variation for failure prediction methods in current design guidelines are defined by evaluating the compiled experimental data. A simple ultimate strength formulation for ring-stiffened cylinders taking into account the interaction between local and global failure modes and an ultimate strength formula for hemispherical shells which have better accuracy and reliability than current design codes are taken as basis for reliability analysis. The effects of randomness of geometrical and material properties on failure are assessed by a prelimnary study on reference models. By evaluation of sensitivity factors important variables are determined and comparesons are made with conclusions of previous reliability studies.

• Structural Engineering and Mechanics
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• 제28권6호
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• pp.727-747
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• 2008

In the framework of the SPEAR (Seismic PErformance Assessment and Rehabilitation) research Project, an under-designed three storey RC frame structure, designed to sustain only gravity loads, was subjected, in three different configurations 'as-built', Fiber Reinforced Polymer (FRP) retrofitted and rehabilitated by reinforced concrete (RC) jacketing, to a series of bi-directional pseudodynamic (PsD) tests under different values of peak ground acceleration (PGA) (from a minimum of 0.20g to a maximum of 0.30g). The seismic deficiencies exhibited by the 'as-built' structure after the test at PGA level of 0.20g were confirmed by a post - test assessment of the structural seismic capacity performed by a nonlinear static pushover analysis implemented on the structure lumped plasticity model. To improve the seismic performance of the 'as-built' structure', two rehabilitation interventions by using either FRP laminates or RC jacketing were designed. Assumptions for the analytical modeling, design criteria and calculation procedures along with local and global intervention measures and their installation details are herein presented and discussed. Nonlinear static pushover analyses for the assessment of the theoretical seismic capacity of the structure in each retrofitted configuration were performed and compared with the experimental outcomes.

• 한국정보통신학회논문지
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• 제18권9호
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• pp.2057-2065
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• 2014

전자책 산업은 인쇄문화와 정보통신의 융합이며, 새로운 비즈니스이지만, 우리나라의 시스템적인 변화는 역동적이지 않다. 세계적인 시장 플레이어들은 단말기, 플랫폼, 네트워크를 활용하여 회원제 또는 커뮤니티형 비즈니스 모델을 만들어가고 있지만 우리나라는 창조적인 콘텐츠 제작에 아쉬움이 많다. 단말기 또는 네트워크 서비스 등에 국한되어 있는 바, 본 연구는 다각적인 모델링의 가능성을 제안했다. 그리고 전자책 산업의 발전을 위한 전략적인 접근방법으로서 플랫폼 기술과 서비스 콘텐츠의 다양한 개발도 중요하지만 개발된 기술의 응용을 시사하고 있다.

• 한국우주과학회:학술대회논문집(한국우주과학회보)
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• 한국우주과학회 2010년도 한국우주과학회보 제19권1호
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• pp.25.1-25.1
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• 2010

This talk outlines the current understanding of solar flares, mainly focusing on magnetohydrodynamic (MHD) processes. A flare causes plasma heating, mass ejection, and particle acceleration that generates high-energy particles. The key physical processes related to a flare are: the emergence of magnetic field from the solar interior to the solar atmosphere (flux emergence), formation of current-concentrated areas (current sheets) in the corona, and magnetic reconnection proceeding in current sheets that causes shock heating, mass ejection, and particle acceleration. A flare starts with the dissipation of electric currents in the corona, followed by various dynamic processes which affect lower atmospheres such as the chromosphere and photosphere. In order to understand the physical mechanism for producing a flare, theoretical modeling has been developed, in which numerical simulation is a strong tool reproducing the time-dependent, nonlinear evolution of plasma before and after the onset of a flare. In this talk we review various models of a flare proposed so far, explaining key features of these models. We show observed properties of flares, and then discuss the processes of energy build-up, release, and transport, all of which are responsible for producing a flare. We come to a concluding view that flares are the manifestation of recovering and ejecting processes of a global magnetic flux tube in the solar atmosphere, which was disrupted via interaction with convective plasma while it was rising through the convection zone.

• International Journal of Automotive Technology
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• 제6권2호
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• pp.95-105
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• 2005

Diesel engines have low specific fuel consumption, but high particulate emissions, mainly soot. Diesel soot is suspected to have significant effects on the health of living beings and might also affect global warming. Hence stringent measures have been put in place in a number of countries and will be even stronger in the near future. Diesel engines require either advanced integrated exhaust after treatment systems or modified engine models to meet the statutory norms. Experimental analysis to study the emission characteristics is a time consuming affair. In such situations, the real picture of engine control can be obtained by the modeling of trend prediction. In this article, an effort has been made to predict emissions smoke and NO$_{x}$ using cylinder combustion derived parameters and diesel particulate filter data, with artificial neural network techniques in MATLAB environment. The model is based on three layer neural network with a back propagation learning algorithm. The training and test data of emissions were collected from experimental set up in the laboratory for different loads. The network is trained to predict the values of emission with training values. Regression analysis between test and predicted value from neural network shows least error. This approach helps in the reduction of the experimentation required to determine the smoke and NO$_{x}$ for the catalyst coated filters.