• Title/Summary/Keyword: approximate model

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Dynamic performance of a composite building structure under seismic ground motions

  • Tsai, Meng-Hao;Zhang, Junfei;Song, Yih-Ping;Lu, Jun-Kai
    • Earthquakes and Structures
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    • v.15 no.2
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    • pp.179-191
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    • 2018
  • This study is aimed at investigating the dynamic performance of a composite building structure under seismic ground motions. The building structure is an official fire department building located in southern Taiwan. It is composed of a seven-story reinforced concrete (RC) and an eight-story steel reinforced concrete (SRC) frame. Both frames share a common basement and are separated by expansion joints from the first to the seventh floor. Recorded floor accelerations of the building structure under eight earthquakes occurring during the period from 2011 to 2013 were examined in this paper. It is found that both frames had similar floor acceleration amplifications in the longitudinal direction, while the SRC frame revealed larger response than the RC frame in the transverse direction. Almost invariant and similar fundamental periods under the eight earthquakes in both directions were obtained from their transfer functions. Furthermore, numerical time-history simulations were carried out for the building structure under the most intensive earthquake. It is realized that the seismic response of the composite building was dominated by the first translational mode in each horizontal direction. Higher modes did not significantly contribute to the structural response. The conventional Rayleigh damping model could be appropriately applied to the time-history simulations under bi-directional excitations. Approximate floor acceleration envelopes were obtained with a compound RC and SRC structural model by using the average damping ratios determined from the different structural arrays.

Sensitivity Approach of Sequential Sampling Using Adaptive Distance Criterion (적응거리 조건을 이용한 순차적 실험계획의 민감도법)

  • Jung, Jae-Jun;Lee, Tae-Hee
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.29 no.9 s.240
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    • pp.1217-1224
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    • 2005
  • To improve the accuracy of a metamodel, additional sample points can be selected by using a specified criterion, which is often called sequential sampling approach. Sequential sampling approach requires small computational cost compared to one-stage optimal sampling. It is also capable of monitoring the process of metamodeling by means of identifying an important design region for approximation and further refining the fidelity in the region. However, the existing critertia such as mean squared error, entropy and maximin distance essentially depend on the distance between previous selected sample points. Therefore, although sufficient sample points are selected, these sequential sampling strategies cannot guarantee the accuracy of metamodel in the nearby optimum points. This is because criteria of the existing sequential sampling approaches are inefficient to approximate extremum and inflection points of original model. In this research, new sequential sampling approach using the sensitivity of metamodel is proposed to reflect the response. Various functions that can represent a variety of features of engineering problems are used to validate the sensitivity approach. In addition to both root mean squared error and maximum error, the error of metamodel at optimum points is tested to access the superiority of the proposed approach. That is, optimum solutions to minimization of metamodel obtained from the proposed approach are compared with those of true functions. For comparison, both mean squared error approach and maximin distance approach are also examined.

Gate Locations Optimization of an Automotive Instrument Panel for Minimizing Cavity Pressure (금형 내부 압력 최소화를 위한 자동차 인스트루먼트 패널의 게이트 위치 최적화)

  • Cho, Sung-Bin;Park, Chang-Hyun;Pyo, Byung-Gi;Cho, Dong-Hoon
    • Journal of the Korean Society for Precision Engineering
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    • v.29 no.6
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    • pp.648-653
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    • 2012
  • Cavity pressure, an important factor in injection molding process, should be minimized to enhance injection molding quality. In this study, we decided the locations of valve gates to minimize the maximum cavity pressure. To solve this problem, we integrated MAPS-3D (Mold Analysis and Plastic Solution-3Dimension), a commercial injection molding analysis CAE tool, using the file parsing method of PIAnO (Process Integration, Automation and Optimization) as a commercial process integration and design optimization tool. In order to reduce the computational time for obtaining the optimal design solution, we performed an approximate optimization using a meta-model that replaced expensive computer simulations. To generate the meta-model, computer simulations were performed at the design points selected using the optimal Latin hypercube design as an experimental design. Then, we used micro genetic algorithm equipped in PIAnO to obtain the optimal design solution. Using the proposed design approach, the maximum cavity pressure was reduced by 17.3% compared to the initial one, which clearly showed the validity of the proposed design approach.

Mixed Operation with Express Train for Urban Railways in Seoul Metropolitan Area (대피선 설치를 통한 수도권 광역철도 급행화 방안)

  • Son, Gi-Min
    • Journal of Korean Society of Transportation
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    • v.25 no.5
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    • pp.195-207
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    • 2007
  • The urban railways connecting between the inner city and suburb of Seoul metropolitan area, has lost the competitiveness against cars because too many stops deteriorated operating speed and passenger's level of service. This paper suggests that an express train should be introduced into the urban railway system in order to sort out such a complication. There are two considerations in the present study. Firstly, train schedule problem should be taken into account. In this regard, a new model for urban railway system was developed by revising the existing models dealing with single line freight railway. Approximate branch and bound algorithm based on conflict group rather than a single conflict was adopted. Consequently, it was found that the time saving in calculating the optimal schedule is the most meaningful contribution of the algorithm. The second consideration is associated with the application of the model. A case study was carried out using the actual operation data from Ansan line. In conclusion, the operation speed of the line can increase considerably with minimal number of new sidings.

Optimization of shock absorption system for lunar lander considering the effect of lunar regolith (달 토양 특성을 고려한 달착륙선 충격흡수장치의 최적화)

  • Yang, Soon Shin;Kang, Yeon Chul;Son, Jae Yeon;Oh, Min Hwan;Kim, Jeong Ho;Cho, Jin Yeon
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.42 no.4
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    • pp.284-290
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    • 2014
  • To successfully explore the moon by lunar lander, it is essential to guarantee the safe landing of lunar lander. Therefore, efficient shock absorption system of lunar lander should be designed in order to reduce landing impact force. Also, for more practical design of lunar lander, it is important to consider the effect of lunar regolith. In the line of thought, finite element model of lunar lander considering the effect of lunar regolith is developed. To reduce landing impact force, optimization of shock absorption system for lunar lander has been carried out. In optimization, sequential approximate optimization method based on meta-model is used. Through the result of optimization, it is verified that landing impact force on lunar lander can be efficiently reduced by the present optimization procedure.

Uncertainty Analysis for Head and Gradient Incorporating Spatial Nonuniformity of Hydraulic Conductivity around Underground Storage Caverns (지하공동주변 수리전도도의 불균일성을 도입한 수두 및 동수경사의 불확실성 해석)

  • Jeong, Il-Mun;Jo, Won-Cheol;Heo, Jun-Haeng
    • Journal of Korea Water Resources Association
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    • v.31 no.5
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    • pp.553-564
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    • 1998
  • For the proper design and management of underground storage cavern, groundwater flow around cavern should be analyzed. Since this flow is influenced by spatial nonuniformity of hudraulic conductivity, the two-dimensional finite element flow model incorporating stochastic concepts was developed to analyze influences due to this nonuniformity. Monte Carlo technique was applied to obtain an approximate solution for two-dimensional, steady flow in a stochastically defined nonuniform medisu. For this purpose, the values of hydraulic conductivity were generated for each element with known mean and standard deviations. The uncertainty in model prediction depends on both the nonuniformity in hydraulic conductivity and the natures of the flow system such as water curtain and boundary condition. Therefore the uncertainties in predicted hydraulic head and gradient are the greatest where the mean hydraulic gradients are relatively large and far from the boundaries. Especially, we relate these uncertainties with well known gas tightness condition.

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Characteristics of Wave Propagation by Water Level Conditions at Wando Sea Area: Numerical Modeling (완도 해역의 해수면 조건에 따른 파랑 변형 특성)

  • Jeon, Yong-Ho;Yoon, Han-Sam;Kim, Dong-Hwan;Kim, Won-Seok;Kim, Heon-Tae
    • Journal of Fisheries and Marine Sciences Education
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    • v.25 no.1
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    • pp.1-11
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    • 2013
  • The aim of this study was estimated the characteristics of the wave propagation by the water level conditions using a numerical modeling method at the Wando sea area. For three cases numerical simulation on the condition of incident and incoming of the deepwater design wave and the season normal wave, the spatial distribution of the incident wave at study area were investigated. And the calculated numerical modeling results were compared with measured field wave data. According to on-site wave data measured for 18 days, the range of the significant wave height and period were 0.10~1.14 m, 4.35~8.74 sec, respectively, and the maximum wave height were 0.15~1.66 m. From the results of numerical model for offshore design wave incident, the wave height attacked from Southern-East direction at this study area were over maximum 10.5 m because of rapidly change of water depth. Numerical modeling by three water level conditions of Approxmate Lowest Low Water Level(Approx. L.L.W), Mean Sea Level(M.S.L) and Approximate Highest High Water Level(Approx. H.H.W) were practiced. From the results for the case of Approx. H.W.L, variations of wave height at the back area of islands were about 1.6 m at maximum value for the case of deepwater design wave incoming. The significant wave heights of winter season were bigger than summer under normal wave condition, the incident wave height over 5.5 m decreased by shielding effect of islands. The change of maximum wave height at summer season were distinct than winter and was about 1.2 m and 0.8 m, respectively.

The Preliminary Design of Stirling Engines Considering the Regenerator Effectiveness (재생기효율을 고려한 스터링기관의 예비설계)

  • 유호선;노승탁
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.14 no.5
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    • pp.1356-1364
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    • 1990
  • This paper deals with the preliminary design conditions of Stirling Engines based on an adiabatic analysis with regenerator effectiveness. The investigation of thermal regeneration process results that the definition of effectiveness proposed by Urieli et al. is appropriate for the present model. Then, it is applied to the already existing approximate analytic solution for the adiabatic model in order to optimize thermal efficiency as well as work parameter. Results show that thermal efficiency is less sensitive to the variation in design parameters than work. Phase angle for the maximum work is also the most efficient at high values of the effectiveness. Swept volume ratio should be chosen with care. The optimum value of dead volume ratio is at least less than the maximum efficiency condition. The feasible design range in compression ratio lies between the maximum efficiency condition and the structural limit of Stilring Engines, where the higher its value, the better. Changes in the temperature ratio do not alter the design conditions. Working fluids with the specific heat ratio 1.67 are more efficient that those with 1.4.

Optimal Fuzzy Filter for Nonlinear Systems with Variance Constraints (분산 제약을 갖는 비선형 시스템의 최적 퍼지 필터)

  • Noh, Sun-Young;Park, Jin-Bae;Joo, Young-Hoon
    • Journal of the Korean Institute of Intelligent Systems
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    • v.22 no.5
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    • pp.549-554
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    • 2012
  • In this paper, we consider the optimal fuzzy filter of nonlinear discrete-time with estimation error variance constraint. First, the Takagi and Sugeno(T-S) fuzzy model is employed to approximate the nonlinear system. Next, the error state is mean square bounded, and the steady state variance of the estimation error of each state is not more than the individual predefined value. It is shown that, the addressed problem can be carried out by solving linear matrix inequality(LMI) and some algebraic quadratic matrix inequalities. Finally, some examples are provided to illustrate the design procedure and expected performance through simulations.

An Optimization Approach for a Spanning Tree-Based Compactness Measure in Contiguous Land Acquisition Problems (토지 획득 문제에서 공간적 밀집도 측정을 위한 최적화 연구)

  • Kim, Myung-Jin;Xiao, Ningchuan
    • Journal of the Korean Geographical Society
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    • v.46 no.6
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    • pp.724-737
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    • 2011
  • The goal of solving a contiguous land acquisition problem is to find an optimal cluster of land parcels so that one can move from an acquired parcel to another without leaving the cluster. In many urban and regional planning applications, criteria such as acquisition cost and compactness of acquired parcels are important. Recent research has demonstrated that spatial contiguity can be formulated in a mixed integer programming framework. Spatial compactness, however, is typically formulated in an approximate manner using parameters such as external border length or other shape indices of acquired land parcels. This paper first develops an alternative measure of spatial compactness utilizing the characteristics of the internal structure of a contiguous set of land parcels and then incorporates this new measure into a mixed integer program of contiguous land acquisition problems. A set of computational experiments are designed to demonstrate the use of our model in a land acquisition context.