• Title, Summary, Keyword: Approximate Model

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Sequential Approximate Optimization Using Kriging Metamodels (크리깅 모델을 이용한 순차적 근사최적화)

  • Shin Yongshik;Lee Yongbin;Ryu Je-Seon;Choi Dong-Hoon
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.29 no.9
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    • pp.1199-1208
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    • 2005
  • Nowadays, it is performed actively to optimize by using an approximate model. This is called the approximate optimization. In addition, the sequential approximate optimization (SAO) is the repetitive method to find an optimum by considering the convergence of an approximate optimum. In some recent studies, it is proposed to increase the fidelity of approximate models by applying the sequential sampling. However, because the accuracy and efficiency of an approximate model is directly connected with the design area and the termination criteria are not clear, sequential sampling method has the disadvantages that could support an unreasonable approximate optimum. In this study, the SAO is executed by using trust region, Kriging model and Optimal Latin Hypercube design (OLHD). Trust region is used to guarantee the convergence and Kriging model and OLHD are suitable for computer experiment. finally, this SAO method is applied to various optimization problems of highly nonlinear mathematical functions. As a result, each approximate optimum is acquired and the accuracy and efficiency of this method is verified by comparing with the result by established method.

Prediction of the Forming Load of Non-Axisymmetric Isothermal Forging using Approximate Similarity Theory (근사 상사 이론을 이용한 비축대칭 등온 단조의 가공하중 예측)

  • 최철현
    • Proceedings of the Korean Society for Technology of Plasticity Conference
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    • pp.71-75
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    • 1999
  • An approximate similarity theory has been applied to predict the forming load of non-axisymmetric forging of aluminum alloys through model material tests. The approximate similarity theory is applicable when strain rate sensitivity geometrical size and die velocity of model materials are different from those of real materials. Actually the forming load of yoke which is an automobile part made of aluminum alloys(Al-6061) is predicted by using this approximate similarity theory. Firstly upset forging tests are have been carried out to determine the flow curves of three model materials and aluminum alloy(Al-6061) and a suitable model material is selected for model material test of Al-6061 And then and forging tests of aluminum yokes have been performed to verify the forming load predicted from the model material which has been selected from above upset forging tests, The forming loads of aluminum yoke forging predicted by this approximate similarity theory are in good agreement with the experimental results of Al-6061 and the results of finite element analysis using DEFORM-3D.

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Adaptive Position Controller Design of Electro-hydraulic Actuator Using Approximate Model Inversion (근사적 모델 역변환을 활용한 전기-유압 액추에이터의 적응 위치 제어기 설계)

  • Lee, Kyeong Ha;Baek, Seung Guk;Koo, Ja Choon
    • The Journal of Korea Robotics Society
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    • v.11 no.2
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    • pp.92-99
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    • 2016
  • An electro-hydraulic actuator (EHA) is widely used in industrial motion systems and the increasing bandwidth of EHA position control is important issue. The model-inverse feedforward controller is known to extend the bandwidth of system. When the system has non-minimum phase (NMP) zeros, direct model inversion makes system unstable. To overcome this problem, an approximate model-inverse method is used. A representative approximate model inversion method is zero phase error tracking control (ZPETC). However, if zeros locate right half plane of z-plane, the approximate inverse model amplifies the high-frequency response. In this paper, to solve the problem of ZPETC, an adaptive model-inverse control is proposed. The adaptive algorithm updates feedforward term in real-time. The effectiveness of the proposed adaptive model-inverse position control strategy is verified by comparison with typical proportional-integral (PI) control and feedforward control by experiments. As a result, the proposed adaptive controller extends the bandwidth of EHA position control.

An Approximate Model for Predicting Roll Force in Rod Rolling

  • Lee, Youngseog;Kim, Hong-Joon
    • Journal of Mechanical Science and Technology
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    • v.16 no.4
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    • pp.501-511
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    • 2002
  • This paper presents a study of the effect of rolling temperature, roll gap (pass height), initial specimen size and steel grades of specimens on the roll force in round-oval-round pass sequence by applying approximate method and verifications through single stand pilot rod rolling tests. The results show that the predicted roll forces are in good agreement with the experimentally measured ones. The approximate model is independent of the change of roll gap, specimen size and temperature. Thus, the generality of the prediction methodology employed in the approximate model is proven. This study also demonstrates that Shida's constitutive equation employed in the approximate model needs to be corrected somehow to be applicable for the medium and high carbon steels in a lower temperature interval (700∼900$\^{C}$).

Prediction of the Forming Load of Non-Axisymmetric Isothermal Forging using Approximate Similarity Theory (근사 상사 이론을 이용한 비축대칭 등온 단조의 가공하중 예측)

  • 한정영;최철현;배원병;김영호;이종헌
    • Journal of the Korean Society for Precision Engineering
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    • v.17 no.1
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    • pp.204-208
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    • 2000
  • An approximate similarity theory has been applied to predict the forming load of non-axisymmetric forging of aluminum alloys through model material tests. The approximate similarity theory is applicable when strain rate sensitivity, geometrical size, and die velocity of model materials are different from those of real materials. Actually, the forming load of yoke, which is an automobile part made of aluminum alloys(Al-6061), is predicted by using this approximate similarity theory. Firstly, upset forging tests are have been carried out to determine the flow curves of three model materials and aluminum alloy(Al-6061), and a suitable model material is selected for model material test of Al-6061. And then hot forging tests of aluminum yokes have been performed to verify the forming load predicted from the model material, which has been selected from above upset forging tests. The forming loads of aluminum yoke forging predicted by this approximate similarity theory are in good agreement with the experimental results of Al-6061 and the results of finite element analysis using DEFORM-3D.

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BPN Based Approximate Optimization for Constraint Feasibility (구속조건의 가용성을 보장하는 신경망기반 근사최적설계)

  • Lee, Jong-Soo;Jeong, Hee-Seok;Kwak, No-Sung
    • Proceedings of the Computational Structural Engineering Institute Conference
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    • pp.141-144
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    • 2007
  • Given a number of training data, a traditional BPN is normally trained by minimizing the absolute difference between target outputs and approximate outputs. When BPN is used as a meta-model for inequality constraint function, approximate optimal solutions are sometimes actually infeasible in a case where they are active at the constraint boundary. The paper describes the development of the efficient BPN based meta-model that enhances the constraint feasibility of approximate optimal solution. The modified BPN based meta-model is obtained by including the decision condition between lower/upper bounds of a constraint and an approximate value. The proposed approach is verified through a simple mathematical function and a ten-bar planar truss problem.

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Space Radiation Shielding Calculation by Approximate Model for LEO Satellites

  • Shin Myung-Won;Kim Myung-Hyun
    • Nuclear Engineering and Technology
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    • v.36 no.1
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    • pp.1-11
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    • 2004
  • Two approximate methods for a cosmic radiation shielding calculation in low earth orbits were developed and assessed. Those are a sectoring method and a chord-length distribution method. In order to simulate a change in cosmic radiation environments along the satellite mission trajectory, IGRF model and AP(E)-8 model were used. When the approximate methods were applied, the geometrical model of satellite structure was approximated as one-dimensional slabs, and a pre-calculated dose-depth conversion function was introduced to simplify the dose calculation process. Verification was performed with mission data of KITSAT-1 and the calculated results were also compared with detailed 3-dimensional calculation results using Monte Carlo calculation. Dose results from the approximate methods were conservatively higher than Monte Carlo results, but were lower than experimental data in total dose rate. Differences between calculation and experimental data seem to come from the AP-8 model, for which it is reported that fluxes of proton are underestimated. We confirmed that the developed approximate method can be applied to commercial satellite shielding calculations. It is also found that commercial products of semi-conductors can be damaged due to total ionizing dose under LEO radiation environment. An intensive shielding analysis should be taken into account when commercial devices are used.

Evaluation of Measurement Precisions Using Approximate F Tests and EMS in the Gauge R&R Studies (게이지 R&R 연구에서 근사 F검정과 EMS를 이용한 측정 정밀도의 평가)

  • Choi, Sung-Woon
    • Journal of the Korea Safety Management and Science
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    • v.11 no.3
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    • pp.209-216
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    • 2009
  • A development in method of evaluating the measurement precisions using approximate F tests and variance components from expected mean square (EMS) is investigated. The research proposes three-factor mixed measurement models with the fixed and random factors. Unrestricted and unconstrained design work was rarely studied, while restricted and constrained designs have been significantly discussed. The unrestricted and unconstrained designs assume to be an independence of interaction. The proposed evaluation method about the measurement precisions can be extended to four-factor random measurement model or mixed measurement model. The study also presents the three evaluation indexes of precisions such as R&RTR (Reproducibility & Repeatability-To-Total Precision Ratio), PTR (Precision-To-Tolerance Ratio), and SNR (Signal-To-Noise Ratio). Numerical examples are proposed to evaluate the approximate F tests with Satterthwaite degrees of freedom and three indexes using the measurement precisions from EMS.

DAM BREAK FLOW ANALYSIS WITH APPROXIMATE RIEMANN SOLVER

  • Kim, Dae-Hong
    • Water Engineering Research
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    • v.4 no.4
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    • pp.175-185
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    • 2003
  • A numerical model to analyze dam break flows has been developed based on approximate Riemann solver. The governing equations of the model are the nonlinear shallow-water equations. The governing equations are discretized explicitly by using finite volume method and the numerical flux are reconstructed with weighted averaged flux (WAF) method. The developed model is verified. The first verification problem is about idealized dam break flow on wet and dry beds. The second problem is about experimental data of dam break flow. From the results of the verifications, very good agreements have been observed

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Confidence intervals on variance components in multiple regression model with one-fold nested error strucutre (중첩오차를 갖는 중회귀모형에서 분산의 신뢰구간)

  • 박동준
    • Proceedings of the Korean Operations and Management Science Society Conference
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    • pp.495-498
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    • 1996
  • Regression model with nested error structure interval estimations about variability on different stages are proposed. This article derives an approximate confidence interval on the variance in the first stage and an exact confidence interval on the variance in the second stage in two stage regression model. The approximate confidence interval is based on Ting et al. (1990) method. Computer simulation is provided to show that the approximate confidence interval maintains the stated confidence coefficient.

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