• Title, Summary, Keyword: nonlinear scaling

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Computational enhancement to the augmented lagrange multiplier method for the constrained nonlinear optimization problems (구속조건식이 있는 비선형 최적화 문제를 위한 ALM방법의 성능향상)

  • 김민수;김한성;최동훈
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.15 no.2
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    • pp.544-556
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    • 1991
  • The optimization of many engineering design problems requires a nonlinear programming algorithm that is robust and efficient. A general-purpose nonlinear optimization program IDOL (Interactive Design Optimization Library) is developed based on the Augmented Lagrange Mulitiplier (ALM) method. The ideas of selecting a good initial design point, using resonable initial values for Lagrange multipliers, constraints scaling, descent vector restarting, and dynamic stopping criterion are employed for computational enhancement to the ALM method. A descent vector is determined by using the Broydon-Fletcher-Goldfarb-Shanno (BFGS) method. For line search, the Incremental-Search method is first used to find bounds on the solution, then the bounds are reduced by the Golden Section method, and finally a cubic polynomial approximation technique is applied to locate the next design point. Seven typical test problems are solved to show IDOL efficient and robust.

The Role of S-Shape Mapping Functions in the SIMP Approach for Topology Optimization

  • Yoon, Gil-Ho;Kim, Yoon-Young
    • Journal of Mechanical Science and Technology
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    • v.17 no.10
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    • pp.1496-1506
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    • 2003
  • The SIMP (solid isotropic material with penalization) approach is perhaps the most popular density variable relaxation method in topology optimization. This method has been very successful in many applications, but the optimization solution convergence can be improved when new variables, not the direct density variables, are used as the design variables. In this work, we newly propose S-shape functions mapping the original density variables nonlinearly to new design variables. The main role of S-shape function is to push intermediate densities to either lower or upper bounds. In particular, this method works well with nonlinear mathematical programming methods. A method of feasible directions is chosen as a nonlinear mathematical programming method in order to show the effects of the S-shape scaling function on the solution convergence.

Design of Fuzzy PD+I Controller Based on PID Controller

  • Oh, Sea-June;Yoo, Heui-Han;Lee, Yun-Hyung;So, Myung-Ok
    • Journal of Navigation and Port Research
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    • v.34 no.2
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    • pp.117-122
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    • 2010
  • Since fuzzy controllers are nonlinear, it is more difficult to set the controller gains and to analyse the stability compared to conventional PID controllers. This paper proposes a fuzzy PD+I controller for tracking control which uses a linear fuzzy inference(product-sum-gravity) method based on a conventional linear PID controller. In this scheme the fuzzy PD+I controller works similar to the control performance as the linear PD plus I(PD+I) controller. Thus it is possible to analyse and design an fuzzy PD+I controller for given systems based on a linear fuzzy PD controller. The scaling factors tuning scheme, another topic of fuzzy controller design procedure, is also introduced in order to fine performance of the fuzzy PD+I controller. The scaling factors are adjusted by a real-coded genetic algorithm(RCGA) in off-line. The simulation results show the effectiveness of the proposed fuzzy PD+I controller for tracking control problems by comparing with the conventional PID controllers.

Analysis of a Modified Stochastic Gradient-Based Filter with Variable Scaling Parameter (가변 축척 매개변수를 가진 변형 확률적 경사도 기반 필터의 해석)

  • Kim, Hae-Jung
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.31 no.12C
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    • pp.1280-1287
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    • 2006
  • We propose a modified stochastic gradient-based (MSGB) filter showing that the filter is the solution to an optimization problem. This paper analyzes the properties of the MSGB filter that corresponds to the nonlinear adaptive filter with additional update terms, parameterized by the variable scaling factor. The variably parameterized MSGB filter plays a role iii connecting the fixed parameterized MSGB filter and the null parameterized MSGB filter through variably scaling parameter. The stability regions and misadjustments are shown. A system identification is utilized to perform the computer simulation and demonstrate the improved performance feature of the MSGB filter.

Conversion of Fisheye Image to Perspective Image Using Nonlinear Scaling Function (비선형 스케일링 함수를 이용한 어안 영상의 원근 변환)

  • Kim, Tae-Woo;Cho, Tae-Kyung
    • Journal of the Korea Academia-Industrial cooperation Society
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    • v.10 no.1
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    • pp.117-121
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    • 2009
  • The fisheye image acquired with a fisheye camera has wider field of view than a general use camera. But large distortion of the object in the image requires conversion of the fisheye image to the perspective image because of user's difficult perception. The existing Ishii's method[1] has the problem that the object can has sire and geometrical distortion in the transformed image because it uses equidistance projection. This paper presented a conversion technique of the fisheye image to the perspective image using sealing function. In the experiments, it was shown that our method reduced size and geometrical distortion by applying the scaling function.

Semi-rigid connection modeling for steel frameworks

  • Liu, Yuxin
    • Structural Engineering and Mechanics
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    • v.35 no.4
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    • pp.431-457
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    • 2010
  • This article provides a discussion of the mathematic modeling of connections for designing and qualifying structures, systems, and components subject to monotonic or cyclic loading. To characterize the force-deformation behavior of connections under monotonic loading, a review of the Ramberg-Osgood, Richard-Abbott, and Menegotto-Pinto models is conducted, and it is shown that these nonlinear functions can be mathematically derived by scaling up or down a linear force-deformation function. A generalized four-parameter model for simulating connection behavior is investigated to facilitate nonlinear regression analysis. In order to perform seismic analysis of frameworks, a hysteretic model accounting for loading, unloading, and reloading is described using the established monotonic model. For preliminary analysis, a method is provided to quickly determine the model parameters that fit approximately with the observed data. To reach more accurate values of the parameters, the methods of nonlinear regression analysis are investigated and the modified Levenberg-Marquardt and separable nonlinear least-square algorithms are applied in determining the model parameters. Example case studies illustrate the procedure for the computation through the use of experimental/analytical data taken form the literature. Transformation of connection curves from the three-parameter model to the four-parameter model for structural analysis is conducted based on the modeling of connections subject to fire.

Assessment of Code-specified Ground Motion Selection Criteria with Accurate Selection and Scaling Methods - I Ground Motion Selection (구조물 동적해석을 위한 현행 내진설계기준의 입력 지반 운동 선정 조건 타당성 평가 - I 선정방법)

  • Ha, Seong Jin;Han, Sang Whan;Ji, Hyun Woo
    • Journal of the Earthquake Engineering Society of Korea
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    • v.21 no.4
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    • pp.171-179
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    • 2017
  • For estimating the seismic demand of buildings, most seismic design provisions permit conducting linear and nonlinear response history analysis. In order to obtain reliable results from response history analyses, a proper selection of input ground motions is required. In this study, an accurate algorithm for selecting and scaling ground motions is proposed, which satisfies the ASCE 7-10 criteria. In the proposed algorithm, a desired number of ground motions are sequentially scaled and selected from a ground motion library without iterations.

A rapid screening method for selection and modification of ground motions for time history analysis

  • Behnamfar, Farhad;Velni, Mehdi Talebi
    • Earthquakes and Structures
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    • v.16 no.1
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    • pp.29-39
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    • 2019
  • A three-step screening process is presented in this article for selection of consistent earthquake records in which number of suitable ground motions is quickly screened and reduced to a handful number. Records that remain at the end of this screening process considerably reduce the dispersion of structural responses. Then, an effective method is presented for spectral matching and modification of the selected records. Dispersion of structural responses is explored using different statistical measures for each scaling procedure. It is shown that the Uniform Design Method, presented in this study for scaling of earthquake records, results in most cases in the least dispersion measure.

A TWO-LEVEL FINITE ELEMENT METHOD FOR THE STEADY-STATE NAVIER-STOKES/DARCY MODEL

  • Fang, Jilin;Huang, Pengzhan;Qin, Yi
    • Journal of the Korean Mathematical Society
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    • v.57 no.4
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    • pp.915-933
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    • 2020
  • A two-level finite element method based on the Newton iterative method is proposed for solving the Navier-Stokes/Darcy model. The algorithm solves a nonlinear system on a coarse mesh H and two linearized problems of different loads on a fine mesh h = O(H4-𝜖). Compared with the common two-grid finite element methods for the considered problem, the presented two-level method allows for larger scaling between the coarse and fine meshes. Moreover, we prove the stability and convergence of the considered two-level method. Finally, we provide numerical experiment to exhibit the effectiveness of the presented method.

Nonlinear Buckling Characteristics of Ring-stiffened Circular Cylinders under Uniform External Pressure (균일한 외압을 받는 원환보강 원통구조의 비선형 좌굴 특성)

  • Ahn, Dang;Kim, Soo-Young;Shin, Sung-Chul;Chung, Bo-Young;Koo, Youn-Hoe
    • Journal of Ocean Engineering and Technology
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    • v.26 no.2
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    • pp.79-84
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    • 2012
  • This study aimed to analyze the nonlinear buckling of ring-stiffened circular cylinders under uniform external pressure, e.g. hydrostatic pressure, considering material nonlinearity and initial imperfection. In the present study, we analyzed the collapse pressure of pressure vessels using ANSYS Workbench, which is a framework of finite element methods. First, linear buckling analysis is performed to find collapse modes of the model. Second, scaling the first mode shape with small factor, geometric model is pre-deformed. And then, by analyzing the nonlinear buckling of the pre-deformed shape, the collapse pressure is estimated. To verify the validity of the analyses, we compared the results with Ross' experimental results. Finally, we applied it to ring-stiffened circular cylindrical shell of the pressure hull of a small submarine.