• Title/Summary/Keyword: variational

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Cross-sectional Optimization of a Human-Powered Aircraft Main Spar using SQP and Geometrically Exact Beam Model (기하학적 정밀 보 이론 및 SQP 기법에 의한 인간동력항공기 Main Spar 단면 설계 최적화 연구)

  • Kang, Seung-Hoon;Im, Byeong-Uk;Cho, Hae-Seong;Shin, Sang-Joon
    • Journal of the Computational Structural Engineering Institute of Korea
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    • v.31 no.4
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    • pp.183-190
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    • 2018
  • This paper presents optimization of the main spar of Human-Powered Aircraft (HPA) wing. Mass minimization was attempted, while considering large torsional deformation of the beam. Sequential Quadratic Programming (SQP) method was adopted as a relevant tool to conduct structural optimization algorithm. An inner diameter and ply thicknesses of the main spar were selected as the design variables. The objective function includes factors such as mass minimization, constant tip bending displacement, and constant tip twist of the beam. For estimation of bending and torsional deformation, the geometrically exact beam model, which is appropriate for large deflection, was adopted. Properties of the cross sectional area which the geometrically exact beam model requires were obtained by Variational Asymptotic Beam Sectional Analysis (VABS), which is a cross sectional analysis program. As a result, maintaining tip bending displacement and tip twist within 1.45%, optimal design that accomplished 7.88% of the mass reduction was acquired. By the stress and strain recovery, structural integrity of the optimal design and validity of the present optimization procedure were authenticated.

Visualization of Korean Speech Based on the Distance of Acoustic Features (음성특징의 거리에 기반한 한국어 발음의 시각화)

  • Pok, Gou-Chol
    • The Journal of Korea Institute of Information, Electronics, and Communication Technology
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    • v.13 no.3
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    • pp.197-205
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    • 2020
  • Korean language has the characteristics that the pronunciation of phoneme units such as vowels and consonants are fixed and the pronunciation associated with a notation does not change, so that foreign learners can approach rather easily Korean language. However, when one pronounces words, phrases, or sentences, the pronunciation changes in a manner of a wide variation and complexity at the boundaries of syllables, and the association of notation and pronunciation does not hold any more. Consequently, it is very difficult for foreign learners to study Korean standard pronunciations. Despite these difficulties, it is believed that systematic analysis of pronunciation errors for Korean words is possible according to the advantageous observations that the relationship between Korean notations and pronunciations can be described as a set of firm rules without exceptions unlike other languages including English. In this paper, we propose a visualization framework which shows the differences between standard pronunciations and erratic ones as quantitative measures on the computer screen. Previous researches only show color representation and 3D graphics of speech properties, or an animated view of changing shapes of lips and mouth cavity. Moreover, the features used in the analysis are only point data such as the average of a speech range. In this study, we propose a method which can directly use the time-series data instead of using summary or distorted data. This was realized by using the deep learning-based technique which combines Self-organizing map, variational autoencoder model, and Markov model, and we achieved a superior performance enhancement compared to the method using the point-based data.

A Comparison of Pan-sharpening Algorithms for GK-2A Satellite Imagery (천리안위성 2A호 위성영상을 위한 영상융합기법의 비교평가)

  • Lee, Soobong;Choi, Jaewan
    • Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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    • v.40 no.4
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    • pp.275-292
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    • 2022
  • In order to detect climate changes using satellite imagery, the GCOS (Global Climate Observing System) defines requirements such as spatio-temporal resolution, stability by the time change, and uncertainty. Due to limitation of GK-2A sensor performance, the level-2 products can not satisfy the requirement, especially for spatial resolution. In this paper, we found the optimal pan-sharpening algorithm for GK-2A products. The six pan-sharpening methods included in CS (Component Substitution), MRA (Multi-Resolution Analysis), VO (Variational Optimization), and DL (Deep Learning) were used. In the case of DL, the synthesis property based method was used to generate training dataset. The process of synthesis property is that pan-sharpening model is applied with Pan (Panchromatic) and MS (Multispectral) images with reduced spatial resolution, and fused image is compared with the original MS image. In the synthesis property based method, fused image with desire level for user can be produced only when the geometric characteristics between the PAN with reduced spatial resolution and MS image are similar. However, since the dissimilarity exists, RD (Random Down-sampling) was additionally used as a way to minimize it. Among the pan-sharpening methods, PSGAN was applied with RD (PSGAN_RD). The fused images are qualitatively and quantitatively validated with consistency property and the synthesis property. As validation result, the GSA algorithm performs well in the evaluation index representing spatial characteristics. In the case of spectral characteristics, the PSGAN_RD has the best accuracy with the original MS image. Therefore, in consideration of spatial and spectral characteristics of fused image, we found that PSGAN_RD is suitable for GK-2A products.

The Landscape Ecological Management System (LEMS) for Assessing the Landscape Ecological Performance of Urban Developments (도시개발의 경관생태적 성능 평가를 위한 경관생태관리시스템(LEMS) 구축에 관한 연구)

  • Oh, Kyushik;Lee, Dongwoo
    • Journal of the Korean Society of Environmental Restoration Technology
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    • v.15 no.5
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    • pp.49-67
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    • 2012
  • Studies on landscape ecology have focused on conceptual aspects, while empirical focus for spatial planning has been rarely conducted. This study conducted an empirical analysis to enhance landscape ecological performance of urban developments using landscape ecology. To do so, concrete criteria and standards to analyze structural, functional and variational mechanisms of urban landscape ecology were developed. An integrated landscape ecology assessment model that can be applied to urban development planning was established by combining the criteria. Next, Landscape Ecological Management System (LEMS) was developed to implement an integrated assessment using GIS. To verify the effectiveness of the system, a case study was conducted using LEMS on Byulnae City in the Seoul Metropolitan Area. The LEMS can be useful for urban planners and policy makers in their selection of desirable planning alternatives. Moreover, the LEMS developed in this study can be a useful tool for academia in terms of the implementation of further related studies, and for planning professionals in their environmental impact assessment tasks.

Structural identification of a steel frame from dynamic test-data

  • Morassi, A.
    • Structural Engineering and Mechanics
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    • v.11 no.3
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    • pp.237-258
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    • 2001
  • Structural identification via modal analysis in structural mechanics is gaining popularity in recent years, despite conceptual difficulties connected with its use. This paper is devoted to illustrate both the capabilities and the indeterminacy characterizing structural identification problems even in quite simple instances, as well as the cautions that should be accordingly adopted. In particular, we discuss an application of an identification technique of variational type, based on the measurement of eigenfrequencies and mode shapes, to a steel frame with friction joints under various assembling conditions. Experience has suggested, so as to restrict the indeterminacy frequently affecting identification issues, having resort to all the a priori acknowledged information on the system, to the symmetry and presence of structural elements with equal stiffness, to mention one example, and mindfully selecting the parameters to be identified. In addition, considering that the identification techniques have a local character and correspond to the updating of a preliminary model of the structure, it is important that the analytical model on the first attempt should be adequately accurate. Secondly, it has proved determinant to cross the results of the dynamic identification with tests of other typology, for instance, static tests, so as to fully understand the structural behavior and avoid the indeterminacy due to the nonuniqueness of the inverse problem.

Free vibrations of anisotropic rectangular plates with holes and attached masses

  • Rossit, C.A.;Ciancio, P.M.
    • Structural Engineering and Mechanics
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    • v.28 no.1
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    • pp.53-67
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    • 2008
  • Anisotropic materials are increasingly required in modern technological applications. Certainly, civil, mechanical and naval engineers frequently deal with the situation of analyzing the dynamical behaviour of structural elements being composed of such materials. For example, panels of anisotropic materials must sometimes support electromechanical engines, and besides, holes are performed in them for operational reasons e.g., conduits, ducts or electrical connections. This study is concerned with the natural frequencies and normal modes of vibration of rectangular anisotropic plates supported by different combinations of the classical boundary conditions: clamped, simply - supported and free, and with additional complexities such holes of free boundaries and attached concentrated masses. A variational approach (the well known Ritz method) is used, where the displacement amplitude is approximated by a set of beam functions in each coordinate direction corresponding to the sides of the rectangular plate. Consequently each coordinate function satisfies the essential boundary conditions at the outer edge of the plate. The influence of the position and magnitude of both hole and mass, on the natural frequencies and modal shapes of vibration are studied for a generic anisotropic material. The classical Ritz method with beam functions as spatial approximation proved to be a suitable procedure to solve a problem of such analytical complexity.

A New Method of Coronal Magnetic Field Reconstruction

  • Yi, Sibaek;Choe, G.S.;Lim, Daye
    • The Bulletin of The Korean Astronomical Society
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    • v.40 no.1
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    • pp.67.1-67.1
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    • 2015
  • In the past two decades, diverse methods and computer codes for reconstruction of coronal magnetic fields have been developed. Some of them can reproduce a known analytic solution quite well when the magnetic field vector is fully specified by the known solution at the domain boundaries. In practical problems, however, we do not know the boundary conditions in the computational domain except the photospheric boundary, where vector magnetogram data are provided. We have developed a new, simple variational method employing vector potentials. We have tested the computational code based on this method for problems with known solutions and those with actual photospheric data. When solutions are fully given at all boundaries, the accuracy of our method is almost comparable to best performing methods in the market. When magnetic field vectors are only given at the photospheric boundary, our method excels other methods in "figures of merit" devised by Schrijver et al. (2006). Our method is expected to contribute to the real time monitoring of the sun required for future space weather prediction.

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Vibration and Stability of Composite Cylindrical Shells Subjected to Electromagnetic and Thermal Fields (자기장 및 열하중을 받는 복합재료 원통셸의 진동 및 안정성해석)

  • Park, Sang-Yun;Kang, Sunghwan;Seo, Jung Seok;Song, Ohseop
    • Transactions of the Korean Society for Noise and Vibration Engineering
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    • v.23 no.9
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    • pp.797-805
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    • 2013
  • In this paper vibration and stability analysis of laminated composite shells based on the first order shear deformation theory(FSDT) for two different boundary conditions(clamped-clamped, simply supported) are performed. Structural model of cross-ply symmetric laminated composite cylindrical shells subjected to a combination of magnetic and thermal fields is developed via Hamilton's variational principle. These coupled equations of motion are based on the electromagnetic equations(Faraday, Ampere, Ohm, and Lorenz equations)and thermal equations which are involved in constitutive equations. Extended Galerkin method is adopted to obtain the discretized equations of motion. Variations of dynamic characteristics of composite shells with applied magnetic field, temperature gradient, laminate thickness-ratio and radius ratio for two boundary conditions are investigated and pertinent conclusions are derived.

Shape Optimal Design of Elastic Concrete Dam (탄성콘크리트 댐의 모양최적설계)

  • Yoo, Yung Myun
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.5 no.4
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    • pp.9-14
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    • 1985
  • In this research mass of a plane strain two dimensional elastic concrete dam under gravitational and hydrostatic loads is minimized, through shape optimization of the dam cross section. Cross sectional area of the dam is taken as cost function of the optimization problem while constraints on the principal stress distribution and dam thickness are imposed. Shape of the boundary of the model is chosen as design variable. Variational formulation of the optimization problem, the material derivative idea of continuum mechanics, and an adjoint variable method are employed for the shape design sensitivity calculation. Then the gradient projection algorithm is utilized to obtain an optimum design iteratively. Research results fully demonstrate that the theory and procedure adopted are quite efficient and can be applicable to a wide class of practical elastic structural design problems.

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Shear Lag in Framed Tube Structures with Multiple Internal Tubes (복수의 내부 튜브를 가진 골조 튜브 구조물의 Shear Lag)

  • 이강건;이리형
    • Journal of the Computational Structural Engineering Institute of Korea
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    • v.13 no.3
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    • pp.351-360
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    • 2000
  • A simple numerical modelling technique is proposed for estimating the shear lag effects of framed-tube system with multiple internal tubes. The tube(s)-in-tube structure is analysed by using an analogy approach in which each tube is individually modelled by a beam that can accounts for the flexural and shear deformations, as well as the shear lag effects. The numerical analysis is based on the minimum potential energy principle in conjunction with the variational approach. The shear lag phenomenon of such structures is studied with additional bending stresses. Structural parameters governing the shear lag behaviour in tube(s)-in-tube structures are also investigated through thirty-three numerical examples.

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