• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.12
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• pp.2503-2510
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• 2002

Since the first shape-form-shading technique was developed by Horn in the early 1970s, many different approaches have been continuously emerging in the past three decades. Some of them improve existing techniques, while others are completely new approaches. Using the image reflectance equation, they estimate the 3-D shape of an object utilizing adequate constraints. Each algorithm applies different constraints such as brightness, smoothness, and integrability to solve the shape-from-shading problem. Especially for symmetric objects, a symmetry constraint is proposed to improve the performance of existing shape-from-shading algorithm in this paper. The symmetry constraint is imposed to a conventional algorithm and then the improvement in the performance of 3-D shape reconstruction is proved by quantitatively comparing the depth and gradient errors.

• Journal of KSNVE
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• v.7 no.4
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• pp.637-644
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• 1997

In this paper, a method of finite element analysis is presented for efficient calculation of vibration characteristics of not only simply interconnected structure with cyclic symmetry but also multiply interconnected structure with cyclic symmetry by using discrete Fourier trandform by means of a computer with small memory in a short time. Simply interconnected structure means it is composed of substructures which are adjacent themselves in circumferential direction. First, a mathematical model of multiply interconnected structure with cyclic symmetry is defined. The multiply interconnected structure is partitioned into substructures with the same goemetric configuration and constraint eqauations to be satisfied on connecting boundaries are defined. Nodal displacements and forces are transformed into complex forms through discrete Fourier transform and then finite element analysis is performed for just only a representative substructure. In free vibration analysis, natural frequencies of a whole structure can be obtained through a series of calculation for a substructure along the number of nodal diameter. And in forced vibration analysis, forced response of whole structure can be achieved by using inverse discrete Fourier transform of results which come from analysis for a substructure.

• Publications of The Korean Astronomical Society
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• v.30 no.2
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• pp.345-347
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• 2015

We present evolutionary models of rotating self-gravitating systems (e.g. globular clusters, galaxy cores). These models are characterized by the presence of an initial axi-symmetry due to rotation. Central black hole seeds are included in our models, and black hole growth due to the consumption of stellar matter is simulated until the central potential dominates the kinematics of the core. Our goal is to study the long-term evolution (Gyr) of relaxed dense stellar systems which deviate from spherical symmetry, and their morphology and final kinematics. With this purpose in mind, we developed a 2D Fokker-Planck analytical code, and confirmed its results using detailed N-Body simulations, applying a high performance code developed for GPU machines. We conclude that the initial rotation significantly modifies the shape and lifetime of these systems, and cannot be neglected in the study of the evolution of globular clusters, and the galaxy itself. Our models give a constraint for the final intermediate black hole masses expected to be present in globular clusters.

• Smart Structures and Systems
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• v.18 no.4
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• pp.733-754
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• 2016

Structural optimization involves a large number of structural analyses. When optimizing large structures, these analyses require a considerable amount of computational time and effort. However, there are specific types of structure for which the results of the analysis can be achieved in a much simpler and quicker way thanks to their special repetitive patterns. In this paper, frequency constraint optimization of cyclically repeated space trusses is considered. An efficient technique is used to decompose the large initial eigenproblem into several smaller ones and thus to decrease the required computational time significantly. Some examples are presented in order to illustrate the efficiency of the presented method.

• JSTS:Journal of Semiconductor Technology and Science
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• v.14 no.5
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• pp.632-639
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• 2014

Mechanical stress and the vacuum level are the two main factors dominating the quality factor of a resonator operated in the vacuum range 1 mTorr to 10 Torr. This means that if the quality factor of a resonator is very insensitive to the mechanical stress in the vacuum range, it is sensitive to mainly the ambient vacuum level. In this paper, a wafer-level packaged MEMS resonator with a highly vacuum-sensitive quality factor is presented. The proposed device is characterized by a package with out-of-plane symmetry and a suspending structure with only a single anchor. Out-of-plane symmetry helps prevent deformation of the packaged device due to thermal mismatch, and a single-clamped structure facilitates constraint-free displacement. As a result, the proposed device is very insensitive to mechanical stress and is sensitive to mainly the ambient vacuum level. The average quality factors of the devices packaged under pressures of 50, 100, and 200 mTorr were 4987, 3415, and 2127, respectively. The results demonstrated the high controllability of the quality factor by vacuum adjustment. The mechanical robustness of the quality factor was confirmed by comparing the quality factors before and after high-temperature storage. Furthermore, through more than 50 days of monitoring, the stability of the quality factor was also certified.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.14 no.3
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• pp.1167-1187
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• 2020

With the development of medical imaging technology, image registration has been widely used in the field of disease diagnosis. The registration between different modal images of brain magnetic resonance (MR) is particularly important for the diagnosis of brain diseases. However, previous registration methods don't take advantage of the prior knowledge of bilateral brain symmetry. Moreover, the difference in gray scale information of different modal images increases the difficulty of registration. In this paper, a multimodal medical image registration method based on image segmentation and symmetric self-similarity is proposed. This method uses modal independent self-similar information and modal consistency information to register images. More particularly, we propose two novel symmetric self-similarity constraint operators to constrain the segmented medical images and convert each modal medical image into a unified modal for multimodal image registration. The experimental results show that the proposed method can effectively reduce the error rate of brain MR multimodal medical image registration with rotation and translation transformations (average 0.43mm and 0.60mm) respectively, whose accuracy is better compared to state-of-the-art image registration methods.

• Geophysics and Geophysical Exploration
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• v.7 no.1
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• pp.51-55
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• 2004

This paper presents a fast and stable imaging scheme using the localized nonlinear (LN) approximation of integral equation (IE) solutions for inverting electromagnetic data obtained in a crosswell survey. The medium is assumed to be cylindrically symmetric about a source borehole, and to maintain the symmetry a vertical magnetic dipole is used as a source. To find an optimum balance between data fitting and smoothness constraint, we introduce an automatic selection scheme for a Lagrange multiplier, which is sought at each iteration with a least misfit criterion. In this selection scheme, the IE algorithm is quite attractive for saving computing time because Green's functions, whose calculation is a most time-consuming part in IE methods, are repeatedly re-usable throughout the inversion process. The inversion scheme using the LN approximation has been tested to show its stability and efficiency, using both synthetic and field data. The inverted image derived from the field data, collected in a pilot experiment of water-flood monitoring in an oil field, is successfully compared with that derived by a 2.5-dimensional inversion scheme.

• Journal of the Korean Society for Precision Engineering
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• v.13 no.9
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• pp.84-93
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• 1996

This paper describes the development of new feature positioning method which embedded into the top-down assembly modeling system supporting conceptual design. In this work, the user provides the geometric constraints representing the position and size of features, then the system calculates their proper solution. The use of geometric constraints which are easy to understand intuitively enables the user to represent his design intents about geometric shapes, and enables the system to propagate the changes automatically when some editing occurs. To find the proper solution of given constraints, the Selective Solving Method in which the redundant or conflict equations are detected and discarded is devised. The validity of feature shapes satisfying the constraints can be maintained by this technique, and under or over constrained user-defined constraints can also be estimated. The problems such as getting the initial guess, controlling the multiple solutions, and dealing with objects of rotational symmetry are also resolved. Through this work, the feature based modeling system can support more general and convenient modeling method, and keeps the model being valid during modifying models.

• Journal of the Korean Institute of Intelligent Systems
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• v.20 no.6
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• pp.748-754
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• 2010

To reduce the computational cost required for assembling vessel fragments using surface geometry, this paper proposes a fast axis estimation method. Using circular constraint of pottery and local planar patch assumption, it finds the axis of the symmetry. First, the circular constraint on each cylinder is used. A circular symmetric pot can be thought of unions of many cylinders with different radii. It selects one arbitrary point on the pot fragment surface and searches a path where a circumference exists on that point. The variance of curvature will be calculated along the path and the path with the minimum variance will be selected. The symmetric axis will pass through the center of that circle. Second, the planar patch assumption and profile curve is used. The surface of fragment is divided into small patches and each patch is assumed as plane. The surface normal of each patch will intersects the axis in 3D space since each planar patch faces the center of the pot. A histogram method and minimization of the profile curve error are utilized to find the probability distribution of the axis location. Experimental results demonstrate the improvement in speed and robustness of the algorithms.

• Structural Engineering and Mechanics
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• v.72 no.2
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• pp.181-190
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• 2019

Topology optimization of structures seeking the best distribution of mass in a design space to improve the structural performance and reduce the weight of a structure is one of the most comprehensive issues in the field of structural optimization. In addition to structures stiffness as the most common objective function, frequency optimization is of great importance in variety of applications too. In this paper, an efficient multi-objective Bi-directional Evolutionary Structural Optimization (BESO) method is developed for topology optimization of frequency and stiffness in continuum structures simultaneously. A software package including a Matlab code and Abaqus FE solver has been created for the numerical implementation of multi-objective BESO utilizing the weighted function method. At the same time, by considering the weaknesses of the optimized structure in single-objective optimizations for stiffness or frequency problems, slight modifications have been done on the numerical algorithm of developed multi-objective BESO in order to overcome challenges due to artificial localized modes, checker boarding and geometrical symmetry constraint during the progressive iterations of optimization. Numerical results show that the proposed Multiobjective BESO method is efficient and optimal solutions can be obtained for continuum structures based on an existent finite element model of the structures.