• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.34 no.1
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• pp.79-90
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• 2016

The study has purposed in evaluating experiences for achievable accuracy and precision of time series at 3-D coordinates. It has been estimated from the kinematic medium-range baseline processing of Continuously Operating Reference Stations (CORS) for the potential application of crustal displacement analysis during an earthquake event. To derive the absolute coordinates of local CORS, it is highly recommended to include some of oversea country references, since it should be compromised of an observation network of the medium-range baselines within the length range from tens of kilometers to about 1,000 kilometers. A data processing procedure has reflected the dynamics of target stations as the parameter estimation stages, which have been applied to a series of experimental analysis in this research at the end. From the analysis of results, we could be concluded in that the subcentimeters-level of positioning accuracy and precision can be achievable. Furthermore, the paper summarizes impacts of satellite ephemeris, data lengths and levels of initial coordinate constraint into the positioning performance.

• Journal of Dental Rehabilitation and Applied Science
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• v.17 no.2
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• pp.75-84
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• 2001

The purpose of this study is to to analyze the mechanical stress on articular disk of the dentated skull with the condition of unilateral posterior molar missing. For this study, the three dimensional finite element model of human skull scanned by means of computed tomography. (G.E. 8800 Quick, USA) was constructed. The finite element model of jaws is composed of 98,394 elements and 38,321 nodes, and it consists of articular disc, maxilla, mandible, teeth, periodontal ligament and cranium. Boundary condition included rigid restraints at the first molar and endosteal cortical surfaces of the insertion points of temporal bone. The data derived from Nelson's study were used for the loading conditions of mandible during clenchings and for maxilla, new loading and constraint conditions were applied. A clenching task during intercuspal position was modeled to the three dimensional finite element model. The stress level and displacement of articualr disc on the model with unilateral posterior molar missing under bilateral clenching task can be analyzed. During bilateral clenchings, the compressive stress level and diplacement of the articular disk on the side of unilateral posterior molar missing is greater than that on the case with full dentition, whereas a higher stress was found on the disk on the balancing side of the full dentition. Although this kind of study is not enough to explain the role of occlusion as an etiologic factor of TMD, there may be a possibiliy that the condition of posterior molar missings may contribute in part to the TMJ biomechanics.

• Journal of Korean Association for Spatial Structures
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• v.9 no.3
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• pp.75-82
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• 2009

This paper investigates the variation of post-buckling behaviours of spatial structures after sizing optimization with linear assumptions. The mathematical programming technique is used to produce the optimum member size of spatial structures against external load. Total weight of structure is considered as the objective function to be minimized and the displacement occurred at loading point and member stresses of structures are used as the constraint functions. The finite difference method is used to calculate the design sensitivity of objective function with respect to design variables. The post-buckling analysis carried out by using the geometrically nonlinear finite element analysis code ISADO-GN. It is found to be that there is a huge difference between the post buckling behaviours of the initial and optimized structures. Therefore, the stability of optimized spatial structures with linear assumption should be throughly checked by appropriate nonlinear analysis techniques. Finally, the present numerical results are provided as benchmark test suite for future study of large spatial structures.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.19 no.1 s.71
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• pp.63-71
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• 2006

This study presents the effective stiffness-based optimal technique to control Quantitatively lateral drift for shear wall-frame structure system using sensitivity analysis. To this end, the element stiffness matrices are constituted to solve the compatibility problem of displacement degree of freedom between the frame and shear wall. Also, lateral drift constraint to introduce the approximation concept that can preserve the generality of the mathematical programming and can effectively solve the large scaled problems is established. And, the section property relationships for shear wall and frame members are considered in order to reduce the number of design variables and differentiate easily the stiffness matrices. Specifically, constant-shape assumption which is uniformly varying in size during optimal process is applied in frame structure. The thickness or length of shear wall can be changed depending on user's intent. Two types of 20 story shear wall-frame structure system are presented to illustrate the features of the stiffness-based optimal design technique.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.20 no.12
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• pp.3792-3803
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• 1996

Since the skew beam element has two curvatures which are a curvature and a torsion, spatial behavior of curved beam which cannot be included in one plane can be anlayzed by emploting the skew beam element. The $C^{0}$-continuous skew beam element shows the stiffness locking phenomenon when full integration is employed. The locking phenomenpn is characterized by two typical phenomena ; one is the much smaller displacement thant the exact one and theother is the undelation phenomenon is stress distribution. In this paper, we examine how unmatched coefficient in the constrained energy brings about the locking by Reduced Minimization theory. We perform the numerical ones. These comparisons show that uniformly full integration(UFI), which employs full integration for the constrained energy, entails the locking phenomenon. But the use of uniformly reduced integration(URI) of selectively reduced integration(SRI), which employs reduced integration for constrained energy, does not produce the significant errors of displacements of the undulation phenomenon in stress distribution since they do not entails the locking, Additionally, the error due to the approximated parameters for describing the geometry of skew beam is examined.d.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.26 no.5
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• pp.351-358
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• 2013

In the electric power supplying industry, outdoor sealing end (pothead) is used and sometimes it is necessary to check the seismic qualification analysis or test which is intended to demonstrate that the equipment have adequate integrity to withstand stress of the specified seismic event and still performs their function. And since the pothead is mounted on the supporting jig, the avoidance of resonance between the pothead and jig is required. In order to design jig, three types of optimization are performed to get the minimum weight while satisfying the natural frequency constraint using ANSYS. Optimal array, position and thickness of truss members of the jig are obtained through topology, shape and sizing optimization process, respectively. And seismic analysis of the pothead on the jig for given RRS acceleration computes the displacement and stress of the pothead which shows the safety of the pothead. The obtained natural frequency, mass, and member thickness of the jig are compared with those of the reference jig which was used for seismic experimental test. The numerical results of the jig in the research is more optimized than the jig used in the experimental test.

• Journal of Korean Association for Spatial Structures
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• v.4 no.4 s.14
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• pp.113-128
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• 2004

A three-dimensional (3-D) method of analysis is presented for determining the free vibration frequencies and mode shapes of solid paraboloidal and complete (that is, without a top opening) paraboloidal shells of revolution with variable wall thickness. Unlike conventional shell theories, which are mathematically two-dimensional (2-D), the present method is based upon the 3-D dynamic equations of elasticity. The ends of the shell may be free or may be subjected to any degree of constraint. Displacement components $u_r,\;u_{\theta},\;and\;u_z$ in the radial, circumferential, and axial directions, respectively, are taken to be sinusoidal in time, periodic in ${\theta}$, and algebraic polynomials in the r and z directions. Potential (strain) and kinetic energies of the paraboloidal shells of revolution are formulated, and the Ritz method is used to solve the eigenvalue problem, thus yielding upper bound values of the frequencies by minimizing the frequencies. As the degree of the polynomials is increased, frequencies converge to the exact values. Convergence to four digit exactitude is demonstrated for the first five frequencies of the complete, shallow and deep paraboloidal shells of revolution with variable thickness. Numerical results are presented for a variety of paraboloidal shells having uniform or variable thickness, and being either shallow or deep. Frequencies for five solid paraboloids of different depth are also given. Comparisons are made between the frequencies from the present 3-D Ritz method and a 2-D thin shell theory.

• Journal of Korean Association for Spatial Structures
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• v.8 no.4
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• pp.47-55
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• 2008

This paper deals with basic theories and some numerical results on structural optimization for geodesic dome. First of all, the space efficiency of geodesic dome is investigated by using the ratio of icosahedron's surface area to the internal volume enclosed by it. The procedure how to create the geodesic dome is also provided in systematic way and implemented and utilized into the design optimization code ISADO-OPT. The mathematical programming technique is introduced to find out the optimum pattern of member size of geodesic dome against a point load. In this study, total weight of structure is considered as the objective function to be minimized and the displacement occurred at loading point and member stresses of geodesic dome are used as the constraint functions. The finite difference method is used to calculate the design sensitivity of objective function with respect to design variables. The SLP, SQP and MFDM available in the optimizer DoT is used to search optimum member size patterns of geodesic dome. It is found to be that the optimum member size pattern can be efficiently obtained by using the proposed design optimization technique and numerical results can be used as benchmark test as a basic reference solution for design optimization of dome structures.

• Journal of the Institute of Electronics and Information Engineers
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• v.51 no.10
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• pp.96-106
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• 2014

Previous academic research on FPGA tools has relied on simple imaginary models for the targeting architecture. As the first step to overcome such restriction, the issues on analytic placement and legalization which are applied to commercial FPGAs have been brought up, and several techniques to remedy them are presented, and evaluated. First of all, the center of gravity of the placed cells may be far displaced from the center of the chip during analytic placement. A function is proposed to be added to the objective function for minimizing this displacement. And then, the density map is expanded into multiple layers to accurately calculate the density distribution for each of the cell types. Early fixation is also proposed for the memory blocks which can be placed at limited sites in small numbers. Since two flip-flops share control pins in a slice, a compatibility constraint is introduced during legalization. Pre-packing compatible flip-flops is proposed as a proactive step. The proposed techniques are implemented on the K-FPGA fabric evaluation framework in which commercial architectures can be precisely modeled, and modified for enhancement, and validated on twelve industrial strength examples. The placement results show that the proposed techniques have reduced the wire length by 22%, and the slice usage by 5% on average. This research is expected to be a development basis of the optimization CAD tools for new as well as the state-of-the-art FPGA architectures.

• International Journal of Aeronautical and Space Sciences
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• v.8 no.1
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• pp.10-20
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• 2007

For spacecraft attitude control, reaction wheel (RW) steering laws with more than three wheels for three-axis attitude control can be derived by using a control allocation (CA) approach.1-2 The CA technique deals with a problem of distributing a given control demand to available sets of actuators.3-4 There are many references for CA with applications to aerospace systems. For spacecraft, the control torque command for three body-fixed reference frames can be constructed by a combination of multiple wheels, usually four-wheel pyramid sets. Multi-wheel configurations can be exploited to satisfy a body-axis control torque requirement while satisfying objectives such as minimum control energy.1-2 In general, the reaction wheel steering laws determine required torque command for each wheel in the form of matrix pseudo-inverse. In general, the attitude control command is generated in the form of a feedback control. The spacecraft body angular rate measured by gyros is used to estimate angular displacement also.⁵ Combination of the body angular rate and attitude parameters such as quaternion and MRPs(Modified Rodrigues Parameters) is typically used in synthesizing the control command which should be produced by RWs.¹ The attitude sensor signals are usually corrupted by noise; gyros tend to contain errors such as drift and random noise. The attitude determination system can estimate such errors, and provide best true signals for feedback control.⁶ Even if the attitude determination system, for instance, sophisticated algorithm such as the EKF(Extended Kalman Filter) algorithm⁶, can eliminate the errors efficiently, it is quite probable that the control command still contains noise sources. The noise and/or other high frequency components in the control command would cause the wheel speed to change in an undesirable manner. The closed-loop system, governed by the feedback control law, is also directly affected by the noise due to imperfect sensor characteristics. The noise components in the sensor signal should be mitigated so that the control command is isolated from the noise effect. This can be done by adding a filter to the sensor output or preventing rapid change in the control command. Dynamic control allocation(DCA), recently studied by Härkegård, is to distribute the control command in the sense of dynamics⁴: the allocation is made over a certain time interval, not a fixed time instant. The dynamic behavior of the control command is taken into account in the course of distributing the control command. Not only the control command requirement, but also variation of the control command over a sampling interval is included in the performance criterion to be optimized. The result is a control command in the form of a finite difference equation over the given time interval.⁴ It results in a filter dynamics by taking the previous control command into account for the synthesis of current control command. Stability of the proposed dynamic control allocation (CA) approach was proved to ensure the control command is bounded at the steady-state. In this study, we extended the results presented in Ref. 4 by adding a two-step dynamic CA term in deriving the control allocation law. Also, the strict equality constraint, between the virtual and actual control inputs, is relaxed in order to construct control command with a smooth profile. The proposed DCA technique is applied to a spacecraft attitude control problem. The sensor noise and/or irregular signals, which are existent in most of spacecraft attitude sensors, can be handled effectively by the proposed approach.