• Journal of Korean Association for Spatial Structures
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• v.10 no.1
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• pp.127-134
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• 2010

The dynamic instability for snapping phenomena has been studied by many researchers. Few paper deal with the dynamic bucking under the load with periodic characteristics, and the behavior under periodic excitation is expected the different behavior against STEP excitation. We investigate the fundamental mechanisms of dynamic instability when shallow EP(Elliptic Paraboliodal) shell of two degree of freedom are subjected to sinusoidal excitation with direct snapping and indirect snapping. By using Newmark-$\beta$ method, we can get the nonlinear response, and characteristics of the dynamic instability through the running response spectrum by FFT(fast Fourier Transform) and attractors are compared in the phase plane. Dynamic buckling loads are strongly influenced by the relationships between the natural frequency of structures and the dominant frequency of incident excitations.

• Bulletin of the Korean Space Science Society
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• 2009.10a
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• pp.26.3-27
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• 2009

한 기의 영상레이더 위성을 이용하여 동일한 촬영지역에 대해 적절한 기선벡터(Baseline)을 유지하는 두 장(scene)의 영상을 획득하여 그 지역의 정밀 표고차를 추출하는 레이더 간섭계(Interferometry) 임무를 수행하기 위해서는 반복지상궤적을 유지하도록 위성의 궤도를 주기적으로 조정해 주어야 한다. 이 연구에서는 반복지상궤적 유지 정밀도를 극대화시키기 위하여 최적의 기준궤도를 생성하고 이를 유지하기 위한 속도증분 및 궤도 조정 일정을 산출할 수 있는 궤도최적화 S/W 를 개발하였다. 이 연구의 최적 궤도 설계 문제는 다음과 같다. "시작시간 $T_0$에서 초기 접촉궤도 상태벡터 (ECEF 위치 및 속도벡터) $x_0$이고, 지상궤적반복주기 p 이후의 시간 $T_0+p$에서도 초기 접촉궤도 상태벡터와 동일한$x_0$가 되도록 궤도를 유지하려고 할 때, 여명 궤도(dawn-dusk and sun-synchronous orbit)에서 운영되는 위성의 연료소모(또는 속도증분)를 최소화시키는 가상의 궤도조정(maneuver) 횟수, 시기, 크기를 찾아라." 이 연구에서는 궤도최적화 문제를 풀기 위하여 GRACE 중력모델(GGM02C)이 적용된 수치적 방법의 위성궤도예측 알고리즘을 시스템 설계에 적용하였고, 매개변수 최적화 방법 중 구속조건이 있는 비선형 최적화 기법의 하나인 연속 2차 계획법(sequential quadratic programming)을 사용하여 해를 구하였다. 개발된 궤도최적화 S/W의 성능을 분석하기 위하여 고도 550km의 여명궤도를 돌며 지상궤적반복주기가 28일인 영상레이더 위성에 대해 적용하였다. 해석 결과를 통해, 비록 시스템의 비선형이 큼에도 불구하고 최소의 속도증분으로 정밀한 반복지상궤적이 유지됨을 알 수 있었다.

• Journal of the Korean Society for Railway
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• v.13 no.6
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• pp.546-551
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• 2010

In this paper, the strain distribution of the bond layer has been compared with the experimental data and analyzed according to the different mesh refinements and element types. The mesh density was changed along the longitudinal direction of adherend, the longitudinal direction of overlapped region, the vertical direction of adherend, the vertical direction of adhesive and the width direction of the joint. In addition, the effect of the different types of element was evaluated using soild, shell and plane strain element. The geometric nonlinear analysis was performed to consider the large deformation of the joint. From the numerical result, at least 2 elements were needed to achieve a reliable result as the solid element used. In case of shell element, the peel strain at x/c=1 showed 22.8% error compared with the experiment but the shear strain showed a good agreement with the experiment within 1.67% error.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37 no.5A
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• pp.290-297
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• 2012

In this paper, we proposed new modulation schemes, Offset Phase Rotation Shift Keying (OPRSK) and Phase Shift Rotation Shift Keying (PSRSK), for medical in-body wireless body area network (WBAN) systems. In IEEE, the WBAN system is assigned as 802.15. Task Group (TG) 6, and the related standardization is being progressed. Recently, in this Group, Phase Silence Shift Keying (PSSK), Phase Silence Position Keying (PSPK) and Phase Rotation Shift Keying (PRSK), which can obtain higher power efficiency, are proposed as new modulation schemes for low-power operation of WBAN system. However, they have a disadvantage for non-linear amplifier distortion. Therefore, in this paper, we proposed OPRSK and PSRSK, which are robust to non-linear amplification, by employing a phase offset in constellation and a power distribution in symbol duration, and verified that the proposed methods have good perfomance and stable operation through performance evaluation.

• Journal of the Korea institute for structural maintenance and inspection
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• v.17 no.5
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• pp.136-145
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• 2013

Social interest in the seismic retrofit of the structure is growing massive earthquake that occurred recently. The brittle fracture of Non-seismically designed Columns lead to full collapse of the building. In the past, cross-sectional expansion method, a steel plate reinforcing method is applied mainly in recent years, fiber-reinforced method utilizing the advantages of the composite material are preferred. However, the reinforcement methods such as this, there is a drawback to induce physical damage to structures, and time consuming work space is large. IIn this study, FRP seismic reinforcement was developed using the Aluminum connector and the composite material (Glass Fiber Reinforced Polymer). Then, the optimum quantities of FRP seismic reinforcement was determined using a nonlinear finite element analysis program. Finally, the quantity decision process through the design and analysis of FRP reinforcement was suggested.

• Journal of the Korea institute for structural maintenance and inspection
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• v.22 no.6
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• pp.63-71
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• 2018

Strands with ultimate strength of 2,400 MPa was developed and applied in the KCI Code and the KS standard. A high-strength prestressed strand to be applied to a structure, a suitable anchorage system should be used together. Recently, a post tension anchorage for 2,400 MPa strands was developed. but there is not much research on performance evaluation. Therefore, in this study, structural analysis of local zone with 9 strands, 15 strands, and 19 strands anchorage were investigated respectively, which are most widely used for post tensioning anchorages with 2,400 MPa strands, according to PTI anchorage zone design method, and Load transfer performance from ETAG013 and/or KCI-PS101 was evaluated. Furthermore, the adequacy of the test was also analyzed by nonlinear numerical analysis. As results, the anchorages with 2,400 MPa strands satisfied the structural performance of the local area and satisfied the load transfer performance condition.

• Proceedings of the Korea Contents Association Conference
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• 2008.05a
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• pp.147-151
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• 2008

Since the first HDV(High Definition Video) camcoder, HDR-FX1 with 1080i resolution, had been launched at 2004, the image capture and record with HD resolution have been possible by the various types of camcoder and recorder which can support the HDV format. At a present day, a non-linear editing system, which is composed of only one computer, can capture, edit and export the image with HDV format. The HDV format has the same class of resolution with HD and the same data transfer bit rate of DV(Digital Video). Additionally, the image with HDV format can be recorded in 6mm DV cassette tape. It is possible because the HDV format uses the concept of Long GOP(Gorup of pictures) method for its compression. In this paper, the characteristic feature of HDV format, the essential factors in editing with HDV format and the concept of Long GOP method for its compression have been studied for the way of effective HDV editing.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.49 no.8
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• pp.627-636
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• 2021

This paper deals with a study for the guidance control of reusable launch vehicle. For this purpose, modeling of the equation of motion of a reusable launch vehicle with 6 degrees of freedom was performed. With this model, an optimal re-entry path was created and a path-following guidance control simulation was performed to follow the optimal re-entry path. For the design of the path-following guidance controller, the attitude controller applying a time-delay technique that is resistant to modeling uncertainty, disturbance and failure. And the nonlinear path-following guidance law were used. Guidance control simulation using a classical PD controller was performed and compared with the guidance control simulation of a reusable launch vehicle applying a time delay technique.

• Journal of Aerospace System Engineering
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• v.18 no.4
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• pp.18-26
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• 2024

This paper describes the results of a study on Generic Quad Tilt Rotor UAM aircraft, focusing on nonlinear mathematical modeling and the development of real-time simulation software. In this research, we designed a configuration for a Generic Quad Tilt Rotor eVTOL UAM aircraft based on NASA's UAM mission requirements. We modeled the aerodynamics using a database, the prop-rotor dynamics with a thrust database, and included a ground reaction and atmospheric model in the flight model. We defined the control concept for various modes(helicopter mode, transition mode, and airplane mode), derived tilt angle corridors, and formulated flight control requirements. The resultant real-time flight simulation software not only performs trim analysis for Tilt Rotor UAM aircraft but also predicts handling qualities, optimizes tilt angle scheduling based on dynamic characteristics, designs and validates flight control laws for helicopter, transition, and airplane modes, and facilitates flight training through simulator integration.

• Proceedings of the KIEE Conference
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• 2008.10b
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• pp.489-490
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• 2008

본 고에서는 체내 심실신호를 농하여 신경학적 분석 및 다형성의 측면에서 심실세동이 일어나는 것을 예측하는 분석 알고리즘을 설계하였다. 신경학적 측면에서는 시계열 신호의 Peak to Peak Interval을 예측법과 0.15Hz를 기준으로 HRV 신호의 AR Burg 모델링을 통하여 고주파성과 저주파성을 나누어 교감신경과 부교감신경의 활동성 통한 신경학적 예측법을 제시하였으며 또한 체내 심실신호의 비선형적 특성을 고려한 Fractal Dimension을 생성시킴으로서 주기성의 특성과 다형성 통한 예측법을 제시하였다. 체내 심전도를 기반으로 Simulation 하였으며 각 분석별 조합을 통하여 최적의 예측 구조를 찾고자 하였다. 의학적 의미가 있는 민감도와 특이도를 판별하였으며 예측을 위한 수행시간을 실험하였다. 이를 통하여 자율신경 활성도와 다형성 판별을 조합한 방법이 심실세동 예측을 위한 민감도의 측면에서 가장 우수함을 나타내었고 시뮬레이션을 위만 시뮬레이터(Simulator) UI(User Interface)를 제시하였다.