• Journal of Mechanical Science and Technology
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• v.17 no.5
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• pp.654-667
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• 2003

This paper presents a consequence of the systematic approach to identify the aerodynamic parameters of an unmanned aerial vehicle (UAV) equipped with the automatic flight control system. A 3-2-1-1 excitation is applied for the longitudinal mode while a multi-step input is applied for lateral/directional excitation. Optimal time step for excitation is sought to provide the broad input bandwidth. A fully automated programmed flight test method provides high-quality flight data for system identification using the flight control computer with longitudinal and lateral/directional autopilots, which enable the separation of each motion during the flight test. The accuracy of the longitudinal system identification is improved by an additional use of the closed-loop flight test data. A constrained optimization scheme is applied to estimate the aerodynamic coefficients that best describe the time response of the vehicle. An appropriate weighting function is introduced to balance the flight modes. As a result, concurrent system models are obtained for a wide envelope of both longitudinal and lateral/directional flight maneuvers while maintaining the physical meanings of each parameter.

• Journal of the Korean Institute of Intelligent Systems
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• v.15 no.7
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• pp.852-857
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• 2005

This paper discusses a human body extraction method for intelligent robot system. The intelligent robot system requires more robust silhouette extraction method because it has internal vibration and low resolution. The new hybrid silhouette extraction method is proposed to overcome this constrained environment. The temporal and gradient information is combined as hybrid silhouette. The motion region model is used to adjust combining parameters in hybrid silhouette. Finally, the experimental results show the superiority of the proposed method.

• Korean Journal of Applied Biomechanics
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• v.15 no.3
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• pp.61-70
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• 2005

The purpose of study was to investigate the kinematic variables of Kenmotsu motion in Parallel bars. To this study, by 3 dimensional kinematical analysis of 4 male national gymnasts participants in the 28th Athens Olympic Game in 2004, kinematic data collected using video camera. Coordinate data were smoothed by using a fourth-order Butterworth low pass digital filter with cutoff frequency of 6Hz. The conclusions were as follows. 1. In P2, because the constrained swing movement made the movement of a rising back difficult7, the movements of Reg. were performed at low position after Air phase. 2. In E5 event, for the shake of a stable handstand and applied techniques like a Belle(E-value), a Belle Piked(super E-value), a vertical velocity in E2, a horizontal velocity in E3 and a vertical velocity in E4 were necessary for high velocities. 3. In E4 event, it was appeared that for a flexible body's movement of a vertical up-flight, the large angle of the shoulder joint and the flexion & extension of the hip joint were necessary in Air phase and a long flight time and vertical displacement made Reg. movements stable at the high position.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2005.11a
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• pp.731-734
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• 2005

Generally, characteristics of electromechanical actuators are coupled with the mechanical and the electrical properties. Important mechanical parameters of these actuators are the achievable force and displacement in the presence of electric field. These mechanical parameters are related to the stress and strain of the materials and the actuator geometry. This paper presents how to measure the blocked force by using the micro-balance. The blocked force is defined as the force produced by the transducer under an applied voltage when the tip is constrained to zero motion. Also, a theoretical force by using the cantilever beam model is calculated under elastic domain. From the sample of 4 cm $\times$ 1 cm $\times$ 20 $\mu$m, the blocked farce measured from the equipment is 20.3 $\mu$N at 8 V$_{DC}$. By comparing it with the theoretical value, 24.9 $\mu$N, the blocked force measurement is acceptable. The furce measurement is also investigated with different AC electric fields and the frequency.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.39 no.5
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• pp.313-319
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• 2021

The national geodetic reference frame of Korea was adopted in 2003, which is referenced to ITRF (International Terrestrial Reference Frame) 2000 at the epoch of January 1, 2002. For precise positioning based on the satellites, it should be thoroughly maintained to the newest global reference frame. Other than plate tectonic motion, there are significant events or changes such as earthquakes, antenna replacement, PSD (Post-Seismic Deformation), seasonal variation etc. We processed three years of GNSS (Global Navigation Satellite System) data(60 NGII CORS stations, 51 IGS core stations) to produce daily solutions minimally constrained to ITRF. From the time series of daily solutions, the sites with unexpected discontinuity were identified to set up an event(mostly antenna replacement). The combined solution with minimum constraints was estimated along with the velocity, the offsets, and the periodic signals. The residuals show that the surrounding environment also affects the time series to a certain degree, thus it should be improved eventually. The transformation parameters to ITRF2014 were calculated with stability and consistency, which means the national geodetic reference frame is properly aligned to the global reference frame.

• Journal of Ocean Engineering and Technology
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• v.36 no.1
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• pp.41-49
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• 2022

With the advancement of intelligent vehicles and unmanned systems, there is a growing interest in underwater surveys using autonomous marine vehicles (AMVs). This study presents an automated planning strategy for a long-term survey mission using a fleet of AMVs consisting of autonomous surface vehicles and autonomous underwater vehicles. Due to the complex nature of the mission, the actions of the vehicle must be of high-level abstraction, which means that the actions indicate not only motion of the vehicle but also symbols and semantics, such as those corresponding to deploy, charge, and survey. For automated planning, the planning domain definition language (PDDL) was employed to construct a mission planner for realizing a powerful and flexible planning system. Despite being able to handle abstract actions, such high-level planners have difficulty in efficiently optimizing numerical objectives such as obtaining the shortest route given multiple destinations. To alleviate this issue, a widely known technique in operations research was additionally employed, which limited the solution space so that the high-level planner could devise efficient plans. For a comprehensive evaluation of the proposed method, various PDDL-based planners with different parameter settings were implemented, and their performances were compared through simulation. The simulation result shows that the proposed method outperformed the baseline solutions by yielding plans that completed the missions more quickly, thereby demonstrating the efficacy of the proposed methodology.

• Steel and Composite Structures
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• v.48 no.4
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• pp.475-483
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• 2023

In this paper, a new energy-efficient semi-active hybrid bulk damper is developed that is cost-effective for use in structural applications. In this work, the possibility of active and semi-active component configurations combined with suitable control algorithms, especially vibration control methods, is explored. The equations of motion for a container bridge equipped with an MDOF Mass Tuned Damper (M-TMD) system are established, and the combination of excitation, adhesion, and control effects are performed by a proprietary package and commercial custom submodel software. Systematic methods for the synthesis of structural components and active systems have been used in many applications because of the main interest in designing efficient devices and high-performance structural systems. A rational strategy can be established by properly controlling the master injection frequency parameter. Simulation results show that the multiscale model approach is achieved and meets accuracy with high computational efficiency. The M-TMD system can significantly improve the overall response of constrained structures by modestly reducing the critical stress amplitude of the frame. This design can be believed to build affordable, safe, environmentally friendly, resilient, sustainable infrastructure and transportation.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2020.07a
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• pp.6-9
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• 2020

최근 몰입형 가상 현실을 제공하기 위한 360 도 영상 전송 기술이 활발히 연구되고 있다. 그러나 현재 가상현실 기기가 가지는 연산 능력 및 대역폭으로는 고화질의 360 도 영상을 전송 및 재생하기에 한계가 있다. 해당 문제점을 극복하기 위해 본 논문에서는 사용자 시점의 고화질 360 도 영상 제공을 위해 사용자 시점 타일을 추출하는 움직임 제한 타일 셋 기반 타일 추출기를 구현한다. Versatile video coding (VVC) 기반 타일 인코더를 이용해 360 도 영상에 대한 비트스트림을 생성한 후, 사용자 시점에 해당하는 타일들을 선택한다. 이후 선택된 타일들은 제안하는 타일 추출기에 의해 추출되고 전송된다. 또한, 전체 360 도 영상에 대한 저화질 비트스트림을 전송하여 갑작스러운 사용자 시점 변경에 대응한다. 제안된 타일 추출기를 기반으로 360 도 영상 전송을 수행하면, 기존 VVC 기반 시스템 대비 대비 평균 24.81%의 bjontegaard delta rate (BD-rate) 감소가 가능함을 확인하였다.

• Journal of Astronomy and Space Sciences
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• v.30 no.4
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• pp.269-277
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• 2013

In this study, we present results of precise orbital geodetic parameter estimation using satellite laser ranging (SLR) observations for the International Laser Ranging Service (ILRS) associate analysis center (AAC). Using normal point observations of LAGEOS-1, LAGEOS-2, ETALON-1, and ETALON-2 in SLR consolidated laser ranging data format, the NASA/GSFC GEODYN II and SOLVE software programs were utilized for precise orbit determination (POD) and finding solutions of a terrestrial reference frame (TRF) and Earth orientation parameters (EOPs). For POD, a weekly-based orbit determination strategy was employed to process SLR observations taken from 20 weeks in 2013. For solutions of TRF and EOPs, loosely constrained scheme was used to integrate POD results of four geodetic SLR satellites. The coordinates of 11 ILRS core sites were determined and daily polar motion and polar motion rates were estimated. The root mean square (RMS) value of post-fit residuals was used for orbit quality assessment, and both the stability of TRF and the precision of EOPs by external comparison were analyzed for verification of our solutions. Results of post-fit residuals show that the RMS of the orbits of LAGEOS-1 and LAGEOS-2 are 1.20 and 1.12 cm, and those of ETALON-1 and ETALON-2 are 1.02 and 1.11 cm, respectively. The stability analysis of TRF shows that the mean value of 3D stability of the coordinates of 11 ILRS core sites is 7.0 mm. An external comparison, with respect to International Earth rotation and Reference systems Service (IERS) 08 C04 results, shows that standard deviations of polar motion $X_P$ and $Y_P$ are 0.754 milliarcseconds (mas) and 0.576 mas, respectively. Our results of precise orbital and geodetic parameter estimation are reasonable and help advance research at ILRS AAC.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.37 no.3
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• pp.229-235
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• 2013

To investigate the effect of the flexible artery wall on the blood flow, three-dimensional numerical simulations were carried out for analyzing the time-dependent incompressible flows of Newtonian fluids constrained by a flexible wall. The Navier-Stokes equations for fluid flow were solved using the P2P1 Galerkin finite element method, and mesh movement was achieved using an arbitrary Lagrangian-Eulerian formulation. The Newmark method was employed for solving the dynamic equilibrium equations for the deformation of a linear elastic solid. To avoid complexity due to the necessity of additional mechanical constraints, we used a combined formulation that includes both the fluid and structure equations of motion to produce a single coupled variational equation. The results showed that the flexibility of the carotid wall significantly affects flow phenomena during the pulse cycle. The flow field was also found to be strongly influenced by the bifurcation angle.