• 한국항공운항학회지
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• 제17권1호
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• pp.1-8
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• 2009

In this paper, reorientation based on angular momentum exchange is applied for a bias momentum stabilized satellite, which is equipped with a spherical fuel tank, and the effect of liquid slosh on the attitude properties such as inertia tensor and angular rate is investigated. In order to represent the slosh motion of liquid an equivalent mechanical model is adopted and full nonlinear equations of motion for three-body system are derived. Computer simulations are performed for several cases, which use the viscosity of liquid and the center location of the tank as input parameters, mainly in order to observe how the viscosity of liquid and the center location of the tank influence the spacecraft’s attitude. The investigation includes observing time-variations of the inertia tensor, especially presence of components of product of inertia during the maneuver.

• 국제학술발표논문집
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• The 9th International Conference on Construction Engineering and Project Management
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• pp.353-360
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• 2022

Due to the dense and complicated working environment, the construction industry is susceptible to many accidents. Worker's fall is a severe problem at the construction site, including falling into holes or openings because of the inadequate coverings as per the safety rules. During the construction or demolition of a building, openings and holes are formed in the floors and roofs. Many workers neglect to cover openings for ease of work while being aware of the risks of holes, openings, and gaps at heights. However, there are safety rules for worker safety; the holes and openings must be covered to prevent falls. The safety inspector typically examines it by visiting the construction site, which is time-consuming and requires safety manager efforts. Therefore, this study presented a worker-driven approach (the worker is involved in the reporting process) to facilitate safety managers by developing integrated computer vision and inertia sensors-based mobile applications to identify openings. The TensorFlow framework is used to design Convolutional Neural Network (CNN); the designed CNN is trained on a custom dataset for binary class openings and covered and deployed on an android smartphone. When an application captures an image, the device also extracts the accelerometer values to determine the inclination in parallel with the classification task of the device to predict the final output as floor (openings/ covered), wall (openings/covered), and roof (openings / covered). The proposed worker-driven approach will be extended with other case scenarios at the construction site.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2009년 추계학술대회논문집
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• pp.88-92
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• 2009

When exposed to uniform magnetic fields externally applied, paramagnetic particles acquire dipole moments and the induced moments interacting with each other lead to the formation of chainlike structures or clusters of particles aligned with the field direction. A direct simulation method, based on the Maxwell stress tensor and a fictitious domain method, is applied to solve flows with magnetic chains in simple shear flow. We assumed that the particles constituting the chains are paramagnetic, and inertia of both flow and magnetic particles is negligible. The numerical scheme enables us to take into account both hydrodynamic and magnetic interactions between particles in a fully coupled manner, enabling us to numerically visualize breakup and reformation of the chains by the combined effect of the external field and the shear flow. Simple shear flow with suspended magnetic chains is solved in a periodic domain for a given magnetic field. Dynamics of interacting magnetic chains is found to be significantly affected by a dimensionless parameter called the Mason number, the ratio of the viscous force to the magnetic force in the shear flow. The effect of particle area fraction on the chain dynamics is investigated as well.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 2005년도 ICCAS
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• pp.1651-1656
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• 2005

This paper describes a natural frequency analysis conducted to find out a suitable working area for a spring-manipulator system generating a large vibrating force with mechanical resonance. Large force generation is one of the functions that we hope for a robot. For example, a weeding robot is required to generate a large force, because some weeds have roots spreading deeply and tightly. The spring-manipulator system has a spring element as an end-effector, so it can be in a state of resonance with the elasticity of the spring element and the inertial characteristics of the manipulator. A force generation method utilizing the mechanical resonance has potential to produce a large force that cannot be realized by a static method. A method for calculating a natural frequency of a spring-manipulator system with the generalized inertia tensor is proposed. Then the suitable working area for the spring-manipulator system is identified based on a natural frequency analysis. If a spring-manipulator system operates in the suitable working area, it can sustain mechanical resonance and generate a large vibrating force. Moreover, it is shown that adding a mass at the tip of the manipulator expands the suitable working area.

• Journal of Astronomy and Space Sciences
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• 제33권4호
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• pp.295-304
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• 2016

The atmosphere strongly affects the Earth's spin rotation in wide range of timescale from daily to annual. Its dominant role in the seasonal perturbations of both the pole position and spinning rate of the Earth is once again confirmed by a comparison of two recent data sets; i) the Earth orientation parameter and ii) the global atmospheric state. The atmospheric semi-diurnal tide has been known to be a source of the Earth's spin acceleration, and its magnitude is re-estimated by using an enhanced formulation and an up-dated empirical atmospheric S2 tide model. During the last twenty years, an unusual eastward drift of the Earth's pole has been observed. The change in the Earth's inertia tensor due to glacier mass redistribution is directly assessed, and the recent eastward movement of the pole is ascribed to this change. Furthermore, the associated changes in the length of day and UT1 are estimated.

• 조명전기설비학회논문지
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• 제13권4호
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• pp.142-151
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• 1999

리니어 펄스 모터(LPM)는 유연한 선형운동이 필요한 분야에 사용되며 LPM의 위치정밀도는 리드스쿠류 보다 매우 높다. LPM은 간단한 기계적 구조, 고 반복성, 정밀한 오픈루프 동작 및 저 관성 등의 장점을 지니고 있으므로 공장 자동화 및 고속 위치제어용과 같은 응용분야에서 광범위하게 활용된다. 본 논문에서는 고 정밀성과 반복성을 지닌 LPM의 힘 특성을 해석하였다. 추력과 수직력은 고정자와 가동자의 치 피치와 공극에 매우 민감하다. 이 때 수직력은 추력에 비해서 매우 높지만 추력도 상당히 크다. 본 LPM의 자기회로는 복잡한 구조이기 때문에, 힘을 계산하기 위한 적합한 방법으로는 유한요소법(FEM)을 적용한다. 여기서는 가상변위와 맥스웰 응력을 이용하였다.

• Bulletin of the Korean Chemical Society
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• 제7권5호
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• pp.367-371
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• 1986

Dynamic and equilibrium properties of n-alkane chains immersed in solvent molecules have been investigated by a molecular dynamics method. The n-alkane chain is assumed to be a chain of elements (CH$_2$) interconnected by bonds having a fixed bond length and bond angle, but each bond of the chain is allowed to execute hindered internal rotation. We studied the effect of the number of the chain elements (N$_c$ = 10, 15 and 20) on the equilibrium properties of the system, e.g., the pair correlation functions between a chain element and solvent molecules, g$_{cs}$(r), and between the chain elements, g$_{cc}$(r), and the configurational properties such as the mean-square end-to-end distance < R$^2$ >, the mean-square radius of gyration < S$^2$ >, and the eigenvalues of the moment-of-inertia tensor < S$_i^2$ > / < S$^2$ > (i = 1, 2 and 3). We also studied the dynamic properties of the system, e.g., the autocorrelation function C(A;t) where A = R$^2$(t), = S$^2$(t), or = ${\vec{V}}(t)({\vec{V}}$ = velocity of the center of mass), and the diffusion coefficient D. The g$_{cs}$(r)'s are almost equal irrespective of the change of Nc while g$_{cc}$(r) becomes larger as N$_c$ increases; The MD computed configurational properties < R$^2$2 > and < S$^2$ > were found to be a little different from the values calculated from the statistical equations of < R$^2$ > and < S$^2$ >, it may be due to the fact that our model for the MD simulations includes a long-range volume effect. From the < S$_i^2$ > / < S$^2$ >, it is found that the chain molecule has a nearly spherical shape irrespective of the variation of N$_c$. For the dynamic properties we found that the C(R$^2$;t) and C(S$^2$;t) of lower N$_c$ decay faster than those of higher N$_c$, while the C($\vec V$;t) of the center of mass in the chain is weakly dependent on the N$_c$. The center of mass diffusion coefficient D$_c$ decreases as N$_c$ increases while the end point diffusion coefficient D$_e$ is nearly equal irrespective of the change of N$_c$.