• 산업경영시스템학회지
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• 제20권43호
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• pp.47-57
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• 1997

As a general index in surface quality of machined products, surface roughness is to measure worker's skill level, a ground product quality and machining accuracy, etc. The surface roughness is defined by a function of rotational speed and radius of a grinding wheel, distances of active grains composed of the wheel, and feed of a grinder's worktable. To predict surface roughness in horizontal surface grinding operations, probability distributions were used. Probability distribution functions(p.d.f.) of surface roughness were found as results when the size of active grains(=the radius of a grinding wheel) is given as uniform, exponential distribution, and the distance between active grains follows the distributions of uniform, exponential. For each pdf case, probabilistic features of surface roughness were also analyzed and presented. This study is a substantial step for determining mathematically the surface roughness instead of using empirical approaches. More works should be presented to develop a general model by which an accurate roughness value can be obtained in horizontal surface grinding operations.

• 천문학회보
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• 제44권2호
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• pp.50.2-50.2
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• 2019

We present the results of high-resolution (R ≥ 30,000) optical and near-infrared spectroscopic monitoring observations of a FU Orionis-type object, 2MASS J06593158-0405277. We have monitored 2MASS J06593158-0405277 with the Bohyunsan Optical Echelle Spectrograph (BOES) and the Immersion GRating INfrared Spectrograph (IGRINS) since December 2014. Various features produced by wind, disk, and outflow/jet were detected. The wind features varied over time and disappeared about a year after the outburst occurred. The double-peaked line profiles were detected in the optical and near-infrared, and the line widths decrease with increasing wavelength. The disk features in the optical spectra are fit well with G2-type or G5-type stellar spectra convolved with a disk rotational profile of about 45 km s^-1, which corresponds to a disk radius of about 71 R_⊙for a central mass of 0.75 M_⊙. Disk features in near-infrared spectra are fit well with a K1-type stellar spectrum convolved with a disk rotational profile of about 35 km s^-1, which corresponds to a disk radius of about 117 R_⊙ for a central mass of 0.75 M_⊙. We also detected [S II] and H2 emission lines, which are rarely found in FUors but are usually found in the earlier stage of young stellar objects. Therefore, we suggest that 2MASS J06593158-0405277 is in the relatively earlier part of Class II stage.

• 천문학회보
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• 제44권1호
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• pp.70.4-70.4
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• 2019

Complex organic molecules (COMs) are increasingly observed in the environs of young stellar objects (YSOs), including hot cores/corinos around high-mass/low-mass protostars and protoplanetary disks. It is widely believed that COMs are first formed in the ice mantle of dust grains and subsequently released to the gas by thermal sublimation at high temperatures (T>100 K) in strong stellar radiation fields. In this paper, we report a new mechanism that can desorb COMs from icy grain mantles at low temperatures (T<100K), which is termed rotational desorption. The rotational desorption process of COMs comprises two stages: (1) ice mantles on suprathermally rotating grains spun-up by radiative torques (RATs) are first disrupted into small fragments by centrifugal stress, and (2) COMs and water ice then evaporate rapidly from the tiny fragments (i.e., radius a <1nm) due to thermal spikes or enhanced thermal sublimation due to increased grain temperature for larger fragments (a>1 nm). We discuss the implications of rotational desorption for releasing COMs and water ice in the inner region of protostellar envelopes (hot cores and corinos), photodissociation regions, and protoplanetary disks (PPDs). In shocked regions of stellar outflows, we find that nanoparticles can be spun-up to suprathermal rotation due to supersonic drift of neutral gas, such that centrifugal force can be sufficient to directly eject some molecules from the grain surface, provided that nanoparticles are made of strong material. Finally, we find that large aggregates (a~ 1-100 micron) exposed to strong stellar radiations can be disrupted into individual icy grains via RAdiative Torque Disruption (RATD) mechanism, which is followed by rotational desorption of ice mantles and evaporation of COMs. In the RATD picture, we expect some correlation between the enhancement of COMs and the depletion of large dust grains in not very dense regions of YSOs.

• 한국기계가공학회지
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• 제19권3호
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• pp.63-70
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• 2020

Two rotational motions of the 5-axis machine tool maximize the degree of freedom of the tool axis vector, which improves tool accessibility; however, this lowers feed speed and rigidity, which impairs machining stability. In addition, cutting efficiency is lowered when compared with a flat end mill because typically, the ball-end mill is used when machining by rotational motion. This study increased cutting efficiency by using a corner radius flat end mill during impeller roughing. Furthermore, we proposed a fixed controlled machining of the rotary motion using geometric shape information to improve the feed speed and machining stability. Finally, we proposed a finishing tool path generation method using a vector net to increase the convenience and practicality of tool path generation. To verify its effectiveness, we compared the machining time, shape accuracy, and surface quality of the proposed method and an existing dedicated module.

• 대한기계학회논문집A
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• 제40권8호
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• pp.731-736
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• 2016

본 연구에서는 의용생체공학에 널리 사용되는 미소바늘과 같은 3차원 고종횡비 미소구조물을 용이하게 제작할 수 있는 하이브리드 자외선 노광법에 대해 기술한다. 하이브리드 자외선 노광법은 기존에 사용되고 있는 경사노광, 회전노광 및 역노광을 혼합한 방법으로, 경사 및 회전노광은 경사진 축대칭 형상을 가지는 3차원 미소구조물의 제작이 가능하도록 하고 역노광은 자외선 노광공정 중 필연적으로 발생하는 하부기판에서의 자외선 반사를 최소화 시킨다. 자체 개발한 자외선 노광시스템과 SU-8 음성감광제를 이용하여 하이브리드 자외선 노광법의 다양한 공정조건이 최종 제작된 3차원 고종횡비 미소구조물 형상(종횡비, 선단의 곡률반경 등)에 미치는 효과를 확인한다. 또한 SU-8의 소프트 베이킹(soft baking) 조건과 미소구조물 선단 형상 사이의 관계에 대해서도 논의한다.

• 한국지능시스템학회논문지
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• 제26권6호
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• pp.505-510
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• 2016

본 논문은 모바일 로봇의 SLAM(Simultaneous Localization and Mapping) 구현 시 사용되는 스캔매칭을 위한 회전오차에 강인한 대응점 탐색 기법을 제시한다. 많은 모바일 로봇의 연구에 차동구동방식의 구동부가 사용되는데, 이는 곡선 주행이나 제자리 회전을 위해 두 모터의 속력을 다르게 하거나, 반대 방향으로 제어하게 된다. 이러한 경우 직선 주행에 비해 비교적 바퀴의 미끄러짐 현상(Wheel Slip)을 심화시켜 모바일 로봇의 누적 위치 오차를 증가시키는 요인이 된다. 따라서 본 논문에서는 모바일 로봇의 회전 반경을 기반으로 최근접점을 추출하는 대응점 탐색 기법을 통해 스캔매칭 성능을 향상시키고자 한다. 제안된 방법의 검증을 위해 LRF(Laser Range Finder)를 이용해 실험을 진행하였으며, 기존 알고리즘에 주로 적용되는 유클리디안 최근접점 기반의 대응점 탐색 알고리즘과 비교한 결과, 제안된 대응점 탐색 기법이 보다 정확하게 대응점 집합을 추출하는 것을 확인했다.

• 한국공간구조학회논문집
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• 제16권3호
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• pp.67-78
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• 2016

Determining of the shape in the process of design for natural draught cooling tower is very important, because the shape of hyperbolic shell is respond sensitively to dynamic behavior of the whole cooling tower against wind load. In engineering practice, the geometric parameters have been determining based on the natural frequency. This study analyses influence of the tower shell geometric parameters on the structural behavior. For three representative models were selected, they were analyzed based on evaluation of damage by means of nonlinear FE-method. As a result, a hyperbolic rotational shell with the small radius overall was the lowest damage index induced by sufficient capacity of the stress redistribution and thus a wind-insensitive structure.

• Structural Engineering and Mechanics
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• 제45권1호
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• pp.69-93
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• 2013

The present study deals with the dynamics of the flapwise (out-of-plane) vibrations of a rotating, internally damped (Kelvin-Voigt model) tapered Bernoulli-Euler beam carrying a heavy tip mass. The centroid of the tip mass is offset from the free end of the beam and is located along its extended axis. The equation of motion and the corresponding boundary conditions are derived via the Hamilton's Principle, leading to a differential eigenvalue problem. Afterwards, this eigenvalue problem is solved by using Frobenius Method of solution in power series. The resulting characteristic equation is then solved numerically. The numerical results are tabulated for a variety of nondimensional rotational speed, tip mass, tip mass offset, mass moment of inertia, internal damping parameter, hub radius and taper ratio. These are compared with the results of a conventional finite element modeling as well, and excellent agreement is obtained.

• 소음진동
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• 제5권2호
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• pp.215-224
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• 1995

In this paper, the three-dimensional finite element model is established to investigate the structural dynamic characteristics of rotor blade using a finite element analysis. Six natural frequencies and mode shapes are calculated by computer simulation. The first three flapping modal frequencies, the first two lead-lag modal frequencies, and the first feathering modal frequency are validated through comparison with the modal test results of the fixed rotor blade. The computer simulation results are found in good agreement with experimentally measured natural frequencies. The important results are obtained as follows: (1) Natural frequencies are changed due to the variation of rotational speed and fiber angle of rotor blade, (2) Weak coupling between flapping mode shape and lead-lag mode shape are detected, (3) Centrifugal force has more effect on flapping modal frequency than lead-lag modal frequency.

• Journal of Electrochemical Science and Technology
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• 제8권1호
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• pp.1-6
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• 2017

The conductivity of the electrolyte used plays a critical role in the optimization of the performance of electrochemical double layer capacitors. However, when the difference in the conductivities of different electrolytes is not significant (only 10-20%), the conductivity has little effect on the capacitance. On the other, unlike the conductivity and viscosity of the electrolyte, the cation size directly influences the capacitance. Cyclic ions have a smaller effective radius than that of the corresponding acyclic ions because the acyclic alkyl groups have a greater number of conformational degrees of freedom, such as the rotational, bending, and stretching modes. Consequently, because of the smaller effective size of the cyclic ions, cells containing electrolytes with such ions exhibit higher capacitances than do those with their acyclic counterparts.