• 한국항공우주학회지
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• 제49권2호
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• pp.121-128
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• 2021

본 논문에서는 초기지점과 최종지점이 주어졌을 때 2차원 평면에서 무인기의 경로 생성 및 추적 문제에 대해 제안한다. Dubins 곡선을 이용한 경로 생성 알고리즘은 계산 속도가 빨라 무인기에 실시간으로 적용 가능하다는 장점이 있다. 경로 추적 알고리즘은 가시거리 유도 알고리즘과 유사한 알고리즘으로 효율적으로 방향각을 제어하기 위해 전방주시거리 개념과 관련된 이득 값을 추가하였다. 무인기의 경우 최대 곡률이 제한된다. 정밀한 제어를 위해 쿼드로터 모델을 사용하였다. 각속도 제한을 고려한 슬라이딩 모드 제어기를 통해 최대 곡률을 벗어나지 않고 경로를 추종하는 시뮬레이션을 진행하였다. 제약조건이 없는 제어기와 제약조건이 있는 제어기를 비교하여 경로 생성 및 추적 성능을 검증하였다.

• 한국도로학회논문집
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• 제16권5호
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• pp.19-28
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• 2014

PURPOSES : This paper evaluates, using LS/DYNA-3D software, the vehicle impact performance of flexible barriers made of steel W-Beam supported by four different types of post configurations. These types include circular post, H-shape post, C-shape post, and square post. METHODS : The post-soil interaction has been investigated according to different impact angles. For this purpose, energy absorption, maximum displacements of post and rail, and occupant risk index of THIV have been compared each other. The three dimensional soil material model, instead of the conventional spring model based on Winkler and p-y curve, has been used to increase the correctness of computational model. RESULTS : It is noted the crash energy absorption has been increased with respect to the increase of impact angle. CONCLUSIONS : In particular, a post with open section(H-shape, C-shape) shows the greater crash energy absorption capability as compared with a post with closed section under the same level of impact conditions.

• 한국기계가공학회지
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• 제10권5호
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• pp.117-124
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• 2011

Tire's performance plays important roles in improving vehicle's performances. Tire makers carry out a lot of research to improve tire's performance. They are making effort to meet multi purposes using various optimization methods. Recently, the tire makers perform the shape optimization using approximation models, which are surrogate models obtained by statistical method. Generally, the reason why we increase sampling points during optimization process, is to get more reliable approximation models, but the more we adopt sampling points, the more we need time to test. So it is important to select approximation model and proper number of sampling points to balance between reliability and time consuming. In this research, we studied to compare two kind cases for a approximation construction. First, we compare RSM and Kriging which are Curve Fitting Method and Interpolation Method, respectively. Second, we construct approximation models using three different number of sampling points. And then, we recommend proper approximation model and orthogonal array adopt tire's design optimization.

• 한국산학기술학회논문지
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• 제12권2호
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• pp.865-871
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• 2011

현재 선박의 자동운항을 위해서는 항체의 위치정보 및 방위정보가 반드시 필요하다. 그 중에서도 방위정보는 자동조타 시스템에 필수적인 요소로 측정 장비로는 자이로컴퍼스, 마그네틱 컴퍼스 그리고 GPS 컴퍼스가 있다. 자이로컴퍼스는 주로 GMDSS(Global Maritime Distress & Safety System)의 대형선박에 사용되고 있으며 정밀도와 신뢰도가 우수하지만 부피가 크고 고가라는 단점이 있다. 그리고 마그네틱 컴퍼스는 비교적 정확하고 저렴하지만 선박의 철제 구조물 등과 같은 자성물체에 의한 영향을 많이 받는다는 단점을 가지고 있다. GPS컴퍼스의 경우는 위치정보의 변화에 따라 진북을 가리키지만 항체가 정지해있거나 오차범위 내에서 운동을 할 경우 정확한 방향을 얻을 수 없다. 본 논문에서는 이러한 방위각 센서의 상호보완을 위해서 least-square curve fitting 방법을 이용하여 GPS 컴퍼스의 성능을 향상시키고 이를 마그네틱 컴퍼스와 공분산 오차의 크기에 따른 가중치를 적용하여 방위각의 정밀도를 향상 시키는 알고리즘을 제안하였다. 실험을 통하여 제안된 알고리즘의 특성을 분석하고 성능을 검증하였으며 실험 결과를 통해 제안된 알고리즘의 적용 가능성을 보여주었다.

• Advances in Traditional Medicine
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• 제7권1호
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• pp.41-45
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• 2007

The roots of the plant Korean ginseng have been extensively used in the traditional Chinese herbal medicine. The effects of chronic administration of Korean ginseng extract (KGE) were investigated on two different anxiety models: the elevated T-maze (for inhibitory avoidance and escape measurements) and the open field test (OFT). Diazepam (1 mg/kg), KGE (10, 30 and 100 mg/kg) were administered orally for 15 days. On the 14th day, mice were previously exposed for 30 min to one of the open arms of the T-maze, 24 h before the test. On 15th day, mice had two exposures to the enclosed and open arm of the elevated T-maze followed by exposure to the open field apparatus. The number of line crossings in the apparatus was used to assess locomotor changes. Cumulative Concentration Response Curve of 5-HT was plotted using rat fundus which were pre-treated in a similar way. Treatment with Diazepam (1 mg/kg) and KGE (10, 30 and 100 mg/kg) significantly (P < 0.05) impaired inhibitory avoidance performance but did not impair escape latency. In OFT, diazepam facilitated locomotion as compared to vehicle and other treatment groups. KGE at any of the selected doses did not impair locomotion. Concentration response curve of 5-HT was shifted towards the right with suppression of maxima in rats treated with KGE. The results suggest that KGE exerts anxiolytic like behaviour in a specific subset of defensive behaviour, particularly those related to generalized anxiety disorder.

• 설비공학논문집
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• 제26권3호
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• pp.122-129
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• 2014

In order to extract shaft power from thermal energy in a R134a Rankine cycle as waste heat recovery system of a passenger car, a scroll expander has been designed. Algebraic spiral is adopted as the base curve for scroll wrap profile in the compact scroll design. About 19% reduction in scroll diameter is accomplished when compared to the conventional involute scroll. Performance analysis on the designed scroll expander shows that the expander efficiency is 85.5% at the vehicle speed of 120 km/hr and it decreases to 67.2% at 60 km/hr, provided that the scroll clearance is kept at 10 ${\mu}m$. The expander can produce shaft power equivalent to about 13~14% of the driving power within the speed range of 60~120 km/hr.

• Steel and Composite Structures
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• 제31권5호
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• pp.437-452
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• 2019

In this study, in-situ static and dynamic tests of four pre-stressed concrete (PC) track beams with different span lengths and curvatures in a straddle monorail transit system were reported. In the static load tests, the strain and deflection at critical sections of the PC track beams were measured to determine the load bearing capacity and stiffness. The dynamic responses of strain, deflection, acceleration, and displacement at key positions of the PC track beams were measured under different train speeds and train loads to systematically study the dynamic behaviors of the PC track beams. A three-dimensional finite element model of the track beam-vehicle coupled vibration system was established to help understand the dynamic behavior of the system, and the model was verified using the test results. The research results show that the curvature, span length, train speed, and train loads have significant influence on the dynamic responses of the PC track beams. The dynamic performance of the PC track beams in the curve section is susceptible to dynamic loads. Appropriate train loads can effectively reduce the impact of the train on the PC track beam. The PC track beams allow good riding comfort.

• International Journal of Naval Architecture and Ocean Engineering
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• 제12권1호
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• pp.832-842
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• 2020

The coordination control of multiple Underactuated Underwater Vehicles (UUVs) moving in three dimensional space is investigated in this paper. The coordinated path following control task is decomposed into two sub tasks, that is, path following control and coordination control. In the spatial curve path following control task, path following error dynamics is build in the Serret-Frenet coordinate frame. The virtual reference object can be chosen freely on the desired spatial path. Considering the speed of the UUV, the line-of-sight navigation is introduced to help the path following errors quickly converge to zero. In the coordination control sub task, the communication topology of multiple UUVs is described by the graph theory. The speed of each UUV is adjusted to achieve the coordination. The path following system and the coordination control system are viewed as the feedback connection system. Input-to-state stable of the coordinated path following system can be proved by small gain theorem. The simulation experiments can further demonstrate the good performance of the control method.

• 한국도로학회논문집
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• 제10권4호
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• pp.151-159
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• 2008

차선의 밝기를 나타내는 반사성능은 교통량, 도색 후 경과시간, 차선재료, 색상 등에 따라 지역별로 차이가 발생한다. 본 연구에서는 고속도로에서 조사된 차선 성능의 자료를 바탕으로 교통량과 차선의 공용수명을 독립변수로 하고 차선의 성능을 종속변수로 하는 회귀식을 산정하였다. 전국의 고속도로를 대상으로 모바일 차선반사 성능 차량을 사용하여 $2005{\sim}2006$년의 2년동안 3개월 간격으로 차선의 성능을 추적 조사하였다. 축적된 DB에는 차선의 성능뿐 아니라 차선의 재료, 색상, 기하구조, 교통량, 도색시기 등이 포함되어 있다. 본 연구에서 추적 조사된 차선성능을 기초로하여 다양한 환경에서의 차선재료의 성능을 비교 분석하여 여러 인자에 의한 차선성능 곡선을 도출하였다. 차선성능 곡선을 통해 지역별 교통량과 도색 이후의 시간의 경과에 따른 차선의 성능을 예측할 수 있었다. 선형함수, 로그함수, 지수함수, 음지수함수 등을 이용하여 차선의 성능을 나타내는 회귀식과 변동을 추정한 후, 결정계수가 가장 높고, 현장측정치와 가장 유사한 모형을 차선의 성능 예측모형으로 결정하였다. 현장조사 결과와의 검증결과, 차선성능 예측 모델은 90% 신뢰도에서 유의함을 볼 수 있었고, 특히 누적 교통량의 증가에 따라 현장 데이터와 높은 연관성을 보여주었다. 따라서 본 방법론에 의한 차선수명 예측 모델을 통해 차선의 공용수명과 잔존수명을 예측하여 도색시기를 결정할 수 있다.

• Journal of Biosystems Engineering
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• 제27권6호
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• pp.501-512
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• 2002

Traction performance of off-road vehicles is estimated using slip-traction relationships Two zero condition accepted by ASAE have been used widely to obtain the slip-traction relationships of off-road vehicles. This study was carried out using the soil bin systems to investigate the characteristic of slip-traction curves obtained using two zero conditions defined by ASAE. which are driving and driven zero condition, and to present disadvantage of slip-traction relationship based on two zero conditions of ASAE. The results of this study are summarized as follows : 1. For the driving zero condition, the curve of slip-traction relationship shows some issues. The first question is that the slip is zero when the traction is zero. The second question is that the value of slip is smaller than that of corresponding real slip, as the rolling radius decreased f3r the setting zero condition with driving wheel. 2. For the driven zero condition. slip occurs when the traction is zero, which is more realistic results than driving zero condition. But when a zero condition is set, skid occurs and this result increased the rolling radius of tire and increased slip value f3r the specific traction value of whole slip range. This kind of trend was getting bigger as the soil is softer, or the tire inflation pressure is higher. 3. From the results of this study, it was found that slip-traction relationship obtained by two zero conditions of ASAE is not realistic in estimating the traction performance of off-road vehicles. And also slip-traction relationship obtained for the same experimental condition showed different result in accordance with chosen zero condition,