• Journal of KSNVE
• /
• v.6 no.1
• /
• pp.65-70
• /
• 1996

The sensor response of a piezoelectric transducer embedded in a fluid loaded structure is modeled using a hybrid numerical approach. The structure is excited by an obliquely incident acoustic wave. Finite element modeling in the structure and fluid surrounding the transducer region, is used and a plane wave representation is exploited to match the displacement field at the mathematical boundary. On this boundary, continuity of field derivatives is enforced by using a penalty factor and to further achieve transparency at the mathematical boundary, drilling degrees of freedom (d.o.f.) are introduced to ensure continuity of all derivatives. Numerical results are presented for the sensor response and it is found that the sensor at that location is not only non-intrusive but also sensitive to the characteristic of the structure.

• Journal of the Korean Magnetics Society
• /
• v.23 no.1
• /
• pp.31-35
• /
• 2013

The objective of this study is numerically analyzed the behavior characteristics of the magnetic fluid in a closed rectangular container using finite element method (FEM). The governing equations are solved with magnetization and Maxwell equations for consideration of rotating effect of the magnetite particle. Then the discretized equations are solved with boundary conditions of the velocity and temperature. The developed model is validated with the results of Davis (1983) and Fusegi et al. (1991) has a good agreement within 5.5 % and 2.7 %, respectively.

• The Journal of the Institute of Internet, Broadcasting and Communication
• /
• v.19 no.1
• /
• pp.133-138
• /
• 2019

The indoor navigation system using smart phone is a very important infrastructure technology for users' location based services in large indoor facilities. For this purpose, if the user can estimate the movement distance and direction by using the acceleration sensor and the gyro sensor built in the smartphone, the additional external environment is not necessary, which is a very useful technique. This paper deals with indoor navigation system technology that uses Pedestrian Dead Reckoning (PDR) technology and Kalman filter on a general smartphone and allows the user to trace the position while moving the smartphone in front of his chest. In particular, an extended Kalman filter was designed to estimate the direction of movement, and its performance was verified when walking at a constant speed.

• Journal of Korean Society of Steel Construction
• /
• v.12 no.6
• /
• pp.661-670
• /
• 2000

To investigate the characteristics of the dynamic response of long-span cable-stayed bridges due to various dynamic loadings likes moving traffic loads, two different 3-D cable-stayed bridge models are considered in this study. Two models are exactly the same in structural configurations but different in finite element discretization. Modal analysis is conducted using the deformed dead-load tangent stiffness matrix. A new concept was presented by using divided a cable into several elements in order to study the effect of the cable vibration (both in-plane and swinging) on the overall bridge dynamics. Futhermore case of asymmetric traffic loading clustered in one direction are also considered to study the torsional response of the bridge. The result of this study demonstrates the importance of cable vibration on the overall bridge dynamics.

• Proceedings of the Korean Society for Agricultural Machinery Conference
• /
• 2017.04a
• /
• pp.19-19
• /
• 2017

자율주행 트랙터를 위한 트랙터 조향제어는 일반적으로 전자모터를 이용한 EPS(Electric Power Steering) 시스템을 스티어링 휠에 연결하여 회전변위를 변경하고 그 결과 오비트롤(Orbitrol) 밸브의 토출유량을 바꾸고 호스로 연결된 조향실린더의 변위를 조절하여 최종적으로 전방 타이어의 방향각을 변경하면서 이루어진다. 이러한 조향방식은 시스템 구조상 조향실린더와 오비트롤 밸브가 상대적으로 멀리 떨어져 있으며, 밸브 특성상 약 ${\pm}5^{\circ}$의 오버랩이 포함되어 있다. 또한, EPS의 전자모터는 관성력, 마찰, 백래시 등의 영향을 가진다. 이와 같은 복합적인 영향은 조향 응답을 느리게 만들어 상대적으로 빠른 속도에서 주행에서 추종성능이 떨어지는 문제가 발생한다. 본 연구에서는 자율주행 트랙터의 조향성능 개선 연구의 일환으로 조향 HILS 시뮬레이터를 설계제작하여 조향 성능의 요인을 실험적으로 구명하고자 하였으며 이를 바탕으로 조향 시스템의 설계개선 방안을 수립하고자 하였다. 시뮬레이터는 동양물산 80 마력급 TX803 트랙터에 사용되는 오픈센터방식의 오비트롤 유압회로 시스템을 기어펌프가 장착된 AC모터로 구동되게 구성하였으며, 유량은 모터의 주파수를 조절 회전속도를 조절 변경하였다. 추가적으로 EPS와 오비트롤 조합의 조향성능을 비교 및 개선하기 위해 비례제어밸브(PVG 32, Danfoss)를 추가 장착하였다. 실제 트랙터 조향 시 나타나는 마찰저항을 모사하기 위해 부하 실린더를 구성하였으며, 조향 실린더의 부하의 크기는 부하 실린더를 폐회로를 구성하고 유량비례제어밸브를 이용한 유로의 개구량 조절을 통해 부하의 크기를 약 4000 N 까지 증가시킬 수 있도록 하였다. EPS와 비례제어밸브를 제어하기 위해 CANoe 8.0 소프트웨어를 이용하여 CAN통신 기반 가상 조향ECU를 구성하였으며 오비트롤의 기본 성능을 확인하기 위해 조향휠에 따른 실린더 동특성 및 계단 추종성능을 비례제어밸브와 비교하였다. 오비트롤 밸브는 약 ${\pm}5^{\circ}$이상 동작 시 실린더 압력이 상승하기 시작하였으며, 이후 약 ${\pm}10^{\circ}$이상 동작 시 조향실린더가 동작하기 시작하였다. 계단 추종성능실험에서는 비례제어밸브가 약 2배 이상의 응답개선을 나타냈다. 자율주행 경로추종 성능을 향상시키기 위해서는 순간적인 출력밀도가 높은 비례제어밸브를 통해 응답개선이 필요한 것으로 나타났다.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.35 no.3
• /
• pp.241-250
• /
• 2011

The new gerotor developed in this paper has an inner rotor in which a circular arc is inserted between the hypocycloid and epicycloid curves, whereas the outer rotor is designed using the simulation results for the rotor and a modification method. The new gerotor has no cusps and loops and no limit on the eccentricity. We increase the average flow rate by adding a new design parameter, $\gamma$, which is the inclined angle of the inner rotor at the intersection of the hypocycloid and the circular arc. A calculation method to calculate the chamber area is also developed. This method can also be used to calculate the flow rate and flow rate irregularity when the contact points are unknown. The control of eccentricity and $\gamma$ is expected to lead to an efficient rotor.

• 유체기계공업학회:학술대회논문집
• /
• 2006.08a
• /
• pp.531-534
• /
• 2006

This study is concerned with radial turbine design and performance improvement of a turbo generator system, which is used for maximizing performance of a 250kW MCFC fuel cell system. A preliminary design of a radial turbine has been performed under the thermodynamic and fluid-dynamic conditions determined by a cycle analysis of the MCFC BOP system. Basic demensions are determined by a meanline analysis and calculation of radial variation at the exit of the turbine. The turbine impeller is designed and modified by iterative processes of three dimensional flow analysis.

• Journal of the Korean Society for Railway
• /
• v.17 no.4
• /
• pp.245-250
• /
• 2014

This paper, as a study for the serviceability design of railway bridges with concrete track, presents the effects of design parameters of tracks and bridges on the forces acting on the rail supports of the track. To calculate the forces acting on the track, an unequal spacing discrete supported model with different spacing of rail supports was induced. Design parameters are the rail support spacing of expansion joints above abutments or piers of bridges, the distance from the support of a girder to the last rail support on the end of the girder, and the number of additional rail supports. The causes of the displacement of track are axial force, unit vertical displacement, and unit rotation. From the analysis, the maximum compressive force and the maximum uplifting force acting on the rail supports were determined and the effects of the rail support spacing on the forces acting on the track were presented.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
• /
• v.33 no.1
• /
• pp.45-52
• /
• 2015

The interoperability of multi-source data has become more important due to various digital maps, produced from public institutions and enterprises. In this study, the automatic matching algorithm of multi-source building data using hierarchical matching was proposed. At first, we divide digital maps into blocks and perform the primary geometric registration of buildings with the ICP algorithm. Then, corresponding building pairs were determined by evaluating the similarity of overlap area, and the matching threshold value of similarity was automatically derived by the Otsu binary thresholding. After the first matching, we extracted error matching candidates buildings which are similar with threshold value to conduct the secondary ICP matching and to make a matching decision using turning angle function analysis. For the evaluation, the proposed method was applied to representative public digital maps, road name address map and digital topographic map 2.0. As a result, the F measures of matching and non-matching buildings increased by 2% and 17%, respectively. Therefore, the proposed method is efficient for the matching of building polygons from multi-source digital maps.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
• /
• v.38 no.6
• /
• pp.663-670
• /
• 2020

In the present study, we assessed the accuracy of aerial triangulation using a UAV (Unmanned Aerial Vehicle) capable of network RTK (Real-Time Kinematic) survey in a disaster situation that may occur in a semi-urban area mixed with buildings. For a reliable survey of check points, they were installed on the roofs of buildings, and static GNSS (Global Navigation Satellite System) survey was conducted for more than four hours. For objective accuracy assessment, coded aerial targets were installed on the check points to be automatically recognized by software. At the instance of image acquisition, the 3D coordinates of the UAV camera were measured using VRS (Virtual Reference Station) method, as a kind of network RTK survey, and the 3-axial angles were achieved using IMU (Inertial Measurement Unit) and gimbal rotation measurement. As a result of estimation and update of the interior and exterior orientation parameters using Agisoft Metashape, the 3D RMSE (Root Mean Square Error) of aerial triangulation ranged from 0.153 m to 0.102 m according to the combination of the image overlap and the angle of the image acquisition. To get higher aerial triangulation accuracy, it was proved to be effective to incorporate oblique images, though it is common to increase the overlap of vertical images. Therefore, to conduct a UAV mapping in an urgent disaster site, it is necessary to acquire oblique images together rather than improving image overlap.