Conventional railroad vehicles, that run on a line with high frequency of sharp curves, have problems such as wheel noise and wear, from insufficient passive steering. To solve this problem, real-time curvature measurement technology must be developed for realizing active steering. In this study, we propose a uniaxial curvature measurement sensor considering applicability to actual railroad vehicles, and analyze its validity in terms of active steering control. Required characteristics of the curvature sensor according to steering control performance, were determined through railroad vehicle dynamics simulations, and actual vehicle driving information. Measurement range of curvature radius is 200 m to 600 m; measurement accuracy is ±3%, and measurement bandwidth is 0.85 Hz. Effectiveness of the developed curvature sensor was analyzed based on behavior of the car body, the bogie and its installation on the vehicle, and curvature of the track was measured in real time on an actual urban railroad vehicle. As a result of the field test, curvature measurement error was obtained within 3%, validating the feasibility of active steering control for the next generation railroad vehicles.
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Verification of Control Algorithm for Improving the Lateral Restoration Performance of an Independently Rotating Wheel Type Railway Vehicle Yonho Cho International Journal of Precision Engineering and Manufacturing.2020; 21(7): 1247. CrossRef
Automation of electronic connectors has been in demand, based on automation of assembly of electronic products. In this study, we propose a new classification of electronic connector, for grasping and assembling. We analyze characteristics of electrical connectors often used at actual industrial sites, from the perspective of the robot, not a person. As a result, it is appropriate to classify the grasp, according to the shape of the electric connector. For the assembly, we suggested that classification should be based on directions are different, because of interference of the electric wire and peripheral parts. We hope that this research will become a new basis, for electrical connector assembly.
Displacement estimation based on inertial sensor signals is usually performed in aid of global positioning systems or barometers. However, due to low accuracy estimation capabilities of such aiding sensors, inertial sensor-based displacement estimation is difficult to achieve high accuracy. This paper will show that it is possible to determine the vertical displacement of a link connected by a joint with higher accuracy while only using the inertial sensor. The proposed method utilizes a predetermined position vector from the joint center to the sensor and link orientation. By combining the joint constraint, accuracy of the orientation estimation is ensured even in highly dynamic conditions, and thus, the vertical displacement estimation with high accuracy can be achieved. Experimental results show that the proposed method outperformed the method by fusing inertial sensor and barometer signals as well as the method using inertial sensor signals only without constraint combination.
The objective of this study is to investigate a novel temperature and humidity prediction algorithm for smart greenhouse based on the machine learning method. The smart greenhouse is known to increase farm production by automatically controlling temperature and humidity and other factors. However, maintaining constant inside temperature and humidity in the conventional smart greenhouse system is still a problem because of the multiple time delay elements. To solve the problems, prediction control scheme is required. But, since the system is highly nonlinear with the lack of sensory data, predicting accurate temperature and humidity is very challenging. In this paper, the multi-dimensional Long Short-Term Memory networks (LSTMs) is being applied to deal with the unstructured greenhouse environmental data. The designed LSTMs learning model is trained with the 27 dimensional data which comprises of all the greenhouse control parameter and environmental sensory data. The prediction performance was evaluated using the short, mid and long term experiments. Also, the comparison with the conventional recurrent neural networks (RNNs) based prediction algorithm was done using the experimental results and later on discussions.
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Data-Driven Optimization Method for Recurrent Neural Network Algorithm: Greenhouse Internal Temperature Prediction Model Kwang Cheol Oh, Sunyong Park, Seok Jun Kim, La Hoon Cho, Chung Geon Lee, Dae Hyun Kim Agronomy.2024; 14(11): 2545. CrossRef
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To secure the precision forming capability of a press while reducing its production and transport costs, the development of stiff and lightweight frame is important. In this study, the topology and multi-objective structural optimization problem of a frame structure was introduced with an effort to develop highly stiff and lightweight frame for a mechanical press with 300 ton capacity. First, a design space model was constructed to derive a new frame structure different from the existing one for topology optimization. Using the design of experiments and the structural analysis model of the frame structure improved based on the topology optimization result, the multi-objective optimization problem was established with loop stiffness and mass of frame as objectives and the steel plate thickness as design variable. The review on Pareto optimum solutions of the multi-objective optimization problem revealed the fact that this optimization method could significantly contribute to the high stiffness and lightweight frame structure for a mechanical press.
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In this study, to develop mine protective design technology for wheeled armored vehicles, designing and simulating of test specimens based on the 8×8 military combat vehicle, were executed and mine protection effectiveness was proven, by testing under the two work steps such as 1st step for conceptual model and 2nd step for vehicle segment. Experiments for both test models of each step were performed according to test conditions of NATO standard, STANAG 4569 Level, and simulations were performed by the commercial code, LS-DYNA. On the 1st step, a conceptual model was designed, and its protection effectiveness was verified by simulation before testing and then it was proven by testing. On the 2nd step, the vehicle segment with protection design technology from the 1st step was designed better, to consider dynamic vertical deformation, injury values of a human dummy, and effects of installed components on the bottom of the model. Finally, satisfaction for protection effectiveness and IARVs (Injury Assessment Reference values) of a human dummy were verified by testing, and also the possibility of application for wheeled armored vehicles were confirmed.
This study focuses on these issues and includes the static fracture experiments with two forms of specimens; aluminum foam DCB and TDCB bonded with the type of mode III, a simulation static analysis to verify this experiment, and analysis of fracture behavior of adhesive interface of structures attached with aluminum foam by shape and thickness. The thickness of DCB and TDCB specimens designed in this study are set as variable t, and each thickness is t = 35 mm, 45 mm, 55 mm. According to forced displacements, the maximum reaction forces of DCB specimens due to thickness were approximately 0.35 kN, 0.45 kN, 0.54 kN, and the maximum reaction force of TDCB were approximately 0.4 kN, 0.52 kN, and 0.63 kN respectively. We expect the data according to variables to be easily investigated without a separate testing process, and effective analysis of the mechanical characteristics of aluminum foam DCB and TDCB.
Isothermal low cycle fatigue (LCF) behavior of a crystal nickel-based superalloy CMSX-4, a material for high-pressure turbine first stage rotor blade, was investigated at elevated temperatures. Strain-controlled LCF tests were performed under various test conditions, such as mechanical strain amplitude. Stress response and cyclic deformation were investigated, and equations of LCF life prediction were derived through the Coffin-Manson method. In addition, fatigue-induced fracture mechanism and microstructural evolution were investigated, using scanning electron microscopy (SEM). Results revealed that cyclic behavior of the CMSX-4 superalloy, was characterized by cyclic softening with increasing number of cycles at 800oC and 900oC. LCF of the CMSX-4 superalloy at 800oC and 900oC could be affected mainly by elastic damage in fatigue processing. Fatigue cracks were initiated in the surface oxide layer of the specimen. The plane of fracture surface was tilted toward <001> direction. The fatigue fracture mechanism was quasi-cleavage fracture at 800oC and 900oC. In all broken specimens, the γˊ phase morphology maintained cuboidal shape.
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Mechanical Loading Effect on Stress States and Failure Behavior in Thermal Barrier Coatings Da Qiao, Wengao Yan, Wu Zeng, Jixin Man, Beirao Xue, Xiangde Bian Crystals.2023; 14(1): 2. CrossRef
A method for predicting the delamination life of thermal barrier coatings under thermal gradient mechanical fatigue condition considering degradation characteristics Damhyun Kim, Kibum Park, Keekeun Kim, Chang-Sung Seok, Jongmin Lee, Kyomin Kim International Journal of Fatigue.2021; 151: 106402. CrossRef
Low-cycle fatigue behavior of K416B Ni-based superalloy at 650 °C Jun Xie, De-long Shu, Gui-chen Hou, Jin-jiang Yu, Yi-zhou Zhou, Xiao-feng Sun Journal of Central South University.2021; 28(9): 2628. CrossRef
Failure of conventional snowplows is usually caused by the strain put it its rotational parts. In the case of the vertical rotation, when the snowplow is rising or falling, the sensor automatically stops the rotation and the wire could be break due to the impact from an endless drive in the reverse direction or conversely from the winding of the wire. While in motion, snowplows are frequently over turned due to their heavy weight. Snowplows are manufactured with conventional steel plates and have heavy hydraulic cylinders which makes them heavy. This can result in the damaging of the vehicle due to the mounted snowplow and its malfunctions. In this study, a composite resin blade with a high-strength and is lightweight was developed for a snowplow. In order to ensure durability of the snowplows, a new bobbin was designed to mimic the clutch of a vehicle. This study was developed to eliminate the tension and fatigue of the wire by winding the chain instead of the wire in the newly designed bobbin.
In this paper, we propose a novel and simple fabrication microchannel with parallelogram cross-section using anisotropic wet etching of Si wafer, and self-alignment between Si channel and PDMS mold. Single crystal Si wafer was used to fabricate microchannel and master for PDMS mold, using photolithography and anisotropic KOH etching. Si structure for microchannel and master were formed on the same Si wafer by KOH etching, and the PDMS mold was made from Si master. Thus, we could fabricate the Si microchannel and PDMS mold, with same structural height. Finally, a microchannel with parallelogram cross-section could be easily formed, through self-alignment between them. Si microchannel and PDMS mold were permanently bonded, using O₂ plasma treatment. It is expected that the fabricated microchannel with parallelogram cross-section, can be used to study inertial focusing, widely used to separate particles continuously and with high-throughput.
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The Fabrication of a High-Aspect-Ratio Microfluidic Device for Microparticle Separation under Viscoelastic Fluid Sung Woo Kim, Joo Yong Kwon, Jihong Hwang, Young Hak Cho Journal of the Korean Society for Precision Engineering.2022; 39(10): 725. CrossRef
Experimental Study on Heat Transfer Performance of Microchannel Applied with Manifold Jungmyung Kim, Hoyong Jang, Heesung Park Journal of the Korean Society for Precision Engineering.2022; 39(12): 923. CrossRef
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[Objective] The objective of this study was to investigate the reliability of smartphone-based measurements of the upper body, thigh, and shin segmental angles, and the hip and knee joint angles when walking. [Method] The sample size of this study included eight young and healthy college students. In this study, smartphones were used to determine the changes in angles when the subjects walked with smartphones attached to their torso (upper body), thigh, and shin. The obtained angles represented segmental angles for the torso, thigh, and shin, and were later used to calculate hip and knee joint angles. Measurements were taken and then the test-retest method was used to evaluate the agreement between the test and retest results. [Results] According to the results, a very high reliability for the torso and shin segmental angles (ICC>0.75) and a high reliability for the thigh segmental angle and hip and knee joint angles (ICC>0.60) were displayed. [Conclusion] According to the results of this study, it was established that smartphones can be sufficiently used as devices for gait analysis.
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Reliability of Measuring Leg Segments and Joint Angles Using Smartphones during Aquatic Exercise Dae Hee Lee, Seulki Han Healthcare Informatics Research.2022; 28(1): 95. CrossRef
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The objective of this study is to verify the accuracy of performing surgery by developing and experimenting orthognathic surgical splints using 3D convergence technology. We performed the computation of the movement of the maxilla on the virtual simulation data for the surgery then designed the surgical splints using 3D CAD. We produced the designed splints and the test object and experimented on them using a 3D printer (accuracy ± 0.025 mm). The subjects were scanned using an optical scanner (accuracy ± 0.01 mm). We then compared and evaluated the simulated data and their accuracy. The evaluation results showed that the mean error range was within +0.313/-0.456 mm (average standard deviation 0.106), which was within the range of ±0.5 mm. These splints did not need for a reference point for external measurement to be set, neither did it need improving of the accuracy nor shortening the operation time. In addition, its advantage is that the amount of bone removal can be known accurately when the maxilla is repositioned.
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Cluster analysis of cloud-to-ground lightning activities near transmission lines in typical terrains Yeqiang Deng, Yuzhe Chen, Yu Wang, Xishan Wen, Lei Lan, Meichen Xiang, Maoheng Jing Electric Power Systems Research.2023; 225: 109876. CrossRef
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In this paper, we compare the cost of the structure due to change of weight of the structure according to change of annual power generation and height, calculated by changing wind speed of a 10kW horizontal small wind turbine, Optimum height of the wind turbine was considered. The cost of each model was calculated by changing height of the structure to 12 m, 24 m, 30 m, and 36 m. Wind speed was calculated by the Deacon formula, and annual power generation was calculated based on annual average wind speed at power generation height of each model. Then, economic efficiency was evaluated by comparing cost of the structure with total profit over the lifetime calculated by annual power generation, and a suitable model was selected based on evaluation. Computer analysis was conducted to evaluate structural stability of the selected model.
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