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UUV Platform Optimal Design for Overcoming Strong Current

  • Kim, Min-Gyu;Kang, Hyungjoo;Lee, Mun-Jik;Cho, Gun Rae;Li, Ji-Hong;Kim, Cheol
    • Journal of Ocean Engineering and Technology
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    • v.35 no.6
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    • pp.434-445
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    • 2021
  • This paper proposes an optimal design method for an unmanned underwater vehicle (UUV) platform to overcome strong current. First, to minimize the hydrodynamic drag components in water, the vehicle is designed to have a streamlined disc shape, which help maintaining horizontal motion (zero roll and pitch angles posture) while overcoming external current. To this end, four vertical thrusters are symmetrically mounted outside of the platform to stabilize the vehicle's horizontal motion. In the horizontal plane, four horizontal thrusters are symmetrically mounted outside of the disc, and each of them has the same forward and reverse thrust performances. With these four thrusters, a specific thrust vector control (TVC) method is proposed, and for external current in any direction, four horizontal thrusters are controlled to generate a vectored thrust force to encounter the current while minimizing the vehicle's rotation and maintaining its heading. However, for the numerical simulations, the vehicle's hydrodynamic coefficients related to the horizontal plane are derived based on both theoretical and empirically derived formulas. In addition to the simulation, experimental studies in both the water tank and circulating water channel are performed to verify the vehicle's various final performances, including its ability to overcome strong current.

Added Mass of Submerged Bodies Obtained by Forced Oscillation Tests and Numerical Calculations of Potential Flow (수중운동체의 강제동요시험 및 포텐셜 계산에 의한 부가질량 추정)

  • Kim, Dong Jin;Lee, Gyeong Joong;Kwon, Chang Seop;Kim, Yeon Gyu;Park, Jin-Yeong;Jun, Bong-Huan
    • Journal of the Society of Naval Architects of Korea
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    • v.59 no.4
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    • pp.214-224
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    • 2022
  • It is necessary to estimate manoeuvring characteristics of submerged bodies at the design stage in order to ensure the safe operations. In this study, added mass coefficients in the mathematical model of submerged bodies are estimated by captive model tests and numerical calculations. Two kinds of models, MARIN 'BB2'submarine model and AUV (Autonomous unmanned vehicle) model are utilized in the forced oscillation tests. Compared to BB2 submarine, AUV with cylindrical type hull form shows relatively small added masses in roll, pitch, and yaw directions. Next, numerical calculations based on potential theory are performed under the assumption that viscous effects on inertia forces are negligible. Added masses obtained by numerical calculations are in good agreements with forced oscillation test results. And if slow manoeuvres of submerged bodies are presumed, some of velocity coupled terms can be approximated by combinations of added mass coefficients.

Structural and Dynamic Analysis of a Unmanned Cargo Multicopter Using Hybrid Power System (하이브리드 추진 시스템을 이용한 수송용 멀티콥터 무인기의 구조 및 동특성 해석)

  • Kee, Youngjung;Kim, Taekyun
    • Journal of Aerospace System Engineering
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    • v.16 no.5
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    • pp.78-85
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    • 2022
  • Multicopter-type unmanned aerial vehicles (UAV) are increasingly for cargo transportation to mountainous and island regions, image information acquisition in disaster areas, and emergency rescue transport. In order to successfully perform these tasks, the aircraft structure must be able to safely support the loads induced by flight conditions while ensuring the vibration and aeroelastic stability of the prop-rotor. This study introduced a structural analysis model of a 40kg payload multicopter with an engine-generator hybrid power system. The deformation and stress distribution are investigated depending on the load conditions. In addition, the vibration characteristics and aeroelastic stability of the prop-rotor were also presented to flight speed and aircraft pitch angle. The maximum thrust generated by the prop-rotor and the landing load applied to the multicopter under normal and emergency landing conditions were reviewed., It confirmed that the structure could support without failure. In addition, it confirmed that the damping characteristics of each primary locate in the constant region according to the aircraft's flight speed and the prop-rotors rotating speed.

Numerical Investigation of Ground Effect of Dual Ducted Fan Aircraft During Hovering Flight (제자리 비행하는 이중 덕트 팬 비행체의 지면 효과에 대한 수치적 연구)

  • Lee, Yujin;Oh, Sejong;Park, Donghun
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.50 no.10
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    • pp.677-690
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    • 2022
  • By using an actuator disk method based flow solver, aerodynamic analysis is carried out for a dual ducted fan aircraft, which is one of the VTOL compound aircrafts, and its associated ground effect is analyzed. The characteristics and accuracy of the solver for ground effect analysis is evaluated through a comparison with the results obtained from the sliding mesh technique. The aerodynamic performance and flow field characteristics with respect to the distance from the ground are analyzed. As the ground distance decreases, the fan thrust increases, but the deterioration of total normal force and hovering flight efficiency is identified owing to the decrease in the vertical force of the duct, fuselage, and wing. By examining the flow field in the bottom of the fuselage, the ground vortices and fountain flow generated by the interaction of the fan wake and ground are identified, and their influence on the aerodynamic performance is analyzed. The strength and characteristics of outwash with respect to the ground distance and azimuth direction are analyzed through comparison/examination of velocity profile. Influence of the ground effect with respect to collective pitch angle is also identified.

Operability Assessment of a Naval Vessel in Seaways Based on Seakeeping Performance and Operation Scenario (내항 성능과 운용 시나리오에 기반한 함정의 실해역 운항성 평가)

  • Choi, Sungeun;Kim, Kiwon;Kim, Hoyong;Seo, Jeonghwa;Yang, Kyung-Kyu;Rhee, Shin Hyung;Kim, Beomjin
    • Journal of the Society of Naval Architects of Korea
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    • v.59 no.5
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    • pp.252-261
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    • 2022
  • The present study concerns assessing the operability of a surface combatant, based on the Percent-Time-Operable (PTO). For validation of the seakeeping analysis in the regular waves, the model test is first conducted in a towing tank. The seakeeping analysis results in the regular waves are expanded to the irregular waves, considering the wave spectra around the Korean peninsula and in North Pacific. The seakeeping criteria of the surface combatant in transit, combat, replenishment operation, and survival condition are defined by the literature review. An annual operation scenario of the surface combatant in two operation areas, i.e., advance speed and wave direction, are combined with the seakeeping analysis results to assess PTO. The main constraints of operability of the surface combatant are identified as the pitch angle and vertical velocity at the helicopter deck.

Smart Helmet for Vital Sign-Based Heatstroke Detection Using Support Vector Machine (SVM 이용한 다중 생체신호기반 온열질환 감지 스마트 안전모 개발)

  • Jaemin, Jang;Kang-Ho, Lee;Subin, Joo;Ohwon, Kwon;Hak, Yi;Dongkyu, Lee
    • Journal of Sensor Science and Technology
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    • v.31 no.6
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    • pp.433-440
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    • 2022
  • Recently, owing to global warming, average summer temperatures are increasing and the number of hot days is increasing is increasing, which leads to an increase in heat stroke. In particular, outdoor workers directly exposed to the heat are at higher risk of heat stroke; therefore, preventing heat-related illnesses and managing safety have become important. Although various wearable devices have been developed to prevent heat stroke for outdoor workers, applying various sensors to the safety helmets that workers must wear is an excellent alternative. In this study, we developed a smart helmet that measures various vital signs of the wearer such as body temperature, heart rate, and sweat rate; external environmental signals such as temperature and humidity; and movement signals of the wearer such as roll and pitch angles. The smart helmet can acquire the various data by connecting with a smartphone application. Environmental data can check the status of heat wave advisory, and the individual vital signs can monitor the health of workers. In addition, we developed an algorithm that classifies the risk of heat-related illness as normal and abnormal by inputting a set of vital signs of the wearer using a support vector machine technique, which is a machine learning technique that allows for rapid binary classification with high reliability. Furthermore, the classified results suggest that the safety manager can supervise the prevention of heat stroke by receiving feedback from the control system.

duoPIXTM X-ray Imaging Sensor Composing of Multiple Thin Film Transistors in a Pixel for Digital X-ray Detector (픽셀내 다수의 박막트랜지스터로 구성된 듀오픽스TM 엑스선 영상센서 제작)

  • Seung Ik, Jun;Bong Goo, Lee
    • Journal of the Korean Society of Radiology
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    • v.16 no.7
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    • pp.969-974
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    • 2022
  • In order to maximize dynamic range and to minimize image lag in digital X-ray imaging, diminishing residual parasitic capacitance in photodiode in pixels is critically necessary. These requirements are more specifically requested in dynamic X-ray imaging with high frame rate and low image lag for industrial 2D/3D automated X-ray inspection and medical CT imaging. This study proposes duoPIXTM X-ray imaging sensor for the first time that is composed of reset thin film transistor, readout thin film transistor and photodiode in a pixel. To verify duoPIXTM X-ray imaging sensor, designing duoPIXTM pixel and imaging sensor was executed first then X-ray imaging sensor with 105 ㎛ pixel pitch, 347 mm × 430 mm imaging area and 3300 × 4096 pixels (13.5M pixels) was fabricated and evaluated by using module tester and image viewer specifically for duoPIXTM imaging sensor.

Optimal Design and Analysis of Ducted Fan Clutch With or Without Mechanical Lock-up (기계적 잠금장치의 적용여부에 따른 덕티드팬 클러치의 최적설계 및 분석)

  • Su-chul Kim;Jae-seung Kim;Sang-gon Moon;Geun-ho Lee
    • Journal of Aerospace System Engineering
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    • v.17 no.1
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    • pp.10-15
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    • 2023
  • Wet multi-disk clutch, a power switching device of the ducted fan, was optimized and results were analyzed. The clutch was divided into two types depending on whether a mechanical lock-up was applied or not. It was optimized under each design condition. Transfer torque capacity, friction material surface pressure, friction surface temperature, and drag torque were calculated as factors to optimize the clutch. The volume of separator plate and drag torque were used as the objective function for optimization. In the case of Type 1, which did not include a mechanical lock-up, the clutch could be operated regardless of the pitch angle of the ducted fan. However, the outer diameter of the friction surface was doubled, the volume was increased by 5~7 times, and the drag torque was increased by 7~12 times compared to those of Type 2, which included a mechanical lock-up.

Feasibility on Statistical Process Control Analysis of Delivery Quality Assurance in Helical Tomotherapy (토모테라피에서 선량품질보증 분석을 위한 통계적공정관리의 타당성)

  • Kyung Hwan, Chang
    • Journal of radiological science and technology
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    • v.45 no.6
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    • pp.491-502
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    • 2022
  • The purpose of this study was to retrospectively investigate the upper and lower control limits of treatment planning parameters using EBT film based delivery quality assurance (DQA) results and to analyze the results of statistical process control (SPC) in helical tomotherapy (HT). A total of 152 patients who passed or failed DQA results were retrospectively included in this study. Prostate (n = 66), rectal (n = 51), and large-field cancer patients, including lymph nodes (n = 35), were randomly selected. The absolute point dose difference (DD) and global gamma passing rate (GPR) were analyzed for all patients. Control charts were used to evaluate the upper and lower control limits (UCL and LCL) for all the assessed treatment planning parameters. Treatment planning parameters such as gantry period, leaf open time (LOT), pitch, field width, actual and planning modulation factor, treatment time, couch speed, and couch travel were analyzed to provide the optimal range using the DQA results. The classification and regression tree (CART) was used to predict the relative importance of variables in the DQA results from various treatment planning parameters. We confirmed that the proportion of patients with an LOT below 100 ms in the failure group was relatively higher than that in the passing group. SPC can detect QA failure prior to over dosimetric QA tolerance levels. The acceptable tolerance range of each planning parameter may assist in the prediction of DQA failures using the SPC tool in the future.