• Journal of Biosystems Engineering
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• 제39권4호
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• pp.274-282
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• 2014

Purpose: In this study, a hybrid power system was developed for agricultural machines with a 20-KW output capacity, and it was attached to a multi-purpose cultivator to improve the performance of the cultivator, which was evaluated using output tests. Methods: The hybrid system combined heterogeneous sources: an internal-combustion engine and an electric power motor. In addition, a power splitter was developed to simplify the power transmission structure. The cultivator using the hybrid system was designed to have increased fuel efficiency and output power and reduced exhaust gas emissions, while maintaining the functions of existing cultivators. Results: The fuel consumption for driving the cultivator in the hybrid engine vehicle (HEV) mode was 341 g/KWh, which was 36% less than the consumption in the engine (ENG) mode for the same load. The maximum power take off output of the hybrid power system was 12.7 KW, which was 38% more than the output of the internal-combustion engine. In the HEV mode, harmful exhaust gas emissions were reduced; i.e., CO emissions were reduced by 36~41% and NOx emissions were reduced by 27~51% compared to the corresponding emissions in the ENG mode. Conclusions: The hybrid power system improved the fuel efficiency and reduced exhaust gas emissions in agricultural machinery. Lower exhaust gas emissions of the hybrid system have considerable advantages in closed work environments such as crop production facilities; therefore, agricultural machinery with less exhaust gas emissions should be commercialized. However, the high manufacturing cost and complexity of the proposed system are challenges which need to be solved in the future.

• 제어로봇시스템학회논문지
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• 제21권5호
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• pp.447-452
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• 2015

A hybrid power system was developed for agricultural machines with a 20kW output capacity, and it was attached to a multi-purpose cultivator to improve the performance of the cultivator. The hybrid system combined heterogeneous sources: an internal-combustion engine and an electric power motor. In addition, a power splitter was developed to simplify the power transmission structure. The cultivator using a hybrid system was designed to have increased fuel efficiency and output power and reduced exhaust gas emissions, while maintaining the functions of existing cultivators. The fuel consumption for driving the cultivator in the hybrid engine vehicle (HEV) mode was 341g/kWh, which was 36% less than the consumption in the engine (ENG) mode for the same load. The maximum power take off output of the hybrid power system was 12.7kW, which was 38% more than the output of the internal-combustion engine. In the HEV mode, harmful exhaust gas emissions were reduced; i.e., CO emissions were reduced by 36~41% and NOx emissions were reduced by 27~51% compared to the corresponding emissions in the ENG mode. The hybrid power system improved the fuel efficiency and reduced exhaust gas emissions in agricultural machinery. The hybrid system's lower exhaust gas emissions have considerable advantages in closed work environments such as crop production facilities. Therefore, agricultural machinery with less exhaust gas emissions should be commercialized.

• 한국항행학회논문지
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• 제23권4호
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• pp.265-272
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• 2019

본 논문에서는 우리나라에서 가장 교통이 혼잡한 수도권에서의 출퇴근 시나리오를 선정하고, 미국연방항공국에서 개발한 AEDT (aviation environmental design tool) 소트프웨어를 사용하여 PAV (personal air vehicle) 운용 시 발생하는 소음분석을 수행하였다. 미항공우주국에서 선보인 ODM (on-demand mobility) 개념에서 PAV를 운용하기 위한 안전성 다음으로 소음이 중요한 고려요소이다. PAV의 정확한 NPD (noise power distance) 데이터가 공개되어 있지 않는 문제를 해결하고자 eVTOL (electric vertical take off and landing) PAV와 같은 저소음 PAV를 민간용 헬리콥터로 모델링하여 소음 분석을 수행하고, 해당지역의 주거 적합성을 예측하였다. 전기추진과 같은 소음 감소 기술의 적용은 소음 노출 레벨을큰 폭으로 감소시켰고, 수도권내에서 소음문제 없이 PAV를 이용한 출퇴근이 실현 가능하다는 결론에 도달하였다.

• 한국산학기술학회논문지
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• 제22권5호
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• pp.15-21
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• 2021

전기동력을 기반으로 하는 전기추진비행기는 화석연료 사용에 따른 CO2 발생을 줄여서 지구온난화에 대응할 수 있고 에너지의 효율적 사용을 통해서 장기적으로 비행기의 운용비용을 줄일 수 있다. 이런 이유로, 미국과 유럽연합 등 선진 항공국가에서는 미래의 완전한 전기비행기 구현을 위한 혁신적 기술개발을 선도적으로 진행하고 있다. 현재, 국내에서는 기존 2인승 엔진 비행기를 전기추진비행기로 개조하는 연구개발이 진행 중에 있다. 개조대상 비행기는 KLA-100으로써 엔진 장착공간과 부조종사 공간을 활용하여 배터리 팩을 설치하고, 30분의 비행시험을 목표로 하고 있다. 해당 목표를 달성하기 위해서는 배터리 성능이 보장되어야 하는데, 개조 비행기에는 비출력 150Wh/kg, 중량 200kg 그리고 C-rate 3~4인 리튬-이온(Li-ion) 배터리가 설치된다. 본 논문에서는 설계된 배터리 팩이 장착된 전기추진비행기의 비행 가능성을 사전에 점검하고자 한다. 이를 위해 30분 비행 프로파일을 시동 및 활주단계, 이륙단계, 상승단계, 순항단계, 하강단계, 착륙 및 활주단계로 구분하고, 각 단계에서 요구되는 배터리 용량을 계산하여 최종 목표로 하고 있는 30분 비행 가능 여부를 평가하였다. 또한, 비행속도에 따른 비행 가능시간과 항속거리를 분석하여 전기추진비행기용 배터리 팩의 비행성능을 파악하였다.

• 한국해양공학회지
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• 제35권3호
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• pp.229-237
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• 2021

A numerical hydrodynamic performance analysis of the pitch-type multibody wave energy converter (WEC) is carried out based on both linear potential flow theory and computational fluid dynamics (CFD) in the unidirectional wave condition. In the present study, Salter's duck (rotor) is chosen for the analysis. The basic concept of the WEC rotor, which nods when the pressure-induced motions are in phase, is that it converts the kinetic and potential energies of the wave into rotational mechanical energy with the proper power-take-off system. This energy is converted to useful electric energy. The analysis is carried out using three WEC rotors. A multibody analysis using linear potential flow theory is performed using WAMIT (three-dimensional diffraction/radiation potential analysis program), and a CFD analysis is performed by placing three WEC rotors in a numerical wave tank. In particular, the spacing between the three rotors is set to 0.8, 1, and 1.2 times the rotor width, and the hydrodynamic interaction between adjacent rotors is checked. Finally, it is confirmed that the dynamic performance of the rotors slightly changes, but the difference due to the spacing is not noticeable. In addition, the CFD analysis shows a lateral flow phenomenon that cannot be confirmed by linear potential theory, and it is confirmed that the CFD analysis is necessary for the motion analysis of the rotor.

• 한국해양공학회지
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• 제29권2호
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• pp.191-198
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• 2015

In this study, we proposed a new type of dual-buoy wave energy converter (WEC) exploiting multi-resonance and analyzed the experimental results from a model test in a 2-D wave flume. A dual-buoy WEC using multi-resonance has two advantages: high efficiency at the resonant frequencies and the potential to extend the frequency range available to extract wave power from the WEC. The suggested WEC was composed of an outer buoy and an inner buoy sliding vertically inside the outer buoy. As the power take-off device, a linear electric generator (LEG) consisting of permanent magnets and coils fixed at each buoy was adopted. Electricity was produced by the relative heave motion between the two buoys. To search for the optimal shape of a dual-buoy WEC, we conducted experiments on the heave motion of a two-body system in regular waves without an LEG installed. Model tests with six combinations of experimental models were conducted in order to find the motion characteristics of a dual-buoy WEC. It was found that model 2, which included a ring-shaped appendage to move the resonant frequency of the outer buoy toward a high value, showed a higher relative heave response amplitude operator (RAO) curve than model 1. In addition, the double-peak shape of the heave RAO curve shown for model 2 indicated the extension of the frequency range for extracting wave power in irregular waves.

• Journal of Biosystems Engineering
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• 제39권1호
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• pp.21-33
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• 2014

Background: Significant technological development and changes happened in the tractor industries. Contrariwise, the test procedures of the major standard development organizations (SDO's) remained unchanged or with a little modification over the years, demanding new tractor test standards or improvement of existing ones for tractor performance, safety, and comfort. Purpose: This study focuses on reviewing the research trends regarding performance, safety and comfort evaluation of agricultural tractors. Based on this review, few recommendations were proposed to revise or improve the current test standards. Review: Tractor power take-off power test using the DC electric dynamometer reduced human error in the testing process and increased the accuracy of the test results. GPS signals were used to determine acceleration and converted into torque. High capacity double extended octagonal ring dynamometer has been designed to measure drawbar forces. Numerical optimization methodology has been used to design three-point hitch. Numerous technologies, driving strategies, and transmission characteristics are being considered for reducing emissions of gaseous and particulate pollutants. Engine emission control technology standards need to be revised to meet the exhaust regulations for agricultural tractors. Finite Element Analysis (FEA) program has been used to design Roll-Over Protective Structures (ROPS). Program and methodology has been presented for testing tractor brake systems. Whole-body vibration emission levels have been found to be very dependent upon the nature of field operation performed, and the test track techniques required development/adaptation to improve their suitability during standardized assessment. Emphasizes should be given to improve visibility and thermal environment inside the cab for tractor operator. Tractors need to be evaluated under electromagnetic compatibility test conditions due to large growing of electronic devices. Research trends reviewed in this paper can be considered for possible revision or improvement of tractor performance, safety, and comfort test standards.

• 한국수소및신에너지학회논문집
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• 제23권4호
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• pp.300-309
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• 2012

Long endurance is a key issue in the application of unmanned aerial vehicles. This study presents feasibility test results when fuel cell system as an alternative to the conventional engine is applied for the power of the UAV after the 150W fuel cell system is developed and packaged to the 1/4 scale super cub airplane. Fuel cell system is operated by dead-end method in the anode part and periodically purged to remove the water droplet in flow field during the operation. Oxygen in the air is supplied to the stack by the two air blowers. And fuel cell stack is water cooled by cooling circuit to dissipate the heat generated during the fuel cell operation. Weight balance is considered to integrate the stack and balance of plant (BOP) in package layout. In flight performance test, we demonstrated 4 times standalone take-off and landing. In the laboratory test simulating the flight condition to quantify the energy flow, the system is analyzed in detail. Sankey diagram shows that electric efficiency of the fuel cell system is 39.2%, heat loss 50.1%, parasitic loss 8.96%, and unreacted purged gas 1.67%, respectively compared to the total hydrogen input energy. Feasibility test results show that fuel cell system is high efficient and appropriate for the power of UAV.

• 한국한의학연구원논문집
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• 제9권2호
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• pp.121-130
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• 2003

The goal of this study is construction and efficacy evaluation of MPC-25 (Magnetic Pain Control-25), a medical device using magnetic stimulation. MPC-25 consists of a main body containing power supply and control module and a bed containing magnetic core and coil. In distinction from electric pain control medical devices, magnetic pain control system is non-contact, so the patients need not take off their clothes to be treated. High amplitude current pulses are applied to a magnetic coil and induce time varying magnetic field generating eddy current in a conductor like human body. Clinical efficacy test was performed in patients suffering from musculoskeletal pain of lumbar, shoulder and joint. Degree of pain before and after treatment for 30 minutes was compared using Visual Analogous Scale. As a result, 14 cases out of 20 showed decreased pain perception, so the rate of efficacy is 70%. Reduction of pain perception was statistically significant (P=0.001 by Wilcoxon Signed Rank Test).

• 한국항행학회논문지
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• 제25권1호
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• pp.29-39
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• 2021

대도시 도심의 교통 정체를 해결하기 위한 방법의 하나로 전기수직이착륙 개인항공기(eVTOL PAV)를 활용한 도심항공 모빌리티(UAM)의 관심이 증가하고 있다. 도심항공 모빌리티에 사용할 비행체인 eVTOL은 추진방식에 따라 복합형, 틸트 로터형, 틸트 날개형, 틸트 덕티드 팬형, 멀티콥터형으로 분류된다. 본 연구에서는 멀티콥터형인 에어버스사의 시티에어버스를 기본 모델로 주어진 임무 형상에 맞게 역설계 기법을 사용하여 기본 개념설계를 수행하였다. 공력해석 프로그램인 OpenVSP를 사용하여 표면적과 양항비, 항력계수를 계산하였다. 각 임무 구간별 소요되는 동력을 계산하였고, 그에 맞는 배터리와 모터를 비교하여 선정하였다. 또한 eVTOL 구성품별 중량을 추정하여 전체 총 중량을 예측하였다.