• Structural Engineering and Mechanics
• /
• 제37권6호
• /
• pp.671-684
• /
• 2011

Deciding on an optimal sensor placement (OSP) is a common problem encountered in many engineering applications and is also a critical issue in the construction and implementation of an effective structural health monitoring (SHM) system. The present study focuses with techniques for selecting optimal sensor locations in a sensor network designed to monitor the health condition of Dalian World Trade Building which is the tallest in the northeast of China. Since the number of degree-of-freedom (DOF) of the building structure is too large, multi-modes should be selected to describe the dynamic behavior of a structural system with sufficient accuracy to allow its health state to be determined effectively. However, it's difficult to accurately distinguish the translational and rotational modes for the flexible structures with closely spaced modes by the modal participation mass ratios. In this paper, a new method of the OSP that computing the mode shape matrix in the weak axis of structure by the simplified multi-DOF system was presented based on the equivalent rigidity parameter identification method. The initial sensor assignment was obtained by the QR-factorization of the structural mode shape matrix. Taking the maximum off-diagonal element of the modal assurance criterion (MAC) matrix as a target function, one more sensor was added each time until the maximum off-diagonal element of the MAC reaches the threshold. Considering the economic factors, the final plan of sensor placement was determined. The numerical example demonstrated the feasibility and effectiveness of the proposed scheme.

• 농업과학연구
• /
• 제51권2호
• /
• pp.133-146
• /
• 2024

Selection of gear reduction ratio is essential for machine design to ensure suitable power and speed during agricultural operations. The goal of the study was to evaluate the gear reduction ratio for a 1.6 kW four-wheel-drive (4WD) multi-purpose agricultural electric vehicle platform using workload data under different off-road conditions. A data acquisition system was fabricated to collect workload (torque) of the vehicle acting on the gear shaft. Field tests were performed under three driving surfaces (asphalt, concrete, and grassland), payload operations (981, 2,942, and 4,903 N), and slope conditions (0 - 4°, 4 - 8°, and 8 - 12°), respectively. Commercial speed reduction gear phases were attached to the input shaft of the vehicle powertrain. The maximum required torque was recorded as 37.5 Nm at a 4,903 N load with 8 - 12° slope levels, and the minimum torque was 12.32 Nm at 0 - 4° slope levels with a 981 Nm load for a 4 km/h speed on asphalt, concrete, and grassland roads. Based on the operating load condition and motor torque and rotational speed (TN) curve, the minimum and maximum gear reduction ratios were chosen as 1 : 50 and 1 : 64, respectively. The selected motor satisfied power requirements by meeting all working torque criteria with the gear reduction ratios. The chosen motor with a gear reduction ratio of 1 : 50 was suitable to fit with the motor T-N curve, and produced the maximum speeds and loads needed for driving and off-road activities. The findings of the study would assist in choosing a suitable gear reduction ratio for electric vehicle multi-purpose field operations.

• 한국자동차공학회논문집
• /
• 제23권1호
• /
• pp.18-24
• /
• 2015

In this study, a $CO_2$ air-conditioning system was investigated with different types of electrically driven compressors, parallel flow type gas cooler, four-pass type evaporator, internal heat exchanger integrated with accumulator, and electric expansion valve. The experimental study was conducted under various operating conditions (ie., different rotational compressor speeds, air inlet temperatures and air velocity coming into heat exchangers). The experimental results showed the cooling capacity was 3.5kW at $35^{\circ}C$ ambient temperature when the vehicle was idle (ie., the worst condition for cooling off the gas cooler). In terms of performance effect of the compressor, the e-RP model had a slightly better cooling capacity and coefficient of performance than the e-GR model under the same test conditions. An experimental equation for optimum cooling-performance control was also suggested based on the results. A high-pressure control algorithm for the super critical cycle was determined to achieve both maximum cooling performance and efficient energy consumption. The results from the experimental equation coincided with those of previous experimental studies.

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

• 대한방사선치료학회지
• /
• 제29권1호
• /
• pp.7-18
• /
• 2017

목 적: 영상유도를 통한 6DoF Couch의 이동 정확성의 검증을 위해 QA Set을 제작하였고, 그 유용성을 평가하였다. 대상 및 방법: 6DoF Couch와 CBCT가 설치된 두 대의 선형가속기를 대상으로 하였으며, 자체 제작한 YCC QA Set을 이용하여 수평수직(Translation; TX, TY, TZ)과 회전(Rotation, Pitch; RX, Roll; RY, Yaw; RZ) 여섯방향의 Off-Set 값이 설정된 Penta-Guide Phantom의 CBCT영상을 각각 15회에 걸쳐 획득하였다. 이를 통해 기준영상(Reference Image)과 보정영상(Registration Image)을 비교하였으며, 보정된 6DoF Couch의 이동정확성을 실측하여 오차를 분석하였다. 결 과: 기준영상과 보정영상의 Air Cavity에 해당하는 Pixel들은 모두 30에서 66 사이에 포함되어 보정정확도가 높게 나타났다. 6DoF Couch의 Off-set의 보정 결과 값과 실측치의 비교에서 수평수직방향의 오차는 TX방향은 $0.25{\pm}.18mm$ TY방향은 $0.25{\pm}.25mm$ TZ방향에서 $0.36{\pm}.2mm$로 나타났다. 그리고 회전방향의 오차는 RX방향은 $0.18{\pm}.08^{\circ}$ RY방향은 $0.26{\pm}.09^{\circ}$ RZ방향에서 $0.11{\pm}.08^{\circ}$로서, 임의의 값에 대하여 정확하게 보정되었다. 결 론: YCC QA Set을 이용해 매우 간단한 방법으로 6DoF Couch의 수평수직방향뿐 아니라 회전방향의 오차에 대한 검증을 할 수 있었으며, 이는 6DoF Couch의 Daily IGRT QA를 수행함에 있어서 유용할 것이라 사료된다.

• 한국기계가공학회지
• /
• 제20권8호
• /
• pp.67-73
• /
• 2021

In this study, we installed forward and reverse rotation rotavators on a tractor to measure the load in the field and analyze the power consumed. The rotavator is attached to the rear of the tractor and transmits the power applied from the power take off (PTO) of the tractor to the rotating shaft of the rotavator, and it plows or reverses the soil according to the rotational direction of the rotating shaft. Depending on the rotational direction of the rotavator, the power consumed in the tractor engine and the power transmitted to the tractor axle and rotavator also vary, thus, research of load and power is an essential factor in designing the system. As a field test results, 84.1-93.5% power was consumed by the forward rotation rotavator, and 37.8-57.5% power was consumed by the reverse rotation rotavator. In addition, depending on the rotation direction of the rotavator, the power consumed by the tractor was in the order of PTO and axle. Based on the research results, development of reliable rotavator systems would be possible in the future research.

• 한국정보전자통신기술학회논문지
• /
• 제13권5호
• /
• pp.452-459
• /
• 2020

전동 엑추에이터는 사용자의 명령 입력 신호(열림/닫힘/정지)를 받아 엑추에이터 내부의 각종 센서(밸브의 위치, 회전력, 모터의 상태 등)들의 상태를 확인하고 모터를 정/역 제어하여 밸브를 개폐하고 엑추에이터(밸브)의 현재 상태를 출력하는 장치로 댐, 발전소, 상하수도 시설, 송유관 시설 등 다양한 분야에서 사용하는 장치이다. 전동 엑추에이터가 발전소 등에 설치되어 가동 중 문제가 발생할 경우 경제적으로 큰 손실이 발생할 수 있으므로 시스템의 신뢰성이 매우 중요하다. 본 연구에서는 전동 엑추에이터의 안전성을 높이기 위해 소프트웨어적으로 발생할 수 있는 신뢰성 문제를 하드웨어적으로 ON/OFF 시간 설정이 가능한 전동 엑추에이터 컨트롤 장치 개발을 진행하였다. 또한 전동 엑추에이터 제어 장치 개발 환경은 Xilinx 사의 Spartan7 FPGA와 Altium 툴을 활용하여 개발하였다.

• 대한설비공학회:학술대회논문집
• /
• 대한설비공학회 2009년도 하계학술발표대회 논문집
• /
• pp.167-171
• /
• 2009

We conducted performance test of a 350 kW class wood pellet boiler installed at a dormitory whose total area is $1,354\;m^2$. The maximum heating capacity of the boiler is 350 kW(300,000 kcal/kg). The wood pellet boiler consists of 3 parts; boiler, hot water storage tank and wood pellet storage tank. In testing the boiler, we shut off hot water utility supply and open up floor heating water system in order to measure exact value of the heating output of the wood pellet boiler. To determine the efficiency and heating output of the wood pellet boiler, we measured mass flow rate of wood pellet, the lower heating value(LHV) of the wood pellet, mass flow rate and temperature of water for floor heating and so on. We measured the mass flow rate of fuel, wood pellet with respect to rotational speed of auger, wood pellet feeding screw. We also measured the flue gas concentration of the wood pellet boiler by using a gas analyser. The result shows that the efficiency of the wood pellet boiler is 80.6% based on lower heating value at 124 kW of heating output. At this condition, O2 concentration of the flue gas is 6.0%, CO and NOx concentrations are 85 and 102 ppm.

• 한국해양공학회지
• /
• 제18권5호
• /
• pp.15-21
• /
• 2004

An edge tone is the discrete tone or narrow-band sound produced by an oscillating free shear layer, impinging on a rigid surface. In this paper, we present a 2-D edge tone to predict the frequency characteristics of the discrete oscillations of a jet-edge feedback cycle, using the finite difference lattice Boltzmann method (FDLBM). We use a modified version of the lattice BGK compressible fluid model, adding an additional term and allowing for longer time increments, compared to a conventional FDLBM, and also use a boundary fitted coordinates system. The jet is chosen long enough in order to guarantee the parabolic velocity profile of the jet at the outlet, and the edge consists of a wedge with an angle of ${\alpha}$ = 23. At a stand-off distance, the edge is inserted along the centerline of the jet, and a sinuous instability wave, with real frequency, is assumed to be created in the vicinity of the nozzle and propagates towards the downstream. We have succeeded in capturing very small pressure fluctuations, resulting from periodical oscillations of a jet around the edge. The pressure fluctuations propagate with the speed of sound. Its interaction with the wedge produces an non-rotational feedback field, which, near the nozzle exit, is a periodic transverse flow, producing the singularities at the nozzle lips.

• 항공우주기술
• /
• 제12권2호
• /
• pp.193-201
• /
• 2013

프로펠러는 인간동력 항공기 추진시스템의 중요한 구성품이다. 높은 프로펠러 효율을 얻기 위하여 프로펠러는 큰 지름을 가지고 느리게 구동된다. 프로펠러는 인간동력 항공기용 프로펠러 설계 프로그램을 사용하여 설계되었다. 프로펠러의 피치는 지상에서 조정이 가능하다. 본 논문에서는 여러 가지 변수에 대하여 설계에 사용된 동일한 프로그램을 통하여 프로펠러의 성능 해석을 수행하였다. 또한, 파일롯의 체력이나 비행속도의 변화에 따른 탈 설계점 해석도 수행하였다. 설계된 프로펠러는 카본 복합재의 초경량 구조로 제작되어 총 950g의 무게로 제작되었다. 제작된 프로펠러는 아이언 버드에서의 지상 성능 시험을 통하여 속도 및 동력을 측정하고 튜닝을 수행하여 실기에 장착되어 최종적으로 291 m 비행에 성공하였다.