• 한국안전학회지
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• 제13권1호
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• pp.40-46
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• 1998

This paper is presented that theoretical optimization design method in order to consider mass reduction for the structural safety In this paper, it described methods for reducing vibration in structural safety by the determination of the optimum sizes and locations of tunning masses through formal mathematical optimization techniques. The optimization procedure which employs the tunning masses and corresponding locations is developed. Design variables are systematically changed to achieve low values of shear without a large mass penalty. Three optimization methods ire developed and tested. The first is based on minimizing the modal shaping parameter which indirectly reduce the modal shear amplitudes corresponding to each harmonic of airload. The second method reduces these amplitudes directly and the third method reduces the shear as a function of time during a revolution of the blade. The first method works well for reducing the shear for one mode responding to a single harmonic of the airload but has been found in some bases to be ineffective for more than one mode.

• Journal of Mechanical Science and Technology
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• 제18권1호
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• pp.145-152
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• 2004

Effects of various baffle designs on acoustic characteristics in combustion chamber are numerically investigated by adopting linear acoustic analysis. A hub-blade configuration with five blades is selected as a candidate baffle and five variants of baffles with various specifications are designed depending on baffle height and hub position. As damping parameters, natural-frequency shift and damping factor are considered and the damping capacity of various baffle designs is evaluated. Increase in baffle height results in more damping capacity and the hub position affects appreciably the damping of the first radial resonant mode. Depending on baffle height, two close resonant modes could be overlapped and thereby the damping factor for one resonant mode is increased exceedingly. The present procedure based on acoustic analysis is expected to be a useful tool to predict acoustic field in combustion chamber and to design the passive control devices such as baffle and acoustic resonator.

• 한국항공우주학회지
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• 제33권9호
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• pp.16-26
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• 2005

본 연구에서는 틸트로터 항공기 개념을 채택하고 있는 스마트무인기의 프롭로터 공력형상 설계를 수행하였다. 틸트로터 항공기의 프롭로터는 단일 형상의 로터가 회전익과 고정익의 두 가지의 비행모드에서 운용되어야 하므로 회전익으로서의 로터와 고정익으로서의 프로펠러 요구 성능을 동시에 만족할 수 있도록 형상 설계가 이루어 져야 한다. 프롭로터의 공력형상 설계는 로터의 성능, 비행체의 공력성능, 그리고 엔진의 성능데이터를 결합하여 이루어 졌다. 모멘텀-깃요소 이론에 바탕을 둔 로터의 성능해석코드에 대한 검증은 TRAM 데이터와의 비교를 통해 이루어 졌다. 프롭로터의 공력형상 설계는 틸트로터 항공기의 고정익과 회전익 성능을 동시에 만족할 수 있는 형상을 구현하기 위하여 다양한 형태의 성능 맵이 작성되었고, 이들 선도 위에서 최적의 성능이 구현될 수 있는 성능 및 형상 파라메타가 결정되도록 하였다.

• 전력전자학회논문지
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• 제11권4호
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• pp.349-360
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• 2006

이중여자 유도형 풍력발전 시스템은 다른 풍력발전 시스템에 비하여 에너지 변환 효율이 우수하고 전력변환 장치의 용량이 작아도 되는 특성이 있다. 이러한 특징을 살리기 위해서는 풍력발전 시스템에 입력되는 에너지의 변화를 고려하여 발전기의 제어기를 설계해야 한다. 본 논문에서는 상위 제어기와 하위 제어기로 구분하여 이중여자 유도 발전기의 제어기를 설계하였다. 상위 제어가는 풍력발전 시스템에 입력되는 에너지가 변화함에 따라서 발전기의 운전모드를 결정하고 제어 기준값을 계산한다. 발전기의 운전모드는 최저 속도 제어와 가변 토크 제어, 그리고 토크 제한 모드로 구성된다. 하위 제어기는 상위 제어기의 지령에 따라서 발전 시스템의 전류를 제어한다. 또한 본 논문에서는 3kW급 권선형 유도기를 사용한 이중여자 유도형 풍력발전기의 시뮬레이터를 제작하였다. 설계한 제어기는 시뮬레이터에 적용하여 실험적으로 검증하였다.

• 한국정밀공학회지
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• 제22권3호
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• pp.46-51
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• 2005

The vacuum cleaner motor runs at very high speed for suction power. Specially, motor power is provided by the impeller being rotated at very high speed. The centrifugal fan consists of the impeller, the diffuser, and the circular casing. Due to the high rotating speed of the impeller and small gap distance between the impeller and the diffuser, the level of noise in the centrifugal fan is at BPF(Blade Passage Frequency) and its harmonic frequencies. In order to calculate the sound pressure of centrifugal fan, unsteady flow data are needed. The cause of noise is obtained by dividing the fluid noise by exhaust flow of fan and vibration noise by rotational vibration of vacuum cleaner fan motor. Until now, an accelerometer has been used to measure vibration. However, it can not measure vibration in some parts of brush and commutator because of motor construction and 3-D vibrating mode. This study was conducted to perform accurate analysis of vibration and aerodynamic sound for fan motor in a vacuum cleaner using a laser vibration analyzer. A silent fan motor can be designed using the data measured in this study.

• Journal of Advanced Marine Engineering and Technology
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• 제31권6호
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• pp.768-776
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• 2007

In this study, axial vibration analysis has been conducted on a propulsion and lift shafting system for an air cushion vehicle using ANSYS code. The shafting system is totally flexible multi-elements system including wood composite material of air propeller. aluminum alloy of lift fan and thin walled shaft with flexible coupling. The analysis calculated the axial natural frequencies and mode shapes of the shafting system taking into account an equivalent mass-elastic model for shafting system as well as the three-dimensional models for propeller blade and fan impeller. Such a flexible shafting system has very intricate vibrating characteristics and especially, axial natural frequencies of flexible components such as propeller blade and impeller of lift fan can be lower to the extent that causes a resonance in the range of operating revolution. The results for axial vibration analysis are presented and compared with the results of axial vibration test for lift fan conducted during Sea Trial.

• 한국소음진동공학회논문집
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• 제14권11호
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• pp.1129-1136
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• 2004

The structural modification to install a heavy sensor was made at the front extremities of the foreign-produced helicopter operated in the Korea Navy Mounting the sensor directly to the nose structure is unlikely to be practical because it lowers a dynamic mode of the airframe close to rotor blade passing frequencies, leading to increased helicopter vibration. Unfortunately we have no information on dynamic characteristics of the imported helicopter. So the experimental modal model derived from shake testing on the overall airframe of a working helicopter was used to solve the sensor Installation problems. The sensitivity analysis was done to evaluate what the best of modification woo)d be. Simple ID model and experimental modal data for mount system with sensor were Incorporated into overall dynamic model to assess the effects of the sensor installation on helicopter. Modal testing for the modified helicopter shows that the airframe modes are sufficiently displaced from rotor passing frequencies. The mount system has been proven fight to be sufficiently stable to meet vibration-level requirement for all required operational profiles.

• 한국소음진동공학회논문집
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• 제23권3호
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• pp.267-273
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• 2013

Recently, turbine-generators have been replaced for the integrity reinforcement and the efficiency improvement, also, the blade's failures of LP turbines due to torsional vibration have been reported. Excessive torsional vibrations can result in failures of components. The severity of torsional oscillations and stress depends upon the separation margin between the excitation frequencies and torsional natural frequencies. Therefore it is needed to measure the torsional natural frequencies after replacement of the components to conform the separation margin of torsional natural frequencies. In this study torsional vibration measurements were performed after LP turbine and generator replacement and the torsional natural frequencies for the turbine-generator train were calculated to evaluate the effects of generator replacement on torsional natural frequencies of turbine-generator train. It is expected that these evaluation results will be used effectively to identify the root causes of torsional vibration problems.

• 한국생산제조학회지
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• 제21권1호
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• pp.102-108
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• 2012

A study of terahertz waves (T-ray) was made for the nondestructive evaluation of FRP (Fiber reinforced plastics) composite materials. The to-be-used systems were time domain spectroscopy (TDS) and continuous wave (CW). The composite materials investigated include both turbine blades of wind energy (non-conducting polymeric composites) and conducting carbon fiber composites. Terahertz signals in the TDS mode resembles that of ultrasound; however, unlike ultrasound, a terahertz pulse was not able to detect a material with conductivity. This was demonstrated in CFRP (Carbon fiber reinforced plastics) laminates. Refractive index (n) was defined as one of mechanical properties; so a method was solved in order solve the "n" in the material with the cut parts of the turbine blades of wind energy. The defects and anomalies investigated by terahertz radiation were foreign material inclusions and simulated disband. Especially, it is found that the T-ray went through the turbine blade with greater thickness (about 90mm).

• 농업과학연구
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• 제22권1호
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• pp.11-23
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• 1995

The CAD/CAM system for the manufacturing automation is the newest technology in mechanical engineering area and becomes the important research subject nowadays. Most of all hardwares and softwares for the CAD/CAM system used in the our manufacturing companies such as automobile company are developed by the foreign country and the purchasing price of them is very expensive but their applicability to a certain area is very limited. This study was conducted to develope a CAD/CAM system for the design and the automatic manufacturing of the iron pattern shaped with 3 - dimensional free curved surface, and to test its applicability to the design and the manufacturing of the rotary blade. The results obtained from the study are as follow; 1. The CAD system which can process graphic procedures from the free curved surface shaped data was developed with personal computer. 2. The CAM main program was developed. This main program could produce CL data from CAD data file by checking the tool interference according to the cutting mode. 3. The sub. program which can simulate the tool trace from the CL data was developed. 4. The post processor for the Deckel FP2NC NC milling machine from CL data file was developed and the sub program could transmit NC program through modem to NC milling machine was developed. 5. The developed CAM system seemed to be applicable to any other system. Because the measuring results of the cross sectional thickness of the plastic model from the manufacturing iron pattern by the system showed that this system could properly check the tool interference. 6. In took 75~90 hours to manufacture two iron patterns of rotary blade. For the sake of convenience in applying to the other systems, this system was developed in BASIC and FORTRAN computer language and minimum portion of machine language as possible.