• Wind and Structures
• /
• 제29권6호
• /
• pp.431-440
• /
• 2019

The aim of this study was to explore the influence of structure coupling effect on structural damping of blade based on the blade vibration characteristic. For this purpose, the scaled blade model of NREL 5 MW offshore wind turbine was processed and employed in the wind tunnel test to validate the reliability of theoretical and numerical models. The attenuation curves of maximum displacement and the varying curves of equivalent damping coefficient of the blade under the rated condition were respectively compared and analyzed by constructing single blade model and whole machine model. The attenuation law of blade dynamic response was obtained and the structure coupling effect was proved to exert a significant influence on the equivalent damping coefficient. The results indicate that the attenuation trend of the maximum displacement response curve of the single blade varies more obviously with the increase of elastic modulus as compared to that under the structure coupling effect. In contrast to the single blade model, the varying curve of equivalent damping coefficient with the period is relatively steep for the whole machine model. The findings are of great significance to guide the structure design and material selection for wind turbine blades.

• 한국음향학회지
• /
• 제37권5호
• /
• pp.300-308
• /
• 2018

자동차 실내음에 대한 다양한 외부 공력 소음원들의 기여도 분석은 저소음 자동차를 개발하기 위해 단순히 외부 공력 소음원들을 파악하는 것보다 개발 효율성 측면에서 더 중요하다. 파악된 외부 공력 소음원들의 실내음 기여도를 분석하기 위하여 촐레스키 분리(Cholesky Decomposition, CD) 방법이라는 새로운 기법을 활용하여 전체 실내 소음 스펙트럼을 다수의 스펙트럼으로 분리하였다. 이를 통해 분리된 각각의 스펙트럼은 실내 소음에 대한 특정한 개별 소음원들의 기여도로 분석될 수 있다. 이 방법을 검증하기 위해 세가지 실험들이 수행되었다. 더 나아가 CD에 기초한 실내음 기여도 분석 방법은 실차 무향 풍동에서 마이크로폰 어레이를 통한 외부 소음원 가시화 결과와 결합하여 바람소리 개발 효율성을 향상시키는 데 활용이 가능한 지를 2개의 스피커 소음원 실험을 통해 검증하였다.

• 한국전기전자재료학회논문지
• /
• 제17권10호
• /
• pp.1049-1055
• /
• 2004

Chemical Mechanical Polishing (CMP) is referred to as a three body tribological system, because it includes two solids in relative motion and the CMP slurry. On the assumption that the abrasives between the pad and the wafer could be a major reason not only for the friction force but also for material removal during polishing, the friction force generated during CMP process was investigated with the change of abrasive size and concentration of CMP slurry. The threshold point of average coefficient of friction (COF) with increase in abrasives concentration during interlayer dielectric (ILD) CMP was found experimentally and verified mathematically based on contact mechanics. The predictable models, Mode I (wafer is in contact with abrasives and pad) and Mode II (wafer is in contact with abrasives only), were proposed and used to explain the threshold point. The average COF value increased in the low abrasives concentration region which might be explained by Mode I. In contrast the average COF value decreased at high abrasives concentration which might be regarded to as Mode II. The threshold point observed seemed to be due to the transition from Mode I to Mode II. The tendency of threshold point with the variation of abrasive size was studied. The increase of particle radius could cause contact status to reach transition area faster. The correlation between COF and material removal rate was also investigated from the tribological and energetic point of view. Due to the energy loss by vibration of polishing equipment, COF value is not proportional to the material removal rate in this experiment.

• Journal of Biosystems Engineering
• /
• 제30권4호
• /
• pp.210-219
• /
• 2005

This study was conducted to solve the problem of crawled spinach harvesting that had been mainly done by manpower on the outdoor fields during the winter season. Moreover, there are not enough workers available for farming at most of rural areas in Korea because farming is getting hard and the number of old-aged workers is increasing. In order to find appropriate methods of digging, picking and collecting of spinach, the tests were examined outdoors. A prototype was designed based on the results of the tests and then fabricated for digging, picking-up and then collecting in continuous operation for harvesting spinach planted in the outdoor fields. In the field test with the prototype, the vibration intensity transmitted to the driver by vibrating blade was low while the vibrating blade reduced digging power by $46\%$ compared to that of the fixed blade. The spinach loss was found to be as low as $0.7\%$ in the condition of digging depth of 40 mm, cam rotational velocity of 748 rpm, and blade amplitude of 16.5 m. The working performance of the prototype spinach harvester was found to be 3.8 hour/10a resulting in $96\%$ of labor saving and $85\%$ of operating cost compared to the conventional manual harvesting.

• Journal of Biosystems Engineering
• /
• 제39권3호
• /
• pp.158-165
• /
• 2014

Purpose: The objective of this paper was to compare test standards regarding the performance and safety of agricultural tractors to identify the differences in test conditions, measurement tolerances, and test procedures. Based on the comparison, some recommendations were proposed for possible revisions or improvements to current tractor test standards. Methods: The test standards and codes of major standards development organizations (SDOs), such as the Organization for Economic Cooperation and Development (OECD), the International Organization for Standardization (ISO), the American Society of Agricultural and Biological Engineers (ASABE), EC type approval, and the board of actions of the Nebraska Tractor Test Laboratories (NTTL), were selected and analyzed. Comparison of the test standards: The ISO provides references for fuel and lubricants for tractor tests, and the OECD provides additional measurements for calculating fuel consumption characteristics during the power take-off (PTO) tests. The ISO, EC type approval, and the ASABE provide PTO protective device and the safety requirements. During drawbar power tests, seven transmission ratios are selected for fully automatic transmissions, according to the OECD. In case of hydraulic lift tests, ISO 789-2 and OECD Code 2 advise the use of a static lift force, while SAE J283 advises the use of additional dynamic lift capacity tests for a better representation of in-field operations. The OECD, the ISO, and EC type approval determine the seat index point (SIP), whereas the ASABE determines the seat reference point (SRP) for roll-over protective structure (ROPS) tests. Diversified measurement tolerances were among the braking performance test standards. The European Union (EU) has developed daily limits for vibration exposures with adaptations from ISO 2631-1. Electromagnetic compatibility evaluations are emerging of high-efficiency tractors due to the long-term conformance to electromagnetic emissions and interferences. Comparisons of tractor test standards discussed in this paper are expected to provide useful information for tractor manufacturers and standards development personnel to improve the performance and safety test standards of tractors.

• Tribology and Lubricants
• /
• 제32권4호
• /
• pp.113-118
• /
• 2016

As an economic, high quality, and highly reliable gear with low noise and low vibration is demanded, an overall finite element analysis regarding a gear is required. Also, an infrared thermography test, which is a quantitative testing technique, is demanded for safety and longer lifespan of gear products. In order to manufacture a gear product or to determine safety of a gear being used, it is necessary to precisely determine ingredients of a material constituting a gear and detect any internal defect. This study aims to realize a design that minimizes the spur gear displacement with respect to power during its rotation and ensures the spur gear control capacity by using a 3D model and the midasNFX program. This facilitates the assessment of the possibility of cracking by evaluating the stress intensity and focusing on the integrity of the spur gear. We prepare the specimen of the spur gear based on the possibility of cranking as per the result of the structural interpretation from an infrared ray thermal measuring technique. After cooling the spur gear, we perform experiments using thermography and halogen lamps and analyze the temperature data according to the results of the experiment. In the experiment which we use thermography after cooling, we find a rise in the temperature of the room. As a result, the defective part show temperatures lower than their surroundings while the normal parts have temperatures higher than the defective parts. Therefore, it possible to precisely identify defective part owing to its low temperature.

• 한국진공학회지
• /
• 제12권2호
• /
• pp.93-104
• /
• 2003

저진공펌프의 내구성평가와 관련하여 펌프의 성능이나 상태의 저하에 관한 기술적 근거를 확보함으로써 펌프의 운전상태를 진단할 수 있는 기초기술을 확보할 수 있으며, 이는 진공펌프의 기계적 결함 및 성능평가 장치의 동적 응답과 신뢰도 구축에 중점을 두고 신호 분석을 통하여 실험적으로 기계적인 동적 특성을 확인하는 과정을 통하여 수행할 수 있다. 저진공펌프의 압축일에 소요되는 전력을 이론적으로 규명하고 펌프의 압축일을 계산하였으며, 소비전력에 대한 진공펌프의 에너지 효율을 예측하여 펌프 노화에 따르는 소비전력의 증가 원인을 규명하는 자료로 활용할 수 있다. 또한 저진공펌프의 가동 중에 측정한 진동, 압력신호, 배기속도 및 소비전력을 측정하고 분석하여 펌프 운전상태를 감시하는데 매우 유용한 인자가 무엇인지 확인하였으며 추후 연구의 방향과 내구성평가의 기초기술을 확보하였다.

• 대한기계학회논문집A
• /
• 제39권8호
• /
• pp.759-763
• /
• 2015

레이저 가공 공정은 마스크 없이 전극을 가공할 수 있다는 장점 때문에 우수한 공정들 중의 하나로 제안되고 있다. 본 논문에서는, 서로 다른 열적 물성을 가지는 금속들에 레이저 가공을 수행하였다. 이 금속들은 서로 다른 표면형상, 열영향부, 그리고 재융착층을 나타내었고 이는 열전도도, 끓는점, 그리고 열확산계수에 의존하였다. 또한 재융착층을 제거하기 위하여 초음파 원용 레이저 가공을 적용, 높은 열확산계수를 가지는 재료에서 그 초음파 가진에 의한 표면 품질의 향상을 발견하였다.

• 대한기계학회논문집A
• /
• 제39권8호
• /
• pp.801-806
• /
• 2015

저널베어링은 회전하는 축과 베어링 지지부 사이에 유막을 형성하여 회전체를 지지하는 구조물이며, 고속 및 고하중 조건에서도 안정적이기 때문에 발전소와 같은 대형 시스템에 널리 사용되고 있다. 본 연구에서는 저널베어링 시스템의 신뢰성을 확보하기 위한 감독학습 기반의 상태진단 알고리즘을 연구하였다. 기존에는 진동신호 특성인자들의 정의에 대한 연구가 주로 진행되었으나, 본 연구에서는 정의된 특성인자의 추출단위인 데이텀의 적용 기준에 대한 연구가 수행되었다. 데이텀의 효용성 평가를 통해 저널베어링 회전체 특성인자의 추출기준은 시간영역에서 1 회전, 주파수영역에서 60 회전 기준이 타당하다는 결론을 도출하였다.

• 대한기계학회논문집A
• /
• 제36권12호
• /
• pp.1669-1674
• /
• 2012

일반적인 고무 부품의 해석적 피로 수명 예측은 다양한 피로시험 결과를 바탕으로 정의되는 피로 수명식이 사용된다. 그러나, 이와 같은 방식은 피로 시험에 사용되는 비용적, 시간적인 문제로 인해 설계과정에서 매우 제한적으로 사용된다. 더욱이, 고무재료의 비규격화 및 임의적인 특성변화가 피로시험 결과의 데이터베이스화를 어렵게 만든다. 본 논문에서는 찢김에너지를 이용한 또다른 피로수명 예측 방식을 제안하였다. 자동차용 방진고무들에 대한 동적, 정적 찢김시험 및 복잡한 형상을 갖는 고무 부품의 찢김에너지를 계산하기 위하여 가상 결함을 고려한 유한요소 정식화를 수행하였다. 제안된 방법을 사용하여, 자동차용 모터 마운트의 피로 수명을 예측해 보았고, 실제 수명과 예측된 수명을 비교하여 신뢰성을 검증해 보았다.