• 한국정밀공학회:학술대회논문집
• /
• 한국정밀공학회 2002년도 추계학술대회 논문집
• /
• pp.904-907
• /
• 2002

Optical disk drive device is improved in rotating speed for faster data reading. In the case of CD-ROM, rotating speed is over 10000 rpm in the practical use. As a result of high rotating speed, unexpected effects as like increasing disk fluctuation and acoustic noise are raised by the air friction on the rotating disk and the eccentricity of rotating parts. The overall acoustic noise of running CD-ROM could be classified into two different characterized noise. The first is the structural-borne noise which is generated from vibrating solid body. By the reason, the signal of structural borne noise has very similar to the signal of surface vibrating one. It has dense noise energy at specific frequency region. The other is the air-borne noise which is generated from turbulence or vortex caused by friction between disk and air. The signal of air-borne noise has no dominant peak point at acoustic pressure-frequency domain. The noise energy is widely distributed while comparatively high and large frequency region. The structural-borne noise could be reduced by reducing vibration of structure and in addition it's target reducing frequency is narrow. However the air-borne noise reduction is effectively needed of enclosing method for the noise source located near the disk surface because it is difficult to define target frequency point. In this study, the acoustic noise at driving CD-ROM is classified by the sides of it's character and tried to reduce the overall acoustic noise.

• 상하수도학회지
• /
• 제27권1호
• /
• pp.1-10
• /
• 2013

Major issues in water supply service have changed from expansion of service area to improvement of service quality, i.e., water quality and safety, and early response to emergency situation. This change in the service concept triggers the perceptions of limitation with the current centralized water supply system and of necessities of decentralized (distributed) water supply system (DWSS), which can make up the limitations. DWSS can reduce the possibility of water supply outage by establishing multiple barriers such as emergency water supply system, and secure better water quality by locating treatment facilities neighboring consumers. On the other hand, fluctuation of water demand will be increased due to the reduced supply area, which makes difficult to promptly respond the fluctuating demand. In order to supplement this, hybrid water supply system was proposed, which combined DWSS with conventional water supply system using distributing reservoir to secure the stability of water supply. The Optimal connection point of DWSS to existing water supply network in urban area was determined by simulating a supply network using EPANET. Optimal location of decentralized water treatment plant (or connection point) is a nodal point where changes in pressure at other nodal points can be minimized. At the same time, the optimal point should be selected to minimize hydraulic retention time in supply network (water age) to secure proper water quality. In order to locate the point where these two criteria are satisfied optimally, Distance measure method, one of multi-criteria decision making was employed to integrate the two results having different dimensions. This methodology can be used as an efficient decision-support criterion for the location of treatment plant in decentralized water supply system.

• International Journal of Naval Architecture and Ocean Engineering
• /
• 제12권1호
• /
• pp.71-84
• /
• 2020

In order to improve the performance of marine centrifugal pump, a centrifugal pump whose specific speed is 66.7 was selected for the research. Outlet diameter D2, outlet width b2, blade outlet angle β2, blade wrap φ and blade number z of the impeller were chosen as the variables. The maximum weighted average efficiency and the minimum vibration intensity at the base were calculated as objectives. Based on the Latin Hypercube method, the impeller was numerically optimized. The numerical results show that after optimization, the amplitudes of pressure fluctuation on the main frequency at different monitoring points decrease in varying degrees. The radial force on impeller decreases obviously under off-design flow rates and is more symmetrical during the operation of the pump. The variation of the axial force is relatively small, which has no obvious relationship with the rotating angle of the impeller. The energy performance and vibration experiment was performed for verifying. The test results show that the weighted average efficiency under 0.8Qd, 1.0Qd and 1.2Qd increases by 4.3% after optimization. The maximal vibration intensity at M1-M4 on the pump base reduced from 0.36 mm/s to 0.25 mm/s, decreasing by 30.5%. In addition, the vibration velocities of bracket in pump side and outlet flange also have significant reductions.

• KDI Journal of Economic Policy
• /
• 제12권3호
• /
• pp.3-26
• /
• 1990

1990년대에 들어 한국(韓國)의 미곡시장(米穀市場)은 대내외적(對內外的)으로 새로운 변화를 겪고 있다. 대외적(對外的)으로는 "우루과이라운드" 및 쌍무협정을 통해 대외개방(對外開放)과 생산보조금(生産補助金)의 감축에 대한 압력에 직면해 있고, 대내적(對內的)으로도 쌀소비의 감소(減少)로 1989년부터는 정부수매가격(政府收買價格)이 도매가격(都賣價格)을 상회하는 구조적(構造的)인 문제가 나타났다. 이러한 가격역전현상(價格逆轉現象)은 민간상인(民間商人)의 재고기능(在庫機能), 계절적(季節的) 가격안정기능(價格安定機能), 유통기능(流通機能)을 위축시키며, 정부재정(政府財政)에 주는 부담을 기하급수적으로 증가시킬 뿐만 아니라 미곡시장(米穀市場)의 가격구조(價格構造) 및 유통과정(流通過程)을 왜곡시키고 있다. 따라서 미가지지정책(米價支持政策)을 통환 증산(增産)보다는 농촌생활기반조성(農村生活基盤造成) 및 농업구조조정(農業構造調整)으로의 전환(轉換)이 필요하다. 그러나 농민들의 농업정책(農業政策)에 대한 불신, 농업기반(農業基盤)의 취약성, 그리고 정치적인 역학관계를 고려할 때 정부(政府)의 일방적인 지시보다는 농민이 선택할 수 있는 대안(代案)을 제시함이 바람직하며, 점진적인 구조개선(構造改善)이 필요하다고 생각된다. 이 논문에서는 전환기에 처한 한국(韓國) 미곡시장(米穀市場) 현황(現況) 대한 경제적(經濟的) 분석(分析)과 사회적(社會的) 비용(費用) 및 마찰(摩擦)을 최소화(最小化)하며 대내외(對內外) 환경변화에 적응할 수 있는 정책대안(政策代案)을 제시하고자 한다.