• 한국음향학회:학술대회논문집
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• 한국음향학회 2002년도 하계학술발표대회 논문집 제21권 1호
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• pp.469-474
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• 2002

In recent years, modularization of engine parts has increased the application of plastic products in air intake systems. Plastic intake manifolds provide many advantages including reduced weight, contracted cost, and lower intake air temperatures. These manifolds, however, have some weakness when compared with customary aluminium intake manifolds, in that they have low sound transmission loss because of their lower material density. This low transmission loss of plastic intake manifolds causes several problems related to flow noise, especially when the throttle is opened quickly. The physical processes, responsible for this flow noise, include turbulent fluid motion and relative motion of the throttle to the airflow. The former is generated by high-speed airflow in the splits between the throttle valve and the inner-surface of the throttle body and surge-tank, which can be categorized into the quadrupole source. The latter induces the unsteady force on the flow, which can be classified into the dipole source. In this paper, the mechanism of noise generation from the turbulence is only investigated as a preliminary study. Stochastic noise source synthesis method is adopted for the analysis of turbulence-induced, i.e. quadrupole noise by throttle at quick opening state. The method consists of three procedures. The first step corresponds to the preliminary time-averaged Navier-Stokes computation with a $k-\varepsilon$ turbulence model providing mean flow field characteristics. The second step is the synthesis of time-dependent turbulent velocity field associated with quadrupole noise sources. The final step is devoted to the determination of acoustic source terms associated with turbulent velocity. For the first step, we used market available analysis tools such as STAR-CD, the trade names of fluid analysis tools available on the market. The steady state flows at three open angle of throttle valve, i.e. 20, 35 and 60 degree, are numerically analyzed. Then, time-dependent turbulent velocity fields are produced by using the stochastic model and the flow analysis results. Using this turbulent velocity field, the turbulence-originated noise sources, i.e. the self-noise and shear-noise sources are synthesized. Based on these numerical results, it is found that the origin of the turbulent flow and noise might be attributed to the process of formulation and the interaction of two vortex lines formed in the downstream of the throttle valve. These vortex lines are produced by the non-uniform splits between the throttle valve and inner cylinder surface. Based on the analysis, we present the low-noise design of the inner geometry of throttle body.

• 대한기계학회논문집A
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• 제37권8호
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• pp.1007-1013
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• 2013

이 논문은 터빈 로터의 형상변화에 따른 공력 특성에 대하여 분석하였다. 본 논문의 터빈은 헬리콥터의 보조동력 장치로 사용되는 소형엔진이다. 소형엔진은 팁 형상의 구조적 취약성 때문에 성능을 향상시키기 어렵다. 그러므로, 터빈의 허브를 개선하는 것이 여러 가지 측면에서 유리하다. 터빈의 작동유체는 고온 고압의 가스이다. 터빈표면의 열전달률이 고려되었을 때, 열부하에 의한 블레이드의 손상을 줄이기 위해서는 블레이드 표면의 열전달률 분포를 고찰하여야 한다. 수치모사 결과를 검증용 실험값과 비교하였을 때, SST난류모델은 공력 특성을 잘 반영하고 열전달 예측성능도 우수하였다. 결론적으로, 허브측 선단에서 구륜설계(bulbous design)를 적용하였을 때 공력효율이 향상되었고, 전체 공력 손실 중 끝벽 손실은 15% 감소되었다.

• Journal of Acupuncture Research
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• 제28권1호
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• pp.15-28
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• 2011

Objectives : To understand the strength and weakness of traditional warm needle acupuncture based on existing research outcomes in Korea mostly and to suggest how to build the desirable warm needle acupuncture apparatus by overcoming demerits of traditional and currently existing ones. Methods : We searched warm needle relating papers in Korean with the key words of '온침, 화침, 열자극' by using DBpia, Journal of Korean Oriental Medical Society, Journal of Korean Acupuncture & Moxibustion Society and Journal of Society for Meridian and Acupoint. Degree dissertations in Korean were also searched with the same words through the search engine of Library of Kyung Hee University. We also searched with words of 'warm, thermal, heat, needle, acupuncture, temperature' via Pubmed and found a small number of English written papers and large number of Chinese written ones. To find english translated version of those papers, we googled with the same words with no success. Results : About 20 papers on warm needle acupuncture written in Korean were found and analyzed with respect to experimental factors that affected the thermal properties or the amount of heat stimulus of the acupuncture. More rigorous descriptions seemed to be required on the insertion depth, duration and manipulation of warm needle treatment. A basic heat transfer model was presented for the clarification of heat loss through the needle of warm needle acupuncture. Environmental factors such as air flow on the properties seems to be considered for the warm needle acupuncture. Conclusions : Papers on warm needle acupuncture were reviewed and analyzed based on their thermal properties and tools such as needles and moxa cones. Several suggestions were made on the descriptions relating the properties. Necessary specifications were introduced to aim modernized warm needle systems.

• International Journal of Automotive Technology
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• 제8권6호
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• pp.687-696
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• 2007

To increase the reliability of auto-ignition in CAI engines, the thermodynamic properties of intake flow is often controlled using recycled exhaust gases, called internal EGR. Because of the internal EGR influence on the overall thermodynamic properties and mixing quality of the gases that affect the subsequent combustion behavior, optimizing the intake and exhaust valve timing for the EGR is important to achieve the reliable auto-ignition and high thermal efficiency. In the present study, fully 3D numerical simulations were carried out to predict the mixing characteristics and flow field inside the cylinder as a function of valve timing. The 3D unsteady Eulerian-Lagrangian two-phase model was used to account for the interaction between the intake air and remaining internal EGR during the under-lap operation while varying three major parameters: the intake valve(IV) and exhaust valve(EV) timings and intake valve lift(IVL). Computational results showed that the largest EVC retardation, as in A6, yielded the optimal mixing of both EGR and fuel. The IV timing had little effect on the mixing quality. However, the IV timing variation caused backflow from the cylinder to the intake port. With respect to reduction of heat loss due to backflow, the case in B6 was considered to present the optimal operating condition. With the variation of the intake valve lift, the A1 case yielded the minimum amount of backflow. The best mixing was delivered when the lift height was at a minimum of 2 mm.

• 한국항해항만학회:학술대회논문집
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• 한국항해항만학회 2004년도 춘계학술대회 논문집
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• pp.343-350
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• 2004

LNG 운반선은 항해중 외부로부터 다량의 열 침임으로 인해 많은 BOG가 발생하며 통상 이는 선박엔진의 연료로 사용된다. 화주의 입장에서 이러한 BOG의 발생과 소비는 화물의 손실을 의미하며, 따라서 선주와 화주 사이에는 BOR(boil off rate)에 대해 만선항해를 기준으로 0.15％／day 이하가 되도록 운송계약을 체결한다. LNG 운반선의 항해사관 입장에서는 자신이 승무하고 있는 선박의 BOR에 대한 정확한 지식을 바탕으로 선박을 운항할 필요가 있으나 실제로는 막연한 경험에 의존하고 있는 실정이다. 따라서 본 연구에서는 선체온도분포 및 외부로부터의 침입열량에 관한 정밀 열설계 기술을 토대로 본선의 해기사들이 보다 간편하게 BOG를 예측할 수 있는 간단한 모델을 제시하였다. 그리고 개발된 모델을 사용하여 연구대상 선박의 실제 기상조건을 토대로 만선 및 공선항해에 대하여 각각 BOR을 계산하였으며 이를 실측자료와 비교, 검토하였다. 본 연구에서 제시된 BOG 예측방법은 현재 운항중인 LNGC에서 BOG를 관리하는 유용한 도구로 사용될 것으로 기대된다.

• 한국항해항만학회지
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• 제28권5호
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• pp.365-372
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• 2004

LNG 운반선은 항해중 외부로부터 다량의 열 침입으로 인해 많은 BOG가 발생하며 통상 이는 선박엔진의 연료로 사용된다. 화주의 입장에서 이러한 BOG의 발생과 소비는 화물의 손실을 의미하며, 따라서 선주와 화주 사이에는 BOR에 대해 만선항해를 기준으로 0.15%/day 이하가 되도록 운송계약을 체결한다. LNG 운반선의 항해사관 입장에서는 자신이 승무하고 있는 선박의 BOR에 대한 정확한 지식을 바탕으로 선박을 운항할 필요가 있으나 실제로는 막연한 경험에 의존하고 있는 실정이다. 따라서 본 연구에서는 신체온도분포 및 외부로부터의 침입열량에 관한 정밀 열설계 기술을 토대로 본선의 해기사들이 보다 간편하게 BO를 예측할 수 있는 간단한 모델을 제시하였다. 그리고 개발된 모델을 사용하여 연구대상 선박의 설제 기상조건을 토대로 만선 및 공선항해에 대하여 각각 BOR을 계산하였으며 이를 실측자료와 비교, 검토하였다. 본 연구에서 제시된 BOG 예측방법은 현재 운항중인 LNGC에서 BOG를 관리하는 유용한 도구로 사용될 것으로 기대된다.

• 대한기계학회논문집B
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• 제30권6호
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• pp.553-559
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• 2006

Most diesel injector, which is currently used in high-pressure common rail fuel injection system of diesel engine, is driven by the solenoid coil energy for its needle movement. The main disadvantage of this solenoid-driven injector is a high power consumption, high power loss through solenoid coil and relatively fixed needle response's problem. In this study, a prototype piezo-driven injector, as a new injector mechanism driven by piezoelectric energy based on the concept of inverse piezo-electric effect, has been designed and fabricated to know the effect of piezo-driven injection processes on the diesel spray structure and internal nozzle flow. Firstly we investigated the spray characteristics in a constant volume chamber pressurized by nitrogen gas using the back diffusion light illumination method for high-speed temporal photography and also analyzed the inside nozzle flow by a fully transient simulation with cavitation model using VOF(volume of fraction) method. The numerical calculation has been performed to simulate the cavitating flow of 3-dimensional real size single hole nozzle along the injection duration. Results were compared between a conventional solenoid-driven injector and piezo-driven injector, both equipped with the same micro-sac multi-hole injection nozzle. The experimental results show that the piezo-driven injector has short injection delay and a faster spray development and produces higher injection velocity than the solenoid-driven injector. And the predicted simulation results with the degree of cavitation's generation inside nozzle for faster needle response In a piezo-driven injector were reflected to spray development in agreement with the experimental spray images.