• 한국자동차공학회논문집
• /
• 제6권6호
• /
• pp.259-266
• /
• 1998

In the SI engine, the improvement of combustion stability is important not only for the fuel consumption rate but also for the emission control at idling of engine. Thus the engine speed fluctuation at idle operation mainly comes from cyclic variation of combustion in the SI engine. In this syudy, the improvement of combustion stability for the SI engine at idle condition by the cooling water temperature, duty ratio of ISC, spark ignition timing as well as the reducement of the harmful exhaust gas emission was discussed.

• International Journal of Naval Architecture and Ocean Engineering
• /
• 제13권1호
• /
• pp.367-378
• /
• 2021

This paper develops a dynamic regression model to quantify the contribution of key external factors to operational energy efficiency of ships. On this basis, kernel density estimation is applied to explore distribution patterns of fluctuations in operational performance. An empirical analysis based on these methods show that distribution of fluctuations in Energy Efficiency Operational Indicator (EEOI) is leptokurtic and fat tailed, rather than a normal one. Around 85% of fluctuations in EEOI can be jointly explained by capacity utilization and sailing speed, while the rest depend on other external factors largely beyond control. The variations in capacity utilization and sailing speed cannot be fully passed on to the energy efficiency performance of ships, due to complex interactions between various external factors. The application of the methods is demonstrated, showing a potential approach to develop a rating mechanism for use in the legally binding framework on operational energy efficiency of ships.

• 대한용접접합학회:학술대회논문집
• /
• 대한용접접합학회 1995년도 특별강연 및 춘계학술발표 개요집
• /
• pp.42-45
• /
• 1995

• 제어로봇시스템학회:학술대회논문집
• /
• 제어로봇시스템학회 1989년도 한국자동제어학술회의논문집; Seoul, Korea; 27-28 Oct. 1989
• /
• pp.766-771
• /
• 1989

The authors tried to make experimentally clear the response of engine speed to stepwise increasing, decreasing or sinusoidally fluctuating load. Based on a simplified model devised from the standpoint of the control theory, analysis was carried out with digital computer and its results obtained coincide well with those of experiment, so that it could be confirmed that it is possible to simulate the speed response to variation of the load.

• 소음진동
• /
• 제10권2호
• /
• pp.345-352
• /
• 2000

최근 여객선이 고속화, 고금화되고 있는 추세에 따라 선실내 소음 저감이 중요한 설계 요소로 간주되고 있다. 일반적으로 선박 소으믄 음암레벨로 평가되나 여객선의 경우 승객에게 더욱 쾌적한 환경을 제공하기 위하여 음질을 개선할 필요가 있다. 본 연구에서는 연근해를 운항 중인 기존 고속 여객선의 소음을 계측하고, 정신음향학 분야에서 제시된 Zwicker Loudness 계산식에 의거하여 음의 크기, 거칙기, 변동세기 및 날카로움으로 음질을 평가하였다. 또한, 각각의 음질 평가요소와 음압간의 상관관계를 분석하였다. 상기 결과로부터 고속여객선의 음의 크기는 음압과 비례하는 반면에 음의 거질치 (roughness),변동세기(fluctuation strength)및 날카로움(sharpness)은 선박의 운동과 추락변동 등으로 인하여 음압과 비선형적인 상관관계를 나타냄을 확인하였다.

• Journal of Advanced Marine Engineering and Technology
• /
• 제31권5호
• /
• pp.522-530
• /
• 2007

In order to extract small hydropower in the very low specific speed range of $n_s<10$, a Positive Displacement Turbine (PDT) has been proposed and steady performances have been determined experimentally. However, the suppression of large pressure fluctuation is inevitable for practical application of PDT. Therefore, present study adopted 4-lobe helical type robe to reduce the pressure fluctuation. The results show that 4-lobe helical type robe can be adopted to suppress the pressure fluctuation drastically. Moreover, efficiency and unit power of the turbine with newly proposed 4-lobe helical type lobe are higher than those of the turbine with 3-lobe straight type robe.

• 대한기계학회논문집B
• /
• 제31권2호
• /
• pp.202-207
• /
• 2007

In order to understand the phenomena of combustion instability, an experimental study was conducted at the moderate pressure and ambient temperature conditions. The flame behavior and the pressure fluctuations were measured in a dump combustor. Various types of combustion modes occurred in accordance with the equivalence ratio and the fuel supplying conditions. The fluctuation of pressure, heat release and equivalence ratio were measured by piezoelectric pressure sensor, high speed Intensified Charge Coupled Device (HICCD) camera and gas chromatography respectively. Two representative modes were self-excited pressure oscillations at the resonance of combustion chamber (200Hz) and instabilities related to the modulated fuel flow rate through the fuel holes (10Hz). It is found that, especially in an unchoked fuel flow condition, the modulation of the fuel flow rate affects the characteristics of flame behavior and pressure fluctuations in a lean premixed flame.

• 한국통신학회논문지
• /
• 제29권8C호
• /
• pp.1104-1112
• /
• 2004

본 논문에서는 레이저와 고속 CCD 카메라를 이용하여 대형 구조물의 3차원 거동 계측을 위해 진동 주파수 계측 방식을 확립하였다. 구조물에 부착한 대상판에 변동(fluctuation)이 작은 다이오드 레이저를 투사하고, 고속 CCD 카메라로 촬영한 영상에 고정도 상대측정 알고리즘을 적용하여 구조물의 변위를 측정하였다. 초당 120 프레임의 고속 카메라를 이용하고 변위에 FFT를 취해 진동주파수를 구한 경우, 0에서 40Hz까지 $\pm$0.5% 이내의 진동주파수의 정확도를 얻을 수 있다. 이를 이용하면 대형 구조물에 대해 보다 저렴하고 간단하게 고유진동수의 측정이 가능하다. 또한 GPS를 이용한 상대측위 기법과의 비교를 통해 레이저를 이용한 변위측정의 정확도를 입증함으로써, 제안한 진동주파수 측정 방법의 신뢰도와 경제성을 검증하였다.

• Wind and Structures
• /
• 제9권1호
• /
• pp.23-35
• /
• 2006

The effect of buildings on flow in urban canopy is one of the most important problems in local/micro-scale meteorology. A large eddy simulation model is used to simulate the flow structure in an urban neighborhood and the bulk effect of the buildings on surrounding flows is analyzed. The results demonstrate that: (a) The inflow conditions affect the detailed flow characteristics much in the building group, including: the distortion or disappearance of the wake vortexes, the change of funneling effect area and the change of location, size of the static-wind area. (b) The bulk effect of the buildings leads to a loss of wind speed in the low layer where height is less than four times of the average building height, and this loss effect changes little when the inflow direction changes. (c) In the bulk effect to environmental fields, the change of inflow direction affects the vertical distribution of turbulence greatly. The peak value of the turbulence energy appears at the height of the average building height. The attribution of fluctuations of different components to turbulence changes greatly at different height levels, in the low levels the horizontal speed fluctuation attribute mostly, while the vertical speed fluctuation does in high levels.

• Journal of Electrical Engineering and Technology
• /
• 제13권2호
• /
• pp.659-668
• /
• 2018

This paper proposes an optimization approach of a grid-connected photovoltaic and wind hybrid energy system including energy storage considering voltage fluctuation in the electricity grid. A techno-economic analysis is carried out in order to minimize the size of hybrid system by considering the benefit-cost. Lithium-ion battery type is used for both managing the electricity selling to the grid and reducing voltage fluctuation. A new technique is developed to limit the voltage perturbation caused by the solar irradiance and the wind speed through determining the state-of-charge of battery for every hour of a day. Improved particle swarm optimization (PSO) methods, referred to as FC-VACPSO which combines Fast Convergence Particle Swarm Optimization (FCPSO) method and Variable Acceleration Coefficient Based Particle Swarm Optimization (VACPSO) method are used to solve the optimization problem. A comparative study has been performed between standard PSO method and PSO based methods to extract the best size with the benefit cost. A sensitivity analysis has been studied for different kinds and costs of batteries, by considering variable and constant state-ofcharge of battery. The simulations, performed under Matlab environment, yield good results using the FC-VACPSO method regarding the convergence and the benefit cost of the hybrid system.