• 대한토목학회논문집
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• 제31권4D호
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• pp.539-546
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• 2011

자동차의 충돌해석은 다양한 형태로 구성되며, 충돌 중 차량에 작용되는 속도변화는 차량 간의 충돌정도나 차량 내에 탑승한 승객의 안전도를 평가하는 매우 중요한 요소로 활용된다. 이로 인해 충돌해석 시뮬레이션 프로그램을 활용한 속도변화의 결과치를 해석하는 방법들이 필요하게 된다. 그러나 다양한 충돌해석 시뮬레이션이 보급됨으로 인해 각 프로그램에 대한 신뢰성 평가가 요구되고 있다. 본 연구에서는 전혀 다른 물리적 접근방식을 채택하는 충돌해석 프로그램인 EDSMAC과 PC-CRASH프로그램을 활용하여 초기 입력조건 중 차량의 무게, 무게중심, 구름저항, 강성계수, 제동력 등 여러 충돌인자들을 일정한 범위 내에서 값을 변화시키면서 1차원 정면 및 2차원 측면직각충돌 실험을 수행하였다. 그리고 충돌인자들이 출력결과 값인 충돌 중 속도변화에 미치는 영향에 대해 알아보았다. 본 연구 결과, 두 시뮬레이션 프로그램 모두 차량의 무게, 무게중심, 제동력에 대해 동일한 속도변화의 패턴을 보였다. 차량의 강성계수는 EDSMAC에만 반응하였으며, 구름저항계수는 속도변화에 별다른 영향을 미치지 못하였다. 그러나 속도변화의 값에 대해서는 다소 상대적인 차이를 나타내었는데, 이는 각 시뮬레이션 프로그램에 고정된 물성치 값이 그대로 적용됨으로 인한 반응의 결과로 해석된다. 따라서 시뮬레이션 프로그램의 고정 값을 고려한 속도분석으로 교통사고 충돌해석에 대한 신뢰성을 향상시켜야 할 것이다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회A
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• pp.873-878
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• 2007

Stability of high-speed roll-to-roll printing machines is one of the most important factors that are required for the printing machines to operate properly and to obtain reasonable printing performance. This paper proposes a new model for the web-tension system of a high-speed gravure printing machine considering span-length variations due to dancer rollers, and analyzes the stability of plant dynamics of the printing machine using the proposed model. Span-length variations due to dancer motions are considered for the modeling of plant dynamics in two ways; one is to include the effect of span-length variations without considering dancer inertias and viscous frictions, and the other is to include the effect of span-length variations with considering dancer inertias and viscous frictions. The stability of the plant model is analyzed for various web-speeds using the eigenvalues of the linearized model about operating points.

• 한국도로학회논문집
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• 제14권6호
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• pp.183-190
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• 2012

PURPOSES : The fundamental diagram provides basic information necessary in the analysis of traffic flow and highway operation. When traffic flow is congested, the density-flow points in the fundamental diagram are widely scattered and move in a stochastic manner. This paper investigates the pattern of density-flow point transitions and identifies car-following behaviors underlying the density-flow transitions. METHODS : From a microscopic analysis of 722 fundamental diagrams of NGSIM data, a total of 20 transition patterns of fundamental diagrams are identified. Prominent features of the transition patterns are explained by the behavior of the leader and follower. RESULTS : It is found out that the average speed and the speed difference between the leader and the follower critically determine the density-flow transition pattern. The density-flow path is very sensitive to the values of vehicle speed and spacing especially at low speed and high density such that most fluctuations in the fundamental diagram in the congested regime is due to the noise of speed and spacing variations. CONCLUSIONS : The result of this study suggests that the average speed, the speed difference between the leader and the follower, and the random variations of speed and spacing are dominant factors that explain the transition patterns of a fundamental diagram.

• 한국유체기계학회 논문집
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• 제19권6호
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• pp.14-18
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• 2016

Multi-MW wind turbines have very large blades over 40~50 m in length. Some factors like wind shear and tower shadow make an effect on asymmetric loads on the blades. Larger asymmetric loads are produced as the length of blade is getting longer. In this paper, a 2 MW on-shore wind turbine is considered and variations of thrust on 3 blades and rotor hub under wind shear are calculated by using a commercial Bladed S/W and dynamic properties of the thrust variations are investigated. It is shown that the amplitude of the asymmetric thrust on each blade under wind shear is getting larger as the wind speed increases, the frequency of the thrust variation on each blade is same as the one of rotor speed, and the frequency of the thrust variation at rotor hub is 3 times as high as the one of rotor speed.

• 품질경영학회지
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• 제43권4호
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• pp.589-606
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• 2015

Purpose: In developing new products, reducing performance variation is important for competitiveness factors such as quality, cost, and delivery. This paper aims at evaluating three performance variations; measurement, performance evaluation, and manufacturing variations, and then improving product and process design, focused on paper helicopter making case study. Methods: For measurement system analysis, gage R&R (repeatability and reproducibility), linearity, stability are evaluated. Since gage R&R are not satisfactory, the measurement system is improved by adopting voice memos application of iPhone and providing standard measurement procedure. To evaluate performance variation, product deterioration and environment factor (wind speed) is considered. Since the existing design is sensitive to these noise factors, a new product design is developed, which is proven to be robust to the noise factors. Finally, manufacturing variations are evaluated with five factors which can cause variation in flight time. To reduce the impact of three significant factors, three improvement methods are applied. Results: Three performance variations are evaluated and robust paper helicopter design is presented. Conclusion: To reduce measurement and process variations, improved measurement method and paper helicopter making procedure are proposed. A new product design is also presented which is robust to deterioration and environmental variation. This paper is expected to benefit students and practitioners who want to have hands-on knowledge on new product quality improvement.

• 대기
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• 제20권3호
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• pp.343-353
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• 2010

A regional wind network with complex surface conditions must be designed with sufficient space and time resolution to resolve the local circulations. In this study, the spatial variations of the wind field observed in the Seoul and Jeju regional networks were evaluated in terms of annual, seasons, and months to assess the spatial homogeneity of wind fields within the regional networks. The coherency of the wind field as a function of separation distance between stations indicated that significant coherency was sometimes not captured by the network, as inferred by low correlations between adjacent stations. A meso-velocity scale was defined in terms of the spatial variability of the wind within the network. This problem is predictably most significant with weak winds, dull prevailing wind, clear skies and significant topography. The relatively small correlations between stations imply that the wind at a given point cannot be estimated by interpolating winds from the nearest stations. For the Seoul and Jeju regional network, the meso-velocity scale has typically a same order of magnitude as the speed of the network averaged wind, revealing the large spatial variability of the Jeju network station imply topography and weather. Significant scatter in the relationship between spatial variability of the wind field and the wind speed is thought to be related to thermally-generated flows. The magnitude of the mesovelocity scale was significantly different along separation distance between stations, wind speed, intensity of prevailing wind, clear and cloudy conditions, topography. Resultant wind vectors indicate much different flow patterns along condition of contributing factors. As a result, the careful considerations on contributing factors such as prevailing wind in season, weather, and complex surface conditions with topography and land/sea contrast are required to assess the spatial variations of wind field on a regional network. The results in the spatial variation from the mesovelocity scale are useful to represent the characteristics of regional wind speed including lower surface conditions over the grid scale of large scale atmospheric model.

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

• Journal of Power Electronics
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• 제14권5호
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• pp.980-988
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• 2014

This paper proposes an online gain tuning algorithm for a robust sliding mode speed controller of surface-mounted permanent magnet synchronous motor (SPMSM) drives. The proposed controller is constructed by a fuzzy neural network control (FNNC) term and a sliding mode control (SMC) term. Based on a fuzzy neural network, the first term is designed to approximate the nonlinear factors while the second term is used to stabilize the system dynamics by employing an online tuning rule. Therefore, unlike conventional speed controllers, the proposed control scheme does not require any knowledge of the system parameters. As a result, it is very robust to system parameter variations. The stability evaluation of the proposed control system is fully described based on the Lyapunov theory and related lemmas. For comparison purposes, a conventional sliding mode control (SMC) scheme is also tested under the same conditions as the proposed control method. It can be seen from the experimental results that the proposed SMC scheme exhibits better control performance (i.e., faster and more robust dynamic behavior, and a smaller steady-state error) than the conventional SMC method.

• 한국생산제조학회지
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• 제25권6호
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• pp.426-433
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• 2016

This paper investigates the effects of operating conditions of an air classifier mill (ACM) on the particle sizes of PVC and rice hull. Based on the Box-Behnken matrix, the pulverization experiments were performed considering three operating factors: the air flow rate, the classifier speed and the mill speed. The response surface methodology was applied to identify the effects of the operating factors on the particle size. Results show that the particle sizes are governed by the linear variations of the operating factors. As less air is supplied and the mill rotates more slowly, the powder of both PVC and rice hull becomes finer. Furthermore, the classifier speed has a significant effect on the PVC powder but almost no effect on the rice hull powder. Thus, it is found that strong interactions exist between the material characteristics of a particle and the operating conditions of the ACM.

• 반도체디스플레이기술학회지
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• 제15권4호
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• pp.86-91
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• 2016

End milling is an important and common machining operation because of its versatility and capability to produce various profiles and curved surfaces. This paper presents an experimental study of the cutting force variations in the end milling of SM25C with HSS(high speed steel) and carbide tool. This paper involves a study of the Taguchi design application to optimize cutting force in a end milling operation. The Taguchi design is an efficient and effective experimental method in which a response variable can be optimized, given various control and noise factors, using fewer resources than a factorial design. This study included feed rate, spindle speed and depth of cut as control factors, and the noise factors were different cutting tool in the same specification. An orthogonal array of $L_9(3^3)$ of ANOVA analyses were carried out to identify the significant factors affecting cutting force, and the optimal cutting combination was determined by seeking the best cutting force and signal-to-noise ratio. Finally, confirmation tests verified that the Taguchi design was successful in optimizing end milling parameters for cutting force.