• 대한조선학회논문집
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• 제42권1호
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• pp.10-17
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• 2005

Due to emission of vehicles during loading/unloading, ventilation system in Roll-on/Roll-off ship is inevitable; however it is very difficult to predict the ventilation performance before it is finally built in. Although the requirements for the ventilation system include air change rate and maximum allowable concentration of CO in the cargo holds, even prototype tests are hardly able to quantify the ventilation performance. In the present paper, a new method to assess the ventilation performance of Roll-on/Roll-off ship is proposed by using computational fluid dynamics. The air exchange is modeled by introducing multi-species transport of existing air In the holds and new air from the ventilation system. Conservation of multi-species as well as 3D Navier-Stokes equation are solved numerically in time dependent manner. Several cases of different configuration are considered. The results include predicted mass fraction of new air in the holds. It is also presented that CO concentration can be estimated based on the predicted air change performance. Due to the lack of experimental data, the computed results are not verified; however the proposed method can be applied as au assessment tool.

• 한국자동차공학회논문집
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• 제24권2호
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• pp.198-204
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• 2016

In this study, a wind tunnel test was conducted to measure the aerodynamic characteristics of a streamline-designed high-speed bus with the change of wind direction and speed and the result is compared with the aerodynamic performance of a commercialized high-speed bus model (Model-0) manufactured by Zyle Daewoo Bus Corp. Aerodynamic performance of the existing rear-spoiler was tested to prove its aerodynamic effect on the test model bus. From the study, it was found that 24.6 % of the total drag of the original bus model (Model-0) was reduced on the streamline-designed model bus(model-1) without the rear-spoiler but only 14.3 % of the total drag was reduced with the spoiler on the streamlined model bus. It means that the rear spoiler does not work properly with the streamlined model bus (model-1) and should be noted that an optimum design of a rear-spoiler of a vehicle is important to reduce the induced pressure drag and increase the driving stability of a vehicle against yaw motion. The experimental outcome was also compared to the previous numerical research result to evaluate the reliability of the numerical algorithm of the aerodynamic performance analysis of a vehicle. The error rate (%) of the numerical result to the experimental output is about 5.4 % and it is due to the simplified body configuration of the numerical model bus. The drag increases at the higher yaw angle because the transparent frontal area of the model vehicle increases and the downward force increases with the yaw angle as well. It has a positive effect to the driving stability of the vehicle but the moderated downward force should be kept for the fuel economy of a vehicle.

• 한국자동차공학회논문집
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• 제19권4호
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• pp.137-145
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• 2011

This paper suggests possible rear body shape modifications of a passenger car for the improvement of aerodynamic performance, based on the CFD analysis results. YF SONATA, a passenger car of Hyundai Motors Company, plays a major role as the baseline car in this research. Representatively, three parts(trunk rear edge, side rear edge and rear undercover) are modified in a small range in order for the total outer shapes not to be changed enough so that the modified car is not considered different, compared with the baseline. Specifically, using computational fluid dynamics, aerodynamic drag reduction is accomplished maximally about 11% in this research. Finally, it is proved that although the range of changes of the rear body shapes of a passenger car is very strictly confined, by changing a small range of rear body shapes alone the enhancement of aerodynamic performance of a passenger car can be significantly accomplished.

• 한국자동차공학회논문집
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• 제18권5호
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• pp.115-123
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• 2010

Cool-down performance after soaking is important because it affects passenger's thermal comfort. The cooling capacity of HVAC system determines initial cool down performance in most cases, the performance is also affected by location, and shape of panel vent, indoor seat arrangement. Therefore, optimal indoor designs are required in developing a new car. In this paper, initial cool down performance is predicted by CFD(computational fluid dynamics) analysis. Experimental time-averaging temperature data are used as inlet boundary condition. For more reliable analysis, real vehicle model and human FE model are used in grid generation procedure. Thermal and aerodynamic characteristics on re-circulation cool vent mode are investigated using CFX 12.0. Thermal comfort represented by PMV(predicted mean vote) is evaluated using acquired numerical data. Temperature and velocity fields show that flow in passenger's compartment after soaking is considerably unstable at the view point of thermodynamics. Volume-averaged temperature is decreased exponentially during overall cool down process. However, temperature monitored at different 16 spots in CFX-Solver shows local variation in head, chest, knee, foot. The cooling speed at the head and chest nearby panel vent are relatively faster than at the knee and foot. Horizontal temperature contour shows asymmetric distribution because of the location of exhaust vent. By evaluating the passenger's thermal comfort, slowest cooling region is found at the driver's seat.

• 한국자동차공학회논문집
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• 제13권2호
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• pp.72-82
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• 2005

The objective of this paper is to describe the optimization of design parameters in a large-sized commercial bus heater system by using CFD(computational fluid dynamics) analysis and Taguchi method. In order to obtain the best combination of each control factor which results in a desired performance of heater system, the parameter design of the Taguchi method is adopted for the robust design considering the dynamic characteristic. The research activity may be divided into four phases. The first one is analyzing the problem, i.e., ascertaining the influential factors. In the second phase the levels were set in such a way that their variation would significantly influence the response. In the third phase the experimental runs were designed. In the final phase the planned runs were carried out numerically to evaluate the optimal combination of factors which is able to provide the best response. In this study, eight factors were considered for the analysis: one with two level and seven with three level combinations comprising the $L_{18}(2^1{\times}3^7)$ orthogonal array. The results of this study can be summarized as follows ; (i)The optimum condition of control factor is a set of <$A_2\;B_1\;C_3\;D_3\;E_1\;F_2\;G_3\;H_2$> where A is shape of the outer fin, B is pitch of the outer fin, C is height of the outer fin, D is the inner fin number, E is the inner fin height, F is length of the flame guide, G is diameter of the heating element and H is clearance between air guide and heating element. (ii)The heat capacity of heated discharge air under the optimum condition satisfies the equation y=0.6M w here M is a signal factor. (iii)The warm-up rate improves about three times, more largely as com pared with the current condition, which results in about 9.2minutes reduction.

• Tribology and Lubricants
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• 제35권1호
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• pp.44-51
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• 2019

The paper presents the rotordynamic performance measurements and model predictions of a fuel cell electric vehicle (FCEV) air compressor supported on gas foil bearings (GFBs). The rotor has an impeller on one end and a thrust runner on the other end. The front (impeller side) and rear (thrust side) gas foil journal bearings (GFJBs) are located between the impeller and thrust runner to support the radial loads, and a pair of gas foil thrust bearings are located on both sides of the thrust runner to support the axial loads. The test GFJBs have a partial arc shim foil installed between the top foil and bump strip layers to enhance hydrodynamic pressure generation. During the rotordynamic performance tests, two sets of orthogonally installed eddy-current displacement sensors measure the rotor radial motions at the rotor impeller and thrust ends. A series of speed-up and coast-down tests to 100k rpm demonstrates the dominant synchronous (1X) rotor responses to imbalance masses without noticeable subsynchronous motions, which indicates a rotordynamically stable rotor-GFB system. Finite element analysis of the rotor determines the rotor free-free (bending) natural modes and frequencies well beyond the maximum rotating frequency. The predicted damped natural frequencies and damping ratios of the rotor-GFB system reveal rotordynamic stability over the speeds of interest. The imbalance response predictions show that the predicted critical speeds and rotor amplitudes strongly agree with the test measurements, thus validating the developed rotordynamic model.

• 한국산학기술학회논문지
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• 제20권3호
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• pp.638-644
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• 2019

본 연구에서는 전산유체역학 해석을 이용하여 알루미늄 피라미드 트러스 심재 샌드위치의 열유동 특성을 분석하였다. 규칙적 다공질 금속인 피라미드 트러스 코어를 샌드위치 구조물에 채용할 경우 공기 매질이 자유롭게 유입, 유출될 수 있는 개방형 코어인 점을 고려하여 하중을 지지할 수 있는 구조성능과 함께 방열체로서 다기능성을 구현할 수 있는 구조가 된다. 따라서, 유입되는 공기의 속도변화, 설계변수인 트러스각에 따른 압력강하와 열전달 메카니즘을 확인하기 위해 ANSYS/Fluent를 이용하여 수치해석을 실시하였다. 해석모델에 사용된 샌드위치 패널은 알루미늄으로 이루어져 있으며, 샌드위치 패널의 위 면재와 아래 면재 사이에는 15개의 피라미드 트러스 유닛셀이 반복되고 있다. 폭 방향으로는 무한히 넓은 유닛셀을 모사하기 위해 대칭조건을 지정하였으며, 입구에는 균일한 속도분포를 경계조건으로 입력하였다. 해석결과 입구부와 첫 유닛셀까지의 구간에서 입구영향이 관찰되었으며, 입구영향을 배제하고 마찰계수와 누셀수를 분석하였다. 공기의 속도가 증가할수록 마찰계수는 감소하였으며, 누셀수는 증가하는 경향을 보인다. 한편, V=1m/s에서 5m/s에서의 마찰계수와 누셀수 변화가 확연하였으며, 이는 층류에서 난류로 유동패턴이 변하기 때문에 거시적으로 열전도보다 대류열전달의 비중이 커졌기 때문이다. 또한, 설계변수인 트러스각에 대해서는 의미가 있을 정도의 마찰계수와 누셀수의 변화는 관찰되지 않았다. 따라서, 트러스각이 강도, 강성 등 구조성능에 민감한 점을 감안하면 다기능성을 염두에 둔 알루미늄 피라미드트러스 심재 설계 시 설계변수의 변화는 구조성능에 더 민감할 것으로 판단된다.