• 대한조선학회논문집
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• 제61권2호
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• pp.68-76
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• 2024

The rotor sail is one of the representative devices in eco-friendly wind-assisted propulsion systems that have been practically applied to commercial ships. The present study proposes an asymmetric vertical folding rotor sail (AFRS) designed for small ships, featuring asymmetric geometry along the vertical direction and the function of vertical folding. To evaluate the aerodynamic performance of rotor sail, the drag, lift and lift-to-drag ratio were derived using computational fluid dynamics. The aerodynamic performance of AFRS was compared with that of normal rotor sail with different aspect ratios and spin ratios. The effect of geometric parameters on the aerodynamic performance of AFRS was assessed by varying the asymmetric diameter ratio. The maximum improvement in lift-to-drag ratio for AFRS was approximately 12% in the considered case. Additionally, the resistance is decreased when AFRS is vertically folded without rotating. Throughout the present study, improved aerodynamic and resistance performances for AFRS were confirmed, which will successfully provide additional propulsion to small ships.

• 한국철도학회논문집
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• 제16권3호
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• pp.169-174
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• 2013

고성능 EMU 열차의 형상 개선을 통한 공기저항 저감 효과를 알아보기 위하여 3차원정상 Navier-Stokes 방정식과 2방정식 난류 모델을 이용한 전산유체역학을 이용하여 수치해석을 수행하였다. 전산시뮬레이션에는 FLUENTTM ver.13과 Gambit 2.4.6이 사용되었으며, 기본 형상과 유선형으로 개선된 형상에 대하여 계산을 수행하였다. 또한, 터널 내 주행 시의 공기저항 특성을 살펴보기 위하여 개활지에서의 공기저항 계산도 수행하였으며, 차량 별 공기저항 기여도에 대한 분석도 수행되었다. 유선형으로 개선된 형상의 열차는 절편형 전두부와 돌출된 상부 및 하부구조를 가진 기본 형상 열차에 비하여 약 9.8%의 공기저항이 저감된 것을 확인하였으며, 공기저항 저감에 따른 주행저항의 저감은 시속 80km/h에서 약 4%에 이르는 것으로 나타났다.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2000년도 추계학술대회 논문집
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• pp.499-505
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• 2000

The shape of the KHST, and of the power car in particular, is largely determined by aerodynamic considerations. At high speeds, air resistance accounts for the major part of overall resistance to forward motion. Further points to be considered are environmentally undesirable acoustic phenomena and pressure waves. Minimizing power requirements and environmentally-unfriendly noise and pressure waves are thus major objectives in the development of the KHST. When deciding on the aerodynamic design of the power car, the entire train set has to be taken into consideration. This paper describes the design process and results about the front shape of the KHST.

• 한국철도학회:학술대회논문집
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• 한국철도학회 1999년도 추계학술대회 논문집
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• pp.115-120
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• 1999

The shape of the KHST, and of the power car in particular. is largely determined by aerodynamic considerations. At high speeds, air resistance accounts for the major part of overall resistance to forward motion. Further points to be considered are environmentally undesirable acoustic phenomena and pressure waves. Minimizing power requirements and environmentally-unfriendly noise and pressure waves are thus major objectives in the development of the KHST. When deciding on the aerodynamic design of the power car, the entire train set has to be taken into consideration. This paper describes the design process and results about the front shape of the KHST.

• 말소리와 음성과학
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• 제8권3호
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• pp.39-49
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• 2016

The present study examined the change of aerodynamic features after laryngomicrosurgery in patients with vocal polyps. Aerodynamic evaluation was performed in thirty-nine patients (15 males and 24 females) one week before surgery and four weeks after surgery. Evaluation protocols of vital capacity, maximum sustained phonation(MXPH), and voicing efficiency(VOFT) were used to collect 29 phonatory aerodynamic measures, requiring voice with a comfortable pitch and loudness. Statistically significant changes were found for phonation time and airflow values in the MXPH protocol, while changes were also found for airflow values, subglottal pressure values and acoustic resistance values in the VOFT protocol. Although phonation time was increased in both male and female patients, gender-dependent changes were found in airflow measurements. Men's phonation time increased with no difference in airflow rate, but women's phonation time increased with decreased airflow rate and lower subglottal pressure. The changes of aerodynamic features may be affected by women's self-perceived change for vocal attitude, which was reducing sense of vocal effort after surgery.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2011년도 춘계학술대회 논문집
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• pp.20-27
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• 2011

High-speed railway system is exposed to severe aerodynamic problems and has various requirements both on design and operation; 80% of running resistance is composed of aerodynamic drag, the cross-sectional area and portal shape of tunnel should be designed under aerodynamic consideration, and natural wind velocity should always be monitored to prevent the overturning of train by crosswinds. In addition, most of the aerodynamic problems are proportional to the running speed or square of the running speed. Thus, when the running speed of a high-speed railway system either on operation or under construction is to be increased, the aerodynamic problems should be assessed in advance and the countermeasures should be prepared to alleviate the aerodynamic problems to meet certain requirements. In this study, aerodynamic problems that could occur at speed up of high-speed line have been investigated and aerodynamic requirements to meet the increased operational speed have been studied referring the international and domestic rules, guidance, and recommendations.

• International Journal of Automotive Technology
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• 제6권3호
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• pp.221-227
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• 2005

Aim of this study is to investigate an aerodynamic effect of a drag-reducing device on a heavy-duty truck. The vehicle experiences two different kinds of aerodynamic forces such as drag and uplifting force (or downward force) as it is traveling straight forward at constant speed. The drag force on a vehicle may cause an increase of the rate of fuel consumption and driving instability. The rolling resistance of the vehicle may be increased as result of the negative uplifting or downward force on the vehicle. A device named roof-fairing system has been applied to examine the reduction of aerodynamic drag force on a heavy-duty truck. As for a engineering design information, the drag-reducing system should be studied theoretically and experimentally for the best efficiency of the device. Four different types of roof-fairing model were considered in this study to investigate the aerodynamic effect on a model truck. The drag and downward force generated by vehicle has been obtained from numerical calculation conducted in this study. The forces produced on four fairing models considered in this study has been compared each other to evaluate the best fairing model in terms of aerodynamic performance. The result shows that the roof-fairing mounted truck has bigger negative uplifting or downward force than that of non-mounted truck in all speed ranges, and drag force on roof-fairing mounted truck has smaller than that of non-mounted truck. The drag coefficient $(C_D)$ of the roof-fairing mounted truck (Model-3) is reduced up to $41.3\%$ than that of non-mounted trucks (Model-1). A downward force generated by a roof-fairing mounted on a truck is linearly proportional to the rolling resistance force. Therefore, the negative lifting force on a heavy-duty truck is another important factor in aerodynamic design parameter and should be considered in the design of a drag-reducing device of a tractor-trailer. According to the numerical result obtained from present study, the drag force produced by the model-3 has the smallest of all in all speed ranges and has reasonable downward force. The smaller drag force on model-3 with 2/3h in height may results of smallest thickness of boundary layer generated on the topside of the container and the lowest intensity of turbulent kinetic energy occurs at the rear side of the container.

• Wind and Structures
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• 제12권4호
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• pp.285-298
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• 2009

For long-span suspension bridges with their intrinsic limit in flutter, some counter measures, for example, central stabilizers, should be adopted to improve aerodynamic stability to meet with the appropriate wind resistance requirements. The present paper introduces aerodynamic stabilization for long-span suspension bridges with box girders by using central stabilizers based on Xihoumen Bridge with the main span of 1650 m. The aerodynamic stabilization study covers experimental investigation of sectional model testing, comprehensive evaluation of three central stabilizers and theoretical analysis of stabilizing mechanism related to flutter derivatives, aerodynamic damping and degree participation.

• 말소리와 음성과학
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• 제5권4호
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• pp.63-70
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• 2013

The purpose of this study is to show the aerodynamic characteristics and differences in muscle tension dysphonia and adductor spasmodic dysphonia to predict factors which will provide additional information while preparing for the objective examination standard to distinguish the two dysphonias. Forty-eight individuals diagnosed with muscle tension dysphonia and adductor spasmodic dysphonia participated in this study. PAS was used in order to find the aerodynamic characteristics for the two dysphonias. The outcomes of this study show that the airflow variation and glottal resistance of the two groups showed noticeable differences. This study concludes that the aerodynamic characteristics may be used as additional information on diverse evaluations to classify muscle tension dysphonia and adductor spasmodic dysphonia.

• 연구논문집
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• 통권25호
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• pp.13-22
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• 1995

At the running speed higher than 250 km/h, several aerodynamic problems such as the increase of aerodynamic resistance, aerodynamic noise, pressure fluctuation at the tunnel entry, impulsive wave at the tunnel exit bring about the power consumption, deterioration of riding quality, and severe environmental noise. To solve these aerodynamic problems, the flow phenomena around the high speed train have to be analyzed in detail. In this study, the flow around the train is modelled as the 2-dimensional viscous compressible flow and the flow field is calculated numerically for the three different types of geometry and running speed. The aerodynamic drag coefficient and the pressure coefficient are evaluated each case.