• Title/Summary/Keyword: drag force

Search Result 312, Processing Time 0.167 seconds

Fairing Design Optimization of Missile Hanger for Drag Reduction (유도탄 행거 항력 저감을 위한 페어링 형상 최적화)

  • Jeong, Sora
    • Journal of the Korea Institute of Military Science and Technology
    • /
    • v.22 no.4
    • /
    • pp.527-535
    • /
    • 2019
  • Hanger in a rail-launched missile protrudes in general and causes to increase significant drag force. One method to avoid the significant increase of drag force is to apply fairings on the hanger. In this paper, sloping shaped fairing parameters of height, width, and length are optimized to minimize the drag force under subsonic speed region by examining three configurations of fairings : front-fairing only, rear-faring only, and the both front and rear fairing. We use Latin Hypercube Sampling method to determine the experimental points, and computational fluid dynamics with incompressible RANS solver was applied to acquire the data at sampling points. Then, we construct a meta model by kriging method. We find the best choice among three configurations examined : both front and rear fairing reduce the drag force by 63 % without the constraint of fairing mass, and front fairing reduced the drag force by 52 % with the constraint of hanger mass.

Effects of the Distance between Houses on the Wind Force Coefficients on the Single-span Arched House (아치형 단동하우스의 동간거리가 풍력계수에 미치는 영향)

  • 이현우;이석건
    • Magazine of the Korean Society of Agricultural Engineers
    • /
    • v.35 no.4
    • /
    • pp.76-85
    • /
    • 1993
  • The purpose of this study was to analyze the wind force distribution on the two single-span arched plastic house depending upon the house spacing and wind direction, which may provide the fundamental criteria for the structural design. In order to specify the wind force distribution, the variation of the wind force coefficients, the mean wind force coefficients and the drag force coefficients were estimated from the wind tunnel test data. The results obtained are as follows : 1. At the wind direction of 90$^{\circ}$, there was a typical span interval at which the maximum negative pressure was occured at the edge of the inside walls. 2. In the consideration of wind loads, the wind force coefficients estimated from independent single-span arched plastic house should not be directly applied to the structural design on the double houses separated. 3. The average maximum negative wind force on the inside walls was occured at the wind direction of 90$^{\circ}$, and the variations depending on the span intervals was not significant. 4. The average maximum drag force was occured at the wind direction of 300, and the magnitude of drag force was more significant at the first house. As the distance between two houses was increased, the drag force was slightly increased for every wind direction.

  • PDF

Effects of cobble shape on coefficient of drag force (항력계수에 미치는 호박돌 형상의 영향)

  • Park, Sang Deog;Yoon, Min Woo;Yoon, Young Ho
    • Journal of Korea Water Resources Association
    • /
    • v.50 no.6
    • /
    • pp.419-427
    • /
    • 2017
  • In mountainous rivers, the drag force acting on cobbles abundant in the riverbed surface is important in predicting behavior and response of the river. However there is little research for the drag coefficients of cobbles. This paper is to carry out the experiments for drag force of cobble and analyze the relation between the cobble shape and the drag coefficient. The effects of the shape factor on the drag coefficients $C_D$ when the long axis or the short axis of the cobbles are parallel to the direction of flow velocity were analyzed. The coefficient of drag force increased with the nominal diameter Reynolds number $R_{ep}$. The drag coefficients are greater in short axis than long axis. The coefficient of determination of the relation between $C_D$ and $R_{ep}$ is greater in long axis than short axis. This means that the drag forces acting on the irregularly-shaped cobbles depend on the axis. A change of the drag force distribution has brought about the alternative swing of cobbles. For $R_{ep}$ > 12,000, the amplitude of the swing has been increased sharply and especially was greater in short axis than long axis.

Earthquake Response Analysis of an Offshore Wind Turbine Considering Effects of Geometric Nonlinearity of a Structure and Drag Force of Sea Water (기하 비선형과 항력 효과를 고려한 해상풍력발전기의 지진 응답해석)

  • Lee, Jin Ho;Bae, Kyung Tae;Jin, Byeong Moo;Kim, Jae Kwan
    • Journal of the Earthquake Engineering Society of Korea
    • /
    • v.17 no.6
    • /
    • pp.257-269
    • /
    • 2013
  • In this study, the capability of an existing analysis method for the fluid-structure-soil interaction of an offshore wind turbine is expanded to account for the geometric nonlinearity and sea water drag force. The geometric stiffness is derived to take care of the large displacement due to the deformation of the tower structure and the rotation of the footing foundation utilizing linearized stability analysis theory. Linearizing the term in Morison's equation concerning the drag force, its effects are considered. The developed analysis method is applied to the earthquake response analysis of a 5 MW offshore wind turbine. Parameters which can influence dynamic behaviors of the system are identified and their significance are examined.

Effect of aerodynamic drag force on liquid metal convection in GTA welding (GTA 용접시 발생하는 용융금속의 유동에 미치는 공기역학적 향력의 영향)

  • 나석주;김성도
    • Transactions of the Korean Society of Mechanical Engineers
    • /
    • v.15 no.2
    • /
    • pp.575-583
    • /
    • 1991
  • The weld pool convection problem that occurs during the stationary GTA welding has been studied, considering the four driving forces for weld pool convection, i.e., the electromagnetic force, the buoyancy force, the aerodynamic drag force, and the surface tension force at the weld pool surface. In the numerical simulation, the difficulties associated with the irregular moving liquid-solid interface have been successfully overcome by adopting a Boundary-Fitted Coordinate system. In the experiments to show the validity of the numerical analysis, a deep periphery and shallow centerpentrated weld pool shape was observed from the etched specimen. It could be revealed that this type of weld pool shape could be simulated, only when some of aerodynamic drag force distributions are considered. Although slight disagreement arose, the calculated and the observed weld pool shapes were in a reasonable agreement.

Flow Analysis around Tilt-rotor Aircraft at Various Tilt Angles (틸트각 변화에 따른 틸트로터 항공기 주위의 유동해석)

  • Kim, Su-Yean;Choi, Jong-Wook
    • Journal of the Korean Society of Visualization
    • /
    • v.9 no.2
    • /
    • pp.40-47
    • /
    • 2011
  • Tilt-rotor aircraft can be used in various fields because they have the capabilities of the vertical take-off and landing and the high-speed cruise flight. In the present study, the flow analysis of a tilt-rotor aircraft is conducted at various tilt angles. The lift and drag forces of the tilt-rotor aircraft are obtained and the wakes by the rotor-blade are visualized. The result shows that the rotor-blade affects the lift force in a hovering mode and the main wing has an influence on the lift force in a cruise mode. Additional thrust is required at the tilt angle of around 40 degree due to the least lift force. The drag force is dependent on the rotor-blade at overall tilt angles. The minus drag force appears between the tilt angles of 90 degree and 55 degree. Also, the drag force is dramatically increased at the other tilt angles. The wake by rotor-blade affects the flow around the fuselage of the tilt-rotor aircraft at the tilt angles of 75 degree and 60 degree.

A fundamental study on drag force of shield TBM cutter bit by scaled model test (축소모형실험을 통한 쉴드 TBM 커터비트의 절삭력 평가를 위한 기초 연구)

  • Kim, Sang-Hwan;Jang, In-Suk;Kim, Ji-Tae
    • Journal of Korean Tunnelling and Underground Space Association
    • /
    • v.14 no.3
    • /
    • pp.277-292
    • /
    • 2012
  • This paper presents the fundamental study on drag force of shield TBM cutter bit by scaled model test. Several theoretical analyses of the drag force of cutter bit have been studied. However, there are still some difference between the theoretical approaches and actual drag bit capacity. In order to study the drag forces of shield TBM cutter bit, the scaled model tests are carried out and analyzed. The results obtained from scaled model tests are compared with the existing theoretical equations. It is highly expected that the results of this study will be very essentially useful to design and develope the TBM cutterhead.

A Transplanting Method of Laminaria japonica Areschoug (Laminariales, Phaeophyta)

  • Kim, Woong-Yong;Choi, Sung-Je;Chung, Ik-Kyo;Shin, Jong-Ahm
    • ALGAE
    • /
    • v.20 no.2
    • /
    • pp.151-155
    • /
    • 2005
  • To obtain basic data, we investigated the effect of blade length on transplants, the transplanting method of Laminaria japonica for creating L. japonica resources and the number of transplanting plates with surviving L. japonica. The survival rate of L. japonica, blade length of transplants and drag force of transplanting plates were also researched. The number of transplanting plates with surviving L. japonica, the survival rate and blade length of 20 cm long-initial transplants were greater than those of 1.5, 5 and 10 cm long-initial transplants in an outdoor aquarium. At the depth of 4 m in the coastal waters, the number of transplanting plates with surviving transplants, the survival rate and the blade length of 30 cm long-initial transplants were higher than those of 10 and 20 cm longinitial transplants. The drag force is calculated by cording up sporophytes of L. japonica into the transplanting plates under water. The drag force in the case of a 2.18 kg-weight transplanting plate and in a current speed of 0.5 m${\cdot}s^{-1}$ for considering stability of the plate was 631.50 g to a concrete substratum on the seabed, 703.92 g to a shingle substratum, 788.00 g to a sand substratum, and 1018.30 g to a silt substratum. If we consider the stability and economic efficiency of the transplanting plate, the proper weight of the plate per one individual of 18.11 cm in blade width and 190.20 cm in total blade length is regarded as 508.2 g when it is calculated with the concrete substratum that shows the lowest drag force.

Evaluation of Wind Force Coefficients of a Box-Type Girder Bridge with Noise Barriers (방음벽의 유무에 따른 박스형 거더교의 풍력계수 평가)

  • Jeong, Seung Hwan;Lee, Youngki
    • KSCE Journal of Civil and Environmental Engineering Research
    • /
    • v.38 no.5
    • /
    • pp.627-634
    • /
    • 2018
  • In the study, computational fluid dynamics analysis was performed to estimate wind force coefficients for a box-type concrete girder bridge under the influence of wind. The drag, lift and pitching moment coefficients were obtained for the bridge section without noise barrier and compared with those of the bridge section with noise barriers of various heights. The shear stress transport $k-{\omega}$ turbulence model was employed to estimate the wind force coefficients, and the contribution of the friction drag force to the total drag force was investigated. It was found from the study that the drag force coefficients increased as the height of noise barrier increased when a wind blew horizontally, and that the contribution of the friction drag force was highest for the bridge section without noise barrier. It is concluded that the impact of the height of noise barriers should be considered in the design of bridges, and the friction force played an important role in evaluating wind forces on bridges.

A Numerical Analysis of Supersonic Counter Jet Flow Effect on Performance of a Supersonic Blunt-Body (초음속 역분사 유동이 초음속 비행체 성능에 미치는 영향에 대한 수치해석적 연구)

  • Seo D. K.;Seo J. I.;Song D. J.
    • Journal of computational fluids engineering
    • /
    • v.7 no.3
    • /
    • pp.1-8
    • /
    • 2002
  • The counter jet flow which is injected against the free stream at stagnation region of blunt body for improvement of aerodynamic performance has been studied by using upwind Navier-Stokes method. The variations of drag force and upwind forward penetration depth due to changes in the stagnation thermodynamic properties of counter jet flow such as total pressure, Mach number, and total temperature have been studied. The results show that the changes in the stagnation pressure and Mach number have large effects on the wall pressure and drag force, but the total temperature does not affect the wall pressure and drag force.