• Title, Summary, Keyword: aerodynamic stability

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Dynamic analysis of long-span cable-stayed bridges under wind and traffic using aerodynamic coefficients considering aerodynamic interference

  • Han, Wanshui;Liu, Huanju;Wu, Jun;Yuan, Yangguang;Chen, Airong
    • Wind and Structures
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    • v.24 no.5
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    • pp.405-430
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    • 2017
  • The aerodynamic characteristics of vehicles are critical to assess vehicle safety and passenger comfort for vehicles running on long span bridges in a windy environment. However, in previous wind-vehicle-bridge (WVB) system analysis, the aerodynamic interference between the vehicle and the bridge was seldom considered, which will result in changing aerodynamic coefficients. In this study, the aerodynamic coefficients of a high-sided truck on the ground (ground case) and a typical bridge deck (bridge deck case) are determined in a wind tunnel. The effects of existent structures including the bridge deck and bridge accessories on the high-sided vehicle's aerodynamic characteristics are investigated. A three-dimensional analytical framework of a fully coupled WVB system is then established based on the finite element method. By inputting the aerodynamic coefficients of both cases into the WVB system separately, the vehicle safety and passenger comfort are assessed, and the critical accidental wind speed for the truck on the bridge in a windy environment is derived. The differences in the bridge response between the windward case and the leeward case are also compared. The results show that the bridge deck and the accessories play a positive role in ensuring vehicle safety and improving passenger comfort, and the influence of aerodynamic interference on the response of the bridge is weak.

An Experimental Study on the Aerodynamic Characteristics of a Streamline-designed High-speed Bus (유선형 고속주행 버스의 공력특성에 관한 실험 연구)

  • Kim, Chul-Ho;Lee, Seung-Hyun
    • Transactions of the Korean Society of Automotive Engineers
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    • v.24 no.2
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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.

Study on Vehicle Stability Enhancement for the PACE Formula Vehicle (PACE 경주용 차량의 조종안정성 개선에 대한 연구)

  • Kim, Kwan-Ju;Kim, Hyun-Jun;Lee, Jun-Heon
    • Transactions of the Korean Society of Automotive Engineers
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    • v.19 no.1
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    • pp.25-31
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    • 2011
  • The purpose of the study is to enhance the vehicle handling stability of the PACE formula vehicle. Required data for the dynamic analysis of the vehicle are as follows: Mass, moment of inertia, and tire's dynamic properties. Mass and moment of inertia data were calculated using Siemens NX 5.0 which results were verified with VIMF measurements of GMDAT. Dynamic data for the tire were supplied by Kumho Tire. Aerodynamic forces play an important role in the formula vehicle which forces were calculated by using Fluent. Full vehicle dynamic analysis using Carsim software has been carried out to find out the improvement of the vehicle stability by changing the shapes of the rear wing.

A Study on the Longitudinal Flight Control Law of T-50 (T-50 세로축 비행제어법칙 설계에 관한 연구)

  • Hwang Byung-moon;Kim Seong-Jun;Kim Chong-sup
    • Journal of Institute of Control, Robotics and Systems
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    • v.11 no.11
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    • pp.963-969
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    • 2005
  • An advanced method of Relaxed Static Stability (RSS) is utilized for improving the aerodynamic performance of modem version supersonic jet fighter aircraft. The flight control system utilizes RSS criteria in both longitudinal and lateral-directional axes to achieve performance enhancements and improve stability. The T-50 advanced trainer employs the RSS concept in order to improve the aerodynamic performance and the flight control law in order to guarantee aircraft stability, The T-50 longitudinal control laws employ the dynamic inversion and proportional-plus-integral control method. This paper details the design process of developing longitudinal control laws for the RSS aircraft, utilizing the requirement of MIL-F-8785C. In addition, This paper addresses the analysis of aircraft characteristics such as damping, natural frequency, gain and phase margin about state variables for longitudinal inner loop feedback design.

Aerodynamic Characteristics and Static Height Stability of WIG Effect Vehicle with Direct Underside Pressurization (DUP 가 있는 위그선의 공력학 특성 및 고도 안정성)

  • Park, Kyoung-Woo;Kim, Jin-Bae;Lee, Ju-Hee
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.33 no.12
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    • pp.961-967
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    • 2009
  • A 3-dimensional numerical investigation of a WIG effect vehicle with DUP (direct underside pressurization) is performed to predict aerodynamic characteristics and the static height stability. DUP can considerably reduce take-off speed and minimize the hump drag while the vehicle accelerates on the water to take off. The DUP of the model vehicle, Aircat, consists of a propeller in the middle of the fuselage and an air chamber under the fuselage. The air accelerated by the propeller comes into the camber through the channel in the middle of fuselage and augments lift by changing its dynamic pressure to static pressure dramatically. However, the air accelerated by a propeller produces excessive drag and reduces static height stability.

Analysis of dynamic characteristics of aerodynamically controlled STT missiles (공력 조종 STT 유도탄의 동특성 해석)

  • 송찬호;전병을
    • 제어로봇시스템학회:학술대회논문집
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    • pp.1308-1311
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    • 1996
  • We propose a new linearized model which can be used very efficiently for the design and analysis of the autopilot of aerodynamically controlled skid-to-turn missiles. Proposed model is based on the linearized equations of the missile dynamics derived in the aerodynamic frame where xz plane contains the missile longitudinal axis and velocity vector. However, to take the effect due to the small perturbation of the missile body into consideration, we introduce a new frame which is identical to the aerodynamic frame in the trim state but after small perturbation it moves fixed with the missile body, and finally, the proposed model is set up in this frame. It is shown by nonlinear simulations and stability analysis of a numerical example that the new model describes the missile motion better than the conventional one linearized in the body frame with a certain amount of simplification.

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Mechanism of ovalling vibrations of cylindrical shells in cross flow

  • Uematsu, Yasushi;Tsujiguchi, Noboru;Yamada, Motohiko
    • Wind and Structures
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    • v.4 no.2
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    • pp.85-100
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    • 2001
  • The mechanism of wind-induced ovalling vibrations of cylindrical shells is numerically investigated by using a vortex method. The subject of this paper is limited to a two-dimensional structure in the subcritical regime. The aerodynamic stability of the ovalling vibrations in the second to fourth circumferential modes is discussed, based on the results of a forced-vibration test. In the analysis, two modal configurations are considered; one is symmetric and the other is anti-symmetric with respect to a diameter parallel to the flow direction. The unsteady pressures acting on a vibrating cylinder are simulated and the work done by them for one cycle of a harmonic motion is computed. The effects of a splitter plate on the flow around the cylinder as well as on the aerodynamic stability of the ovalling vibrations are also discussed. The consideration on the mechanism of ovalling vibrations is verified by the results of a free-vibration test.

Experimental analysis of aerodynamic stability of stress-ribbon footbridges

  • Pirner, Miros;Fischer, Ondrej
    • Wind and Structures
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    • v.2 no.2
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    • pp.95-104
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    • 1999
  • The dynamic properties of one-span or multi-span reinforced concrete footbridges of catenary form (see e.g., Fig. 1) include the very low fundamental natural frequency, usually near the step-frequency of pedestrians, and the low damping of bending vibrations. The paper summarized the results of model as well as full-scale measurements with particular reference to the influence of torsional rigidity of the stress-ribbon on the magnitude of aerodynamic response, the results of measurements on footbridges of catenary form being completed by results obtained on footbridges of some other types. Additionally the influence of the local broadening of the bridge deck on the bridge response was tested. Starting from these results the criterion has been derived for the decision, whether the flutter analysis is necessary for the design of the footbridge.

Aerodynamic Stability Assessment of PWS and CFRC Hanger Ropes for Suspension Bridge by Experiments (현수교 PWS 및 CFRC 행어로프의 내풍안정성 실험 평가)

  • Park, Hyung-Ghee;Kang, Seon-Jin
    • Journal of Korean Society of Hazard Mitigation
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    • v.8 no.6
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    • pp.21-30
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    • 2008
  • In this study, to evaluate the aerodynamic stability of suspension bridge hanger ropes, the wind tunnel tests are carried out. It is found that the vortex induced vibration is detected only in single PE-coated PWS cable case. And the wake galloping is occurred in twin cables spaced $3\sim6$ cable diameters of cable center to center when the incidence angle of wind is only zero degree. In case of other incidence angles of wind except zero degree, the wake galloping or the wake flutter are showed in twin cables even outside range of the bounds of $3\sim6$ cable diameters. CFRC cable shows very stable for the twin cables regardless of the distance between two cables, and also for various incidence angles of wind. Thus the characteristic of CFRC rope overwhelms one of PWS cable in aerodynamic stability.

Application of an Adaptive Autopilot Design and Stability Analysis to an Anti-Ship Missile

  • Han, Kwang-Ho;Sung, Jae-Min;Kim, Byoung-Soo
    • International Journal of Aeronautical and Space Sciences
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    • v.12 no.1
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    • pp.78-83
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    • 2011
  • Traditional autopilot design requires an accurate aerodynamic model and relies on a gain schedule to account for system nonlinearities. This paper presents the control architecture applied to a dynamic model inversion at a single flight condition with an on-line neural network (NN) in order to regulate errors caused by approximate inversion. This eliminates the need for an extensive design process and accurate aerodynamic data. The simulation results using a developed full nonlinear 6 degree of freedom model are presented. This paper also presents the stability evaluation for control systems to which NNs were applied. Although feedback can accommodate uncertainty to meet system performance specifications, uncertainty can also affect the stability of the control system. The importance of robustness has long been recognized and stability margins were developed to quantify it. However, the traditional stability margin techniques based on linear control theory can not be applied to control systems upon which a representative non-linear control method, such as NNs, has been applied. This paper presents an alternative stability margin technique for NNs applied to control systems based on the system responses to an inserted gain multiplier or time delay element.