• Title, Summary, Keyword: Lift-offset

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Validation on Conceptual Design and Performance Analyses for Compound Rotorcrafts Considering Lift-offset

  • Go, Jeong-In;Park, Jae-Sang;Choi, Jong-Soo
    • International Journal of Aeronautical and Space Sciences
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    • v.18 no.1
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    • pp.154-164
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    • 2017
  • This work conducts a validation study for the XH-59A helicopter using a rigid coaxial rotor system in order to establish the techniques of the conceptual design and performance analysis for the lift-offset compound rotorcraft. As a tool for conceptual design and performance analysis, NDARC (NASA Design and Analysis of Rotorcraft) is used for the present study. An assumed mission profile is considered for the conceptual design of the XH-59A. As a validation result of the design, the dimensions and weight of the XH-59A are appropriately designed when compared to the target values since the relative error is less than 0.5%. Then, performance analyses are conducted for the designed XH-59A model with and without auxiliary propulsion in hover and forward flight conditions. The present analyses show good validity since the prediction results compare well with both the flight test and previous analyses. Therefore, the techniques for the conceptual design and performance analysis of the lift-offset compound helicopter are overall considered to be appropriately established. In addition, this study investigates the influence of the lift-offset on the rotor effective lift-to-drag ratio of the XH-59A helicopter with auxiliary propulsion. As a result, the improvement of the rotor effective lift-to-drag ratio can be obtained by appropriately increasing the lift-offset in high-speed flight.

Dynamic contact response of a finite beam on a tensionless Pasternak foundation under symmetric and asymmetric loading

  • Coskun, Irfan
    • Structural Engineering and Mechanics
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    • v.34 no.3
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    • pp.319-334
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    • 2010
  • The dynamic response of a finite Bernoulli-Euler beam resting on a tensionless Pasternak foundation and subjected to a concentrated harmonic load is investigated in this study. This load may be applied at the center of the beam, or it may be offset from the center. Since the elastic foundation is assumed to be tensionless, the beam may lift off the foundation, resulting in contact and non-contact regions in the system. An analytical/numerical solution is obtained from the governing equations of the contact and non-contact regions to determine the coordinates of the lift-off points. Although there is no nonlinear term in the equations, the problem appears to be nonlinear since the contact regions are not known in advance. Due to that nonlinearity, the essentials of the problem (the coordinates of the lift-off points) are calculated numerically using the Newton-Raphson technique. The results, which represent the symmetric and asymmetric responses of the beam, are presented graphically in this work. They illustrate the effects of the forcing frequency and the beam length on the extent of the contact regions and displacements.

Response of a finite beam on a tensionless Pasternak foundation under symmetric and asymmetric loading

  • Coskun, Irfan;Engin, Hasan;Ozmutlu, Aydin
    • Structural Engineering and Mechanics
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    • v.30 no.1
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    • pp.21-36
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    • 2008
  • The static response of a finite beam resting on a tensionless Pasternak foundation and subjected to a concentrated vertical load is assessed in this study. The concentrated vertical load may be applied at the center of the beam, or it may be offset from the center. The tensionless character of the foundation results in the creation of lift-off regions between the beam and the foundation. An analytical/ numerical solution is obtained from the governing equations of the contact and lift-off regions to determine the extent of the contact region. Although there is no nonlinear term in the equations, the problem shows a nonlinear character since the contact region is not known in advance. Due to that nonlinearity, the essentials of the problem (the coordinates of the lift-off points) are calculated numerically using the Newton-Raphson technique. The numerical results are presented in figures to illustrate the behaviours of the free-free and pinned-pinned beams under symmetric or asymmetric loading. The figures illustrate the effects of the shear foundation parameter and the symmetric and asymmetric loading options on the variation of the contact lengths and the displacement of the beam.

Performance and Airloads Analyses for a Rigid Coaxial Rotor of High-Speed Compound Unmanned Rotorcrafts (고속 비행 복합형 무인 회전익기의 강체 동축반전 로터의 성능 및 공력 하중 해석)

  • Kwon, Young-Min;Park, Jae-Sang
    • Journal of the Korea Institute of Military Science and Technology
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    • v.23 no.4
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    • pp.311-318
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    • 2020
  • This study investigates the performance and blade airloads for a rigid coaxial rotor of high-speed compound unmanned rotorcrafts. The present compound unmanned rotorcraft uses not only a rigid coaxial rotor, but also wings and propellers for high-speed flights. For the rigid coaxial rotor in this work, CAMRAD II, a rotorcraft comprehensive analysis code, is used to study the performance at a flight speed of up to 250 knots and blade section lift forces at 230 knots. As the flight speed increases, the rotor power decreases; however, the power of propellers increases to overcome the drag force of a rotorcraft in high-speed flight. The effective lift-to-drag ratio of a rotor has the maximum value of about 11.6 which is much higher than the value of the conventional helicopter. The blade section lift forces of the upper and lower rotors at 230 knots show the similar variation trends for one rotor revolution, and the impulses because of the aerodynamic interaction between both rotors are observed.

Further Improvement in Rotor Aerodynamics Estimation in Helicopter Conceptual Design and Optimization Framework for a Compound Rotorcraft

  • Lim, JaeHoon;Shin, SangJoon;Kee, YoungJung
    • International Journal of Aeronautical and Space Sciences
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    • v.18 no.4
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    • pp.641-650
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    • 2017
  • In order to include the design capability for a compound rotorcraft in a helicopter conceptual design and optimization framework, relevant further improvement was planned and conducted. Previously, a certain conceptual design optimization framework was developed by the present authors to design a modern rotorcraft with single main and tail rotor. The previously developed framework was further improved to expand its capability for a compound rotorcraft. Specifically, its power estimation algorithm was upgraded by using a comprehensive rotorcraft analysis program, CAMRAD II. The presently improved conceptual design and optimization framework was validated using data of the XH-59A aircraft.

Study on Evaluation Method of Flow Characteristics in Steady Flow Bench(5)-Effect of Evaluation Position (정상유동 장치에서 유동 특성 평가 방법에 대한 연구(5) - 평가위치의 영향)

  • Cho, Siehyung;Ohm, Inyong
    • Transactions of the Korean Society of Automotive Engineers
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    • v.25 no.2
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    • pp.179-189
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    • 2017
  • This paper is the fifth investigation on the methods of evaluating flow characteristics in a steady flow bench. In previous studies, several assumptions used in the steady flow bench were examined and it was concluded that the assumption of the solid rotation may lead to serious problems. In addition, though the velocity profiles were improved as the measuring position went downstream, the distributions were far from ideal regardless of the valve angle and evaluation position. The eccentricities were also not sufficiently small to disregard the effect on impulse swirl meter (ISM) measurement. Therefore, the effect of these distribution and eccentricity changes according to the positions needs to be analyzed to discuss the method of flow characteristics estimation. In this context, the effects of evaluation position on the steady flow characteristics were studied. For this purpose, the swirl coefficient and swirl ratio were assessed and compared via measurement of the conventional ISM and calculation based on the velocity by particle image velocimetry(PIV) from 1.75B, 1.75 times bore position apart from the cylinder head, to the 6.00B position. The results show that the swirl coefficients by ISM strictly decrease and the curves as a function of the valve lift become smooth and linear as the measuring position goes downstream. However, the values through the calculation based on the PIV are higher at the farther position due to the approach of the tangential velocity profile to ideal. In addition, there exists an offset effect between the velocity distribution and eccentricity in the low valve lift range when the coefficients are estimated based on the swirl center. Finally, the curve of the swirl ratio by ISM and by PIV evaluation as a function the measuring position intersect around 5.00B plane except at $26^{\circ}$ valve angle.

Effects of Port Shape on Steady Flow Characteristics in an SI Engine with Semi-Wedge Combustion Chamber (2) - Velocity Distribution (2) (반 쐐기형 연소실을 채택한 SI 기관에서 포트형상이 정상유동 특성에 미치는 영향 (2) - 유속분포 (2))

  • Yoon, Inkyoung;Ohm, Inyong
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.41 no.2
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    • pp.97-107
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    • 2017
  • This study is the second investigation on the steady flow characteristics of an SI engine with a semi-edge combustion chamber as a function of the port shape with varying evaluation positions. For this purpose, the planar velocity profiles were measured from 1.75B, 1.75 times of bore position apart from the bottom of head, to 6.00B positions using particle - image velocimetry. The flow patterns were examined with both a straight and a helical port. The velocity profiles, streamlines, and centers of swirl were almost the same at the same valve lift regardless of the measuring position, which is quite different from the case of the pent-roof combustion chamber. All the eccentricity values of the straight port were out of distortion criterion 0.15 through the lifts and the position. However, the values of the helical port exceeded the distortion criterion by up to 4 mm lift, but decreased rapidly above the 3.00B position and the 5 mm lift. There always existed a relative offset effect in the evaluation of the swirl coefficient using the PIV method due to the difference of the ideal impulse swirl meter velocity profile assumption, except for the cylinder-center-base estimation that was below 4 mm of the straight port. Finally, it was concluded that taking the center as an evaluation basis and the assumption about the axial velocity profile did not have any qualitative effect on swirl evaluation, but affected the value owing to the detailed profile.

Journal Bearing Design Retrofit for Process Large Motor-Generator - Part I : Bearing Performance Analysis (프로세스 대형 모터-발전기의 저어널 베어링 설계 개선 - Part I : 베어링 성능해석)

  • Lee, An Sung
    • Tribology and Lubricants
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    • v.28 no.5
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    • pp.197-202
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    • 2012
  • In this study, with the purpose of fundamentally improving the unbalance response vibration of a large PRT motor-generator rotor by design, a performance improvement design analysis is carried-out by retrofitting tilting pad bearings, replacing the plain partial journal bearings that were originally applied for operation at a rated speed of 1,800 rpm. In this process, a goal of the design analysis is to obtain a design solution for maximizing the direct stiffness of the bearings while satisfying the key basic lubrication performance requirements such as the minimum lift-off speed and maximum oil-film temperature. The results show that with a careful design application of tilting pad journal bearings for operation at such a relatively low speed of 1,800 rpm, direct stiffness increment of the bearings by about two times can be effectively achieved. Prevention of pad unloading is also considered in the analysis. Moreover, the designs of elliptical and offset half journal bearings are also analyzed and reviewed.

An Experimental Study of Performance Characteristics on a Double Chamber Rotor Operated by High Pressure Air with Various Vanes (공압용 더블챔버 로터에서 베인개수에 따른 성능특성에 관한 실험적연구)

  • Cho, Chong-Hyun;Choi, Sang-Kyu;Cho, Soo-Yong
    • The KSFM Journal of Fluid Machinery
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    • v.9 no.6
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    • pp.54-62
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    • 2006
  • An experiment about performance characteristics is conducted on a double chamber vane-type rotor. Three different rotors, which have 6, 8 and 9 vanes, are applied to the driver and various lift holes at the rear plate are used to increase the effective vane height. The inner diameter of a double chamber cylinder is ${\phi}27mm$, and the length of the cylinder is 65 mm. The maximum offset length between the rotor outer surface and the cylinder inner surface is 4.5 mm. In this study, specific output torques and powers are measured, and also noise and vibration are measured at the real operating situation. The operating torque on the double chamber is increased to 17% compared to the operating torque obtained at the single chamber which has the same size. The experimental results of noise and vibration show that the operating sound and vibration are directly related to the operating power generated by the double chamber rotor.

Transfer System using Radial Electrodynamic Wheel over Conductive Track (래디얼 동전기 휠을 이용한 전도성 트랙 위에서의 이송 시스템)

  • Jung, Kwang Suk
    • Journal of the Korea Academia-Industrial cooperation Society
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    • v.18 no.11
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    • pp.794-801
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    • 2017
  • When a radial wheel is placed so as to partially overlap a conductive plate and rotated, a lift force is generated on the wheel, a thrust force along the edge, and a lateral force which tends to reduce the overlap region. When several of these wheels are combined, it is possible to realize a system in which the stability of the remaining axes is ensured, except in the traveling direction. To validate the overall characteristics of the multi-wheel system, we propose a transfer system levitated magnetically using radial electrodynamic wheels. The proposed system is floated and propelled by four wheels and arranged in a structure that allows the thrusts generated by the front and rear wheels to offset each other. The dynamic stability of the wheel and the effect of the pole number on the three-axial forces are analyzed by the finite element method. At this time, the thrust and levitation force are strongly coupled, and the only factor affecting them is the wheel rotation speed. Therefore, in order to control these two forces independently, we make use of the fact that the ratio of the thrust to the levitation force is proportional to the velocity and is independent of the size of the gap. The in-plane and out-of-plane motion control of the system is achieved by this control method and compared with the simulation results. The experimental results show that the coupled degrees of freedom can be effectively controlled by the wheel speed alone.