• Title/Summary/Keyword: 초기 비틀림각

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Vibration Analysis of a Rotating Blade Considering Pre-twist Angle, Cross Section Taper and a Concentrated Mass (초기 비틀림 각과 단면 테이퍼 그리고 집중질량을 갖는 회전하는 블레이드의 진동해석)

  • Kim, Hyung Yung;Yoo, Hong Hee
    • Transactions of the Korean Society for Noise and Vibration Engineering
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    • v.23 no.4
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    • pp.338-346
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    • 2013
  • Equations of motion of a rotating blade considering pre-twist angle, cross section taper and a concentrated mass are derived using the hybrid deformation variable modeling method. For the modeling of a concentrated mass which is located at an arbitrary position of the blade, a Dirac delta function is employed for the mass density function. The final equations for the vibration analysis are transformed into a dimensionless form using several dimensionless parameters. The effects of the dimensionless parameters on the vibration characteristics of the rotating blade are investigated through numerical analysis.

Modal Analysis of a Rotating Multi-Packet Pre-twisted Blade System (초기 비틀림각을 갖는 회전하는 다중 패킷 블레이드 시스템의 고유 진동 해석)

  • Kim, Min-Kwon;Yoo, Hong-Hee
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2008.04a
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    • pp.393-399
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    • 2008
  • A modeling method for the modal analysis of a pre-twisted multi-packet blade system undergoing rotational motion is presented in this paper. Blades are idealized as pre-twisted cantilever beams that are fixed to a rotating disc. The stiffness coupling effects between blades due to the flexibilities of the disc and the shroud are modeled with discrete springs. The coupling effect between chordwise and flapwise bending deflection is also considered. Hybrid deformation variables are employed to derive the equations of motion. To obtain more general information, the equations of motion are transformed into dimensionless forms in which dimensionless parameters are identified. The effects of the dimensionless parameters and the number of packets as well as blades on the modal characteristics of the rotating multi-packet pre-twisted blade system are investigated with some numerical examples.

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Vibration Analysis of Pre-twisted Blades with Functionally Graded Material Properties Based on Timoshenko Beam Theory (티모센코 보 이론에 따른 초기 비틀림각을 갖는 경사기능재 블레이드의 진동 해석)

  • Yoo, Hong Hee;Oh, Yutaek
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2014.10a
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    • pp.285-287
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    • 2014
  • Equations of motion for the vibration analysis of rotating pre-twisted beams with functionally graded material properties are derived in this paper. Based on Timoshenko beam theory, the effects of shear and rotary inertia are considered. The pre-twisted beam has a rectangular cross-section and is mounted on a rotating rigid hub with a setting angle. Functionally graded material (FGM) properties are considered along the height direction of the beam. The equations of stretching and bending motion are derived by Kane's method employing hybrid deformation variables. To validate the derived equations, natural frequencies of a rotating FGM pre-twisted beam are compared to those obtained by a commercial software ANSYS. The effects of the pre-twisted angle, slenderness ratio, hub radius, volume fraction exponent, and angular speed on the modal characteristics of the system are investigated with the proposed model.

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Torsional Behavior of Core Structures according to the Location of Reinforcement (보강재의 위치변화에 따른 코아구조물의 비틀림거동)

  • 정동조
    • Journal of the Computational Structural Engineering Institute of Korea
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    • v.15 no.3
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    • pp.545-555
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    • 2002
  • This paper presents a matrix analysis to get the torsional behavior of core structures with torsional reinforcements. Based on simplified assumptions, formulae for the forces and displacements of cote structures subjected to three typical load cases, i.e. uniformly distributed torque, triangularly distributed torque and a concentrated torque at the top of the structure, are derived analytically. The behavior of the cote according to the variation of reinforcement locations is investigated to estimate the optimum locations of reinforcements to minimize the core rotations and bimoments. The results by the program MIDAS-GEN have shown that this analysis can give quite satisfactory results for structural models with torsional reinforcements. Although three dimensional analysis by computer has come within reach as a normal structural design procedure, its use as an optimization tool may not be desirable in view of the expense and time required. Formulae that we presented here can be used to estimate the torsional rotations and forces of practical cote structures at the preliminary design stages.

Simplified 2D Analysis for Suspension Bridges Subject to Wind Excitation (현수교 풍진동에 관한 2D 간단해석 및 변수연구)

  • Kim, Woo Seok;Lee, Jaeha
    • Journal of the Computational Structural Engineering Institute of Korea
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    • v.26 no.6
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    • pp.463-470
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    • 2013
  • In this paper, 2D simple analyses were performed in order to predict the large torsional oscillations in a suspension bridge based on Makenna and Tuama model(2001). The existing model(Makenna and Tuama, 2001) has shown unrealistic results as the wind speed increases and frequency decreases. Furthermore, resonance could not be simulated by the existing model. Therefore, in this study, new model was proposed with a consideration of the torsional resistance. The vertical and rotational behaviors of the deck in the suspension bridge were analyzed. Analysis results showed that at first vertical oscillations were observed and it was gradually transformed to the rotation oscillations. With the consideration of the torsional resistance, it was shown that vertical behavior were stabilized as time passed. However, the rotational behavior was not stabilized and was kept until the end of analysis. Beat periods decreased while the wind speed increased. The resonance of the rotational mode was dependent to the rotational resistance. Obtained results could be applied for the design of the suspension bridge under the wind load.

The influence of iatrogenic mobilization in the initial stage of implant installation on final osteointegration (임플란트 식립 초기 의원성 동요가 최종 골결합에 미치는 영향)

  • Kwak, Myeong-Bae;Cho, Jin-Hyun;Lee, Du-Heong;Lee, Cheong-Hee
    • The Journal of Korean Academy of Prosthodontics
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    • v.52 no.2
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    • pp.105-112
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    • 2014
  • Purpose: The aim of present investigation was to find out the influence of several times iatrogenic mobilization in the initial stage of implant installation on bone-implant osteointegration. Materials and methods: The experimental implants (3.75 mm in diameter, 8.0 mm in length) were made of commercially pure (Grade IV) titanium, and were treated with RBM ($MegaGen^{(R)}$: Ca-P) on lower 4.0 mm part. Only lower part of implant was inserted to bone and the implants were nonsubmerged. The 130 implants (two in each tibia) were inserted into the monocortical tibias of 33 rabbits which each weighed more than 3.5 kg (Female, New Zealand White). According to the removal torque interval, the groups were divided into 13 groups, group I (1 day), group II (1 day + 2 days), group III (1 day + 2 days + 3 days), group IV (1 day + 2 days + 3 days + 4 days), group V (2 days), group VI (2 days + 4 days), group VII (2 days + 4 days + 6 days), group VIII (2 days + 4 days + 6 days + 8 days), group IX (4 days), group X (4 days + 7 days), group XI (4 days + 7 days + 10 days), group XII (4 days + 7 days + 10 days + 14 days) and control group. In the control group, the removal torque was measured at 8 weeks with a digital torque gauge (Mark-10, USA). In the experimental groups, the removal torque was given once, twice, three times or four times by experiment design before the final removal torque and the value was measured each time. The implants were then screwed back to their original positions. All the experimental groups were given a final healing time of 8 weeks after placement, in which values were compared with the control groups and the 1st, 2nd, 3rd or 4th removal torque values in each experimental group. Results: In comparison of the final removal torque tests among experimental groups, the removal torque value of experimental groups except group XII were not statistically different that of control group. And the values of group I and II were significantly higher than the values of group VI, VIII, X, XI, and XII. In addition, the values of group III, IV, and V were significantly higher than group XI and XII. In comparison of the removal torque in the each experimental group, the final removal torque were significantly higher in all groups except group VIII, X, XI, and XII. Conclusion: If sufficient healing time was allowed, a few mobilization of fixture at the very early stage after the implant placement in the rabbits didn't interrupt the final bone to implant osseointegration.

Parametric Numerical Study on the Performance of Helical Tidal Stream Turbines (헬리컬 터빈의 설계인자에 따른 성능 연구)

  • Han, Jun-Sun;Choi, Da-Hye;Hyun, Beom-Soo;Kim, Moon-Chan;Rhee, Shin-Hyung;Song, Mu-Seok
    • Journal of the Korean Society for Marine Environment & Energy
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    • v.14 no.2
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    • pp.114-120
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    • 2011
  • The characteristics of a helical turbine to be used for tidal stream energy conversion have been numerically studied with varying a few design parameters. The helical turbines were proposed aiming at mitgating the well known poor cut-in characteristics and the structural vibration caused by the fluctuating torque, and the basic concept is introducing some twisting angle of the vertical blade along the rotation axis of the turbine. Among many potential controling parameters, we focused, in this paper, on the twisting angle and the height to diameter ratio of the turbine, and, based on the numerical experiment, We tried to propose a configuration of such turbine for which better performance can be expected. The three-dimensional unsteady RANS equations were solved by using the commercial CFD software, FLUENT with k-${\omega}$ SST turbulence model, and the grid was generated by GAMBIT. It is shown that there are a range of the twisting angle producing better efficiency with less vibration and the minimum height to diameter ratio above which the efficiency does not improve considerably.