• Title/Summary/Keyword: Quasi-dimensional

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Static Aeroelastic Analysis of Hingeless Rotor System in Hover Using Free-Wake Method (자유후류기법을 이용한 무힌지 로터 시스템의 정지비행시 정적 공탄성 해석)

  • Yoo, Seung-Jae;Lim, In-Gyu;Lee, In;Kim, Do-Hyung;Kim, Doeg-Kwan
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • 제36권2호
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    • pp.156-162
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    • 2008
  • The static aeroelastic analysis of composite hingeless rotor blades in hover was performed using free-wake method. Large deflection beam theory was applied to analyze blade motions as a one-dimension beam. Anisotropic beam theory was applied to perform a cross-sectional analysis for composite rotor blades. Aerodynamic loads were calculated through a three-dimensional aerodynamic model which is based on the unsteady vortex lattice method. The wake geometry in hover was described using a time-marching free-wake method. Numerical results of the steady-state deflections for the composite hingeless rotor blades were presented and compared with those results based on two-dimensional quasi-steady strip theory and prescribed wake method. It was shown that wakes affect the steady-state deflections.

Numerical Model for Predicting Sand Bar Formation around River Mouth (하구역의 사주 형성 예측을 위한 수치 모델)

  • Kuroiwa, Masamitsu;Matsubara, Yuhei;Suzuki, Yoko;Kuchiishi, Takayuki
    • Journal of Korean Society of Coastal and Ocean Engineers
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    • 제26권2호
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    • pp.96-102
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    • 2014
  • A three-dimensional beach evolution model was presented to predict morphodynamics around a river mouth. The presented model was based on the depth-averaged (2DH) and quasi three-dimensional (Q-3D) nearshore current modules, and the model took into account shoreline changes, the effect of advection diffusion of suspended load and discharged sediments from the river. First, the 3D beach evolution model was applied to the formation of sand spits and terrace at the river mouth in order to investigate the performance of the model. Secondly, the model was applied to the river mouth at the Ara River, facing the Sea of Japan. The formation of sand spit at the Ara River in winter season was reproduced. The computed result showed qualitatively agreement with field site observation.

A Study on the Development of 2-Dimensional Numerical Wave Tank by the High-Order Spectral Method (고차 스펙트럴법에 의한 2차원 수치 파수조 개발에 관한 연구)

  • Y.J. Kim;J.H. Hwang
    • Journal of the Society of Naval Architects of Korea
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    • 제29권3호
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    • pp.131-139
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    • 1992
  • By introducing a body potential, the high-oder spectal method of Dommermuth and Yue(1987) is extended to treat the nonlinear interactions between the free surface and the submerged cylinder. A 2-dimensional numerical wave tank is developed based on this numerical scheme, and applied to the wave resistance problem and the wave maker problem. In the simulations, it is shown that the transient waves due to the impulsive start of the body motion make a practical obstacle to the acquisition of useful data from the numerical experiments. Gradual starting procedures are devised, and successful result of the quasi-steady state or the uniform regular wave group was obtained. Within the author's present knowledge, the present numerical scheme is one of the most efficient numerical schemes which can treat the nonlinear interactions between the free surface and the body motion in time-domain.

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Transverse dynamics of slender piezoelectric bimorphs with resistive-inductive electrodes

  • Schoeftner, Juergen;Buchberger, Gerda;Benjeddou, Ayech
    • Smart Structures and Systems
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    • 제18권2호
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    • pp.355-374
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    • 2016
  • This paper presents and compares a one-dimensional (1D) bending theory for piezoelectric thin beam-type structures with resistive-inductive electrodes to ANSYS$^{(R)}$ three-dimensional (3D) finite element (FE) analysis. In particular, the lateral deflections and vibrations of slender piezoelectric beams are considered. The peculiarity of the piezoelectric beam model is the modeling of electrodes in such a manner that is does not fulfill the equipotential area condition. The case of ideal, perfectly conductive electrodes is a special case of our 1D model. Two-coupled partial differential equations are obtained for the lateral deflection and for the voltage distribution along the electrodes: the first one is an extended Bernoulli-Euler beam equation (second-order in time, forth order in space) and the second one the so-called Telegrapher's equation (second-order in time and space). Analytical results of our theory are validated by 3D electromechanically coupled FE simulations with ANSYS$^{(R)}$. A clamped-hinged beam is considered with various types of electrodes for the piezoelectric layers, which can be either resistive and/or inductive. A natural frequency analysis as well as quasi-static and dynamic simulations are performed. A good agreement between the extended beam theory and the FE results is found. Finally, the practical relevance of this type of electrodes is shown. It is found that the damping capability of properly tuned resistive or resistive-inductive electrodes exceeds the damping performance of beams, where the electrodes are simply linked to an optimized impedance.

Kirigami-inspired Composite Metastructure for Low-frequency Vibration Reduction (저주파 진동 저감을 위한 키리가미 구조 영감의 복합재료 메타구조)

  • Hyunsoo Hong;Samuel Kim;Wonvin Kim;Wonki Kim;Jae-moon Jeong;Seong Su Kim
    • Composites Research
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    • 제37권4호
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    • pp.291-295
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    • 2024
  • Vibration occurs not only in daily life but also in various fields such as semiconductors, aerospace, vehicles, and ships. Unexpected vibrations can cause fatigue damage to structures and degrade the performance of the entire system, having very detrimental effects. Particularly, low-frequency vibrations can be very harmful to precision equipment, human bodies, and buildings. Therefore, mitigating low-frequency vibrations is essential for effective vibration reduction. In this study, a kirigami-inspired composite meta-structure is proposed for low-frequency vibration reduction. Inspired by kirigami, the meta-structure is designed to transform from a three-dimensional to a two-dimensional form upon compression, leveraging structural advantages. Additionally, it is designed to have quasizero stiffness characteristics, providing excellent vibration reduction performance even at low frequencies. The kirigami composite meta-structure was fabricated using carbon fiber reinforced TPU through 3D printing. Its structural and vibrational characteristics were evaluated and analyzed through compression and vibration tests.

Prediction of through the width delamination growth in post-buckled laminates under fatigue loading using de-cohesive law

  • Hosseini-Toudeshky, Hossein;Goodarzi, M. Saeed;Mohammadi, Bijan
    • Structural Engineering and Mechanics
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    • 제48권1호
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    • pp.41-56
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    • 2013
  • Initiation and growth of delamination is a great concern of designers of composite structures. Interface elements with de-cohesive constitutive law in the content of continuum damage mechanics can be used to predict initiation and growth of delamination in single and mixed mode conditions. In this paper, an interface element based on the cohesive zone method has been developed to simulate delaminatoin growth of post-buckled laminate under fatigue loading. The model was programmed as the user element and user material by the "User Programmable Features" in ANSYS finite element software. The interface element is a three-dimensional 20 node brick with small thickness. Because of mixed-mode condition of stress field at the delamination-front of post-buckled laminates, a mixed-mode bilinear constitutive law has been used as user material in this model. The constitutive law of interface element has been verified by modelling of a single element. A composite laminate with initial delamination under quasi-static compressive Loading available from literature has been remodeled with the present approach. Moreover, it will be shown that, the closer the delamination to the free surface of laminate, the slower the delamination growth under compressive fatigue loading. The effects of laminate configuration on delamination growth are also investigated.

Global MHD Simulation of a Prolonged Steady Weak Southward Interplanetary Magnetic Field Condition

  • Park, Kyung Sun;Lee, Dae-Young;Kim, Khan-Hyuk
    • Journal of Astronomy and Space Sciences
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    • 제37권2호
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    • pp.77-84
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    • 2020
  • We performed high-resolution three-dimensional global magnetohydrodynamic (MHD) simulations to study the interaction between the Earth's magnetosphere and a prolonged steady southward interplanetary magnetic field (IMF) (Bz = -2nT) and slow solar wind. The simulation results show that dayside magnetic reconnection continuously occurs at the subsolar region where the magnetosheath magnetic field is antiparallel to the geomagnetic field. The plasmoid developed on closed plasma sheet field lines. We found that the vortex was generated at the magnetic equator such as (X, Y) = (7.6, 8.9) RE due to the viscous-like interaction, which was strengthened by dayside reconnection. The magnetic field and plasma properties clearly showed quasiperiodic variations with a period of 8-10 min across the vortex. Additionally, double twin parallel vorticity in the polar region was clearly seen. The peak value of the cross-polar cap potential fluctuated between 17 and 20 kV during the tail reconnection.

Small-Signal Modeling of Gate-All-Around (GAA) Junctionless (JL) MOSFETs for Sub-millimeter Wave Applications

  • Lee, Jae-Sung;Cho, Seong-Jae;Park, Byung-Gook;Harris, James S. Jr.;Kang, In-Man
    • JSTS:Journal of Semiconductor Technology and Science
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    • 제12권2호
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    • pp.230-239
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    • 2012
  • In this paper, we present the radio-frequency (RF) modeling for gate-all-around (GAA) junctionless (JL) MOSFETs with 30-nm channel length. The presented non-quasi-static (NQS) model has included the gate-bias-dependent components of the source and drain (S/D) resistances. RF characteristics of GAA junctionless MOSFETs have been obtained by 3-dimensional (3D) device simulation up to 1 THz. The modeling results were verified under bias conditions of linear region (VGS = 1 V, VDS = 0.5 V) and saturation region (VGS = VDS = 1 V). Under these conditions, the root-mean-square (RMS) modeling error of $Y_{22}$-parameters was calculated to be below 2.4%, which was reduced from a previous NQS modeling error of 10.2%.

Fluttering Characteristics of Free-falling Plates (자유낙하하는 판의 fluttering 특성 연구)

  • Hong, Seulki;Chae, Seokbong;Kim, Jooha
    • Journal of the Korean Society of Visualization
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    • 제15권2호
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    • pp.33-40
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    • 2017
  • Abstract In the present study, the characteristics of kinematics and dynamics in the fluttering motion of free-falling plates are investigated at Reynolds number of $10^5$. We record quasi-two-dimensional trajectories of free-falling plates with and without superhydrophobic coating using high-speed camera, and compute the drag and lift forces by trajectory analysis. Translational and angular velocities are modeled as harmonic functions with specific phase differences. In particular, periodic mass elevations near turning points are explained using the suggested models. At each turning point, a sudden drop in lift and a rapid increase in drag occur simultaneously due to fast increase in angle of attack. However, the lift is increased over the buoyancy-corrected weight of plate during gliding flight, resulting in periodic mass elevations near turning points. Superhydrophobicity is shown to increase lift but to reduce drag on a fluttering plate, resulting in the decrease of mean descent speed.

Ultimate strength behavior of steel-concrete-steel sandwich beams with ultra-lightweight cement composite, Part 2: Finite element analysis

  • Yan, Jia-Bao;Liew, J.Y. Richard;Zhang, Min-Hong
    • Steel and Composite Structures
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    • 제18권4호
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    • pp.1001-1021
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    • 2015
  • Ultra-lightweight cement composite (ULCC) with a compressive strength of 60 MPa and density of $1,450kg/m^3$ has been developed and used in the steel-concrete-steel (SCS) sandwich structures. This paper investigates the structural performances of SCS sandwich composite beams with ULCC as filled material. Overlapped headed shear studs were used to provide shear and tensile bond between the face plate and the lightweight core. Three-dimensional nonlinear finite element (FE) model was developed for the ultimate strength analysis of such SCS sandwich composite beams. The accuracy of the FE analysis was established by comparing the predicted results with the quasi-static tests on the SCS sandwich beams. The FE model was also applied to the nonlinear analysis on curved SCS sandwich beam and shells and the SCS sandwich beams with J-hook connectors and different concrete core including ULCC, lightweight concrete (LWC) and normal weight concrete (NWC). Validations were also carried out to check the accuracy of the FE analysis on the SCS sandwich beams with J-hook connectors and curved SCS sandwich structure. Finally, recommended FE analysis procedures were given.