• Title/Summary/Keyword: time marching

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Numerical Investigation on Interference Effects of Tandem Rotor in Forward Flight (전진 비행하는 탠덤로터의 간섭효과에 대한 수치적 연구)

  • Lee, Jae-Won;Oh, Se-Jong;Yee, Kwan-Jung;Kim, Deog-Kwan
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.37 no.7
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    • pp.615-626
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    • 2009
  • The objective of this study is to investigate the interference effects due to tandem rotor's overlap in the forward flight. To resolve the instabilities caused by close proximity of the wake to the blade surface, the field velocity approach is implemented to the existing unsteady panel code coupled with a time-marching free wake model. The modified code is then used to investigate the effects of the selected parameters on the forward flight performance of the tandem rotor. The calculated results for rotor separation effect indicate that stagger(d/D) appears to have little effects on the forward flight performance at high advance ratio and the square of gap(H/D) is inversely proportional to overlap induced power factor. In addition, it is also shown that the overlap induced power factor increases to a certain extent and decrease back as the advance ratio increases.

Development and Validations of the Aerodynamic Analysis Program of Multi-Rotors by Using a Free-Wake Method (자유후류 기법을 이용한 다중로터 공력해석 프로그램의 개발 및 검증)

  • Park, Sang-Gyoo;Lee, Jae-Won;Lee, Sang-Il;Oh, Se-Jong;Yee, Kwang-Jung
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.35 no.10
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    • pp.859-867
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    • 2007
  • The objective of this study is to develop and validate a numerical method which can handle the multi-rotor aerodynamic characteristics. For the purpose of power estimation, table look-up method is implemented to the existing unsteady panel code that is coupled with a time-marching free wake model. Also, the Reynolds number scaling is implemented for the application to various regions of Reynolds number. The computed results are validated against the available experimental data for coaxial and tandem rotors. In the validation case for the coaxial rotor, more accurate result is acquired when the thickness effect is considered. The wake instability problem occurs at a particular separation distance between the rotors for tandem rotors. The wake instability is avoided by setting the single-rotor wake geometry as the initial wake geometry for the multi-rotor analysis. The estimated result for rotor separation effect is compared with the result of the momentum theory.

Simulation of Unsteady Rotor-Fuselage Interaction Using an Improved Free-Wake Method (향상된 자유후류 기법을 이용한 비정상 로터-동체 상호작용 시뮬레이션)

  • Lee, Joon-Bae;Seo, Jin-Woo;Lee, Jae-Won;Yee, Kwan-Jung;Oh, Se-Jong
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.38 no.7
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    • pp.629-636
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    • 2010
  • This study is to investigate the aerodynamic effects of the Rotor-Fuselage Interactions in forward flight, and is conducted by using an improved time-marching free-wake panel method. To resolve the instability caused by the close proximity of the wake to the blade surface, the field velocity approach is added to the prior unsteady panel code. This modified method is applied to the ROBIN(ROtor Body Interaction) problem, which had been conducted experimentally in NASA. The calculated results, pressure distribution on fuselage surface and induced inflow ratio without and with the rotor, are compared with the experimental results. The developed code shows not only very accurate prediction of the aerodynamic characteristics for the rotor-fuselage interaction problem but also the rotor wake development.

Numerical Dispersion Relation for the 2-D ADI-FDTD Method (2-D ADI-FDTD의 수치적 분산특성에 관한 연구)

  • 주세훈;김형동
    • Journal of the Institute of Electronics Engineers of Korea TC
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    • v.40 no.5
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    • pp.181-186
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    • 2003
  • This paper presents a numerical dispersion relation for the two-dimensional finite-difference time-domain method based on the alternating-direction implicit time-marching scheme(2-D ADI-FDTD), which method has the potential to considerably reduce tile number of time iterations especially in case where the fine spatial lattice relative to the wavelength is used to resolve fine geometrical features. The proposed analytical relation for 2-D ADI-FDTD is compared with those relations in the Previous works. Through numerical tests, the dispersion equation of this work was shown as correct one for 2-D ADI-FDTD.

Unsteady Transonic Flow Analysis over an Oscillatory Airfoil using upwind Navier-Stokes Method (Upwind Navier-Stokes 방법을 이용한 진동하는 익형 주위의 비정상 천음속 유동해석)

  • O Tae Hun;Kim Sang Deok;Song Dong Ju
    • 한국전산유체공학회:학술대회논문집
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    • 1999.05a
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    • pp.137-143
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    • 1999
  • The unsteady transonic viscous flow has been analyzed over an oscillatory airfoil. The CSCM(Conservative Supra Characteristic Method) upwind flux difference splitting method and the iterative time marching scheme having first order accuracy in time and second to third order accuracy in space was applied on dynamic meshes. A steady flow field of Mach number 0.7 has been calculated for the verification of unsteady algorithm. The time-accurate unsteady calculations have been done for NACA 0012 airfoil oscillating around quarter chord about freestream Mach number 0.6 on dynamic meshes. The results have been compared with the AGARD Case 3 experimental data. The periodic characteristics have been compared with the experimental results.

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Analysis of linear viscoelastic problems using boundary element method (경계요소법을 사용한 선형 점탄성문제의 해석)

  • 심우진;곽병만
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.11 no.2
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    • pp.322-330
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    • 1987
  • Isotropic linear viscoelasticity problems are analyzed numerically in time domain by Boundary Element Method with quadratic isoparametric boundary elements. Viscoelastic fundamental solutions are newly derived by using the elastic-viscoelastic correspondence principle and corresponding boundary integral equations are also presented. Numerical results of two examples are compared with the derived exact solutions to verify the accuracy and validity of the method. A detailed study on the accuracy of displacement and stress in terms of time integration step is given.

Lagrangian Finite Element Analysis of Water Impact Problem (강체-유체 충격문제에 대한 Lagrangian 유한요소 해석)

  • Bum-Sang Yoon
    • Journal of the Society of Naval Architects of Korea
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    • v.28 no.1
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    • pp.60-68
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    • 1991
  • The updated Lagrangian Finite Element Method is introduced to analyse rigid body-fluid impact problem which is characterized by incompressible Navier-Stokes equations and impact-contact conditions between free surface and rigid body. For the convenience of numerical computation, velocity fields are splinted into vicous and pressure parts, and then the governing equations and boundary conditions are decomposed in accordance with the decomposition. However, Viscous stresses acting an the solid boundaries are neglected on the assumption that very small velocity gradients may occur during extremely small time interval of the impact. Four coded quadrilateral elements are used to discretize the space domain and the fully explicit time-marching algorithm is employed with a reasonably small time step. At the beginning of each time step, contact velocity of the rigid body is computed from the momentum balance between the body and the fluid. The velocity field is then computed to satisfy the discretized equations of motions and incompressibility and contact constraints as well as an exact free surface boundary condition. At the end of each time step, the fluid domain is updated from the velocity field. In the present time stepping numerical analysis, behaviour of the free surface near the body can be observed without any difficulty which is very important in the water impact problem. The applicability of the algorithm is illustrated by a wedge type falling body problem. The numerical solutions for time-varying pressure distributions and impact loadings acting ion the surface are obtained.

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DEVELOPMENT OF A 2-D UNSTEADY FLOW SIMULATION CODE USING CARTESIAN MESHES (직교격자를 이용한 2차원 비정상 유동해석 코드 개발)

  • Jung, Min-Kyu;Lee, Jae-Eun;Park, Se-Youn;Kwon, Oh-Joon;Kwon, Jang-Hyuk;Shin, Ha-Yong
    • 한국전산유체공학회:학술대회논문집
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    • 2009.04a
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    • pp.116-120
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    • 2009
  • A two-dimensional unsteady inviscid flow solver has been developed for the simulation of complex geometric configurations on adaptive Cartesian meshes. Embedded condition was used for boundary condition and a predictor-corrector explicit time marching scheme was used for time-accurate numerical simulation. The Cartesian mesh generator, which was previously developed for steady problem, was used grid generation for unsteady flow. The solver was based on ALE formulation for body motion. For diminishing the effects of cut-cells, the cell merging method was used. Using cell merging method, it was eliminated the CFL constraints. The conservation problem, which is caused cell-type variation around region swept by solid boundary, was also solved using cell merging method. The results are presented for 2D circular cylinder and missile launching problem.

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Numerical Simulation of a Near shore Tsunami Using a Digital Wave Tank Simulation Technique (디지털 수치수조 기법에 의한 연안 Tsunami의 수치 시뮬레이션)

  • 박종천;전호환
    • Journal of Ocean Engineering and Technology
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    • v.17 no.6
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    • pp.7-15
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    • 2003
  • A Digital Wave Tank simulation technique, based on a finite-difference method and a modified marker-and-cell (MAC) algorithm, is applied in order to investigate the characteristics of nonlinear Tsunami propagations and their interactions with a 2D sloping beach, Ohkushiri Island, and to predict maximum wove run-up around the island. The Navier-Stokes (NS) and continuity equation are governed in the computational domain, and the boundary values are updated at each time step, by a finite-difference time-marching scheme in the frame of the rectangular coordinate system. The fully nonlinear, kinematic, free-surface condition is satisfied by the modified marker-density function technique. The near shore Tsunami is assumed to be a solitary wave, and is generated from the numerical wave-maker in the developed Digital Wave Tank. The simulation results are compared with the experiments and other numerical methods, based on the shallow-water wave theory.

Noise Optimization of the Cooling Fan in an Engine Room by using Neural Network (신경망이론을 적용한 엔진룸내의 냉각팬 소음 최적화 연구)

  • Chung, Ki-Hoon;Choi, Han-Lim;Kim, Bum-Sub;Kim, Jae-Seung;Lee, Duck-Joo
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2002.11b
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    • pp.116-121
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    • 2002
  • Axial fans are widely used in heavy machines due to their ability to produce high flow rate for cooling of engines. At the same time, the noise generated by these fans causes one of the most serious problems. This work is concerned with the low noise technique of discrete frequency noise. To calculate the unsteady resultant force over the fan blade in an unsymmetric engine room. Time-Marching Free-Wake Method is used. From the calculations of unsteady force on fan blades, noise signal of an engine cooling fan is calculated by using an acoustic similarity law. Noise optimization is obtained from Neural Network which is constructed based on the calculated flow rate and noise spectrum.

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