• Title/Summary/Keyword: circular frequency

Search Result 791, Processing Time 0.021 seconds

COMPUTATION OF AERODYNAMIC SOUNDS AT LOW MACH NUMBERS USING FINITE DIFFERENCE LATTICE BOLTZMANN METHOD

  • Kang H. K;Tsutahara M;Shikata K;Kim E. R;Kim Y. T;Lee Y. H
    • Journal of computational fluids engineering
    • /
    • v.10 no.1
    • /
    • pp.8-15
    • /
    • 2005
  • Aerodynamic sounds generated by a uniform flow around a two-dimensional circular cylinder at Re=150 are simulated by applying the finite difference lattice Boltzmann method. Thethird-order-accurate up-wind scheme (UTOPIA) is used for the spatial derivatives, and the second-order-accurate Runge-Kutta scheme is applied for the time marching. We have succeed in capturing very small pressure fluctuations with the same frequency of the Karman vortex street compared with the pressure fluctuation around a circular cylinder. The propagation velocity of the acoustic waves shows that the points of peak pressure are biased upstream due to the Doppler effect in the uniform flow. For the downstream, on the other hand, it is faster. It is also apparent that the amplitude of sound pressure is proportional to r /sup -1/2/,r being the distance from the center of the circular cylinder. To investigate the effect of the lattice dependence, furthermore, 2D computations of the tone noises radiated by a square cylinder and NACA0012 with a blunt trailing edge at high incidence and low Reynolds number are also investigate.

Finite Element Analysis on the Improvement of Residual Deformation of the Part After Pulse Laser Welding of Circular Cover (원형 커버의 펄스 레이저 용접 후 부품 잔류변형 개선에 관한 유한요소해석)

  • Kim, Kwan-Woo;Cho, Hae-Yong
    • Journal of Welding and Joining
    • /
    • v.33 no.6
    • /
    • pp.60-66
    • /
    • 2015
  • Molten zone shape of pulse laser welding is affected by welding conditions such as beam power, beam speed, irradiation time, pulse frequency, etc. and is divided into conduction type and keyhole type. It is necessary to design heat source model for irradiation of laser beam in the pulse laser welding. Shape variables and the maximum energy density value of the heat source model are different depending on the molten zone shape. In this paper, pulse laser welding simulation for joining of cylindrical part and circular cover was carried out. The heat source model for pulse laser beam with circular path was applied to the heat input boundary condition, radiative and conductive heat transfer were considered for the thermal boundary condition. For each phase, thermal and mechanical properties according to temperature were also applied to analysis. Analytical results were in good agreement with the molten zone size of specimen under the same welding conditions. So, the reliability of the welding simulation was verified. Finally, the improvements for reducing residual deformation after cover welding could be reviewed analytically.

Design and Fabrication of LHCP Antenna for UHF RFID reader (UHF RFID 리더기용 LHCP 안테나 설계 및 제작)

  • Park, Sung-Il;Kim, Sun-Il;Ko, Young-Hyuk
    • Journal of the Korea Institute of Information and Communication Engineering
    • /
    • v.14 no.1
    • /
    • pp.23-30
    • /
    • 2010
  • In this paper, a design for the 900MHz bandwidth RFID reader antenna with circular polarization is proposed and experimentally investigated. The 900MHz bandwidth RFID reader antenna is proposed as a simple radiator with loading capacitor to generate LHCP(Left Hand Circular Polarization). Also, the design and fabrication of antenna has the returnloss of -32.28dB at the center frequency of 1010MHz and Bandwidth of 12.5% at 905Hz~1030MHz. Proposed LHCP antenna of maximum gain is 6dBi and satisfy axial ratio based on 2. From the measured result, axial ratios based on 2 are observed at the operating frequencies. The proposed antenna is suitable for RFID applications in wireless communications.

A Circular Micro-Strip Patch Antenna Using a PBG (광 밴드 갭(Photonic Band Gap) 구조를 응용한 원형 마이크로스트립 패치 안테나)

  • Lee Bong-Geol;Jung Chun-Suk;Woo Jong-Woon;Ahn Sang-Chul
    • The Journal of Korean Institute of Electromagnetic Engineering and Science
    • /
    • v.16 no.11 s.102
    • /
    • pp.1067-1074
    • /
    • 2005
  • Studied antenna's basic structure was circular micro-strip patch antenna. Bandwidth was broaden and back-radiation pattern was decreased because studied antenna had PBG on a ground for improvement in its defect which is skin-effects. And character of antenna according to different shape of PBG was observed. Finally, air-gap whose dielectric constant is lower than substrates was added between substrates sc respond frequency was higher despite small size antenna.

PIV Measurement of Circular Cylinder Wake Using Vortex Tracking Phase-Average Technique (와추적 위상평균 기법을 이용한 원주후류의 PIV측정)

  • Kim, Gyeong-Cheon;Yun, Sang-Yeol;Kim, Sang-Gi;Bu, Jeong-Suk
    • Transactions of the Korean Society of Mechanical Engineers B
    • /
    • v.25 no.7
    • /
    • pp.915-922
    • /
    • 2001
  • A new phase-average technique using instantaneous velocity fields obtained by a PIV method has been developed. The technique tracks vorticity centers and estimates the value of circulation for a chosen domain. The locations of vortex-centers and the magnitudes of circulation are matched together then showing a sine wave feature due to the periodic vortex shedding from the circular cylinder. Ensemble averaged and phase averaged velocity fields are successfully measured for the circular cylinder wake where Reynolds number is 3900 based on free stream velocity and cylinder diameter. The convection velocities of the vortices center and the vortex shedding frequency were measured by a single hot-wire probe.

FLUID-STRUCTURE INTERACTION ANALYSIS FOR VORTEX-INDUCED VIBRATION OF CIRCULAR CYLINDER (유체-구조 연성해석을 통한 원주의 와유기 진동 해석)

  • Kim, S.H.;Ahn, H.T.;Ryue, J.S.;Shin, H.K.;Kwon, O.J.;Seo, H.S.
    • Journal of computational fluids engineering
    • /
    • v.17 no.1
    • /
    • pp.29-35
    • /
    • 2012
  • Fluid-Structure Interaction analysis of a circular cylinder surrounded by incompressible turbulent flow is presented. The fluid flow is modeled by incompressible Navier-Stokes equations in conjunction with large-eddy simulation for turbulent vortical flows. The circular cylinder is modeled as elastic continuum described by elasto-dynamic equation of motion. Finite element method based approach is utilized for unified formulation of fluid-structure interaction analysis. The magnitude and frequency of structural response is analysed in comparison to the driving fluid forces.

Nonlinear Analysis of a Forced Circular Plate with Internal Resonance (내부공진을 가진 원판의 비선형 강제진동해석)

  • 김철홍;이원경
    • Transactions of the Korean Society of Mechanical Engineers
    • /
    • v.16 no.11
    • /
    • pp.2098-2110
    • /
    • 1992
  • An analysis is presented for the combination resonance of a clamped circular plate, which occurs when the frequency of the excitation is near the combination of the natural frequencies, that is, when ohm.=2.0mega./sub 1/+omega./sub 2/. The internal resonance, Omega./sub 3/=omega./sub 1/+2.omega./sub 2/, is considered and its influence on the response is studied. The clamped circular plate experiencing mid-plane stretching is governed by a nonlinear partial differential equation. By using Galerkin's method the governing equation is reduced to a system of nonautonomous ordinary differential equations. The method of multiple scales is used to obtain steady-state responses of the system. Results of numerical investigations show that the increase of the excitation amplitude can reduce the amplitudes of steady-state responses. We can not find this kind of results in linear systems.

A Simplified Zero-Forcing Receiver for Multi-User Uplink Systems Based on CB-OSFB Modulation

  • Bian, Xin;Tian, Jinfeng;Wang, Hong;Li, Mingqi;Song, Rongfang
    • KSII Transactions on Internet and Information Systems (TIIS)
    • /
    • v.14 no.5
    • /
    • pp.2275-2293
    • /
    • 2020
  • This paper focuses on the simplified receiver design for multi-user circular block oversampled filter bank (CB-OSFB) uplink systems. Through application of discrete Fourier transform (DFT), the special banded structure and circular properties of the modulation matrix in the frequency domain of each user are derived. By exploiting the newly derived properties, a simplified zero-forcing (ZF) receiver is proposed for multi-user CB-OSFB uplink systems in the multipath channels. In the proposed receiver, the matrix inversion operation of the large dimension multi-user equivalent channel matrix is transformed into DFTs and smaller size matrix inversion operations. Simulation is given to show that the proposed ZF receiver can dramatically reduce the computational complexity while with almost the same symbol error rate as that of the traditional ZF receiver.

Numerical Simulation of Aeroacoustic Noise at Low Mach Number Flows by Using the Finite Difference Lattice Boltzmann Method (차분래티스 볼츠만 법을 이용한 저Mach수 흐름에서의 유동소음해석)

  • Eun-Ra Kim;Jeong-Hwan Kim;Ho-Keun Kang
    • Journal of Advanced Marine Engineering and Technology
    • /
    • v.28 no.5
    • /
    • pp.717-727
    • /
    • 2004
  • In this study, we simulate the aerodynamic sounds generated by a two-dimensional circular cylinder in a uniform flow are simulated by applying the finite difference lattice Boltzmann method (FDLBM). The third-order-accurate up-wind scheme (UTOPIA) is used for the spatial derivatives. and the second-order-accurate Runge-Kutta scheme is applied for the time marching. The results show that we successively capture very small acoustic pressure fluctuations with the same frequency of the Karman vortex street compared with the Pressure fluctuation around a circular cylinder The propagation velocity of the acoustic waves shows that the points of peak pressure are biased upstream due to the Doppler effect in the uniform flow For the downstream. on the other hand. it quickly Propagates. It is also apparent that the amplitude of sound Pressure is Proportional to $r^{-1/2}$, r being the distance from the center of the circular cylinder. To investigate the effect of the lattice dependence furthermore a 2D computation of the tone noise radiated by a NACA0012 with a blunt trailing edge at high incidence and low Reynolds number is also investigated.

Flow characteristics of a cross jet issued in the fully developed pipe flow (파이프유동장에 분사되는 제트의 유동특성 연구)

  • Kim, Gyeong-Cheon;Sin, Dae-Sik
    • Transactions of the Korean Society of Mechanical Engineers B
    • /
    • v.22 no.7
    • /
    • pp.927-936
    • /
    • 1998
  • In the fully developed pipe flow, when jet is injected in cross to the flow there are complex transition flows caused by interaction of the cross flow and jet. These interactions are studied by means of the flow visualization methods and frequency analysis using a hot-wire anemometer. The velocity range of cross flow of the pipe is 0.3 m/s ~ 1.2 m/s and the corresponding Reynolds number, R$\sub$p/, based on the pipe diameter is 2.25 * 10$\^$3/ ~ 9.02 * 10$\^$3/. The velocity ratio (R), jet velocity/cross flow velocity, is chosen from 2 to 10. A circular cylinder is placed in the pipe instead of jet to observe the vortex shedding from the solid body. To compare the jet and circular cylinder flow, the vortical structure is analyzed in both cases and the structure of vortices and the origin of its formation are investigated, especially. The vortex shedding of the dominant coherent structure is compared between the jet flow and the circular cylinder flow. In the case of the jet flow, the Strouhal numbers are different depending on the existence of the upright vortex as well as the velocity ratio (R).