• Title/Summary/Keyword: Cross Cylinder Method

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On the Flow Characteristics around a Circular Cylinder according as the Water Depth from the Free Surface (자유수면에 인접한 원형실린더형 몰수체 주위의 유동특성에 관한 연구)

  • Gim, Ok-Sok;Shon, Chang-Bae;Lee, Gyoung-Woo
    • Journal of Navigation and Port Research
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    • v.34 no.5
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    • pp.331-336
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    • 2010
  • The free surface influenced the wake behind a circular cylinder and its effects were investigated experimentally in a circulating water channel with the variation of water depth. Instantaneous velocity fields were measured in this paper. The measured results has been compared with each other to investigate the flow characteristics of the circular cylinder's 2-dimensional section at $Re=1.0{\times}10^3$ using 2-frame grey level cross correlation PIV method. The flow around the circular cylinder with free surface affected the wake structure. Especially, in case of d=1.0D, the boundary layer was measured in the whole area. The separation point and boundary layer of the circular cylinder could be controlled by the water depth.

Microwave Imaging of a Perfectly Conducting Cylinder by Using Modified Newton's Algorithm in the Angular Spectral Domain (각 스펙트럼 영역에서 개선된 Newton 알고리듬을 이용한 완전도체의 역산란 방법)

  • 박선규;박정석;라정웅
    • Journal of the Korean Institute of Telematics and Electronics A
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    • v.31A no.6
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    • pp.34-44
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    • 1994
  • In this paper, an iterative inversion method in angular spectral domain is presented for microwave imaging of a perfectly conducting cylinder. Angular spectra are calculated from measured far-field scattered fields. And then both the propagating modes and the evanescent modes are defined. The center and initial shape of an unknown conductor may be obtained by the characteristics of angular spectra and the total scattering cross section (TSCS). Finally, the orignal shape is reconstructed by the modified Newton algorithm. By using well estimated initial shape the local minima can be avoided, which might appear when the nonlinear equation is solved with Newton algorithm. It is shown to be robust to noise in scattered fields via numerical examples by keeping only the propagating modes and filtering out the evanescent modes.

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Nonhomogeneous atherosclerotic plaque analysis via enhanced 1D structural models

  • Varello, Alberto;Carrera, Erasmo
    • Smart Structures and Systems
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    • v.13 no.4
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    • pp.659-683
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    • 2014
  • The static analysis of structures with arbitrary cross-section geometry and material lamination via a refined one-dimensional (1D) approach is presented in this paper. Higher-order 1D models with a variable order of expansion for the displacement field are developed on the basis of Carrera Unified Formulation (CUF). Classical Euler-Bernoulli and Timoshenko beam theories are obtained as particular cases of the first-order model. Numerical results of displacement, strain and stress are provided by using the finite element method (FEM) along the longitudinal direction for different configurations in excellent agreement with three-dimensional (3D) finite element solutions. In particular, a layered thin-walled cylinder is considered as first assessment with a laminated conventional cross-section. An atherosclerotic plaque is introduced as a typical structure with arbitrary cross-section geometry and studied for both the homogeneous and nonhomogeneous material cases through the 1D variable kinematic models. The analyses highlight limitations of classical beam theories and the importance of higher-order terms in accurately detecting in-plane cross-section deformation without introducing additional numerical problems. Comparisons with 3D finite element solutions prove that 1D CUF provides remarkable three-dimensional accuracy in the analysis of even short and nonhomogeneous structures with arbitrary geometry through a significant reduction in computational cost.

Modified Finite Volume Time Domain Method for Efficient Prediction of Radar Cross Section at High Frequencies

  • Chatterjee, Avijit;Myong, Rho-Shin
    • Journal of electromagnetic engineering and science
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    • v.8 no.3
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    • pp.100-109
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    • 2008
  • The finite volume time domain(FVTD) technique faces serious limitations in simulating electromagnetic scattering at high frequencies due to requirements related to discretization. A modified FVTD method is proposed for electrically large, perfectly conducting scatterers by partially incorporating a time-domain physical optics(PO) approximation for the surface current. Dominant specular returns in the modified FVTD method are modeled using a PO approximation of the surface current allowing for a much coarser discretization at high electrical sizes compared to the original FVTD scheme. This coarse discretization can be based on the minimum surface resolution required for a satisfactory numerical evaluation of the PO integral for the scattered far-field. Non-uniform discretization and spatial accuracy can also be used in the context of the modified FVTD method. The modified FVTD method is aimed at simulating electromagnetic scattering from geometries containing long smooth illuminated sections with respect to the incident wave. The computational efficiency of the modified FVTD method for higher electrical sizes are shown by solving two-dimensional test cases involving electromagnetic scattering from a circular cylinder and a symmetric airfoil.

Wake Patterns of Two Oscillating Cylinders

  • Lee, Dae-Sung;Ha, Man-Yeong;Yoon, Hyun-Sik
    • 한국가시화정보학회:학술대회논문집
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    • 2006.12a
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    • pp.78-85
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    • 2006
  • Flows around two oscillating cylinders in side-by-side arrangement at Re=185 are simulated using immersed boundary method. The cylinders oscillate vertically with prescribed sinusoidal function in opposite directions in uniform cross-flow. Flow patterns and drag & lift forces are described by varying distance between two cylinders and oscillating frequency. Time series of flow patterns are investigated along with corresponding drag k lift coefficients.

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Flow control on the near wake of a circular cylinder attached with control rods (제어봉 부착에 따른 원형실린더 근접 후류 유동제어에 관한 실험적 연구)

  • Gim, Ok-Sok;Lee, Gyoung-Woo
    • Journal of Navigation and Port Research
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    • v.32 no.6
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    • pp.453-458
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    • 2008
  • Flow characteristics of the control-rod-attached 2-dimensional circular cylinder was accomplished using by PIV techniques. model tests had been carried out with different diameters of control rods(d/D=0.1 through d/D=0.5). and the Reynolds number Re=15,000 based on the cylinder diameter(D=50mm) to predict the performance of the model and the two-frame grey-level cross-correlation method had been used to obtain the velocity distribution in the flow field. 50mm circular cylinder had been used during the whole experiments and measured results had been compared with each other. The measured results have been compared with each case. therefore this article identifies not only the mean velocity profiles but also the control effects of the control rods.

Mechanical Effects of Pipe Drawing Angle and Reduction Rate on Material (파이프 인발 각도에 따른 기계적 효과 및 재료에 따른 감소율에 관한 연구)

  • Seo, Youngjin
    • Journal of the Korean Society of Manufacturing Process Engineers
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    • v.19 no.12
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    • pp.8-13
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    • 2020
  • Seamless pipes are fabricated by drilling a hole in a cylindrical material and drawing the material to the desired diameter. These pipes are used in environments where high reliability is required. In this study, the pipe drawing process was simulated using DEFORM, a commercial finite element method (FEM) analysis program. The outer diameter of the steel cylinder used herein before drawing was 70 mm, and the target outer diameter was 58 mm. The drawing process consisted of two stages. In this study, the effect of cross-sectional reduction rate on the pipe was investigated by varying the cross-sectional reduction rate in each step to achieve the target outer diameter. The results of this study showed that the first section reduction rate of 26% and the second section reduction rate of 13.9% caused the lowest damage to the material. Moreover, the FEM simulation results confirmed the influence of the drawing die angle on the pipe drawing process. The drawing die angles of 15° in the first step and 9° in the second step caused the least damage to the material.

Cross-Borehole Incoherent Tomography for High-Contrast Cylindrical Cavity in Lossy Medium by Using Single-Frequency Time-Harmonic Signal (단일 주파수 시간조화 신호를 사용한 손실 매질내에 있는 high-contrast 원기둥 공동의 cross-borehole incoherent 단면영상법)

  • 강진섭
    • Journal of the Korean Institute of Telematics and Electronics D
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    • v.35D no.11
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    • pp.1-9
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    • 1998
  • In this paper, an incoherent imaging of a high-contrast cylindrical cavity in a lossy medium illuminated by the time-harmonic cylindrical wave is obtained via the backprojections of the intensity patterns of the forward total electric field in the cross-borehole measurement configuration. The phenomenon that the interference fringes in the intensity pattern, which are caused by the superposition of the incident field and the scattered field with different optical paths, are removed in the backprojection process is interpreted numerically. This imaging method is validated by imaging an air circular cylinder in a lossy medium of $\varepsilon$$_{r}$=9 and $\sigma$ = 0.0005, 0.002 S/m, and the conditions for obtaining better images are investigated.d.

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Allowable limit of physical optics in radar cross section analysis of edge shape (가장자리 형상의 레이더 반사 면적 해석에서 물리광학기법의 적용 한계)

  • Baek, Sang-Min
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.46 no.1
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    • pp.78-85
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    • 2018
  • As a numerical analysis technique to predict the radar cross section of an aircraft, a full wave method or an asymptotic method is mainly used. The full-wave method is expected to be relatively accurate compared with the asymptotic method. The asymptotic method is numerically efficient, and it is more widely used in the RCS analysis. However, the error that occurs when estimating the RCS using the asymptotic method is difficult to predict easily. In this paper, we analyze the allowable limits of physical optics by constructing a wedge-cylinder model and comparing the RCS prediction results between the method of moment and physical optics while changing the edge shape. Finally, this study proposes a criterion for allowable limit of physical optics in the RCS estimation.

A Clinical Study on Presbyopia in Wearing the Near Spectacle for the First Time (근용 안경을 최초 장용하는 노안에 대한 임상적 연구)

  • Yoo, Jong-Sook;Lim, Hyeon-Seon;Lee, Soo-Cheon;Hwang, Jung-Hee;Kim, Hyo-Jung
    • Journal of Korean Ophthalmic Optics Society
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    • v.13 no.4
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    • pp.103-107
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    • 2008
  • Purpose: This research measured the near addition powers of presbyopia in wearing the near spectacle for the first time. Methods: We evaluated age, sex, working group, spherical power and cylindrical power and measured the power of refractive error performed the both eyes (310 eyes) of 155 subjects subjectively noncycloplegic and power of addition using the cross cylinder method. Results: There were measured the near addition powers in the range of +0.75D ~ +1.75D. In case of the average addition, they were measured with +1.06D in subjects under 43 years of age, +1.08D in 44 to 46 years, +1.23D in 47 to 49 years and +1.46D in over 50 years of age. The average age in subjects was 47.6 years old and 74 male, 81 female, 71 near sighted working group and 83 far sighted working group. Conclusions: Near addition was correlated with age, working group and cylindrical power (P<0.05, P<0.05, P<0.05).

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