• ETRI Journal
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• 제46권3호
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• pp.392-403
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• 2024

Even though generalized frequency division multiplexing is an alternative waveform method expected to replace the orthogonal frequency division multiplexing in the future, its implementation must alleviate channel effects. Least-squares (LS), a low-complexity channel estimation technique, could be improved by using the discrete Fourier transform (DFT) without increasing complexity. Unlike the usage of the LS method, the DFT-based method requires the receiver to know the channel impulse response (CIR) length, which is unknown. This study introduces a simple, yet effective, CIR length estimator by utilizing LS estimation. As the cyclic prefix (CP) length is commonly set to be longer than the CIR length, it is possible to search through the first samples if CP is larger than a threshold set using the remaining samples. An adaptive scale is also designed to lower the error probability of the estimation, and a simple signal-to-interference-noise ratio estimation is also proposed by utilizing a sparse preamble to support the use of the scale. A software simulation is used to show the ability of the proposed system to estimate the CIR length. Due to shorter CIR length of rural area, the performance is slightly poorer compared to urban environment. Nevertheless, satisfactory performance is shown for both environments.

• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 1999년도 춘계학술대회 논문집
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• pp.170-174
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• 1999

The main scale of linear scale greatly affects on the precision of displacement measurement. Especially when needing the long range measurement, the length of main scale should be increased accordingly. In this paper, we propose a linear scale that uses laser interference pattern as main scale for long range measurement. The linear scale is similar to Michelson interferometer excepting that the reference mirror is tilted so as to obtain interference fringe pattern and a grating panel is attached on a quadratic photo diodes. Four kinds of grating having phase differences of 0, $\pi$ /4, $\pi$ /2, 3 $\pi$ /4 are arranged on the panel. The experimental results show that signals of - quadratic photo diode, A, B,$\overline{A}$ and $\overline{B}$ are cosine wavelike and successive signals have phase difference of $\pi$/4 each other. So the proposed method can achieve improved measurement resolution.

• Advances in materials Research
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• 제1권1호
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• pp.13-29
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• 2012

In order to simultaneously enhance the strength and plasticity in nanostructured / ultrafine-grained alloys, a strategy of introducing multiple length scales into microstructure (or called bimodal composite microstructure) has been developed recently. This paper presents a brief overview of the alloy developement and the mechanical behavior of ultrafine-grained Ti-Fe-based alloys with different length-scale phases, i.e., micrometer-sized primary phases (dendrites or eutectic) embedded in an ultrafine-grained eutectic matrix. These ultrafine-grained titanium bimodal composites could be directly obtained through a simple single-step solidification process. The as-prepared composites exhibit superior mechanical properties, including high strength of 2000-2700 MPa, large plasticity up to 15-20% and high specific strength. Plastic deformation of the ultrafine-grained titanium bimodal composites occurs through a combination of dislocation-based slip in the nano-/ultrafine scale matrix and constraint multiple shear banding around the micrometer-sized primary phase. The microstructural charactersitcs associated to the mechanical behaivor have been detailed discussed.

• Wind and Structures
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• 제15권6호
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• pp.463-480
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• 2012

The effects of Reynolds number (Re), freestream turbulence intensity (Tu) and integral length scale (${\Lambda}$) on the drag coefficient ($C_d$) of a circular cylinder in cross flow were experimentally studied for $6.45{\times}10^3$ < Re < $1.82{\times}10^4$. With the help of orificed plates, Tu was fixed at approximately 0.5%, 5%, 7% and 9% and the normalized integral length scale (L/D) was varied from 0.35 to 1.05. Our turbulent results confirmed the general trend of decreasing $C_d$ with increasing Tu. The effectiveness of Tu in reducing $C_d$ is found to lessen with increasing ${\Lambda}$/D. Most interestingly, freestream turbulence of low Tu (${\approx}5%$) and large ${\Lambda}$/D (${\approx}1.05$) can increase the $C_d$ above the corresponding smooth flow value.

• Structural Engineering and Mechanics
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• 제71권3호
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• pp.223-232
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• 2019

Since the actuators with small- scale structures may be exposed to external reciprocal actions lead to create undesirable loads causing instability, the buckling behaviors of them are interested to make reliable or accurate actions. Therefore, the purpose of this paper is to analyze plastic buckling behavior of the micro beam structures by adopting a Conventional Mechanism-based Strain Gradient plasticity (CMSG) theory. The effect of length scale on critical force is considered for three types of boundary conditions, i.e. the simply supported, cantilever and clamped - simply supported micro beams. For each case, the stability equations of the buckling are calculated to obtain related critical forces. The constitutive equation involves work hardening phenomenon through defining an index of multiple plastic hardening exponent. In addition, the Euler-Bernoulli hypothesis is used for kinematic of deflection. Corresponding to each length scale and index of the plastic work hardening, the critical forces are determined to compare them together.

• 한국해양공학회지
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• 제28권4호
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• pp.268-273
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• 2014

To investigate the turbulence characteristics within the boundary layer over a flat plate, an experimental study was performed using a PIV technique in a circular water channel. For two water velocities, 0.92 and 1.99 m/s, the water velocity profiles were taken and analyzed to determine turbulent characteristics such as the Reynolds stress, Taylor micro-length scale, and Kolmogorov length scale within the defect law region of the boundary layer. These analysis methods may be applied to research on the friction drag reduction technology using micro-bubbles or an air sheet over the surface of a ship's hull, because the physical reason for the friction drag reduction could be found by understanding the variation of the turbulence characteristics and structures in the boundary layer.

• 화약ㆍ발파
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• 제22권4호
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• pp.1-6
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• 2004

본 연구에서는 발파해체에 대한 축소모형실험의 폭원에 대한 차원과 축소율을 산정하고, 이로부터 축소모형실험의 적정 길이의 축소율을 고찰하였다. 그 결과 길이 축소비를 1/4로 할 때 축원의 축소율은 1/256로 모형실험과 실제 구조물에서 사용한 화약량의 비로 구한 축소율과 유사한 값을 보였다. 길이 축소율은 1/4 이상으로 하는 것이 바람직하다고 판단된다

• 한국조경학회지
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• 제18권1호
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• pp.69-79
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• 1990

This study intends to define the concept of human scale and visual preference which is frequently being used by environmental designers, and to explore the dimension of buildings and courtyards which is perceived as "human scale" and "visually preferable" by users (college students). As the subjects of this experiment were college students, "human scale" and "visual preferenoe" that were professional terms must be changed to understandable and compatible concept. The compatible concept for human scale was defined as the degree of friendliness and comfort, and that for visual preference was declined as the degree of like or dislike. The subjects thought that buildings with the height of 2.73 ∼5. 83 storides, the length of 27.44∼44.00m and the height ratio of 1.81 ∼5.41 were in human scale, and that buildings with height 2.60 ∼ 6.00 stories, the length of 25.7∼55.00 and the height ratio of 1.32∼6.41 were visually preferred. The block game used in this study was Proved to he a reliable and valid experimental method.

• 대한토목학회논문집
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• 제12권4_1호
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• pp.97-106
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• 1992

하천 수로망(水路網)의 수로길이와 본류(本流) 수로길이는 사용된 지형도(地形圖) 축척(縮尺)에 따라 각각 다른 값을 나타내며, 이와 같은 지형도상(地形圖上)의 수로길이는 Fractal로 간주할 수 있다. 수로망(水路網)의 하천길이와 본류(本流) 수로길이를 Horton 법칙을 적용함으로써 유역면적비(Ra)만의 함수로 나타내어, 수로망(水路網)의 하천길이에 관한 Fractal Dimension(D)와 본류(本流) 수로길이에 관한 Fractal Dimension(d)를 길이의 비(比)($R_L$)과 유역면적비(比)($R_a$)의 함수로 각각 유도하였다. 유도된 결과식을 금강수계내(錦江水系內) 산성(山城)유역의 수로망(水路網)에 적용하여 기(旣) 발표된 공식과 비교 검토하였으며, Fractal Dimension은 수로망(水路網)의 경우 지형도(地形圖) 축척(縮尺)이 클수록 2에 가까운 값을 나타낸 반면에, 본류(本流)수로의 경우는 1에 가까운 값을 나타내었다. 본 연구의 결과는 지형도(地形圖) 축척(縮尺)에 따르는 수로망(水路網)구성의 정량적(定量的) 분석에 도움이 되리라 생각된다.

• Journal of the korean society of oceanography
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• 제32권2호
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• pp.75-84
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• 1997

Relation between the length scale and the wall proximity function in the Mellor-Yamada level 2.5 turbulence closure model has been investigated through various experiments using a range of wall proximity functions. The model performance has been evaluated quantitatively by comparing with laboratory data for wind-driven flow (Baines and Knapp, 1965) and for open-channel flows without and with adverse wind action (Tsuruya, 1985). Comparison shows that a symmetric wall proximity function used by Blumberg and Mellor(1987) gives rise to current profiles with better accuracy than asymmetric wall proximity functions considered. It is noted that in modelling homogeneous flows the length scale 1= 0.31${\|}$z${\|}$(1+z/h) can be used with tolerable accuracy.