• Title/Summary/Keyword: frequency characteristics

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Instability of High-Speed Impinging Jets(II) (고속 충돌제트의 불안정 특성)

  • Gwon, Yeong-Pil;Im, Jeong-Bin
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.22 no.4
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    • pp.450-467
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    • 1998
  • The characteristics of the unstable impinging circular jet is investigated based on the frequency characteristics and the sound field of the impinging-tones. Two symmetric modes S1 and S2, associated with low frequency and high frequency respectively, and one helical mode H have been observed. At low speed the S2 mode is dominant and switched by the S1 mode as the speed increases. When the jet speed is high the S1 mode is very active over the impinging distance from half the nozzle diameter to its ten times, while the S2 mode occurs at shorter distance corresponding to stage 2 and 3. The helical mode H seems unstable, likely to be influenced much by the experimental environment, and occurs at relatively high speed with almost the same frequency characteristics as the S2 mode. By estimating the convection speed of the unstable jet, it is found that the ratio of the convection speed to the jet speed decreases with both Strouhal number and Reynolds number and the speed of S2 mode is faster than the Si mode. When the present experimental results are compared with the previous investigations performed for the hole tone and the impinging tone with a small plate, the S1 mode is found to be associated with the ring vortex of large diameter with low speed, but the S2 mode with the vortex of small diameter with high speed. In addition, the frequency is found to be influenced by the nozzle configuration but the characteristics is almost the same. From the impinging distance and frequency range, it can be deduced that S1 mode is related with the jet column mode and S2 mode with the shear mode.

Development of Hierarchical Bayesian Spatial Regional Frequency Analysis Model Considering Geographical Characteristics (지형특성을 활용한 계층적 Bayesian Spatial 지역빈도해석)

  • Kim, Jin-Young;Kwon, Hyun-Han;Lim, Jeong-Yeul
    • Journal of Korea Water Resources Association
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    • v.47 no.5
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    • pp.469-482
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    • 2014
  • This study developed a Bayesian spatial regional frequency analysis, which aimed to analyze spatial patterns of design rainfall by incorporating geographical information (e.g. latitude, longitude and altitude) and climate characteristics (e.g. annual maximum series) within a Bayesian framework. There are disadvantages to considering geographical characteristics and to increasing uncertainties associated with areal rainfall estimation on the existing regional frequency analysis. In this sense, this study estimated the parameters of Gumbel distribution which is a function of geographical and climate characteristics, and the estimated parameters were spatially interpolated to derive design rainfall over the entire Han-river watershed. The proposed Bayesian spatial regional frequency analysis model showed similar results compared to L-moment based regional frequency analysis, and even better performance in terms of quantifying uncertainty of design rainfall and considering geographical information as a predictor.

Study on Frequency Characteristics for Single-Layer Symmetric Spiral Inductor (단층 나선형 인덕터에 대한 주파수 특성 연구)

  • Kim, Jae-Wook
    • The Journal of Korea Institute of Information, Electronics, and Communication Technology
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    • v.13 no.5
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    • pp.353-358
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    • 2020
  • In the case of a general spiral inductor, the orientation of the port is affected as it has an asymmetric structure. In this paper, a single-layered spiral inductor that can have a symmetrical structure is proposed, and the simulation and frequency characteristics are analyzed. The general spiral inductor shows a large difference in frequency-inductance characteristics, frequency-quality factor characteristics, and self-resonant frequency according to the standard of the port, while the proposed symmetric spiral inductor has an inductance of 2.7nH, a quality factor of about 7.86, and a self-resonant frequency of about 14.1GHz without changing the port. Compared to the general spiral inductor having a large difference depending on the port, it was confirmed that the influence on the port direction was small. However, it was confirmed that the mutual inductance decreased compared to the occupied area of the coil, resulting in a low inductance, and the resistance of the coil increased more than the increase in the inductance, and the quality factor was also lowered. In the future, it is expected that inductance and quality factor can be improved through a 2-layer symmetrical spiral structure.

Analysis of the Frequency for Cable of Cable-Stayed Bridges to Temperature Variation (온도변화에 따른 사장교 케이블 고유진동수 분석)

  • Lee, Hyun-Chol;Kim, Jin-Soo;Park, Kyoung-Ho;Lee, Jong-Jae
    • Journal of the Korea institute for structural maintenance and inspection
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    • v.25 no.2
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    • pp.23-34
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    • 2021
  • Cable was targeted for cable, which is a main material of cable-stayed bridges that have high frequency of use at home and abroad and many future construction plans. First of all, experiments were conducted on temperature loads that were permanently used due to changes in temperature of cables and changes in air temperature, taking into account changes in normal fat. The dynamic characteristics of cables were compared and analyzed by applying various systems to change dynamic characteristics by applying temperature change of cables. Comparing and analyzing the dynamic characteristics of cables, the acceleration, frequency and tension of cables due to temperature rise tended to decrease, the degree of influence of displacement of cables was analyzed, and the results of the mode characteristics of cables were analyzed. In particular, the correlation of cable acceleration, natural frequency, and tension due to changes in cable temperature showed that the cable tension is highly sensitive to acceleration and natural frequency.

Gate length scaling behavior and improved frequency characteristics of In0.8Ga0.2As high-electron-mobility transistor, a core device for sensor and communication applications (센서 및 통신 응용 핵심 소재 In0.8Ga0.2As HEMT 소자의 게이트 길이 스케일링 및 주파수 특성 개선 연구)

  • Jo, Hyeon-Bhin;Kim, Dae-Hyun
    • Journal of Sensor Science and Technology
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    • v.30 no.6
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    • pp.436-440
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    • 2021
  • The impact of the gate length (Lg) on the DC and high-frequency characteristics of indium-rich In0.8Ga0.2As channel high-electron mobility transistors (HEMTs) on a 3-inch InP substrate was inverstigated. HEMTs with a source-to-drain spacing (LSD) of 0.8 ㎛ with different values of Lg ranging from 1 ㎛ to 19 nm were fabricated, and their DC and RF responses were measured and analyzed in detail. In addition, a T-shaped gate with a gate stem height as high as 200 nm was utilized to minimize the parasitic gate capacitance during device fabrication. The threshold voltage (VT) roll-off behavior against Lg was observed clearly, and the maximum transconductance (gm_max) improved as Lg scaled down to 19 nm. In particular, the device with an Lg of 19 nm with an LSD of 0.8 mm exhibited an excellent combination of DC and RF characteristics, such as a gm_max of 2.5 mS/㎛, On resistance (RON) of 261 Ω·㎛, current-gain cutoff frequency (fT) of 738 GHz, and maximum oscillation frequency (fmax) of 492 GHz. The results indicate that the reduction of Lg to 19 nm improves the DC and RF characteristics of InGaAs HEMTs, and a possible increase in the parasitic capacitance component, associated with T-shap, remains negligible in the device architecture.

Shaking table test and numerical analysis of nuclear piping under low- and high-frequency earthquake motions

  • Kwag, Shinyoung;Eem, Seunghyun;Kwak, Jinsung;Lee, Hwanho;Oh, Jinho;Koo, Gyeong-Hoi;Chang, Sungjin;Jeon, Bubgyu
    • Nuclear Engineering and Technology
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    • v.54 no.9
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    • pp.3361-3379
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    • 2022
  • A nuclear power plant (NPP) piping is designed against low-frequency earthquakes. However, earthquakes that can occur at NPP sites in the eastern part of the United States, northern Europe, and Korea are high-frequency earthquakes. Therefore, this study conducts bi-directional shaking table tests on actual-scale NPP piping and studies the response characteristics of low- and high-frequency earthquake motions. Such response characteristics are analyzed by comparing several responses that occur in the piping. Also, based on the test results, a piping numerical analysis model is developed and validated. The piping seismic performance under high-frequency earthquakes is derived. Consequently, the high-frequency excitation caused a large amplification in the measured peak acceleration responses compared to the low-frequency excitation. Conversely, concerning relative displacements, strains, and normal stresses, low-frequency excitation responses were larger than high-frequency excitation responses. Main peak relative displacements and peak normal stresses were 60%-69% and 24%-49% smaller in the high-frequency earthquake response than the low-frequency earthquake response. This phenomenon was noticeable when the earthquake motion intensity was large. The piping numerical model simulated the main natural frequencies and relative displacement responses well. Finally, for the stress limit state, the seismic performance for high-frequency earthquakes was about 2.7 times greater than for low-frequency earthquakes.

Seismic Amplitude and Frequency Characteristics of Gas hydrate Bearing Geologic Model (가스 하이드레이트 지층 모델의 탄성파 진폭 및 주파수 특성)

  • Shin, Sung-Ryul;Lee, Sang-Cheol;Park, Keun-Pil;Lee, Ho-Young;Yoo, Dong-Geun;Kim, Young-Jun
    • Geophysics and Geophysical Exploration
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    • v.11 no.2
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    • pp.116-126
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    • 2008
  • In gas hydrate survey, seismic amplitude and frequency characteristics play a very important role in determining whether gas hydrate exists. According to the variation of source frequency and scatterer size, we study seismic amplitude characteristics using elastic modeling applied at staggered grids. Generally speaking, scattering occurs in proportion to the square of source frequency and the scatterer volume, which has an effect on seismic amplitude. The higher source frequency is, the more scattering occurs in gas hydrate bearing zone. Therefore, BSR is hardly observed in high frequencies. On the other side, amplitude blanking zone and BSR is clearly observed in lower frequencies although the resolution is poor as a whole. Seismic reflections traveling through free-gas layer below gas hydrate bearing zone decay so severely a high frequency component that a low frequency term is dominant. Amplitude anomaly of BSR result from high acoustic impedance contrast due to free-gas, which is a very crucial factor to estimate gas hydrate bearing zone. Seismic frequency analysis is carried out using wavelet transform method that frequency component could be decomposed with time variation. In application of wavelet transform to the seismic physical experiments data, we can observe that reflections traveling through air layer, which corresponds to the free-gas layer, decay a high frequency component.

Effects of deformation of elastic constraints on free vibration characteristics of cantilever Bernoulli-Euler beams

  • Wang, Tong;He, Tao;Li, Hongjing
    • Structural Engineering and Mechanics
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    • v.59 no.6
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    • pp.1139-1153
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    • 2016
  • Elastic constraints are usually simplified as "spring forces" exerted on beam ends without considering the "spring deformation". The partial differential equation governing the free vibrations of a cantilever Bernoulli-Euler beam considering the deformation of elastic constraints is firstly established, and is nondimensionalized to obtain two dimensionless factors, $k_v$ and $k_r$, describing the effects of elastically vertical and rotational end constraints, respectively. Then the frequency equation for the above Bernoulli-Euler beam model is derived using the method of separation of variables. A numerical analysis method is proposed to solve the transcendental frequency equation for the continuous change of the frequency with $k_v$ and $k_r$. Then the mode shape functions are given. Finally, effects of $k_v$ and $k_r$ on free vibration characteristics of the beam with different slenderness ratios are calculated and analyzed. The results indicate that the effects of $k_v$ are larger on higher-order free vibration characteristics than on lower-order ones, and the impact strength decreases with slenderness ratio. Under a relatively larger slenderness ratio, the effects of $k_v$ can be neglected for the fundamental frequency characteristics, while cannot for higher-order ones. However, the effects of $k_r$ are large on both higher- and lower-order free vibration characteristics, and cannot be neglected no matter the slenderness ratio is large or small.

Response Characteristics of Forced Vibration Model with Sinusoidal Exciting Force (정현파로 가진한 강제진동 해석과 응답특성)

  • Kim, Jong-Do;Yoon, Moon-Chul
    • Journal of Convergence for Information Technology
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    • v.10 no.7
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    • pp.131-137
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    • 2020
  • The characteristics of forced vibration with excited sinusoidal force was introduced. Also, numerical analyses and FRF in frequency domain were performed in detail. In this regard, the responses of displacement, velocity and acceleration were investigated in a forced vibration model. The FRF characteristics in real and imaginary part around natural frequency are also discussed. This response approach of forced vibration in time domain is used for the identification and monitoring of sinusoidal forced vibration. For acquiring a displacement, velocity and acceleration, a numerical technique of Runge-Kutta-Gill method was performed. For the FRF(frequency response function), These responses are used. Also, the FRF can represent the intrinsic characteristics of the forced vibration. These performed results and analysis are successful in each damped condition for the forced vibration model. After numerical analysis of the different mass, damping and stiffness, the forced vibration response characteristics with sinusoidal force was discriminated considering its amplitude and frequency simultaneously.

The Study of Algorithm for Communication Environment Channel Characteristic Embedded Control System and Wireless Communication (무선통신과 임베디드 제어시스템 통신환경의 채널특성 알고리즘에 관한 연구)

  • Kang, Jeong-Yong
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.36 no.3B
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    • pp.297-304
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    • 2011
  • MIMO wireless communication embedded systems, and for propagation prediction for indoor and outdoor propagation prediction program incorporates an indoor/outdoor propagation through the simulator can be predicted. This analysis technique developed by the interference between multiple transmitters and a maximum transmission distance issues, the frequency utilization efficiency for a variety of issues, including analysis and prediction becomes possible. Development of the prediction of the conventional methods, but I can consider the environmental characteristics of the ray tracing simulation software to develop and implement an efficient ray tracing, ray tracing techniques and are designed to enable tracked beam analysis of propagation characteristics using information technology by combining the theoretical characteristics of an efficient and well-reflected propagation prediction technique was employed. The frequency of domestic embedded systems, ensure the frequency characteristics and frequency of 3-5GHz band for propagation to investigate the development of local wireless communication technology-based skills needed for securing and jeonpaganseopdeung frequency management techniques to ensure the verification and verified through experiments.