• Title, Summary, Keyword: fundamental mode

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A Study of the comparison of Inversion of Rayleigh wave Group and Phase Velocities for Regional Near-Surface 2-Dimensional Velocity Structure (천부지각 2차원 속도구조를 위한 레일리파의 군속도와 위상속도 역산의 비교 연구)

  • Lee, Bo-Ra;Jung, Hee-Ok
    • 한국지구물리탐사학회:학술대회논문집
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    • pp.51-59
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    • 2006
  • The surface wave data obtained in a tidal flat located in the sw coast of the Korean Peninsula were used to analyse the shear wave velocity structure of the area. First, the phase velocity dispersion curves were obtained by the tau-p stacking method and the group velocity dispersion curves by a wavelet transform method and the Multiple Filtering Technique by Dziewonski. The phase velocity dispersion curves exhibited bigger errors than the group velocity curves. The results showed that the wavelet transform method was more effective in separating the fundamental and the 1st higher mode group velocity curves than the Multiple Filtering Technique. Combined use of the fundamental and the 1st higher mode group velocity dispersion curves in the inversion for the shear wave velocity structure gave better spatial resolution compared when the fundamental mode group velocity was used alone. This study indicates that the group velocity dispersion curves can be used in the inversion of Rayleigh waves for the shear wave velocity structure, especially effectively with the higher mode group velocity curves together.

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An analysis of the lateral first-order mode characteristics for the semiconductor laser diodes (반도체 레이저 다이오드의 횡방향 1차모드의 특성 해석)

  • 김형래;곽계달
    • Journal of the Korean Institute of Telematics and Electronics A
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    • v.32A no.12
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    • pp.91-100
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    • 1995
  • This paper represents the lateral first-order mode characteristics for the semiconductor laser diodes using a two-dimensional numerical simulator. In order to analyze the lateral first-order mode characteristics, Helmholtz wave equation is solved twice for the lateral fundamental and the first-order mode considering the mode gain, total losses, and the recombination rate due to the stimulated emission radiation for the each mode independantly. Through this procedure, we find that the lateral first-order mode was easily guided as increasing the stripe width for the index-guiding structures, and that the lateral first-order mode seems to be dominated in the distribution of total light intensity when its output power reaches nearly half of that of the lateral fundamental mode. This results may be used to design the device structure which guides only the lateral fundamental mode.

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Performance of Hybrid Laser Diodes Consisting of Silicon Slab and InP/InGaAsP Deep-Ridge Waveguides

  • Leem, Young-Ahn;Kim, Ki-Soo;Song, Jung-Ho;Kwon, O-Kyun;Kim, Gyung-Ock
    • ETRI Journal
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    • v.32 no.2
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    • pp.339-341
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    • 2010
  • The fundamental transverse mode lasing of a hybrid laser diode is a prerequisite for efficient coupling to a single-mode silicon waveguide, which is necessary for a wavelength-division multiplexing silicon interconnection. We investigate the lasing mode profile for a hybrid laser diode consisting of silicon slab and InP/InGaAsP deep ridge waveguides. When the thickness of the top silicon is 220 nm, the fundamental transverse mode is lasing in spite of the wide waveguide width of $3.7{\mu}m$. The threshold current is 40 mA, and the maximum output power is 5 mW under CW current operation. In the case of a thick top silicon layer (1 ${\mu}m$), the higher modes are lasing. There is no significant difference in the thermal resistance of the two devices.

In-plane Vibration Characteristics of Piezoelectric Ring Transducers (링형 압전 변환기의 면내 진동 특성)

  • Piao, Chunguang;Kim, Jin Oh
    • Transactions of the Korean Society for Noise and Vibration Engineering
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    • v.24 no.10
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    • pp.780-787
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    • 2014
  • This paper experimentally deals with the vibration characteristics of flat ring transducers used for ultrasonic sensors and actuators. Radial vibration mode, which is the fundamental mode of a thin piezoelectric transducer, was measured by a laser in-plane vibrometer. An impedance analyzer was used to measure natural frequencies. The results measured by experiments verified theoretical predictions. The vibration characteristics of ring transducers were identified according to the outer diameter size. The shape of the fundamental mode is almost uniform but slightly decreases from the inner to the outer circumferential surfaces. The natural frequency of the fundamental mode decreases as the outer diameter increases. It appears that the ring type transducer is suitable to excite uniformly distributed vibration on a flat surface.

THE CONTROL OF THIRD HARMONICS INJECTED PWM INVERTER IN OVER MODULATION MODE

  • Kim, Young-Real;Kim, Yuen-Chung;Kim, Jae-Mun;Won, Chung-Yuen
    • Proceedings of the KIPE Conference
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    • pp.362-365
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    • 1998
  • A new modified command voltage of the third harmonics injected PWM inverter is proposed in overmodulation mode. By analyzing the relationship between the modulation index and the peak of the fundamental component of the modified reference voltage, we can settle the problem in over modulation mode without iteration. Then we can increase the maximum fundamental component of the third harmonic injected PWM inverter comparative to six-step inverter continuously in over modulation mode.

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A Method of Lamb-Wave Modes Decomposition for Structural Health Monitoring (구조물 건전성 모니터링을 위한 Lamb파 모드 구별법)

  • Jun, Yong-Ju;Park, Il-Wook;Lee, U-Sik
    • Journal of the Korean Society for Precision Engineering
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    • v.29 no.8
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    • pp.887-895
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    • 2012
  • Lamb waves have received a great attention in the structural health monitoring (SHM) societies because they can propagate over relatively large distances in wave guides such as thin plates and shells. The time-of-flights of Lamb waves can be used to detect damages in a wave guide. However, due to the inherent dispersive and multi-mode characteristics of Lamb waves, one must decompose the Lamb wave modes into the symmetric and anti-symmetric modes for SHM applications. Thus, this paper proposes a decomposition method for the two-mode Lamb waves based on two rules: the group velocity ratio rule and the mode amplitude ratio rule. The group velocity ratio rule means that the ratio of the group velocities of fundamental symmetric and anti-symmetric modes is constant, while the mode amplitude ratio rule means that the magnitude of the fundamental symmetric modes of all measured response signals should be always larger than those of the anti-symmetric mode once the input signal is applied so that the magnitude of fundamental symmetric mode of excited Lamb-wave is larger than that of anti-symmetric mode, and vice versa. The proposed method is verified through the experiments ducted for an aluminum plate specimen.

Dynamic behaviour of semi-rigid jointed cold-formed steel hollow frames

  • Joanna, P.S.;Samuel Knight, G.M.;Rajaraman, A.
    • Steel and Composite Structures
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    • v.6 no.6
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    • pp.513-529
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    • 2006
  • This paper deals with the dynamic behaviour of cold-formed steel hollow frames with different connection stiffnesses. An analytical model of a semi-rigid frame was developed to study the influence of connection stiffnesses on the fundamental frequency and dynamic response of the frames. The flexibilities of the connections are modeled by rotational springs. Neglect of semi-rigidity leads to an artificial stiffening of frames resulting in shorter fundamental period, which in turn results in a significant error in the evaluation of dynamic loads. In the seismic design of structures, of all the principal modes, the fundamental mode of translational vibration is the most critical. Hence, experiments were conducted to study the influence of the connection stiffnesses on the fundamental mode of translational vibration of the steel hollow frames. From the experimental study it was found that the fundamental frequency of the frames lie in the semi-rigid region. From the theoretical investigation it was found that the flexibly connected frames subjected to lateral loads exhibit larger deflection as compared to rigidly connected frames.

Attenuation of Fundamental Longitudinal Guided Wave Mode in Steel Pipes Embedded in Soil

  • Lee, Ju-Won;Shin, Sung-Woo;Na, Won-Bae
    • Journal of the Korean Society for Nondestructive Testing
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    • v.30 no.6
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    • pp.539-547
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    • 2010
  • In this study, characteristics of the fundamental longitudinal guided wave mode, L(0,1), which is a usual mode employed in the inspection of the above-ground pipe, of the buried pipe were numerically investigated considering property changes in the surrounding soil. Results showed that soil conditions are significantly affecting the attenuation of L(0,1) mode in the pipe embedded in soil. Especially, if the soil is partially saturated, the attenuation of L(0,1) mode is larger and is very similar regardless of the degree of water saturation in the surrounding soil. However, when the soil is fully saturated, the attenuation of L(0,1) mode is less and show different trend with its partially saturated counterparts.

Damage Detection in a Bean Via the Wavelet Transform of Mode Shapes (모드형상의 웨이블렛 변환을 이용한 보의 결함 진단)

  • Lee, Yong-Uk;Kim, Yun-Yeong;Lee, Ho-Cheol
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.24 no.4
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    • pp.916-925
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    • 2000
  • Perhaps, this is the first attempt which applies the wavelet transform to the fundamental vibration mode for damage detection in a beam. Contrary to most existing detection methods on mode shapes, the present method directly works only with the fundamental mode of a damaged beam: no vibration mode shape of a undamaged beam is necessary. Applying the concept of vanishing moments of wavelet functions, we show that wavelet functions are effective damage detectors. Both numerical and experimental results confirm the effectiveness of the present method.

Computing input energy response of MDOF systems to actual ground motions based on modal contributions

  • Ucar, Taner
    • Earthquakes and Structures
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    • v.18 no.2
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    • pp.263-273
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    • 2020
  • The use of energy concepts in seismic analysis and design of structures requires the understanding of the input energy response of multi-degree-of-freedom (MDOF) systems subjected to strong ground motions. For design purposes and non-time consuming analysis, however, it would be beneficial to associate the input energy response of MDOF systems with those of single-degree-of-freedom (SDOF) systems. In this paper, the theoretical formulation of energy input to MDOF systems is developed on the basis that only a particular portion of the total mass distributed among floor levels is effective in the nth-mode response. The input energy response histories of several reinforced concrete frames subjected to a set of eleven horizontal acceleration histories selected from actual recorded events and scaled in time domain are obtained. The contribution of the fundamental mode to the total input energy response of MDOF frames is demonstrated both graphically and numerically. The input energy of the fundamental mode is found to be a good indicator of the total energy input to two-dimensional regular MDOF structures. The numerical results computed by the proposed formulation are verified with relative input energy time histories directly computed from linear time history analysis. Finally, the elastic input energies are compared with those computed from time history analysis of nonlinear MDOF systems.