• Smart Structures and Systems
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• 제25권3호
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• pp.265-277
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• 2020

Recently, the concept of "drive-by" bridge monitoring system using indirect measurements from a passing vehicle to extract key parameters of a bridge has been rapidly developed. As one of the most key parameters of a bridge, the natural frequency has been successfully extracted theoretically and in practice using indirect measurements. The frequency of bridge is generally calculated applying Fast Fourier Transform (FFT) directly. However, it has been demonstrated that with the increase in vehicle velocity, the estimated frequency resolution of FFT will be very low causing a great extracted error. Moreover, because of the low frequency resolution, it is hard to detect the frequency drop caused by any damages or degradation of the bridge structural integrity. This paper will introduce a new technique of bridge frequency extraction based on Hilbert Transform (HT) that is not restricted to frequency resolution and can, therefore, improve identification accuracy. In this paper, deriving from the vehicle response, the closed-form solution associated with bridge frequency removing the effect of vehicle velocity is discussed in the analytical study. Then a numerical Vehicle-Bridge Interaction (VBI) model with a quarter car model is adopted to demonstrate the proposed approach. Finally, factors that affect the proposed approach are studied, including vehicle velocity, signal noise, and road roughness profile.

• Smart Structures and Systems
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• 제13권5호
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• pp.755-773
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• 2014

The natural frequency of a bridge is an important parameter in many engineering applications such as bridge seismic design and modal-based bridge health monitoring. The natural frequency of a bridge vibrating alone may differ from that vibrating along with a vehicle. Although such vehicle-induced variability in bridge frequency is revealed in several experimental and numerical simulation studies, few attempts have been made on the theoretical descriptions. In this study, both theoretically and experimentally, the variability in the bridge frequency induced by a parked vehicle is verified, and is therefore suggested to be considered in bridge-related engineering, especially for those cases with near vehicle-bridge resonance conditions or with large vehicle-to-bridge mass ratios. Moreover, the variability ranges could be estimated by an analytical formula presented herein.

• Structural Engineering and Mechanics
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• 제77권3호
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• pp.343-354
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• 2021

The frequencies formulas of the bridge are of great importance in the design process since these formulas provide insight dynamic characteristics of the structure, which guides the designers to parametric analyses and the layout of the bridge in conceptual or preliminary design. Continuous rigid frame bridge is popular in the mountainous area. Mostly, this type of bridge was simplified either as a girder or cantilever when calculating the frequency, however, studies showed that the different configuration of the bridge made the problem more complex, and there is no unified fundamental calculation pattern for this kind of bridge. In this study, an empirical frequency equation is proposed as a function of pier's height, stiffness of pier and the weight of the structure. A unified fundamental frequency formula is presented based on the energy principle, then the typical continuous rigid frame bridge is investigated by finite element method (FEM) to study the dynamic characteristics of the structure, and then several key parameters are investigated on the effect of structural frequency. These parameters include the number, position and stiffness of the tie beam. Nonlinear regression analyses are conducted with a comprehensive statistical study from plenty of engineering structures. Finally, the proposed frequency equation is validated by field test results. The results show that the fundamental frequency of the continuous rigid frame bridge increases more than 15% when the tie beams are set, and it increases with the stiffness ratio of tie beam to pier. The results also show that the presented unified fundamental frequency has an error of 4.6% compared with the measured results. The investigation can predicate the approximate longitudinal fundamental frequency of continuous ridged frame bridge, which can provide reference for the seismic response and dynamic impact factor design of the pier.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2005년도 춘계학술대회
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• pp.117-122
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• 2005

This paper proposes an inverter for the grid-connected photovoltaic system based on the transformer-less inverter. This system consists of a high frequency converter bridge, high frequency transformer, diode bridge rectifiers, a DC filter, a low frequency inverter bridge, and an AC filter. The high frequency converter bridge switching at 20kHz is used to generate bipolar PWM pulse, and the high frequency transformer raise its voltage twice, which is subsequently rectified by diode bridge rectifiers to result in a full-wave rectified sine wave. Finally, it is unfolded by a low frequency inverter bridge to result in a 60Hz sine wave power output. Even though the high frequency link system needs more power semiconductors, a reduced size, light weight, and saved parts cost make this system more comparative than the other systems due to elimination of 60Hz transformer.

• Interaction and multiscale mechanics
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• 제3권4호
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• pp.373-387
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• 2010

This study is intended to assess low frequency sound radiated from a viaduct under normal traffic. The bridge comprises steel box girders and wide cantilever decks on which vehicles pass. The low frequency sound and the acceleration response of the bridge under normal traffic are measured to investigate how bridge vibrations affect the low frequency sound observed near the bridge. Observations demonstrate that strong relationships exist between frequency characteristic of bridge's acceleration response and the sound pressure level of low frequency sound. A noteworthy point is that the dynamic feature of the sound pressure level is mostly affected by dynamic feature of the span locating near the observation point.

• Interaction and multiscale mechanics
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• 제5권3호
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• pp.169-185
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• 2012

The concrete bridge is likely to produce fatigue cracks during long period of service due to the moving vehicular loads and the degeneration of materials. This paper deals with the time-frequency analysis of a coupled bridge-vehicle system. The bridge is modeled as an Euler beam with breathing cracks. The vehicle is represented by a two-axle vehicle model. The equation of motion of the coupled bridge-vehicle system is established using the finite element method, and the Newmark direct integration method is adopted to calculate the dynamic responses of the system. The effect of breathing cracks on the dynamic responses of the bridge is investigated. The time-frequency characteristics of the responses are analyzed using both the Hilbert-Huang transform and wavelet transform. The results of time-frequency analysis indicate that complicated non-linear and non-stationary features will appear due to the breathing effect of the cracks.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2002년도 하계학술대회 논문집 B
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• pp.1313-1315
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• 2002

This paper proposes an inverter for the grid-connected photovoltaic system based on the transformer-less inverter. This system consists of a high frequency inverter bridge, high frequency transformer, diode bridge rectifiers, a DC filter, a low frequency inverter bridge, and an AD filter. The high frequency inverter bridge switching at 20kHz is used to generate bipolar PWM pulse, which is subsequently rectified by diode bridge rectifiers to result in a full-wave rectified sine wave. Finally, it is unfolded by a low frequency inverter bridge to result in a 60Hz sine wave power output. In this paper, the control algorithm for synchronous current feedback control method and a maximum power point tracking (MPPT) method using DSP are described. And, the simulation and experimental results are shown to verify the validity of the proposed system.

• 한국가구학회지
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• 제16권1호
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• pp.17-23
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• 2005

European maple is famous for the optimum solid wood for making bridge which is the most important part in violin acoustics. This study was carried out to investigate the variation of main features, i. e. annual ring width and cutting direction of costly imported violin bridge blanks and to examine the effect of these features of the blanks on the vibrational characteristics of bridge blanks. Imported violin bridge blanks had somewhat large variation in major macroscopical and physical properties and there was little relationship between annual ring density and weight of maple blanks. Resonant frequency of violin bridge blanks had some positive correlation with weight, however, damping having negative relationship with frequency was seldom affected by any physical properties of the maple blanks. Deviation from the radial cutting of tail side(ray direction from top toward feet on the edge of bridge blank) lowered the resonant frequency. Consequently, weight and ray direction should be taken for the critical quality decisive factors(QDF) of incoming bridge blanks by not only inspectors also luthiers who tune the bridge by shaping and are responsible for the final timbre quality of this complicate instrument.

• 전력전자학회논문지
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• 제15권5호
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• pp.394-400
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• 2010

본 논문에서는 Buck Converter 동작 원리를 Full -Bridge Inverter에 적용한 전자식 안정기를 제안하였다. 전자식안정기는 EMI 필터, 수동 PFC, Full-Bridge Inverter로 2-stage로 구성되어 있다. PFC는 신뢰성 확보를 위해 수동 PFC를 사용하였다. Full-Bridge Inverter는 High Side와 Low Side 스위치의 구동 주파수를 각각 고주파와 저주파로 구동하여 Buck Converter의 동작을 구현 하였다. 램프를 저주파수 구형파로 구동하여 음향공명현상을 피하게 되었으며, 고주파수 스위칭으로 인덕터의 부피를 줄였다. 제안한 방법은 시뮬레이션과 실험을 통해 증명하였다.

• Structural Engineering and Mechanics
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• 제84권3호
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• pp.413-421
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• 2022

Modal parameters are the main dynamic characteristics of bridge. This study aims to propose an innovative route to estimate the modal parameters for bridges by using a parked vehicle in which mode shapes with high accuracy and spatial resolution are identified by frequency measurement. Based on the theory of dynamic modification and modal identification, the mathematical formulation between the parked mass induced frequency variation and the modal parameters of a bridge is derived. Then this mathematical formulation is extended to a parked vehicle-bridge system. The arithmetic and processes for estimating the modal parameters based on the identified frequency variation of the vehicle-bridge systems when the vehicle locates at sequentially arranged positions are presented. Finally the proposed method is applied to several simulated bridges of different types. The results indicate that it can estimate the modal parameters with high accuracy and efficiency.