• Wind and Structures
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• v.14 no.3
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• pp.239-252
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• 2011

The wind-induced mean, background and resonant responses of Beijing National Stadium are investigated in this paper. Based on the concepts of potential and kinetic energies, the mode participation factors for the background and the resonant components are presented and the dominant modes are identified. The coupling effect between different modes of the resonant response and the coupling effect between the background and resonant responses are analyzed. The coupling effects between the background and resonant components and between different modes are found all negligible. The mean response is approximately analogous to the peak responses induced by the fluctuating wind. The background responses are significant in the fluctuating responses and it is much larger than the resonant responses at the measurement locations.

• Structural Engineering and Mechanics
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• v.53 no.3
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• pp.607-623
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• 2015

The wind-induced dynamic response of large-span flexible structures includes two important components-background response and resonant response. However, it is difficult to separate the two components in time-domain. To solve the problem, a relational expression of wavelet packet coefficients and power spectrum is derived based on the principles of digital signal processing and the theories of wavelet packet analysis. Further, a new approach is proposed for separation of the background response from the resonant response. Then a numerical example of frequency detection is provided to test the accuracy and the spectral resolution of the proposed approach. In the engineering example, the approach is applied to compute the power spectra of the wind-induced response of a large-span roof structure, and the accuracy of spectral estimation for stochastic signals is verified. The numerical results indicate that the proposed approach is efficient and accurate with high spectral resolution, so it is applicable for power spectral computation of various response signals of structures induced by the wind. Moreover, the background and the resonant response time histories are separated successfully using the proposed approach, which is sufficiently proved by detailed verifications. Therefore, the proposed approach is a powerful tool for the verification of the existing frequency-domain formulations.

• Structural Engineering and Mechanics
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• v.54 no.5
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• pp.891-908
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• 2015

For a systematic study on wind-induced vibration characteristics of large hyperbolic cooling towers with different feature sizes, the pressure measurement tests are finished on the rigid body models of three representative cooling towers with the height of 155 m, 177 m and 215 m respectively. Combining the refined frequency-domain algorithm of wind-induced responses, the wind-induced average response, resonant response, background response, coupling response and wind vibration coefficients of large cooling towers with different feature sizes are obtained. Based on the calculating results, the parametric analysis on wind-induced vibration of cooling towers is carried out, e.g. the feature sizes, damping ratio and the interference effect of surrounding buildings. The discussion shows that the increase of feature sizes makes wind-induced average response and fluctuating response larger correspondingly, and the proportion of resonant response also gradually increased, but it has little effect on the wind vibration coefficient. The increase of damping ratio makes resonant response and the wind vibration coefficient decreases obviously, which brings about no effect on average response and background response. The interference effect of surrounding buildings makes the fluctuating response and wind vibration coefficient increased significantly, furthermore, the increase ranges of resonant response is greater than background response.

• Journal of the Korea Institute of Military Science and Technology
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• v.6 no.4
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• pp.100-112
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• 2003

This paper presents the transient response analysis of a rotating blade in resonant frequency range. It is shown that the modeling is considered in elastic foundation and friction damping effect. The equations of motion are derived and transformed into a dimensionless form to investigate general phenomena. Numerical results show that the magnitude of friction damping to reduce maximum transient response in near the critical angular speed. The method can be applied to a number of examples of the practical rotating blade system to minimize transient response in resonant frequency range.

• Geomechanics and Engineering
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• v.33 no.6
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• pp.583-596
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• 2023

The interlayers, either softer or stiffer than the surrounding layers, are usually overlooked during field investigation due to the small thickness. They may be neglected through the analysis process for simplicity. However, they may significantly affect the dynamic behavior of the soil-foundation system. In this study, a series of 3D finite-element Direct-solution steady-state harmonic analyses were carried out using ABAQUS/CAE software to investigate the impacts of interlayers on the dynamic response of a cast in place pile group subjected to horizontal harmonic load. The experimental data of a 3×2 pile group testing was used to verify the numerical modeling. The effects of thickness, depth, and shear modulus of the interlayers on the dynamic response of the pile group are investigated. The simulations were conducted on both stiff and soft soils. It was found that the soft interlayers affect the frequency-amplitude curve of the system only in frequencies higher than 70% of the resonant frequency of the base soil. While, the effect of stiff interlayer in soft base soil started at frequency of 35% of the resonant frequency of the base soil. Also, it was observed that a shallow stiff interlayer increased the resonant amplitude by 11%, while a deep one only increased the resonant frequency by 7%. Moreover, a shallow soft interlayer increased the resonant frequency by 20% in soft base soils, whereas, it had an effect as low as 6% on resonant amplitude. Also, the results showed that deep soft interlayers increased the resonant amplitude by 17 to 20% in both soft and stiff base soils due to a reduction in lateral support of the piles. In the cases of deep thick, soft interlayers, the resonant frequency reduced significantly, i.e., 16 to 20%. It was found that the stiff interlayers were most effective on the amplitude and frequency of the pile group.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2000.11a
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• pp.317-319
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• 2000

We fabricated the QCM with Langmuir-Blodgett(LB) film deposited at the different subphase pH and investigated the resonant frequency response by the injection of organic gas response. In the $\pi$-A isotherms, the monolayer on the air/water interface had different limiting area per molecule and showed more condensed status as increasing the subphase pH. When palmitic acid LB film was deposited on the QCM, the resonant frequency shift was proportional to the deposited layer and had more resonant frequency shift in the case of the higher pH range as expected. In the resonant frequency for the injection of organic gas, it has been improved in the case of LB film fabricated at the lower subphase pH range and dependant upon the molecular weight of organic gas.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1997.04a
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• pp.198-201
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• 1997

The new system for identification of organic vapours and analysis method of mechanism between organic vapours and sensitive materials were attempted using the resonant resistance and resonant frequency of Quartz Crystal Analyzer (Q. C. A.). The resonant resistance shift means rheological changes in sensitive LB films occurred by the adsorption of organic vapours, while the resonant frequency shift represent the mass of organic vapour loaded in or on the sensitive LB films. It is thought that we can obtain more accurate response mechanism of organic vapour using the resonant frequency and resonant resistance diagram. The polymeric sensitive material were quantitively depositied using the LB method. In the experimental results, the adsorption behavior of organic vapour response can be decided by two type ; surface adsorption and penetration into sensitive material. Organic vapours had different positions in the Frequency-Resistance (F-R) diagram as to the kinds and concentrations of organic vapours. Thus F-R diagram can be applied to the development of one channel gas sensing system using the Quartz Crystal Analyzer.

• Journal of Power Electronics
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• v.12 no.2
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• pp.317-325
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• 2012

Resonant immittance converter (RIC) topologies can transform a current source into a voltage source (Type-I RICs) and vice versa (Type-II RICs), thereby making them suitable for many power electronics applications. RICs are operated at a fixed frequency where the resonant immittance network (RIN) exhibits immittance conversion characteristics. It is observed that the low-frequency response of Type-II RINs is relatively flat and that the state variables associated with Type-II RINs affect the response only at the high frequencies in the vicinity of the switching frequency. The overall response of a Type-II RIC is thus dominated by the filter response, which is particularly important for the controller design. Therefore, an approximate equivalent circuit model and a small-signal model of Type-II RICs are proposed in this paper, neglecting the high-frequency response of Type-II RINs. While the proposed models greatly simplify and speed-up the analysis, it adequately predicts the open-loop transient and small-signal ac behavior of Type-II RICs. The validity of the proposed models is confirmed by comparisons of their results with those obtained from a cycle-by-cycle simulation and with an experimental prototype.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.50 no.5
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• pp.605-615
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• 2017

A multi-resonant broadband acoustic transducer with six Tonpilz elements operating at different resonant frequencies in a transducer assembly was fabricated, tested, and analyzed. A compensated transducer, modified by adding series inductance to the developed multi-resonant broadband transducer, was shown to provide improved bandwidth performance with a relatively more uniform frequency response compared with the uncompensated transducer. By controlling the series inductance, flat frequency response characteristics at two frequency bands were obtained over the range 38-52 kHz with 1.1 mH inductance and 50-60 kHz with 0.4 mH inductance. These results suggest that the operating frequency of the developed multi-resonant broadband transducer in a chirp echo sounder can be shifted to a different frequency band that is optimized according to the environment for more effective echo surveys of fishing grounds.

• Structural Engineering and Mechanics
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• v.32 no.6
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• pp.725-740
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• 2009

A new simple relation for the estimation of modal correlation coefficients is presented. It is obtained from the decomposition of covariances of modal responses into background and resonant contributions, as it is commonly done for the variances. Thanks to appropriate assumptions, the modal correlation coefficients are estimated as weighted sums of two limit values, corresponding to the background and resonant responses respectively. The weighting coefficients are expressed as functions of the background-to-resonant ratios, which makes the proposed formulation convenient and easily accessible. The simplicity of the mathematical formulation facilitates the physical interpretation. It is for example proved that modal correlation coefficients can be non negligable even in case of well separated natural frequencies, which is sometimes unclear in the litterature. The new relation is mainly efficient in case of large finite element models. It is applied and validated on a finite element buffeting analysis of the Viaduct of Millau, the highest bridge deck ever built so far.