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Time-domain and frequency-domain approaches to identification of bridge flutter derivatives

Zhengqing CHEN

《结构与土木工程前沿（英文）》 2009年第3卷第2期页码 173-179 doi: 10.1007/s11709-009-0034-1

摘要： Flutter derivatives are essential for flutter analysis of long-span bridges, and they are generally identified from the vibration testing data of a sectional model suspended in a wind tunnel. Making use of the forced vibration testing data of three sectional models, namely, a thin-plate model, a nearly streamlined model, and a bluff-body model, a comparative study was made to identify the flutter derivatives of each model by using a time-domain method and a frequency-domain method. It was shown that all the flutter derivatives of the thin-plate model identified with the frequency-domain method and time-domain method, respectively, agree very well. Moreover, some of the flutter derivatives of each of the other two models identified with the two methods deviate to some extent. More precisely, the frequency-domain method usually results in smooth curves of the flutter derivatives. The formulation of time-domain method makes the identification results of flutter derivatives relatively sensitive to the signal phase lag between vibration state vector and aerodynamic forces and also prone to be disturbed by noise and nonlinearity.

关键词： long-span bridges wind-induced vibration flutter derivatives forced vibration test time-domain method frequency-domain method

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Multi-harmonic forced vibration and resonance of simple beams to moving vehicles

《结构与土木工程前沿（英文）》页码 981-993 doi: 10.1007/s11709-023-0979-5

摘要： This study modeled the moving-vehicle-induced forcing excitation on a single-span prismatic bridge as a multiple frequency-multiplication harmonic load on the modal coordinates of a linear elastic simple Euler–Bernoulli beam, and investigated the forced modal oscillation and resonance behavior of this type of dynamic system. The forced modal responses consist of multiple frequency-multiplication steady-state harmonics and one damped mono-frequency complementary harmonic. The analysis revealed that a moving load induces high-harmonic forced resonance amplification when the moving speed is low. To verify the occurrence of high-harmonic forced resonance, numerical tests were conducted on single-span simple beams based on structural modeling using the finite element method (FEM) and a moving sprung-mass oscillator vehicle model. The forced resonance amplification characteristics of the fundamental mode for beam response estimation are presented with consideration to different end restraint conditions. The results reveal that the high-harmonic forced resonance may be significant for the investigated beams subjected to vehicle loads moving at specific low speeds. For the investigated single-span simple beams, the moving vehicle carriage heaving oscillation modulates the beam modal frequency, but does not induce notable variation of the modal oscillation harmonic structure for the cases that vehicle of small mass moves in low speed.

关键词： forced vibration linear Euler beam moving load harmonic structure frequency modulation end restraints

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移动荷载作用下三塔悬索桥的强迫振动研究

冯兆祥,陈亮,缪长青

《中国工程科学》 2012年第14卷第5期页码 80-84

摘要：

针对泰州大桥开展结构动力特性计算，分析了不同移动速度以及不同移动荷载大小对于三塔两跨悬索桥结构动力响应的影响。结果表明，三塔两跨悬索桥的一阶竖弯振动基频约为0.08 Hz,远低于载重汽车的固有频率，不会形成共振条件。简单的移动荷载作用下三塔两跨连续支承悬索桥的内力、位移响应与同等静力荷载作用效果比较接近。移动荷载的质量越大、速度越大，结构的内力、位移响应就越大，并与车重呈近似正比例关系。结构内力、位移的荷载放大系数不随移动荷载质量的大小而改变。

关键词：动力特性强迫振动响应荷载放大系数

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Similitude design for the vibration problems of plates and shells: A review

Yunpeng ZHU, You WANG, Zhong LUO, Qingkai HAN, Deyou WANG

《机械工程前沿（英文）》 2017年第12卷第2期页码 253-264 doi: 10.1007/s11465-017-0418-1

摘要：

Similitude design plays a vital role in the analysis of vibration and shock problems encountered in large engineering equipment. Similitude design, including dimensional analysis and governing equation method, is founded on the dynamic similitude theory. This study reviews the application of similitude design methods in engineering practice and summarizes the major achievements of the dynamic similitude theory in structural vibration and shock problems in different fields, including marine structures, civil engineering structures, and large power equipment. This study also reviews the dynamic similitude design methods for thin-walled and composite material plates and shells, including the most recent work published by the authors. Structure sensitivity analysis is used to evaluate the scaling factors to attain accurate distorted scaling laws. Finally, this study discusses the existing problems and the potential of the dynamic similitude theory for the analysis of vibration and shock problems of structures.

关键词： review dynamic similitude vibration model test

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工程因素对结构振动环境试验响应的影响

陈幼玲,朱学旺,朱长春

《中国工程科学》 2006年第8卷第12期页码 62-65

摘要：

工程因素如试件装配技术状态、试验夹具、控制点位置、载荷控制等对振动试验结构响应的影响一直受到广泛的关注。分析了振动试验中几种主要的工程因素对响应的影响；分析表明，振动试验的识别结果可以预测稳定结构在使用环境下的振动响应。

关键词：复杂结构振动试验结构响应工程因素

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Ambient vibration testing and updating of the finite element model of a simply supported beam bridge

Ivan Gomez ARAUJO, Esperanza MALDONADO, Gustavo Chio CHO

《结构与土木工程前沿（英文）》 2011年第5卷第3期页码 344-354 doi: 10.1007/s11709-011-0124-8

摘要： An ambient vibration test on a concrete bridge constructed in 1971 and calibration of its finite element model are presented. The bridge is characterized by a system of post-tensioned and simply supported beams. The dynamic characteristics of the bridge, i.e. natural frequencies, mode shapes and damping ratios were computed from the ambient vibration tests by using the Eigensystem Realization Algorithm (ERA). Then, these characteristics were used to update the finite element model of the bridge by formulating an optimization problem and then using Genetic Algorithms (GA) to solve it. From the results of the ambient vibration test of this type of bridge, it is concluded that two-dimensional mode shapes exist: in the longitudinal and transverse; and these experimentally obtained dynamic characteristics were also achieved in the analytical model through updating. The application of GAs as optimization techniques showed great versatility to optimize any number and type of variables in the model.

关键词： modal analysis parameter identification ambient vibration test Eigensystem Realization Algorithm (ERA) method finite element method

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Dynamic test and finite element model updating of bridge structures based on ambient vibration

HUANG Minshui, ZHU Hongping, LI Lin, GUO Wenzeng

《结构与土木工程前沿（英文）》 2008年第2卷第2期页码 139-144 doi: 10.1007/s11709-008-0028-4

摘要： The dynamic characteristics of bridge structures are the basis of structural dynamic response and seismic analysis, and are also an important target of health condition monitoring. In this paper, a three-dimensional finite-element model is first established for a highway bridge over a railroad on No.312 National Highway. Based on design drawings, the dynamic characteristics of the bridge are studied using finite element analysis and ambient vibration measurements. Thus, a set of data is selected based on sensitivity analysis and optimization theory; the finite element model of the bridge is updated. The numerical and experimental results show that the updated method is more simple and effective, the updated finite element model can reflect the dynamic characteristics of the bridge better, and it can be used to predict the dynamic response under complex external forces. It is also helpful for further damage identification and health condition monitoring.

关键词： numerical effective Highway vibration complex external

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data enhancement for implementation in purification of modal frequency for extremely noisy ambient vibration

Hassan YOUSEFI, Alireza TAGHAVI KANI, Iradj MAHMOUDZADEH KANI, Soheil MOHAMMADI

《结构与土木工程前沿（英文）》 2020年第14卷第2期页码 446-472 doi: 10.1007/s11709-019-0605-8

摘要： The main purpose of the present study is to enhance high-level noisy data by a wavelet-based iterative filtering algorithm for identification of natural frequencies during ambient wind vibrational tests on a petrochemical process tower. Most of denoising methods fail to filter such noise properly. Both the signal-to-noise ratio and the peak signal-to-noise ratio are small. Multiresolution-based one-step and variational-based filtering methods fail to denoise properly with thresholds obtained by theoretical or empirical method. Due to the fact that it is impossible to completely denoise such high-level noisy data, the enhancing approach is used to improve the data quality, which is the main novelty from the application point of view here. For this iterative method, a simple computational approach is proposed to estimate the dynamic threshold values. Hence, different thresholds can be obtained for different recorded signals in one ambient test. This is in contrast to commonly used approaches recommending one global threshold estimated mainly by an empirical method. After the enhancements, modal frequencies are directly detected by the cross wavelet transform (XWT), the spectral power density and autocorrelation of wavelet coefficients. Estimated frequencies are then compared with those of an undamaged-model, simulated by the finite element method.

关键词： ambient vibration test high level noise iterative signal enhancement wavelet cross and autocorrelation of wavelets

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Study on forced air convection cooling for electronic assemblies

LI Bin, TAO Wenquan, HE Yaling

《能源前沿（英文）》 2008年第2卷第2期页码 158-163 doi: 10.1007/s11708-008-0009-2

摘要： The slotted fin concept was employed to improve the air cooling performance of plate-fin in heat sinks. Numerical simulations of laminar heat transfer and flow pressure drop were conducted for the integral plate fin, discrete plate fin and discrete slotted fin heat sinks. It is found that the performance of the discrete plate fin is better than that of the integral continuum plate fin and the performance of slotted fin is better than that of the discrete plate fin at the same pumping power of the fan. A new type of heat sink characterized by discrete and slotted fin surfaces with thinner fins and smaller spaces between fins is then proposed. Preliminary computation shows that this type of heat sink may be useful for the next generation of higher thermal load CPUs. The limit of cooling capacity for air-cooling techniques was also addressed.

关键词： concept slotted air-cooling Preliminary computation generation

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Thermally developing forced convection and the corresponding thermal stresses in a porous plate channel

YANG Xiao, LIU Xuemei

《机械工程前沿（英文）》 2007年第2卷第1期页码 57-61 doi: 10.1007/s11465-007-0009-7

摘要： Based on the Darcy fluid model, by considering the effects of viscous dissipation due to the interaction between solid skeleton and pore fluid flow and thermal conduction in the direction of the fluid flow, the thermally developing forced convection of the local thermal equilibrium and the corresponding thermal stresses in a semi-infinite saturated porous plate channel are investigated in this paper. The expressions of temperature, local Nusselt number and corresponding thermal stresses are obtained by means of the Fourier series, and the distributions of the same are also shown. Furthermore, influences of the P晱let number () and Brinkman number () on temperature, Nusselt number () and thermal stress are revealed numerically.

关键词： semi-infinite saturated direction interaction skeleton thermal equilibrium

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Soybean drying characteristics in microwave rotary dryer with forced convection

Ruifang WANG, Zhanyong LI, Yanhua LI, Jingsheng YE

《化学科学与工程前沿（英文）》 2009年第3卷第3期页码 289-292 doi: 10.1007/s11705-009-0022-y

摘要： A new hybrid drying technique by combining microwave and forced convection drying within a rotary drum, i.e., microwave rotary drying, was developed with the purpose to improve the uniformity of microwave drying. In a laboratory microwave rotary dryer, rewetted soybean was utilized as experimental material to study the effects of drum rotating speed, ventilation flow rate, and specific microwave power on the drying kinetics and cracking ratio of soybean. It was found that, with rotation, the cracking ratio can be lowered but without distinct improvement in the drying rate. Increasing ventilation flow rate and specific microwave power can improve the drying rate, but the cracking ratio also increases as a negative result. The cracking ratio lower than 10% can be attained for ventilation flow rate lower than 2.0 m ·h or specific microwave energy lower than 0.4 kW·kg in the present experiments.

关键词： cracking microwave rotary drying soybean

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An invariant descriptor for conjugate forced convection-conduction cooling of 3D protruding heaters in

Thiago ANTONINI ALVES,Paulo H. D. SANTOS,Murilo A. BARBUR

《机械工程前沿（英文）》 2015年第10卷第3期页码 263-276 doi: 10.1007/s11465-015-0345-y

摘要：

In this research, the temperatures of three-dimensional (3D) protruding heaters mounted on a conductive substrate in a horizontal rectangular channel with laminar airflow are related to the independent power dissipation in each heater by using a matrix G⁺ with invariant coefficients, which are dimensionless. These coefficients are defined in this study as the conjugate influence coefficients (g⁺) caused by the forced convection-conduction nature of the heaters’ cooling process. The temperature increase of each heater in the channel is quantified to clearly identify the contributions attributed to the self-heating and power dissipation in the other heaters (both upstream and downstream). The conjugate coefficients are invariant with the heat generation rate in the array of heaters when assuming a defined geometry, invariable fluid and flow rate, and constant substrate and heater conductivities. The results are numerically obtained by considering three 3D protruding heaters on a two-dimensional (2D) array by ANSYS/Fluent^TM 15.0 software. The conservation equations are solved by a coupled procedure within a single calculation domain comprising of solid and fluid regions and by considering a steady state laminar airflow with constant properties. Some examples are shown, indicating the effects of substrate thermal conductivity and Reynolds number on conjugate influence coefficients.

关键词： channel flow conjugate forced convection-conduction cooling conjugate influence coefficients discrete heating invariant descriptor thermal management

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地铁火灾中强制通风烟控系统作用的模拟

蔡波,李辉亮,廖光煊

《中国工程科学》 2005年第7卷第8期页码 80-83

摘要：

地铁火灾比地面火灾具有更大的危险性。通过对地铁火灾的模拟可以重现火灾过程，研究火灾现象，分析火灾原因。通过FDS模拟，对比大邱市地铁火灾在有无强制通风烟控系统条件下，火灾现场的温度场和烟尘分布，研究讨论其对控制地铁火灾的重要作用。

关键词：地铁火灾 FDS数值模拟强制通风烟控系统

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Vibration characteristics and machining performance of a novel perforated ultrasonic vibration platform

《机械工程前沿（英文）》 2023年第18卷第1期 doi: 10.1007/s11465-022-0730-2

摘要： Ultrasonic vibration-assisted grinding (UVAG) is an advanced hybrid process for the precision machining of difficult-to-cut materials. The resonator is a critical part of the UVAG system. Its performance considerably influences the vibration amplitude and resonant frequency. In this work, a novel perforated ultrasonic vibration platform resonator was developed for UVAG. The holes were evenly arranged at the top and side surfaces of the vibration platform to improve the vibration characteristics. A modified apparent elasticity method (AEM) was proposed to reveal the influence of holes on the vibration mode. The performance of the vibration platform was evaluated by the vibration tests and UVAG experiments of particulate-reinforced titanium matrix composites. Results indicate that the reasonable distribution of holes helps improve the resonant frequency and vibration mode. The modified AEM, the finite element method, and the vibration tests show a high degree of consistency for developing the perforated ultrasonic vibration platform with a maximum frequency error of 3%. The employment of ultrasonic vibration reduces the grinding force by 36% at most, thereby decreasing the machined surface defects, such as voids, cracks, and burnout.

关键词： ultrasonic vibration-assisted grinding perforated ultrasonic vibration platform vibration characteristics apparent elasticity method grinding force surface integrity

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Recent development of vibration utilization engineering

WEN Bangchun

《机械工程前沿（英文）》 2008年第3卷第1期页码 1-9 doi: 10.1007/s11465-008-0017-2

摘要： The utilization of vibration and wave, which was developed during the latter half of the 20th century, is one of the most valueable technology applications and has been rapidly developing recently . Because the technique is closely associated with industry and agriculture, it can create huge social and economical benefits and provide excellent services for society. Thus, due to its necessity in industry and daily life, extensive research has been devoted to vibration utillization engineering. In this paper, vibration utilization is classified into linear or non-linear vibrations, waves, and electric-magnetic oscillations. Their phenomena, patterns, and applications in nature and society are introduced. Some research results about vibration utilization engineering are described.

关键词： utilization engineering non-linear vibration vibration utillization utillization engineering