The state equation and observation equation of the structural dynamic systems under various analysis scales are derived based on wavelet packet analysis. The time-frequency properties of structural dynamic response un...The state equation and observation equation of the structural dynamic systems under various analysis scales are derived based on wavelet packet analysis. The time-frequency properties of structural dynamic response under various scales are further formulated. The theoretical analysis results reveal that the wavelet packet energy spectrum （WPES） obtained from wavelet packet decomposition of structural dynamic response will detect the presence of structural damage. The sensitivity analysis of the WPES to structural damage and measurement noise is also performed. The transfer properties of the structural system matrix and the observation noise under various analysis scales are formulated, which verify the damage alarming reliability using the proposed WPES with preferable damage sensitivity and noise robusticity.展开更多
Robert James Waller （1939-2014） does not catch readers＇ attention until his popular novel The Bridges of Madison County （1996） wins him great admirations since its publication in 1992 which brings him instant suc...Robert James Waller （1939-2014） does not catch readers＇ attention until his popular novel The Bridges of Madison County （1996） wins him great admirations since its publication in 1992 which brings him instant success. The story explores the dilemma between responsibility of family and fulfillment of desires. Set in America in the 1960s, the novel is woven by the romantic story of the two middle-aged man and woman after they countered and gathered together for four days. Though simple in plot, it really deserves detailed interpretation and appreciation. This paper will mainly discuss Kincaid＇s cultural values reflected not only in the romance between his lover and him, but also in his attitudes towards women＇s rights.展开更多
By using the output inductors and body capacitances without adding any component compared with hard switching synchronous rectifier,the topology of a soft switched synchronous rectifier with phase-shifted full bridge ...By using the output inductors and body capacitances without adding any component compared with hard switching synchronous rectifier,the topology of a soft switched synchronous rectifier with phase-shifted full bridge zero voltage switching DC/DC converter is proposed. The converter efficiency is maximized due to soft switching of the full bridge MOSFETs and the synchronous MOSFETs, and also the low conduction loss of synchronous MOSFET. The operation principles of the circuit are analyzed in detail and the small-signal model is derived, also the converter dynamic characteristics are analyzed. Frequency responses of transfer functions under different values of transformer primary leakage inductance are discussed. The experimental results were obtained from a 400 V input and 100 A/12 V output DC/DC converter operating at 100 kHz. The results show that the converter efficiency is 2% higher in rated power than traditional diode rectifier.展开更多
Over the past decades, there has been continual construction of sea-crossing bridges as the technology of transportation improves. The probability of bridge pier being subjected to more vehicular impact is also growin...Over the past decades, there has been continual construction of sea-crossing bridges as the technology of transportation improves. The probability of bridge pier being subjected to more vehicular impact is also growing. This study performed scale model tests and analyzed a collision mechanism considering the non-navigable span of a sea-crossing bridge in East China Sea as an engineering background. Comparing the test results with the finite element calculations, the dynamic response of the sample bridge and local damages of the fragile components under impact force were evaluated. Subsequently, the time-frequency characteristics of the vibration signal were analyzed based on wavelet packet analysis, and the multi-resolution characteristics as well as energy distribution of the vibration signal were discussed. It was observed that the impact energy transferred from ship to pier during the period of collision distributed different frequency bands with varying characteristics. The main frequency band(0–62.5 Hz) contains more than 75% of the vibration energy. The analysis can provide a basis for structural damage identification after the collision and anti-collision design of bridges.展开更多
文摘The state equation and observation equation of the structural dynamic systems under various analysis scales are derived based on wavelet packet analysis. The time-frequency properties of structural dynamic response under various scales are further formulated. The theoretical analysis results reveal that the wavelet packet energy spectrum （WPES） obtained from wavelet packet decomposition of structural dynamic response will detect the presence of structural damage. The sensitivity analysis of the WPES to structural damage and measurement noise is also performed. The transfer properties of the structural system matrix and the observation noise under various analysis scales are formulated, which verify the damage alarming reliability using the proposed WPES with preferable damage sensitivity and noise robusticity.
文摘Robert James Waller （1939-2014） does not catch readers＇ attention until his popular novel The Bridges of Madison County （1996） wins him great admirations since its publication in 1992 which brings him instant success. The story explores the dilemma between responsibility of family and fulfillment of desires. Set in America in the 1960s, the novel is woven by the romantic story of the two middle-aged man and woman after they countered and gathered together for four days. Though simple in plot, it really deserves detailed interpretation and appreciation. This paper will mainly discuss Kincaid＇s cultural values reflected not only in the romance between his lover and him, but also in his attitudes towards women＇s rights.
文摘By using the output inductors and body capacitances without adding any component compared with hard switching synchronous rectifier,the topology of a soft switched synchronous rectifier with phase-shifted full bridge zero voltage switching DC/DC converter is proposed. The converter efficiency is maximized due to soft switching of the full bridge MOSFETs and the synchronous MOSFETs, and also the low conduction loss of synchronous MOSFET. The operation principles of the circuit are analyzed in detail and the small-signal model is derived, also the converter dynamic characteristics are analyzed. Frequency responses of transfer functions under different values of transformer primary leakage inductance are discussed. The experimental results were obtained from a 400 V input and 100 A/12 V output DC/DC converter operating at 100 kHz. The results show that the converter efficiency is 2% higher in rated power than traditional diode rectifier.
基金supported by the National Key Research and Development Program of China(No.2018YFC0809604)the National Natural Science Foundation of China(Nos.U1709207 and 51578506)。
文摘Over the past decades, there has been continual construction of sea-crossing bridges as the technology of transportation improves. The probability of bridge pier being subjected to more vehicular impact is also growing. This study performed scale model tests and analyzed a collision mechanism considering the non-navigable span of a sea-crossing bridge in East China Sea as an engineering background. Comparing the test results with the finite element calculations, the dynamic response of the sample bridge and local damages of the fragile components under impact force were evaluated. Subsequently, the time-frequency characteristics of the vibration signal were analyzed based on wavelet packet analysis, and the multi-resolution characteristics as well as energy distribution of the vibration signal were discussed. It was observed that the impact energy transferred from ship to pier during the period of collision distributed different frequency bands with varying characteristics. The main frequency band(0–62.5 Hz) contains more than 75% of the vibration energy. The analysis can provide a basis for structural damage identification after the collision and anti-collision design of bridges.
