Structural design simultaneously governed by earthquakes and environmental vibrations has received a lot of attention in recent years.Base-isolated composite structures are typically used in the above-mentioned struct...Structural design simultaneously governed by earthquakes and environmental vibrations has received a lot of attention in recent years.Base-isolated composite structures are typically used in the above-mentioned structural design.The corresponding analysis involves validating structural safety under earthquakes and human comfort under environmental vibrations through a time-history analysis.Thus,a reasonable damping model is essential.In this work,the representatives of viscous damping model and rate-independent damping model,namely the Rayleigh damping model and uniform damping model,were adopted to investigate the influence of damping models on the time-history analysis of such structural designs.The energy dissipation characteristics of the above-mentioned damping models were illustrated via a dynamic test of recycled aggregate concrete specimens.A case study was performed on a base-isolated steelconcrete composite structure.The dynamic responses under the excitation of earthquakes and environmental vibrations were compared using different damping models.The uniform damping model was found to be more flexible than the Rayleigh damping model in dealing with excitations with different frequency components.The uniform damping model is both theoretically advantageous and easy to use,demonstrating its potential in dynamic analysis of structures designed simultaneously governed by earthquakes and environmental vibrations.展开更多
This paper contrasts predicted X-band sea surface backscattering from slick-free and oil-covered sea surfaces with actual measurements acquired by the X-band satellite TerraSAR-X and COSMO-SkyMed Synthetic Aperture Ra...This paper contrasts predicted X-band sea surface backscattering from slick-free and oil-covered sea surfaces with actual measurements acquired by the X-band satellite TerraSAR-X and COSMO-SkyMed Synthetic Aperture Radar(SAR)missions.Two SAR scenes were acquired with a temporal difference of about 36 minutes,under similar met-ocean conditions,during the North Sea’s Gannet Alpha oil spill accident.The normalized radar cross section of the slick-free sea surface is predicted using the Advanced Integral Equation Model(AIEM)while the backscatter from the oiled sea surface is predicted by the AIEM augmented with the Model of Local Balance(MLB)to include the damping effect of oil slicks.Experimental results show that X-band co-polarized numerical predictions agree reasonably well with both TSX and CSK actual measurements collected over slick-free sea surfaces.When dealing with oil-covered sea surfaces,the predicted backscattering reasonably agrees with TSX measurements,while it overestimates the CSK ones.This is likely due to the different spreading conditions of the oil imaged by the two satellite missions.展开更多
A method for simultaneous determination of mixed model parameters,which have different physical dimensions or different responses to data,is presented.Mixed parameter estimation from observed data within a single mode...A method for simultaneous determination of mixed model parameters,which have different physical dimensions or different responses to data,is presented.Mixed parameter estimation from observed data within a single model space shows instabilities and trade-offs of the solutions. We separate the model space into N-subspaces based on their physical properties or computational convenience and solve the N-subspaces systems by damped least-squares and singular-value decomposition. Since the condition number of each subsystem is smaller than that of the single global system,the approach can greatly increase the stability of the inversion. We also introduce different damping factors into the subsystems to reduce the tradeoffs between the different parameters. The damping factors depend on the conditioning of the subsystems and may be adequately chosen in a range from 0.1 % to 10 % of the largest singular value. We illustrate the method with an example of simultaneous determination of source history,source geometry,and hypocentral location from regional seismograms,although it is applicable to any geophysical inversion.展开更多
Diurnal wind （DW） and nonlinear interaction between inertial and tidal currents near the Xisha Islands of the South China Sea （SCS） during the passage of Typhoon Conson （2010） are investigated using observationa...Diurnal wind （DW） and nonlinear interaction between inertial and tidal currents near the Xisha Islands of the South China Sea （SCS） during the passage of Typhoon Conson （2010） are investigated using observational data and a damped slab model. It is found that the DWs, which are dominated by clockwise wind components, are prominent at our observational site. The DWs increase after the passage of the typhoon from 1 to about 4 m/s, which may be due to the decrease of the sea surface temperature caused by the passage of the typhoon. Kinetic energy spectra and bicoherence methods reveal nonlinear interactions between the inertial currents and the 2MK3 tidal constituent at our observational site. The slab damped model reproduces the inertial currents successfully induced by the total observed winds, and it is shown that the inertial currents induced by DWs are positively proportional to the DWs speed. Even though the observed inertial currents are distinct, the proportion of inertial currents induced by DWs to those induced by the total observed winds is just 0.7%/4% before/after the passage of typhoon. This shows that the inertial currents induced by the DWs are unimportant near the Xisha Islands during the typhoon season.展开更多
The purpose is to design the control method for a single-degree-of-freedom(SDOF)exponentially damped oscillator.Based on the Lyapunov stability theory,sliding mode control and adaptive sliding mode control have been p...The purpose is to design the control method for a single-degree-of-freedom(SDOF)exponentially damped oscillator.Based on the Lyapunov stability theory,sliding mode control and adaptive sliding mode control have been proposed.Sliding control laws and adaptive sliding laws are designed for exponentially damped oscillator respectively in cases that the bound of the external exciting force is known or unknown.The viability and effectiveness of the above control designs have been validated by numerical simulations.展开更多
A numerical solution was derived to determine wave field in a converging channel bounded by rubble-mound jetties. The solution was achieved by applying boundary element method. The model was applied to analyze the eff...A numerical solution was derived to determine wave field in a converging channel bounded by rubble-mound jetties. The solution was achieved by applying boundary element method. The model was applied to analyze the effect of channel convergence, the cross-section of the jetties and their physical and damping properties on wave field in the channel. The study reveals numerous non-intuitive results specific for jetted and convergent channels. The analysis shows that wave reflection is usually low and is of secondary practical importance. Wave transmission strongly depends on the channel geometry and transmitted waves may be higher than incident waves, despite reflection and damping processes. Moreover, wave transmission depends on physical and damping properties of rubble jetties and the results show that wave transmission may increase with the increasing damping properties of jetties, which is a non-intuitive feature of wave fields in jetted channels. The analysis reveals several novel results of practical importance. It is shown that the rubble-mound jetties should be constructed from the material of high porosity, which ensures low transmission. More attention should be devoted to hydraulic properties of porous materials. It is recommended to use the material of moderate damping properties. The material of high damping properties often increases the wave transmission. It is possible, by a selection of rubble-mound material, to obtain lower transmission level for steep waves than for waves of moderate steepness. A series of laboratory experiments were conducted in the wave flume to verify the theoretical results. The comparisons show that theoretical results are in fairly good agreement with experimental data.展开更多
Piezoresponse Force Spectroscopy(PFS)is a powerful technique widely used for measuring the nanoscale electromechanical coupling of the ferro-/piezo-electric materials.However,it is found that certain nonferroelectric ...Piezoresponse Force Spectroscopy(PFS)is a powerful technique widely used for measuring the nanoscale electromechanical coupling of the ferro-/piezo-electric materials.However,it is found that certain nonferroelectric materials can also generate the“hysteresis-loop-like”responses from the PFS measurements due to many other factors such as electrostatic effects.This work therefore studies the signal of the contact resonance frequency during the PFS measurements.By comparing the results from ferroelectric and non-ferroelectric materials,it is found there are distinct differences between these two types of materials in the variation of the contact resonance frequency during the PFS measurements.A momentary and sharp increase of the contact resonance frequency occurs when the domain is switched by applying the DC bias,which can be regarded as a unique characteristic for the ferroelectric materials.After analyzing the reliability and mechanism of this method,it is proposed that the contact resonance frequency variation at the coercive bias is capable to differentiate the electromechanical responses of the ferroelectric and non-ferroelectric materials during the PFS measurements.展开更多
In the Phase Ⅱ Project at the Hefei Light Source, a fourth-harmonic ＂Landau＂ cavity will be operated in order to suppress the coupled-bunch instabilities and increase the beam lifetime of the Hefei storage ring. In...In the Phase Ⅱ Project at the Hefei Light Source, a fourth-harmonic ＂Landau＂ cavity will be operated in order to suppress the coupled-bunch instabilities and increase the beam lifetime of the Hefei storage ring. Instabilities limit the utility of the higher-harmonic cavity when the storage ring is operated with a small momentum compaction. Analytical modeling and simulations show that the instabilities result from Robinson mode coupling. In the analytic modeling, we operate an algorithm to consider the Robinson instabilities. To study the evolution of unstable behavior, simulations have been performed in which macroparticles are distributed among the buckets. Both the analytic modeling and simulations agree for passive operation of the harmonic cavity.展开更多
文摘Structural design simultaneously governed by earthquakes and environmental vibrations has received a lot of attention in recent years.Base-isolated composite structures are typically used in the above-mentioned structural design.The corresponding analysis involves validating structural safety under earthquakes and human comfort under environmental vibrations through a time-history analysis.Thus,a reasonable damping model is essential.In this work,the representatives of viscous damping model and rate-independent damping model,namely the Rayleigh damping model and uniform damping model,were adopted to investigate the influence of damping models on the time-history analysis of such structural designs.The energy dissipation characteristics of the above-mentioned damping models were illustrated via a dynamic test of recycled aggregate concrete specimens.A case study was performed on a base-isolated steelconcrete composite structure.The dynamic responses under the excitation of earthquakes and environmental vibrations were compared using different damping models.The uniform damping model was found to be more flexible than the Rayleigh damping model in dealing with excitations with different frequency components.The uniform damping model is both theoretically advantageous and easy to use,demonstrating its potential in dynamic analysis of structures designed simultaneously governed by earthquakes and environmental vibrations.
基金supported by the National Key R&D Program of China[Grant number 2021YFB3901300]the ESA-NRSCC Dragon-5 cooperation project[ID 57979]+1 种基金the Agenzia Spaziale Italiana under the APPLICAVEMARS project[ASI contract n.2021-4-U.0]the China Scholarship Council.
文摘This paper contrasts predicted X-band sea surface backscattering from slick-free and oil-covered sea surfaces with actual measurements acquired by the X-band satellite TerraSAR-X and COSMO-SkyMed Synthetic Aperture Radar(SAR)missions.Two SAR scenes were acquired with a temporal difference of about 36 minutes,under similar met-ocean conditions,during the North Sea’s Gannet Alpha oil spill accident.The normalized radar cross section of the slick-free sea surface is predicted using the Advanced Integral Equation Model(AIEM)while the backscatter from the oiled sea surface is predicted by the AIEM augmented with the Model of Local Balance(MLB)to include the damping effect of oil slicks.Experimental results show that X-band co-polarized numerical predictions agree reasonably well with both TSX and CSK actual measurements collected over slick-free sea surfaces.When dealing with oil-covered sea surfaces,the predicted backscattering reasonably agrees with TSX measurements,while it overestimates the CSK ones.This is likely due to the different spreading conditions of the oil imaged by the two satellite missions.
基金supported by Innovation Project of Chinese Academy of Sciences
文摘A method for simultaneous determination of mixed model parameters,which have different physical dimensions or different responses to data,is presented.Mixed parameter estimation from observed data within a single model space shows instabilities and trade-offs of the solutions. We separate the model space into N-subspaces based on their physical properties or computational convenience and solve the N-subspaces systems by damped least-squares and singular-value decomposition. Since the condition number of each subsystem is smaller than that of the single global system,the approach can greatly increase the stability of the inversion. We also introduce different damping factors into the subsystems to reduce the tradeoffs between the different parameters. The damping factors depend on the conditioning of the subsystems and may be adequately chosen in a range from 0.1 % to 10 % of the largest singular value. We illustrate the method with an example of simultaneous determination of source history,source geometry,and hypocentral location from regional seismograms,although it is applicable to any geophysical inversion.
基金The Knowledge Innovation Program of the Chinese Academy of Sciences under contract No.SQ201206the Innovation Group Program of State Key Laboratory of Tropical Oceanography,South China Sea Institute of Oceanology,Chinese Academy of Sciences,under contract No.LTOZZ1201+1 种基金the National Basic Research Program under contract No.2013CB956101the National Natural Science Foundation of China under contract No.41025019
文摘Diurnal wind （DW） and nonlinear interaction between inertial and tidal currents near the Xisha Islands of the South China Sea （SCS） during the passage of Typhoon Conson （2010） are investigated using observational data and a damped slab model. It is found that the DWs, which are dominated by clockwise wind components, are prominent at our observational site. The DWs increase after the passage of the typhoon from 1 to about 4 m/s, which may be due to the decrease of the sea surface temperature caused by the passage of the typhoon. Kinetic energy spectra and bicoherence methods reveal nonlinear interactions between the inertial currents and the 2MK3 tidal constituent at our observational site. The slab damped model reproduces the inertial currents successfully induced by the total observed winds, and it is shown that the inertial currents induced by DWs are positively proportional to the DWs speed. Even though the observed inertial currents are distinct, the proportion of inertial currents induced by DWs to those induced by the total observed winds is just 0.7%/4% before/after the passage of typhoon. This shows that the inertial currents induced by the DWs are unimportant near the Xisha Islands during the typhoon season.
基金National Natural Science Foundation of China(No.11802338)
文摘The purpose is to design the control method for a single-degree-of-freedom(SDOF)exponentially damped oscillator.Based on the Lyapunov stability theory,sliding mode control and adaptive sliding mode control have been proposed.Sliding control laws and adaptive sliding laws are designed for exponentially damped oscillator respectively in cases that the bound of the external exciting force is known or unknown.The viability and effectiveness of the above control designs have been validated by numerical simulations.
文摘A numerical solution was derived to determine wave field in a converging channel bounded by rubble-mound jetties. The solution was achieved by applying boundary element method. The model was applied to analyze the effect of channel convergence, the cross-section of the jetties and their physical and damping properties on wave field in the channel. The study reveals numerous non-intuitive results specific for jetted and convergent channels. The analysis shows that wave reflection is usually low and is of secondary practical importance. Wave transmission strongly depends on the channel geometry and transmitted waves may be higher than incident waves, despite reflection and damping processes. Moreover, wave transmission depends on physical and damping properties of rubble jetties and the results show that wave transmission may increase with the increasing damping properties of jetties, which is a non-intuitive feature of wave fields in jetted channels. The analysis reveals several novel results of practical importance. It is shown that the rubble-mound jetties should be constructed from the material of high porosity, which ensures low transmission. More attention should be devoted to hydraulic properties of porous materials. It is recommended to use the material of moderate damping properties. The material of high damping properties often increases the wave transmission. It is possible, by a selection of rubble-mound material, to obtain lower transmission level for steep waves than for waves of moderate steepness. A series of laboratory experiments were conducted in the wave flume to verify the theoretical results. The comparisons show that theoretical results are in fairly good agreement with experimental data.
基金the financial support by Ministry of Education,Singapore,through National University of Singapore(NUS)under the Academic Research Fund(ARF)of grant number R-265-000-596-112the post-graduate scholarship provide by NUSthe support for post-doctoral research fellow from ARF of R-265-000-596-112 by Ministry of Education,Singapore.
文摘Piezoresponse Force Spectroscopy(PFS)is a powerful technique widely used for measuring the nanoscale electromechanical coupling of the ferro-/piezo-electric materials.However,it is found that certain nonferroelectric materials can also generate the“hysteresis-loop-like”responses from the PFS measurements due to many other factors such as electrostatic effects.This work therefore studies the signal of the contact resonance frequency during the PFS measurements.By comparing the results from ferroelectric and non-ferroelectric materials,it is found there are distinct differences between these two types of materials in the variation of the contact resonance frequency during the PFS measurements.A momentary and sharp increase of the contact resonance frequency occurs when the domain is switched by applying the DC bias,which can be regarded as a unique characteristic for the ferroelectric materials.After analyzing the reliability and mechanism of this method,it is proposed that the contact resonance frequency variation at the coercive bias is capable to differentiate the electromechanical responses of the ferroelectric and non-ferroelectric materials during the PFS measurements.
基金Supported by National Natural Science Foundation of China(10979045,11175180,11175182)
文摘In the Phase Ⅱ Project at the Hefei Light Source, a fourth-harmonic ＂Landau＂ cavity will be operated in order to suppress the coupled-bunch instabilities and increase the beam lifetime of the Hefei storage ring. Instabilities limit the utility of the higher-harmonic cavity when the storage ring is operated with a small momentum compaction. Analytical modeling and simulations show that the instabilities result from Robinson mode coupling. In the analytic modeling, we operate an algorithm to consider the Robinson instabilities. To study the evolution of unstable behavior, simulations have been performed in which macroparticles are distributed among the buckets. Both the analytic modeling and simulations agree for passive operation of the harmonic cavity.
